Heart Rate Recovery Index and Improved Diastolic Dyssynchrony in Fusion Pacing Cardiac Resynchronization Therapy

Background: Restoring electrical synchrony with cardiac resynchronization therapy (CRT) reverses the heart failure phenotype developed by left-ventricular (LV) dyssynchrony. This study aimed to identify new predictors of response to LV-only fusion pacing CRT. Methods: A select group of patients with CRT-P indications received a right atrium (RA)/LV DDD pacing system. LV dyssynchrony was assessed via offline TDI timing focusing on the temporal difference between peak septal (E″T) and lateral wall (A"T) motion. CRT effectiveness was evaluated at each follow-up, involving the heart rate recovery index (HRRI) parameter (acceleration/deceleration time) derived from exercise testing along with the echocardiographic parameters. Patients were classified into super-responders (SR), responders (R), and non-responders (NR). Results: Baseline initial characteristics: 62 patients (35 male) aged 62 ± 11 y.o. with non-ischemic dilated cardiomyopathy (DCM). Ejection fraction (EF) 27 ± 5.2%; QRS 164 ± 18 ms; 29% had type III diastolic dysfunction (DD), 63% type II DD, and 8% type I DD. Average follow-up was 45 ± 19 months: 34% of patients were SR, 61% R, and 5% NR. The E″T decreased from 90 ± 20 ms to 25 ± 10 ms in SR, with a shorter deceleration time (DT) during exercise test compared to NR (109 ± 68 ms vs. 330 ± 30 ms; p < 0.0001). The responders present a higher HRRI (2.87 ± 1.47 vs. 0.98 ± 0.08; p = 0.03) compared to NR and a significantly decrease in E"T and A"T from 76 ± 13 ms to 51 ± 11 ms (p < 0.0001). Prolonged DT was associated with an accentuated LV dyssynchrony and nonoptimal response to CRT. Conclusions: The study identified new parameters for assessing responsiveness to LV-only fusion pacing CRT, which could improve candidate selection and CRT implementation.

Biventricular pacing in heart failure: a review

Biventricular pacing has been an exciting recent advance in the management of drug-refractory heart failure. This new therapy has evolved as much from necessity as scientific observation, since benefits derived from pharmacotherapy currently appear to have reached their peak. Clinical trials of biventricular pacing are establishing morbidity and mortality benefits in heart failure. New challenges in the use of these pacemakers are now arising. These include the accurate diagnosis of ventricular dyssynchrony and, hence, potential responders to the refinement of implantation of the left ventricular lead to the appropriate dyssynchronous ventricular area and optimization of pacemaker programming. This review gives a general overview of the principles and the current evidence for the use of biventricular pacemakers in the treatment of heart failure. In addition, a discussion of current research and future projects is included.

Anti- and pro-arrhythmic effects of cardiac resynchronization therapy: point of view

Cardiac resynchronization therapy (CRT) in patients with heart failure and bundle branch block (BBB) improves regional muscle mechanics and mechanical pump function of the heart. In addition, modulation of wall motion timing and contraction can exert an antiarrhythmic effect, reducing the potential of sudden cardiac death. This effect of CRT could also be attributed to the improvement in excitation-contraction coupling, mechanical synchronization, and improved myocardial perfusion. However, it can be hypothesized that the BBB results in a concealed reentry, in which a delayed depolarization wave re-enters during phase two of the action potential. This concealed phase 2 reentry can lead to early after depolarizations and cardiac arrhythmias. By synchronizing the two ventricles, CRT eliminates the reentry substrate and the resulting arrhythmias. This hypothesis and the potential arrhythmogenic effects of CRT are discussed with regard to ventricular remodeling and mechano-electrical feedback in this setting.