[Spontaneous grade I bundle of His block. Clinical, electrocardiographic and electrophysiological studies in 37 patients].

The clinical, ECG and electrophysiological data of 37 patients (28 males and 9 females) with spontaneous intra-hisian block are reported. Of these patients, 11 had hypertensive heart disease and 5 had ischemic heart disease with previous myocardial infarction; in 21 patients, clinical signs of heart disease were not evident. In 18 patients, a single or recurrent episode of syncope had occurred. One patient had junctional rhythm and 36 sinus rhythm; among these, 12 patients presented PR greater than 200 msec (7 with a narrow and 5 with a wide QRS); 12 patients had a single or bilateral bundle branch block; 12 had a normal ECG. The electrophysiological study showed a split H-H1 in 22 patients, a wide His deflection (H greater than 25 msec) in 4 and HV greater than 65 msec with narrow QRS in 11. In 17 patients a more or less marked sinoatrial node and/or atrioventricular node dysfunction was present. Atrial pacing, performed in all, induced 2nd degree Mobitz 2 intra-hisian block in 9 patients. Ajmaline was used in 16 patients but induced a complete intra-hisian block in only one. In 28 patients a preventive pacemaker was implanted after electrophysiological study. During the follow-up (mean 25 months/pt.), 38% of the patients developed complete atrioventricular block. No recurrence of syncope occurred in the paced patients. Comparison of patients who developed atrioventricular block and those who maintained normal atrioventricular conduction did not show differences as far as heart disease, previous syncope, ECG pattern and results were concerned.(ABSTRACT TRUNCATED AT 250 WORDS)