The right ventricle in pulmonary arterial hypertension

Abstract

Pulmonary arterial hypertension (PAH) is a right heart failure syndrome. In early-stage PAH, the right ventricle tends to remain adapted to afterload with increased contractility and little or no increase in right heart chamber dimensions. However, less than optimal right ventricular (RV)-arterial coupling may already cause a decreased aerobic exercise capacity by limiting maximum cardiac output. In more advanced stages, RV systolic function cannot remain matched to afterload and dilatation of the right heart chamber progressively develops. In addition, diastolic dysfunction occurs due to myocardial fibrosis and sarcomeric stiffening. All these changes lead to limitation of RV flow output, increased right-sided filling pressures and under-filling of the left ventricle, with eventual decrease in systemic blood pressure and altered systolic ventricular interaction. These pathophysiological changes account for exertional dyspnoea and systemic venous congestion typical of PAH. Complete evaluation of RV failure requires echocardiographic or magnetic resonance imaging, and right heart catheterisation measurements. Treatment of RV failure in PAH relies on: decreasing afterload with drugs targeting pulmonary circulation; fluid management to optimise ventricular diastolic interactions; and inotropic interventions to reverse cardiogenic shock. To date, there has been no report of the efficacy of drug treatments that specifically target the right ventricle.

Figure 1.

Right ventricular (RV) pressure–volume loops at decreasing venous return in a patient with a) systemic sclerosis-associated pulmonary arterial hypertension (PAH) and b) idiopathic PAH. The mean pulmonary artery pressure of both patients was similar. The slope of linearised maximum elastance pressure–volume relationship was higher in the patient with IPAH, indicating higher contractility. Note the maximum RV pressure close to the pressure at maximum elastance in both patients. Reproduced from [14] with permission from the publisher.

Figure 2.

The a) volume, b) pressure, c) single-beat and d) diastolic stiffness methods used to estimate right ventricular (RV)–arterial coupling and diastolic stiffness. a, b), Arterial elastance (Ea) is calculated from the ratio of end-systolic pressure (ESP) to stroke volume (SV). a) End-systolic elastance (Ees) as an approximation of maximum elastance is estimated by the ratio of ESP to end systolic volume (ESV), which results in a simplified Ees/Ea of SV/ESV. b) Maximum pressure (P_max) is estimated from the non-linear extrapolation of the early systolic and diastolic portions of the RV pressure curve. Ees is then the ratio of P_max−mPAP/SV, where mPAP is mean pulmonary artery pressure. This results in a simplified Ees/Ea of P_max/ESP−1. c) Ees is calculated as a straight line drawn from the P_max tangent to sRVP–relative change in volume relationship. d) Diastolic stiffness (β) is calculated by fitting the non-linear exponential, P = α(e^Vβ−1), to the pressure and volume measured at the beginning of diastole. Where P is pressure, α is curve fit constant and V is volume. EDV: end diastolic volume; Evol: Ees by the volume method; sRVP: systolic RV pressure; PA: pulmonary artery; BDP: beginning diastolic pressure; EDP: end-diastolic pressure. Reproduced from [17] with permission from the publisher.

Figure 3.

The right ventricle between “a rock and a hard place”, challenged by the pressure overload and the sick lung circulation. The grey circles symbolise cellular and molecular mechanisms. RVF: right ventricular failure. Reproduced from [25] with permission from the publisher.

Figure 4.

A pump function graph demonstrating mean right ventricular pressure as a function of stroke volume (SV). Maximum mean right ventricular pressure is calculated from nonlinear extrapolations of early and late systolic portions of the right ventricular pressure curve. SV is calculated by dividing cardiac output by heart rate. The curve is a parabolic fit of two data points: maximum mean right ventricular pressure and measured mean right ventricular pressure/SV. At high right ventricular pressure, a small decrease in pressure results in a large increase in SV. PVR: pulmonary vascular resistance. Reproduced from [2] with permission from the publisher.

Figure 5.

Pathophysiology of right ventricular (RV) failure. Pulmonary hypertension increases RV afterload requiring a homeometric adaptation, i.e. an increased RV contractility. When this adaptation fails, the RV enlarges with increased end-diastolic volume (EDV), decreasing left ventricle preloading because of competition for space within the pericardium. This decreases stroke volume (SV) and blood pressure, with negative systolic interaction as a cause of further RV–arterial uncoupling, which may be aggravated by RV ischaemia from decreased coronary perfusion pressure (gradient between diastolic blood pressure and right atrial pressure). Obvious targets for interventions are indicated as 1 to 4. See the A global view on RV failure section for further details. iNO: inhaled nitric oxide; iILO: inhaled iloprost; PDE5i: phosphodiesterase type-5 inhibitor; ERA: endothelin receptor antagonist; PGI₂: prostaglandin I₂; FRC: functional residual capacity.