Context.— Approximately 0.5% of all patients who undergo exercise testing 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, 17277 exercise stress tests were performed on patients.
Setting.— Tertiary care, academic medical center.
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 β-blocker use.
Main Outcome Measures.— All-cause mortality, percutaneous coronary intervention, open heart
surgery, nonfatal myocardial infarction, documented symptomatic or sustained
ventricular tachydysrhythmia, or implantation of a permanent pacemaker or
an implantable cardiac defibrillator.
Results.— A total of 37 events (28 events from the exercise-induced LBBB cases
and 9 from the control cohort) occurred in 25 patients (17 exercise-induced
LBBB patients and 8 control patients) during a mean follow-up period of 3.7
(0.9 years) (median, 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 χ2, 5.2; P =.02). After
further adjusting for small differences in age, exercise-induced LBBB remained
associated with a higher risk of primary events (adjusted relative risk, 2.78;
95% confidence interval, 1.16-6.65; P =.02).
Conclusion.— Exercise-induced LBBB independently predicts a higher risk of death
and major cardiac events.