Wenckebach atrioventricular block (Mobitz type I) in children and adolescents

Mobitz type I atrioventricular block in children, adolescents and young adults without overt heart disease or drug intoxication has been considered less significant than Mobitz type II block. In highly trained athletes and some nonathletes it has been presumed to be a benign manifestation of heightened vagal tone. Experience with 16 young patients, 6 female and 10 male, tends to alter the concept of benignity. Known onset of Wenckebach and varying first degree block was between 6 months and 17 years of age. Of eight patients followed up for 5 to 18 years, five have fixed complete heart block and three first degree block. Of eight followed up for 1 to 4 years, two have fixed complete heart block and the others varying first, second and third degree block. Two have required a pacemaker implant. On intracardiac electrography performed in seven patients, four manifested during sinus rhythm a Wenckebach response to atrial pacing at abnormally slow rates; in addition, the His bundle electrograms showed A-H delay in one patient, H-V delay in two patients and delay in both intervals in one patient. Of three patients studied during complete heart block all manifested A-H block and one also H-V prolongation. The occurrence of Wenckebach block in 7 of 16 children and adolescents before the development of fixed complete heart block suggests that such block is probably more common than heretofore recognized and may be a phase in the natural history of the development of idiopathic heart block. It often represents significant disease of the cardiac conduction system, which may be progressive, and it has a guarded prognosis.