Assessment of T-wave alternans after acute myocardial infarction: influence of the timing of PTCA on cardiac electrical stabilization

Abstract

It is accepted that the timing of myocardial revascularization in patients undergoing PTCA for the treatment of acute myocardial infarction (AMI) may improve the clinical outcome. However, its impact on microvolt T-wave alternans (TWA), a recognized tool for assessing vulnerability to ventricular tachyarrhythmias that can cause sudden cardiac death in infarction survivors, remains unknown.

Aim: To analyze TWA in patients with AMI treated by PTCA and assess whether the timing of myocardial revascularization can influence TWA measurements.

Methods: We studied 79 patients (67 male; 57 +/- 11 years) who underwent successful PTCA for the treatment of AMI. The presence of TWA was assessed using a HearTwave system (Cambridge Heart, Inc.) within 30 days of AMI. Orthogonal Frank XYZ leads and associated vector magnitude (microvolt alternans sensors) and 7 standard ECG leads were recorded during a treadmill manual exercise protocol to increase heart rate slowly to approximately 110 bpm. TWA was considered positive if the sustained alternans microvoltage was > or = 1.9 microV at heart rates of > 100 bpm, negative if the criteria for positivity were not met while maintaining heart rate at > or =105 bpm (maximum negative heart rate), and inconclusive if it could not be definitively classified as either positive or negative. Patients were excluded if they had atrial fibrillation, > 10 extrasystoles/min, bradycardia 40 beats/min, wide QRS complex, congestive heart failure or implanted pacemaker, or were under antiarrhythmic therapy. The presence of positive or inconclusive TWA (non-negative TWA) was considered a risk marker for the occurrence of life-threatening ventricular arrhythmias. TWA results were compared between the group of patients who underwent PTCA within 24h of AMI (early PTCA; n=45) and those treated >24h after hospital admission (late PTCA; n=34).

Results: TWA was positive in 16 patients (20.2%), negative in 56 (70.9%) and inconclusive in 7 (8.9%). Overall, TWA was non-negative in 29.1% of the patients. In the early PTCA group, TWA was non-negative in 9 patients (20%) (6 positive and 3 inconclusive) and negative in 36 (80%). In the late PTCA group, TWA was non-negative in 14 patients (41%) (10 positive and 4 inconclusive) and negative in 20 (59%) (p < 0.05). There were no differences in left ventricular ejection fraction between the two groups. No spontaneous ventricular arrhythmias, syncope or deaths were recorded in the first 60 days after hospital discharge. Five patients (7%) were re-admitted with angina.

Conclusions: In a population of AMI survivors: a) the prevalence of non-negative TWA was 25%, despite myocardial revascularization by PTCA; b) PTCA performed within 24h of onset of AMI significantly reduced the number of patients with non-negative TWA, suggesting a lower arrhythmic risk. These findings should be investigated in larger studies.