Biventricular pacing may prevent the adverse left ventricular modeling and reduction in LV function often seen with RV pacing, according to results of the PACE Trial presented at the AHA and published online in the New England Journal of Medicine.

Chinese investigators randomized 177 patients with bradycardia and preserved LV function to biventricular pacing or RV apical pacing. At 12 months, LV EF was 54.8% in the RV pacing group compared to 62.2% in the Biventricular pacing group, a highly significant difference (p<0.001). LV end systolic volume was 35.7ml vs 27.6 ml, a relative difference of 25% that was highly significant.

In an accompanying editorial, Bruce Lindsay said that the trial does not provide “compelling evidence should be selected at the time of implantation in all patients who have normal ventricular function and high-grade atrioventricular block. An alternative approach is to follow the patients carefully by obtaining annual echocardiograms and to convert patients to biventricular pacing systems only if a clinically significant change in left ventricular function or functional capacity is observed.” The PACE study, he writes, “provides additional evidence that right ventricular pacing can be deleterious, but it should not change current guidelines.”

Here is the AHA press release on PACE:

Two-ventricle pacing reduces heart enlargement that accompanies single chamber pacing

Biventricular pacing could alleviate the effects of artificial pacemakers that enlarge the left ventricle, the heart’s main pumping chamber, according to new research.

The PACE Trial involved 177 participants implanted with a biventricular pacemaker and then randomized to receive either pacing at the top of the right ventricle (88 patients) or both ventricles (89 patients). To enter PACE, a person had to eject more than 45 percent of the blood in the left ventricle with each contraction.

The heart’s natural pacemaker consists of a tiny clump of cells atop the right atrium, one of its two upper chambers.  These specialized cells generate electrical impulses that control the heart’s rhythmic pumping of blood.

If the natural pacemaker malfunctions or electrical pathways are blocked, the heart can go into fibrillation, a potentially fatal quivering of the organ.  Artificial pacemakers – small battery-powered devices that maintain a normal heartbeat – have saved many lives.  However, their use also can enlarge the left ventricle and questions remain on precisely where to best initiate pacing.

In the PACE trial, left ventricle size and ejection fraction remained unchanged in the biventricular-paced patients one year after implantation.  However, the right-ventricle group showed a significant increase in left ventricle size, a sign of potential heart failure, and the average ejection fraction fell 6.7 percent.

Furthermore, the synchronization of electrical signals decreased during heart contraction and left ventricle functioning deteriorated only in the right-ventricle group during the year.