A Rare Presentation of Systolic Anterior Motion Occurring Eight Years After Mitral Valve Replacement

Systolic anterior motion (SAM) is the dynamic displacement of mitral valve leaflets anteriorly toward the left ventricular outflow tract (LVOT) during systole. SAM-like physiology has been reported to occur shortly after mitral valve replacement (MVR) surgery; occurrence beyond two years after surgery is very rare. A 55-year-old woman who had bioprosthetic MVR eight years earlier for non-rheumatic mitral stenosis presented to the emergency room with progressive dyspnea and sudden-onset chest pressure. Physical examination noted a grade 3/6 systolic murmur at the cardiac apex, a soft diastolic murmur at the left sternal border, and diffuse expiratory wheezing. B-type natriuretic peptide (BNP) was elevated (286 pg/mL). Transthoracic echocardiography (TTE) showed mitral regurgitation and severe aortic insufficiency; the mitral prosthesis was protruding into the LVOT, causing LVOT obstruction with a peak gradient of 16.3 mmHg and peak velocity of 2.0 m/s. Transesophageal echocardiography (TEE) confirmed severe bioprosthetic MV dysfunction, severe aortic regurgitation, and SAM-like physiology. Left cardiac catheterization showed normal coronaries. She underwent repeat MVR and aortic valve replacement. She was started on daily aspirin and warfarin post-operatively, then discharged home on post-operative day 10. During post-operative office visits, she reported no complications. SAM-like physiology was absent in a two-month follow-up TTE, with reduced LVOT peak gradient of 6.5 mmHg and peak velocity of 1.3 m/s. Dynamic SAM-induced LVOT obstruction could be asymptomatic or result in severe heart failure with 20% risk of sudden cardiac death. SAM may occur within days following MVR or may have a delayed presentation. Medical management, including beta-blockade, is the cornerstone of initial management, while structural damage to the prosthetic valve mandates repeating mitral valve replacement surgery. This case highlights the importance of long-term follow-up of patients after MVR to assess for SAM, which could occur with or without degenerative changes of the prosthetic valve.