Unusual forms of second-degree atrioventricular block, including Mobitz Type-II block, associated with the Morgagni-Adams-Stokes syndrome

Abstract

Several unusual forms of second-degree atrioventricular block associated with the Morgagni-Adams-Stokes (M-A-S) syndrome are discussed. Three out of 100 patients with the M-A-S syndrome demonstrated a transient Mobitz Type-II block. Seven additional cases are reviewed from the literature. All of the patients had frequently changing degrees of heart block, and in only 1 patient did the Mobitz Type-II block persist. In all cases in which a clinical history is available, Mobitz Type-II block was associated with an Adams-Stokes syndrome. Although a particularly poor prognosis has been indicated for this type of block, the outlook appeared to be no different from that in other cases of M-A-S syndrome in our series. On the other hand, Mobitz Type-II block is of prognostic importance if it indicates that the M-A-S syndrome is likely to develop. Two patients who had 2:1 A-V block with A-V interference dissociation presented with the M-A-S syndrome. Neither of these cases was caused by excessive administration of digitalis. Eight patients had advanced or high-grade A-V block related to their M-A-S syndrome. All of them subsequently developed complete heart block. Although odd-numbered ratios of advanced heart block are said to be rare, such forms were present in all 8 cases, whereas 4:1 block was present in only 2 cases. This may indicate that M-A-S syndrome is more likely to occur in the odd-ratio type of advanced heart block. Awareness that these unusual forms of second-degree block are associated with M-A-S syndrome may enable the prediction of later development of complete heart block and M-A-S syndrome.