Optimizing Cardiac Assessment in Idiopathic Inflammatory Myopathies

Extra-muscular organ dysfunction and cancer association are crucial factors that determine outcomes in idiopathic inflammatory myopathies (IIMs). Cardiac involvement is increasingly recognized as an important cause of morbidity and mortality in IIMs, accounting for nearly one-third of deaths in them.[1] Clinical cardiac disease may manifest in myriad fashions, including heart failure, arrhythmias and other conduction abnormalities, and myocarditis, but typically affects fewer than 10%.[1,2] Apparent subclinical cardiac involvement is far more common (in more than 50%) than clinical disease. Cardiac dysfunction may result from direct disease activity leading to myocarditis, secondary to systemic inflammation, or related to comorbid vascular diseases (often worsened with corticosteroid use).[2] Cardiac enzymes, electrocardiography (ECG), transthoracic echocardiography, and cardiac magnetic resonance imaging (CMR) are the common modalities by which cardiac involvement may be explored.[3] The former two are relatively nonspecific. Cardiac troponin T and myocardial creatine kinase may be elevated solely due to skeletal muscle inflammation. N-terminal pro brain natriuretic peptide correlates well with imaging-confirmed cardiac abnormalities.[2] Echocardiogram infrequently shows reduced ejection fraction and almost always in symptomatic patients. Speckle-tracking global longitudinal strain in echocardiography is a technique that can detect subclinical left ventricular systolic dysfunction in a larger subgroup.[3] While left ventricular diastolic dysfunction has been frequently documented, the findings were not corrected for confounding variables such as cardiovascular risk factors.[2,3] The gold standard noninvasive technique for cardiac assessment is CMR, which gives information on the cardiac structure, function, blood vessels, and metabolism. Multiparametric CMR has high sensitivity and accuracy in detecting subclinical disease. The CMR parameters that best reflect IIM-induced myocardial pathology are late gadolinium enhancement (LGE), which identifies myocardial fibrosis or necrosis, and CMR mapping techniques (T1, T2, and extracellular volume mapping), which provide quantitative measurements of tissue properties such as edema, fibrosis, and infiltration.[4] In the first study of its kind from India, Samim et al.[5] compared CMR parameters in a well-defined cohort of IIMs and normal controls. The positive association of myositis activity score with CMR and clinical cardiac scores strongly indicate an inflammatory etiology for cardiac dysfunction. Previous studies have shown the highest cardiovascular risk within 5 years of IIM diagnosis, indicating similar causation.[2] Despite low LGE prevalence (<10%), patients showed worse native T1 mapping values than controls, reflecting underlying myocardial inflammation.[5] Earlier research showed that LGE was the most frequently observed abnormality, found in 20%–62% of cases with subclinical disease.[3] This carries immense prognostic significance because of its association with cardiac arrhythmias.[6] Elevated CMR mapping parameters suggesting edema and inflammation were also consistently reported in studies.[3] As with echocardiography, systolic dysfunction and reduced ejection fraction were rare in asymptomatic patients. Interestingly, CMR provides modest additional insights in diagnostic evaluation when patients have clinically evident cardiac dysfunction.[6] Some algorithms suggest the application of fluorodeoxyglucose positron emission tomography/computed tomography and endomyocardial biopsy when the presence of myocarditis remains uncertain.[4] Myocarditis in IIM provides an avenue for therapeutic intervention and reversibility. Certain clinical and serological features portend an increased likelihood of cardiac complications. Inflammatory myopathies harboring antisignal recognition particle, antiRo, or antimitochondrial antibodies have higher risk.[1,7] Overlap myositis with well-defined connective tissue disorders have frequent cardiac comorbidities.[3] Older age and vascular risk factors are obvious contributors to cardiovascular disease. More frequent cardiac evaluation is warranted in these subgroups.[7] Notwithstanding its safety and high resolution, there are notable limitations to the regular application of CMR in IIMs. A primary logistical constraint is the limited access to the facility and scarcity of specialized expertise for interpretation. Unlike echocardiogram and ECG, repeated measurements are cumbersome. Another clear and present dilemma is determining the importance of imaging-defined asymptomatic cardiac disease. Currently, there is no established definition for what constitutes definitive subclinical cardiac disease in IIMs. CMR abnormalities without clinical syndrome have been shown to be relevant in muscular dystrophies and infiltrative cardiac diseases, but there is little data for the same in IIMs.[3] This renders prognostication and therapy based on CMR challenging. Resolution of these issues requires longitudinal follow-up in large, homogeneous patient cohorts.