Pulmonic Stenosis

What is Pulmonic Stenosis ?

Pulmonic stenosis (PS) is a congenital (present from birth) condition that results in obstruction of flow from the right ventricle out to the pulmonary artery. The most common form of pulmonic stenosis is valvular pulmonic stenosis, and is the most amenable to correction. Valvular PS is a congenital defect whereby the pulmonic valve leaflets open incompletely in the contraction phase (systole) of the cardiac cycle. Supravalvular PS is when there is a ring or ridge of issue above the pulmonic valve causing obstruction of outflow while subvalvular PS refers to obstruction below the pulmonic valve. The rest of this discussion will focus on valvular PS but the pathophysiology is the same for all three types.

Dogs with PS have partial fusion of the valve leaflets that causes an acceleration of blood flow as it crosses the valve, forcing the right ventricle to pump harder to push blood through the valve. The abnormal blood flow is what causes the heart murmur that was ausculted by your veterinarian. Because the outflow tract is abnormally narrowed, the pressure the right ventricle must overcome in order to pump blood into the pulmonary artery is elevated. This change in pressure is termed the pressure gradient and the degree of elevation of the pressure gradient is how PS is classified. Like any muscle, the right ventricular muscle thickens and enlarges because it has to work harder to overcome the increase in pressure.