Identifying pulmonary arterial hypertension (PAH) and distinguishing it from other subtypes of pulmonary hypertension (PH) can be challenging. Diagnostic testing does not always provide definitive results.
The session, Is This Really PAH? My Spidey Sense Is Tingling, at the CHEST Annual Meeting in Honolulu, used a case study to test attendees’ understanding of the diagnostic workup for PAH and explored common challenges in establishing a definitive diagnosis.
Interpreting the right heart catheterization
Francisco J. Soto, MD, MS, FCCP, Associate Professor of Pulmonary, Critical Care, and Sleep Medicine and Director of the Pulmonary Hypertension Program at the University of Tennessee, reviewed various sources of pulmonary arterial catheterization setup errors, best practices for measuring patients’ pressure values, and recommendations for which cardiac output to use for measurements.
The first quality control measure introduced was the importance of zeroing a patient’s transducer.
“When we do the zeroing, essentially what we’re trying to do is remove any extra pressure that the system is detecting,” Dr. Soto explained.
The next step was leveling to identify the zero-reference level for the transducer. Dr. Soto clarified that the appropriate point can be identified by drawing a line through the fourth intercostal space and locating the spot at which it intersects with the midaxillary line to level the readings.
“You have to memorize this: For every 10 centimeters that your transducer is above or below the phlebostatic axis, your pressure is going to change by about 7.5 millimeters of mercury,” he said.
Dr. Soto also highlighted the importance of measuring pressure values at the end of patients’ exhalations. This is when the esophageal pressure gets back to zero. To measure wedge pressures, clinicians must identify the A waveform.
“If there is no A waveform, measure about 130 to 160 milliseconds after the start of the QRS, like somebody who has atrial fibrillation, for example,” Dr. Soto said.
Direct Fick is the gold standard when considering which cardiac output to use for measurements. However, less than 20% of PH centers in the United States use this method. According to Dr. Soto, the next best option is thermodilution.
PAH- or PH-associated ILD?
Arun Jose, MD, MS, Assistant Professor of Medicine at the University of Cincinnati and Director of Pulmonary Hypertension at the Cincinnati VA Medical Center, reviewed the epidemiology of PH in interstitial lung disease (ILD) and interstitial abnormalities in PAH to distinguish one from the other while diagnosing a patient.
According to 2022 European Society of Cardiology/European Respiratory Society guidelines, PH is defined as an elevated mean pulmonary arterial pressure greater than 20 millimeters of mercury, with the addition of precapillary PAH as an elevated pulmonary vascular resistance (PVR) greater than 2 Wood units (WU).
The same guidelines note that PH-ILD can occur in different types of lung diseases, including COPD, emphysema, and ILD. The guidelines distinguish two distinct phenotypes of PH-ILD.
“You have more of a pulmonary phenotype where there is an impairment in pulmonary physiology but not really a whole lot of pulmonary vascular disease, and more of a pulmonary vascular disease predominant phenotype where you have relatively intact spirometry but severe elevation in PVR, in this case, greater than 5 WU, and that’s how they sort of distinguish the two as a spectrum,” Dr. Jose explained.
While analyzing the epidemiology, Dr. Jose shared that PH is not uncommon alongside ILD. Between 8% and 15% of all patients with ILD will also show symptoms of PH. He clarified that while PH is more likely in patients with severe ILD, the severity of PH is not related to the severity of the underlying lung disease.
Dr. Jose asserted that distinguishing the presence of ILD in PAH is not as well-defined as PH-ILD. A UK/Ireland study found considerable abnormalities in CT scans of patients with idiopathic PAH, with up to 7% showing fibrosis in their lungs and 3.5% with both emphysema and fibrosis.
“In this group, they were also older and male-predominant. They were more likely to be exposed to tobacco smoke,” Dr. Jose said, “and, they had worse survival [rates]. They also had lower DLCO, and the two are correlated.”
PAH or PH with left heart disease?
Paresh C. Giri, MD, FCCP, discussed strategies to identify and discriminate PAH vs PH with left heart disease.
Dr. Giri defined three subphenotypes within WHO Group 1 PAH: Classic PAH, the left-heart phenotype, and the cardiopulmonary phenotype. Patients with the classic PAH phenotype tend to be younger women (mean age of 45). Patients with the left-heart phenotype tend to be older women (mean age of 75), while patients with the cardiopulmonary phenotype are predominantly older men (mean age of 72).
“They [patients with left-heart and cardiopulmonary phenotypes] both have precapillary PH by definition, so hemodynamics are insufficient to separate them,” Dr. Giri said.
Due to the absence of established guidelines for distinguishing these phenotypes, when hemodynamics are insufficient to determine a phenotype diagnosis, Dr. Giri asserted that providers must assess comorbidities.
Patients who exhibit the classic PAH phenotype have no comorbidities. Patients with the left-heart and cardiopulmonary phenotypes both carry risk factors for left-heart disease. However, individuals in the cardiopulmonary phenotype have more pulmonary manifestations and higher mortality rates than the left-heart phenotype.
“They recommended monotherapy initially for patients with comorbidities with close assessment and follow-up,” he said. “For [patients with postcapillary PH], PH therapy is not recommended, and for [patients with combined precapillary and postcapillary PH], there are insufficient data to actually make a recommendation.”