Double and Triple Combination Therapy for Pulmonary Hypertension

The pulmonary valve opens against a high-pressure circuit, so when it closes, it's slammed shut by that elevated pressure — a forceful, rapid closure that produces the loud P2. It isn't the size of the valve that determines the loudness, it's the closing pressure. That's why even in conditions like tetralogy of Fallot, where pulmonary stenosis would normally produce a soft P2, elevated pulmonary arterial pressure from collateral flow can still produce a loud P2 despite the outflow obstruction.

After the first trimester, amlodipine and other calcium channel blockers are reasonably safe. For eclampsia or hypertension specifically during pregnancy, the preferred agent is a direct alpha agonist, such as prazosin.

Any mean pulmonary artery pressure greater than 20 mmHg combined with a pulmonary vascular resistance greater than 2 Wood units should be started on therapy — at minimum, a PDE5 inhibitor plus an endothelin receptor antagonist as double therapy. If the patient remains symptomatic, we add a prostacyclin analog to complete triple therapy. Escalating beyond triple therapy to sotatercept should only be considered after at least six months to a year of adequate triple therapy without sufficient response.

First, PDE5 inhibition, to promote vascular relaxation via the cGMP pathway. Second, soluble guanylate cyclase stimulation, to address back-pressure and encourage vasodilation. Third, endothelin receptor blockade, to retard smooth muscle cell hypertrophy and reduce pulmonary vascular resistance. Sotatercept adds a fourth, distinct pathway — anti-proliferative inhibition of activin signalling — which addresses the underlying vascular remodelling rather than just haemodynamics.

The right ventricle is a volume-handling ventricle, not designed for pressure overload — you can load it with considerable volume and it won't fail, because volume is its domain. But impose a pressure overload, as in pulmonary hypertension, and it hypertrophies to compensate before eventually failing. The left ventricle is a pressure-handling ventricle, built for exactly that load. That's why pulmonary hypertension causes right heart failure long before it affects the left.

Double therapy combines a PDE5 inhibitor, typically tadalafil, with an endothelin receptor antagonist, typically macitentan, both given in the morning during active hours to minimise the risk of hypotension.

A prostacyclin analogue, given orally as selexipag or by inhalation as iloprost, is added if symptoms persist or if the mean pulmonary artery pressure remains elevated despite double therapy.

Triple therapy should be maintained for at least six to twelve months before a clinician concludes a patient is not responding.

Early vasoreactivity, meaning a measurable reduction in pulmonary artery pressure soon after starting double therapy, is a positive sign and predicts a better overall course and outcome.

Escalation to sotatercept should be considered once a patient has been on adequate triple therapy for six months to a year without sufficient response.