[Bundle-branch block depending on the heart rate]

Twenty nine patients are described with transitory bundle branch block due to medicamentosus treatment of 386 patients with paroxysmal tachycardia. The block lasted from 1 to 48 hours and faded without any drug therapy. Three of the patients followed up for about two years died suddenly (very likely rhythm death), 8 had no further paroxysmal tachycardia, 18 patients had from 8 to 12 paroxysms during that period and in only 6 (20.7%) -- a second transitory bundle branch block recorded. The transitory bundle branch block, depending on heart rate could be explained by the latently existing lesion of one of His bundle branches. That lesion could be manifested during a longlasting paroxysm, due to the highly accelerated cardiac activity, developing into a disorder in the repolarization of branches of the bundle.