Narrow QRS mobitz type II second-degree atrioventricular block in acute myocardial infarction: True or false?

Abstract

S everal workers have indicated that narrow QRS type II second-degree atrioventricular (AV) block can occur in inferior wall acute myocardial infarction (AMI). l-6 Furthermore, statements from well-known textbooks, “Mobitz Type II heart block occurs most often as a consequence of anterior myocardial infarction” 7 or “In a patient with AMI, Type I AV block usually accompanies inferior infarction, is transient, and does not require temporary pacing, whereas Type II AV block usually accompanies anterior myocardial infarction, may require temporary pacing or permanent pacing” 8 imply that type II second-degree AV block, although rare, may occur in inferior wall AMI. Lamas et al4 recently brought this issue into the limelight in their analysis of the Multicenter Investigation of the Limitation of Infarct Size (MILIS) data when they concluded that narrow QRS type II seconddegree AV block is not uncommon in AM1 without specifying infarct location. Lamas et al4 analyzed data from 698 patients with acute Q-wave and non-Q-wave AM1 and proposed a scoring system to predict the occurrence of complete heart block so as to simplify the decision process related to the use of prophylactic temporary pacing. A complete heart block risk score was devised on the basis of abnormalities of AV or intraventricular conduction appearing on the standard 12-lead electrocardiogram or electrocardiographic monitor recording. Major abnormalities of AV or intraventricular conduction that occurred before the development of complete heart block were analyzed as potential predictors of complete heart block. Each of the following risk factors was assigned a score of I: first-degree AV block, type I second-degree AV block, type II second-degree AV block, left anterior hemiblock, left posterior hemiblock, right bundle branch block and left bundle branch block. A patient’s