Suspected myocardial infarction and left bundle branch block: electrocardiographic indicators of acute ischaemia

Abstract

Objectives: To examine the use of thrombolytic treatment in patients with suspected acute myocardial infarction (AMI) and left bundle branch block (LBBB). To evaluate electrocardiographic criteria for the identification of AMI in the presence of LBBB, and examine the implications of using these criteria in the clinical setting.

Methods: A retrospective study over two years, based in two Sheffield teaching hospitals. Patients presenting with LBBB and suspected AMI were studied by analysis of an AMI database. The proportion of patients with LBBB and AMI receiving thrombolysis, and the in-hospital delay before the start of treatment, were used as indicators of current performance. Three predictive criteria were applied to the electrocardiograms (ECGs) retrospectively, and their ability to identify acute ischaemic change assessed. The implications of using the predictive criteria in the clinical setting were explored.

Result: Twenty three per cent (5/22) of patients with LBBB and AMI did not receive thrombolysis, in the absence of documented contraindications. The mean in-hospital treatment delay for thrombolysed patients was 154 minutes. Forty eight per cent (16/33) of those thrombolysed did not have a final clinical diagnosis of AMI. In the majority of cases (8/12), the decision not to administer thrombolysis was based on a single ECG recording. The presence of any of the predictive electrocardiographic criteria was associated with a diagnosis of AMI, with a sensitivity of 0.79 (95% confidence interval 0.63 to 0.95), specificity 1, positive predictive value 1, and negative predictive value 0.79. The kappa scores between four independent observers showed either substantial or near perfect agreement.

Conclusion: Currently, thrombolytic treatment is under-utilised in patients with LBBB and AMI, and those who are thrombolysed endure lengthy delays before treatment. Patients with any of the predictive criteria should be thrombolysed immediately. When the diagnosis is in doubt, serial ECGs may demonstrate evolving ischaemic change.