Risk Stratification in Pulmonary Hypertension: What Low-Risk Disease Looks Like

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.

Two mechanisms operate together. Viral proteins cause stiffness in the lung's interstitial tissue, which physically compresses the pulmonary blood vessels. At the same time, the immunocompromised state associated with HIV promotes smooth muscle hyperplasia within the vessel walls, narrowing the lumen from within. It's the combination of external compression and internal luminal narrowing that drives HIV-associated 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.

Low-risk disease is defined by a specific cluster of criteria: no history of syncope, no progression of symptoms, no signs of right heart failure, a six-minute walk distance greater than 440 metres, a TAPSE greater than 2.3 cm, a stroke volume index greater than 40 mL per square metre of body surface area, and a cardiac index greater than 2.5 litres per minute per square metre.

Patients who meet low-risk criteria have mild, non-life-threatening disease with a good overall prognosis, though this does not mean the disease can be ignored.

Risk stratification directly guides how aggressively treatment should be escalated; low-risk patients can generally proceed in a stepwise fashion starting with standard combination therapy, rather than escalating immediately to the most aggressive options.

Patients with a history of syncope, progressive symptoms, signs of right heart failure, reduced exercise capacity, or worse haemodynamic markers are considered higher risk and require closer monitoring and typically more rapid escalation of therapy.