De subitaneis mortibus. XXIV. Ruptured interventricular septum and heart block.

Five patients with acute posterior myocardial infarction developed varying degrees of atrioventricular (A-V) block prior to rupture of their interventricular septums (IVS). In three of these five the times of septal rupture coincided with the resumption of conduced synus rhythm. During the period of A-V block, the only stable escape rhythm appeared to originate in the A-V junctional region, and in two patients early in their course there was evidence of enhanced A-V junctional automaticity. Although the A-V node contained extensive infarction in all five hearts, its distal part, and the entire His bundle and proximal branches appeared to be spared. The anatomical pattern of dissection within the ruptured IVS was similar in three hearts, extending upward to the crest of the IVS and penetrating into the interatrial septum in two of these. Multiple major coronary narrowing were present in all five hearts, especially of a dominating right coronary artery; recent thrombosis was present in the right coronary artery in four of the five cases. The A-V node artery was markedly narrowed by focal fibromuscular dysplasia in three hearts, compounding the ischemia for the A-V node and eliminating one important source of collateral circulation to the interventricular septum.