[Paroxysmal atrioventricular block, cause of syncope in pulmonary embolism. 2 cases].

Two cases of pulmonary embolism accompanied by syncope in patients with pre-existing left bundle branch block are reported. Contrary to classical descriptions, the syncopes in these two patients could not be ascribed to cardiovascular collapse, but several arguments (such as the clinical features of the syncope and its coexistence in one case with ECG evidence of complete atrio-ventricular dissociation) were in favour of a paroxysmal disorder of conduction. Right bundle branch block is known to be common in pulmonary embolism and may even be more frequent in patients with left bundle branch block. In such cases, sudden and transient arrest of conduction in the right bundle would complete the left bundle branch block, thus accounting for a paroxysmal atrio-ventricular block.