Bradyarrhythmias, abnormalities of conduction, and indications for pacing in acute myocardial infarction.

Bradyarrhythmias and conduction disturbances are not infrequently observed in association with acute MI. The sinus node artery is supplied by the right coronary circulation only slightly more often than the left. As a result of concomitant vagotonia, however, sinus node dysfunction is more common with inferior infarction. This influence, as well as a predominantly right-sided circulation, also makes AV nodal block more frequent with such infarctions. Bradyarrhythmias due to sinus or AV nodal dysfunction often require only observation. If symptomatic, they are usually responsive to vagolytic or chronotropic drugs, but may necessitate pacemaker therapy often only on a temporary basis. The distal conduction system including the bundle branches is supplied mainly, but not exclusively, by the left anterior descending artery. Thus, acute bundle branch block is often associated with anterior MI. The indications for both temporary and permanent prophylactic pacing in this situation remain controversial. Several authors have made recommendations based on risk stratification. We would temporarily pace patients with anterior or indeterminate infarctions and new right or left bundle branch block, and probably those with bilateral bundle branch block of indeterminate age. All patients with new bilateral or alternating bundle branch block should be paced, regardless of infarct site. Permanent prophylactic pacing would appear indicated in patients exhibiting alternating bundle branch block or perhaps new right bundle branch block and left posterior hemiblock. In contrast to this group, the treatment of patients who develop sudden complete heart block, whether transient or permanent, is clear-cut. These patients require continuous (temporary followed without interruption by permanent) pacemaker therapy (Table 3).