Complete Bundle Branch Block in Acute MI
Complete Bundle Branch Block in Acute MI
ABSTRACT & COMMENTARY
Synopsis: Bundle branch block at hospital admission in patients with acute myocardial infarction is a predictor of in-hospital complications and an increased short-term mortality.
Source: Sgarbossa EB, et al. J Am Coll Cardiol 1998; 31:105-110.
Sgarbossa and associates in the gusto-i trial investigated the significance of finding a complete bundle branch block pattern on the admission ECG in patients undergoing thrombolysis at the time of acute myocardial infarction in the GUSTO-I trial. Sgarbossa et al identified 420 patients who had bundle branch block on their admission ECG out of 26,003 North American GUSTO-I patients. This was an incidence of 1.6%. One hundred thirty-one patients had left bundle branch block, and 289 patients had right bundle branch block. Of the latter patients, 145 patients had associated left anterior fascicular block, and 11 had associated left posterior fascicular block. The patients were then matched for age and initial age and initial Killip class to patients without bundle branch block. Then, the two groups were compared. There was a slight predominance of males in the group with bundle branch block, and the peak CK was significantly higher (1964 vs 1557, P < 0.001). There was also a higher proportion of patients with anterior wall myocardial infarction (56% vs 44%, P < 0.001) in the group with bundle branch block.Patients with bundle branch block had an 18% 30-day mortality in comparison to an 11% 30-day mortality in the matched control group. Interestingly, right bundle branch block and right bundle plus left anterior fascicular block had the highest mortality odds ratios (2.17 and 2.19, respectively) among the various conduction lesions studied. When other clinical risk factors were analyzed in a multivariate model, bundle branch block still carried a 53% higher risk for 30-day mortality. Other predictors of mortality in the group were age, systolic blood pressure, presence of anterior myocardial infarction, increasing Killip class, abnormal heart rate, and diabetes.
Patients with bundle branch block were more likely to experience in-hospital asystole or AV block. However, they were also more likely to develop sustained ventricular tachycardia, ventricular fibrillation, and cardiogenic shock.
Sgarbossa et al also investigated whether reversion of bundle branch block was associated with an improved prognosis. Patients who had complete, partial, and no reversion of their bundle branch block had 30-day mortality rates of 8%, 12%, and 18%, respectively. Sgarbossa et al conclude that bundle branch block at hospital admission in patients with acute myocardial infarction is a predictor of in-hospital complications and an increased short-term mortality.
COMMENT BY JOHN P. DiMARCO, MD, PhD
Prior studies on the significance of bundle branch block in myocardial infarction have largely focused on the risks of developing complete AV block and sudden death—both during the in-hospital phase and late recovery period after myocardial infarction. However, these prior studies had concentrated on patients with "new bundle branch block." In this study, the investigators had no way to determine the age of the bundle branch block, and it is likely that many of those identified were chronic rather than new and associated with the index myocardial infarction. This significantly limits the values of these observations, but it is still possible to conclude that the presence of conduction abnormalities remains an independent predictive factor of short- and long-term morbidity and mortality. It is important to note that the increased mortality does not seem to be related specifically to high grades of AV block. These patients seem to be at risk for all serious events including asystole (usually a terminal event not related to specific conduction system disease), ventricular arrhythmias, and cardiogenic shock, as well as AV block.Unfortunately, the GUSTO-I trial did not have systematic evaluation of myocardial ejection fraction or other indices of myocardial function. I suspect that, if these data were included, bundle branch block would no longer be an independent prognostic indicator. However, if only clinical data are available, the presence of a bundle branch block can serve as a warning of future high risk.
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