PROGNOSTIC-SIGNIFICANCE OF EXERCISE-INDUCED LEFT-BUNDLE-BRANCH BLOCK

Context.-Approximately 0.5% of all patients who undergo exercise testi ng develop a transient left bundle-branch block (LBBB) during exercise , but its prognostic significance is unclear. Objective.-To determine whether exercise-induced LBBB is an independent predictor of mortality and cardiac morbidity. Design.-Matched control cohort study. Between September 1990 and February 10, 1994, 17 277 exercise stress tests wer e performed on patients. Setting.-Tertiary care, academic medical cent er. Patients.-From the cohort, 70 cases of exercise-induced LBBB were identified. The controls comprised 70 individuals without LBBB at rest or during exercise that matched the 70 cases based on age, test date, sex, prior history of coronary artery disease, hypertension, diabetes , smoking, and beta-blocker use. Main Outcome Measures.-All-cause mort ality, percutaneous coronary intervention, open heart surgery, nonfata l myocardial infarction, documented symptomatic or sustained ventricul ar tachydysrhythmia, or implantation of a permanent pacemaker or an im plantable cardiac defibrillator. Results.-A total of 37 events (28 eve nts from the exercise-induced LBBB cases and 9 from the control cohort ) occurred in 25 patients (17 exercise-induced LBBB patients and 8 con trol patients) during a mean follow-up period of 3.7 (0.9 years) (medi an, 3.8 years [range, 0.9-5.2 years]). There were 7 deaths, of which 5 occurred among patients with exercise-induced LBBB. Four-year Kaplan- Meier event rates were 19% among exercise-induced LBBB patients and 10 % among controls (log-rank chi(2), 5.2; P=.02). After further adjustin g for small differences in age, exercise-induced LBBB remained associa ted with a higher risk of primary events (adjusted relative risk, 2.78 ; 95% confidence interval, 1.16-6.65; P=.02). Conclusion.-Exercise-ind uced LBBB independently predicts a higher risk of death and major card iac events.