Background
Pulmonary hypertension (PH) is divided into five distinct groups, which are categorized according to similar pathophysiologic changes, clinical presentation, and available therapies. Pulmonary hypertension due to left-sided heart disease (PH-LHD), classified by the World Health Organization (WHO) into group 2 pulmonary hypertension, is the most common cause of pulmonary hypertension and is associated with impaired exercise capacity and reduced survival. [1] It is defined by a mean pulmonary arterial pressure (mPAP) greater than 20 mm Hg and pulmonary capillary wedge pressure (PCWP) greater than 15 mm Hg. [2]
PH-LHD is further categorized by the underlying etiology, including due to systolic dysfunction, diastolic dysfunction, valvular defects, congenital or acquired left-sided heart inflow/outflow tract obstruction, and congenital cardiomyopathies. The pathophysiology is complex and features both a passive and an active mechanism of changes to the pulmonary vasculature.
Pathophysiology
Pulmonary hypertension due to left-sided heart disease (PH-LHD) results from pulmonary venous stretching due to elevated upstream left-sided heart filling pressures. As a result, the right ventricular systolic pressure increases in order to maintain adequate cardiac output.
The term isolated postcapillary pulmonary hypertension (Ipc-PH, formerly called “passive”) is used to describe those patients whose pulmonary hypertension is merely due to passive pulmonary venous congestion. [3] A minority of PH-LHD patients subject to longstanding elevated left-sided heart filling pressures undergo structural and functional pathophysiologic changes in the precapillary vasculature, including remodeling and vasoconstriction resulting in mean pulmonary arterial pressure (mPAP) disproportionately elevated relative to the pulmonary capillary wedge pressure (PCWP). Such patients are described as having combined postcapillary and precapillary pulmonary hypertension (Cpc-PH, formerly called “reactive” or “out of proportion”). [4]
Unlike certain other causes of pulmonary hypertension, particularly WHO group I, which tends to demonstrate more intimal proliferation and plexiform lesions, the pulmonary vasculature of PH-LHD shows greater intimal fibrosis and myofibroblast proliferation. [5] Specifically, the precapillary vasculature of Cpc-PH patients has been noted to have increased capillary endothelial basement membrane thickness, which subsequently leads to narrowing of the pulmonary arteriolar lumen, further worsening pulmonary vascular resistance. Pressure elevation in the pulmonary vessels along with changes in the endothelium result in the release of growth factors that increase elastin production, causing smooth muscle hypertrophy and stiffening of the pulmonary vessel. [6]
Epidemiology
There are approximately 6.5 million people in Europe and 5 million people in the United States with heart failure. [7] About 60% of patients with heart failure with reduced ejection fraction (HFrEF) have been noted to have pulmonary hypertension at presentation. The prevalence of pulmonary hypertension due to diastolic dysfunction is not known. [8]
Prognosis
The development of pulmonary hypertension due to left-sided heart disease (PH-LHD) is associated with a poor prognosis, particularly in relation to patients with LHD without associated development of pulmonary hypertension. Patients with heart failure with reduced ejection fraction (HFrEF) and pulmonary hypertension have a higher mortality rate (28%) than those without pulmonary hypertension (17%) at 28 months. [9, 10] The prognosis for patients with pulmonary hypertension and heart failure with preserved ejection fraction (HFpEF) has not been well studied.
Since patients with combined postcapillary and precapillary pulmonary hypertension (Cpc-PH) have higher pulmonary pressures compared with isolated postcapillary pulmonary hypertension (Ipc-PH) patients, they generally have increased dyspnea, lower exercise tolerance, and shorter survival. [11]
Patient Education
Patients should be educated about the expected symptoms of pulmonary hypertension due to left-sided heart disease (PH-LHD) as well as the importance of strict medication and diet adherence in order to avoid worsening symptoms or hospitalization. Additionally, patients should be encouraged to monitor their weight and fluid intake at daily intervals.
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Chest radiograph of a patient with pulmonary hypertension due to left-sided heart disease from heart failure with reduced ejection fraction showing enlarged pulmonary arteries, mild pulmonary vascular congestion, and dilated right atrium and left atrium.
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Transthoracic echocardiograph showing an apical four-chamber view of the same patient with pulmonary hypertension due to heart failure with reduced ejection fraction. The right atrium and ventricle are notably dilated.
