Left Ventricular Dyssynchrony Resulting from Right Ventricular Apical Pacing: Relevance of Baseline Assessment

Objectives: Evaluation of left ventricular (LV) dyssynchrony in patients undergoing short-term right ventricular apical (RVA) pacing and correlation with baseline echocardiographic and clinical characteristics. Background: RVA pacing causes abnormal ventricular depolarization that may lead to mechanical LV dyssynchrony. The relationships between pacing-induced LV dyssynchrony and baseline echocardiographic and clinical variables have not been fully clarified. Methods: Tissue Doppler echocardiography was performed in 153 patients before and after RVA pacing. LV dyssynchrony was measured by the time between the shortest and longest electromechanical delays in the five basal LV segments (intra-LV). The prevalence and degree of LV dyssynchrony after RVA pacing was evaluated in three groups: baseline LV ejection fraction (LVEF) < 35%, 35 - 55%, and >= 55%. The intrapatient effect of RVA pacing was determined as the percent increase in intra-LV value (Delta intra-LV%). The pacing-induced intra-LV was correlated with baseline variables. Results: The prevalence and degree of LV dyssynchrony after RVA pacing was significantly higher in patients with lower LVEF (P < 0.001). Delta Intra-LV% was inversely correlated with baseline intra-LV and LVEF (B = -2.6, B = -4.2, P < 0.001). Baseline intra-LV and LV end-systolic volume correlated positively with intra-LV after RVA pacing (B = 0.49, B = 0.6, P < 0.001), whereas LVEF showed an inverse correlation. Conclusions: The degree of LV dyssynchrony induced by RVA is variable. Patients with higher baseline LV dyssynchrony, more dilated LV, and more depressed LVEF showed a higher degree of LV dyssynchrony during pacing. These findings may assume importance in predicting the risk of heart failure in pacemaker patients. (PACE 2008; 31: 1456 - 1462)