Abstract 12522: Non-Ischemic Papillary Muscle Rupture Due to MRSA Myocarditis

Abstract

Case Presentation: A 46-year-old male with diabetes, ESRD, and recurrent MRSA bacteremia, presented with septic shock and suffered cardiac arrest. Following resuscitation EKG showed inferolateral ischemia. TTE revealed acute mitral valve regurgitation resulting from posteromedial papillary muscle rupture (PMR). An intra-aortic balloon pump was implanted for cardiogenic shock. Coronary angiography revealed right dominant circulation and thrombotic occlusion of a small caliber distal left circumflex artery (LCX). Emergent mitral valve replacement surgery was performed. Pathologic analysis of the excised muscle and leaflet showed marked acute inflammation, bacterial invasion, and myocyte necrosis, confirming non-ischemic rupture due to MRSA myocarditis. Discussion: PMR predominantly occurs after MI, complicating 0.03% of STEMI cases in the reperfusion era. Non-ischemic causes are rare. Coexistence of myocarditis, infective endocarditis (IE), and MI poses a challenge in determining etiology. Establishing causation guides whether to expedite emergent valve surgery or focus on cardiomyocyte salvage by revascularization. The posteromedial papillary muscle is most commonly involved in PMR due to single blood supply from the PDA (most commonly a branch of the RCA, and less commonly the LCX). Coronary angiography, postoperative histopathology, and culture results determined the etiology of PMR was fulminant MRSA bacteremia culminating in myocarditis. Bacterial colonization and resultant inflammation induced physical and mechanical strain leading to complete rupture. The occluded LCX was incidental, and may have been the result of septic embolization, which occurs in up to 65% of left-sided IE. Albeit rare, non-ischemic etiologies must be considered when the anatomic presentation of acute PMR on TTE is incongruent with angiography. Definitive treatment relies on surgical intervention and mechanical circulatory support is often necessary.