title: Electrophysiologic findings in patients with idiopathic hypertrophic subaortic stenosis.
abstract: Thirteen patients with catheterization-proved idiopathic hypertrophic subaortic stenosis underwent intracardiac electrophysiologic study. There was a large incidence of arrhythmias and a strikingly large incidence of conduction system abnormalities among these patients. The P-A and A-H intervals were normal in all patients. Atrial pacing resulted in Mobitz type 1 block proximal to the His bundle at an abnormal rate (less than 140/min) in 2 of 12 patients (17 percent). H-V intervals were prolonged (greater than 50 msec) in 10 of 12 patients (83 percent) and were greater than 60 msec in 7 patients (58 percent). The atrial effective refractory period was prolonged in 3 of 12 patients and was markedly prolonged in 1 of them. Effective refractory period of the atrioventricular (A-V) node, determined  in five patients, was prolonged in three. Dual responses of the A-V node to atrial extrastimuli were found in seven patients. Dual A-V nodal repsonses were evoked with propranolol in three patients and persisted in the other four patients with dual responses despite propranolol administration.
mesh_terms: D000328:Adult; D000368:Aged; D001145:Arrhythmias, Cardiac / Q000209:etiology* / Q000503:physiopathology; D001281:Atrial Fibrillation / Q000209:etiology; D001283:Atrioventricular Node / Q000187:drug effects / Q000503:physiopathology; D002036:Bundle of His / Q000503:physiopathology; D002037:Bundle-Branch Block / Q000209:etiology; D002304:Cardiac Pacing, Artificial; D002312:Cardiomyopathy, Hypertrophic / Q000503:physiopathology*; D005260:Female; D006327:Heart Block / Q000209:etiology; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011433:Propranolol; D013614:Tachycardia, Paroxysmal / Q000209:etiology
chemical_list: D011433:Propranolol