LETTERS TO THE EDITOR: LETTERS TO THE EDITOR
Mitral Prosthesis Mismatch: Hemodynamic Phenomenon or Geometric Discrepancy?
Ganesh Shanmugam, MBBS, MS, MCh, FRCS*
* Department of Cardiac Surgery, Royal Hospital for Sick Children, Dalnair Street, Glasgow G3 8SJ United Kingdom (Email: sgunpat{at}hotmail.com).
The recent study by Li et al. (1) has several limitations. The absence of information on functional capacities, symptoms, preoperative pressure data, or left ventricular (LV) function indices limits the significance of the data.
Perioperative mortality increases when pulmonary artery (PA) pressures exceed 60 mm Hg, which is the cutoff in risk-stratification systems like the Euroscore. A cutoff of 40 mm Hg overestimates the incidence of severe pulmonary hypertension (PHT). Significantly, 15 of 40 patients with prosthesis-patient mismatch (PPM) had postoperative atrial fibrillation (AF). The difference in mean gradients between the PPM and non-PPM groups is merely statistical, but insignificant. The investigators suggest a "simple" strategy of implanting a prosthesis to obtain an indexed effective orifice area (EOA) [EOAI] >1.2 cm2/m2. This arbitrary classification based on EOAI has no surgical significance. There is no mention of valve annular diameters, which is an important consideration in the choice of prosthesis size. The EOAIs for the different prosthesis sizes are unavailable.
Most patients have body surface areas (BSAs) between 1.5 and 2 m2. This translates to absolute EOAs between 1.8 and 2.4 cm2. The minimum absolute EOA of any size 23 prosthesis is 2.54 cm2, which produces an EOAI >1.2 cm2/m2. However, a 23-mm mitral prosthesis is clearly hemodynamically restrictive. Most surgeons would implant larger valves than these; it follows that no patient should have PPM if an EOAI of 1.2 cm2/m2 is considered the minimum! In consequence, the recommendations by Li et al. (1) are nonspecific and impractical.
Twenty-one of 32 patients with preoperative PHT had PPM. In essence, the smallest valves were implanted in those with large BSAs and preoperative PHT. Naturally, many patients would have residual PHT. Could the investigators have actually undersized the prosthesis in many patients?
Native annular diameter places a major restriction on the maximum implantable prosthesis size. Problems with disproportionately large mitral prostheses include LV outflow obstruction, restriction of prosthetic mobility, circumflex artery and conduction system injury. Complications like atrioventricular groove dehiscence and ventricular rupture with large valves are every surgeon's nightmare. A murine annulus will not take an elephantine prosthesis!
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References
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- Li M, Dumesnil JG, Mathieu P, Pibarot P. Impact of valve prosthesis–patient mismatch on pulmonary arterial pressure after mitral valve replacement J Am Coll Cardiol 2005;45:1034-1040.[Abstract/Free Full Text]
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