PAH is a common complication of severe mitral valve disease [3, 4]. Raised pulmonary arterial pressure initially results from increased left atrial pressure, pulmonary arteriolar vasoconstriction, and ultimately obliterative changes in the pulmonary vascular bed. Excessive thickening of the media and intimal fibrosis of small muscular pulmonary arteries are typical changes of long-term mitral stenosis as well as other conditions associated with severe PAH . In our study, the statistics of preoperative and postoperative echocardiographic data showed significant decline in PASP(101.2 ± 20.3 versus 48.1 ± 14.3 mmHg, P < 0.05), LAD(67.6 ± 15.7 versus 54.4 ± 11.4 mm, P < 0.05) and LVDd(52.3 ± 9.5 versus 49.2 ± 5.9 mm, P < 0.05) after mitral valve replacement which led to the complete resolution of mitral stenosis or regurgitation. The retraction of the left atrium and left ventricle decreases the pulmonary arterial pressure which further improves the function of the right ventricle.
PAH has been considered a risk factor in patients undergoing mitral valve replacement, with a high operative mortality rates. Najafi et al.  found the degree of PAH is strongly associated with perioperative mortality rate, ranging from 16 % in patients with mild PAH to 61 % in patients with systemic PAH. Several reports had demonstrated an improved outcome of the perioperative mortality rate with the times, from 5.6 % to 12 %, in patients with PAH underwent mitral valve replacement [7–11]. In our study, all patients with mitral valve disease and severe PAH were treated surgically in our hospital with a decreased perioperative mortality of 3.1 %,which was a satisfactory outcome. The improved outcome can be managed through the following respects. First of all, it is very important to improve preoperative cardiac function. All patients admitted to hospital were given cardiotonic, diuretic, vasodilator and oxygen therapy before cardiac surgery in this study. Secondly, selection of suitable type of mitral prosthetic valve is crucial to avoid acute left heart failure. The posterior mitral leaflet and mitral subvalvular apparatus were preserved as much as possible in mitral valve surgery since it is beneficial to maintain normal left ventricular geometry, stabilize and even improve left ventricular systolic and diastolic functions. Incidence of postoperative low cardiac output syndrome can be reduced as well. In this study, there was no significant difference in LVEF(59.2 ± 6.5 versus 57.9 ± 7.6, P = NS). Result of LVEF demonstrated left ventricular systolic function was not impaired by mitral valve replacement. Tricuspid annuloplasty was performed in 28(87.5 %) patients with severe tricuspid regurgitation. This procedure alleviates tricuspid regurgitation, decreases the preload of right ventricle and avoids the occurrence of the right ventricular dysfunction. Thirdly, comparing with left ventricle, right ventricular muscle contraction force is weaker, which means the self-regulation becomes poor when preload or afterload of right heart increase. Therefore, it is crucial to decrease cardiac preload and afterload of right heart through the usage of diuretics and vasodilators. Fluids management should be done under closed hemodynamic monitoring. Fluid restriction must be strictly followed once the hemodynamics became stable after cardiac surgery. Diuretic therapy is a good choice for reducing preload in both preoperative and postoperative period. More attention should be paid on to decreasing afterload of heart after mitral valve replacement in patients with severe PAH. If an inotropic agent is required, phosphodiesterase inhibitor is a better choice (e.g., milrinone) to increase cAMP concentration and improve myocardial contractility and diastolic relaxation. Furthermore, the vasodilator effect of milrinone can reduce afterload and pulmonary arterial pressure . Fourthly, pulmonary arterial pressure decrease significantly after mitral valve replacement with relief of mitral stenosis or regurgitation. However, many factors including pain, anxiety and anoxia are still present which can increase pulmonary arterial pressure after cardiac surgery. Therefore, moderate sedation and analgesia are beneficial to patients. Lastly, postoperative mechanical ventilation is the first step to avoid occurrence of hypoxia. When the tissue becomes hypoxic, pulmonary arteriole starts to constrict and pulmonary arterial pressure increases. Ventilator associated pneumonia(VAP) is one of the most serious but common complication of patients with mechanical ventilator. This will not only prolong the hospital stay but also burden the medical expenses of the patient. The use of noninvasive positive pressure ventilation(NPPV) can shorten the duration of ventilatory support, decrease the incidence of ventilator associated pneumonia and reduce reintubation rates. Furthermore, the application of noninvasive positive pressure ventilation in the patients with respiratory insufficiency can reduce pulmonary interstitial edema, improve lung compliance and supply enough oxygen. In this study, six patients were treated with noninvasive positive pressure ventilation and none of those experienced further need for invasive mechanical ventilation.
Other risk factors for patients undergoing mitral valve surgery include age [10, 13, 14] and left ventricular ejection fraction [15, 16]. In this study, the mean age were 53.1 ± 9.7 years and mean LVEF were 59.2 ± 6.5 %, which contributed to the decreased perioperative mortality of 3.1 %.
Mitral valve repair offers several advantages which include the avoidance of long-term anticoagulation and the preservation of the continuity between the mitral annulus and papillary muscles. Mitral valve repair should be Superior to mitral valve replacement for mitral regurgitation . However, it was rarely performed because of the high rate of repair failure in patients with rheumatic etiologic mitral regurgitation as well as severe subvalvular pathology with heavy calcification of leaflets [18, 19].
NYHA functional status was improved by one class or more in 29(93.5 %) patients and no incidence of death occurred during a mean follow-up period of 26.3 ± 10.7 months (range, 12–45 months).
Limitations of the study
The limitations of our study are the small sample size and short follow-up interval. The small number of subjects limits the statistical power of the study. With regard to the short follow-up period, it cannot demonstrate long-term survival rate and living quality of the patients. Despite these limitations, this study results showed an improved outcome of surgical treatment in patients with severe pulmonary arterial hypertension following mitral valve disease. Surgical management should be encouraged to more cardiac surgeons to appreciate its better effect on those high-risk patients.