Left bundle, right diagnosis

The partial electrocardiogram (Fig. 1) shows a left bundle branch block (LBBB), possibly caused by acute coronary syndrome (ACS). However, it can also be pre-existent, or based on other cardiac disease. To evaluate ACS in patients with LBBB, the Sgarbossa criteria should be used [1]. Sgarbossa criteria comprise three electrocardiographic criteria for diagnosis of ACS in patients with LBBB: ST-segment elevation of 1？mm or more that is concordant with the QRS complex; ST-segment depression of 1？mm or more in leads V1, V2, or V3; and ST-segment elevation of 5？mm or more that is disconcordant with (in the direction opposite) the QRS complex. Each criterion increases the chance of ACS in patients presenting with LBBB. Smith et al. modified these criteria by replacing the third criterion with an ST/S ratio less than ？0.25, improving the diagnosis of STEMI in these patients [2]