INFLUENCE OF ATENOLOL ON THE RELATIONSHIP BETWEEN HEART-RATE AND QT INTERVAL IN PATIENTS WITH EXERCISE-INDUCED MYOCARDIAL-ISCHEMIA

The aim of this study was to analyze the relationship between heart rate and QT interval (HR-QT) during exercise in control subjects (Group A) and in patients with coronary artery disease (CAD) with effort angina and without previous myocardial infarction (MI) (Group B). The diagnosis of CAD was confirmed by coronarographic examination. The correlation HR-QT was significant (p < 0.001) in both groups on effort and at recovery. The analysis of the regression HR-QT was carried out separately, both on effort in upright position and at rest in supine position, to avoid the influence of posture on QT length. During effort, the regression line showed lower slope and intercept values in Group B (p<0.001) than those for Group A. A similar behavior was also observed at rest. Thus, at the highest heart rate, where ECG signs of ischemia (ST depression >1 mm) frequently occurred, a longer QT interval was present in Group B. Moreover, in Group B, the QT interval in the presence of ECG signs of ischemia was significantly longer (p<0.01) than in Group A at comparable heart rates both on effort and at rest, thereby confirming the result obtained by comparing both regression lines. The same effort protocol was repeated in Group B patients after acute administration of atenolol 100 mg per os. After atenolol administration, the analysis of the regression HR-QT in Group B clearly showed a shorter QT interval than that obtained in washout period during the baseline test at the highest heart rates where the ECG frequently showed signs of ischemia. This was proven by the presence of a higher slope (p<0.05) of the regression line HR-QT during treatment compared with that obtained in the same group without therapy. In conclusion, transient myocardial ischemia provokes a longer QT interval in patients with CAD in comparison with normal subjects. Atenolol affected the HR-QT relationship showing a shorter QT interval at the highest heart rates, particularly when ECG showed signs of ischemia, compared with that achieved in the same patients in washout.