Ventricular arrhythmias during acute myocardial ischaemia in man. The role and significance of R-ST-T alternans and the prevention of ischaemic sudden death by medical treatment.

Malignant ventricular arrhythmias appearing during acute myocardial ischaemia, are the most frequent mechanism of sudden death. ST-T alternans is the result of an intraischaemic conduction delay and is frequently associated with those potentially lethal arrhythmias. In fact, such a phenomenon was seen in 35% of 46/86 patients with Prinzmetal's variant angina who showed ventricular arrhythmias during ischaemia, while it was never observed in the remaining 40 patients without arrhythmias during ischaemia. Therefore ST-segment alternans should be considered a reliable marker of the possible occurrence of ventricular arrhythmias during myocardial ischaemia. ST-T-segment alternans is associated with R alternans, as clearly demonstrated by thoracic maps, and this phenomenon is due to a 2:1 intraischaemic block. The patients with Prinzmetal's variant angina who present ventricular arrhythmias during ischaemia, show a more prominent increase of the positive area of the QRS (411.75 +/- 102.5 vs 294.05 +/- 80.3 mu volts ms), that is, a more relevant intraischaemic conduction delay. The effects of different pretreatments (lidocaine, propranolol and diltiazem) on arrhythmias related to vasospastic myocardial ischaemia induced by ergonovine maleate, were evaluated in four patients with Prinzmetal's variant angina. As in experimental observations, neither a 'pure' antiarrhythmic agent like lidocaine, nor a betablocking agent like propranolol, prevented acute ischaemic ventricular arrhythmias. Only the calcium antagonist, diltiazem, seemed to prevent such arrhythmias. However, these findings necessitate further confirmation.