**Left heart disease**

Left ventricular disease represents the most frequent cause of PH in cardiac surgery (Oudiz, 2007). Left-sided dysfunction includes three distinct etiologies: systolic dysfunction, diastolic dysfunction, and valvular heart disease (mitral and/or aortic). Pre- or postoperative left-sided ventricular or valvular diseases may produce an increase in left atrial pressure, with passive backward transmission of the pressure leading to increased PAP. The elevation of PAP and PVR is due to either the increase of pulmonary artery vasomotor tone and/or pulmonary vascular remodeling (Delgado et al., 2005; Moraes et al., 2000).

#### **Patient-prosthesis mismatch**

Aortic patient-protheis mismatch (PPM) through a reduction in coronary reserve would also contribute to postoperative PH (Bakhtiary et al., 2007) and persistent postoperative valvular gradients (Fig. **9**). There is general agreement that the postoperative indexed effective orifice area (EOA) of the prosthesis being implanted should not be < 0.85 to 0.90 cm2/m2. Mitral PPM was recently described as another cause of residual postoperative PH. Magne *et al.*

Fig. 9. Patient-prosthesis aortic valve mismatch. A 71-year-old man with a body surface area of 1.89 m2 was re-operated for symptoms of severe aortic valve stenosis. He had an aortic vavle replacement (AVR) 4 years before with a Carbomedics 19 mm mechanical bileaflet prosthesis (non-indexed effective orifice area = 1.06 cm2). (**A**) The preoperative mean gradient was 41 mmHg although the intraoperative inspection of the prosthetic valve was completely normal. (**B**) Intraoperative view of an aortic root enlargement procedure in a 69 year-old patient with a reduced aortic diameter requiring AVR. Courtesy of Dr. Michel Carrier. With permission from Denault *et al*. (Denault et al., 2010a).

(Magne et al., 2007) studied 929 patients who underwent mitral valve replacement (MVR), following them up to 15 years. Mitral valve PPM was defined according to the indexed valve EOA as not clinically significant (EOA > 1.2 cm²/m²), moderate (1.2 cm²/m² ≥ EOA > 0.9 cm²/m²), and severe (EOA 0.9 cm²/m²). Prevalence of moderate and severe PPM was 69% and 9%, respectively. In addition, severe PPM was found to be associated with residual PH and a 3-fold increase in postoperative mortality after adjustment for other risk factors. This relevant new finding is currently absent from the majority of studies involving predictors of survival in mitral valve surgery.
