Update on the pathophysiological basics of cardiac resynchronization therapy

25 years of basic and translational science in EP Europace: novel insights into arrhythmia mechanisms and therapeutic strategies

In the last 25 years, EP Europace has published more than 300 basic and translational science articles covering different arrhythmia types (ranging from atrial fibrillation to ventricular tachyarrhythmias), different diseases predisposing to arrhythmia formation (such as genetic arrhythmia disorders and heart failure), and different interventional and pharmacological anti-arrhythmic treatment strategies (ranging from pacing and defibrillation to different ablation approaches and novel drug-therapies). These studies have been conducted in cellular models, small and large animal models, and in the last couple of years increasingly in silico using computational approaches. In sum, these articles have contributed substantially to our pathophysiological understanding of arrhythmia mechanisms and treatment options; many of which have made their way into clinical applications. This review discusses a representative selection of EP Europace manuscripts covering the topics of pacing and ablation, atrial fibrillation, heart failure and pro-arrhythmic ventricular remodelling, ion channel (dys)function and pharmacology, inherited arrhythmia syndromes, and arrhythmogenic cardiomyopathies, highlighting some of the advances of the past 25 years. Given the increasingly recognized complexity and multidisciplinary nature of arrhythmogenesis and continued technological developments, basic and translational electrophysiological research is key advancing the field. EP Europace aims to further increase its contribution to the discovery of arrhythmia mechanisms and the implementation of mechanism-based precision therapy approaches in arrhythmia management.

Conduction system pacing on track to replace CRT? Review of current evidence and prospects of conduction system pacing

Conduction system pacing (CSP) has been emerging over the last decade as a pacing option instead of conventional right ventricular (RV) pacing and biventricular (BiV) pacing. Numerous case reports, some observational studies and a few randomized control trials have looked at optimum pacing strategies for heart failure (HF) with left bundle branch block (LBBB) or cases where left ventricular (LV) dysfunction is anticipated due to chronic RV pacing (RVP). Evolution of pacing strategies from standard RVP to septal RVP, BiV pacing and now CSP have shown improving hemodynamic responses and possible ease of implantation of CSP systems. In this review article, we review the literature on the evolution of CSP and common scenarios where it might be beneficial.

[Resynchronization Therapy for Chronic Heart Failure: Diagnostic and Therapeutic Approaches]

Chronic heart failure (CHF) remains one of the most important problems of modern cardiology. One of the effective treatment methods is resynchronization therapy (RT). The article presents an analysis of literature data on the effectiveness of RT in improving the quality of life, reducing the number of hospitalizations and mortality in patients with heart failure with severe left ventricular systolic dysfunction and expanding QRS complex, and also discusses key methods for optimizing RT.

Acute Effects of Biventricular Pacing in Heart Failure Patients with a Normal Ejection Fraction and Mechanical Dyssynchrony

Objectives: We tested the acute effects of resynchronization in heart failure patients with a normal (>50%) left ventricular (LV) ejection fraction (HFNEF) and mechanical dyssynchrony. Methods: Twenty-four HFNEF patients (72 ± 6 years, 5 male) with mechanical dyssynchrony (standard deviation of electromechanical time delay among 12 LV segments >35 ms) were studied with temporary pacing catheters in the right atrium, LV, and right ventricle (RV), and high-fidelity catheters for pressure recording. Using selected atrioventricular (AV) intervals of 60, 90, 120, 150, and 180 ms to optimize transmitral flow during simultaneous biventricular pacing, the RV-LV (VV) interval was then evaluated at RV30, RV15, 0, LV15, LV30, and LV45 (RV or LV indicates which ventricle was paced first, the number indicates by how many ms). Results: During simultaneous pacing, longer AV intervals were associated with improved LV pressure-derivative minimums and increased aortic pressures (p < 0.05 vs. normal sinus rhythm). In the VV interval from RV30 to LV45, there was a graded increase in the aortic velocity time integral and a decrease in dyssynchrony during simultaneous or LV-first pacing (p < 0.05 vs. normal sinus rhythm). Conclusions: For HFNEF patients with mechanical dyssynchrony, acute simultaneous biventricular or LV-first pacing with longer AV intervals reduced mechanical dyssynchrony and improved diastolic and systolic hemodynamics.

Mechanical dyssynchrony precedes QRS widening in ATP-sensitive K⁺ channel-deficient dilated cardiomyopathy

Background

Contractile discordance exacerbates cardiac dysfunction, aggravating heart failure outcome. Dissecting the genesis of mechanical dyssynchrony would enable an early diagnosis before advanced disease.

Methods and Results

High‐resolution speckle‐tracking echocardiography was applied in a knockout murine surrogate of adult‐onset human cardiomyopathy caused by mutations in cardioprotective ATP‐sensitive K⁺ (K_ATP) channels. Preceding the established criteria of cardiac dyssynchrony, multiparametric speckle‐based strain resolved nascent erosion of dysfunctional regions within cardiomyopathic ventricles of the K_ATP channel–null mutant exposed to hemodynamic stress. Not observed in wild‐type counterparts, intraventricular disparity in wall motion, validated by the degree, direction, and delay of myocardial speckle patterns, unmasked the disease substrate from asymptomatic to overt heart failure. Mechanical dyssynchrony preceded widening of the QRS complex and exercise intolerance and progressed into global myocardial discoordination and decompensated cardiac pump function, precipitating a low output syndrome.

Conclusions

The present study, with the use of high‐resolution imaging, prospectively resolved the origin and extent of intraventricular motion disparity in a K_ATP channel–knockout model of dilated cardiomyopathy. Mechanical dyssynchrony established as an early marker of cardiomyopathic disease offers novel insight into the pathodynamics of dyssynchronous heart failure.

Induced pluripotent stem cell intervention rescues ventricular wall motion disparity, achieving biological cardiac resynchronization post-infarction

Dyssynchronous myocardial motion aggravates cardiac pump function. Cardiac resynchronization using pacing devices is a standard-of-care in the management of heart failure. Post-infarction, however, scar tissue formation impedes the efficacy of device-based therapy. The present study tests a regenerative approach aimed at targeting the origin of abnormal motion to prevent dyssynchronous organ failure. Induced pluripotent stem (iPS) cells harbour a reparative potential, and were here bioengineered from somatic fibroblasts reprogrammed with the stemness factors OCT3/4, SOX2, KLF4, and c-MYC. In a murine infarction model, within 30 min of coronary ligation, iPS cells were delivered to mapped infarcted areas. Focal deformation and dysfunction underlying progressive heart failure was resolved prospectively using speckle-tracking imaging. Tracked at high temporal and spatial resolution, regional iPS cell transplantation restored, within 10 days post-infarction, the contractility of targeted infarcted foci and nullified conduction delay in adjacent non-infarcted regions. Local iPS cell therapy, but not delivery of parental fibroblasts or vehicle, prevented or normalized abnormal strain patterns correcting the decrease in peak strain, disparity of time-to-peak strain, and pathological systolic stretch. Focal benefit of iPS cell intervention translated into improved left ventricular conduction and contractility, reduced scar, and reversal of structural remodelling, protecting from organ decompensation. Thus, in ischaemic cardiomyopathy, targeted iPS cell transplantation synchronized failing ventricles, offering a regenerative strategy to achieve biological resynchronization.

Left ventricular performance during para-His pacing in patients with high-grade atrioventricular block: an acute study

AIM

To compare changes in left ventricular (LV) performance and mechanical synchrony between atrial-based pacing with intrinsic conduction (AAI), dual-chamber para-His Pacing (DDD-PHP) and dual-chamber right ventricular septal pacing (DDD-RVS) in patients with high-grade atrioventricular block (AVB).

METHODS AND RESULTS

Patients with high-grade AVB and QRS <120 ms, who had temporary intrinsic atrioventricular (AV) conduction the day after the implantation were included in the study. All patients received a biventricular pacemaker with a para-His lead in the LV port, and a RVS lead in the right ventricular port. Left ventricular three-dimensional echocardiograms, LV outlet tract-velocity time integrals (LVOT-VTI), and LV synchrony with tissue Doppler imaging were recorded during AAI, DDD-PHP, and DDD-RVS. Eleven patients were included. The mean LVOT-VTI was significant lower during DDD-RVS (19.2 ± 5.5 cm) as compared with DDD-PHP (21.4 ± 5.5 cm), P = 0.006 and AAI (21.6 ± 6.8 cm), P = 0.016. The LVEF was higher during AAI than during DDD-PHP (P= 0.02) and DDD-RVS (P< 0.01). The maximal time to peak velocity between basal segments was significant longer with DDD-RVS (95 ± 26 ms) than with AAI (72 ± 30 ms), P = 0.028, whereas no difference was observed between AAI and DDD-PHP (81 ± 42 ms), P = 0.20.

CONCLUSIONS

Acutely, DDD-PHP preserves LV systolic performance and mechanical synchrony as compared with DDD-RVS.

Dynamic and site-specific impact of ventricular pacing on left ventricular ejection fraction

BACKGROUND

Some studies suggest that right ventricular (RV) pacing has an adverse impact on left ventricular ejection fraction (LVEF), particularly in subjects with preexisting left ventricular (LV) dysfunction, and that direct LV pacing may be relatively protective. Interactions between pacing site and LVEF remain unclear.

OBJECTIVE

The purpose of this study was to examine the relative impact of RV and LV pacing on LVEF by serial study during a period in which LV dysfunction, induced by tachypacing, was introduced and then resolved.

METHODS

In each of five dogs, RV, LV, and simultaneous RV and LV (BiV) pacing modes were compared to native ventricular activation (1) prior to tachypacing (baseline), (2) weekly during a 5-week continuous tachypacing period, and (3) weekly during a 3-week post-tachypacing recovery period. At each evaluation, LVEF and LV contraction synchrony were assessed during each pacing mode.

RESULTS

The decrease in LVEF during the tachypacing period was more pronounced during RV pacing than during native activation or LV or BiV pacing. The magnitude of this effect correlated with a diminishment in LV contraction synchrony that was not observed during native activation or LV or BiV pacing. During the post-tachypacing period, gradual reversal of these changes toward baseline was observed.

CONCLUSION

Compared to native activation, RV pacing worsens LVEF in a manner proportional to the severity of preexisting LV dysfunction, attributable to reduced LV contraction synchrony. In comparison, both LV and BiV pacing preserve LVEF and contraction synchrony.

Association of electrostimulation with cell transplantation in ischemic heart disease

BACKGROUND

Until now, cell therapy has constituted a passive therapeutic approach; the only effects seem to be related to the reduction of the myocardial fibrosis and the limitation of the adverse ventricular remodeling. Cardiac resynchronization therapy is indicated in patients with heart failure to correct conduction disorders associated with chronic systolic and diastolic dysfunction. The association of electrostimulation with cellular cardiomyoplasty could be a way to transform passive cell therapy into "dynamic cellular support." Electrostimulation of ventricles following skeletal myoblast implantation should induce the contraction of the transplanted cells and a higher expression of slow myosin, which is better adapted for chronic ventricular assistance. The purpose of this study is to evaluate myogenic cell transplantation in an ischemic heart model associated with cardiac resynchronization therapy.

METHODS

Twenty two sheep were included. All animals underwent myocardial infarction by ligation of 2 coronary artery branches (distal left anterior descending artery and D2). After 4 weeks, autologous cultured myoblasts were injected in the infarcted areas with or without pacemaker implantation. Atrial synchronized biventricular pacing was performed using epicardial electrodes. Echocardiography was performed at 4 weeks (baseline) and 12 weeks after infarction.

RESULTS

Echocardiography showed a significant improvement in ejection fraction and limitation of left ventricular dilatation in cell therapy with cardiac resynchronization therapy as compared with the other groups. Viable cells were identified in the infarcted areas. Differentiation of myoblasts into myotubes and enhanced expression of slow myosin heavy chain was observed in the electrostimulated group. Transplantation of cells with cardiac resynchronization therapy caused an increase in diastolic wall thickening in the infarcted zone relative to cells-only group and cardiac resynchronization therapy-only group.

CONCLUSIONS

Biventricular pacing seems to induce synchronous contraction of transplanted myoblasts and the host myocardium, thus improving ventricular function. Electrostimulation was related with enhanced expression of slow myosin and the organization of myoblasts in myotubes, which are better adapted at performing cardiac work. Patients with heart failure presenting myocardial infarct scars and indication for cardiac resynchronization therapy might benefit from simultaneous cardiac pacing and cell therapy.