Rate-adaptive AV delay and exercise performance following cardiac resynchronization therapy

Usefulness of Cardiac Resynchronization Therapy Optimization Using Combined Electrocardiography and Echocardiography

Introduction Optimization of cardiac resynchronization therapy (CRT) using a 12-lead electrocardiogram (ECG) alone may not sufficiently improve left ventricular (LV) function in all cases. Therefore, we aimed to investigate whether additional optimization using transthoracic echocardiography (TTE) could further enhance CRT efficacy. Methods Sixty-five patients who underwent CRT implantation between March 2018 and July 2022 at Sakakibara Heart Institute, Japan, were included in this study. Data were collected at three points: before optimization (point A), after ECG-based optimization (point B), and after TTE-based adjustments (point C). Results The mean age was 74±11 years (male: 78.4%). The PR interval was significantly prolonged at points B and C compared with that at point A. The QRS width narrowed significantly at point B (119±20 ms vs. 137±20 ms, p<0.01) but increased at point C (124±20 ms), approaching point A levels. Thirty-six patients achieved LV dyssynchrony improvement with ECG optimization alone, whereas 29 required TTE adjustments for further improvement. Patients needing TTE optimization had higher QRS width at point C than at point B. TTE adjustments significantly improved LV ejection fraction (28.1±6.8% to 31.5±8.0%, p=0.01) and reduced septal flash (46.2% to 15.4%, p=0.04). The need for TTE adjustments was similar to the usage of CRT devices with and without auto-adjustment functions. Conclusion TTE-based optimization enhances LV function and synchrony in cases where ECG-based adjustments alone are insufficient, highlighting the importance of TTE evaluation in CRT optimization.

Accelerated atrial pacing reduces left-heart filling pressure: a combined clinical-computational study

BACKGROUND AND AIMS

Accelerated atrial pacing offers potential benefits for patients with heart failure with preserved ejection fraction (HFpEF) and atrial fibrillation (AF), compared with standard lower-rate pacing. The study investigates the relationship between atrial pacing rate and left-heart filling pressure.

METHODS

Seventy-five consecutive patients undergoing catheter ablation for AF underwent assessment of mean left atrial pressure (mLAP) and atrioventricular (AV) conduction delay (PR interval) in sinus rhythm and accelerated atrial pacing with 10 bpm increments up to Wenckebach block. Computer simulations (CircAdapt) of a virtual HFpEF cohort complemented clinical observations and hypothesized the modulating effects of AV coupling and atrial (dys)function.

RESULTS

In the study cohort, 49(65%) patients had a high HFpEF likelihood (H2FPEF ≥ 5.0), and 28(37%) an elevated mLAP ≥ 15 mmHg at sinus rhythm. Optimal pacing rates of 100 [70-110]bpm (median [IQR]) significantly reduced mLAP from 12.8 [10.0-17.4]mmHg in sinus rhythm (55 [52-61]bpm) to 10.4 [7.8-14.8]mmHg (P < .001). Conversely, higher pacing rates (130 [110-140]bpm) significantly increased mLAP to 14.7 [11.0-17.8]mmHg (P < .05). PR interval and, hence, AV conduction delay prolonged incrementally with increasing pacing rates. Simulations corroborated these clinical findings, showing mLAP reduction at a moderately increased pacing rate and a subsequent increase at higher rates. Moreover, simulations suggested that mLAP reduction is optimized when AV conduction delay shortens with increasing rate.

CONCLUSIONS

Accelerated pacing acutely reduces left-heart filling pressure in patients undergoing AF catheter ablation and computer simulations with HFpEF features, suggesting it as a potential therapeutic strategy to alleviate congestion symptoms. Virtual HFpEF patient cohorts hypothesize that AV sequential pacing may further optimize this therapy's beneficial effects.

Effect of adaptive cardiac resynchronization therapy in heart failure patients with pacemaker dependency

BACKGROUND

An adaptive cardiac resynchronization therapy (aCRT) algorithm allows continuous adjustments of pacing timings of atrioventricular delays by periodic automatic evaluation of electrical conduction. This applies to patients with an atrioventricular block and is effective in cardiac resynchronization therapy (CRT) devices; however, whether this algorithm benefits patients with pacemaker dependency is uncertain.

METHODS

This study examined the clinical impact of an aCRT algorithm in patients diagnosed with heart failure with reduced ejection fraction and pacemaker dependency. A total of 359 patients underwent CRT between January 2016 and December 2022. Patients undergoing pacemaker-dependent CRT with the aCRT algorithm function were selected. Sixty-four patients with pacemaker dependency (31 with aCRT algorithm and 33 without) were included. Pacemaker dependency was defined as the absence of spontaneous ventricular activity during the sensing test at VVI 30 bpm or prolonged atrioventricular delay (> 300 ms). The primary endpoint was the composite clinical outcome of all-cause death or hospitalization for heart failure.

RESULTS

No significant differences were observed in baseline characteristics between groups. During a median follow-up of 1,067 days (interquartile range 553-1,776 days), aCRT reduced the risk of composite clinical outcomes in patients with pacemaker dependency (log-rank P = 0.028). In addition, using the aCRT algorithm was an independent predictor of the composite clinical outcomes in the multivariate analysis (hazard ratio 0.34, 95% confidence interval: 0.12-0.94, P = 0.038).

CONCLUSION

The aCRT algorithm significantly reduced the risk of adverse clinical outcomes in patients with pacemaker dependency. This algorithm may be an important tool for managing such patients.

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.

The impact of chronotropic incompetence on atrioventricular conduction times in heart failure patients

BACKGROUND

Intrinsic atrioventricular (AV) conduction is used to optimize AV intervals with cardiac resynchronization therapy (CRT) in most device algorithms. Atrial pacing and heart rate affect conduction times, but little is known regarding differeces among chronotropic incompetent(CI) and competent(CC) patients to guide programming.

METHODS

RAVE was a multicenter prospective trial of CRT patients. Heart rate was increased with incremental atrial pacing and with submaximal exercise. According to the maximal heart rate achieved during exercise, patients were classified as either CI or CC. For CI patients, an additional symptom-limited exercise with rate-adaptive pacing activated was performed. Intracardiac intervals were measured from the implantable lead electrograms in multiple postures.

RESULTS

There were 12 subjects with CI and 24 with CC. With atrial pacing, AV interval immediately increased and gradually increased with incremental atrial pacing in all patients. However, the changes in the atrial to right ventricular (ARV) and atrial to left ventricular (ALV) intervals with increasing atrial pacing rates were about threefold greater in CI patients compared to CC patients (24.3 ± 28.9 vs. 7.2 ± 5.5 ms/10 bpm for ARV and 22.7 ± 25.6 vs. 7.1 ± 5.7 ms/10 bpm for ALV in the standing position, p < 0.05). In CI pacing with rate-adaptive pacing during exercise, AV interval changes with paced heart rate were variable.

CONCLUSIONS

The AV response to overdrive atrial pacing at rest may provide a simple means of identifying chronotropic competence in CRT patients. For patients with CI, who often require rate-adaptive atrial pacing, rate-adaptive AV algorithms should be adjusted individually.

Progress in Cardiac Resynchronisation Therapy and Optimisation

Cardiac resynchronisation therapy (CRT) has become the cornerstone of heart failure (HF) treatment. Despite the obvious benefit from this therapy, an estimated 30% of CRT patients do not respond ("non-responders"). The cause of "non-response" is multi-factorial and includes suboptimal device settings. To optimise CRT settings, echocardiography has been considered the gold standard but has limitations: it is user dependent and consumes time and resources. CRT proprietary algorithms have been developed to perform device optimisation efficiently and with limited resources. In this review, we discuss CRT optimisation including the various adopted proprietary algorithms and conduction system pacing.

Rate adaptive pacing in people with chronic heart failure increases peak heart rate but not peak exercise capacity: a systematic review

Rate adaptive cardiac pacing (RAP) allows increased heart rate (HR) in response to metabolic demand in people with implantable electronic cardiac devices (IECD). The aim of this work was to conduct a systematic review to determine if RAP increases peak exercise capacity (peak VO₂) in line with peak HR in people with chronic heart failure. We conducted a systematic literature search from 1980, when IECD and RAP were first introduced, until 31 July 2021. Databases searched include PubMed, Medline, EMBASE, EBSCO, and the Clinical Trials Register. A comprehensive search of the literature produced a total of 246 possible studies; of these, 14 studies were included. Studies and subsequent analyses were segregated according to comparison, specifically standard RAP (RAPON) vs fixed rate pacing (RAPOFF), and tailored RAP (TLD RAPON) vs standard RAP (RAPON). Pooled analyses were conducted for peak VO₂ and peak HR for RAPON vs RAPOFF. Peak HR significantly increased by 15 bpm with RAPON compared to RAPOFF (95%CI, 7.98-21.97, P < 0.0001). There was no significant difference between pacing mode for peak VO₂ 0.45 ml kg^-1 min^-1 (95%CI, - 0.55-1.47, P = 0.38). This systematic review revealed RAP increased peak HR in people with CHF; however, there was no concomitant improvement in peak VO₂. Rather RAP may provide benefits at submaximal intensities by controlling the rise in HR to optimise cardiac output at lower workloads. HR may be an important outcome of CHF management, reflecting myocardial efficiency.

What Have We Learned in the Last 20 Years About CRT Non-Responders?

Although cardiac resynchronization therapy (CRT) has become well established in the treatment of heart failure, the management of patients who do not respond after CRT remains a key challenge. This review will summarize what we have learned about non-responders over the last 20 years and discuss methods for optimizing response, including the introduction of novel therapies.

Efficacy of a Device-Based Continuous Optimization Algorithm for Patients With Cardiac Resynchronization Therapy

BACKGROUND

Cardiac resynchronization therapy (CRT) is less effective in patients with mildly wide QRS or non-left bundle branch block (non-LBBB). A new algorithm of every minute's optimization (adaptive CRT: aCRT algorithm) is effective in patients with CRT devices. This study investigated the clinical effect of the aCRT algorithm, especially in mildly wide QRS (120≤QRS<150 ms) or non-LBBB patients receiving CRT.

METHODS AND RESULTS

This study included 104 CRT patients (48 patients using the aCRT algorithm [adaptive group] and 56 patients not using the aCRT algorithm [non-adaptive group]). The primary endpoint was a composite clinical outcome of cardiac death and/or heart failure (HF) hospitalization. During a median follow-up of 700 days (interquartile range 362-1,173 days), aCRT reduced the risk of the clinical outcome, even in patients with mildly wide QRS or non-LBBB (log-rank P=0.0030 and P=0.0077, respectively) by Kaplan-Meier analysis. Use of the aCRT algorithm was an independent predictor of clinical outcomes in the multivariate analysis (hazard ratio (HR) 0.28, 95% confidence interval (CI): 0.096-0.78, P=0.015), the same as in patients with mildly wide QRS (HR 0.12, 95% CI: 0.006-0.69, P=0.015).

CONCLUSIONS

The new aCRT algorithm was useful and significantly reduced the risk of the clinical outcome, even in patients with mildly wide QRS.

The effect of posture, exercise, and atrial pacing on atrioventricular conduction in systolic heart failure

BACKGROUND

Optimization of atrioventricular (AV) intervals for cardiac resynchronization therapy (CRT) programming is typically performed in supine patients at rest, which may not reflect AV timing in other conditions.

OBJECTIVE

To evaluate the effects of posture, exercise, and atrial pacing on intrinsic AV intervals in patients with CRT devices.

METHODS

Rate-dependent A-V delay by exercise was a multicenter, prospective trial of patients in sinus rhythm following CRT implantation. Intracardiac electrograms were recorded to analyze atrial to right ventricular (ARV), atrial to left ventricular (ALV), and RV to LV (VV) time intervals. Heart rate was increased with incremental atrial pacing in different postures, followed by an exercise treadmill test.

RESULTS

This study included 36 patients. At rest, AV intervals changed minimally with posture. With atrial pacing, AV interval immediately increased compared with sinus rhythm, with ARV slopes being 8.1 ± 7.7, 8.8 ± 13.4, and 6.8 ± 6.5 milliseconds per beat per minute (ms/bpm) and ALV slopes being 8.2 ± 7.7, 9.1 ± 12.8, and 7.0 ± 6.5 ms/bpm for supine, standing and sitting positions, respectively. As the paced heart rate increased, ARV and ALV intervals increased more gradually with similar trends. Interventricular conduction times changed less than 0.2 ms/bpm with atrial pacing. During exercise, the direction of change of intrinsic ARV intervals, as heart rate increased, was variable between patients with relatively small overall group changes (0.1 ± 1.4 and 0.2 ± 1.2 ms/bpm for ARV and ALV, respectively).

CONCLUSION

Posture and exercise have a smaller effect on AV timing compared with atrial pacing. However, individualized optimization and dynamic rate related changes may be needed to maintain optimal fusion with left ventricular (LV) stimulation.

Novel Device-Based Algorithm Provides Optimal Hemodynamics During Exercise in Patients With Cardiac Resynchronization Therapy

BACKGROUND

An adaptive cardiac resynchronization therapy (aCRT) algorithm has been described for synchronized left ventricular (LV) pacing and continuous optimization of cardiac resynchronization therapy (CRT). However, there are few algorithmic data on the effect of changes during exercise.

METHODS AND RESULTS

We enrolled 27 patients with availability of the aCRT algorithm. Eligible patients were manually programmed to optimal atrioventricular (AV) and interventricular (VV) delays by using echocardiograms at rest or during 2 stages of supine bicycle exercise. We compared the maximum cardiac output between manual echo-optimization and aCRT-on during each phase. After initiating exercise, the optimal AV delay progressively shortened (P<0.05) with incremental exercise levels. The manual-optimized settings and aCRT resulted in similar cardiac performance, as demonstrated by a high concordance correlation coefficient between the LV outflow tract velocity time integral (LVOT-VTI) during each exercise stage (Ex.1: r=0.94 P<0.0008, Ex.2: r=0.88 P<0.001, respectively). Synchronized LV-only pacing in patients with normal AV conduction could provide a higher LVOT-VTI as compared with manual-optimized conventional biventricular pacing at peak exercise (P<0.05).

CONCLUSIONS

The aCRT algorithm was physiologically sound during exercise by patients.

Current role of echocardiography in cardiac resynchronization therapy

Cardiac resynchronization therapy (CRT) is an established treatment for patients with heart failure and left ventricular systolic dysfunction. Patients are usually assessed by echocardiography, which provides a number of anatomical and functional information used for cardiac dyssynchrony assessment, prognostic stratification, identification of the optimal site of pacing in the left ventricle, optimization of the CRT device, and patient follow-up. Compared to other cardiac imaging techniques, echocardiography has the advantage to be non-invasive, repeatable, and safe, without exposure to ionizing radiation or nefrotoxic contrast. In this article, we review current evidence about the role of echocardiography before, during, and after the implantation of a CRT device.

Advances in atrioventricular and interventricular optimization of cardiac resynchronization therapy - what's the gold standard?

INTRODUCTION

Cardiac resynchronization therapy (CRT) is one of the most important advances in heart failure management in the last twenty years. Approximately one-third of patients appear not to respond to therapy. Although there are a number of possible mechanisms for non-response, an important factor is suboptimal atrioventricular (AV) and interventricular (VV) timing intervals. There remains controversy over whether routinely optimizing intervals is necessary and there is no agreed gold standard methodology. Optimization has classically been performed using echocardiography which has limits related to resource use, time-cost and variable reproducibility. Newer optimization methods using device-based sensors and algorithms show promise in reducing heart-failure hospitalization compared with echocardiography. Areas covered: This review outlines the rationale for optimization, the principles of AV and VV optimization, the standard echocardiographic approach and newer device-based algorithms and the evidence base for their use. Expert commentary: The incremental gains of optimization are likely to be real, but small, compared to the overall improvement gained from cardiac resynchronization itself. At this time routine optimization may not be mandatory but should be performed where there is no response to CRT. Device-based optimization algorithms appear to be practical and in some cases, deliver superior clinical outcomes compared to echocardiography.

Adaptive CRT in patients with normal AV conduction and left bundle branch block: Does QRS duration matter?

BACKGROUND

Adaptive cardiac resynchronization therapy (aCRT) is a dynamic optimization algorithm which paces only the left ventricle (LV) when atrio-ventricular (AV) conduction is normal, thus reducing right ventricular (RV) pacing. However, the impact of QRS duration on aCRT efficacy remains uncertain. We examined whether QRS duration impacts aCRT effectiveness in patients with left bundle branch block (LBBB) and preserved AV conduction.

METHODS

Randomized patients in the Adaptive CRT trial, which enrolled NYHA III/IV patients, were used in this analysis. Patients were randomized to receive aCRT or echo-optimized bi-ventricular CRT (control arm). Endpoints for this analysis were clinical composite score (CCS) at 6months post-implant and time to first heart failure (HF) hospitalization or death.

RESULTS

Among the 199 patients with LBBB and normal AV intervals at baseline, 80 patients (40%) had a baseline moderately wide QRS of 120-150ms. In this subgroup, a greater proportion of aCRT patients had an improved CCS (79% vs. 50%) at 6months compared to the control group (p=0.03). There was also a trend toward a lower risk of death or HF hospitalization (hazard ratio: 0.53; 95% CI: 0.24-1.15; p=0.10) in the moderately wide QRS subgroup with aCRT compared to the control arm. In the wide QRS subgroup, the efficacy was comparable in both treatment arms.

CONCLUSION

Adaptive CRT was associated with improved patient outcomes over echo-optimized bi-ventricular CRT in patients with preserved AV conduction, LBBB, and moderately wide QRS. The adaptive cardiac resynchronization therapy trial (ClinicalTrials.gov Identifier: NCT00980057) was sponsored by Medtronic plc, Mounds View, MN.

The Role of Atrioventricular and Interventricular Optimization for Cardiac Resynchronization Therapy

Many patients with left ventricular systolic dysfunction may benefit from cardiac resynchronization therapy; however, approximately 30% of patients do not experience significant clinical improvement with this treatment. AV and VV delay optimization techniques have included echocardiography, device-based algorithms, and several other novel noninvasive techniques. Using these techniques to optimize device settings has been shown to improve hemodynamic function acutely; however, the long-term clinical benefit is limited. In most cases, an empiric AV delay with simultaneous biventricular or left ventricular pacing is adequate. The value of optimization of these intervals in "nonresponders" still requires further investigation.

Optimal pacing for right ventricular and biventricular devices: minimizing, maximizing, and right ventricular/left ventricular site considerations

The results from numerous clinical studies provide guidance for optimizing outcomes related to RV or biventricular pacing in the pacemaker and ICD populations. (1) Programming algorithms to minimize RV pacing is imperative in patients with dual-chamber pacemakers who have intrinsic AV conduction or intermittent AV conduction block. (2) Dual-chamber ICDs should be avoided in candidates without an indication for bradycardia pacing. (3) Alternate RV septal pacing sites may be considered at the time of pacemaker implantation. (4) Biventricular pacing may be beneficial in some patients with mild LV dysfunction. (5) LV lead placement at the site of latest LV activation is desirable. (6) Programming CRT systems to achieve biventricular/LV pacing >98.5% is important. (7) Protocols for AV and VV optimization in patients with CRT are not recommended after device implantation but may be considered for CRT nonresponders. (8) Novel algorithms to maximize the benefit of CRT are in evolution further.

Optimisation of cardiac resynchronization therapy in clinical practice during exercise

Aims

Although cardiac resynchronisation therapy (CRT) is an established treatment to improve cardiac function, a significant amount of patients do not experience noticeable improvement in their cardiac function. Optimal timing of the delay between atrial and ventricular pacing pulses (AV delay) is of major importance for effective CRT treatment and this optimum may differ between resting and exercise conditions. In this study the feasibility of haemodynamic measurements by the non-invasive finger plethysmographic method (Nexfin) was used to optimise the AV delay during exercise.

Methods and results

Thirty-one patients implanted with a CRT device in the last 4 years participated in the study. During rest and in exercise, stroke volume (SV) was measured using the Nexfin device for several AV delays. The optimal AV delay at rest and in exercise was determined using the least squares estimates (LSE) method. Optimisation created a clinically significant improvement in SV of 10 %. The relation between HR and the optimal AV delay was patient dependent.

Conclusion

A potential increase in SV of 10 % can be achieved using Nexfin for optimisation of AV delay during exercise. A considerable number of patients showed benefit with lengthening of the AV delay during exercise.