Baturova MA, et al. - In this MADIT-CRT sub-study, heart failure (HF) patients treated with cardiac resynchronization therapy (CRT) were assessed to determine the effect of electrocardiographic left atrial (LA) abnormality for prognosis in these patients. P-wave terminal force in lead V₁ (PTF-V1) ≥ 0.04 mm*s was considered abnormal. With regard to CRT therapy, PTF-V1 provided additive prognostic information, thereby reinforcing the role of ECG diagnostics in risk stratification of patients with HF. Electrocardiographic LA abnormality appeared to be an ECG indicator of poor long-term outcome among patients with left bundle branch block, among CRT-treated patients with HF.