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 <0.001), and TWA responses were higher in ICD patients than in controls (arithmetic Δ=8.9±1.4 versus 4.3±2.2 μV, P=0.043; exercise Δ=21.4±2.8 versus 13.8±3.2 μV, P=0.038). TWA increases with mental stress occurred at substantially lower heart rates (anger recall Δ=9.7±7.7 bpm, arithmetic Δ=14.3±133 bpm) versus exercise (Δ=53.7± 22.7 bpm; P values <0.001). After adjustment for heart rate increases, mental stress and exercise provoked increased TWA in ICD patients (P values <0.05), but not in controls (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.