Immediate and Remote Prognostic Significance of Fascicular Block during Acute Myocardial Infarction

The electrocardiograms of 538 patients with acute myocardial infarction were searched to identify all instances of atrioventricular (A-V) and intraventricular (I-V) conduction disturbances. Data concerning mode of therapy and clinical complications were obtained by review of the record. These variables were then analyzed for significance in relation to the development of type II A-V block acutely and syncope or sudden death during the first year of follow-up.The most accurate predictor for both these events was the status of A-V conduction in combination with the status of I-V conduction. At highest risk (50%) for type II progression were patients with acute adjacent fascicular block plus P-R prolongation, i.e., left anterior hemiblock plus right bundle-branch block (RBBB), or left bundle-branch block (LBBB), or patients with acute nonadjacent fascicular block, i.e., RBBB plus left posterior hemiblock or alternating bundle-branch block. The nonpaced survivors from this same group, plus any other patients with transient type II progression, were also at high risk (45%) for syncope or sudden death in follow-up. No syncope or sudden death has occurred in seven patients with type II progression discharged with a pacemaker. All other patients were at lower risk for these acute and chronic complications.Thus, the electrocardiogram in acute myocardial infarction can identify a high-risk group for acute type II progression in whom prophylactic pacer insertion may be beneficial. Similarly, the electrocardiogram can identify a high-risk group for syncope or sudden death in follow-up and implicates progression to higher degrees of A-V block as an important pathophysiologic mechanism.The possible role of permanent pacemaker therapy in preventing syncope or sudden death in this high-risk group is also suggested.