DISCUSSION
Cardiac sarcoidosis is the most ominous manifestation of sarcoidosis accounting for as much as 50% of deaths in patients with sarcoidosis.8 The prevalence of cardiac involvement amongst patients with systemic sarcoidosis varies widely for unknown reasons, but ranges between 3.7 to 54.9% depending upon the imaging techniques used and the population studied.4,14 There is scanty data on CS in our setting and in Africa as a whole with no case reports identified. The triad of cardiac manifestations are conduction abnormality, ventricular tachycardia and heart failure.
CS though often clinically silent is frequently fatal. It’s wide spectrum of clinical manifestations arise from the variable locations of sarcoid lesions in the myocardium.4 There is however a predilection for the base of the interventricular septum, the conduction system and the left ventricular (LV) free wall, although, other parts of heart including the papillary muscles, right ventricular wall, atria, valve leaflets, intramyocardial vessels, pericardium and endocardium may be involved.3,7,22 Indeed, both patients reported here had involvement of the base of the interventricular septum, the conduction system and the left ventricular (LV) free wall.
Conduction disease as observed in our report, is the most common electrophysiologic manifestation of CS with a prevalence up to 62%.14 Complete heart block and bundle branch blocks have been reported in 23-30% and 12-32%, respectively of patients with myocardial sarcoidosis.7 Advanced AV blocks may lead to syncope or sudden cardiac death, warranting inclusion of sarcoidosis as a differential in the evaluation of patients with syncope, especially when it occurs in young and middle-aged patients. Studies suggest CS may be accountable for unexplained second or third degree atrioventricular (AV) block in patients less than 60 years old 14,23. Indeed, implantable cardioverter-defibrillators (ICDs) are recommended for CS patients with complete heart block, prior ventricular arrhythmias, cardiac arrest or LV ejection fraction of <35%.24
A prospective evaluation of patients aged 18 to 60 years presenting with unexplained Mobitz II or 3rd degree AVB and no previous history of sarcoidosis by Nery et al found that 34% of patients had CS and were more likely to experience major adverse cardiac events.25 Data from the National Inpatient Sample (NIS) database from 2012-2014 has shown that complete heart block is more prevalent among patients with sarcoidosis compared to those without a diagnosis of sarcoidosis and increased the odds of developing complete heart block among other medical comorbidities like coronary artery disease, age, gender and heart failure.26
A recent Finnish study of 325 cases of cardiac sarcoidosis from the Myocardial Inflammatory Diseases in Finland Study Group Registry diagnosed from 1988 to 2015, reports that 143 (44%) patients presented with Mobitz II second degree or third degree AVB in the absence of other explanatory cardiac disease.27 Likewise, another Finnish study of 72 patients aged <55 presenting with new-onset, unexplainable Mobitz II second degree or third degree AVB, 14 of 72 (19%) patients had histologically confirmed CS whilst another 4 (6%) had giant cell myocarditis.23
Bundle branch blocks are also a frequent occurrence in CS patients. Our first case had left bundle branch block (LBBB) which is known to be less common compared to right bundle branch blocks (RBBB).7,28,29 Schuller et al found that among a cohort of patients with biopsy – proven pulmonary sarcoidosis a BBB pattern is associated with cardiac involvement 29 and RBBB pattern was more prevalent than LBBB in the CS population in a Danish study.28
Cardiac sarcoidosis is frequently overlooked as the underlying cause of heart failure and accounts for 25 – 75% of cardiac deaths in patients with cardiac sarcoidosis. Left ventricular systolic and diastolic dysfunction leading to progressive congestive heart failure often occurs due to conduction or rhythmic abnormalities, or as a result of extensive myocardial infiltration or both.7,10,30 A study of core LV biopsies obtained during LV assist device implantation showed granulomatous myocarditis consistent with sarcoidosis in previously undiagnosed CS in 6 of 177 mixed cardiomyopathy patients (3.4%).31 In an examination of explanted hearts, Roberts et al found that among 130 heart transplants with a clinical diagnosis of non-ischaemic cardiomyopathy, 8 (6.2%) had undiagnosed CS.32
Due to the low sensitivity of endomyocardial biopsy, cardiac MRI has become the investigation of choice for cardiac sarcoidosis in the patient with a high clinical suspicion. As recommended by experts’ consensus, clinical symptoms with consistent advanced cardiac MRI findings should be combined with histological presence of noncaseating granulomas demonstrated in biopsy of other sites of involvement such as the skin or lungs. In both cases presented, the presence of cardiac complications prevented biopsy of lung tissue via CT-guided biopsy as endobronchial ultrasound transbronchial needle aspiration (EBUS-TBNA) is not available in our practice. High resolution CT-scan (HRCT) of the chest which has significant correlation with histology in the diagnosis of pulmonary sarcoidosis was highly suggestive in both cases and supported by some laboratory markers such as serum ACE level and hypercalcaemia. 33
Broadly, current treatment for CS involves immunosuppression and antiarrhythmic agents for inflammation and antiarrhythmic drugs and/or ablation for scar formation/fibrosis. Optimal duration of treatment remain controversial, but corticosteroids and other immunosuppressive agents improve cardiac function, prevent further formation of granulomas, and reduce arrhythmias and incidence of sudden cardiac death as depicted in the cases presented, but patients with advanced cardiac dysfunction (LV ejection fraction <30%) may remain unresponsive to corticosteroid therapy.3,15,34–36Even though corticosteroids remain the cornerstone in the treatment of clinically active or symptomatic CS, dosing, selection and timing and duration of therapy for cardiac sarcoido­sis remains controversial.20,36 Late gadolinium enhancement in Cardiac MRI has emerged as an important tool for risk stratification for sudden cardiac death (SCD) in CS and is of key importance in the decision for ICD implantation in CS patients considered at high risk for SCD. Although both patients in this report had LGE on their cardiac MRI scans for which an ICD was indicated, this service was not available in our country.