Simultaneous variation of ventricular pacing site and timing with biventricular pacing in acute ventricular failure improves function by interventricular assist

Abstract

The goal of this work was to investigate the hemodynamic effects of simultaneous left ventricular (LV) pacing site (LVPS) and interventricular pacing delay (VVD) variation with biventricular pacing (BiVP) during acute LV failure. Simultaneously varying LVPS and VVD with BiVP has been shown to improve hemodynamics during acute right ventricular (RV) failure. However, effects during acute LV failure have not been reported. In six open-chest pigs, acute LV volume overload was induced by regurgitant flow via an aortic-LV conduit. Epicardial BiVP was implemented with right atrial and ventricular leads and a custom LV pacing array. Fifty-four LVPS-VVD combinations were tested in random order. Cardiac output was evaluated by aortic flow probe, ventricular systolic function by maximum rate of ventricular pressure change, and mechanical interventricular synchrony by normalized RV-LV pressure diagram area. Simultaneous LVPS-VVD variation improved all measures of cardiac function. The observed effect was different for each functional index, with evidence of LVPS-VVD interaction. Compared with effects of LVPS-VVD variation in a model of acute RV failure, hemodynamic changes were markedly different. However, in both models, maximum rate of ventricular pressure change of the failing ventricle was improved with synchronous interventricular contraction, suggesting that, in acute ventricular failure, BiVP can recruit the unstressed ventricle to support systolic function of the failing one. Thus simultaneously varying LVPS and VVD with BiVP during acute ventricular failure can improve cardiac function by "interventricular assist", with hemodynamic effects dependent on the type of failure. This supports the potential utility of temporary BiVP for the treatment of acute ventricular failure commonly seen after cardiac surgery.

Optimized temporary biventricular pacing acutely improves intraoperative cardiac output after weaning from cardiopulmonary bypass: A substudy of a randomized clinical trial

“…We have previously described animal models of acute right- and left-sided heart failure and found BiVP to be beneficial in those settings 32-34. The mechanism of action appears to be synchronization of pressure development across the interventricular septum, which allows the less impaired ventricle to assist the failing one 34. These findings provide further rationale for studying temporary BiVP in the perioperative setting and will serve as a guide for future studies examining the mechanism behind the effect demonstrated in this study.…”

Primary Endpoints of the Biventricular Pacing After Cardiac Surgery Trial

“…Previous studies reported pressure-volume loops during BiVP without optimization [18,26]. Our laboratory studies suggest that BiVP can synchronize pressure development across the interventricular septum, bringing pressure work from the less compromised ventricle to the assistance of the distressed ventricle [35]. Those studies did not involve cardioplegia and cardioplegic arrest, however.…”

“…LV1 was used preferentially during phase I. An InSync III biventricular pacemaker (Medtronic, Inc, Minneapolis, MN) was used for pacing and electromagnetic (Carolina Medical Electronics, East Bend, NC) or ultrasonic (Transonics Systems Inc, Ithaca NY) probes measured aortic flow [35–37]. …”

“…The mechanism of postbypass BiVP benefits is undefined [18,26,28,35,40]. Previous studies reported pressure-volume loops during BiVP without optimization [18,26].…”

Wall Thickness, Pulmonary Hypertension, and Diastolic Filling Abnormalities Predict Response to Postoperative Biventricular Pacing

“…3 However, a number of preclinical studies have shown BiVP improves hemodynamics in acute volume and pressure overload states when atrioventricular (AVD) and ventriculoventricular delays (VVD) are varied to directly optimize hemodynamics despite normal ventricular electrical conduction and contractility. 4,5 This model of BiVP was adapted to the post-cardiopulmonary bypass state to act as an adjunct to inotropes or vasopressors. In the Biventricular Pacing After Cardiac Surgery Trial, it was shown that this technique can improve hemodynamics in the first hours after bypass 6,7 and postoperative day 1 in patients who underwent aortic valve replacement.…”