Mitral Valve Disease: Will this Complicate My Pregnancy?

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Virtually any type of heart condition makes pregnancy more complicated. Just how problematic the disease will be for you, whether it will put your life at risk, or whether it should lead you to consider avoiding pregnancy, or terminating a pregnancy, depends on the degree to which the condition combined with pregnancy interferes with your heart function. As pregnancy advances, the cardiovascular system changes as well. The volume of blood increases and to allow such a volume increase, blood vessels widen to decrease the resistance to flow through the blood vessels. Just as there is resistance to the flow of electricity through wires and devices and resistance of the flow of water through pipes, various parts of the cardiovascular system provide resistance to blood flow and that resistance can be changed.

Let’s talk about the mitral valve, a valve that also has two other names: the left atrioventricular valve and the bicuspid valve. If you hear any of these words, they are referring to the same valve, which regulates blood flow from the heart’s left atrium to the left ventricle. Problems can develop in any of the heart’s valves, but the mitral is the valve most often affected in women of childbearing age. Different things can happen with the mitral valve. It can be leaky, on account of prolapse, meaning that the leaflets of the valve balloon back into the atrium, or on account of other processes resulting in the leaflets not coming together completely, as they need to do to keep the blood from moving backward. More common with the mitral valve in women of childbearing age, the valve can be stenotic; mitral stenosis (MS) is narrowing of the valve opening. This can happen as a result of rheumatic fever many years before. Rheumatic fever is a complication of a group A Streptococcus infection (the group of bacteria that causes strep throat among other things), when it is not treated early enough with antibiotics.

Normally, the mitral valve has a wide opening, but stenosis means that the blood will have trouble getting through the valve. Consequently, the left atrium has to pump harder than usual. If the condition deteriorates, pressure then can increase in the lungs and meanwhile not enough blood is pumped from the left atrium to the left ventricle into the body’s systemic circulation, including the circulation to the heart itself, so you can imagine this can become a vicious cycle.

While MS is the more common mitral condition in women of childbearing age, rheumatic fever also can lead to mitral valve prolapse (MVP), although it’s not uncommon to have a MVP simply because of the particular anatomy of your heart. As mentioned above, a prolapsed mitral valve can be leaky, meaning there is a backflow of blood, or regurgitation, when the atrium relaxes. However, regurgitation does not happen in all cases of prolapse, since prolapse means simply that the leaflets are too stretchy an it’s possible for them to balloon into the atrium without leaking.

Since pregnancy puts extra demands on the mother’s cardiovascular system, mitral regurgitation (MR) could develop for the first time, or worsen, as a result of the pregnancy. Similarly, the effects of MS can be exacerbated. MS from rheumatic disease affects 1-2 percent of people in developed countries, but it is much more common in developing countries, accounting for 40–50 percent of the heart disease during pregnancy. This is because rheumatic fever is common in the developing world. On the other hand, due to immigration, mitral disease, including during pregnancy, is on the rise in some cities of developed countries; this makes it the most common kind of heart disease during pregnancy. MVP accounts more than 39 percent of heart disease in pregnancy; just over half of these women also have MR. Meanwhile, MS accounts for nearly 17 percent of heart disease in pregnancy.

So, how do you find out that you have mitral valve disease? The most important tool is echocardiography. Your doctors also will do a medical history and physical examination, blood tests, and an electrocardiogram (ECG), all of which can provide various clues that something is wrong with the mitral valve.

To support the fetus during pregnancy, the cardiac output (the volume of blood pumped by the heart over time) increases by 40-50 percent. During the first trimester, this may not a problem in women with mild to moderate mitral disease, because the decrease in resistance to blood flow causes a blood pressure drop. But the situation starts reversing by the third trimester and blood pressure begins to rise. Together with the increased blood volume, the increasing pressure can challenge a heart that has a mitral valve that is either stenotic or prolapsed. Women with severe MS are, thus, at risk for a variety of complications. These include pulmonary edema (lungs fill with fluid), because the buildup of blood and pressure in the left atrium. Complications also can include arrhythmias (including atrial fibrillation). This can generate what’s called thromboembolism, a clot that travels until it gets stuck somewhere, for instance in the brain. If the latter, a stroke can occur. Arrhythmias also can happen in pregnant women with MVP, if there is a substantial amount of MR (regurgitation). These arrhythmias can be potentially fatal themselves, or they can produce thromboembolism and stroke as in MS, plus MVP carries a slight risk of an infection of the inner layer of the heart. All of this can lead to premature labor and delivery, intrauterine growth retardation (the fetus grows too slowly in the womb, low birth weight, fetal death, and death of the newborn soon after birth. There is some evidence that these problems also can happen in pregnant women with MVP, if the leaflets of the prolapsed mitral valve are deteriorated (what doctors call myxomatous).

In MS, the main strategy is to increase the stroke volume, the amount of blood that is pumped from the heart with each beat. The main way to do this is by increasing the volume of blood that fills the left ventricle prior to each heartbeat, which can be achieved by slowing the heart rate with drugs called beta blockers, or with drugs called calcium channel blockers. Stroke volume increases from the presence of more blood in the ventricle available to be pumped out, but also because stretching of the ventricular muscle actually triggers a stronger contraction. Another medication that increases the strength of the contraction is called digoxin. There also are drugs that are given to open up blood vessels so that the blood can move more easily. One category of such drugs are the angiotension-converting enzyme (ACE) inhibitors, but these must never be taken during pregnancy, because they can damage the fetal kidneys. However, a group of drugs called nitrates can be used more safely to produce the same effect.

These approaches to MS carry over to the treatment of women with MR. In both cases, beta blockers are the most commonly used drugs. To prevent straining the heart with too much fluid as the volume of blood increases over the course of pregnancy, some pregnant women with mitral valve problems also may be given drugs that decrease the amount of water in blood by increasing urination (diuretics). This has to be done extremely carefully, because there is concern that removing fluid with diuretics can reduce the circulation of blood through the placenta that nourishes the fetus. There also is some concern that beta blockers can get through the placenta and into the fetal blood, causing problems for the baby, but each case of mitral valve disease is a complex balance between the benefits and drawbacks of the medication. Generally, cardiologists and obstetricians who specialize in high risk pregnancies are comfortable with beta blockers, and with other drug categories, such as calcium channel blockers.

Pregnant women whose valve condition causes the type of arrhythmia that can produce a thromboembolism cannot be given high doses of warfarin during the first trimester, nor within a few weeks of delivery, but women who need high doses of warfarin often are given low molecular weight heparin (LMWH), or unfractionated heparin (UFH), instead for the parts of pregnancy when they cannot be given high dose warfarin, or sometimes throughout pregnancy. There is actually a debate about how best to manage blood thinning drugs during pregnancy. As for breast feeding, the American Academy of Pediatrics suggests that beta-blockers are safe, but that low doses should be considered until you are finished the breast-feeding period. LMWH enters breast milk only in very tiny amounts and is not harmful because it is degraded in the infant’s digestive system.

If your valve problem is severe, you may be counseled to avoid pregnancy, or to terminate a pregnancy that has begun. However, if you still wish to pursue the pregnancy, the next option is to perform a surgical procedure to improve the function of the valve. However, surgery is complicated to perform on a pregnant woman. There are two general approaches to valve surgery. If the mitral valve is stenotic, but without anything else wrong with it, there is an option called valvoplasty. This means that the valve is literally widened by pushing it open with a balloon that is delivered through special tubing that is inserted through a blood vessel and directed to the heart. The other option is called mitral valve replacement, which means that an artificial valve is inserted to replace the failing valve. This strategy can be used as an alternative to valvoplasty in a valve that is only stenotic, and is the only option when the valve also has other things going wrong, such as regurgitation. When valvoplasty and valve replacement become necessary, it is better to perform the surgery earlier in the pregnancy than later.

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

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