Ventricular hypertrophy in aortic and pulmonary stenosis
Narrowing (stenosis) of the aortic or pulmonary valve makes the ventricle feeding it generate more pressure, so that ventricle's wall thickens.
Remember
Match the ventricle to the narrowed valve: aortic stenosis thickens the left ventricle, and pulmonary stenosis thickens the right.
The semilunar valves are the half-moon-shaped aortic and pulmonary valves, which guard the exits from the left and right ventricles. In congenital stenosis (narrowing), the valve has not developed normally, so it is narrow from birth.
A narrow valve resists blood leaving the heart. The ventricle just before it, the proximal ventricle, must generate a higher pressure to push blood through. The pressure a ventricle works against is its afterload, so stenosis raises the afterload. Sustained high afterload is called pressure overload.
The muscle responds as any muscle does to a heavier load: it thickens. This change is concentric hypertrophy, in which the wall becomes thicker without the chamber enlarging. Which ventricle thickens depends on the valve: aortic stenosis loads the left ventricle, and pulmonary stenosis loads the right.
In volume overload, as in aortic regurgitation (a leaking aortic valve), the ventricle receives extra blood and the chamber dilates (enlarges) as the wall thickens. This is eccentric hypertrophy. So pressure overload thickens the wall, while volume overload stretches the chamber.
The thickening helps at first, but with time the ventricle can no longer compensate and may fail. So the hypertrophy can lead to heart failure.
Key facts
- Lesion
- a semilunar valve, either the aortic or the pulmonary valve, is narrow from birth.
- Load
- the ventricle just before the narrowed valve must generate a higher pressure, and this sustained pressure load on the ventricle is called pressure overload.
- Response
- concentric hypertrophy, where the wall thickens without enlargement of the chamber.
- Which ventricle
- left for aortic stenosis, right for pulmonary stenosis.
- Pressure versus volume
- pressure overload gives concentric hypertrophy, while volume overload gives eccentric hypertrophy.
- Late effect
- the thick ventricle can eventually fail, so heart failure can follow.
Exam traps
- Eccentric hypertrophy, where the chamber dilates as the wall thickens, is the usual response when the problem is volume overload, such as a leaking valve. A narrowed valve instead places a pressure load on the ventricle, so concentric change is what to expect.
- Thinning of the ventricular wall with enlargement of the chamber can follow late in the disease, when the thickened ventricle can no longer compensate and begins to fail. It is not the early response to a raised afterload, which is thickening.
- A narrowed outflow valve makes the ventricle work harder rather than less, so the wall thickens instead of thinning. Wasting from underuse is the opposite of the response to pressure overload.
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