Alternating left anterior hemiblock without associated tachycardia.

This case report describes a 64-year-old woman with a cardiomyopathy and associated fascicular conduction disturbances partly related to digitalis therapy. Electrocardiograms showed incomplete left bundle branch block with left anterior hemiblock the latter, consistently changing in pattern and rhythm as in bidirectional tachycardia but at a relatively normal heart rate. The relationship of severe myocardial disease to the apparent likelihood of pre-existing depression of fascicular conduction in cases of bidirectional tachycardia precipitated by digitalis, is exemplified.