Optimized cardiac resynchronization therapy is achieved over a broad area of the left ventricular lateral wall, covering approximately 43% of the free wall in both normal and failing canine hearts.
Does the location of the left ventricular pacing site affect global cardiac function and mechanical synchrony in dyssynchronous canine hearts?
Optimized CRT can be achieved over a broad area of the LV lateral wall, and sites that maximize mechanical synchrony generally align with those that most improve global function.
BACKGROUND: The efficacy of cardiac resynchronization therapy (CRT) depends on placement of the left ventricular lead within the late-activated territory. The geographic extent and 3-dimensional distribution of left ventricular (LV) locations yielding optimal CRT remain unknown. METHODS AND RESULTS: Normal or tachypacing-induced failing canine hearts made dyssynchronous by right ventricular free wall pacing or chronic left bundle-branch ablation were acutely instrumented with a nonconstraining epicardial elastic sock containing 128 electrodes interfaced with a computer-controlled stimulation/recording system. Biventricular CRT was performed using a fixed right ventricular site and randomly selected LV sites covering the entire free wall. For each LV site, global cardiac function (conductance catheter) and mechanical synchrony (magnetic resonance imaging tagging) were determined to yield 3-dimensional maps reflecting CRT impact. Optimal CRT was achieved from LV lateral wall sites, slightly more anterior than posterior and more apical than basal. LV sites yielding > or = 70% of the maximal dP/dtmax increase covered approximately 43% of the LV free wall. This distribution and size were similar in both normal and failing hearts. The region was similar for various systolic and diastolic parameters and correlated with 3-dimensional maps based on mechanical synchrony from magnetic resonance imaging strain analysis. CONCLUSIONS: In hearts with delayed lateral contraction, optimized CRT is achieved over a fairly broad area of LV lateral wall in both nonfailing and failing hearts, with modest anterior or posterior deviation still capable of providing effective CRT. Sites selected to achieve the most mechanical synchrony are generally similar to those that most improve global function, confirming a key assumption underlying the use of wall motion analysis to optimize CRT.
Helm et al. (2007) studied Dyssynchronous canine hearts. Biventricular CRT at various left ventricular sites was evaluated on Global cardiac function and mechanical synchrony. Optimized cardiac resynchronization therapy is achieved over a broad area of the left ventricular lateral wall, covering approximately 43% of the free wall in both normal and failing canine hearts.