What Is Pulmonary Hypertension? The Updated Diagnostic Threshold

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.

Any mean pulmonary artery pressure greater than 20 mmHg, measured by right heart catheterisation, is now classified as pulmonary hypertension, down from the previous threshold of 25 mmHg.

Precapillary pulmonary hypertension has a raised pulmonary vascular resistance and typically arises from lung disease, CTEPH, or obstruction to right ventricular forward flow. Post-capillary pulmonary hypertension does not have raised resistance and results from left-sided heart disease such as mitral stenosis or significant mitral regurgitation.

It is defined by the slope of mean pulmonary artery pressure against cardiac output during exertion, a slope greater than 3 mmHg per litre per minute on exercise.

A normal right ventricular systolic pressure is around 25 mmHg, compared with a normal left ventricular systolic pressure of around 120 mmHg, and a normal mean pulmonary artery pressure of approximately 15 mmHg.

As the catheter passes from the right ventricle into the pulmonary artery, a diastolic lift appears on the pressure trace, reflecting the fact the catheter has entered a structure with its own diastolic back-pressure.