ONSET HEART-RATE OF T-WAVE ALTERNANS - AN INDICATOR FOR DIFFERENT ARRHYTHMIA RISK GROUPS

T wave alternans is closely related to the electrical myocardial vulne rability. It appears frequently during higher heart rates and is there fore detected during exercise and atrial pacing. However, positive res ults can also be found in patient groups with low or no risk for life threatening arrhythmias. Methods: In order to find parameters to disti nguish between different risk profiles, we studied three groups: I. Po st MI patients without documented ventricular arrhythmias (CAD), 2. Po st MI patients with already documented ventricular tachyarrhythmias (V TA), 3. Patients with idiopathic ventricular tachycardia without struc tural heart disease. We analyzed 81 post MI patients (15 VTA patients, 66 CAD patients) and 15 patients with idiopathic ventricular tachycar dia. TWA was calculated during bicycle stress test using spectral meth od. Alternans voltage, ratio, noise, maximum heart rate, and threshold heart rate (i.e. the onset heart rate of sustained alternans) were co mpared. Results: VTA patients showed a lower threshold heart rate (94/- 18bpm) as compared with CAD (118+/- 14 bpm) and patients with idiop athic ventricular tachycardia (123+/- 20 bpm). Alternans voltage, rati o, and maximum heart rate were identical in both post MI groups. Due t o higher maximum heart rates alternans voltage and ratio were higher i n patients with idiopathic ventricular tachycardia. Conclusion: Beside alternans voltage and ratio, heart rate threshold has to be considere d as a crucial part of alternans classification.