In this recent paper investigators found a surprisingly high prevalence of cardiac sarcoidosis and giant cell myocarditis among patients aged 18-55 with unexplained AV block requiring pacing:
Conclusions—CS and GCM explain greater than or equal to 25% of initially unexplained AVB in young and middle-aged adults. These patients are at high risk for adverse cardiac events.
A high rate of adverse events was noted in follow up of the CS and GCM patients. In contrast, those patients whose heart block remained idiopathic after investigation had a benign course.
The Clinical Perspective piece related to this article stated:
These data suggest that CS and GCM are not uncommon causes of AVB in young and middle-aged adults and that the prognosis of CS and GCM is poor even when the first manifestation is AVB. We encourage a policy of active and systematic screening for CS and GCM in all adults aged less than 55 presenting with unexplained high-degree AVB.