Patients with a pulmonary artery pressure/cardiac output slope greater than 3 mm Hg/L/min on cardiopulmonary exercise tests have more than double the risk of cardiovascular hospitalization and all-cause mortality, according to a prospective study of 714 subjects with exertional dyspnea but preserved ejection fractions.
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Colored angiogram (x-ray) of left and right pulmonary arteries in healthy lungs. The common pulmonary artery divides (at center, dark blue) into thick left and right branches.
The findings “suggest that across a wide range of individuals with chronic dyspnea, exercise can unmask abnormal pulmonary vascular responses that in turn bear significant clinical implications. These findings, coupled with a growing body of work ... suggest that reintroduction of an exercise based definition of [pulmonary hypertension (PH)] in PH guidelines” – using the pulmonary artery pressure/cardiac output slope – “merits consideration,” wrote Jennifer Ho, MD, a heart failure and transplantation cardiologist at Massachusetts General Hospital, Boston, and colleagues (J Am Coll Cardiol. 2020 Jan 7;75[1]:17-26. doi: 10.1016/j.jacc.2019.10.048).
A new definition takes hold
The slope captures the steepness of pulmonary artery pressure increase as cardiac output goes up, giving a measure of overall pulmonary resistance. A value above 3 mm Hg/L/min means that pulmonary artery pressure (PAP) is too high for a given cardiac output (CO). The slope “is preferable to using a single absolute cut point value for exercise PAP” to define exercise pulmonary hypertension.“ Indeed, we confirm that in the absence of elevated PAP/CO, an absolute exercise PAP [above] 30 mm Hg” – the definition of exercise-induced pulmonary hypertension in years past – “does not portend worse outcomes,” Dr. Ho and her team noted.
In an accompanying editorial titled, “Exercise Pulmonary Hypertension Is Back,” Marius Hoeper, MD, a senior physician in the department of respiratory medicine at Hannover (Germany) Medical School, explained that the findings likely signal the revival of exercise pulmonary hypertension as a useful clinical concept (J Am Coll Cardiol. 2020 Jan 7;75[1]:27-8. doi: 10.1016/j.jacc.2019.11.010).
The standalone 30 mm Hg cut point was largely abandoned about a decade ago when it was realized that pressures above that mark were “not necessarily abnormal in certain subjects, for instance in athletes or elderly individuals,” he said.
But it’s become clear in recent years, and now confirmed by Dr. Ho and her team, that what matters is not the stand-alone measurement, but it’s relationship to cardiac output. “There is now sufficient evidence to define exercise PH by an abnormal [mean]PAP/CO slope [above] 3 mm Hg/L/min,” Dr. Hoeper said.
Abnormal slopes in over 40%
Each subject in the Massachusetts General study had an average of 10 paired PAP and CO measurements taken by invasive hemodynamic monitoring, including pulmonary artery catheterization via the internal jugular vein, while they road a stationary bicycle. The measurements were used to calculate the PAP/CO slope. A slope greater than 3 mm Hg/L/min was defined as abnormal based on previous research.