Repolarization heterogeneity in patients with cardiac resynchronization therapy and its relation to ventricular tachyarrhythmias

Ryanodine receptor 2 inhibition reduces dispersion of cardiac repolarization, improves contractile function, and prevents sudden arrhythmic death in failing hearts

Sudden cardiac death (SCD) from ventricular tachycardia/fibrillation (VT/VF) is a leading cause of death, but current therapies are limited. Despite extensive research on drugs targeting sarcolemmal ion channels, none have proven sufficiently effective for preventing SCD. Sarcoplasmic ryanodine receptor 2 (RyR2) Ca2+ release channels, the downstream effectors of sarcolemmal ion channels, are underexplored in this context. Recent evidence implicates reactive oxygen species (ROS)-mediated oxidation and hyperactivity of RyR2s in the pathophysiology of SCD. We tested the hypothesis that RyR2 inhibition of failing arrhythmogenic hearts reduces sarcoplasmic Ca2+ leak and repolarization lability, mitigates VT/VF/SCD and improves contractile function. We used a guinea pig model that replicates key clinical aspects of human nonischemic HF, such as a prolonged QT interval, a high prevalence of spontaneous arrhythmic SCD, and profound Ca2+ leak via a hyperactive RyR2. HF animals were randomized to receive dantrolene (DS) or placebo in early or chronic HF. We assessed the incidence of VT/VF and SCD (primary outcome), ECG heart rate and QT variability, echocardiographic left ventricular (LV) structure and function, immunohistochemical LV fibrosis, and sarcoplasmic RyR2 oxidation. DS treatment prevented VT/VF and SCD by decreasing dispersion of repolarization and ventricular arrhythmias. Compared to placebo, DS lowered resting heart rate, preserved chronotropic competency during transient β-adrenergic challenge, and improved heart rate variability and cardiac function. Inhibition of RyR2 hyperactivity with dantrolene mitigates the vicious cycle of sarcoplasmic Ca2+ leak-induced increases in diastolic Ca2+ and ROS-mediated RyR2 oxidation, thereby reducing repolarization lability and protecting against VT/VF/SCD. Moreover, the consequent increase in sarcoplasmic Ca2+ load improves contractile function. These potentially life-saving effects of RyR2 inhibition warrant further investigation, such as clinical studies of repurposing dantrolene as a potential new therapy for heart failure and/or SCD.

Ryanodine receptor 2 inhibition reduces dispersion of cardiac repolarization, improves contractile function and prevents sudden arrhythmic death in failing hearts

Introduction

Sudden cardiac death (SCD) from ventricular tachycardia/fibrillation (VT/VF) are a leading cause of death, but current therapies are limited. Despite extensive research on drugs targeting sarcolemmal ion channels, none have proven sufficiently effective for preventing SCD. Sarcoplasmic ryanodine receptor 2 (RyR2) Ca 2+ release channels, the downstream effectors of sarcolemmal ion channels, are underexplored in this context. Recent evidence implicates reactive oxygen species (ROS)- mediated oxidation and hyperactivity of RyR2s in the pathophysiology of SCD.

Objective

To test the hypothesis that RyR2 inhibition of failing arrhythmogenic hearts reduces sarcoplasmic Ca 2+ leak and repolarization lability, mitigates VT/VF/SCD and improves contractile function.

Methods

We used a guinea pig model that replicates key clinical aspects of human nonischemic HF, such as a prolonged QT interval, a high prevalence of spontaneous arrhythmic SCD, and profound Ca 2+ leak via a hyperactive RyR2. HF animals were randomized to receive dantrolene (DS) or placebo in early or chronic HF. We assessed the incidence of VT/VF and SCD (primary outcome), ECG heart rate and QT variability, echocardiographic left ventricular (LV) structure and function, immunohistochemical LV fibrosis, and sarcoplasmic RyR2 oxidation.

Results

DS treatment prevented VT/VF and SCD by decreasing dispersion of repolarization and ventricular arrhythmias. Compared to placebo, DS lowered resting heart rate, preserved chronotropic competency during transient β-adrenergic challenge, and improved heart rate variability and cardiac function.

Conclusion

Inhibition of RyR2 hyperactivity with dantrolene mitigates the vicious cycle of sarcoplasmic Ca 2+ leak-induced increases in diastolic Ca 2+ and ROS-mediated RyR2 oxidation, thereby increasing repolarization lability and protecting against VT/VF/SCD. Moreover, the consequent increase in sarcoplasmic Ca 2+ load improves contractile function. These potentially life-saving effects of RyR2 inhibition warrant further investigation, such as clinical studies of repurposing dantrolene as a potential new therapy for heart failure and/or SCD.

Changes of repolarization parameters after left bundle branch area pacing and the association with echocardiographic response in heart failure patients

Background: Left bundle branch area pacing (LBBAP) has become a safe and effective option for heart failure (HF) patients indicated for cardiac resynchronization therapy (CRT) and/or ventricular pacing, yet the response rate was only 70%. Repolarization parameters were demonstrated to be associated with cardiac mechanics and systolic function. This study aimed to investigate the effects of LBBAP on repolarization parameters and the potential association between those parameters and echocardiographic response.

Methods and results: A total of 59 HF patients undergoing successful LBBAP were consecutively included. QTc, Tpeak-Tend (TpTe), and TpTe/QTc were measured before and after the implantation. The results turned out that the dispersion of ventricular repolarization (DVR) improved after LBBAP among the total population. Although trends of repolarization parameters varied according to different QRS configurations at baseline, the post-implant parameters showed no significant difference between groups. The association between repolarization parameters and LBBAP response was then evaluated among patients with wide QRS. Multivariate analysis demonstrated that post-implant TpTe was the independent predictor of LBBAP response (p < 0.05). Receiver operating characteristic analysis indicated an area under the curve of 0.77 (95% CI, 0.60–0.93) with a cutoff value of 81.2 ms (p < 0.01). Patients with post-implant TpTe<81.2 ms had a significantly higher rate of echocardiographic response (93.3 vs. 44.4%, p < 0.01). Further subgroup analysis indicated that the predictive value of post-implant TpTe for LBBAP response was more significant in non-left bundle branch block (LBBB) patients than in LBBB patients.

Conclusion: LBBAP improved DVR significantly in HF patients. Post-implant TpTe was associated with the echocardiographic response after LBBAP among patients with wide QRS, especially for non-LBBB patients.

Depolarization and repolarization dynamics after His-bundle pacing: Comparison with right ventricular pacing and native ventricular conduction

Background

The current study aimed to evaluate changes in electrical depolarization and repolarization parameters after His‐bundle pacing (HBP) compared with right ventricular pacing (RVP) and its association with ventricular arrhythmia (VA).

Methods

Forty‐one patients (13 with HBP, 14 with RVP, and 14 controls [AAI mode]) were evaluated. After continuous pacing algorithm, QRS duration, QT interval, QTc, JT interval, T‐peak to T‐end (Tpe), and Tpe/QT ratio were measured on electrocardiography at baseline and 1 week, 1 month, and 6 months postoperatively. We investigated VA occurrence and adverse events after implantation.

Results

At 6 months, QRS duration was significantly shorter in the HBP (121.6 ± 15.6 ms) than in the RVP (150.1 ± 14.9 ms) group. The QT intervals were lower in the HBP (424.0 ± 40.9 ms) and control (405.9 ± 23.0 ms) groups than in the RVP (453.0 ± 40.2 ms) group. The Tpe and Tpe/QT ratios at 6 months differed significantly between the HBP and RVP groups (Tpe, 69.8 ± 19.7 ms vs 87.4 ± 11.9 ms and Tpe/QT, 0.16 ± 0.03 vs 0.19 ± 0.02, respectively). The Tpe and Tpe/QT ratios were similarly shortened in the HBP and control groups. VA occurred less frequently in the HBP (15%) and control (7.1%) groups than in the RVP (50%) group (p = 0.020). The non‐RVP group showed significantly lower rates of VA and major adverse events than the RVP group. Patients with VA demonstrated significantly longer QRS duration, QT interval, Tpe, and Tpe/QT at 6 months than those without VA.

Conclusion

HBP showed better depolarization and repolarization stability than RVP.

Ten-year follow-up of cardiac resynchronization therapy patients with non-ischemic dilated cardiomyopathy assessed by radionuclide angiography: a single-center cohort study

PURPOSE

Relatively few data are available on long-term survival and incidence of ventricular arrhythmias in cardiac resynchronization therapy (CRT) patients. We investigated long-term outcomes of CRT patients with non-ischemic dilated cardiomyopathy stratified as responders or non-responders according to radionuclide angiography.

METHODS

Fifty patients with non-ischemic dilated cardiomyopathy undergoing CRT were assessed by equilibrium Tc⁹⁹ radionuclide angiography with bicycle exercise at baseline and after 3 months. Intra- and interventricular dyssynchrony were derived by Fourier phase analysis. Patient clinical outcome was assessed after 10 years.

RESULTS

At 3 months, 50% of patients were identified as CRT responders according to an increase in LV ejection fraction ≥ 5%. During a follow-up of 109 ± 48 months, 30% of patients died and 6% underwent heart transplantation. Age and history of paroxysmal atrial fibrillation were found to be predictors of all-cause mortality. CRT responders showed lower risk of death from cardiac causes than non-responders. At follow-up, 38% of patients presented at least one episode of sustained ventricular tachycardia, with a similar percentage between responders and non-responders.

CONCLUSION

At long-term follow-up, non-ischemic CRT recipients identified as responders by radionuclide angiography were found to be at lower risk of worsening heart failure death than non-responders. Long-term risk for sustained ventricular arrhythmia was similar between CRT responders and non-responders.

Excitation and Contraction of the Failing Human Heart In Situ and Effects of Cardiac Resynchronization Therapy: Application of Electrocardiographic Imaging and Speckle Tracking Echo-Cardiography

Despite the success of cardiac resynchronization therapy (CRT) for treating heart failure (HF), the rate of nonresponders remains 30%. Improvements to CRT require understanding of reverse remodeling and the relationship between electrical and mechanical measures of synchrony. The objective was to utilize electrocardiographic imaging (ECGI, a method for noninvasive cardiac electrophysiology mapping) and speckle tracking echocardiography (STE) to study the physiology of HF and reverse remodeling induced by CRT. We imaged 30 patients (63% male, mean age 63.7 years) longitudinally using ECGI and STE. We quantified CRT-induced remodeling of electromechanical parameters and evaluated a novel index, the electromechanical delay (EMD, the delay from activation to peak contraction). We also measured dyssynchrony using ECGI and STE and compared their effectiveness for predicting response to CRT. EMD values were elevated in HF patients compared to controls. However, the EMD values were dependent on the activation sequence (CRT-paced vs. un-paced), indicating that the EMD is not intrinsic to the local tissue, but is influenced by factors such as opposing wall contractions. After 6 months of CRT, patients had increased contraction in native rhythm compared to baseline pre-CRT (baseline: −8.55%, 6 months: −10.14%, p = 0.008). They also had prolonged repolarization at the location of the LV pacing lead. The pre-CRT delay between mean lateral LV and RV electrical activation time was the best predictor of beneficial reduction in LV end systolic volume by CRT (Spearman’s Rho: −0.722, p < 0.001); it outperformed mechanical indices and 12-lead ECG criteria. HF patients have abnormal EMD. The EMD depends upon the activation sequence and is not predictive of response to CRT. ECGI-measured LV activation delay is an effective index for CRT patient selection. CRT causes persistent improvements in contractile function.

Concomitant changes in ventricular depolarization and repolarization and long-term outcomes of biventricular pacing

BACKGROUND

Biventricular (BiV) pacing increases transmural repolarization heterogeneity due to epicardial to endocardial conduction from the left ventricular (LV) lead. However, limited evidence is available on concomitant changes in ventricular depolarization and repolarization and long-term outcomes of BiV pacing. Therefore, we investigated associations of BiV pacing-induced concomitant changes in ventricular depolarization and repolarization with mortality (i.e., LV assist device, heart transplantation, or all-cause mortality) and sustained ventricular arrhythmia endpoints.

METHODS

Consecutive BiV-defibrillator recipients with digital preimplantation and postimplantation electrocardiograms recorded between 2006 and 2015 at Duke University Medical Center were included. We calculated changes in QRS duration and corrected JT (JTc) interval and split them by median values. For simplicity, these variables were named QRS_decreased (≤ -12 ms), QRS_increased (> -12 ms), JTc_decreased (≤22 ms), and JTc_increased (> 22 ms) and subsequently used to construct four mutually exclusive groups.

RESULTS

We included 528 patients (median age, 68 years; male, 69%). No correlation between changes in QRS duration and JTc interval was observed (P = .295). Compared to QRS_decreased /JTc_increased , increased risk of the composite mortality endpoint was associated with QRS_decreased /JTc_decreased (hazard ratio [HR] = 1.62; 95% confidence interval [CI] = 1.09-2.43), QRS_increased /JTc_decreased (HR = 1.86; 95% CI = 1.27-2.71), and QRS_increased /JTc_increased (HR = 2.25; 95% CI = 1.52-3.35). No QRS/JTc group was associated with excess sustained ventricular arrhythmia risk (P = .400).

CONCLUSION

Among BiV-defibrillator recipients, QRS_decreased /JTc_increased was associated with the most favorable long-term survival free of LV assist device, heart transplantation, and sustained ventricular arrhythmias. Our findings suggest that improved electrical resynchronization may be achieved by assessing concomitant changes in ventricular depolarization and repolarization.

Preimplantation interlead ECG heterogeneity is superior to QRS complex duration in predicting mechanical super-response in patients with non-left bundle branch block receiving cardiac resynchronization therapy

BACKGROUND

Reliable quantitative preimplantation predictors of response to cardiac resynchronization therapy (CRT) are needed.

OBJECTIVE

We tested the utility of preimplantation R-wave and T-wave heterogeneity (RWH and TWH, respectively) compared to standard QRS complex duration in identifying mechanical super-responders to CRT and mortality risk.

METHODS

We analyzed resting 12-lead electrocardiographic recordings from all 155 patients who received CRT devices between 2006 and 2018 at our institution and met class I and IIA American College of Cardiology/American Heart Association/Heart Rhythm Society guidelines with echocardiograms before and after implantation. Super-responders (n=35, 23%) had ≥20% increase in left ventricular ejection fraction and/or ≥20% decrease in left ventricular end-systolic diameter and were compared with non-super-responders (n=120, 77%), who did not meet these criteria. RWH and TWH were measured using second central moment analysis.

RESULTS

Among patients with non-left bundle branch block (LBBB), preimplantation RWH was significantly lower in super-responders than in non-super-responders in 3 of 4 lead sets (P=.001 to P=.038) and TWH in 2 lead sets (both, P=.05), with the corresponding areas under the curve (RWH: 0.810-0.891, P<.001; TWH: 0.759-0.810, P≤.005). No differences were observed in the LBBB group. Preimplantation QRS complex duration also did not differ between super-responders and non-super-responders among patients with (P=.856) or without (P=.724) LBBB; the areas under the curve were nonsignificant (both, P=.69). RWH_V1-3LILII ≥ 420 μV predicted 3-year all-cause mortality in the entire cohort (P=.037), with a hazard ratio of 7.440 (95% confidence interval 1.015-54.527; P=.048); QRS complex duration ≥ 150 ms did not predict mortality (P=.27).

CONCLUSION

Preimplantation interlead electrocardiographic heterogeneity but not QRS complex duration predicts mechanical super-response to CRT in patients with non-LBBB.

Inhalation of printer-emitted particles impairs cardiac conduction, hemodynamics, and autonomic regulation and induces arrhythmia and electrical remodeling in rats

BACKGROUND

Using engineered nanomaterial-based toners, laser printers generate aerosols with alarming levels of nanoparticles that bear high bioactivity and potential health risks. Yet, the cardiac impacts of printer-emitted particles (PEPs) are unknown. Inhalation of particulate matter (PM) promotes cardiovascular morbidity and mortality, and ultra-fine particulates (< 0.1 μm aerodynamic diameter) may bear toxicity unique from larger particles. Toxicological studies suggest that PM impairs left ventricular (LV) performance; however, such investigations have heretofore required animal restraint, anesthesia, or ex vivo preparations that can confound physiologic endpoints and/or prohibit LV mechanical assessments during exposure. To assess the acute and chronic effects of PEPs on cardiac physiology, male Sprague Dawley rats were exposed to PEPs (21 days, 5 h/day) while monitoring LV pressure (LVP) and electrocardiogram (ECG) via conscious telemetry, analyzing LVP and heart rate variability (HRV) in four-day increments from exposure days 1 to 21, as well as ECG and baroreflex sensitivity. At 2, 35, and 70 days after PEPs exposure ceased, rats received stress tests.

RESULTS

On day 21 of exposure, PEPs significantly (P < 0.05 vs. Air) increased LV end systolic pressure (LVESP, + 18 mmHg) and rate-pressure-product (+ 19%), and decreased HRV indicating sympathetic dominance (root means squared of successive differences [RMSSD], - 21%). Overall, PEPs decreased LV ejection time (- 9%), relaxation time (- 3%), tau (- 5%), RMSSD (- 21%), and P-wave duration (- 9%). PEPs increased QTc interval (+ 5%) and low:high frequency HRV (+ 24%; all P < 0.05 vs. Air), while tending to decrease baroreflex sensitivity and contractility index (- 15% and - 3%, P < 0.10 vs. Air). Relative to Air, at both 2 and 35 days after PEPs, ventricular arrhythmias increased, and at 70 days post-exposure LVESP increased. PEPs impaired ventricular repolarization at 2 and 35 days post-exposure, but only during stress tests. At 72 days post-exposure, PEPs increased urinary dopamine 5-fold and protein expression of ventricular repolarizing channels, Kv1.5, Kv4.2, and Kv7.1, by 50%.

CONCLUSIONS

Our findings suggest exposure to PEPs increases cardiovascular risk by augmenting sympathetic influence, impairing ventricular performance and repolarization, and inducing hypertension and arrhythmia. PEPs may present significant health risks through adverse cardiovascular effects, especially in occupational settings, among susceptible individuals, and with long-term exposure.

Can cardiac resynchronization therapy be used as a tool to reduce sudden cardiac arrest risk?

Patients with cardiomyopathy and reduced left ventricular (LV) ejection fraction are at risk of heart failure (HF) symptoms and sudden cardiac arrest (SCA). In selected HF patients, cardiac resynchronization therapy (CRT) provides LV reverse remodeling and improves the cellular and molecular function. However controversial results have been published regarding the effect of CRT on the residual ventricular arrhythmia risk. Indeed, the decrease in SCA risk is inconsistent and some factors strongly influence the residual post implantation arrhythmic risk. Conversely, proarrhythmic effect of CRT has been previously described. In this review we aim to describe the relationship between CRT implantation and the SCA risk decrease and discuss the patients who only require cardiac resynchronization therapy-pacemaker and those who need a concomitant implantable cardioverter defibrillator.