Natural history of chronic second-degree atrioventricular nodal block.

This report details our experience with documented chronic second-degree atrioventricular (AV) nodal block (proximal to His [H]) in 56 patients. Forty-six men (82%) and 10 women (18%), ages 18-87 years, were studied. Nineteen of the patients (34%) had no organic heart disease (including seven trained athletes) and 37 (66%) had organic heart disease. ECGs in all patients demonstrated episodes of type I second-degree block; five patients also had periods of 2:1 block. Prospective follow-up patients with no organic heart disease (157-2280 days, mean 1395 +/- 636 days) revealed one patient with clear indication for permanent pacing because of bradyarrhythmic symptoms (permanently placed on day 220 of follow-up). Two patients died nonsuddenly. In patients with organic heart disease (prospective follow-up of 60-2950 days, mean 1347 +/- 825 days), pacemakers were implanted in 10 patients, primarily for treatment of congestive heart failure in eight and syncope in two. Sixteen patients died -- three suddenly, seven with congestive heart failure, two of an acute myocardial infarction and four of causes unrelated to cardiac disease. In summary, chronic second-degree AV nodal block has a relatively benign course in patients without organic heart disease. In patients with organic heart disease, prognosis is poor and related to the severity of underlying heart disease.