Aortic Valve Stenosis

Aortic Valve Stenosis: Definition

Aortic valve stenosis (AS) is a heart condition caused by the incomplete opening of the aortic valve.

The aortic valve controls the direction of blood flow from the left ventricle to the aorta. When in good working order, the aortic valve does not impede the flow of blood between these two spaces. Under some circumstances, the aortic valve becomes narrower than normal, impeding the flow of blood. This is known as aortic valve stenosis, or aortic stenosis, often abbreviated as AS.

Simultaneous left ventricular and aortic pressure tracings demonstrate a pressure gradient between the left ventricle and aorta, suggesting aortic stenosis. The left ventricle generates higher pressures than what is transmitted to the aorta. When the aortic valve becomes stenotic (blocked), it causes a pressure gradient between the left ventricle (LV) and the aorta. The more constricted the valve, the higher the gradient between the LV and the aorta. For instance, with a mild AS, the gradient may be 20 mmHg. This means that, at peak systole, while the LV may generate a pressure of 140 mmHg, the pressure that is transmitted to the aorta will only be 120 mmHg. So, while a blood pressure cuff may measure a normal systolic blood pressure, the actual pressure generated by the LV would be considerably higher.

In individuals with aortic valve stenosis, the left ventricle (LV) has to generate an increased pressure in order to overcome the increased afterload caused by the stenotic aortic valve and eject blood out of the LV. The more severe the aortic stenosis, the higher the gradient is between the left ventricular systolic pressures and the aortic systolic pressures. Due to the increased pressures generated by the left ventricle, the myocardium (muscle) of the LV undergoes hypertrophy (increase in muscle mass). This is seen as thickening of the walls of the LV. The type of hypertrophy most commonly seen in aortic valve stenosis is concentric hypertrophy, meaning that all the walls of the LV are (approximately) equally thickened.

Aortic Valve Stenosis: Causes

Causes of aortic valve stenosis include acute rheumatic fever, bicuspid aortic valve and congenital anomalies. As individuals age, calcification of the aortic valves may occur and result in stenosis.

Aortic Valve Stenosis: Diagnosis

It is most often diagnosed when it is asymptomatic. It is found on routine examination of the heart. A fairly loud systolic, crescendo-decrescendo murmur is heard loudest at the upper right sternal border, and radiates to the carotid arteries. The murmur increases with squatting, decreases with standing and isometric muscular contraction, which helps distinguish it from hypertrophic obstructive cardiomyopathy (HOCM). Respiration has no effect on the loudness of the murmur. The more severe the degree of the stenosis, the later the peak occurs in the crescendo-decrescendo of the murmur. Due to increases in left ventricular pressure from the stenotic aortic valve, over time the ventricle may hypertrophy, resulting in a diastolic dysfunction. As a result, one may hear a 4th heart sound due to the stiff ventricle. With continued increases in ventricular pressure, dilatation of the ventricle will occur, and a 3rd heart sound may be manifest.

Aortic Valve Stenosis: Associated Symptoms

When symptomatic, aortic valve stenosis can cause syncope, angina and congestive heart failure. More symptoms indicate a worse prognosis.

Aortic Valve Stenosis: Congestive Heart Failure

Congestive heart failure (CHF) is a grave prognosis in patients with aortic valve stenosis. Patients with CHF that is attributed to aortic valve stenosis have a 2 year mortality rate of 50%, if the aortic valve is not replaced.

Congestive heart failure (CHF) in the setting of AS is due to a combination of systolic dysfunction (a decrease in the ejection fraction) and diastolic dysfunction (elevated filling pressure of the LV).

Aortic Valve Stenosis: Syncope

Syncope in the setting of heart failure increases the risk of death. In patients with syncope, the 3 year mortality rate is 50%, if the aortic valve is not replaced.

While it is unclear why aortic valve stenosis would cause syncope, the most popular theory is that severe aortic valve stenosis produces a nearly fixed cardiac output. When the patient exercises, their peripheral vascular resistance will decrease as the blood vesels of the skeletal muscles dilate to allow the muscles to receive more blood to allow them to do more work. This decrease in peripheral vascular resistance is normally compensated for by an increase in the cardiac output. Since patients with severe aortic valve stenosis cannot increase their cardiac output, the blood pressure falls and the patient will syncopize due to decreased blood perfusion to the brain.

A second theory as to why syncope may occur in aortic valve stenosis is that during exercise, the high pressures generated in the hypertrophied LV causes a vasodepressor response, which causes a secondary peripheral vasodilatation that will then cause decreased perfusion to the brain.

Aortic Valve Stenosis: Angina

Angina in the setting of heart failure also increases the risk of death. In patients with angina, the 5 year mortality rate is 50%, if the aortic valve is not replaced.

Angina in the setting of aortic valve stenosis is secondary to the left ventricular hypertrophy (LVH) that is caused by the constant production of increased pressure required to overcome the pressure gradient caused by the aortic valve stenosis. While the myocardium of the LV gets thicker, the arteries that supply the muscle does not get significantly longer or bigger, so the muscle may become ischemic. The ischemia may first be evident during exercise, when the muscle requires increased blood supply to compensate for the increased workload. The individual may complain of exertional angina. At this stage, a stress test with imaging may be suggestive of ischemia.

Eventually, however, the muscle will require more blood supply at rest than can be supplied by the coronary artery branches. At this point there may be signs of ventricular strain pattern on the EKG, suggesting subendocardial ischemia. The subendocardium is the region that becomes ischemic because it is the most distant from the epicardial coronary arteries.

Aortic Valve Stenosis: Associated Conditions

In Heyde's syndrome, aortic valve stenosis is associated with angiodysplasia of the colon. Recent research has shown that the aortic valve stenosis causes a form of von Willebrand disease by breaking down its associated coagulation factor (factor VIII-associated antigen, also called von Willebrand factor), due to increased turbulence around the stenosed valve.

Aortic Valve Stenosis: Treatment

Treatment requires replacement of the diseased valve with either a porcine aortic valve or a cadaveric aortic valve, or an prosthetic aortic valve.