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Pulmonary Hypertension Update, Part 1: Classification & Diagnosis (Review)
Pulmonary Hypertension Update/Review Part 1 of 2: Classification and Diagnosis
Pulmonary hypertension (PH) is defined simply as a mean pulmonary artery pressure of 25 mmHg or greater. However, this entity encompasses a heterogeneous group of patients and underlying etiologies where accurate diagnosis, correct physiologic classification, and careful evaluation for right heart dysfunction are essential for appropriate management. Clinical guidelines for the diagnosis and treatment of PH have been published in the US and Europe. Exertional lightheadedness (presyncope or syncope) may be a clue to the presence of PH in the dyspneic patient. Other signals may be present on physical exam, EKG, and CXR, especially if there's RV failure. PH is generally initially screened for by echocardiography and confirmed with right heart catheterization. It is estimated that 10-20% of the general population has PH by echocardiography, but the majority of these will be due to left heart disease.
WHO Pulmonary Hypertension Diagnostic Groups: Refresher
Group 1 is pulmonary arterial hypertension. Although it is the group we most commonly think of when discussing PH, it is actually quite rare (15/million overall). The poster child is idiopathic pulmonary arterial hypertension (iPAH), but PAH can be secondary to heritable genetic mutations (e.g. BMPR2), medications/toxins (e.g. anorexigens), portal hypertension, connective tissue disease, infection (e.g. HIV, schistosomiasis), chronic hemolytic anemias, and congenital heart disease (Eisenmenger syndrome). This group, particularly iPAH, has the best evidence for benefit from pulmonary vasodilator therapies. Though survival is improving, mortality is still nearly one in three within 5 years. Group 2 is due to pulmonary venous hypertension (i.e. left heart disease), which is by far the most common cause (an estimated 3-4 million cases in the US). On right heart cath, these patients will have an elevated pulmonary capillary wedge pressure (PCWP), in contrast to the other groups. Group 3 is due to chronic lung disease/hypoxemia. It is estimated that 20% of patients with COPD and previous hospitalization for exacerbation have PH; and up to one-third with ILD have PH. Group 4 is chronic thromboembolic PH. This group comprises 2% or less of the cases of PH overall. Nearly 4% of patients may develop CTEPH after an episode of acute PE. Group 5 is a grab bag of rare diseases that can cause PH. Examples include sarcoidosis, Langerhans cell histiocytosis, lymphangioleiomyomatosis, and compression of the pulmonary vessels.
When PH of any cause is suspected, the best first step is doppler echocardiography to estimate the pulmonary artery systolic pressure (PASP) and to evaluate for right ventricular dysfunction, left heart disease, and intracardiac shunt with agitated saline.
If the PASP is <35-40 AND there is no evidence of RV dysfunction, then other causes for the patient’s symptoms should be considered
If the PASP is >35-40 and/or there is evidence of RV dysfunction AND a common cause is present (left heart disease, high output state, chronic lung disease, sleep apnea, chronic thromboembolic disease), then the suspected common cause should be treated
If the PASP is >35-40 and/or there is evidence of RV dysfunction AND a common cause is not clearly present OR a common cause was treated and symptoms persist/worsen, then the patient should be further evaluated with:
Invasive hemodynamic testing to confirm PH (mean PAP >= 25), categorize as pulmonary arterial hypertension (PCWP< =15 and PVR > 240 dynes/s/cm5; includes groups 1, 3, 4, 5) or pulmonary venous hypertension (PCWP > 15; group 2), and evaluate prognostic variables (right atrial pressure, cardiac output, pulmonary vascular resistance)
Functional testing (most commonly six-minute walk test)
Etiologic evaluation as appropriate: lab tests (e.g. HIV, LFTs, ANA), PFTs, VQ scan, sleep testing
Note on the PASP: It is important to stress that although the echo estimate of PASP is an invaluable tool for evaluating PH, because it is noninvasive and readily available, it is only an estimate and has several limitations that the ordering clinician should consider. Echo PASP correlates well with cath PASP, but large discrepancies in the actual numbers (10-20mmHg or more difference between cath and echo) are common in the clinical setting. These discrepancies may be due to invalid assumptions of the equation used to estimate PASP from the tricuspid regurgitation (TR) jet velocity or poor measurement of the TR jet velocity itself. Echo is further limited by its inability to evaluate pulmonary vascular resistance (PVR) because PASP is often elevated for reasons other than increased PVR including elevated left atrial pressure (left heart diseases), high cardiac output states (anemia, cirrhosis, AV fistulas, hyperthyroidism), and increased systemic systolic blood pressure (especially with chronic kidney disease and heart failure). Read More:
Sanjiv J. Shah. Pulmonary Hypertension. JAMA 2012;308(13):1366-1374.