When should high-grade heart block trigger a search for a treatable cardiomyopathy?

High-degree heart block is an uncommon manifestation of acute myocarditis in adults. The rate of heart block requiring a pacemaker in biopsy-proven acute lymphocytic myocarditis generally is low but has been reported in up to 8.3% of cases.1 Important exceptions include cardiac sarcoidosis and giant cell myocarditis (GCM), 2 uncommon and idiopathic disorders for which early immunosuppression may improve clinical outcomes. High-degree heart block occurs in the course of biopsy-proven cardiac sarcoidosis in 23% to 30% of cases (Table).2 In GCM, secondor third-degree heart block requiring a pacemaker occurs in 25% of cases.3