Intermittent complete left bundle branch block during general anesthesia

We report a case of intermittent complete left bundle branch block (CLBBB) which occurred during general anesthesia. An 83-year-old female was scheduled for upper lobectomy of the right lung under general anesthesia. Her preoperative 12-lead ECG showed atrial fibrillation and ST-depression in V4-6. Anesthesia was induced with propofol and pentazocine, and maintained with 0.5-1.5% isoflurane, 0-50% nitrous oxide in oxygen under close monitoring and appropriate respiratory management. The operation was performed uneventfully. Several minutes after the end of surgery, on converting her into the supine position from the left lateral decubitus position, widened QRS complexes, later diagnosed as CLBBB, appeared on ECG. At that time, heart rate was 92 beats x min(-1). After the administration of esmolol hydrochloride, heart rate decreased rapidly in a few minutes and ECG returned to normal conduction from CLBBB. We diagnosed this as rate-dependent intermittent CLBBB. Although intermittent CLBBB continued until the next day, the patient was asymptomatic and cardiac enzymes were within normal ranges. The intermittent CLBBB, which occasionally occurs during anesthesia, makes the diagnosis of myocardial ischemia and acute myocardial infarction difficult. The present case suggests that esmolol can be used effectively and safely to distinguish CLBBB as a benign disorder from myocardial ischemia in a patient with CLBBB.