Introduction: Early identification of high-risk patients is crucial for appropriate management in type A acute aortic dissection (AAD). ECG is useful for this purpose because it is readily available and rapidly interpretable at presentation. Hypothesis: In type A AAD, ischemic ST-T change at presentation is associated with poor outcomes. ST-segment elevation in lead aVR (ST↑aVR) is an ECG marker of severe acute myocardial ischemia, and therefore, may provide important prognostic information. Methods: We studied the relation of ECG findings to clinical features on admission and in-hospital death in 294 patients who were admitted within 12 h from symptom onset and underwent urgent surgery for type A AAD. Patients with bundle branch block or left ventricular hypertrophy were excluded. Patients were divided into the 3 groups according to admission ECG findings: no significant ST-T changes (n=99, G-A); the absence (n=151, G-B) or the presence (n=44, G-C) of ST↑aVR ≥0.5 mm with ST-T changes in other leads. Hemoglobin (Hb), creatinine (Cr), D-dimer, and cardiac-specific troponin were measured on admission. Results: There were no differences in age, sex, time to admission or Hb level in the 3 groups. In G-A, G-B, and G-C, systolic blood pressure was 130±23, 131±33, and 88±27 mmHg (p<0.01); heart rate was 70±14, 72±19, and 94±23 bpm (p<0.01); the levels of Cr were 0.9±0.6, 1.0±0.7, and 1.3±1.0 mg/dl (p=0.01); D-dimer was 26±43, 33±40, 62±50 μg/ml (p=0.02), the rates of positive-troponin were 3%, 14%, and 41% (p<0.01); shock were 2%, 21%, and 71% (p<0.01); cardiac tamponade was 3%, 19%, and 64% (p<0.01); moderate/severe aortic regurgitation was 4%, 28%, and 43% (p<0.01); coronary ostial involvement was 3%, 10%, and 32% (p<0.01); concomitant coronary artery bypass surgery was 2%, 7%, and 14% (p=0.03); in-hospital death was 1%, 6%, and 36% (p<0.01), respectively. Multivariate analysis showed that as compared with G-A, odds ratio (95%CI) for in-hospital death associated with G-B and G-C were 1.90 (0.68-4.08; p=0.19), and 34.4 (8.01-73.2; p<0.01), respectively. Conclusions: In patients with type A AAD, ST↑aVR on admission ECG strongly predicts in-hospital death. Our findings suggest that ST↑aVR is a simple but reliable tool for an early identification of high-risk patients.