Cardiac resynchronization therapy special populations

Synonyms and Keywords: CRT
 * : Bhaskar Purushottam, M.D. [mailto:bpurushottam@gmail.com]

Overview
The patient with atrial fibrillation and heart failure poses a challenge in optimizing the benefits of cardiac resynchronization therapy (CRT). The rapid ventricular response (RVR) associated with atrial fibrillation can minimize the benefits of CRT, and pharmacologic rate control or AV ablation may optimize the benefit of CRT.

Challenges Posed by Atrial Fibrillation and CRT
Atrial fibrillation poses several challenges to effective biventricular pacing.
 * 1) The intrinsic, intermediate-to-high irregular atrial fibrillation rhythm reduces the number of biventricular paced captured beats.
 * 2) Even in atrial fibrillation patients who have a normal ventricular response rate, there is the occurrence of spontaneous, fusion and pseudofusion beats, which once again minimize the biventricular pacing.
 * 3) Rapid heart rates reduce diastolic filling time and hence reduce stroke volume.
 * 4) Irregular rhythm negatively impacts left ventricular function.

Solutions to the Challenges Posed by Atrial Fibrillation and CRT

 * 1) The heart rate can be slowed with negative chronotropic agents which may in turn optimize CRT.
 * 2) Atrioventricular junction ablation and device mediated treatment, such as ‘Ventricular Rate Regularization. The OPISTE and PAVE trials confirmed the clinical benefits of atrioventricular ablation with adequate rate control. The PAVE study showed a greater benefit of biventricular pacing. On the basis of these trials and recent observational data, atrioventricular junction ablation may represent a fundamental tool in improving cardiac resynchronization response.

Cardiac Resynchronization Therapy in Minimal Heart Failure
A recent systematic review and meta-analysis of prospective randomized trials of CRT in patients with reduced LVEF, prolonged QRS interval (QRS duration greater than or equal to 0.12 seconds) and New York Heart Association (NYHA) functional class I and II heart failure showed a decrease in all-cause mortality, reduced heart failure hospitalizations and improved LVEF. Five prospective randomized trials have evaluated the benefit of CRT in patients with NYHA functional class I or II. The trials include the RAFT trial (1,438 patients), MADIT-CRT (1,820 patients), REVERSE (610 patients), MIRACLE ICD II (186 patients) and CONTAK CD (263 patients) trials (compromising a total of >4000 patients with NYHA functional class I/II). This systematic review and meta-analysis found a 19% reduction in mortality, 32% reduction in heart failure events or hospitalization, mean increase in LVEF by 4.1% and reductions in left ventricular end-diastolic dimensions and volume in comparison with ICD (Implantable Cardioverter-Defibrillator) therapy alone. Furthermore Adabag et al. were the first to show that CRT was associated with a significant reduction in heart failure hospitalizations in asymptomatic heart failure patients (NYHA functional class I). The mortality benefit derived in these patients (NYHA functional class I/II) were largely dervied from the RAFT trial (1,438 patients with NYHA functional class II). The survival benefit was seen especially after 2.5 years, which highlights the delayed mortality benefit for CRT in these patients. Currently, the application of the above results in clinical practice should be individualized.