[Alterations of ventricular repolarization at rest, in young asymptomatic subjects. Diagnostic and predictive value...

In 34 asymptomatic subjects, aged 16 to 39 years, with clearcut abnormalities of ventricular repolarization on resting electrocardiogram, a forced hyperventilation and maximal exercise test were performed. The stress test was repeated, using the same protocol, after sublingual administration of nitroglycerin (0.3 mg) and of i.v. injection of propranolol (0.1 mg/Kg). In 24 subjects an echocardiogram was recorded: a mitral valve prolapse was present in 6 cases, while in 11 cases minor abnormalities were found. The response to exercise test was positive in 50% of cases. After nitroglycerin the ischemic threshold increased in 7 subjects while it remained unchanged or even lowered in 10 cases. In subjects with a negative stress test nitroglycerin did not produce any important electrocardiographic variations both at rest and during exercise. After propranolol injection the repolarization abnormalities on resting electrocardiogram disappeared or decreased in 23 subjects. The drug increased the exercise tolerance in 4 cases; in other 12 subjects the electrocardiographic response to stress testing became normal. During the follow-up period coronary events occurred in 3 cases; in all of them nitroglycerin had induced an increase of ischemic threshold. Our study suggests that the evaluation of the exercise ischemic threshold after nitroglycerin can be useful in order to identify subjects at high coronary risk.