Dissolving Left Atrial Clots in Patients with Mitral Stenosis

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The summary below is from the full report titled "Resolution of Left Atrial Thrombus after 6 Months of Anticoagulation in Candidates for Percutaneous Transvenous Mitral Commissurotomy." It is in the 20 January 2004 issue of Annals of Internal Medicine (volume 140, pages 101-105). The authors are S. Silaruks, B. Thinkhamrop, S. Kiatchoosakun, C. Wongvipaporn, and P. Tatsanavivat.

What is the problem and what is known about it so far?

There are 4 valves that open and close to control the flow of blood into and out of the heart. The mitral valve is the valve that lies between the left atrium and the left ventricle (main pumping chamber of the heart). This valve allows blood to flow into the ventricle and then prevents the back flow of blood into the atrium during ventricular contraction. Mitral stenosis is a condition in which the valve narrows and prevents the flow of blood into the left ventricle. People with mitral stenosis usually have a large, flabby left atrium, and some develop a thrombus (blood clot) in the atrium.

Several surgical procedures can open up narrowed valves. Sometimes surgeons do open-heart surgery and cut open narrowed valves with scalpels. In other cases, doctors insert a balloon catheter into the heart through a patient's veins. They then inflate the balloon to split open the valve. Doctors do this procedure (percutaneous transvenous mitral commissurotomy [PTMC]) in the cardiac catheterization laboratory. They cannot do PTMC if there is a blood clot in the atrium because the catheter may cause parts of the clot to break free and travel to other areas of the body. Although blood-thinning medicines (anticoagulants) help dissolve blood clots, we do not know how often the medicines actually get rid of left atrial clots so that patients can undergo PTMC safely.

Why did the researchers do this particular study?

To see how often anticoagulation dissolves left atrial clots in patients with mitral stenosis.

Who was studied?

219 patients from a university medical center with mitral stenosis and a left atrial clot.

How was the study done?

The researchers recruited patients from a university referral hospital in northeastern Thailand. All patients had symptoms, such as difficulty with breathing, from severe mitral stenosis. The researchers used heart sonograms to identify the patients with a clot in their left atrium. They gave these patients blood thinners (by mouth) for 6 months. They regularly tested patients to make sure that their blood was not "too thin" and to guide appropriate doses of the medicine. After 6 months, patients received sonography again. Those with no evidence of clot on the second sonogram underwent PTMC.

What did the researchers find?

Anticoagulation dissolved the atrial clot in 53 of the 219 patients (24%). All 53 patients subsequently had successful PTMC without adverse events. Eighteen of the 219 patients had minor bleeding during anticoagulation.

What were the limitations of the study?

The study had no control group. We do not know what would have happened to patients who did not receive anticoagulation or who received differing levels of anticoagulation.

What are the implications of the study?

Anticoagulation for 6 months dissolves left atrial clots in some patients with severe mitral stenosis so that they can undergo PTMC.