Patient with known or suspected cardiac sarcoidosis

Prevalence and prognosis of cardiac sarcoidosis

Prior data have estimated that 5% of patients with sarcoidosis have clinically manifest cardiac involvement. Autopsy and imaging series, however, report a substantially higher occurrence, ranging from more than 20% in the United States to more than 50% in Japan. Based on imaging studies, 20% to 25% of patients with sarcoidosis have cardiac involvement. The rate of isolated cardiac involvement among patients with cardiac sarcoidosis (CS) is approximately 25%. Cardiac involvement accounts for 10% to 25% of all deaths from sarcoidosis in the United States and more than half of all deaths from sarcoidosis in Japan, where studies have identified the extent of left ventricular (LV) dysfunction as an independent predictor of mortality. Notably, among patients with CS, the most common mode of death is sudden cardiac death (SCD).

Clinical manifestations and presentation of cardiac sarcoidosis

Depending on the type and extent of involvement, the presentation of CS is highly variable ( Table 23.1 ), ranging from asymptomatic heart involvement to sudden death as the initial presentation. CS most commonly involves the myocardium, particularly the basal ventricular septum, followed by the LV free wall, papillary muscles, and right ventricle (RV). Conduction abnormalities are common because of the predilection for granulomas along the conduction system. Although complete heart block in a young patient should raise suspicion for CS, other causes of such a presentation, including Lyme disease and congenital heart block, should be excluded. Acute sarcoid myocarditis, a rare presentation of CS characterized by high-grade atrioventricular block, malignant ventricular arrhythmias, and congestive heart failure (HF), may be indistinguishable clinically from giant cell myocarditis. Frequent ventricular arrhythmias may mimic arrhythmogenic RV cardiomyopathy, classic outflow tract or fascicular ventricular tachycardia (VT), or VT secondary to coronary artery disease (CAD). Establishing the diagnosis is essential given the distinct management of the different conditions. Atrial arrhythmias are increasingly recognized in CS, but small autopsy series previously suggested that CS may involve the atria less extensively than ventricles. Systolic and diastolic HF may also occur because of myocardial changes caused by granulomatous deposition and subsequent fibrosis, which typically occurs in a noncoronary distribution but may be indistinguishable from other infiltrative cardiomyopathies. Valvular disorders have also been reported as a result of papillary muscle involvement. Pericardial effusion, with or without hemodynamic instability, may result from sarcoidosis of the pericardium, but frank clinical pericarditis is relatively uncommon. Myocardial ischemia and infarction from coronary involvement is relatively rare; however, CAD is likely more common among individuals with sarcoidosis.

Echocardiography

Echocardiography generally demonstrates nonspecific findings in the presence of CS but may be most helpful if abnormal in the presence of extracardiac sarcoidosis. Several studies have estimated that the sensitivity of echocardiography to detect CS ranges from 25% to 30%. Nevertheless, the HRS Expert Consensus Statement suggests echocardiography as one of the initial screening tests in conjunction with a clinical history and a 12-lead electrocardiogram (ECG) in patients with biopsy-proven extracardiac sarcoidosis ( Fig. 23.1 ). Echocardiographic findings in CS include reduced LV function, wall motion abnormalities, and changes in ventricular wall thickness, particularly basal septal thinning or aneurysm. Per the HRS algorithm, cardiac symptoms, an abnormal ECG, or abnormal echocardiographic findings in the setting of biopsy-proven extracardiac sarcoidosis should prompt referral to advanced imaging (see Fig. 23.1 ).

Among patients who are found to have CS, echocardiography may be useful to evaluate the extent of involvement (particularly nonmyocardial involvement, such as the valves or pericardium) and LV and RV function. Given the prognostic importance of LV systolic function in CS, echocardiography may be helpful in identifying high-risk patients.

Single photon emission computed tomography myocardial perfusion imaging and ⁶⁷ gallium

SPECT ²⁰¹ thallium (Tl)-based and ^99m technetium (Tc)-based findings in CS may also be nonspecific and include focal perfusion defects at rest. When performed in conjunction with radionuclide-based inflammation imaging, SPECT MPI may help differentiate areas of scar or fibrosis from active inflammation. A reverse-redistribution pattern on rest and stress SPECT MPI has also been described whereby focal resting perfusion defects decrease in size or even disappear with vasodilator stress. ^, This is believed to be due to focal reversible microvascular constriction in the coronary arterioles surrounding the granulomatous inflammation. Although the HRS clinical algorithm does not include SPECT myocardial perfusion defects in its diagnostic pathway, likely because of the low sensitivity and specificity of these findings for CS, the 2017 revised Japanese clinical diagnostic pathway lists SPECT perfusion defects as minor criteria. SPECT MPI may be combined with ¹⁸ F-fluorodeoxyglucose (FDG) PET imaging for evaluating CS when perfusion PET is not available.

⁶⁷ Gallium ( ⁶⁷ Ga) accumulates in areas of active inflammation and is included as a major criterion in the 2017 revised Japanese criteria. ⁶⁷ Ga has a high specificity but low sensitivity (<50%), in part because of the challenges of distinguishing cardiac from pulmonary and mediastinal tracer uptake. Combined SPECT MPI and ⁶⁷ Ga scintigraphy has not been extensively evaluated but may have higher diagnostic accuracy; however, higher radiation exposure from ⁶⁷ Ga and its relatively low-contrast resolution, along with the availability of superior imaging techniques, have limited its use.