Fusion Pacing with Biventricular, Left Ventricular-only and Multipoint Pacing in Cardiac Resynchronisation Therapy: Latest Evidence and Strategies for Use

Physiological Pacing: Historical Review With an Eye to the Future

This review provides a history of physiological pacing from inception to current practice and into the future. This review stems from personal experience and is not formally systematic. Physiological cardiac pacing is covered from 1960s to date. Concepts, and major milestones with their practical applications are reviewed including possible applications in the future. Huge strides have been made in the last 50 years, but consequences of developments have not always been well considered resulting in important adverse effects. The future requires deep electrophysiological thinking to achieve further benefits for our patients.

Association Between the Use of an Adaptive Cardiac Resynchronization Therapy Algorithm and Health Care Use and Cost

OBJECTIVES

To assess the association between the use of adaptive pacing on clinical and economic outcomes of cardiac resynchronization therapy (CRT) recipients in a real-world analysis.

BACKGROUND

The adaptivCRT (aCRT) algorithm was shown in prior subgroup analyses of prospective trials to achieve clinical benefits, but a large prospective trial showed nonsignificant changes in the endpoint of mortality or hospitalizations due to heart failure.

METHODS

CRT-implanted patients from the Optum Clinformatics database with ≥ 90 days of follow-up were included. Remote monitoring data were used to classify patients based on CRT setting-adaptive biventricular and left ventricular pacing (aCRT) vs standard biventricular pacing (Standard CRT). Inverse probability of treatment weighting was used to adjust for baseline differences between groups. Mortality, 30-day readmissions, health care use, and payer and patients' costs were evaluated post-implantation.

RESULTS

This study included 2412 aCRT and 1638 Standard CRT patients (mean follow-up: 2.4 ± 1.4 years), with balanced baseline characteristics after adjustment. The aCRT group was associated with lower all-cause mortality rates (adjusted hazard ratio = 0.88 [95% confidence interval (CI):0.80, 0.96]), fewer all-cause 30-day readmissions (adjusted incidence rate ratio = 0.87 [CI:0.81, 0.94]), and fewer all-cause and HF-related inpatient, outpatient and emergency department visits. The aCRT cohort was also associated with lower all-cause outpatient payer-paid amounts and lower all-cause and HF-related inpatient and emergency department patient-paid amounts.

CONCLUSIONS

In this retrospective analysis of a large real-world cohort, the use of an adaptive CRT algorithm was associated with lower mortality rates, reduced health care resource use and lower payer and patient costs.

The Suboptimal QLV Ratio May Indicate the Need for a Left Bundle Branch Area Pacing-Optimized Cardiac Resynchronization Therapy Upgrade

Background: The QLV ratio (QLV/baseline QRS width) is an established intraoperative-measurable parameter during cardiac resynchronization therapy (CRT) device implantation, potentially predicting the efficacy of electrical resynchronization. Methods: Left bundle branch area pacing-optimized CRT (LOT-CRT) is a novel approach with the potential to improve both responder rate and responder level in the CRT candidate patient group, even when an optimal electro-anatomical left ventricular lead position is not achievable. In our observational study, 72 CRT-defibrillator candidate patients with a QRS duration of 160 ± 12 ms were consecutively implanted. Using a QLV-ratio-based implant strategy, 40 patients received a biventricular CRT device (Biv-CRT) with an optimal QLV ratio (≥70%). Twenty-eight patients with a suboptimal QLV ratio (<70%) were upgraded intraoperatively to a LOT-CRT system. Patients were followed for 12 months. Results: The postoperative results showed a significantly greater reduction in QRS width in the LOT-CRT patient group compared to the Biv-CRT patients (40.4 ± 14 ms vs. 32 ± 13 ms; p = 0.024). At 12 months, the LOT-CRT group also demonstrated a significantly greater improvement in left ventricular ejection fraction (14.9 ± 8% vs. 10.3 ± 7.4%; p = 0.001), and New York Heart Association functional class (1.2 ± 0.5 vs. 0.8 ± 0.4; p = 0.031), and a significant decrease in NT-pro-BNP levels (1863± 380 pg/mL vs. 1238 ± 412 pg/mL; p = 0.012). Notably, the LOT-CRT patients showed results comparable to Biv-CRT patients with a super-optimal QLV ratio (>80%) in terms of QRS width reduction and LVEF improvement. Conclusions: Our single-center study demonstrated the feasibility of a QLV-ratio-based implantation strategy during CRT implantation. Patients with a LOT-CRT system showed significant improvements, whereas Biv-CRT patients with a super-optimal QLV ratio may not be expected to benefit from an additional LOT-CRT upgrade.

Left Atrium Reverse Remodeling in Fusion CRT Pacing: Implications in Cardiac Resynchronization Response and Atrial Fibrillation Incidence

Background: When compared to biventricular pacing, fusion CRT pacing was linked to a decreased incidence of atrial fibrillation (AF). There is a gap in the knowledge regarding exclusive fusion CRT without interference with RV pacing, and all the current data are based on populations of patients with intermittent fusion pacing. Purpose: To assess left atrium remodeling and AF incidence in a real-life population of permanent fusion CRT-P. Methods: Retrospective data were analyzed from a cohort of patients with exclusive fusion CRT-P. Device interrogation, exercise testing, transthoracic echocardiography (TE), and customized medication optimization were all part of the six-monthly individual follow-up. Results: Study population: 73 patients (38 males) with non-ischemic dilated cardiomyopathy aged 63.7 ± 9.3 y.o. Baseline characteristic: QRS 159.8 ± 18.2 ms; EF 27.9 ± 5.1%; mitral regurgitation was severe in 38% of patients, moderate in 47% of patients, and mild in 15% of patients; 43% had type III diastolic dysfunction (DD), 49% had type II DD, 8% had type I DD. Average follow-up was 6.4 years ± 27 months: 93% of patients were responders (including 31% super-responders); EF increased to 40.4 ± 8.5%; mitral regurgitation decreased in 69% of patients; diastolic profile improved in 64% of patients. Paroxysmal and persistent AF incidence was 11%, with only 2% of patients developing permanent AF. Regarding LA volume, statistically significant LA reverse remodeling was observed. Conclusions: Exclusive fusion CRT-P was associated with important LA reverse remodeling and a low incidence of AF.

Optimizing electrical efficacy of leadless cardiac resynchronization therapy and leadless left ventricular septal pacing: Insights on left and right ventricular activation from electrocardiographic imaging

Background

Leadless cardiac resynchronization therapy (CRT) is an emerging heart failure treatment. An implanted electrode delivers lateral or septal endocardial left ventricular (LV) pacing (LVP) upon detection of a right ventricular (RV) pacing stimulus from a coimplanted device, thus generating biventricular pacing (BiVP). Electrical efficacy data regarding this therapy, particularly leadless LV septal pacing (LVSP) for potential conduction system capture, are limited.

Objectives

The purpose of this study was to evaluate the acute performance of leadless CRT using electrocardiographic imaging (ECGi) and assess the optimal pacing modality (OPM) of LVSP on the basis of RV and LV activation.

Methods

Ten WiSE-CRT recipients underwent an ECGi study testing: RV pacing, BiVP, LVP only, and LVP with an optimized atrioventricular delay (LV-OPT). BiV, LV, and RV activation times (shortest time taken to activate 90% of the ventricles [BIVAT-90], shortest time taken to activate 95% of the LV, and shortest time taken to activate 90% of the RV) plus LV and BiV dyssynchrony index (standard deviation of LV activation times and standard deviation of all activation times) were calculated from reconstructed epicardial electrograms. The individual OPM yielding the greatest improvement from baseline was determined.

Results

BiVP generated a 23.7% improvement in BiVAT-90 (P = .002). An improvement of 43.3% was observed at the OPM (P = .0001), primarily through reductions in shortest time taken to activate 90% of the RV. At the OPM, BiVAT-90 improved in patients with lateral (43.3%; P = .0001; n = 5) and septal (42.4%; P = .009; n = 5) LV implants. The OPM varied by individual. LVP and LV-OPT were mostly superior in patients with LVSP, and in those with sinus rhythm and left bundle branch block (n = 4).

Conclusion

Leadless CRT significantly improves acute ECGi-derived activation and dyssynchrony metrics. Using an individualized OPM improves efficacy in selected patients. Effective LVSP is feasible, with fusion pacing at LV-OPT mitigating the potential deleterious effects on RV activation.

Cardiac resynchronization using fusion pacing during exercise

INTRODUCTION

Fusion pacing requires correct timing of left ventricular pacing to right ventricular activation, although it is unclear whether this is maintained when atrioventricular (AV) conduction changes during exercise. We used cardiopulmonary exercise testing (CPET) to compare cardiac resynchronization therapy (CRT) using fusion pacing or fixed AV delays (AVD).

METHODS

Patients 6 months post-CRT implant with PR intervals < 250 ms performed two CPET tests, using either the SyncAV™ algorithm or fixed AVD of 120 ms in a double-blinded, randomized, crossover study. All other programming was optimized to produce the narrowest QRS duration (QRSd) possible.

RESULTS

Twenty patients (11 male, age 71 [65-77] years) were recruited. Fixed AVD and fusion programming resulted in similar narrowing of QRSd from intrinsic rhythm at rest (p = .85). Overall, there was no difference in peak oxygen consumption (V̇O2 PEAK , p = .19), oxygen consumption at anaerobic threshold (VT1, p = .42), or in the time to reach either V̇O2 PEAK (p = .81) or VT1 (p = .39). The BORG rating of perceived exertion was similar between groups. CPET performance was also analyzed comparing whichever programming gave the narrowest QRSd at rest (119 [96-136] vs. 134 [119-142] ms, p < .01). QRSd during exercise (p = .03), peak O2 pulse (mL/beat, a surrogate of stroke volume, p = .03), and cardiac efficiency (watts/mL/kg/min, p = .04) were significantly improved.

CONCLUSION

Fusion pacing is maintained during exercise without impairing exercise capacity compared with fixed AVD. However, using whichever algorithm gives the narrowest QRSd at rest is associated with a narrower QRSd during exercise, higher peak stroke volume, and improved cardiac efficiency.

Predictors for Super-Responders in Cardiac Resynchronization Therapy

BACKGROUND

Prediction of cardiac resynchronization therapy (CRT) response, particularly a super-response, is of great importance.

STUDY QUESTION

The aim of our study was to assess the predictors for super-responders in CRT.

STUDY DESIGN

We conducted a retrospective, observational study, which finally included 622 patients with heart failure treated with CRT between January 2008 and May 2020 who had a minimal follow-up of 6 months after CRT.

MEASURES AND OUTCOMES

A total of 192 super-responders, defined by a left ventricular ejection fraction (LVEF) of at least 45%, and/or minimum 15% increase in LVEF and an improvement of the New York Heart Association functional class by at least 2 degrees at the last follow-up, and the rest of 430 patients who did not fulfill the super-responder criteria.

RESULTS

The highest rate of super-responders (41.91%, n = 171) was at patients with left ventricle-only pacing with optimal fusion (OPT) compared with patients with biventricular (BiV) pacing (9.81%, n = 21, P < 0.000). In the OPT group, univariable analysis showed that nonischemic cardiomyopathy, a smaller degree of mitral regurgitation, and better left ventricle function at enrollment were predictors for super-response compared with the BiV group where a narrower QRS after implantation, nonischemic cardiomyopathy, and a better baseline LVEF were predictors for super-responders. In the multivariable analysis, both narrower QRS after implantation and nonischemic cardiomyopathy were independent predictors for super-response in the BiV group compared with OPT where nonischemic cardiomyopathy remained the only independent predictor for super-response.

CONCLUSIONS

In this retrospective study, OPT CRT programing was an additional predictor of super-response to CRT besides nonischemic cardiomyopathy.

The role of conduction system pacing in patients with atrial fibrillation

Conduction system pacing (CSP) has emerged as a promising novel delivery method for Cardiac Resynchronisation Therapy (CRT), providing an alternative to conventional biventricular epicardial (BiV) pacing in indicated patients. Despite increasing popularity and widespread uptake, CSP has rarely been specifically examined in patients with atrial fibrillation (AF), a cohort which forms a significant proportion of the heart failure (HF) population. In this review, we first examine the mechanistic evidence for the importance of sinus rhythm (SR) in CSP by allowing adjustment of atrioventricular delays (AVD) to achieve the optimal electrical response, and thus, whether the efficacy of CSP may be significantly attenuated compared to conventional BiV pacing in the presence of AF. We next evaluate the largest clinical body of evidence in this field, related to patients receiving CSP following atrioventricular nodal ablation (AVNA) for AF. Finally, we discuss how future research may be designed to address the vital question of how effective CSP in AF patients is, and the potential hurdles we may face in delivering such studies.

Electrocardiographic imaging demonstrates electrical synchrony improvement by dynamic atrioventricular delays in patients with left bundle branch block and preserved atrioventricular conduction

AIMS

Cardiac resynchronization therapy programmed to dynamically fuse pacing with intrinsic conduction using atrioventricular (AV) timing algorithms (e.g. SyncAV) has shown promise; however, mechanistic data are lacking. This study assessed the impact of SyncAV on electrical dyssynchrony across various pacing modalities using non-invasive epicardial electrocardiographic imaging (ECGi).

METHODS AND RESULTS

Twenty-five patients with left bundle-branch block (median QRS duration (QRSd) 162.7 ms) and intact AV conduction (PR interval 174.0 ms) were prospectively enrolled. ECGi was performed acutely during biventricular pacing with fixed nominal AV delays (BiV) and using SyncAV (optimized for the narrowest QRSd) during: BiV + SyncAV, LV-only single-site (LVSS + SyncAV), MultiPoint pacing (MPP + SyncAV), and LV-only MPP (LVMPP + SyncAV). Dyssynchrony was quantified via ECGi (LV activation time, LVAT; RV activation time, RVAT; LV electrical dispersion index, LVEDi; ventricular electrical uncoupling index, VEU; and biventricular total activation time, VVtat). Intrinsic conduction LVAT (124 ms) was significantly reduced by BiV pacing (109 ms) (P = 0.001) and further reduced by LVSS + SyncAV (103 ms), BiV + SyncAV (103 ms), LVMPP + SyncAV (95 ms), and MPP + SyncAV (90 ms). Intrinsic RVAT (93 ms), VVtat (130 ms), LVEDi (36 ms), VEU (50 ms), and QRSd (163 ms) were reduced by SyncAV across all pacing modes. More patients exhibited minimal LVAT, VVtat, LVEDi, and QRSd with MPP + SyncAV than any other modality.

CONCLUSION

Dynamic AV delay programming targeting fusion with intrinsic conduction significantly reduced dyssynchrony, as quantified by ECGi and QRSd for all evaluated pacing modes. MPP + SyncAV achieved the greatest synchrony overall but not for all patients, highlighting the value of pacing mode individualization during fusion optimization.

Betablockers and Ivabradine Titration According to Exercise Test in LV Only Fusion CRT Pacing

Background: Betablockers (BB)/ivabradine titration in fusion CRT pacing (CRTP) is understudied. Aim: To assess drug optimization using systematic exercise tests (ET) in fusion CRTP with preserved atrioventricular conduction (AVc). Methods: Changes in drug management were assessed during systematic follow-ups in CRTP patients without right ventricle lead. Shorter AVc (PR interval) allowed BB up-titration, while longer AVc needed BB down-titration, favoring ivabradine. Constant fusion pacing was the goal to improve outcomes. Results: 64 patients, 62.5 ± 9.5 y.o divided into three groups: shorter PR (<160 ms), normal (160−200 ms), longer (200−240 ms); follow-up 59 ± 26 months. Drugs were titrated in case of: capture loss due to AVc shortening (14%), AVc lengthening (5%), chronotropic incompetence (11%), maximum tracking rate issues (9%), brady/tachyarrhythmias (8%). Interventions: BB up-titration (78% shorter PR, 19% normal PR, 5% longer PR), BB down-titration (22% shorter PR, 14% normal PR), BB exclusion (16% longer PR), adding/up-titration ivabradine (22% shorter PR, 19% normal PR, 5% longer PR), ivabradine down-titration (22% shorter PR, 3% normal PR), ivabradine exclusion (11% normal PR, 5% longer PR). Drug strategy was changed in 165 follow-ups from 371 recorded (42% patients). Conclusions: BBs/ivabradine titration and routine ET during follow-ups in patients with fusion CRTP should be a standard approach to maximize resynchronization response. Fusion CRTP showed a positive outcome with important LV reverse remodeling and significant LVEF improvement in carefully selected patients.