Effects of Acute Mental Stress and Exercise on T-Wave Alternans in Patients With Implantable Cardioverter Defibrillators and Controls

BACKGROUND: Malignant cardiac arrhythmias can be triggered by exercise and by mental stress in vulnerable patients. Exercise-induced T-wave alternans (TWA) is an established marker of cardiac electrical instability. However, the effects of acute mental stress on TWA have not been investigated as a vulnerability marker in humans. METHODS AND RESULTS: TWA responses to mental stress (anger recall and mental arithmetic) and bicycle ergometry were evaluated in patients with implantable cardioverter defibrillators (ICDs) and documented coronary artery disease (n=23, age 62.1+/-12.3 years) and controls (n=17, age 54.2+/-12.1 years). TWA was assessed from digitized ECGs by modified moving average analysis. Dual-isotope single photon emission computed tomography was used to assess myocardial ischemia. TWA increased during mental stress and exercise (P values 0.2). Ejection fraction and stress-induced myocardial ischemia were not associated with TWA. CONCLUSIONS: Mental stress can induce cardiac electrical instability, as assessed via TWA, among patients with arrhythmic vulnerability and occurs at lower heart rates than with exercise. Pathophysiological mechanisms of mental stress-induced arrhythmias may therefore involve central and autonomic nervous system pathways that differ from exercise-induced arrhythmias.