A bicuspid aortic valve is a congenital heart defect where the aortic valve only has two leaflets instead of the normal three. This abnormal valve can lead to problems later in life, including aortic stenosis, regurgitation, and less commonly, an increased risk of stroke. In this article, we will examine the evidence on whether a bicuspid aortic valve increases stroke risk and the potential mechanisms for how it could contribute to stroke.
What is a bicuspid aortic valve?
During normal fetal development, the aortic valve forms with three leaflets or cusps. A bicuspid aortic valve only has two leaflets instead of three, which occurs in around 1-2% of the population. Some people are born with this abnormality while others develop it later in life. The cause is usually genetic but can also result from calcium deposits on the valve that fuse the leaflets.
A bicuspid valve functions abnormally compared to a normal tricuspid valve. The leaflets are often asymmetrical in size and dome-shaped. This can cause turbulence in blood flow, damage to the valve leaflets, and eventually problems such as:
- Aortic stenosis – narrowing of the valve opening
- Aortic regurgitation – backward leakage of blood through the valve
- Endocarditis – infection of the valve
- Aortic dilation or aneurysm – abnormal enlargement of the aorta
These complications usually develop gradually over decades. However, some people develop severe valve problems at a younger age. Without treatment, these issues can cause chest pain, heart failure, and death.
Does a bicuspid aortic valve increase stroke risk?
There is still some debate over whether a bicuspid aortic valve is an independent risk factor for stroke. Here is what the research says so far:
Population studies
Several large population studies have found an association between bicuspid aortic valves and ischemic stroke, where a blood clot blocks an artery supplying blood to the brain. In a study of over 8000 patients, the stroke risk was 1.3 times higher with a bicuspid valve compared to a normal tricuspid valve.
However, critics argue this could be due to other stroke risk factors in these patients, and not the bicuspid valve itself. The valve abnormalities result in turbulence and damage to the aorta over time, which themselves can increase clotting risk.
Underlying aortic abnormalities
Most experts now think the main stroke risk comes from the underlying problems with the aorta that develop over time with a bicuspid valve:
- Aortic stenosis – narrowing of the valve opening causes turbulence in blood flow. This can damage the lining of the aorta, causing platelet activation and clot formation.
- Aortic aneurysm – ballooning weakens the aortic wall, allowing the formation of blood clots in the dilated area which can dislodge.
- Endocarditis – infection on the abnormal valve can dislodge and travel to the brain, blocking arteries.
One study found the risk of stroke was 8 times higher in patients with both a bicuspid valve and a dilated aorta compared to those with just a bicuspid valve.
Evidence summary
In summary, current evidence suggests:
- People with a bicuspid valve have a slightly higher lifetime risk of ischemic stroke compared to the general population.
- However, the main driver is likely the aortic valve damage and abnormalities of the aorta that develop over time.
- Properly managing these complications may help lower the stroke risk.
How could a bicuspid valve contribute to stroke?
There are several ways in which an abnormal bicuspid valve is thought to potentially increase stroke risk:
Blood clots formed due to abnormal turbulence
Turbulent blood flow through the stenotic bicuspid valve and any dilated portion of aorta can injure the vessel lining. This leads to inflammation, platelets clumping on the area of injury, and formation of blood clots.
Pieces of clot can then break off and travel up the arteries to the brain, blocking blood flow and causing an ischemic stroke.
Dislodged heart valve infection
Endocarditis, an infection on the heart valve surface, occurs more often with a bicuspid valve. Bacteria can stick to the damaged valve area and cause vegetations or clumps of platelets and bacteria.
Parts of this infected tissue can dislodge into the bloodstream and travel to the brain, causing either an embolic stroke or brain abscess.
Atrial fibrillation
Many patients with a bicuspid aortic valve develop atrial fibrillation (Afib), an irregular quivering heartbeat. This allows blood clots to form in the heart chambers which can travel to the brain.
Paradoxical embolism
Some people with a bicuspid valve have an atrial septal defect, a hole between the upper heart chambers. Clots that form in the veins may bypass the lungs and enter the heart to be pumped out to the body and brain.
Who is at highest risk of stroke with a bicuspid valve?
While all patients with a bicuspid valve have a potentially elevated stroke risk, certain groups have the highest odds of having a stroke:
- Older patients – risk increases with age as valve deterioration develops.
- Those with aortic stenosis or regurgitation
- People with aortic dilation or aneurysms
- Patients with an ascending aortic diameter over 4.5 cm
- Individuals with a family history and genetic syndromes like Turner syndrome
- Those with other health conditions like atrial fibrillation, hypertension, diabetes
Adults over 50 with a bicuspid valve, especially those with aortic dilation or valve complications, should have a thorough discussion with their doctor about stroke prevention.
Can treating a bicuspid valve lower stroke risk?
Properly managing valvular and aortic complications from a bicuspid valve may help lower the associated stroke risk. Treatment options include:
Medications
Drugs that treat high blood pressure, high cholesterol, and abnormal heart rhythms may help stabilize the valve area and decrease clot formation. Anticoagulants or blood thinners can prevent clots in those at high risk.
Surgery
Severely stenotic or leaky bicuspid valves that cause symptoms are repaired or replaced with surgery. This helps normalize blood flow and limit damage to the aorta.
A dilated aorta may also need surgical repair to prevent dissection or rupture. This also lowers stroke risk from ascending aortic clots.
TAVR
For those at high surgical risk, transcatheter aortic valve replacement (TAVR) can be done to replace the valve through catheters and without open heart surgery.
Lifestyle changes
Eating healthy, exercising, stopping smoking, and limiting alcohol intake helps stabilize the valve area and lowers other stroke risk factors.
Conclusion
In summary, there appears to be a moderately elevated lifetime stroke risk with a bicuspid aortic valve. However, most experts believe the increased risk is primarily driven by progressive valve dysfunction and aortic abnormalities that develop over someone’s lifetime due to abnormal anatomy.
Carefully monitoring for aortic dilation, valve stenosis and regurgitation, and heart rhythm disorders can help guide treatment to stabilize valve and aortic function. This preventive approach is important for lowering the stroke risk associated with a bicuspid aortic valve.