Intermittent left bundle branch block: an overlooked cause of electrocardiographic changes that mimic high-grade stenosis of the left anterior descending coronary artery.

Context: The electrocardiographic (ECG) pattern of high-grade stenosis of the left anterior descending coronary artery (LAD) is important clinically because of the high risk of myocardial infarction and cardiac death if the pattern is not recognized. Although the recognition of this pattern is currently widespread, false-positive ECG changes that mimic this pattern are infrequently reported.

Objective: To demonstrate that ECG changes from intermittent left bundle branch block (LBBB) and cardiac memory can mimic anterior ischemia.

Methods: Medical record review of cardiology patients in whom ECG tracings showed intermittent LBBB and anterior T-wave changes during normal QRS conduction. Patients were included if ECG changes suggestive of high-grade LAD stenosis in leads V2 and V3 met the following criteria: (1) the QRS conduction was essentially normal during periods of absent LBBB; (2) the ST segment took off from an isoelectric point or only slightly elevated from baseline; and (3) the ST segment sloped up gradually with an abrupt and sharp down stroke leading to terminal T-wave inversion. Additional criteria were little or no ST segment elevation, no loss of precordial R waves, and ECG changes suggestive of high-grade LAD stenosis demonstrated in precordial leads V2 and V3. All patients demonstrated intermittent LBBB, and patients were excluded if a ventricular pacemaker was present. The case series began in 2003 and continued until 2011.

Results: Sixteen patients (3 male) with intermittent LBBB were identified with ST- and T-wave changes during normal ventricular conduction that matched the pattern described by Hein J.J. Wellens, MD. Of these patients, none had evidence of clinically substantial coronary artery disease. Eleven patients had stress testing with myocardial perfusion imaging, and 5 patients underwent cardiac catheterization. In 1 patient whose ECG pattern showed high-grade LAD stenosis but normal coronary arteries at catheterization, a stress test was later performed, which provoked LBBB. All other patients had spontaneous, intermittent periods of LBBB and normal conduction.

Conclusion: The ECG pattern of high-grade LAD stenosis has proven to be an important marker of high-risk patients with chest pain. This pattern may also be seen in patients with a right ventricular pacemaker on resumption of native QRS conduction. Intermittent LBBB is a less obvious cause of a similar ECG pattern that may mimic anterior ischemia due to high-grade stenosis.