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

- In patients presenting with a new LBBB, the diagnosis of acute ST-segment elevation myocardial infarction-equivalent (STEMI-equivalent) is uncommon.
- Troponin I elevation (0.04-1 ng/ml) and left ventricular dysfunction are highly prevalent among patients with a new or presumably new LBBB, even in the absence of acute myocardial infarction (MI).
- Novel electrocardiographic features of relative discordance of the ST segment and the T wave discriminate STEMI-equivalent from the non-MI and non-ST-segment elevation MI groups (discordant ST/QRS ratio ≥ 0.2, T/QRS ratio ≥ 0.5). These findings are limited by the small population size and are mainly hypothesis-generating rather than conclusive.

BackgroundIn 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.MethodsFrom 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).ResultsTroponin 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.ConclusionOnly 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.