Antisynthetase Syndrome With Cardiac Involvement: Role of Cardiac Magnetic Resonance Imaging in Its Diagnosis and Management.

We present a case of newly diagnosed heart failure with reduced ejection fraction secondary to antisynthetase syndrome (ATS) in a 63-year-old female patient. The patient presented with symptoms and laboratory findings indicative of an ATS flare, which included inflammatory arthritis, muscular involvement, and exertional dyspnea. A systematic and structured diagnostic approach was undertaken, commencing with transthoracic echocardiography (TTE) to evaluate cardiac function and morphology. This was followed by ischemic assessment through coronary angiography to rule out ischemic heart disease, and subsequently, cardiac magnetic resonance imaging (CMR) based on findings from the TTE. The initial TTE revealed a newly reduced ejection fraction of 30-35%, a significant decline from previous normal echocardiograms. The ischemic evaluation identified mild, non-obstructive coronary artery disease, effectively excluding ischemic cardiomyopathy as a contributing factor. CMR was pursued due to concerns for myocarditis and provided further diagnostic clarity, revealing impaired left ventricular (LV) systolic function and near-transmural late gadolinium enhancement (LGE) in the inferolateral and anterolateral wall segments, along with subendocardial LGE in the inferoseptal wall segment. These findings were consistent with regional wall motion abnormalities observed on TTE. In response, the patient's baseline immunosuppressive therapy was optimized with the addition of mycophenolic acid. No additional etiologies were identified to account for the new LV dysfunction. Following optimization of immunosuppressive therapy and heart failure management, the patient exhibited significant clinical improvement, including stabilization of cardiac function and resolution of inflammatory markers. This case report adds to sparse literature describing ATS-induced myocarditis and helps highlight integration of advanced imaging modalities like CMR, which provides critical insights into myocardial tissue characterization and helps guide management strategies.