NEW YORK (Reuters Health) – Contrary to expectations, left ventricular (LV) pacing is not superior to simultaneous biventricular (BiV) pacing in certain patients with symptoms of heart failure, a Canadian team reports.

“However, nonresponders to BiV pacing may respond favorably to LV pacing, suggesting a potential role as tiered therapy,” they comment in their report in Circulation online November 21.

Dr. Bernard Thibault, with the Montreal Heart Institute, Quebec, and colleagues hypothesized that exercise tolerance in patients with an indication for an implantable cardioverter-defibrillator (ICD) would improve more with LV pacing than BiV pacing. As they explain, LV pacing alone preserves intrinsic conduction via the right bundle branch and may avoid deleterious effects from right ventricular pacing.

To test this, they conducted a randomized, crossover study involving 121 patients with an LV ejection fraction of 35% or less, a QRS complex at least 120 milliseconds, and symptoms of heart failure. The patients received a cardiac resynchronization therapy (CRT)-ICD device, and were assigned in random order to 6 months with the device in the LV pacing mode and 6 months with BiV pacing.

Exercise duration at 75% maximal — the primary outcome — increased from 9.3 minutes at baseline to 14.0 minutes with LV pacing and 14.3 minutes during BiV pacing (p=0.432), the team found. Similarly, there was no significant difference in improvement in LV ejection fraction, which increased from 24.4% to 31.9% with LV pacing and to 30.9% with BiV pacing.

In terms of cardiac remodeling, a reduction of at least 15% in LV end-diastolic volume was documented in 46.7% and 55.4% (p=0.088) of patients with the two pacing modes, respectively.

Only about half the patients responded to one modality or the other. However, 30.6% of LV nonresponders improved with BiV pacing, while 17.1% of BiV nonresponders improved with LV pacing, Dr. Thibault and colleagues report.

“The results of our study suggest that LV pacing alone appears less favorable than previously suggested, with the 2 pacing strategies resulting in similar improvements in exercise capacity and reverse LV remodeling,” they conclude. “Underlying reasons as to why LV mechanics may improve to a greater or similar extent with BiV and LV-only pacing remain speculative and merit further investigation.”

Reference:

Left Ventricular Versus Simultaneous Biventricular Pacing in Patients With Heart Failure and a QRS Complex ?120 Milliseconds

Circulation 2011;124.