[Depressed conduction and increased automaticity in acute septal myocardial infarction]

A patient with an established LBBB suffered an acute septal myocardial infarction complicated with a 2:1 infranodal AV block. As the ventricular rate decreased, the preexisting LBBB disappeared, and, in its place, a RBBB bradycardia-dependent appeared. Later on, an escape rhythm emerged, and competition between the two rhythms evolved. These disturbances were short-lived, and took place in the first 24 h. It is postulated that an increase in the rate of diastolic depolarization, ischemia related, may cause, in the same area, impairment of conduction and increased automaticity accounting for the findings previously mentioned. In an acute septal infarction conduction disturbances usually are progressive; ischemia rarely may induce hypopolarization rise giving to complex, but reversible, phenomena.