What is PAH?

Pulmonary arterial hypertension (PAH) is a syndrome characterised by a progressive increase in pulmonary vascular resistance leading to right ventricular overload and eventually to right ventricular failure and premature death.¹

The increase in pulmonary vascular resistance is related to a number of progressive changes in the pulmonary arterioles, including:

• Vasoconstriction

• obstructive Remodelling of the pulmonary vessel wall through proliferation in the various layers of the blood vessel wall (smooth muscle cell and endothelial cell proliferation)

• Inflammation

• in-situ thrombosis.

The main histological features include medial Hypertrophy, intimal thickening, adventitial thickening, plexiform lesions and in-situ thrombosis (Figure 1). The plexifom lesion represents a focal proliferation of endothelial and smooth muscle cells and is pathognomonic of Pulmonary Arterial Hypertension (PAH).

  Figure 1: Click to enlarge

Pulmonary Arterial Hypertension (PAH) is defined as a sustained elevation of mean pulmonary arterial pressure to more than 25 mmHg at rest or to more than 30 mmHg while exercising, with a normal pulmonary wedge pressure (< 15 mmHg).²

In most cases the earliest symptom is Dyspnoea on physical exertion. Other symptoms include syncope or near syncope, fatigue and peripheral oedema.^3,4 Chest tightness and pain similar to angina may occur, particularly on physical exertion.

References
1. Sitbon O et al. Long-term response to calcium channel blockers in idiopathic pulmonary arterial hypertension. Circulation 2005; 111: 3105-3111
2. Galiè N, Torbicki A, Barst RJ, et al. Guidelines on diagnosis and treatment of pulmonary arterial hypertension. Eur Heart J 2004;25:2243-2278.
3. Gaine SP, Rubin LJ. Primary Pulmonary Hypertension. Lancet 1998; 352: 719−25.
4. Barst RJ et al. Diagnosis and differential assessment of pulmonary arterial hypertension. J Am Coll Cardiol 2004; 43(Suppl S): 40S-47S