TAPSE/PASP ratio could help prioritize lung transplant referrals
Echocardiographic index lower in PAH patients with transplant
A noninvasive measure of heart and blood vessel function called the TAPSE/PASP ratio could help prioritize people with pulmonary arterial hypertension (PAH) who may benefit most from a lung transplant, according to a new study.
“We demonstrated that the echocardiographic index of TAPSE/PASP … was lower in patients who had undergone [lung transplant] or died during the follow-up period, and was significantly associated with prognosis after referral [for transplant],” the researchers wrote in the study, “The ratio of TAPSE to PASP predicts prognosis in lung transplant candidates with pulmonary arterial hypertension,” which was published in Scientific Reports.
Lung transplants with PAH have become less common with recent treatment advances, but may still be recommended for patients with severe disease who aren’t responding to other treatments. Since there can be so much variation in how PAH progresses among patients, it’s often impossible to identify reliably who would benefit most from a transplant, however.
Scientists at the University of Tokyo Hospital, Japan assessed whether the TAPSE/PASP ratio could help identify the highest risk patients for whom a transplant would be most beneficial.
“There is an unmet need for establishing a straightforward prognostic clinical index for clinical predictions about patients with severe PAH who are deteriorating under [standard] combination therapy,” the researchers wrote.
TAPSE, short for tricuspid annular plane systolic excursion, is a measurement obtained by imaging of the heart (echocardiography) that reflects the health of the right ventricle — the part responsible for pumping blood to the lungs to pick up oxygen.
PASP, or pulmonary arterial systolic pressure, is a measure of the pressure in the pulmonary arteries, the vessels that carry blood from the heart to the lungs. Measuring TAPSE and PASP as a ratio can assess how the heart and pulmonary arteries are working as a system to deliver blood to the lungs, the researchers said.
Measuring TAPSE/PASP as prognostic marker
To evaluate whether the TAPSE/PASP ratio could help prioritize PAH patients for lung transplant, the researchers used data for 34 people with PAH who were referred to their center for a transplant from May 2014 to June 2020. Among them, the mean age was 29 and about three-quarters were female. They were in World Health Organization functional class III or IV (meaning limitations in normal activities or symptoms present even at rest) and had compromised blood flow dynamics despite optimal medical therapy.
The patients were followed for a median of about 2.5 years and during that time eight had a lung transplant. Another eight died of severe respiratory and circulatory failure. The researchers compared the TAPSE/PASP ratio in these patients to the other 18 who were still alive without a transplant at the end of follow-up.
To assess the ratio’s utility as a prognostic marker, the team calculated the area under the receiver operating characteristic curve (AUC), a statistical measure of how well measures like TAPSE/PASP ratio can differentiate between two groups. AUC values range from 0.5 to 1, with higher numbers reflecting a better ability to accurately tell the difference.
The AUC for the TAPSE/PASP ratio was 0.759, notably higher than for TAPSE (0.674) or PASP (0.688) individually. The optimal cutoff for the ratio was 0.30 mm/mmHg, the researchers noted.
“TAPSE/PASP had a highly sensitive and specific predictive value of death or need for LT [lung transplant],” they wrote.
Patients with a TAPSE/PASP ratio of 0.30 mm/mmHg or higher were significantly more likely to be alive without a transplant at the end of follow-up, analyses consistently showed. Estimates suggested that 81.5% of patients with a TAPSE/PASP ratio at or above the cutoff would still be alive without a transplant after three years, compared to just 15.6% with a ratio under the cutoff.
“Patients with TAPSE/PASP [less than] 0.30 mm/mmHg were more likely to undergo [transplant] or die, whereas those with TAPSE/PASP [at or above] 0.30 mm/mmHg had a better [transplant]-free survival even after referral for [transplant] evaluation,” the researchers wrote, noting their analysis was limited by the small number of patients, which underscored the need for more research to validate their findings.
They called for “further investigation on larger cohorts … to confirm whether TAPSE/PASP can … add a practical value in stratifying patients with severe PAH referred for [lung transplant] evaluation.”