When Should High-Grade Heart Block Trigger a Search for a Treatable Cardiomyopathy?

Abstract

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, second- or third-degree heart block requiring a pacemaker occurs in 25% of cases.3 View this table: Table. Prevalence of Various Cardiac Findings in Cardiac Sarcoidosis During the Course of Disease Article see p 303 This relatively high rate of heart block reflects the severity of the clinical course of cardiac sarcoidosis and GCM, which have a higher rate of death and heart transplantation than lymphocytic myocarditis.1,4 Unlike acute lymphocytic myocarditis, for which immunosuppression usually is not beneficial,5 GCM or cardiac sarcoidosis may improve with certain combinations of immunosuppressive drugs. In the case of acute GCM, cyclosporine combined with corticosteroids and usually a T-cell lytic agent like muromonab-CD3 improves transplant-free survival.6 Uncontrolled case series also suggested that left ventricular (LV) dysfunction due to cardiac sarcoidosis may improve with corticosteroid therapy.7 Because GCM and cardiac sarcoidosis are rare disorders, endomyocardial biopsy is not routinely recommended to detect them in the setting of complete heart block unless cardiomyopathy is present.8 Although a recommendation class was not assigned to …