Abstract P373: Cardiac Depolarization and Repolarization Changes with Mental Stress are Associated with Mental Stress- Induced Ischemia

Introduction: QRS duration and frontal QRS/T angle are simple and easily available electrocardiographic measures of cardiac depolarization and repolarization that predict cardiovascular disease (CVD) events and mortality. Such measures may be indicative of cardiac structural disease, ischemia, or primary conduction abnormalities. Mental stress-induced myocardial ischemia (MSI) is also associated with increased CVD risk, but the underlying mechanisms are unknown. We hypothesized that MSI is associated with stress-induced abnormalities in cardiac depolarization and repolarization, QRS duration and frontal QRS/T angle. Methods: We compared QRS duration & frontal QRS/T angle during mental stress between coronary artery disease (CAD) patients who were MSI positive (MSI+) and CAD patients who were MSI negative (MSI-). For each MSI+ case (n=22), one or two MSI- controls were matched for age, gender and race- ethnicity (n=41). QRS duration and frontal QRS/T angle were automatically computed by a 12-lead ECG (GE MAC 5000). QRS/T angle was calculated as absolute minimal difference between the frontal R and T axes in patients with QRS duration < 120 ms (n= 50). Mental stress was induced via speech stressor, and nuclear 99m-Tc-sestamibi gated Single-Photon Emission Computed Tomography (SPECT) was used to assess MSI. Results: Mean age was 65 years, 20 patients were black, and 55 were males. The two groups were similar in terms of demographics and past medical history. Both MSI+ and MSI- groups had similar QRS duration at baseline, but MSI+ patients had an adjusted 3.1 ms higher increase in QRS duration with mental stress than MSI- patients (95% CI: 0.5 to 5.7), after adjusting for CVD risk factors, hemodynamic changes during mental stress (blood pressure, heart rate), and baseline QRS duration. MSI+ patients had an adjusted 28.2 degrees larger QRS/T angle at baseline (95% CI: 2.5 to 53.9) compared to MSI- patients, but did not differ with regards to change in QRS/T angle with mental stress. However, among those with normal baseline conduction (QRS<100 ms, n=36), MSI+ patients had an adjusted 17.8 degrees larger change in QRS/T angle with mental stress compared to MSI- patients (95% CI: 3.1 to 32.4). In patients with mildly abnormal conduction (QRS duration between 100 and 119 ms, n=14), no differences were found, p=0.059 for QRS duration x MSI interaction. Conclusion: CAD patients exhibit changes in cardiac depolarization and repolarization during acute mental stress. Those with MSI have greater baseline QRS/T angle and larger changes in QRS/T angle and QRS duration with mental stress. These findings may help to explain the pathophysiology linking mental stress and CVD, as well as the increased risk in patients with MSI.