Effects of single-site versus biventricular epicardial pacing on myocardial performance in an immature animal model of atrioventricular block.

Background: Single-site ventricular pacing results in dyssynchronous ventricular activation and may contribute to ventricular dysfunction. We evaluated epicardial biventricular (BiV) pacing as a means of maintaining synchronous ventricular activation in an acute piglet model of AV block with normal ventricular anatomy and function.

Results: We used left ventricular (LV) impedance catheters and tissue Doppler imaging to assess the cardiodynamics of immature piglets (n = 6, 33-78 days, 9.35 +/- 0.85 kg). Following catheter ablation of the AV node, a pacemaker was programmed 20 beats per minute above the intrinsic atrial rate. The animals were paced at 5-minute intervals via the following AV sequential configurations: Right atrial appendage (RA)-RV apex (RVA), RA-LV apex (LVA), and RA-biventricular (RVA/LVA). RA-RVA was the experimental control. LV systolic mechanics, measured by the slope of the end-systolic pressure-volume relationship (E(es)), increased with BiV pacing (12.8 +/- 3.4 mmHg/mL, P < 0.02) or single-site LVA pacing (10.6 +/- 3.4 mmHg/mL, P < 0.05) compared with single-site RVA pacing (8.3 +/- 1.4 mmHg/mL). QRS duration lengthened compared with sinus rhythm (42 +/- 8 msec) with either RVA (56 +/- 9 msec, P < 0.02) or LVA (54 +/- 7 msec, P < 0.03), but not with BiV (48 +/- 7 msec, P = 0.08) pacing. Tissue Doppler imaging showed LV dyssynchrony with RVA (septal-to-lateral delay 46.0 +/- 51.7 msec), with return toward normal with LVA (-9.6 +/- 33.6 msec, P < 0.04) or BiV (-4.1 +/- 33.8 msec, P < 0.04) pacing.

Conclusions: In this acute immature piglet model of AV block, LV performance improved with single-site pacing from the LVA and BiV pacing (RVA/LVA), as compared with single-site pacing from the RVA. These changes correlated with tissue Doppler indices of mechanical synchrony, though not necessarily with QRS duration.