By Akshay Bhatnagar, MD, Raed Dweik, MD, and Neal F. Chaisson, MD
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Pulmonary arterial hypertension (PAH) is a hemodynamic disorder that affects small and medium-size pulmonary arteries through cellular proliferation and luminal narrowing. Increased pulmonary vascular resistance causes restricted blood flow in these arteries, leading to elevated pulmonary arterial pressure and afterload on the right ventricle. Despite advances in therapy, death usually occurs as a result of right ventricular failure.
However, PAH is neither the only form of pulmonary hypertension nor the most common. Pulmonary hypertension, defined as an elevated pulmonary arterial pressure (≥ 25 mm Hg) on right heart catheterization, has a myriad of causes. The World Health Organization (WHO) classifies pulmonary hypertension into 5 separate groups based on the pathophysiologic mechanism:
- Group 1 — PAH, due to narrowed pulmonary arteries
- Group 2 — due to left heart disease
- Group 3 — due to lung disease or hypoxia, or both
- Group 4 — due to chronic thromboembolism or other pulmonary artery obstruction
- Group 5 — due to uncertain or multifactorial causes
Experts recognize the morbidity and mortality associated with pulmonary hypertension now more than in the past, and they emphasize recognizing it early. Guidelines for its diagnosis and treatment were updated in 2015.
Diagnostic evaluation of suspected pulmonary hypertension
Accurate diagnosis and classification of pulmonary hypertension requires both a high level of suspicion for the disease and appropriate diagnostic testing. The above figure depicts current recommendations for evaluating a patient suspected of having pulmonary hypertension. We use this algorithm to guide proper risk stratification, classification, and invasive testing.
Clinical manifestations of pulmonary hypertension are invariably related to right ventricular dysfunction. As pulmonary arterial pressure and pulmonary vascular resistance increase, the right ventricle initially compensates to preserve cardiac output through up-regulation of sympathetic responses, dilation and myocardial hypertrophy. For this reason, early clinical signs are either absent or nonspecific. Eventually, however, the right ventricle can no longer compensate, and cardiac output declines.
Symptoms and signs. The first symptoms such as exertional dyspnea, fatigue and lightheadedness usually arise in situations that call for increased cardiac output. As right ventricular function worsens, symptoms start to occur at rest, and signs of increased right ventricular preload appear, such as abdominal and lower-extremity edema and pericardial effusion. Syncope is a sign of severe right ventricular dysfunction.
Physical examination. Look for signs of increased right ventricular loading and failure, e.g.:
- An accentuated intensity and persistent splitting of the second heart sound
- A prominent parasternal heave
- A prominent jugular “a” wave
- A systolic murmur along the left sternal border at the fourth intercostal space, which may worsen with breath-holding
- Pitting lower-extremity edema
- Hepatojugular reflux
- Hepatic pulsatility.
Echocardiography in suspected pulmonary hypertension
Since the early signs and symptoms of pulmonary hypertension are often nonspecific, the diagnosis is often delayed, and it is first suspected when transthoracic echocardiography reveals signs of right ventricular dysfunction. Transthoracic echocardiography is relatively inexpensive, noninvasiv, and reproducible, and it can give estimated values of several measures of right ventricular function, size and pressure.
Echocardiographic views of a patient with pulmonary hypertension (left) and a patient without (right). Note the increased right ventricular-left ventricular ratio and right atrial enlargement in the patient with pulmonary hypertension.
Many practitioners rely heavily on the estimated right ventricular systolic pressure in diagnosing pulmonary hypertension. In theory, this number should be nearly the same as the pulmonary arterial systolic pressure. However, technical and patient-related aspects of transthoracic echocardiography often limit accurate measurement of the right ventricular systolic pressure, and readings often differ from those measured with right heart catheterization.
The 2015 European Respiratory Society and European Society of Cardiology guidelines recommend using additional echocardiographic variables to determine the probability that a patient has pulmonary hypertension. While this recommendation is largely based on expert opinion, it supports the notion that right ventricular systolic pressure alone is not enough to determine the probability of pulmonary hypertension. Accordingly, patients with a right ventricular systolic pressure that is significantly elevated (> 50 mm Hg) or moderately elevated (> 40 mm Hg), along with other signs of right ventricular dysfunction (e.g., a dilated right ventricle or atrium, septal flattening), should be considered for additional diagnostic testing.
Future posts will discuss WHO Groups 2-5.
Dr. Bhatnagar is staff in the Department of Regional Anesthesiology. Dr. Dweik is Interim Institute Chair, Respiratory Institute. Dr. Chaisson is staff in the Departments of Critical Care Medicine and Pulmonary Medicine, Respiratory Institute.
This abridged article originally appeared in Cleveland Clinic Journal of Medicine.