Cardiac sarcoidosis and giant cell myocarditis as causes of atrioventricular block in young and middle-aged adults.

BACKGROUND Cardiac sarcoidosis (CS) and giant cell myocarditis (GCM) may present as high-degree atrioventricular block (AVB), but their proportion of the causal spectrum of AVB is not well-known. We investigated the prevalence of biopsy-verified CS and GCM in young and middle-aged adults undergoing pacemaker (PM) implantation for AVB. METHODS AND RESULTS We used the PM registry of Helsinki University Central Hospital to identify all patients aged 18 to 55 years who underwent PM implantation for AVB between January 1999 and April 2009 and reviewed their medical records. In total, 133 patients had either second- or third-degree AVB as an indication for PM. Of them, 61 had a known cause for AVB, and they were excluded from further analyses. Among the remaining 72 patients with initially unexplained AVB, biopsy-verified CS or GCM was found in 14 (19%) and 4 (6%) patients, respectively. The majority (16/18, 89%) were women. Among the adult patients aged <55 years, the prevalence of CS and GCM combined was 14% (95% CI, 7.7% to 19.3%) of the whole AVB population and 25% (95% CI, 15% to 35%) of those with an initially unexplained AVB. Over an average of 48 months of follow-up, 7 (39%) of 18 patients with CS or GCM versus 1 of the 54 patients in whom AVB remained idiopathic, experienced either cardiac death, cardiac transplantation, ventricular fibrillation, or treated sustained ventricular tachycardia (P<0.001). CONCLUSIONS CS and GCM explain ≥25% of initially unexplained AVB in young and middle-aged adults. These patients are at high risk for adverse cardiac events.