Understanding ST depression in the stress-test ECG.

OBJECTIVE The electrocardiogram (ECG) obtained during stress testing often shows a typical pattern of primary ST depression. A similar pattern can occur in unstable angina. Current textbooks consider ST depression as a direct result of partial occlusion of a coronary artery. However, animal models could not reproduce this phenomenon. An alternative explanation for ST depression specific to stress testing involves global subendocardial ischemia. In this study, we evaluated both explanations with a realistic mathematical model of the human heart. METHODS The ECG was simulated with an anisotropic reaction-diffusion model of the human heart and an inhomogeneous boundary-element model of the human torso. RESULTS Limited subendocardial ischemic zones caused small ST depression in ECG leads not overlying the ischemic region. An ischemic zone of 50% transmural extent covering the entire left ventricular subendocardium caused an ST-depression pattern similar to that observed during stress test. CONCLUSION In contrast to regional subendocardial ischemia, global subendocardial ischemia can explain ST depression in our model.