Right Ventricular Apical Pacing Acutely Impairs Left Ventricular Function and Induces Mechanical Dyssynchrony in Patients with Sick Sinus Syndrome: A Real-time Three-dimensional Echocardiographic Study

Background: Chronic right ventricular apical (RVA) pacing can lead to an increased risk of heart failure. However, assessment of left ventricular mechanical dyssynchrony in the whole left ventricle simultaneously with acute RVA pacing has never been investigated. Methods and Results: This study included 35 patients with sick sinus syndrome and intact intrinsic atrioventricular conduction. All patients received dual-chamber pacemaker implants with atrial leads placed in the right atrial appendage and right ventricle leads positioned in the RVA. Transthoracic two-dimensional echocardiography, tissue Doppler echocardiography, and real-time three-dimensional echocardiography were performed to determine the chamber size, dyssynchronization index, myocardial performance index, and global left ventricular ejection fraction. The myocardial performance index was significantly higher with RVA pacing (with RVA 0.42 ± 0.18 vs. without RVA 0.31 ± 0.14; P = .004), and left ventricular ejection fraction derived by real-time three-dimensional echocardiography was significantly lower with RVA pacing (with RVA 54.4% ± 7.7% vs. without RVA 56.7% ± 7.9%; P = .013), indicating deteriorated left ventricular function with RVA pacing. In addition, there was significant difference in the intraventricular delays in favor of without RVA pacing when assessed by the septal-to-posterior wall motion delay on the midventricular level (with RVA 91.9 ± 52.5 msec vs. without RVA 38.6 ± 28.9 msec; P < .0001) and when assessed by real-time three-dimensional echocardiography-derived systolic dyssynchrony index (with RVA 7.00% ± 2.54% vs. without RVA 5.36 ± 2.17%; P = .0003). Conclusion: Acute RVA pacing can induce left ventricular mechanical dyssynchrony and impair left ventricular function in patients with sick sinus syndrome.