LVOTO with an incidence rate of up to 6% is one of the most common complications in patients undergoing PASD repair[5, 6]. In this case series, we performed MVR on the 5 patients who had MI at hospital admission and had previous PASD repair. All of them were implanted with a Medtronic AP360 mechanical mitral valve including one re-MVR, and only one patient developed mild postoperative LVOTO.
We used AP360 valves in these 5 patients because we believe the design of AP360 could reduce the risk of LVOTO. In the normal anatomy, LVOT is only a few millimeters long and the aorta is “wedged” between the mitral and tricuspid valves. However, in patients with PASD, the aortic valve is anterior and rightward but is not positioned between the two normal atrioventricular (AV) valves, which consequently changes the anteroposterior dimension of the LVOT. The should-be position of the aortic root creates extra length of LVOT, which is absent in the heart with the normal anatomy. Moreover, the deficiency of the septum makes a convexity towards the ventricular side, narrowing the LVOT. These anatomic abnormalities lead to a narrow and elongated LVOT with an abnormal outlet angle, which is described classically as the “goose neck” deformity in angiography.
Because of the anatomic characteristics of PASD, a prosthetic valve protruding into the LVOT may worsen LVOTO[7, 8]. A prosthetic valve with pannus and hyperplastic annulus fibrous tissue can partially block the LVOT and thus increase the risk of LVOTO. In Case 1 of this report, we found that part of the sewing cuff of the previously implanted prosthetic valve was covered with hyperplastic annulus fibrous tissue protruding into the LVOT. The development of the hyperplastic anulus fibrous tissue may be associated with the blood flow. Medtronic AP360 mechanical prosthesis, whose sewing cuff is different from that of other prosthetic valves in terms of positioning, can possibly avoid hyperplastic anulus fibrous tissue formation. According to the unique design of AP360, an implanted AP360 prosthesis locates mostly in the atrial side, while an implanted other mechanical valve, such as ATS mechanical mitral valve, locates partly in the ventricular side (Figure. 2A&B). Thus, the potential risk of LVOTO associated with AP360 prosthesis implantation can be reduced.
Notable, for Carbomedics Orbis Universal mechanical mitral valve, because of its flexible and longitudinal symmetrical sewing cuff, the Carbomedics Orbis Universal mechanical mitral prosthesis can be squeezed by the scarred annulus and thus sink into the ventricular side (normally pushed to the atrial side due to pressure difference) and worsen LVOTO. Although other types of mechanical valves with a similar design as the ATS prosthetic valves may be not as bad as the Carbomedics Orbis valves in terms of the risk of LVOTO, could still sink to the LV to some degree. Implantation of Medtronic AP360 prosthesis using non-everting suture can lift the prosthesis up to the left atrium (LA) and avoid this situation.
We had encountered a case showing a Carbomedics Orbis valve implantation associated LVOTO. A 40-year-old female was diagnosed with primum ASD, anterior mitral valve leaflet cleft and moderate tricuspid regurgitation. She underwent tricuspid valvuloplasty and PASD repair. However, her mitral valve was beyond repair and thus a 27# Carbomedics mechanical mitral valve was then implanted. Her postoperative TEE showed the well-performed implanted prosthetic mitral valve, a peak LVOT pressure gradient of 34 mmHg, and left ventricular outflow peak velocity of 2.9 m/s. Her postoperative 3-month follow up echocardiography showed a moderate LVOT stenosis with a peak LVOT pressure gradient of 73 mmHg, left ventricular outflow peak velocity of 4.2 m/s, minimum LVOT diameter in anteroposterior dimension of 13 mm, and interventricular septum thickness of 10mm. Postopoerative 18-month follow-up echocardiography showed a severe LVOT stenosis with a peak LVOT pressure gradient of 92 mmHg, left ventricular outflow peak velocity of 4.8 m/s, minimum LVOT diameter in anteroposterior dimension of 6.6 mm and interventricular septum thickness of 12 mm. The patient refused a re-MVR.
Based on our experience, we believe choosing a AP360 prosthesis with a proper size matching the patient’s anatomic structure is critical for good clinical outcome. An oversized AP360 may cause valve dysfunction. One of the lobes of an oversized prosthesis could be blocked by the thickened interventricular septum, leading to valve dysfunction. Aggressive implantation of an oversized prosthetic valve to avoid mitral prosthesis-patient mismatch, which remains to be controversial regarding patient outcome, is not recommended.
Some pediatric cardiac surgeons suggest that the chimney technique can be used to avoid LVOTO in young patients undergoing MVR. THE Chimney technique is to suture a several-millimeter-long tubular dacron graft to the sewing cuff of a prosthetic valve and then suture the graft to the native mitral annulus, forming a composite graft floating in the LA like a “chimney”. Although the chimney technique shows promising LVOTO prevention in children, the long-term effect is still unknown in patients with PASD.