Association Between Right Bundle Branch Block and Ventricular Arrhythmia in Patients With Cardiac Sarcoidosis

Background: Ventricular arrhythmia (VA) is a life-threatening condition associated with cardiac sarcoidosis (CS). Right bundle branch block (RBBB) is a common conduction disorder in CS; however, its association with VA remains unknown. Objectives: This study aimed to investigate the relationship between RBBB and VA in patients with CS. Methods: This was a post hoc analysis of ILLUMINATE-CS (Illustration of the Management and Prognosis of Japanese Patients with Cardiac Sarcoidosis), a multicenter, retrospective, and observational study that evaluated the clinical characteristics and prognosis of CS. Eligible patients were divided into two groups based on the presence or absence of RBBB at the time of diagnosis. The primary outcome was serious ventricular arrhythmia events (SVAEs), defined as a combination of sudden cardiac death and documented ventricular fibrillation, sustained ventricular tachycardia, or appropriate implantable cardioverter-defibrillator therapy. Results: Overall, 312 patients were studied, with 155 (49.7%) patients presenting with RBBB (RBBB group). Patients in the RBBB group had a higher prevalence of basal interventricular septum (IVS) thinning and prominent late gadolinium enhancement in the basal IVS on cardiac magnetic resonance imaging than those in the non-RBBB group. During a median follow-up of 3.0 years (IQR: 1.6-6.0 years), 66 patients experienced SVAE. In multivariable Cox regression analysis, the RBBB group was independently associated with a higher incidence of SVAEs (HR: 1.93 [95% CI: 1.14-3.28]; P = 0.015). Conclusions: In patients with CS, RBBB was an independent predictor of SVAEs, which might reflect the specific scar distribution that is predominant in the IVS.