Pulmonary Hypertension in Mitral Regurgitation | Ten Points to Remember

Patel H, Desai M, Tuzcu EM, Griffin B, Kapadia S.
J Am Heart Assoc 2014;3:e000748.
The following are 10 points to remember about pulmonary hypertension (PH) in mitral regurgitation (MR):

1. Moderate to severe MR is estimated to be present in 2.5 million people in the United States, and may double by 2030. Several studies have demonstrated the key significance of right ventricular dysfunction in determining the natural history and prognosis of patients with chronic MR and PH associated with elevated pulmonary venous pressure (group 2 PH).

2. Because of its impact on outcome, guidelines (American College of Cardiology/American Heart Association and European Society of Cardiology) for mitral valve (MV) surgery in asymptomatic MR include significant PH defined as a systolic pulmonary artery pressure (sPAP) >50 mm Hg at rest or >60 mm Hg with exercise (Level IIA indication). Preoperative sPAP >30 mm Hg and normal left ventricular ejection fraction (LVEF) are associated with a significant reduction in postoperative LVEF in patients with degenerative MR. sPAP >50 mm Hg is associated with lower postoperative LVEF and worse symptoms after MV surgery; and in studies assessing the perioperative risks in MV surgery, a sPAP >65 mm Hg has the highest sensitivity and specificity for risk of perioperative death.

3. A sPAP >50 mm Hg is present in 23% of patients with severe degenerative MR and complicates the course of patients with functional MR in both systolic and diastolic LV dysfunction. Considering the variable severity of PH in MR, it is likely that there are genetic susceptibility factors, but no evidence that they are related to those seen in inheritable PAH.

4. Severe MR induces compensatory LV and left atrial (LA) dilation in the initial phase, but over time, leads to LV systolic and diastolic dysfunction, reduced LA compliance, and elevated LA pressure in the decompensated phase.

5. Long-standing passive PH resulting from venous congestion can lead to structural changes in the distal pulmonary arterioles and endothelial injury with vascular functional abnormalities, which can result in reactive precapillary pulmonary arterial hypertension (PAH). Sustained elevation of RV afterload causes tricuspid regurgitation, impairment of RV function, and rise in RA pressure. Increase in RAP can exacerbate the heart failure in severe MR by causing renal dysfunction as a result of venous congestion and expansion of intravascular volume leading to a cycle of worsening MR, pulmonary venous congestion, and PH.

6. Echocardiography is the primary tool for evaluating the severity and etiology of MR and estimating sPAP. The Doppler and direct measurement of RV systolic pressure and sPAP lack correlation in the presence of significant tricuspid regurgitation, when the Doppler tricuspid regurgitant velocity envelope is incomplete, and in the presence of significant RV contractile dysfunction.

7. Exercise echocardiography may help identify asymptomatic patients with severe MR and apparently normal resting LVEF in the transitional phase, who would benefit from referral for mitral valve surgery (exercise sPA >60 mm Hg).

8. Invasive measurement of PAPs through right heart catheterization (RHC) is essential to confirm the diagnosis and severity of PH. PH resulting from left heart diseases such as MR is distinguished from PAH by the pulmonary capillary wedge pressure (PCWP) >15 mm Hg. RHC also allows for differentiation of “passive” and “reactive” PH by calculation of transpulmonary gradient (= mPA – PCWP). In passive PH, the transpulmonary gradient is normal (<12 mm Hg), but is elevated (>12 mm Hg) in those with reactive or out-of-proportion PH.

9. Patients with PH resulting from MR were excluded from studies that led to Food and Drug Administration (FDA) approval of drugs that specifically target the pulmonary vasculature. However, recent studies have shown that inhaled prostacyclins and inhaled nitric oxide can be used to reduce mPAP and pulmonary vascular resistance (PVR), and improve cardiac output in patients with PH resulting from MV disease after surgery. Although appearing safe in the postoperative period, careful monitoring of PCWP is necessary during administration to avoid development of pulmonary edema.

10. There is increasing emphasis on referral of patients for MV repair prior to the development of impaired LV function or PH. In the future, LV end-systolic pressure volume loops may be used to assess end-systolic elastance, a powerful load-independent indicator of myocardial contractility.
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