Adams-Stokes syndrome caused by paroxysmal third-degree atrioventricular block.

Among I70 patients with Adams-Stokes syndrome, the majority had sinus rhythm between attacks. Clinical and electrocardiographic features of 67 patients in whom syncope was caused by paroxysmal third-degree atrioventricular block are discussed. The patients had normal pulse rates between attacks, their cerebral symptoms were usually not accompanied by cardiac symptoms, and 25 per cent had no symptoms suggesting heart disease. However, in 83 per cent the electrocardiogram showed constantly interventricular conduction disturbances and 7I per cent episodically atrioventricular conduction disturbances. It appears that the diagnosis, which otherwise may be missed, may be greatly facilitated by electrocardiograms. The variability and complexity of the QRS patterns suggest a development of third-degree AV block in the form of an 'additive' block. The final lesion in the complete block may vary both in location, proximall distal, in the conduction system, and in degree of involvement of the pacemaking tissue. Both factors may contribute to an alternation between episodes of third-degree AV block with and without escape rhythm, and correspondingly without and with Adams-Stokes attacks.