Electrical alternans. An association with coronary artery spasm.

A patient's condition was unique for having both QRS- and ST-segment alternans. The close association between ST-segment alternans and ischemic episodes is reproducible in an animal experimental study. Although such phenomena are usually associated with extensive myocardial disease, the postulated mechanism is far from perfected. It is more than likely that no single hypothesis will explain all types of phasic cardiac electrical phenomena.