New or presumably new left bundle branch block in patients with suspected acute coronary syndrome: Clinical, echocardiographic, and electrocardiographic features from a single-center registry.

BACKGROUND: In patients with suspected acute coronary syndrome, a new or presumably new left bundle branch block (LBBB) does not always imply ST-segment elevation myocardial infarction (STEMI). We aimed to show the low frequency of STEMI-equivalent in this population and determine the diagnostic value of electrocardiographic and echocardiographic features.

METHODS: From the 387 patients captured by the Louisiana State University code STEMI registry between 2009 and 2012, we examined data on 26 patients with LBBB. These patients were divided into 3 groups according to the final diagnosis: (1) STEMI-equivalent, defined as an acute coronary occlusion on angiography (2 patients), (2) non-ST-segment elevation myocardial infarction (4 patients), and (3) diagnoses other than myocardial infarction (non-MI) (20 patients).

RESULTS: Troponin elevation and left ventricular systolic dysfunction were common in all 3 groups (non-significant p-values). Compared with non-MI patients, patients with STEMI-equivalent had a larger degree of ST-segment discordance and T-wave discordance, as assessed by ST/QRS and T/QRS ratios (p<0.001). ST/QRS ratio ≥ 0.2 and T/QRS ratio ≥ 0.5 were sensitive and specific for the diagnosis of STEMI-equivalent in the setting of LBBB. Conversely, absolute values of ST-segment and T-wave discordance were not significantly different between groups. ST-segment concordance was highly specific for the diagnosis of STEMI-equivalent, but had a limited sensitivity.

CONCLUSION: Only a minority of patients with suspected acute coronary syndrome and LBBB have a STEMI-equivalent. Excessive relative discordance of the ST segment or the T wave appears predictive of STEMI-equivalent, but this is only hypothesis-generating considering the small population size.