[Coronary angioplasty and electric alternans of the ST segment].

Alternans of the ST segment is a rare phenomenon during coronary angioplasty. The authors report three cases. It is usually observed in left anterior descending arteries without collateral circulation. Alternans is not accompanied by haemodynamic changes and does not initiate malignant ventricular arrhythmias. It is a transient phenomenon. Electrical alternans is thought to be due to changes in the configuration of the transmembrane action potential and modifications of calcium exchanges.