Cardiac resynchronization therapy: a breakthrough in heart failure management

Cardiac resynchronization therapy: results, challenges and perspectives for the future

Heart failure (HF) is considered as an epidemic and affects 2% of the population in the Western world. About 15-30% of patients with HF and reduced ejection fraction (HFrEF) also have prolonged QRS duration on the surface ECG, most commonly as a result of left-bundle branch block (LBBB). Increased QRS duration is a marker of a dyssynchronous activation, and subsequent contraction, pattern in the left ventricle (LV). When dyssynchrony is superimposed on the failing heart it further reduced systolic function and ultimately worsens outcome. During the past 15 years several randomized controlled clinical trials have documented that resynchronization of the dyssynchronous failing heart with a biventricular pacemaker - cardiac resynchronization therapy (CRT) - which can restore a more synchronous activation and contraction pattern. This translates in halted or reversed disease progression and improved clinical outcome, including reduced mortality. In this review, we will discuss several aspects of CRT including mechanisms of dyssynchrony and resynchronization in the failing heart, evidence of CRT efficacy derived from clinical trials and current challenges in CRT including patient selection and optimization of therapy delivery. Last, we will discuss future perspectives including the role of CRT to prevent adverse events in patients with an indication for antibradycardia pacing, the role of leadless pacing in the CRT setting as well as a new clinical arena where dyssynchrony and resynchronization may be important.

Optimal Cardiac Resynchronization Therapy Pacing Rate in Non-Ischemic Heart Failure Patients: A Randomized Crossover Pilot Trial

Background

The optimal pacing rate during cardiac resynchronization therapy (CRT) is unknown. Therefore, we investigated the impact of changing basal pacing frequencies on autonomic nerve function, cardiopulmonary exercise capacity and self-perceived quality of life (QoL).

Methods

Twelve CRT patients with non-ischemic heart failure (NYHA class II–III) were enrolled in a randomized, double-blind, crossover trial, in which the basal pacing rate was set at DDD-60 and DDD-80 for 3 months (DDD-R for 2 patients). At baseline, 3 months and 6 months, we assessed sympathetic nerve activity by microneurography (MSNA), peak oxygen consumption (pVO₂), N-terminal pro-brain natriuretic peptide (p-NT-proBNP), echocardiography and QoL.

Results

DDD-80 pacing for 3 months increased the mean heart rate from 77.3 to 86.1 (p = 0.001) and reduced sympathetic activity compared to DDD-60 (51±14 bursts/100 cardiac cycles vs. 64±14 bursts/100 cardiac cycles, p<0.05). The mean pVO₂ increased non-significantly from 15.6±6 mL/min/kg during DDD-60 to 16.7±6 mL/min/kg during DDD-80, and p-NT-proBNP remained unchanged. The QoL score indicated that DDD-60 was better tolerated.

Conclusion

In CRT patients with non-ischemic heart failure, 3 months of DDD-80 pacing decreased sympathetic outflow (burst incidence only) compared to DDD-60 pacing. However, Qol scores were better during the lower pacing rate. Further and larger scale investigations are indicated.

Trial Registration

ClinicalTrials.gov NCT02258061

Increase in paced heart rate reduces muscle sympathetic nerve activity in heart failure patients treated with cardiac resynchronization therapy

AIMS

To test the hypothesis that acute increased biventricularly (BiV) paced heart rate (pHR) results in decreased muscle sympathetic nerve activity (MSNA), and that dyssynchronous pacing (AAI) attenuates this effect, in heart failure patients receiving cardiac resynchronization therapy (CRT).

METHODS AND RESULTS

Fourteen CRT patients (NYHA II-III, 12 males, mean EF 28 ± 14%) were recruited. Three different pHRs (50-90 b.p.m.) were randomly programmed in BiV- and AAI-pacing modes. Muscle sympathetic nerve activity (total sympathetic nerve activity/min (units) and number of bursts/100 RR) were recorded from the peroneal nerve using a microelectrode. In addition, cardiac output (CO) and mean blood pressure (mBP) were measured. With BiV pacing, the total MSNA/min was lower at 70 b.p.m. (-7 ± 21%, P = 0.18) and 90 b.p.m. (-29 ± 18%, P = 0.01) compared with at 50 b.p.m. (280 ± 180 U). Similarly, bursts/100RR decreased with increased BiV pHR. Cardiac output (3.7 L/min at 50 b.p.m., +12 ± 12% at 70 b.p.m., and +18 ± 19% at 90 b.p.m.) and mBP (78 ± 11 mmHg at 50 b.p.m., +6 ± 6% at 70 b.p.m. and +11 ± 8% at 90 b.p.m.) increased significantly at elevated pHRs in BiV-pacing mode. The effect on MSNA, CO, and mBP was less pronounced in AAImode but we found no significant differences between the pacing modes.

CONCLUSION

Increased pHR acutely reduces MSNA and improves haemodynamics in HF patients treated with CRT with no evident differences between BiV- and AAI-pacing modes. Further studies are warranted to guide the programming of basic pHR in CRT patients.

Utility of the Seattle Heart Failure Model in patients with cardiac resynchronization therapy and implantable cardioverter defibrillator referred for heart transplantation

BACKGROUND

The Seattle Heart Failure Model (SHFM) predicts survival in heart failure but may underestimate risk in severe heart failure, and the performance has not been evaluated explicitly in patients with cardiac resynchronization therapy (CRT) and/or implantable cardioverter defibrillator (ICD) referred for heart transplantation. We aimed to assess the utility of the SHFM by validation in patients with CRT and/or ICD referred for heart transplantation.

METHODS

We assessed the SHFM performance in 382 patients with CRT and/or ICD referred for heart transplantation. Outcome was survival free from urgent transplantation or left ventricular assist device. Model discrimination and calibration were assessed graphically and by formal tests.

RESULTS

During a mean follow-up of 2.3 years, 195 events occurred. One-, 2-, and 3-year observed event-free survival was 77%, 62%, and 52%, and the observed to predicted event-free survival ratio was 0.89, 0.80, and 0.76. Calibration plots demonstrated results deviating from the ideal calibration line at 1, 2, and 3 years. The SHFM score adequately assigned patients in discrete risk strata, according to Kaplan-Meier estimated survival. Time-dependent receiver operating characteristic curve analyses demonstrated good discrimination overall, which was slightly better for 1-year (area under the curve [AUC] 0.774) compared with 2-year (AUC 0.742) and 3-year (AUC 0.728) event-free survival.

CONCLUSIONS

The SHFM has good discrimination but underestimates risk of adverse outcomes in patients with CRT and/or ICD referred for heart transplantation. The SHFM may be used to assess relative risk and changes over time, but when assessing absolute percentage of event-free survival, the overestimation of event-free survival should be accounted for.