Objective: To discern if the prognostic meaning of QRS prolongation differs according to the location of ST elevation acute myocardial infarction.
Design: Measuring QRS duration in patients with normal conduction or right bundle branch block.
Setting: HERO-2 trial with prospective collection of electrocardiograms at randomization and at 60 minutes after fibrinolytic therapy.
Patients: 12,456 patients with normal conduction at both randomization and 60-minutes time points and 510 with RBBB at both time points.
Main outcome measure: 30-days mortality.
Results: On the baseline ECG, there was a positive association between QRS duration and 30-day mortality with anterior AMI (P<0.0001 for those with normal conduction and =0.007 for those with RBBB) but not with inferior AMI (P=0.29 and P=0.32 respectively). For anterior AMI, with or without RBBB, an increment of 20 msec increase in QRS duration predicted a significant 30%-40% relative increase in 30-day mortality both before and after adjusting for clinical and ECG variables including baseline ST elevation and presence of Q wave. The association was not present for inferior AMI. Changes in QRS duration over 60 minutes after fibrinolytic therapy were uncommon and unrelated to mortality.
Conclusion: Baseline QRS duration independently stratifies 30-day mortality in patients with anterior AMI even when unaccompanied by RBBB, but does not stratify mortality risk in patients with inferior AMI.
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