Cardiac contractility modulation electrical signals normalize activity, expression, and phosphorylation of the Na+-Ca2+ exchanger in heart failure

Arrhythmogenic Remodeling in the Failing Heart

Chronic heart failure is a clinical syndrome with multiple etiologies, associated with significant morbidity and mortality. Cardiac arrhythmias, including ventricular tachyarrhythmias and atrial fibrillation, are common in heart failure. A number of cardiac diseases including heart failure alter the expression and regulation of ion channels and transporters leading to arrhythmogenic electrical remodeling. Myocardial hypertrophy, fibrosis and scar formation are key elements of arrhythmogenic structural remodeling in heart failure. In this article, the mechanisms responsible for increased arrhythmia susceptibility as well as the underlying changes in ion channel, transporter expression and function as well as alterations in calcium handling in heart failure are discussed. Understanding the mechanisms of arrhythmogenic remodeling is key to improving arrhythmia management and the prevention of sudden cardiac death in patients with heart failure.

Cardiac Contractility Modulation in Patients with Heart Failure with Reduced Left Ventricular Ejection Fraction

Cardiac contractility modulation is an innovative therapy conceived for the treatment of heart failure. It is a device-based therapy, employing multiple electrodes to deliver relatively high-voltage (~7.5 V) biphasic signals to the endocardium of the right ventricular septum, in order to improve heart failure symptoms, exercise capacity and quality of life. Multiple clinical and mechanistic studies have been conducted to investigate the potential usefulness of this technology and, as of now, they suggest that it could have a place in therapy and meet a relevant medical need for a specific sub-category of underserved heart failure patients with reduced left ventricular ejection fraction. More studies are needed to further investigate its effect on outcomes such as mortality and rate of hospitalizations.

Cardiac contractility modulation in left ventricular systolic dysfunction: one-year experience in a pilot study and design of a prospective registry

BACKGROUND

Cardiac contractility modulation (CCM) is a treatment option for patients suffering symptomatic chronic heart failure (CHF) with reduced left ventricular ejection fraction (LVEF) who are not eligible for cardiac resynchronization. Data on mid-term follow-up are limited to small observational studies. The aim of this study was to assess the impact of CCM on quality of life, symptoms, exercise tolerance and left ventricular function in patients with CHF and moderate-to-severe left ventricular systolic dysfunction.

METHODS

Patients suffering CHF with LVEF <45% and NYHA class >II despite optimal medical therapy, underwent CCM implantation. Enrolled patients underwent baseline and 3, 6 and 12-months evaluation with ECG, echocardiogram, clinical assessment, 6-minute walking test and Minnesota Living with Heart Failure Questionnaire (MLWHFQ).

RESULTS

Ten patients underwent CCM implantation. All patients were actively treated with the optimal pharmacological therapy as tolerated and had at least one hospitalization for worsening heart failure during the previous year. After a mean follow-up of 15 months, 9 patients were alive, while one patient died for worsening heart failure precipitated by pneumonia. Among the remaining 9 patients, LVEF improved non-significantly from 29.4±8% to 32.2±10% (P=0.092), 6-minute walking test distance improved from 179±73 m to 304±99 m (P<0.001), NYHA class reduced from 3.0±0.4 to 1.6±0.5 (P=0.003) and MLWHFQ score improved from 59.6±49 to 34.2±32 (P=0.037). Only 2 patients have been hospitalized during the 12 months. Overall, a net clinical benefit was detected in 6 out of 9 patients.

CONCLUSIONS

CCM could be effective in improving quality of life, symptoms and exercise tolerance, and reduces hospitalizations in patients with symptomatic CHF on top of optimal medical and electrical therapy. A prospective registry has been designed to identify the subsets of patients gaining more benefit, and to assess the long-term effect of CCM on those clinical endpoints.

Effects of Intravenous Infusion of Vepoloxamer on Left Ventricular Function in Dogs with Advanced Heart Failure

PURPOSE

Vepoloxamer (VEPO), a rheologic agent, repairs damaged cell membranes, thus inhibiting unregulated Ca²⁺ entry into cardiomyocytes. This study examined the effects of i.v. infusion of VEPO on LV function in dogs with coronary microembolization-induced heart failure (HF) (LV ejection fraction, EF ~ 30%).

METHODS

Thirty-five HF dogs were studied. Study 1: 21 of 35 dogs were randomized to 2-h infusion of VEPO at dose of 450 mg/kg (n = 7) or VEPO at 225 mg/kg (n = 7) or normal saline (control, n = 7). Hemodynamics were measured at 2 h, 24 h, 1 week, and 2 weeks after infusion. Study 2: 14 HF dogs were randomized to 2-h infusions of VEPO (450 mg/kg, n = 7) or normal saline (control, n = 7). Each dog received 2 infusions of VEPO or saline (pulsed therapy) 3 weeks apart and hemodynamics measured at 24 h, and 1, 2, and 3 weeks after each infusion. In both studies, the change between pre-infusion measures and measures at other time points (treatment effect, Δ) was calculated.

RESULTS

Study 1: compared to pre-infusion, high dose VEPO increased LVEF by 11 ± 2% at 2 h, 8 ± 2% at 24 h (p < 0.05), 8 ± 2% at 1 week (p < 0.05), and 4 ± 2% at 2 weeks. LV EF also increased with low-dose VEPO but not with saline. Study 2: VEPO but not saline significantly increased LVEF by 6.0 ± 0.7% at 2 h (p < 0.05); 7.0 ± 0.7%% at 1 week (p < 0.05); 1.0 ± 0.6% at 3 weeks; 6.0 ± 1.3% at 4 weeks (p < 0.05); and 5.9 ± 1.3% at 6 weeks (p < 0.05).

CONCLUSIONS

Intravenous VEPO improves LV function for at least 1 week after infusion. The benefits can be extended with pulsed VEPO therapy. The results support development of VEPO for treating patients with acute on chronic HF.

Cardiac Contractility Modulation Attenuates Chronic Heart Failure in a Rabbit Model via the PI3K/AKT Pathway

The Akt plays an important role in regulating cardiac growth, myocardial angiogenesis, and cell death in cardiac myocytes. However, there are few studies to focus on the responses of the Akt pathway to cardiac contractility modulation (CCM) in a chronic heart failure (HF) model. In this study, the effects of CCM on the treatment of HF in a rabbit model were investigated. Thirty six-month-old rabbits were randomly separated into control, HF, and CCM groups. The rabbits in HF and CCM groups were pressure uploaded, which can cause an aortic constriction. Then, CCM was gradually injected to the myocardium of rabbits in the CCM group, and this process lasted for four weeks with six hours per day. Rabbit body weight, heart weight, and heart beating rates were recorded during the experiment. To assess the CCM impacts, rabbit myocardial histology was examined as well. Additionally, western blot analysis was employed to measure the protein levels of Akt, FOXO3, Beclin, Pi3k, mTOR, GSK-3β, and TORC2 in the myocardial histology of rabbits. Results showed that the body and heart weight of rabbits decreased significantly after suffering HF when compared with those in the control group. However, they gradually recovered after CCM application. The CCM significantly decreased collagen volume fraction in myocardial histology of HF rabbits, indicating that CCM therapy attenuated myocardial fibrosis and collagen deposition. The levels of Akt, FOXO3, Beclin, mTOR, GSK-3β, and TORC2 were significantly downregulated, but Pi3k concentration was greatly upregulated after CCM utilization. Based on these findings, it was concluded that CCM could elicit positive effects on HF therapy, which was potentially due to the variation in the Pi3k/Akt signaling pathway.

Optimizer Smart in the treatment of moderate-to-severe chronic heart failure

Cardiac contractility modulation, also referred to as CCM™, by the Optimizer Smart device is an innovative intracardiac device-based therapy that has been recently US FDA-approved for the treatment of patients with chronic heart failure, left ventricular ejection fraction (LVEF) between 25 and 45%, QRS <130 ms who remain symptomatic despite optimal medical therapy. Clinical trials demonstrate that CCM therapy is safe and effective in reducing heart failure hospitalization and improving heart failure symptoms, quality of life and functional performance. This novel device-based therapeutic offers benefits to patients who do not otherwise qualify for cardiac resynchronization therapy. CCM expands the indication beyond the traditional LVEF cutoff of 35% to a newer group including patients who fall in midrange LVEF group, up to 45%.

Post-extrasystolic Potentiation: Link between Ca(2+) Homeostasis and Heart Failure?

Post-extrasystolic potentiation (PESP) describes the phenomenon of increased contractility of the beat following an extrasystole and has been attributed to changes in Ca(2+) homeostasis. While this effect has long been regarded to be a normal physiological phenomenon, a number of reports describe an enhanced potentiation of the post-extrasystolic beat in heart failure patients. The exact mechanism of this increased PESP is unknown, but disruption of normal Ca(2+) handling in heart failure may be the underlying cause. The use of PESP as a prognostic marker or therapeutic intervention have recently regained new attention, however, the value of the application of PESP in the clinic is still under debate. In this review, the mechanism of PESP with regard to Ca(2+) in the normal and failing heart will be discussed and the possible diagnostic and therapeutic role of this phenomenon will be explored.

Cardiac Contractility Modulation in a Model of Repaired Tetralogy of Fallot: A Sheep Model

The onset of right ventricular dysfunction in patients presenting with congenital heart disease is associated with a dismal long-term outcome and often represents a therapeutic dead end. Our study had several objectives: (1) to analyse the anatomical, functional, histological and cellular characteristics of an animal model of repaired tetralogy of Fallot with right ventricular dysfunction (2) to test the new electrical treatment known as cardiac contractility modulation in this animal model. Seven sheep underwent a first surgery at the age of three weeks aiming to mimic the characteristics of a repaired tetralogy of Fallot. Five controls were sham-operated. Experimental studies were performed 12 months after the initial operation. The hemodynamic, echocardiographic, and mitochondrial function studies were carried out before and after cardiac contractility modulation in closed- and open-chest conditions. In this animal model of right ventricular dysfunction, short-term cardiac contractility modulation was associated with a significant improvement in (a) right ventricular function, as evidenced by a significant increase in right ventricular dP/dt (p < 0.05) (b) left ventricular function evidenced by the increase in left ventricular dP/dt max (p < 0.05) (c) in mitochondrial function (p < 0.05). In this animal model of chronic right ventricular dysfunction, cardiac contractility modulation significantly improved acute cardiac hemodynamic and mitochondrial functions of both ventricles and may represent a promising option in patients with right heart failure.

Role of the dysfunctional ryanodine receptor - Na(+)-Ca(2+)exchanger axis in progression of cardiovascular diseases: What we can learn from pharmacological studies?

Abnormal Ca(2+)homeostasis is often associated with chronic cardiovascular diseases, such as hypertension, heart failure or cardiac arrhythmias, and typically contributes to the basic ethiology of the disease. Pharmacological targeting of cardiac Ca(2+)handling has great therapeutic potential offering invaluable options for the prevention, slowing down the progression or suppression of the harmful outcomes like life threatening cardiac arrhythmias. In this review we outline the existing knowledge on the involvement of malfunction of the ryanodine receptor and the Na(+)-Ca(2+)exchanger in disturbances of Ca(2+)homeostasis and discuss important proof of concept pharmacological studies targeting these mechanisms in context of hypertension, heart failure, atrial fibrillation and ventricular arrhythmias. We emphasize the promising results of preclinical studies underpinning the potential benefits of the therapeutic strategies based on ryanodine receptor or Na(+)-Ca(2+)exchanger inhibition.

The effect of SN-6, a novel sodium-calcium exchange inhibitor, on contractility and calcium handling in isolated failing rat ventricular myocytes

BACKGROUND AND PURPOSE

Specific Na(+) /Ca(2+) exchanger (NCX) inhibition is a potential strategy to correct reduced contractility and depleted sarcoplasmic reticulum (SR) Ca(2+) content in heart failure (HF). SN-6, a benzyloxyphenyl derivative and proposed selective NCX inhibitor, could be used for this purpose. This study aimed to evaluate the effects of SN-6 on contractility and Ca(2+) handling in normal and failing rat cardiomyocytes.

EXPERIMENTAL APPROACH

HF was induced in rats by coronary artery ligation. Left ventricular myocytes were isolated and superfused with increasing concentrations of SN-6.

KEY RESULTS

Sarcomere shortening, induced by field-stimulation, was reduced in amplitude with increasing concentrations of SN-6 compared with control solution. This effect was greater in failing cells. Kinetics of contractility (time to 90% peak and time to 50% relaxation) were significantly faster. Despite this, intracellular Ca(2+) transients demonstrated no change in the peak amplitude at low concentrations of SN-6, suggesting that SN-6 may affect myofilament sensitivity to Ca(2+) . Ten micro molar SN-6 significantly reduced peak Ca(2+) amplitude by 61.57% and 64.73% in normal and failing cells, respectively. Diastolic Ca(2+) was significantly increased at 1 μM SN-6. SR Ca(2+) content, assessed by rapid application of caffeine, was reduced in failing cells with 1 μM SN-6. Peak ICa , measured by whole-cell patch clamping, was significantly reduced in normal and failing myocytes at 1 μM SN-6.

CONCLUSIONS AND IMPLICATIONS

Our data suggest that SN-6 is not a selective inhibitor of NCX and impairs contractility and Ca(2+) handling. Its use, together with similar putative NCX blockers, in correcting the contractile abnormalities of heart failure requires further studies.

Acute effects of nonexcitatory electrical stimulation during systole in isolated cardiac myocytes and perfused heart

Application of electrical field to the heart during the refractory period of the beat has been shown to increase the force of contraction both in animal models and in heart failure patients (cardiac contractility modulation, or CCM). A direct increase in intracellular calcium during CCM has been suggested to be the mechanism behind the positive inotropic effect of CCM. We studied the effect of CCM on isolated rabbit cardiomyocytes and perfused whole rat hearts. The effect of CCM was observed in single cells via fluorescent measurements of intracellular calcium concentration ([Ca²⁺]_i) and cell length (L). Cells were paced once per second throughout these recordings, and CCM stimulation was delivered via biphasic electric fields of 20 ms duration applied during the refractory period. CCM increased the peak amplitude of both [Ca²⁺]_i and L for the first beat during CCM compared to control, but then [Ca²⁺]_i and L decayed to levels lower than the control. During CCM, all contractions had a faster time to peak for both [Ca²⁺]_i and L; after stopping CCM the rise times returned to control levels. In the whole rat heart, the positive inotropic effect of CCM stimulation on left ventricular pressure was completely abolished in the presence of metoprolol, a beta‐1 adrenergic blocker. In summary, the CCM‐induced changes in intracellular calcium handling by cardiomyocytes did not explain the sustained positive inotropic effect in the whole heart and the β‐adrenergic pathway may be involved in the CCM mechanism of action.

Cardiac contractility modulation (CCM) is a heart failure therapy which delivers electrical pulses to the heart during refractory period. While there are some promising reports on the therapy's safety and effectiveness in humans, the underlining mechanism remains unknown. We studied the effect of CCM pulses in isolated rabbit cardiomyocytes and isolated rat heart in the presence of beta adrenergic blocker and recorded intracellular calcium transients and contractions. We concluded that the CCM‐induced changes in intracellular calcium handling by cardiomyocytes did not explain the sustained positive iotropic efect in the whole heart and beta‐adrenergic pathway may be involved in the CCM mechanism of action.

Effects of acute intravenous infusion of apelin on left ventricular function in dogs with advanced heart failure

BACKGROUND

Apelin-13 (APLN) through apelin receptor (APJ) exerts peripheral vasodilatory and potent positive inotropic effects. We examined the effects of exogenous intravenous infusion of APLN on left ventricular (LV) systolic function in dogs with heart failure (HF, LV ejection fraction, EF~30%).

METHODS AND RESULTS

Studies were performed in 7 dogs with microembolization-induced HF. Each dog received an intravenous infusion of low dose and high dose APLN followed by washout period. LV end-diastolic volume (EDV), end-systolic volume (ESV) and LV EF were measured at specified time points. APLN protein level was determined in plasma at all time points. mRNA and protein levels of APLN and APJ in LV tissue were also measured in 7 normal (NL) and 7 heart failure (HF) dogs. APLN reduced EDV only at the high dose, significantly reduced ESV and increased EF with both doses. In plasma of HF dogs, APLN levels were reduced significantly compared to NL dogs. APLN treatment in HF dogs significantly increased the plasma APLN levels at both low and high doses. Expression of APLN, but not of APJ, was reduced in LV tissue of HF dogs compared to NL.

CONCLUSIONS

Exogenous administration of APLN improved LV systolic function in dogs with advanced HF.

Electrical modalities beyond pacing for the treatment of heart failure

In this review, we report on electrical modalities, which do not fit the definition of pacemaker, but increase cardiac performance either by direct application to the heart (e.g., post-extrasystolic potentiation or non-excitatory stimulation) or indirectly through activation of the nervous system (e.g., vagal or sympathetic activation). The physiological background of the possible mechanisms of these electrical modalities and their potential application to treat heart failure are discussed.

Effects of electric stimulations applied during absolute refractory period on cardiac function of rabbits with heart failure

The effects of electric currents applied during absolute refractory period (ARP) on the cardiac function of rabbits with heart failure due to myocardial infarction (MI), and the safety of this method were investigated. Thirty rabbits were randomly assigned equally to 3 groups: sham-operated group, LV-anterior wall cardiac contractility modulation (LV-CCM) group, and septum-CCM (S-CCM) group. A thoracotomy was performed on all the rabbits. Electric pulses were delivered during the ARP on the anterior wall of left ventricle in CCM group and in the septum in S-CCM group, respectively. The left ventricular systolic pressure (LVSP) and maximum positive left ventricular pressure change (+dp/dt(max)), heart rates, ventricular tachycardia, ventricular fibrillation were observed. It was found that, as compared with the baseline, LVSP, and +dp/dtmax were significantly increased, on average, by 15.2% and 19.5% in LV-CCM group (P<0.05), and by 8.5% and 10.8% in S-CCM group (P<0.05). LVEDP was significantly decreased and -dp/dt(max) increased both in LV-CCM group and S-CCM group (P<0.05). CCM had no effect on heart rate and induced no arrhythmia in short time. It is concluded that electric currents delivered during the ARP could significantly enhance the contractility of myocardium safely, suggesting that CCM stimulation is a novel potent method for contractility modulation.