By Van Selby, MD

Assistant Professor of Medicine, University of California, San Francisco Cardiology Division, Advanced Heart Failure Section

Dr. Selby reports no financial relationships relevant to this field of study.

SYNOPSIS: Among patients with extracardiac sarcoidosis, cardiac MRI was the best test for diagnosing cardiac involvement and the strongest independent predictor of adverse outcomes.

SOURCE: Kouranos V, Tzelepis GE, Rapti A, et al. Complementary role of CMR to conventional screening in the diagnosis and prognosis of cardiac sarcoidosis. JACC Cardiovasc Imaging 2017;10:1437-1447.

There is no gold standard criterion for diagnosing cardiac sarcoidosis. Cardiac MRI, specifically evaluation for late gadolinium enhancement (LGE), carries both diagnostic and prognostic utility. However, few studies have examined how cardiac MRI should be incorporated into standard diagnostic testing algorithms for cardiac sarcoidosis.

Kouranos et al studied 321 patients with biopsy-proven extracardiac sarcoidosis. All patients underwent standard diagnostic testing for cardiac involvement (ECG, Holter monitor, and echocardiography), as well as cardiac MRI with LGE. Patients were followed for the primary composite outcome of all-cause mortality, sustained ventricular tachycardia, or hospitalization for heart failure.

Using the Heart Rhythm Society consensus criteria, cardiac sarcoidosis was diagnosed in 29.9% of patients. Of all the diagnostic tests and clinical characteristics studied, cardiac MRI was the most accurate diagnostic tool (area under the curve = 0.984). Echocardiography exhibited high specificity but poor sensitivity for the detection of cardiac involvement, and adding echocardiography to cardiac history and ECG did not improve sensitivity significantly. During a median follow-up of 84 months, the primary outcome occurred in 7.2% of patients. Among the entire study population, LGE was a strong independent predictor of the primary outcome (hazard ratio [HR], 5.8; P = 0.004). In patients with cardiac symptoms and/or an abnormal ECG, cardiac MRI was the only independent predictor of the primary outcome (HR, 12.71; P = 0.021). Among 126 patients with no cardiac symptoms and no abnormalities on ECG or echocardiography, cardiac MRI identified cardiac sarcoidosis in 26 patients, although the presence of LGE was not associated with increased risk of the primary outcome. The authors concluded that cardiac MRI is the most valuable test in the diagnosis and prognosis of cardiac sarcoidosis in a general sarcoidosis population.

COMMENTARY

Cardiac involvement is identified in approximately 5-10% of patients with sarcoidosis. However, autopsy studies suggest the true prevalence is significantly higher (between 20-30%), and cardiac disease contributes disproportionately to morbidity and mortality in patients with sarcoidosis. Cardiac sarcoidosis is characterized by patchy involvement, limiting the utility of standard diagnostic tools, including endomyocardial biopsy. Cardiac MRI offers a more comprehensive evaluation of the myocardium, making it better suited for evaluating such a disease. Previous studies have shown the diagnostic and prognostic significance of LGE identified by cardiac MRI in sarcoidosis.

The study by Kouranos et al represents the largest published cohort to date of cardiac MRI in sarcoidosis patients and clearly demonstrates the superiority of cardiac MRI over echocardiography and other testing for both diagnosing cardiac sarcoid and determining prognosis in patients with extracardiac sarcoidosis. In particular, cardiac MRI is a valuable tool for determining the risk of adverse events in patients with sarcoidosis and either abnormal ECG or cardiac symptoms. On the other hand, in patients with normal ECG and no symptoms, the utility of cardiac MRI is less clear; in this group, LGE was identified in some patients, but its presence was not associated with increased risk of adverse events.

The study also highlights the poor sensitivity of routine echocardiography for the diagnosis of cardiac involvement in patients with sarcoidosis. Current guidelines from the Heart Rhythm Society recommend screening all patients with echocardiography, but adding echocardiography to clinical history and ECG added little diagnostic utility in this study. It is important to note that newer echocardiographic techniques, including strain imaging, may improve accuracy for diagnosing cardiac sarcoidosis. These techniques were not included in this study, and based on the findings, we can only conclude that a standard echocardiographic examination has poor sensitivity for the identification of cardiac involvement in patients with extracardiac sarcoidosis.

Although the study convincingly demonstrated the strengths of cardiac MRI in the evaluation of suspected cardiac sarcoidosis, widespread expansion will be limited by both cost and availability of cardiac MRI. There also was significant interobserver variability in the interpretation of cardiac MRI studies (all images were reviewed by two radiologists). This highlights the importance of performing cardiac MRI in a center with experienced radiologists skilled in the interpretation of LGE. The patients studied were all Caucasian, and, therefore, it is unknown how the findings will translate to the United States, where the sarcoidosis population is racially diverse.

Cardiac sarcoidosis can be missed easily using standard diagnostic testing. When available, cardiac MRI should be strongly considered for further evaluation and estimation of prognosis in patients with known extracardiac sarcoidosis. Future studies will further clarify the use of cardiac MRI in these patients, including how often screening should be performed and how cardiac MRI findings can guide clinical therapy.