The article by the group in Toronto concludes that an increase in the ratio of systolic to diastolic intervals in patients with pulmonary arterial hypertension predicts poorer survival. That ratio is determined by heart rate, and tachycardia in basal conditions has long been regarded an indicator of decreased functional capacity. It is not clear whether their method, requiring a Doppler echocardiogram focused on tricuspid regurgitation, is superior to heart rate alone.

A major limitation of their method is that it requires the presence of tricuspid regurgitation, itself an indicator of deterioration. Twenty-four percent of their patients were excluded because they had no tricuspid regurgitation.

The cost/benefit of their method does not support its general application.