Optogenetic confirmation of transverse-tubular membrane excitability in intact cardiac myocytes

T-tubules (TT) form a complex network of sarcolemmal membrane invaginations, essential for well-co-ordinated excitation-contraction coupling (ECC) and thus homogeneous mechanical activation of cardiomyocytes. ECC is initiated by rapid depolarization of the sarcolemmal membrane. Whether TT membrane depolarization is active (local generation of action potentials; AP) or passive (following depolarization of the outer cell surface sarcolemma; SS) has not been experimentally validated in cardiomyocytes. Based on the assessment of ion flux pathways needed for AP generation, we hypothesize that TT are excitable. We therefore explored TT excitability experimentally, using an all-optical approach to stimulate and record trans-membrane potential changes in TT that were structurally disconnected, and hence electrically insulated, from the SS membrane by transient osmotic shock. Our results establish that cardiomyocyte TT can generate AP. These AP show electrical features that differ substantially from those observed in SS, consistent with differences in the density of ion channels and transporters in the two different membrane domains. We propose that TT-generated AP represent a safety mechanism for TT AP propagation and ECC, which may be particularly relevant in pathophysiological settings where morpho-functional changes reduce the electrical connectivity between SS and TT membranes. KEY POINTS: Cardiomyocytes are characterized by a complex network of membrane invaginations (the T-tubular system) that propagate action potentials to the core of the cell, causing uniform excitation-contraction coupling across the cell. In the present study, we investigated whether the T-tubular system is able to generate action potentials autonomously, rather than following depolarization of the outer cell surface sarcolemma. For this purpose, we developed a fully optical platform to probe and manipulate the electrical dynamics of subcellular membrane domains. Our findings demonstrate that T-tubules are intrinsically excitable, revealing distinct characteristics of self-generated T-tubular action potentials. This active electrical capability would protect cells from voltage drops potentially occurring within the T-tubular network.

Cardiac safety assessment of a novel recombinant bispecific antibody targeting the ether-à-go-go related gene 1 (hERG1)-β1 integrin macromolecular complex

Introduction: In the last decades, mounting evidence has pointed out the human ether-á-go-go-related gene (hERG1) potassium channel as a novel biomarker in human cancers. However, hERG1 sustains the cardiac repolarizing current IKr and its blockade can induce a prolonged QT interval at the ECG, which increases the risk of life-threatening arrhythmias. This represents a major hindrance for targeting hERG1 for antineoplastic therapeutic purposes. Based on our discovery that hERG1 resides in a macromolecular complex with the β1 subunit of integrin adhesion receptors only in tumors, and not in the heart, we generated (and patented WO2019/015936) a novel engineered, single chain, bispecific antibody in the format of a diabody (scDb-hERG1-β1). This antibody has been proven to target with high affinity the hERG1/β1 integrin complex and to exert a good antineoplastic activity in preclinical mouse models. Methods: In the present study, we evaluated the cardiac safety of the scDb-hERG1-β1, determining the action potential duration (APD) of human cardiomyocytes, either atrial (from valve-disease patients) or ventricular (from aortic stenosis patients). Cardiac cells were incubated in vitro with i) the scDb-hERG1-β1, ii) the full length anti-hERG1 monoclonal antibody (mAb-hERG1) and iii) its single chain Fragment variable derivative (scFv-hERG1), from which the scDb-hERG1-β1 was assembled. All the tests were performed before and after treatment with the specific hERG1 blocker E4031. In addition, we have performed preliminary experiments, analyzing the effects of the scDb-hERG1/β1 in vivo measuring the QT interval length of the surface ECG after its injection intravenously in farm-pigs. Results: The scDb-hERG1-β1 did not produce any lengthening of APD compared to control (vehicle) conditions, either in atrial or ventricular cardiomyocytes, whereas both the hERG1-mAb and the scFv-hERG1 produced a significant APD prolongation. The addition of E4031 further prolonged APD. The scDb-hERG1-β1 did not produce any alterations of the QT (and QTc) interval values, once injected intravenously in farm pigs. Discussion: Overall, the above evidences plead for the cardiac safety of the scDb-hERG1-β1, suggesting that an application of this antibody for anti-cancer therapy will be untainted by cardiotoxicity.

Corrigendum: Calcium handling maturation and adaptation to increased substrate stiffness in human iPSC-derived cardiomyocytes: the impact of full-length dystrophin deficiency

[This corrects the article DOI: 10.3389/fphys.2022.1030920.].

Slower Calcium Handling Balances Faster Cross-Bridge Cycling in Human MYBPC3 HCM

BACKGROUND

The pathogenesis of MYBPC3-associated hypertrophic cardiomyopathy (HCM) is still unresolved. In our HCM patient cohort, a large and well-characterized population carrying the MYBPC3:c772G>A variant (p.Glu258Lys, E258K) provides the unique opportunity to study the basic mechanisms of MYBPC3-HCM with a comprehensive translational approach.

METHODS

We collected clinical and genetic data from 93 HCM patients carrying the MYBPC3:c772G>A variant. Functional perturbations were investigated using different biophysical techniques in left ventricular samples from 4 patients who underwent myectomy for refractory outflow obstruction, compared with samples from non-failing non-hypertrophic surgical patients and healthy donors. Human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes and engineered heart tissues (EHTs) were also investigated.

RESULTS

Haplotype analysis revealed MYBPC3:c772G>A as a founder mutation in Tuscany. In ventricular myocardium, the mutation leads to reduced cMyBP-C (cardiac myosin binding protein-C) expression, supporting haploinsufficiency as the main primary disease mechanism. Mechanical studies in single myofibrils and permeabilized muscle strips highlighted faster cross-bridge cycling, and higher energy cost of tension generation. A novel approach based on tissue clearing and advanced optical microscopy supported the idea that the sarcomere energetics dysfunction is intrinsically related with the reduction in cMyBP-C. Studies in single cardiomyocytes (native and hiPSC-derived), intact trabeculae and hiPSC-EHTs revealed prolonged action potentials, slower Ca2+ transients and preserved twitch duration, suggesting that the slower excitation-contraction coupling counterbalanced the faster sarcomere kinetics. This conclusion was strengthened by in silico simulations.

CONCLUSIONS

HCM-related MYBPC3:c772G>A mutation invariably impairs sarcomere energetics and cross-bridge cycling. Compensatory electrophysiological changes (eg, reduced potassium channel expression) appear to preserve twitch contraction parameters, but may expose patients to greater arrhythmic propensity and disease progression. Therapeutic approaches correcting the primary sarcomeric defects may prevent secondary cardiomyocyte remodeling.

Five waves of COVID-19 pandemic in Italy: results of a national survey evaluating the impact on activities related to arrhythmias, pacing, and electrophysiology promoted by AIAC (Italian Association of Arrhythmology and Cardiac Pacing)

BACKGROUND

The subsequent waves of the COVID-19 pandemic in Italy had a major impact on cardiac care.

METHODS

A survey to evaluate the dynamic changes in arrhythmia care during the first five waves of COVID-19 in Italy (first: March-May 2020; second: October 2020-January 2021; third: February-May 2021; fourth: June-October 2021; fifth: November 2021-February 2022) was launched.

RESULTS

A total of 127 physicians from arrhythmia centers (34% of Italian centers) took part in the survey. As compared to 2019, a reduction in 40% of elective pacemaker (PM), defibrillators (ICD), and cardiac resynchronization devices (CRT) implantations, with a 70% reduction for ablations, was reported during the first wave, with a progressive and gradual return to pre-pandemic volumes, generally during the third-fourth waves, slower for ablations. For emergency procedures (PM, ICD, CRT, and ablations), recovery from the initial 10% decline occurred in most cases during the second wave, with some variability. However, acute care for atrial fibrillation, electrical cardioversions, and evaluations for syncope showed a prolonged reduction of activity. The number of patients with devices which started remote monitoring increased by 40% during the first wave, but then the adoption of remote monitoring declined.

CONCLUSIONS

The dramatic and profound derangement in arrhythmia management that characterized the first wave of the COVID-19 pandemic was followed by a progressive return to the volume of activities of the pre-pandemic periods, even if with different temporal dynamics and some heterogeneity. Remote monitoring was largely implemented during the first wave, but full implementation is needed.

Calcium handling maturation and adaptation to increased substrate stiffness in human iPSC-derived cardiomyocytes: The impact of full-length dystrophin deficiency

Cardiomyocytes differentiated from human induced Pluripotent Stem Cells (hiPSC- CMs) are a unique source for modelling inherited cardiomyopathies. In particular, the possibility of observing maturation processes in a simple culture dish opens novel perspectives in the study of early-disease defects caused by genetic mutations before the onset of clinical manifestations. For instance, calcium handling abnormalities are considered as a leading cause of cardiomyocyte dysfunction in several genetic-based dilated cardiomyopathies, including rare types such as Duchenne Muscular Dystrophy (DMD)-associated cardiomyopathy. To better define the maturation of calcium handling we simultaneously measured action potential and calcium transients (Ca-Ts) using fluorescent indicators at specific time points. We combined micropatterned substrates with long-term cultures to improve maturation of hiPSC-CMs (60, 75 or 90 days post-differentiation). Control-(hiPSC)-CMs displayed increased maturation over time (90 vs 60 days), with longer action potential duration (APD), increased Ca-T amplitude, faster Ca-T rise (time to peak) and Ca-T decay (RT50). The progressively increased contribution of the SR to Ca release (estimated by post-rest potentiation or Caffeine-induced Ca-Ts) appeared as the main determinant of the progressive rise of Ca-T amplitude during maturation. As an example of severe cardiomyopathy with early onset, we compared hiPSC-CMs generated from a DMD patient (DMD-ΔExon50) and a CRISPR-Cas9 genome edited cell line isogenic to the healthy control with deletion of a G base at position 263 of the DMD gene (c.263delG-CMs). In DMD-hiPSC-CMs, changes of Ca-Ts during maturation were less pronounced: indeed, DMD cells at 90 days showed reduced Ca-T amplitude and faster Ca-T rise and RT50, as compared with control hiPSC-CMs. Caffeine-Ca-T was reduced in amplitude and had a slower time course, suggesting lower SR calcium content and NCX function in DMD vs control cells. Nonetheless, the inotropic and lusitropic responses to forskolin were preserved. CRISPR-induced c.263delG-CM line recapitulated the same developmental calcium handling alterations observed in DMD-CMs. We then tested the effects of micropatterned substrates with higher stiffness. In control hiPSC-CMs, higher stiffness leads to higher amplitude of Ca-T with faster decay kinetics. In hiPSC-CMs lacking full-length dystrophin, however, stiffer substrates did not modify Ca-Ts but only led to higher SR Ca content. These findings highlighted the inability of dystrophin-deficient cardiomyocytes to adjust their calcium homeostasis in response to increases of extracellular matrix stiffness, which suggests a mechanism occurring during the physiological and pathological development (i.e. fibrosis).

Implantable defibrillator-detected heart failure status predicts ventricular tachyarrhythmias

Background

The occurrence of ventricular tachyarrhythmias is associated with increased mortality and hospitalizations for heart failure in implantable cardioverter defibrillator (ICD) patients. Nonetheless, the temporal relationship between heart failure worsening and ventricular tachyarrhythmias has been scarcely explored so far.

Purpose

We hypothesized that in patients with heart failure and reduced ejection fraction with ICDs, physiological sensor-based heart failure status, as reflected in the HeartLogic index, would predict appropriate device therapies for ventricular tachyarrhythmias (shocks and antitachycardia pacing).

Methods and results

568 patients implanted with ICDs (n=410, 72%) or cardiac resynchronization therapy-defibrillators (CRT-D, n=158, 28%) endowed with the HeartLogic algorithm were included in this prospective observational multicenter analysis. Over a follow-up of 25 [25th-75th percentile: 15–35] months, 122 (21%) patients received an appropriate device therapy (shock, n=74, 13%), while the HeartLogic index crossed the threshold value 1200 times (0.71 alerts/patient-year) in 370 subjects (65%). The occurrence of at least one HeartLogic alert was significantly associated with both appropriate shocks (HR: 2.44, 95% CI: 1.49–3.97, p=0.003) and any ICD therapies (HR: 1.95, 95% CI: 1.37–2.85, p=0.003). Using a time-dependent Cox model, the weekly IN-alert state was the strongest predictor of ICD shocks (HR: 2.94, 95% CI: 1.73–5.01, p<0.001), after correction for age, secondary prevention, and use of CRT. As compared to clinically stable subjects with no therapies, patients experiencing shocks had significantly higher baseline values of the HeartLogic index, third heart sound amplitude, and respiratory rate. Beginning about one month prior to the arrhythmic event, we noticed further increase of the combined index and the third heart sound amplitude, a decrease of thoracic impedance, and higher resting heart rate (Figure 1).

Conclusions

The HeartLogic index is an independent predictor of appropriate defibrillator therapies. The combined index and its individual physiological components change well before the arrhythmic event, suggesting the existence of a window of opportunity to prevent shocks.

Funding Acknowledgement

Type of funding sources: None.

Performance of a multisensor implantable defibrillator algorithm for HF monitoring in presence of comorbidities

Background

Cardiovascular and non-cardiovascular comorbidities are common in heart failure (HF) patients and impact disease severity and prognosis. Select modern implantable defibrillators (ICDs) are equipped with multisensor algorithms for HF monitoring. The HeartLogic index combines multiple ICD-based sensor data (heart rate, heart sounds, thoracic impedance, respiration, activity), and the associated alert has proved to be a sensitive and timely predictor of impending HF decompensation in cardiac resynchronization therapy (CRT-D) patients The algorithm was developed using data from CRT-D patients; the performance in non-CRT ICD patients and the impact of selected comorbidities on performance requires further study.

Methods

The HeartLogic feature was activated in 568 ICD patients (410 with CRT) from 26 centers. The median follow-up was 25 months [25th–75th percentile: 15–35].

Results

During follow-up, 97 hospitalizations were reported (53 cardiovascular) and 55 patients died. We recorded 1200 HeartLogic alerts (0.71 alerts/patient-year) in 370 patients. Overall, the time IN the alert state was 13% of the total observation period. The rate of cardiovascular hospitalizations or death was 0.48/patient-year (95% CI: 0.37–0.60) with the HeartLogic IN alert state and 0.04/patient-year (95% CI: 0.03–0.05) OUT of alert state, with an incidence rate ratio of 13.35 (95% CI: 8.83–20.51, p<0.001). Among patient characteristics, atrial fibrillation (AF) at implantation (HR: 1.62, 95% CI: 1.27–2.07, p<0.001) and chronic kidney disease (CKD) (HR: 1.53, 95% CI: 1.21–1.93, p<0.001) independently predicted alerts. HeartLogic alerts were not associated with CRT vs. non-CRT device implantation (HR: 1.03, 95% CI: 0.82–1.30, p=0.775). The comparisons of the clinical event rates in the IN alert state with those in the OUT of alert state yielded incidence rate ratios ranging from 9.72 to 14.54 (all p<0.001) in all groups of patients stratified by: CRT/non-CRT, AF/non-AF, CKD/non-CKD. Indeed, after multivariate correction for CKD and AF at implantation, the time IN the HeartLogic alert state >13% was associated with the occurrence of the combined endpoint of cardiovascular hospitalization or death (HR: 2.54, 95% CI: 1.61–4.01, p<0.001).

Conclusions

The burden of HeartLogic alerts appears similar between CRT and non-CRT patients, while patients with AF and CKD seem more exposed to alerts. Nonetheless, the ability of the HeartLogic algorithm to identify patients during periods of significantly increased risk of clinical events is confirmed regardless of the type of device, the presence of AF, or CKD.

Funding Acknowledgement

Type of funding sources: None.

Early- and delayed-afterdepolarizations as cellular promoter of ventricular fibrillation in hypertrophic cardiomyopathy

Funding Acknowledgements

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): In Silico project

Background

Hypertrophic cardiomyopathy (HCM) represents the commonest inherited cardiac disease, with a prevalence of 1/500 in the general population. The most devastating consequence of HCM is sudden cardiac death (SCD) due to ventricular fibrillation, particularly common in children and young adults. The positive correlation between the extent of late gadolinium enhancement (LGE, reflecting myocardial fibrosis) and the arrhythmic risk suggests that ventricular arrhythmias are held to originate from the fibrotic regions, by a mechanism of electrical re-entry. However, recent data suggest that enhanced cellular automaticity (i.e.  early- or delayed-afterdepolarizations, EADs or DADs-) may be clinically more relevant in promoting ventricular arrhythmias in patients.

Purpose

Aiming to better understand the cellular and molecular mechanisms of arrhythmogenesis in HCM and to establish a reliable arrhythmic risk stratification in patients, we performed a translational and retrospective study in 61 HCM patients who underwent surgical myectomy, by combining a clinical follow-up study with in vitro assessments of cellular arrhythmogenicity.

Methods

We retrospectively studied 61 HCM patients who underwent surgical interventricular-septum myectomy to relieve refractory obstruction-related symptoms. At the time of surgery, fresh ventricular tissue was collected and used to isolate single ventricular cardiomyocytes (CMs), which were used for patch-clamp measurements and Ca2+ imaging experiments to assess the occurrence of EADs and DADs. Patients were followed up for a median time of 8 years and the occurrence of non-sustained ventricular tachycardia (NSVT) or life-threatening arrhythmic events (LAE, including sustained VT and ventricular fibrillation, VF) was monitored. Moreover, data from ECG and cardiac magnetic-resonance studies were collected.

Results

EADs occurred in CMs from 36% of patients and were associated with prolonged action potential duration while DADs occurred in 24% of patients and correlated with abnormalities of intracellular Ca2+ handling. During follow up, NSVT events occurred in 19/61 patients while LAE occurred in 4/61 patients. Their combined occurrence (37%) strongly correlated with the presence of DADs in cardiomyocytes. Patients with NSVT/LAE were more likely to show specific "pro-arrhythmic" pathological ECG-patterns. Among patients with LGE, the presence of DADs in cells behaved as a necessary pre-requisite for NSVT/LAE, as none of the patients with evidence of fibrosis but negative for DADs had arrhythmic events.

Conclusions

The presence of pro-arrhythmic changes appears to be necessary for arrhythmia generation in HCM and seems to be related with specific alterations at ECG level, that might be used as clinical arrhythmia predictors in HCM patients. Fibrosis per se is not a major predictor of arrhythmias in HCM but may contribute to generate sustained arrhythmias in the presence of substantial cellular triggers (DADs).

Electrophysiological remodeling in primary versus secondary cardiac hypertrophy: a study in human cardiomyocytes

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Ministero dell'università e della ricerca

Electrophysiological remodeling in primary versus secondary cardiac hypertrophy: a study in human cardiomyocytes

Introduction

Myocardial hypertrophy is an adaptive condition to hemodynamic stress, characterized by the increase in size of the cardiomyocytes and in the cardiac mass. It involves more frequently the left ventricle (LV) and leads to an enhanced risk of arrhythmias; it’s characterized by the increase walls thickness and by a large remodelling of the cardiac tissue in terms of fibrosis, impaired calcium handling and ion current balance. The LV hypertrophy could be induced by genetic abnormalities, such as in hypertrophic cardiomyopathy (HCM) or it could be secondary to other pathological conditions, like aortic stenosis (SAO-HT).

Purpose

In this work we will compare the mechanisms that mainly determine primitive (HCM samples) or secondary (to aortic stenosis: SAO-HT) LV hypertrophy to assess common points and disagreements.

Methods

Human septal specimens from HCM, SAO-HT and control (CTRL) surgical patients were collected, tissue was in part rapidly frozen, in part processed to isolate responsive single cells or trabeculae. We performed patch clamp experiments to measured action potential duration (APD) and calcium current (ICaL). To study the Ca2+ handling we performed imaging analysis; isolated cardiomyocytes were loaded with a Ca2+ sensitive dye (CAL530) by incubating cells for 30 min, then we evaluate the calcium transients at different stimulation frequencies.

Results

We evaluated APD, ICaL, and Ca2+ handling in the 3 groups: HCM, SAO-HT and CTRL cardiomyocytes. Both pathological groups show to be depolarized, to have a prolonged APD, diastolic Ca2+ concentration is higher and the kinetics are slower than in CTRL cardiomyocytes. HCM cardiomyocytes has longer APD than SAO-HT and higher diastolic Ca2+ concentration, HCM also shows longer kinetics of the decay phase of the Ca2+ transient compare to SAO-HT. The ICaL is comparable between CTRL and SAO-HT, it is higher in HCM and the inactivation kinetics are slower.

Discussion and Conclusion

We evaluate the electrophysiological differences among cardiomyocytes derived from a secondary or primary myocardial hypertrophy and from non-hypertrophic myocardia. Alterations in the two groups of pathological samples are similar. Both shows slowed Ca2+ transient kinetics, that slow down the relaxation machinery, and increase diastolic Ca2+ concentration, that could cause arrhythmic events (DAD). The increase in diastolic Ca2+ could also be responsible for the hyperactivation of the CAMK-II that has among its target ICaL channel and the Na2+ channel that are hyperactivated causing the prolongation of APD. The functional alterations observed in the hypertrophic cardiomyocytes could be considered not as disease specific response but a mechanism of adaptation to the hypertrophy and to diastolic dysfunction, those are more serious where the hypertrophy is genetic determined.

Extracellular stiffness as a determinant of cardiac dysfunction in duchenne muscular distrophy: a study on human iPSC derived cardiomyocytes

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): Fondazione Intesa San Paolo

Introduction

Duchenne muscular dystrophy (DMD) is a genetic disorder characterized by progressive degeneration of striated muscles; in addition to skeletal muscle impairment, DMD is also characterized by progressive myocardial disfunction. The low translational value of animal models and the low availability of human samples make DMD hard to investigate; induced pluripotent stem cells (iPSCs) represent a novel tool to model this disease, preserving the genetic heritage of the patient, including the pathogenic mutation causing dystrophy.

Aim

Our aim is to characterize cardiomyocytes differentiated from iPSCs (iPSC-CMs) derived from healthy donors (CTRL) and DMD patients, to identify the pathophysiological mechanisms of DMD-related cardiomyopathy.

Materials and Methods

Cardiomyocytes are differentiated from IPSCs obtained by reprogramming isolated mononucleated blood cells from healthy donors and DMD patients. IPSC-CMs are cultured until day 60, 75 or 90 post-differentiation after plating on nanostructured substrates with two different stiffness levels: PEG-substrates, with lower rigidity, mimicking healthy extracellular tissue, and DEG-substrates, with greater rigidity, that mimic the presence of myocardial fibrosis. Through imaging techniques, we evaluated calcium handling and action potentials (AP) on DMD and CTRL iPSC-CMs by using specific fluorescent dyes for Ca2+ (CAL630) and membrane voltage (Fluovolt). Cells were stimulated at different pacing rates.

Results

The calcium transient amplitude of CTRL-iPSC-CMs became larger during maturation. This adaptation did not occur in DMD lines, showing a deficit calcium release due to poor maturation of the sarcoplasmic reticulum (SR). AP duration was shorter in the DMD line at d75 but at d90 we observed no differences when compared with the CTRL line. CTRL iPSC-CMs showed a marked ability to adapt to different substrate stiffnesses. Indeed, the calcium transient amplitude was larger and its kinetics faster when cells were grown on the rigid DEG substrates rather than on PEG plates. In the DMD line, however, no differences were observed between the substrates.

Conclusions

Our results highlight a scarce ability of DMD iPSC-CM to adapt to different substrate stiffness, resulting in mechanical and electrical impairment, especially in the presence of stiffer substrates. This might explain why cardiac impairment is usually absent in the early stages of DMD, when cardiac structural changes are still absent. However, the electrophysiological and mechanical impairment of DMD hearts may precipitate rapidly when extracellular stiffness starts to increase due to development of cardiac fibrosis.

Optogenetic manipulation of cardiac electrical dynamics using sub-threshold illumination: dissecting the role of cardiac alternans in terminating rapid rhythms

Funding Acknowledgements

Type of funding sources: None.

Cardiac action potential (AP) shape and propagation are regulated by several key dynamic factors such as ions channel recovery and intracellular Ca2+-cycling. Experimental methods for manipulating AP electrical dynamics commonly use ion channel inhibitors that lack spatial and temporal specificity. In this work, we propose a novel approach based on optogenetics to manipulate cardiac electrical activity employing a light-modulated depolarizing current with intensities that are too low to elicit APs (sub-threshold illumination) but are sufficient to fine-tune AP electrical dynamics. We investigated the effects of sub-threshold illumination in isolated cardiomyocytes and whole hearts by using transgenic mice constitutively expressing a light-gated ion channel (channelrhodopsins-2, ChR2). We find that ChR2-mediated depolarizing current prolongs APs and reduces conduction velocity (CV) in a space-selective and reversible manner. Sub-threshold manipulation also affects the dynamics of cardiac electrical activity, increasing the magnitude of cardiac alternans. We use an optical system that uses real-time feedback control to generate re-entrant circuits with user-defined cycle lengths to explore the role that cardiac alternans plays in spontaneous termination of ventricular tachycardias (VTs). We find that VT stability significantly decreases during sub-threshold illumination primarily due to an increase in the amplitude of electrical oscillations, which implies that cardiac alternans may be beneficial in the context of self-termination of VT.

Paradoxical prolongation of QT interval during exercise in patients with hypertrophic cardiomyopathy: cellular mechanisms and implications for diastolic function

Aims

Ventricular cardiomyocytes from hypertrophic cardiomyopathy (HCM) patient hearts show prolonged action potential duration (APD), impaired intracellular Ca²⁺ homeostasis and abnormal electrical response to beta -adrenergic stimulation. We sought to determine whether this behaviour is associated with abnormal changes of repolarization during exercise and worsening of diastolic function, ultimately explaining the intolerance to exercise experienced by some patients without obstruction.

Methods and results

Non-obstructive HCM patients (178) and control subjects (81) underwent standard exercise testing, including exercise echocardiography. Ventricular myocytes were isolated from myocardial samples of 23 HCM and eight non-failing non-hypertrophic surgical patients. The APD shortening in response to high frequencies was maintained in HCM myocytes, while β-adrenergic stimulation unexpectedly prolonged APDs, ultimately leading to a lesser shortening of APDs in response to exercise. In HCM vs. control subjects, we observed a lesser shortening of QT interval at peak exercise (QTc: +27 ± 52 ms in HCM, −4 ± 50 ms in controls, P < 0.0001). In patients showing a marked QTc prolongation (>30 ms), the excessive shortening of the electrical diastolic period was linked with a limited increase of heart-rate and deterioration of diastolic function at peak effort.

Conclusions

Abnormal balance of Ca²⁺- and K⁺-currents in HCM cardiomyocytes determines insufficient APD and Ca²⁺-transient shortening with exercise. In HCM patients, exercise-induced QTc prolongation was associated with impaired diastolic reserve, contributing to the reduced exercise tolerance. Our results support the idea that severe electrical cardiomyocyte abnormalities underlie exercise intolerance in a subgroup of HCM patients without obstruction.

Association between atrial fibrillation and cardiac implantable defibrillator detected heart failure status

Funding Acknowledgements

Type of funding sources: None.

Background

In heart failure (HF) patients, atrial fibrillation (AF) is a common comorbidity and is associated with a worse prognosis. Implantable defibrillator (ICD) diagnostics allow continuous monitoring of atrial high-rate events (AHRE), as a surrogate of AF, and are equipped with algorithms for HF monitoring. We evaluated the association between the values of the multisensor HF HeartLogic Index and the incidence of AF, and assessed the performance of the Index in detecting follow-up periods of significantly increased AF risk.

Methods

The HeartLogic feature was activated in 568 ICD patients. The median follow-up was 25 months [25th–75th percentile: 15-35]. The HeartLogic algorithm calculates a daily HF index and identifies periods IN the alert state on the basis of a configurable threshold. The endpoints were: daily AF burden of ≥5 minutes, ≥6 hours and ≥23 hours.

Results

The HeartLogic index crossed the threshold value 1200 times (0.71 alerts/patient-year). The time IN the alert state was 13% of the total observation period. During the observation period, an AF burden of ≥5 minutes/day was documented in 183 (32%) patients, ≥6 hours/day in 118 (21%) patients, and ≥23 hours/day in 89 (16%). On using a time-dependent Cox model, the weekly time IN the alert state was independently associated with an AF burden of ≥5 minutes/day (HR:1.95, 95%CI:1.22-3.13, p=0.005), ≥6 hours/day (HR:2.66, 95%CI:1.60-4.44, p&lt;0.001), and ≥23 hours/day (HR:3.32, 95%CI:1.83-6.02, p&lt;0.001), after correction for baseline confounders. Comparison of the episode rates in the IN-alert state with those in the OUT-of-alert state yielded HRs ranging from 1.57 to 3.11 for AF burden from ≥5 minutes to ≥23 hours.

Conclusions

The HeartLogic alert state was independently associated with AF occurrence. The intervals of time defined by the algorithm as periods of increased risk of HF allow risk stratification of AF according to various thresholds of daily burden.

Remotely-driven management of diuretic therapy in heart failure patients with a multiparametric ICD algorithm

Funding Acknowledgements

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): Boston Scientific

Background

HeartLogic algorithm combines data from multiple sensors to predict future heart failure (HF) decompensation in patients with an implantable defibrillator (ICD) . An optimal strategy to manage algorithm alerts is not yet known, although decongestive treatment with diuretics is the most frequent alert-triggered action reported so far.

Purpose

We describe the implementation of HeartLogic for remote monitoring of HF patients, and we evaluate the approach to diuretic dosing and timing of the intervention in patients with device alerts.

Methods

The study was conducted in eight Italian high-volume arrhythmia centers. The algorithm was activated in 229 ICD patients during a median follow-up was 17 months [25th–75th percentile: 11-24] between December 2017 and July 2020. Remote data reviews and patient phone contacts were undertaken at the time of HeartLogic alerts, to assess the patient’s status and to prevent HF worsening. The study protocol did not mandate any specific intervention algorithm, and physicians were free to remotely implement clinical actions, to schedule extra in-office visits when deemed necessary for additional investigations or for interventions, or to adopt an active monitoring approach. We analyzed alert-triggered augmented HF treatments, consisting of isolated increases in diuretics dosage.

Results

We reported 242 alerts (0.8 alerts/patient-year) in 123 patients, 137 (56%) alerts triggered clinical actions to treat HF. Overall, timely diuretic changes were associated with a shorter "in-alert" state duration in comparison with late changes, i.e. 28 days [25th-75th percentile: 20-43] versus 62 days [25th-75th percentile: 44-118], p&lt;0.001. By contrast, major and minor diuretic augmentations resulted in comparable durations, i.e. 47 days [25th-75th percentile: 30-58] versus 38 days [25th-75th percentile: 23-79], p=0.954. Of the 56 decongestive treatment adjustments, 47 resolved the alert condition, while in the remaining 9 cases, further treatments were required (augmented HF therapy during hospitalization or unscheduled intravenous decongestive therapy in outpatients). The need of hospitalization for further treatments to resolve the alert condition was associated with higher HeartLogic index values on the day of the diuretics increase (odds ratio: 1.11, 95%CI: 1.02-1.20, p=0.013) and with late interventions (odds ratio: 5.11, 95%CI: 1.09-24.48, p=0.041). No complications were reported after drug adjustments.

Conclusions

Decongestive treatment adjustments triggered by HeartLogic alerts, even when such adjustments were completely dependent on the physicians’ clinical expertise and were not standardized. The early use of decongestive treatment and the use of high doses of diuretics seem to be associated with more favorable outcomes.

Predictors of heart failure events detected by a multisensor implantable defibrillator algorithm

Funding Acknowledgements

Type of funding sources: None.

Background

Cardiovascular and non-cardiovascular comorbidities are common in heart failure (HF) patients and determine disease severity and prognosis. Select modern implantable defibrillators (ICDs) are equipped with multisensor algorithms for HF monitoring. The HeartLogic index combines multiple ICD-based sensor data (heart rate, heart sounds, thoracic impedance, respiration, activity), and the associated alert has proved to be a sensitive and timely predictor of impending HF decompensation in cardiac resynchronization therapy (CRT) patients.

Purpose

This analysis aims to investigate the performance of the algorithm in non-CRT patients, as well as in relation to the presence of comorbidities.

Methods

The HeartLogic feature was activated in 568 ICD patients (410 with CRT) from 26 centers. The median follow-up was 25 months [25th–75th percentile: 15-35].

Results

We recorded 1200 HeartLogic alerts (0.71 alerts per patient-year) in 370 patients. Among patient characteristics, atrial fibrillation (AF) at implantation (HR: 1.62, 95%CI: 1.27-2.07, p&lt;0.001) and chronic kidney disease (CKD) (HR: 1.53, 95%CI: 1.21-1.93, p&lt;0.001) independently predicted alerts. HeartLogic alerts were not associated with CRT vs. non-CRT device implantation (HR: 1.03, 95%CI: 0.82-1.30, p=0.775). Comparing the combined index and all physiologic parameters during clinically stable periods we did not notice differences between CRT and non-CRT patients. Thoracic impedance was significantly lower in CKD than non-CKD patients. (46±11ohm versus 49±10ohm; p=0.047). We found a higher S3 amplitude (0.9±0.3mG versus 0.8±0.2mG; p=0.005) and nocturnal heart rate (72±9bpm versus 66±7bpm; p&lt;0.001), and lower S1 amplitude (2.0±0.8mG versus 2.4±0.9mG; p&lt;0.001) in AF patients vs non-AF. These differences persisted at the time of alerts (all p&lt;0.05). In the overall population, and in patients stratified by device type, CKD and AF, we measured significant changes of all contributing sensors (paired t-test; p&lt;0.05) from clinically stable periods to the time of alert.

Conclusions

The burden of HeartLogic alerts appears similar between CRT and non-CRT patients, while patients with AF and CKD seem more exposed to alerts. ICD-measured thoracic impedance is sensitive to the fluid overload that characterizes kidney disease, as well as the first and third heart sound amplitudes seem sensitive to the reduced ventricular efficiency during AF. Nonetheless, ICD sensors seem to equally contribute to the HeartLogic alerts in all patient subgroups.

C9 SUBCUTANEOUS IMPLANTABLE CARDIOVERTER DEFIBRILLATOR IN PATIENTS WITH LOW BMI: REAL–WORLD DATA FROM A EUROPEAN MULTICENTER ANALYSIS

Background

One of the current limitations of the S–ICD is the relatively large size of the generator compared to the TV (transvenous) ICD. There is little evidence whether the size of the current S–ICD generator is associated with an elevated risk of device–related complications in patients with a low body mass index (BMI).

Purpose

Aim of this study was to compare the device–related complications and long–term outcomes in a large real world cohort of S–ICD recipients in patients with a BMI &lt;18 kg/m2 compared to patients with a BMI &gt;18 kg/m2.

Methods

All consecutive patients meeting current guideline indications for ICD implantation and undergoing implantation of a S–ICD device (Boston Scientific, Marlborough, Massachusetts, USA) at 21 European institutions enrolled in the extended ELISIR registry were used for the current analysis. Patients were classified into two cohorts, depending on the BMI at the time of device implantations: BMI &lt; 18 kg/m2 versus &gt; 18 kg/m2.

Results

Out of a total of 1497 pts, 58 pts (3.9%) had a BMI &lt; 18 kg/m2. Patients with BMI &lt;18 kg/m2 were younger (44.6±2.4 vs 50.8±0.4; p = 0.004) and more frequently female (58.6% vs 22.3%, p &lt; 0.001). No differences in any of the other baseline characteristic were observed. Implantation techniques resulted comparable between the groups (rates of 2–incision technique: 87.8% vs 91.9%; p = 0.256; inter–muscular placement: 89.7% vs 83.3%; p = 0.198). Of note, the mean PRAETORIAN score at implantation of patients with BMI &lt;18 kg/m2 was significantly lower (33.8±9.1 vs 54.1±47.3; p = 0.035), although the vast majority of patients in both cohorts qualified as at low risk of conversion failure (100% vs 91.4%; p = 0.436). Over a median follow up time of 22.4 [11.6–36.8] months, both overall device–related complications (5.2% vs 7.4%) and rates of inappropriate shocks (12.0% vs 8.8%) resulted comparable between the two groups (p = 0.517 and p = 0.385, respectively). Figure 1 reports Kaplan–Meier curves showing the combined incidence of device–related complications and inappropriate shocks in the two groups (log–rank p = 0.576).

Conclusion

No differences in device–related complications and long–term outcomes after S–ICD implantation were observed in patients with BMI &lt;18 kg/m2 compared to the remaining recipients in a large multicentered real–world analysis.

P21 AGE–RELATED DIFFERENCES AND ASSOCIATED OUTCOMES OF S–ICD: INSIGHTS FROM A LARGE, EUROPEAN, MULTICENTER REGISTRY

Background

The subcutaneous implantable cardioverter defibrillator (S–ICD) has become an alternative to transvenous ICDs (TV–ICD) in patients who do not need pacing. To date, there is little evidence directly comparing the rates of inappropriate shocks (IAS) in young vs old S–ICD recipients.

Purpose

Aim of our study was to assess differences in device–related complications and inappropriate shocks (IS) between teenagers/young adults and adult recipients of a subcutabeous implantable cardioverter defibrillator (S–ICD) device.

Methods

Two propensity–matched cohorts of teenagers + young adults (≤ 30–year–old) and adults (&gt; 30–year–old) were retrieved from the ELISIR registry. The primary outcome was the comparison of the inappropriate shock (IAS) rate; complications, freedom from sustained ventricular arrhythmic events, overall and cardiovascular mortality were deemed secondary outcomes.

Results

A total of 1491 patients were extracted from the ELISIR project. Teenagers + young adults represented 11.0% of the entire cohort. Two propensity–matched groups of 161 patients each were used for the analysis (Figure 1); median follow–up was 23.1 [13.2–40.5] months. 15.2% patients experienced inappropriate S–ICD shocks and 9.3% device related complications were observed with no age–related differences in IAS (16.1% vs 14.3%; p = 0.642) and complication rates (9.9% vs 8.7%; p = 0.701); Figure 2 shows a survival analysis from inappropriate shocks in the teen–ager/young adult cohort (red) and in the adult cohort (blue). At univariate analysis, young age was not associated with increased rates of IAS (HR 1.204 [0.675–2.148]: p = 0.529). At multivariate analysis (Figure 3), the use of SMART pass algorithm was associated to a strong reduction in IAS (aHR 0.292 [0.161–0.525]; p &lt; 0.001), while ARVC was associated with higher rates of IAS (aHR 2.380 [1.205–4.697]; p = 0.012).

Conclusion

In a large multicentered European registry of patients with S–ICD, 11.0% of all recipients were teenagers or young adults. The use of S–ICD in teenagers/young adults resulted safe and effective, and the rates of complications and IAS between teenagers/young adults and adults were not significantly different. The only predictor of increased IAS was a diagnosis of ARVC.

P25 SUBCUTANEOUS–ICD IN PATIENTS WITH HEART FAILURE: RESULTS FROM A MULTICENTER, EUROPEAN ANALYSIS

Background

Data on patients with heart failure (HF) with a subcutaneous implantable cardioverter defibrillator (S–ICD) are scarce.

Objective

Aim of this study was to assess clinical outcomes of the S–ICD in HF patients in a real–world analysis from the largest European retrospective S–ICD registry (ELISIR).

Methods

All consecutive patients undergoing S–ICD implantation at several European institutions were used for the current analysis. The population was classified into two groups: the HF (classified as HF with reduced and mid–range ejection fraction – HFrEF and HFmrEF) vs the no–HF cohort. The primary outcome of the study was the inappropriate shock (IS) rate across the two cohorts. As secondary outcomes, appropriate shocks, cardiovascular mortality and device–related complications during follow–up were assessed

Results

A total of 1409 patients from the ELISIR registry were included; HF patients represented 57.3% of the entire cohort (n = 701, 86.9% HFrEF; n = 106,13.1% HFmrEF). Over a median follow–up of approximately 2 years, a total of 133 inappropriate shocks were observed in the entire cohort, without significant differences among the two groups (9.2% vs 9.8%, p = 0.689). 133 complex ventricular arrhythmias were adequately recognized and treated, with similar rates of appropriate shocks (9.2% vs 9.8%, p = 0.689). Inappropriate and effective shocks–free survival has been represented in Figure 1 (Kaplan–Meier estimates). At multivariate analysis (Figure 2), age (HR = 0.974 [0.955–0.992], p = 0.005), LVEF (HR = 0.954 [0.926–0.984], p = 0.003), arrhythmogenic right ventricular cardiomyopathy – ARVC (HR = 3.364 [1.206–9.384], p = 0.020) and smart pass + (HR = 0.321 [0.184–0.560], p &lt; 0.001) remained associated with inappropriate shocks. Moreover, a low number of patients (n = 76) experienced device–related complications, more frequently in the HF cohort (6.2% vs 3.8%, p = 0.031) with no significant differences regarding any specific outcome of interest: lead infection (1.1% vs 0.7%, p = 0.381), pocket infection (1.9% vs 0.8%, p = 0.107), pocket hematoma (3.2% vs 2.8%, p = 0.668).

Conclusion

The use of S–ICD in HF patients did not result in a higher rate of inappropriate shocks when compared to no–HF patients, even when stratifying for LVEF. Only age, LVEF, ARVC e Smart Pass algorithm were predictors of the primary outcome at multivariate analysis. Despite a lower overall rate of complications in the entire cohort, HF patients experienced device–related complications more frequently.

Cellular determinants of arrhythmic rysk in hypertrophic cardiomyopathy

Background

Hypertrophic cardiomyopathy (HCM) is the commonest inherited cardiac disease, with a prevalence of 1/500 in the general population. The most devastating consequence of HCM is sudden cardiac death (SCD) due to ventricular fibrillation, particularly common in children and young adults (age &lt;30 years). The positive correlation between the extent of late gadolinium enhancement (LGE, reflecting myocardial fibrosis) and the arrhythmic risk in HCM suggests that ventricular arrhythmias are held to originate from the fibrotic regions, by a mechanism of electrical re-entry. However, recent data suggest that enhanced cellular automaticity (i.e. early- or delayed-afterdepolarizations, EADs or DADs-), rather than macro-reentry, may be clinically relevant in promoting ventricular arrhythmias in patients.

Purpose

Aiming to better understand the cellular and molecular mechanisms of arrhythmogenesis in HCM and to establish a reliable arrhythmic risk stratification in patients, we performed a translational study in HCM patients who underwent surgical myectomy, by combining a clinical follow-up study with in vitro assessments of cellular arrhythmogenicity in ventricular cardiomyocytes.

Methods

We retrospectively studied 61 HCM patients who underwent surgical interventricular-septum myectomy to relieve refractory obstruction-related symptoms. At the time of surgery, fresh ventricular tissue was collected and used to isolate single ventricular cardiomyocytes (CMs), which were used for patch-clamp measurements to assess the occurrence of EADs and DADs. Patients were followed up for a median time of 8 years and the occurrence of non-sustained ventricular tachycardia (NSVT) or life-threatening arrhythmic events (LAE) was monitored. Moreover, data from ECG and contract cardiac magnetic-resonance studies were collected.

Results

EADs occurred in CMs from 36% of patients and were associated with prolonged action potential duration. DADs occurred in 24% of patients and were associated with abnormalities of CM intracellular Ca2+ handling. The occurrence of NSVT/ LAE in patients was strongly associated with the presence of DADs in cardiomyocytes but not with the presence of EADs. Patients with NSVT/LAE were more likely to show specific “pro-arrhythmic” pathological ECG-patterns. Among patients with LGE, the presence of DADs in cells behaved as a necessary pre-requisite for NSVT/LAE, as none of the patients with evidence of fibrosis who were negative for DADs had arrhythmic events.

Conclusions

The presence of pro-arrhythmic changes appears to be necessary for arrhythmia generation in HCM and seems to be related with specific alterations at ECG level, that might be used as clinical arrhythmia predictors in HCM patients. Fibrosis per se is not a major predictor of arrhythmias in HCM but may contribute to generate sustained arrhythmias in the presence of substantial cellular triggers (DADs).

Funding Acknowledgement

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): EU Horizon 2020. Grant number 777204 (silico FCM).

Abnormalities in sodium current and calcium homoeostasis as drivers of arrhythmogenesis in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a common inherited monogenic disease with a prevalence of 1/500 in the general population, representing an important cause of arrhythmic sudden cardiac death (SCD), heart failure, and atrial fibrillation in the young. HCM is a global condition, diagnosed in >50 countries and in all continents. HCM affects people of both sexes and various ethnic and racial origins, with similar clinical course and phenotypic expression. The most unpredictable and devastating consequence of HCM is represented by arrhythmic SCD, most commonly caused by sustained ventricular tachycardia or ventricular fibrillation. Indeed, HCM represents one of the main causes of arrhythmic SCD in the young, with a marked preference for children and adults <30 years. SCD is most prevalent in patients with paediatric onset of HCM but may occur at any age. However, risk is substantially lower after 60 years, suggesting that the potential for ventricular tachyarrhythmias is mitigated by ageing. SCD had been linked originally to sports and vigorous activity in HCM patients. However, it is increasingly clear that the majority of events occurs at rest or during routine daily occupations, suggesting that triggers are far from consistent. In general, the pathophysiology of SCD in HCM remains unresolved. While the pathologic and physiologic substrates abound and have been described in detail, specific factors precipitating ventricular tachyarrhythmias are still unknown. SCD is a rare phenomenon in HCM cohorts (<1%/year) and attempts to identify patients at risk, while generating clinically useful algorithms for primary prevention, remain very inaccurate on an individual basis. One of the reasons for our limited understanding of these phenomena is that limited translational research exists in the field, while most efforts have focused on clinical markers of risk derived from pathology, instrumental patient evaluation, and imaging. Specifically, few studies conducted in animal models and human samples have focused on targeting the cellular mechanisms of arrhythmogenesis in HCM, despite potential implications for therapeutic innovation and SCD prevention. These studies found that altered intracellular Ca2+ homoeostasis and increased late Na+ current, leading to an increased likelihood of early and delayed after-depolarizations, contribute to generate arrhythmic events in diseased cardiomyocytes. As an array of novel experimental opportunities have emerged to investigate these mechanisms, including novel 'disease-in-the-dish' cellular models with patient-specific induced pluripotent stem cell-derived cardiomyocytes, important gaps in knowledge remain. Accordingly, the aim of the present review is to provide a contemporary reappraisal of the cellular basis of SCD-predisposing arrhythmias in patients with HCM and discuss the implications for risk stratification and management.

A multiparametric ICD algorithm for heart failure risk stratification and management: an analysis in clinical practice

Funding Acknowledgements

Type of funding sources: None.

Introduction

The HeartLogic algorithm combines multiple implantable cardioverter defibrillator (ICD) sensors to identify patients at risk of heart failure (HF) events.

Purpose

We sought to evaluate the risk stratification ability of this algorithm in clinical practice. We also analyzed the alert management strategies adopted in the study group and their association with the occurrence of HF events.

Methods

The HeartLogic feature was activated in 366 ICD and cardiac resynchronization therapy ICD patients at 22 centers. The HeartLogic algorithm automatically calculates a daily HF index and identifies periods IN or OUT of an alert state on the basis of a configurable threshold (in this analysis set to 16).

Results

The HeartLogic index crossed the threshold value 273 times (0.76 alerts/patient-year) in 150 patients over a median follow-up of 11 months [25-75 percentile: 6-16]. Overall, the time IN the alert state was 11% of the total observation period. Patients experienced 36 HF hospitalizations and 8 patients died of HF (rate: 0.12 events/patient-year) during the observation period. Thirty-five events were associated with the IN alert state (0.92 events/patient-year versus 0.03 events/patient-year in the OUT of alert state). The hazard ratio in the IN/OUT of alert state comparison was (HR: 24.53, 95% CI: 8.55-70.38, p &lt; 0.001), after adjustment for baseline clinical confounders. Alerts followed by clinical actions were associated with a lower rate of HF events (HR: 0.37, 95% CI: 0.14-0.99, p = 0.047). No differences in event rates were observed between in-office and remote alert management. By contrast, verification of HF symptoms during post-alert examination was associated with a higher risk of HF events (HR: 5.23, 95% CI: 1.98-13.83, p &lt; 0.001).

Conclusions

This multiparametric ICD algorithm identifies patients during periods of significantly increased risk of HF events. The rate of HF events seemed lower when clinical actions were undertaken in response to alerts. Extra in-office visits did not seem to be required in order to effectively manage HeartLogic alerts, while post-alert verification of symptoms seemed useful in order to better stratify patients at risk of HF events.

Implantable cardioverter defibrillator multisensor monitoring during home confinement caused by the covid-19 pandemic

Funding Acknowledgements

Type of funding sources: None.

Background

Utilization of remote monitoring platforms was recommended amidst the COVID-19 pandemic. The HeartLogic algorithm combines data from multiple implantable cardioverter defibrillator (ICD) sensors (first and third heart sounds, intrathoracic impedance, respirations, night heart rate, and patient activity) to provide integrated data that may allow for detection of early signs of worsening HF.

Purpose

We examined whether the HeartLogic platform may elucidate behavioral changes that impact HF decompensation, and the possible consequences of home confinement caused by the COVID-19 pandemic.

Methods

The Italian lockdown was imposed from March 8th to May 18th. On March 8th 2020, the HeartLogic feature was active in 349 ICD and cardiac resynchronization therapy ICD patients at 20 Italian centers. The period from January 1st to July 19th was divided in 3 phases: Pre-Lockdown (weeks 1-11), Lockdown (weeks 12-20), Post-Lockdown (weeks 21-29).

Results

Immediately after the implementation of stay at home orders (week 12) we observed a significant drop in median activity level (65min [36-103] in week 12 vs. 101min [61-140] in Pre-Lockdown; p < 0.001), while there was no difference in the other contributing sensors. The median composite HeartLogic index increased at the end of Lockdown (4.7 [1.3-10.2] in week 20 vs. 2.5 [0.7-7.0] in Pre-Lockdown; p = 0.019). The weekly rate of HeartLogic alerts was significantly higher during Lockdown (1.56 alerts/week/100pts, 95%CI:1.15-2.06; IRR = 1.71, p = 0.014) and Post-Lockdown (1.37 alerts/week/100pts, 95%CI:0.99-1.84; IRR = 1.50, p = 0.072) than that reported in Pre-Lockdown (0.91 alerts/week/100pts, 95%CI:0.64-1.27). However, the median duration of alert state and the maximum index value did not change among phases, as well as the proportion of alerts followed by clinical actions at the centers (Pre-Lockdown: 31%, Lockdown: 22%, Post-Lockdown: 28%), and the proportion of alerts fully managed remotely (i.e. no in-clinic visits) (Pre-Lockdown: 89%, Lockdown: 90%, Post-Lockdown: 88%).

Conclusions

The system was sensitive to the behavioral changes occurred during the lockdown, i.e. decrease in activity. However, the home confinement had no impact on the other sensors. The higher rate of HeartLogic alerts during lockdown and the increase in the median index after 8 weeks of home confinement suggest the worsening of the HF status, possibly explained by the behavioral changes. Nonetheless, the management of the HF detected events (actions performed and management strategy) was not impacted by the restrictions.

P529Efficacy and safety of S-ICD implantation without use of defibrillation threshold testing: a retrospective multicentric observational study

Introduction

The subcutaneous ICD (S-ICD) is a valid alternative to transvenous systems (TV-ICD) for the treatment of life-threatening arrhythmias, and the extravascular position of the lead allows a significant reduction of the risk of infection. Current guidelines recommend defibrillation threshold testing (DFT) at the time of S-ICD implantation (class I). Although randomised trials have proven the safety of TV-ICD implantation with no DFT, it is unclear whether such an approach could be adopted for S-ICD as well. The PRAETORIAN score, based on post-implantation chest X-ray, can accurately predict a high defibrillation threshold after S-ICD implantation. The aim of this retrospective multicentre study was to evaluate the efficacy and safety of S-ICD implantation with no DFT.

Methods

We enrolled 203 consecutive patients undergoing S-ICD implantation in six different centres between October 2012 and January 2019. It was left at discretion of the operator whether performing or not DFT at the time of the procedure. Baseline device settings were collected, and the PRAETORIAN score was retrospectively calculated whenever chest X-ray was available. Both remote or in-clinic device interrogation reports were systemically analysed, and all the shocks and arrhythmia episodes identified. All the patients provided consent form and ethical approval was obtained.

Results

The population (mean age 57.6 ± 14.2) was divided in two groups, based on whether DFT was performed at the time of the S-ICD implantation: 72 patients (35.4%) underwent DFT (DFT+ group), while 131 patients (64.5%) did not (DFT- group). In the DFT- group, mean LVEF was lower (32 ± 8% vs 42 ± 17%, p &lt; 0.0001) and prevalence of diabetes mellitus and atrial fibrillation higher compared to the DFT+ group (27.5% vs 13.9%, p = 0.04 and 38.9% vs 19.44%, p = 0.007; respectively). In addition, the indication for S-ICD was more frequently primary prevention in the DFT- vs DFT+ group (70.8% vs 90.8%, p = 0.0004; respectively). No differences in terms of device programming were identified between the two cohorts. The PRAETORIAN score was significantly higher in the DFT- vs DFT+ patients (50 ± 26 vs 36 ± 18, p = 0.032; respectively). After a median follow-up of … months, we observed 5 appropriate shocks in 3 patients from the DFT+ group vs. 15 shocks in 8 patients from the DFT- group (p = 0.81). All the life-threatening arrhythmias were successfully recognised and treated by the device. DFT was complicated by pulseless electrical activity in one patient. One patient in the DFT- group suffered from an episode of ventricular tachycardia requiring a total of 4 shocks for being terminated. Six patients in the DFT- group died for non-arrhythmic causes. On the Kaplan-Meier analysis, cumulative survival was comparable between the two groups (log rank p value = 0.13).

Conclusions

This study suggests that implantation of S-ICD with no DFT might be reasonable. These results should be confirmed in prospective randomised trials.

48Remote monitoring of Heart Failure patients with a Multisensor ICD Algorithm: value of an alert-based follow-up strategy

Background

The HeartLogic algorithm measures and combines multiple parameters, i.e. heart sounds, intrathoracic impedance, respiration pattern, night heart rate, and patient activity, in a single index. The associated alert has proved to be a sensitive and timely predictor of impending heart failure (HF) decompensation, and the HeartLogic alert condition was shown to identify patients during periods of significantly increased risk of HF events.

Purpose

To report the results of a multicenter experience of remote HF management with HeartLogic algorithm and appraise the value of an alert-based follow-up strategy.

Methods

The HeartLogic feature was activated in 104 patients (76 male, 71 ± 10 years, left ventricular ejection fraction 29 ± 7%). All patients were followed according to a standardized protocol that included remote data reviews and patient phone contacts every month and at the time of HeartLogic alerts. In-office visits were performed every 6 months or when deemed necessary.

Results

During a median follow-up of 13[11-18] months, centers performed remote follow-up at the time of 1284 scheduled monthly transmissions (10.5 per pt-year) and 100 HeartLogic alerts (0.82 alerts/pt-year). The mean delay from alert to the next monthly remote data review was 14 ± 8 days. Overall, the patient time in the alert state (i.e. HeartLogic index above the threshold) was 14% of the total observation period. HF events requiring active clinical actions were detected at the time of 11 (0.9%) monthly remote data reviews and at 43 (43%, p &lt; 0.001) HeartLogic alerts. Moderate to severe symptoms of HF were reported during 2% of remote visits when the patient was out of HeartLogic alert condition and during 15% of remote visits performed in alert condition (p &lt; 0.001). Out of 100 alerts, 17 required an in-office visit and 5 a hospitalization to manage the clinical condition. Overall, 282 scheduled and 56 unscheduled in-office visits were performed during follow-up. Any HF sign (i.e. S3 gallop, rales, jugular venous distension, edema) was detected during 18% of in-office visits when the patient was out of HeartLogic alert condition and during 34% of visits performed in alert condition (p = 0.002).

Conclusions

HeartLogic alerts are frequently associated with relevant actionable HF events. Events are detected earlier and the volume of alert-driven remote follow-ups is limited when compared with a monthly remote follow-up scheme. The probability of detecting common signs and symptoms of HF at regular remote or in-office assessment is extremely low when the patient is out of HeartLogic alert state. These results support the adoption of an alert-based follow-up strategy.

P538Single- and Multi-Site Pacing Strategies for Optimal Cardiac Resynchronization Therapy: Impact on Device Longevity and Therapy Cost

Funding Acknowledgements

No funding

Introduction

Multiple left ventricular pacing strategies have been suggested for improving response to cardiac resynchronization therapy (CRT). However, these programming strategies can be obtained by accepting configurations with high pacing threshold and accelerated battery drain. We assessed the feasibility of predefined pacing programming protocols and we evaluated their impact on device longevity and their cost-impact.

Methods

We estimated battery longevity in 167 CRT-D (RESONATE, Boston Scientific) patients based on measured pacing parameters and according to multiple programming strategies: single-site pacing associated with lowest threshold, non-apical location, longest interventricular delay, pacing from two electrodes. To determine the economic impact of each programming strategy, we applied the results of a published model-based cost analysis to a 15-year time-horizon.

Results

Selecting the electrode with the lowest threshold resulted in a median device longevity of 11.5 years. Non-apical pacing and interventricular delay maximization were feasible in most patients (99% non-apical pacing, 65% RV-to-LV interval &gt;80ms), and were obtained at the price of a few months of battery life. Device longevity of &gt;10 years was preserved in 87% of cases of non-apical pacing and in 77% on pacing at the longest interventricular delay. The mean reduction in battery life when the second electrode was activated was 1.5 years. Single-site pacing strategies increased the therapy cost by 4-6%, and multi-site pacing by 12-13%, in comparison with the best-case scenario.

Conclusions

Modern CRT-D systems ensure effective pacing and allow multiple optimization strategies for maximizing service life or for enhancing effectiveness. Single- or multi-site pacing strategies can be implemented without compromising device service life and at an acceptable increase in therapy cost.

Abstract Figure. Image1

855Performance of a multisensor icd algorithm in heart failure patient management

Funding Acknowledgements

No funding

Background

The HeartLogic index combines data from multiple implantable cardioverter-defibrillator (ICD)-based sensors and has proved to be a sensitive and timely predictor of impending heart failure (HF) decompensation.

Purpose

To describe a multicenter experience of remote HF management of patients who received a HeartLogic-enabled ICD or cardiac resynchronization therapy ICD (CRT-D).

Methods

The HeartLogic feature was activated in 104 patients (76 male, 71 ± 10 years, left ventricular ejection fraction 29 ± 7%). In accordance with a standardized follow-up protocol, remote data reviews and patient phone contacts were performed monthly and at the time of HeartLogic alerts (when the index crossed the nominal threshold value of 16), to assess the patient decompensation status. In-office visits were performed every 6 months or when deemed necessary.

Results

During a median follow-up of 13[11-18] months, 100 HeartLogic alerts were reported (0.82 alerts/pt-year) in 53 patients. 60 HeartLogic alerts were judged clinically meaningful (i.e. associated with worsening of HF or resulted in active clinical actions). Specifically, multiple associated conditions were reported: 45 (75%) symptoms or signs of clinical deterioration of HF, 13 (22%) discontinuations or reductions of prescribed HF therapy, 11 (18%) declines in CRT percentage (with or without new onset atrial fibrillation), 8 (13%) recurrences of previous HF events. For 48 out of 60 alerts the clinician was not previously aware of the condition. Of these, 43 alerts triggered multiple clinical actions. Alert-triggered actions were: 30 (70%) diuretic dosage increases, 15 (35%) other drug adjustments, 6 (14%) HF hospitalizations, 3 (7%) device reprogramming/revisions, 1 (2%) cardioversion, 1 (2%) patient education on therapy adherence. Out of 40 non-clinically meaningful alerts (0.33 alerts/pt-year), 8 (20%) were associated with non-HF therapy changes or interventions, 3 (8%) with pulmonary events, 29 (72%) remained unexplained. The overall number of HF hospitalizations was 16 (rate 0.13 hospitalizations/pt-year). Five HF hospitalizations were not preceded by HeartLogic alert (0.04 hospitalizations/pt-year).

Conclusions

The HeartLogic index provided clinically meaningful information and allowed to remotely identify relevant HF related clinical conditions, with a low rate of unexplained detections and undetected HF events. In this experience, remote monitoring using HeartLogic alerts allowed to drive HF care and take effective clinical actions.

Pharmacological Inhibition of Serine Proteases to Reduce Cardiac Inflammation and Fibrosis in Atrial Fibrillation

Systemic inflammation correlates with an increased risk of atrial fibrillation (AF) and thrombogenesis. Systemic inflammation alters vessel permeability, allowing inflammatory and immune cell migration toward target organs, including the heart. Among inflammatory cells infiltrating the atria, macrophages and mast cell have recently attracted the interest of basic researchers due to the pathogenic mechanisms triggered by their activation. This chemotactic invasion is likely implicated in short- and long-term changes in cardiac cell-to-cell communication and in triggering fibrous tissue accumulation in the atrial myocardium and electrophysiological re-arrangements of atrial cardiomyocytes, thus favoring the onset and progression of AF. Serine proteases are a large and heterogeneous class of proteases involved in several processes that are important for cardiac function and are involved in cardiac diseases, such as (i) coagulation, (ii) fibrinolysis, (iii) extracellular matrix degradation, (iv) activation of receptors (i.e., protease-activated receptors [PPARs]), and (v) modulation of the activity of endogenous signals. The recognition of serine proteases substrates and their involvement in inflammatory/profibrotic mechanisms allowed the identification of novel cardio-protective mechanisms for commonly used drugs that inhibit serine proteases. The aim of this review is to summarize knowledge on the role of inflammation and fibrosis as determinants of AF. Moreover, we will recapitulate current findings on the role of serine proteases in the pathogenesis of AF and the possible beneficial effects of drugs inhibiting serine proteases in reducing the risk of AF through decrease of cardiac inflammation and fibrosis. These drugs include thrombin and factor Xa inhibitors (used as oral anticoagulants), dipeptidyl-peptidase 4 (DPP4) inhibitors, used for type-2 diabetes, as well as novel experimental inhibitors of mast cell chymases.

Electrophysiological and Contractile Effects of Disopyramide in Patients With Obstructive Hypertrophic Cardiomyopathy: A Translational Study

•

In patients with HCM and symptomatic LVOT-obstruction, first treatment with disopyramide leads to a marked reduction of LVOT gradients, with a slight decrease of resting ejection fraction and a modest increase of corrected QT interval, highlighting high efficacy and safety.

•

In single cardiomyocytes and intact trabeculae from surgical samples of patients with obstructive HCM, in vitro treatment with 5 μmol/l disopyramide lowered force and Ca2⁺ transients while reducing action potential duration and the rate of arrhythmic afterdepolarizations.

•

These effects are mediated by the combined inhibition of peak and late Na⁺ currents, L-type Ca²⁺ current, delayed-rectifier K⁺ current, and ryanodine receptors.

•

In addition to the negative inotropic effect of disopyramide, in vitro results suggest additional antiarrhythmic actions.

Disopyramide is effective and safe in patients with obstructive hypertrophic cardiomyopathy. However, its cellular and molecular mechanisms of action are unknown. We tested disopyramide in cardiomyocytes from the septum of surgical myectomy patients: disopyramide inhibits multiple ion channels, leading to lower Ca transients and force, and shortens action potentials, thus reducing cellular arrhythmias. The electrophysiological profile of disopyramide explains the efficient reduction of outflow gradients but also the limited prolongation of the QT interval and the absence of arrhythmic side effects observed in 39 disopyramide-treated patients. In conclusion, our results support the idea that disopyramide is safe for outpatient use in obstructive patients.

Optical Investigation of Action Potential and Calcium Handling Maturation of hiPSC-Cardiomyocytes on Biomimetic Substrates

Cardiomyocytes from human induced pluripotent stem cells (hiPSC-CMs) are the most promising human source with preserved genetic background of healthy individuals or patients. This study aimed to establish a systematic procedure for exploring development of hiPSC-CM functional output to predict genetic cardiomyopathy outcomes and identify molecular targets for therapy. Biomimetic substrates with microtopography and physiological stiffness can overcome the immaturity of hiPSC-CM function. We have developed a custom-made apparatus for simultaneous optical measurements of hiPSC-CM action potential and calcium transients to correlate these parameters at specific time points (day 60, 75 and 90 post differentiation) and under inotropic interventions. In later-stages, single hiPSC-CMs revealed prolonged action potential duration, increased calcium transient amplitude and shorter duration that closely resembled those of human adult cardiomyocytes from fresh ventricular tissue of patients. Thus, the major contribution of sarcoplasmic reticulum and positive inotropic response to β-adrenergic stimulation are time-dependent events underlying excitation contraction coupling (ECC) maturation of hiPSC-CM; biomimetic substrates can promote calcium-handling regulation towards adult-like kinetics. Simultaneous optical recordings of long-term cultured hiPSC-CMs on biomimetic substrates favor high-throughput electrophysiological analysis aimed at testing (mechanistic hypothesis on) disease progression and pharmacological interventions in patient-derived hiPSC-CMs.

Nodal metastases distribution in laryngeal cancer requiring total laryngectomy: Therapeutic implications for the N0 Neck

OBJECTIVES

Neck dissection is a controversial surgical procedure in patients with squamous cell carcinoma of the Larynx free of any node metastasis detected in preoperative staging. The aim of this study was to investigate the distributions of lymph node metastases in laryngeal squamous cell carcinoma and improve the rationale for elective treatment of N0 neck.

MATERIAL AND METHODS

Retrospective single-center series of Seventy-eight successive patients with laryngeal squamous cell carcinoma who underwent neck dissection between 2008 and 2015.

RESULTS

Surgery was first-line treatment in 37 patients (47%) and for recurrent disease in 41 (53%). The rate of occult nodal metastasis was 14% (n=11): levels IIa and/or III were affected in 9 cases (11.5%) compared with single cases of IIb and IV involvement (1.3% each). The rate of occult nodal metastasis was significantly lower among patients operated on for recurrent disease after radiotherapy than in patients who never had any radiotherapy of the cervical lymph nodes (0% vs. 16.7%, P=0.03).

CONCLUSIONS

Selective cervical lymph node dissection in levels IIa and III sparing levels IIb and IV seems to be ideal in total laryngectomy in patients with cN0 laryngeal squamous cell carcinoma. Omitting lymph node dissection altogether may be considered in total laryngectomy on a cN0 patient showing recurrence after radiotherapy.

Human protective response induced by meningococcus B vaccine is mediated by the synergy of multiple bactericidal epitopes

4CMenB is the first broad coverage vaccine for the prevention of invasive meningococcal disease caused by serogroup B strains. To gain a comprehensive picture of the antibody response induced upon 4CMenB vaccination and to obtain relevant translational information directly from human studies, we have isolated a panel of human monoclonal antibodies from adult vaccinees. Based on the Ig-gene sequence of the variable region, 37 antigen-specific monoclonal antibodies were identified and produced as recombinant Fab fragments, and a subset also produced as full length recombinant IgG1 and functionally characterized. We found that the monoclonal antibodies were cross-reactive against different antigen variants and recognized multiple epitopes on each of the antigens. Interestingly, synergy between antibodies targeting different epitopes enhanced the potency of the bactericidal response. This work represents the first extensive characterization of monoclonal antibodies generated in humans upon 4CMenB immunization and contributes to further unraveling the immunological and functional properties of the vaccine antigens. Moreover, understanding the mechanistic nature of protection induced by vaccination paves the way to more rational vaccine design and implementation.

Towards a Personalized and Dynamic CRT-D

Background: In spite of cardiac resynchronization therapy (CRT) benefits, 25 – 30% of patients are still non responders. One of the possible reasons could be the non optimal atrioventricular (AV) and interventricular (VV) intervals settings. Our aim was to exploit a numerical model of cardiovascular system for AV and VV intervals optimization in CRT.

Methods: A numerical model of the cardiovascular system CRT-dedicated was previously developed. Echocardiographic parameters, Systemic aortic pressure and ECG were collected in 20 consecutive patients before and after CRT. Patient data were simulated by the model that was used to optimize and set into the device the intervals at the baseline and at the follow up. The optimal AV and VV intervals were chosen to optimize the simulated selected variable/s on the base of both echocardiographic and electrocardiographic parameters.

Results: Intervals were different for each patient and in most cases, they changed at follow up. The model can well reproduce clinical data as verified with Bland Altman analysis and T-test (p > 0.05). Left ventricular remodeling was 38.7% and left ventricular ejection fraction increasing was 11% against the 15% and 6% reported in literature, respectively.

Conclusions: The developed numerical model could reproduce patients conditions at the baseline and at the follow up including the CRT effects. The model could be used to optimize AV and VV intervals at the baseline and at the follow up realizing a personalized and dynamic CRT. A patient tailored CRT could improve patients outcome in comparison to literature data.

Liquid Crystalline Networks toward Regenerative Medicine and Tissue Repair

The communication reports the use of liquid crystalline networks (LCNs) for engineering tissue cultures with human cells. Their ability as cell scaffolds for different cell lines is demonstrated. Preliminary assessments of the material biocompatibility are performed on human dermal fibroblasts and murine muscle cells (C2C12), demonstrating that coatings or other treatments are not needed to use the acrylate-based materials as support. Moreover, it is found that adherent C2C12 cells undergo differentiation, forming multinucleated myotubes, which show the typical elongated shape, and contain bundles of stress fibers. Once biocompatibility is demonstrated, the same LCN films are used as a substrate for culturing human induced pluripotent stem cell-derived cardiomyocites (hiPSC-CMs) proving that LCNs are capable to develop adult-like dimensions and a more mature cell function in a short period of culture in respect to standard supports. The demonstrated biocompatibility together with the extraordinary features of LCNs opens to preparation of complex cell scaffolds, both patterned and stimulated, for dynamic cell culturing. The ability of these materials to improve cell maturation and differentiation will be developed toward engineered heart and skeletal muscular tissues exploring regenerative medicine toward bioartificial muscles for injured sites replacement.

Outcomes of septorhinoplasty: a new approach comparing functional and aesthetic results

The aim of this study was to compare objective and subjective functional results of septorhinoplasty with subjective aesthetic results. A prospective study was performed including global and subgroup analyses (primary versus secondary septorhinoplasty). Three instruments were used to evaluate pre- and postoperative results: rhinomanometry for the objective functional analysis, the Nasal Symptom Obstruction Evaluation (NOSE) scale for the subjective functional analysis, and the Rhinoplasty Outcome Evaluation (ROE) scale for the subjective aesthetic analysis. A septorhinoplasty was performed in all cases. Thirty-five patients were included (22 female), of whom 74% underwent primary septorhinoplasty. The correlation between rhinomanometry, NOSE and ROE scores was analysed. Mean resistance of the two nasal cavities was 4.9 (standard deviation (SD) 8.35) sPa/ml before surgery and 0.8 (SD 0.7) sPa/ml after surgery. NOSE and ROE scores were, respectively, 72.5/100 (SD 21.7) and 7.5/24 (SD 11.3) before surgery and 22/100 (SD 20.6) and 18/24 (SD 17.3) after surgery. Patients complaining of postoperative nasal obstruction had a worse aesthetic evaluation. Correction of the functional disease appears to be as important as aesthetic correction. This study comparing functional and aesthetic results after septorhinoplasty could provide a basis for future studies.

Pathogenesis of Hypertrophic Cardiomyopathy is Mutation Rather Than Disease Specific: A Comparison of the Cardiac Troponin T E163R and R92Q Mouse Models

Background

In cardiomyocytes from patients with hypertrophic cardiomyopathy, mechanical dysfunction and arrhythmogenicity are caused by mutation‐driven changes in myofilament function combined with excitation‐contraction (E‐C) coupling abnormalities related to adverse remodeling. Whether myofilament or E‐C coupling alterations are more relevant in disease development is unknown. Here, we aim to investigate whether the relative roles of myofilament dysfunction and E‐C coupling remodeling in determining the hypertrophic cardiomyopathy phenotype are mutation specific.

Methods and Results

Two hypertrophic cardiomyopathy mouse models carrying the R92Q and the E163R TNNT2 mutations were investigated. Echocardiography showed left ventricular hypertrophy, enhanced contractility, and diastolic dysfunction in both models; however, these phenotypes were more pronounced in the R92Q mice. Both E163R and R92Q trabeculae showed prolonged twitch relaxation and increased occurrence of premature beats. In E163R ventricular myofibrils or skinned trabeculae, relaxation following Ca²⁺ removal was prolonged; resting tension and resting ATPase were higher; and isometric ATPase at maximal Ca²⁺ activation, the energy cost of tension generation, and myofilament Ca²⁺ sensitivity were increased compared with that in wild‐type mice. No sarcomeric changes were observed in R92Q versus wild‐type mice, except for a large increase in myofilament Ca²⁺ sensitivity. In R92Q myocardium, we found a blunted response to inotropic interventions, slower decay of Ca²⁺ transients, reduced SERCA function, and increased Ca²⁺/calmodulin kinase II activity. Contrarily, secondary alterations of E‐C coupling and signaling were minimal in E163R myocardium.

Conclusions

In E163R models, mutation‐driven myofilament abnormalities directly cause myocardial dysfunction. In R92Q, diastolic dysfunction and arrhythmogenicity are mediated by profound cardiomyocyte signaling and E‐C coupling changes. Similar hypertrophic cardiomyopathy phenotypes can be generated through different pathways, implying different strategies for a precision medicine approach to treatment.

Ranolazine Prevents Phenotype Development in a Mouse Model of Hypertrophic Cardiomyopathy

BACKGROUND

Current therapies are ineffective in preventing the development of cardiac phenotype in young carriers of mutations associated with hypertrophic cardiomyopathy (HCM). Ranolazine, a late Na⁺ current blocker, reduced the electromechanical dysfunction of human HCM myocardium in vitro.

METHODS AND RESULTS

To test whether long-term treatment prevents cardiomyopathy in vivo, transgenic mice harboring the R92Q troponin-T mutation and wild-type littermates received an oral lifelong treatment with ranolazine and were compared with age-matched vehicle-treated animals. In 12-months-old male R92Q mice, ranolazine at therapeutic plasma concentrations prevented the development of HCM-related cardiac phenotype, including thickening of the interventricular septum, left ventricular volume reduction, left ventricular hypercontractility, diastolic dysfunction, left-atrial enlargement and left ventricular fibrosis, as evaluated in vivo using echocardiography and magnetic resonance. Left ventricular cardiomyocytes from vehicle-treated R92Q mice showed marked excitation-contraction coupling abnormalities, including increased diastolic [Ca²⁺] and Ca²⁺ waves, whereas cells from treated mutants were undistinguishable from those from wild-type mice. Intact trabeculae from vehicle-treated mutants displayed inotropic insufficiency, increased diastolic tension, and premature contractions; ranolazine treatment counteracted the development of myocardial mechanical abnormalities. In mutant myocytes, ranolazine inhibited the enhanced late Na⁺ current and reduced intracellular [Na⁺] and diastolic [Ca²⁺], ultimately preventing the pathological increase of calmodulin kinase activity in treated mice.

CONCLUSIONS

Owing to the sustained reduction of intracellular Ca²⁺ and calmodulin kinase activity, ranolazine prevented the development of morphological and functional cardiac phenotype in mice carrying a clinically relevant HCM-related mutation. Pharmacological inhibitors of late Na⁺ current are promising candidates for an early preventive therapy in young phenotype-negative subjects carrying high-risk HCM-related mutations.