More on ECG Diagnosis of Acute MI with Concurrent LBBB

ABSTRACT & COMMENTARY

Synopsis: Electrocardiographic criteria are poor indicators of AMI in LBBB situations; they further suggested that all patients suspected of AMI with LBBB should be considered for thrombolysis.

Source: Shlipak MG, et al. JAMA 1999;281:714-719.

Shlipak and colleagues performed a retrospective, cohort study to investigate the impact of the ECG on diagnosis and treatment of patients with LBBB pattern and suspected acute myocardial infarction (AMI). The study population was composed of patients with LBBB and possible AMI on ED presentation; 30% of the study group was ultimately found to have AMI by CPK-MB elevations. In the first portion of this study, a single physician who was blinded to the clinical information interpreted the ECGs in retrospective fashion, using pre-existing criteria for AMI diagnosis developed by previous investigators. The ECGs were interpreted as either diagnostic or not diagnostic for AMI; the electrocardiographic diagnosis was then compared to the clinical diagnosis.

In the second phase of the study, Shlipak et al investigated the impact of the ECG on specific management—the administration of a thrombolytic agent. This question was explored by means of a decision tree that compared three treatment pathways: thrombolysis for all patients, thrombolysis for only those patients with an ECG diagnostic for AMI, or no thrombolysis regardless of the ECG interpretation; the treatment algorithm was also evaluated from the perspective of stroke occurrence. Outcomes were then assessed and compared among the three management strategies.

One hundred three patient encounters made up the study population. Of the electrocardiographic features assessed, none effectively distinguished the patients who had AMI from those patients with noncoronary diagnoses. The various electrocardiographic criteria indicated AMI in only 3% of cases, with a sensitivity for the diagnosis of only 10% (95% confidence intervals, 2-26%). Using the management strategy of thrombolysis for all patients with suspected AMI and LBBB, out of 1000 patient presentations, 929 patients would survive without stroke if all patients were treated, compared to 918 patients if the electrocardiographic criteria were used as the only indication for thrombolysis.

Shlipak et al concluded that electrocardiographic criteria are poor indicators of AMI in LBBB situations; they further suggested that all patients suspected of AMI with LBBB should be considered for thrombolysis.

Comment by William J. Brady, MD

Common medical opinion holds that the electrocardiographic diagnosis of AMI is impossible in the presence of LBBB. Such a statement, however, is too encompassing; alternatively, the electrocardiographic diagnosis of ischemic heart disease—both its acute and chronic manifestations—is made more difficult in the setting of LBBB. Shlipack et al provide support for this statement; further, they have begun to explore the manifestations of this thought process on management and outcome issues.

Previously, authors developed criteria that assist the physician in a complicated scenario—the electrocardiographic diagnosis of AMI in the setting of LBBB.1 More recent work has tested these criteria in ED patients, suggesting that the recommendations of the original investigation are much less helpful than was previously thought.2 This study by Shlipak et al reinforces the opinion that the Sgarbossa criteria must be used with caution. AMI is still a possibility, given the appropriate clinical scenario, even if an ECG with LBBB is not diagnostic of AMI using the Sgarbossa criteria. (Dr. Brady is Assistant Professor of Emergency Medicine and Internal Medicine, Medical Director, Chest Pain Center, University of Virginia, Charlottesville.)

References

    1. Sgarbossa EB, et al. N Engl J Med 1996;335:481-487.

    2. Shapiro NI, et al. Acad Emerg Med 1998;5:508.