What are the criteria for the ECG diagnosis of acute STEMI in the setting of LBBB?
Criteria for ECG diagnosis of acute STEMI in the setting of LBBB have been proposed (see Online Data Supplement 1). Baseline ECG abnormalities other than LBBB (eg, paced rhythm, LV hypertrophy, Brugada syndrome) may obscure interpretation. In addition, ST depression in 2 precordial leads (V1 V4) may indicate transmural posterior injury; multilead ST depression with coexistent ST elevation in lead aVR has been described in patients with left main or proximal left anterior descending artery occlusion.9 Rarely, hyperacute T-wave changes may be observed in the very early phase of STEMI, before the development of ST elevation. Transthoracic echocardiography may provide evidence of focal wall motion abnormalities and facilitate triage in patients with ECG findings that are difficult to interpret. If doubt persists, immediate referral for invasive angiography may be necessary to guide therapy in the appropriate clinical context.10,11