Reduced RV functional reserve may explain poor SSc-PAH outcomes

By Eleanor McDermid

Patients who develop pulmonary arterial hypertension (PAH) as a consequence of systemic sclerosis (SSc) have poorer right ventricular (RV) functional reserve than those with idiopathic disease, research published in Circulation shows.

In an accompanying editorial, Bradley Maron (Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, USA) describes the finding as "a critical clue that may ultimately resolve the unexplained difference in clinical outcome among SSc-PAH patients relative to other pulmonary vascular disease subgroups".

During atrial pacing, RV contractile function increased with faster heart rate in all study participants, but this response was significantly reduced in the 15 SSc-PAH patients compared with the nine with idiopathic PAH.

In line with the reduced contractile function, intracellular calcium recycling was significantly reduced in the SSc-PAH patients, who had an average recirculation fraction of 32%, compared with 50% in the idiopathic PAH patients.

End-diastolic volume decreased in both groups at faster heart rates, but end-diastolic pressure decreased only in the idiopathic group, ie, heart-rate-dependent RV relaxation was compromised in SSc-PAH patients.

And there was similar evidence of reduced RV functional reserve in the patients during exercise, report Ryan Tedford (Johns Hopkins Medical Institutions, Baltimore, Maryland, USA) and co-researchers. They note that these experiments were conducted at matched submaximal exercise, because idiopathic PAH patients were able to exercise nearly twice as hard and long as the SSc-PAH group.

Arterial elastance, indicating RV afterload, increased during exercise in both groups, whereas end-systolic elastance increased only in the idiopathic PAH patients, indicating an absence of contractile augmentation in the SSc-PAH. Consequently, RV-pulmonary artery coupling was significantly reduced in the SSc-PAH group relative to the idiopathic group.

The lack of contractile augmentation was partly compensated for by increased RV dilation, leading to a slightly reduced ejection fraction.

RV-pulmonary artery coupling at rest correlated with ventilator efficiency, which the team says is "a known correlate of RV functional reserve". They found it was also associated with RV dilatation during exercises, showing a strong correlation with the exercise-induced increase in end-diastolic volume.

In his editorial, Maron suggests that RV-pulmonary artery coupling may prove useful for early risk stratification of SSc-PAH patients.

And he says that, more generally, the findings "expose the importance of rigorous RV physiological assessment for elucidating the clinical profile of cardiopulmonary disease."

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