Electrophysiological study of atrio-ventricular block and ventricular conduction defects. Prognostic and therapeutical implications.

His bundle study with long term follow-up (mean 42 months) was performed in 155 patients (107 with previous syncope, 48 without or with few symptoms). The electrocardiogram showed various conduction abnormalities, but in some cases it was normal. Patients were excluded at the beginning of the study, if they showed sick sinus syndrome, recorded 3rd degree atrioventricular block, angina pectoris, recent myocardial infarction, congenital or surgical cardiac block. In previous studies the diagnostic sensibility and specificity of ajmaline (1 mg/kg/1' i.v.) and overdriving tests have been evaluated. In this study the prognostic meaning of these tests has been evaluated. During a mean 42 months follow-up, 17 patients (10.9%) developed advanced atrioventricular block. A higher risk of developing advanced atrioventricular block below the AV node was detected in patients who showed: basal HV greater than or equal to 65 ms (33% developed advanced atrioventricular block vs 4.7% of patients with basal HV less than 65 ms; p less than 0.001); HV value greater than or equal to 120 ms or 2nd-3rd degree atrioventricular block during ajmaline test (40% progressed to advanced atrio-ventricular block vs 0.85%; p less than 0.001); HV prolonged greater than 10 ms or 2nd-3rd degree atrioventricular block during atrial pacing (40% progressed to a atrioventricular block vs 3.4%; p less than 0.001) regardless of previous syncope.(ABSTRACT TRUNCATED AT 250 WORDS)