Pathology of primary congenital complete heart block.

Studies were done on the hearts of 4 infants and 2 adults with the clinical diagnosis of congenital complete heart block (CCHB) and on the hearts of 6 control patients of similar age groups but without any significant arrhythmia. All 6 patients with CCHB had absence of the fibers [approaches to atrioventricular node (AVN)] connecting the atrium and the AVN and common bundle (CB), as well as having partial or complete absence of the AVN. The mothers of 2 of the 4 infants with CCHB had antibodies to Ro antigen, and one mother (with Ro antibody) had evidence of having had active systemic lupus erythematosus (SLE). One infant developed SLE before the age of 1 yr. In one of the 2 adult cases with CCHB, the patient had evidence of having developed his CHB after birth, and the other adult patient probably had his CCHB since birth. It was suggested that these findings--and others in the literature--could be explained by there being two factors that lead to the occurrence of idiopathic heart block, whether it be truly congenital or acquired later in life: (a) a genetic predisposition to the condition together with (b) a precipitating injury. Thus, a patient with a genetic predisposition to insults to his conducting fibers might develop CCHB in utero due to some insult (e.g., due to damage by circulating anti-DNA antibodies in patients with SLE or by other unknown insults); or the "weak" fibers could be affected later in life by many different injuries--whether viral, hypersensitivity, anoxic, or due to aging.