Biventricular pacing improves left ventricular function by 2-D strain in right ventricular failure

Abstract

Background

We used speckle-tracking echocardiography to test the hypothesis that regional left ventricular (LV) strain would improve during optimized biventricular pacing (BiVP) in acute right ventricular (RV) pressure overload (PO).

Materials and methods

Complete heart block and RVPO were induced in five open-chest fully anesthetized pigs. BiVP was optimized by adjusting atrioventricular and interventricular delays to maximize cardiac output derived from an aortic flow probe. LV short axis views were obtained during atrio-RV pacing (RVP), atrio-LV pacing (LVP), and BiVP. Intraventricular synchrony was assessed by comparing speckle-tracking echocardiography–derived time to peak (TTP) strain in the anterior septal (AS) and posterior wall segments. Segmental function was assessed using radial strain.

Results

Cardiac output was higher with optimized (RV first) BiVP than with LVP (0.96 ± 0.26 L/min versus 0.89 ± 0.27 L/min; P = 0.05). AS TTP strain (502 ± 19 ms) during LVP was prolonged versus BiVP (392 ± 58 ms) and versus RVP (390 ± 53 ms) (P = 0.0018). AS TTP strain during LVP was prolonged versus posterior (502 ± 19 ms versus 396 ± 72 ms, P = 0.0011). No significant difference in TTP strain in these segments was seen with BiVP or RVP. Posterior strain (20% ± 5%) increased 66% versus AS strain (12% ± 6%) during BiVP (P = 0.0029). A similar increase occurred during RVP (posterior 20% ± 3% versus AS 12% ± 7%, P = 0.0002). Posterior strain did not increase during LVP.

Conclusions

BiVP and RVP restore intraventricular LV synchrony and increase regional function versus LVP during RVPO. RV pre-excitation unloads the RV and reduces the duration of AS contraction, facilitating synchrony of all LV segments and increasing free wall LV contraction.

Introduction

Acute right ventricular (RV) failure is a well-recognized problem after acute pulmonary embolism, after cardiac transplantation, during pulmonary thromboendarterectomy for chronic thromboembolic pulmonary hypertension, and during surgical correction of congenital heart disease. Registry data from the International Society of Heart and Lung Transplantation show that, despite advances in perioperative management, RV dysfunction accounts for 50% of all cardiac complications and 19% of all early deaths in patients after heart transplantation [1]. Current therapies for the failing RV are limited to preload optimization, vasopressors and vasodilators to adjust afterload, and inotropic support to improve contractility [2]. Mechanical circulatory assistance is available for end-stage RV failure.

Clinical studies have demonstrated that pathologic increases in pulmonary pressures not only affect the RV, but also worsen left ventricular (LV) synchrony and function and alter function of the interventricular septum. Dohi et al. [3] used speckle-tracking echocardiography (STE) to demonstrate LV regional dyssynchrony with paradoxical motion of the interventricular septum in patients with chronic RV pressure overload (RVPO). Takamura et al. [4] showed that acute pulmonary embolism reduces LV strain in patients. They concluded that coordination of radial LV wall motion plays a key role in the short-term regulation of cardiac output (CO) in patients with acute pulmonary embolism.

These observations suggest that resynchronization therapy based on biventricular pacing (BiVP) might be of value in RVPO. However, there is little experience with cardiac pacing in acute RV failure [5]. Preliminary studies report improved hemodynamics with temporary atrial-RV pacing in patients with RV dysfunction and after surgery for congenital heart defects [6], [7]. Our laboratory demonstrated in a pig model of critical pulmonary stenosis that sequential BiVP with RV pre-excitation can improve CO by more than 20% [8]. Potential mechanisms include increased RV contractility, improved RV and LV synchrony [9], and enhanced LV geometry and fractional shortening [10]. We have not, however, explored the effects of pacing on LV synchrony and radial strain.

STE is a novel strain imaging technique that quantifies regional LV deformation and synchrony [11]. Radial strain has been useful in assessing the response to BiVP and has been recognized as an accurate and noninvasive measure of cardiac function and mechanical synchrony [12], [13]. In the current study, we apply STE to define the effects of BiVP in a RVPO model, seeking mechanisms that may be of value in clinical studies.