Biventricular pacing and QT interval prolongation

Introduction: The purpose of this study was to examine BiV pacing-dependent changes in QT interval and the related potential for proarrhythmia. Biventricular (BiV) pacing has emerged as a promising therapy for patients with advanced congestive heart failure (CHF) and bundle branch block (BBB).
Methods and Results: One hundred and seventy-six consecutive patients (123 men and 53 women; mean age 67 ± 16 years) with ischemic (n = 128) or nonischemic (n = 48) cardiomyopathy in New York Heart Association Class II (8%) or III (92%) CHF (ejection fraction 24 ± 9%) underwent atrial synchronous BiV pacing. The QRS, QT, and JT intervals were measured at 30 minutes after initiation of BiV pacing, at 24 hours, and at 1 month postimplant. QT interval was defined as the time interval between the initial deflection of the QRS complex and the point at which the T wave crossed the isoelectric line. At baseline, the average QRS duration was 178 ± 10 ms, attributable to left BBB (n = 158) or intraventricular conduction delay (n = 18). BiV pacing resulted in a small but statistically significant reduction in QRS duration (148 ± 9 ms during BiV pacing vs 178 ± 10 ms at baseline [P < 0.0001]), yet the QT increased to 470 ± 34 ms with BiV pacing versus 445 ± 32 ms at baseline [P < 0.0001]). The JTc interval during BiV pacing was significantly shorter than during LV pacing (290 ± 9 ms vs 320 ± 20 ms, P < 0.0001). During a mean follow-up of 24 ± 6 months, one patient developed recurrent torsade de pointes. That was eliminated once left ventricular pacing was discontinued.
Conclusion: Biventricular pacing prolongs QT interval. However, the occurrence of torsade de pointes is uncommon.