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Figure 10: Mitral valve anatomy |
The mitral valve functions as a one-way valve between the left atrium and left ventricle of the heart. Blood flows from the lungs into the left atrium and then through the mitral valve into the left ventricle (see Figure 10). As the left ventricle contracts, pumping blood out through the aorta to the rest of the body, the mitral valve closes ... preventing blood from flowing backwards into the left atrium. Damage to the mitral valve can occur from a congenital defect, the natural process of aging, infection, or from a heart attack. This damage will cause the valve to either "leak" resulting in "mitral regurgitation", or to become "restricted" and not open fully, resulting in "mitral stenosis". Damage to the mitral valve interferes with the normal passage of blood through the heart, and ultimately causes blood to back-up into the lungs. This can cause significant respiratory symptoms, and eventually congestive heart failure. It is for this reason, that a damaged mitral valve may eventually need to be either repaired or replaced.
An operation to repair or replace a mitral valve takes 2-3 hours to perform. The damaged valve is either repaired and supported with a "ring" or it is replaced with either a "tissue" or "mechanical" valve (see Figures 11,12,13). Although tissue and mechanical valves function similarly, there are distinct advantages and disadvantages of each. The advantage of mechanical valves, which are made from ceramic, is that they last forever. The disadvantage of mechanical valves is that they require anticoagulation with blood thinners for the remainder of a patient's life.
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| Figure 11: Mitral valve ring |
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Figure 12: Tissue valve |
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Figure 13: Mechanical valve |
The advantage of tissue valves, which are made from cow or pig hearts, is that they do not require formal anticoagulation. The disadvantage of tissue valves, however, is that they generally wear out after 12-15 years, at which time another operation would be required to replace the worn out valve.
The operation itself requires general anesthesia ... the patient is asleep for the entire course of the operation. The surgeon opens the chest by dividing the breast bone or sternum. Tubes and cannulae are inserted into the heart and major blood vessels surrounding the heart in preparation for cardiopulmonary bypass with the heart-lung machine. At this point, blood is redirected from the heart into the heart-lung machine, the heart is stopped, and the aorta is clamped. This permits the surgeon to safely open and operate on the heart without blood pumping through it. The heart-lung machine continues to pump freshly oxygenated blood to the rest of the body, in effect, taking over the roles of the heart and lungs.
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| Figure 14: Exposing the mitral valve |
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The surgeon then opens the heart, usually through the left atrium, and exposes the mitral valve (see Figure 14). If the valve is only partially damaged, it is repaired and the rim or "annulus" of the valve is supported with a "ring" (see Figure 15). If, however, the valve cannot be repaired, it is removed. Non-absorbable sutures with bolsters or "pledgets" are used to sew the new valve into position (see Figure 16). The valve is tested, to ensure that it opens and closes safely, and then the left atrium of the heart is closed. The clamp on the aorta is removed, and all air is evacuated from the heart. As the heart regains its strength, the patient is weaned from the heart-lung machine and the heart and lungs resume their normal functions.
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| Figure 15: Mitral valve ring in place |
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Figure 16: Mechanical mitral valve in place |
Drainage catheters are place around the heart ... these are usually removed after 24 hours. Temporary pacing wires to regulate the patient's heart rate, are sewn to the surface of the heart ... these are removed before the patient goes home. The cannulae are removed from in and around the heart, and the sternum and skin are closed.
Following the operation, patients are transported to the Cardiac Post-Anesthesia Care Unit, a specialized unit caring exclusively for open-heart surgery patients. Patients generally awaken from anesthesia 4-6hr after the operation. The following morning all drainage catheters and monitoring lines are usually removed, and patients are transferred to a standard hospital room in the cardiac recovery wing of the hospital. Patients undergoing an MVR operation are usually hospitalized for 5-7 days following the surgery. To see what to expect during the recovery of this operation, please refer to our education section.
