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Cardiovascular complications of systemic sclerosis: What to look for

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PULMONARY ARTERIAL HYPERTENSION

Systemic sclerosis can be associated with World Health Organization (WHO) groups 1, 2, 3, and 4 pulmonary hypertension. WHO group 1, called pulmonary arterial hypertension or PAH, is one of the most common cardiac complications of systemic sclerosis, with a reported prevalence as high as 12%.22 Systemic sclerosis-associated PAH carries a high mortality rate, with a mean survival of only 3 years.23

With advances in treatments for other complications of systemic sclerosis, the percentage of systemic sclerosis patients who die of PAH has increased from 6% to 33%.24

Compared with patients with idiopathic PAH, those with systemic sclerosis get less of a response from therapy and have poorer outcomes despite lower mean pulmonary artery pressures and similar reductions in cardiac index. However, recent studies have suggested that with aggressive treatment, patients with systemic sclerosis-related PAH can achieve outcomes similar to those with idiopathic PAH.25 Thus, recognizing this condition early is imperative.

Pulmonary arterial hypertension defined

PAH is defined as the combination of all of the following26:

  • Mean pulmonary artery pressure > 20 mm Hg at rest
  • Normal pulmonary capillary wedge pressure (≤ 15 mm Hg)
  • Pulmonary vascular resistance ≥ 3 Wood units on right heart catheterization.

Other causes of pulmonary hypertension such as interstitial lung disease, chronic pulmonary thromboembolic disease, and left heart disease must be excluded.24,27

Remodeling in the pulmonary arteries

The events that lead to PAH in systemic sclerosis remain unclear but are believed to involve initial inflammation or endothelial injury that leads to a dysequilibrium between proliferative mediators and antiproliferative vasodilators. This dysequilibrium, along with endothelial dysfunction, causes an obliterative vasculopathy in the pulmonary artery branches and arterioles. Sympathetic overactivity, hypoxemia, and ischemia-reperfusion injury additionally promote vascular proliferation, fibrosis, and remodeling, leading to increased pulmonary vascular resistance, PAH, and increased right ventricular pressures.23,27

The subtype of systemic sclerosis is an important factor in the development and progression of PAH. PAH appears to be the major cause of death in limited cutaneous systemic sclerosis, while interstitial lung disease is the major cause of death in diffuse cutaneous systemic sclerosis.28

Pulmonary arterial hypertension is a late complication of systemic sclerosis

Data from the South Australian Scleroderma Registry29 revealed that PAH tends to be a late complication of systemic sclerosis, occurring around 20 years after disease onset. In this study of 608 patients, no patient with diffuse cutaneous systemic sclerosis developed PAH.

Systemic sclerosis-related PAH initially follows an indolent course with few symptoms until right ventricular function deteriorates. Early in the disease, patients may experience nonspecific symptoms of fatigue, lightheadedness, and dyspnea on exertion.23 As it progresses, they tend to have worsening dyspnea and may experience exertional syncope, palpitations, and chest pain.

Physical findings may suggest elevated right ventricular pressure and right ventricular failure; these include a loud P2, a prominent jugular a wave, a tricuspid regurgitant murmur, jugular venous distention, and lower-extremity edema.27

Screening for pulmonary arterial hypertension in systemic sclerosis

Significant signs and symptoms usually occur late in the disease; thus, it is important to appropriately screen patients who are at risk so that they can begin aggressive treatment.

Doppler echocardiography is recommended by European and American guidelines to screen for PAH in patients who have systemic sclerosis, and most agree that screening is appropriate even if the patient has no symptoms.30 European consensus documents recommend that transthoracic echocardiography be done annually for the first 5 years of disease and be continued every year in patients at high risk, ie, those with anticentromere antibodies, anti-Th/To antibodies, or interstitial lung disease. Patients not at high risk of developing pulmonary hypertension should also have regular transthoracic echocardiography, though the exact timing is not defined.31 While American societies have not issued corresponding recommendations, many experts follow the European recommendations.

Worrisome features on echocardiography in asymptomatic patients should be followed up with right heart catheterization to assess mean right ventricular pressure. These include:

  • Estimated right ventricular systolic pressure ≥ 40 mm Hg
  • Tricuspid regurgitant jet velocity > 2.8 m/s
  • Right atrial enlargement > 53 mm
  • Right ventricular enlargement (mid-cavity dimension > 35 mm).32

Although echocardiography is the most common form of screening, it gives only an estimate of right ventricular systolic pressure, which is imprecise. Other noninvasive markers are helpful and necessary to appropriately screen this population.

Diffusion capacity. The Itinerair study33 found that a diffusing capacity for carbon monoxide (DLCO) of 60% or higher has a high specificity in excluding PAH.

Uric acid has been found to be elevated in patients with systemic sclerosis-related PAH, and levels inversely correlate with 6-minute walking distance.34

Other predictors. N-terminal pro-B-type natriuretic peptide (NT-proBNP), left atrial volume, and the right ventricular myocardial performance index have also been shown to be independent predictors of PAH in patients with systemic sclerosis.35

An algorithm. The DETECT study36 enrolled patients at increased risk who had had systemic sclerosis longer than 3 years and a DLCO less than 60%. The investigators developed a 2-step algorithm to determine which patients should be referred for right heart catheterization to try to detect PAH earlier while minimizing the number of missed diagnoses and optimizing the use of invasive diagnostic right heart catheterization.

The first step was to assess serum values of anticentromere antibodies, NT-proBNP, and urate, and clinical features (telangiectasias), forced vital capacity, and electrocardiographic changes of right axis deviation to derive a prediction score. The second step was to assess surface echocardiographic features of the right atrial area and tricuspid regurgitation velocity.

This approach led to right heart catheterization in 62% of patients and was associated with a false-negative rate of 4%. Importantly, of the patients with PAH, 1 in 5 had no symptoms, and 33% had tricuspid regurgitation velocity less than 2.8 m/s. No single measurement performed well in isolation in this study.37

Thus, we recommend that, in addition to routine surface echocardiography, a multimodal approach be used that includes laboratory testing, clinical features, and electrocardiographic findings when screening this high-risk patient population.

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