Abstract 15766: Repolarization Parameters are Significantly Prolonged in Many Patients With Left Bundle Branch Block and Acute Myocardial Infarction

Abstract

Introduction: In patients with normal conduction, prolongation of repolarization parameters such as the QTc interval, JTc interval, and T-wave peak to end (Tpe) interval are associated with cardiac ischemia, ventricular tachydysrhythmias, and sudden cardiac death. These intervals are often considered “prolonged” at QTc >450 ms, JTc > 360 ms, and Tpe > 120 ms. We are unable to find published manuscripts that report these parameters in LBBB. Furthermore, it has been proposed that the Bazett correction formula for QTc and JTc overestimates repolarization duration in patients with conduction disturbances. Aim: To report the QTc, JTc, and Tpe intervals in ED patients with LBBB with and without MI and to compare common correction formulas. Methods: Retrospectively, we identified ED patients with LBBB and ischemic symptoms: with no MI, with NSTEMI, and with angiographically-proven acute coronary occlusion (STEMI). The QT, JT, and Tpe intervals were measured manually in leads II, V3, and V5; the longest of each was used. QTc and JTc intervals were calculated by Bazett’s, Hodges’ and Framingham formulas. Statistics were by two-tailed Student’s t-test and Mann-Whitney U test. Results: The no-MI, NSTEMI, and STEMI groups consisted of 105, 24 and 33 patients. In the STEMI group, 24.3% of patients had Tpe >= 120 ms compared to 4.8% of no-MI patients (p < 0.001). By Hodges’ formula, 53.1% of patients with LBBB had QTc >= 450 ms and 12.3% had JTc >= 360 ms. Conclusion: Repolarizaton parameters are prolonged in many patients with LBBB. The Tpe interval, which has been proposed as a marker of transmural repolarization heterogeneity due to ischemia, is significantly prolonged in patients with STEMI and LBBB when compared to LBBB patients without MI. Between the STEMI, NSTEMI, and no-MI groups there was no significant difference in QTc or JTc by any formula (see Table 1). However, the overall mean QTc by Bazett’s was significantly longer than Hodge’s or Framingham (see Table 2).