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Monday, February 14, 2011
Atrial fibrillation (AF) is the most common type of sustained irregular heartbeat. It affects approximately 6 million U.S. adults, mainly those ages 65 and older. As the population continues aging, that number is expected to rise to almost 16 million by 2050. This growing prevalence lends increased urgency to the search for additional ways of preventing stroke, the most devastating complication of AF. The Watchman® Left Atrial Appendage (LAA) Closure Technology device may offer a new option for stroke prevention.
The Watchman device permanently plugs the LAA, a small pouch in the heart’s left upper chamber. In people with AF, blood that enters the LAA tends to pool there, and this stagnant blood can form clots. If a clot breaks off and travels to the brain, it may cause an ischemic stroke. About 15 to 20 percent of all ischemic strokes occur in people with AF, and most of those strokes are attributable to clots that originated in the LAA.
The Watchman device is inserted through a minimally invasive catheterization procedure. The Massachusetts General Hospital Heart Center was among the first sites in the United States to offer the Watchman on an investigational basis. Heart Center clinicians are currently involved in research to evaluate the technology’s safety and effectiveness.
Alternative to Warfarin Needed
The current most common treatment for stroke prevention in people with AF is a prescription for warfarin (Coumadin), an oral anticoagulant. However, there are several major drawbacks to warfarin therapy. An increased risk of serious bleeding means that warfarin may be contraindicated for some people, including older adults who are at high risk for falls. In other cases, warfarin may still be prescribed, but the risk of dangerous bleeding means that people may be advised to curtail activities they once enjoyed, such as skiing and other sports in which falls are common.
Another key disadvantage of warfarin is its narrow therapeutic window coupled with wide variability in how individual patients respond to the drug. It takes careful calibration to find the safe and effective dose for a particular patient, and monthly blood draws to monitor blood levels of the drug are required indefinitely. Warfarin also interacts with a number of prescription and over-the-counter medicines, such as antibiotics, salicylates, nonsteroidal anti-inflammatory drugs, beta-adrenergic blockers, diuretics, antidepressants, diabetes agents, and gastric acidity and peptic ulcer agents. Drug-drug interactions can be problematic for older adults, who are often taking multiple medications. In addition, certain foods interfere with how warfarin works, which necessitates some dietary restrictions, such as limiting green leafy vegetables, Brussels sprouts, and broccoli.
Warfarin therapy is contraindicated for a sizable minority of patients with AF. Even when there is no clear contraindication to its use, the drug often is not prescribed. And when it is prescribed, many patients take more or less than the optimal dose. Clearly, there is a pressing need for more options.
The Watchman device, designed to be a nonpharmacological alternative to warfarin, is a new option that researchers are now exploring. If the LAA is blocked off successfully, as it is in the large majority of cases, warfarin can be discontinued. Thus, one potential benefit of the Watchman is removing the side effects and lifestyle restrictions that go along with taking warfarin.
Watchman vs. Warfarin
The Mass General Heart Center is one of 59 sites in the United States and Europe taking part in the trial known as PROTECT AF (Embolic Protection in Patients with Atrial Fibrillation), a randomized study comparing the Watchman device with warfarin. In the first phase of the study, 707 AF patients at risk for stroke were randomly assigned to receive either the Watchman device or warfarin therapy. The results, published in the Lancet in August 2009, showed that the Watchman device was at least as effective as warfarin at preventing stroke.
Most of the serious complications associated with the Watchman device occurred during or soon after LAA closure; 55 percent occurred on the day of the procedure. Moreover, the procedural complication rate with the Watchman has been shown to decrease with experience. By comparison, the risks associated with warfarin are continuous—and so is the need for monthly monitoring and lifestyle restrictions to manage those risks.
Patients in the Watchman group took warfarin for 45 days after the procedure, allowing time for the healing process of tissue regrowth around the device. At the 45-day follow-up, patients were examined with transesophageal echocardiography (TEE), which produces clear ultrasound images of the heart. If TEE demonstrated that the Watchman device was in place and well seated, and if there was a good seal of the LAA, warfarin was discontinued at that time. Eighty-seven percent of the patients were able to stop warfarin at 45 days. If there was still a small gap alongside the device, patients kept taking warfarin and were reexamined at six months. By the six-month follow-up, 92 percent of patients were able to stop taking warfarin.
Longer-term research is needed to determine whether the Watchman device will replace warfarin permanently for these patients. Data from the second phase of the PROTECT AF trial are currently being analyzed, and a third study will soon be under way.
Minimally Invasive Procedure
Massachusetts General Hospital is the only hospital in New England participating in the PROTECT AF trial. The Watchman device is implanted with a catheter-based delivery system via a transseptal approach; that is, by passing a catheter from the right into the left side of the heart. An access sheath and dilator are first advanced into the left atrium over a guide wire, and the access sheath is then further advanced into the LAA over a pigtail catheter. Finally, the Watchman is inserted into the access sheath and carefully guided into position, using TEE and fluoroscopy to verify positioning and stability. Once deployed, the device opens up like a parachute, creating a plug for the LAA.
The LAA closure procedure is performed under general anesthesia. It takes approximately an hour to perform—and the closure time is decreasing as surgical expertise increases. Patients typically stay in the hospital for one night. Walking is generally permitted the same night as the procedure, but heavy lifting is avoided for a week. After a week, most patients can resume their regular activities.
Studies have yet to be performed comparing the cost-effectiveness of the Watchman device with warfarin. Implantation of the Watchman is a one-time investment, while warfarin therapy is a continuous expense. However, any economic analysis would also need to factor in the cost of both treatment options, including medical follow-up and any complications.
In summary, the procedure to insert the investigational Watchman device is minimally invasive. In the first phase of the PROTECT AF trial, the device was as effective as warfarin for preventing stroke in AF patients. If ongoing research continues to bear out these findings, the Watchman may offer a new option for people with AF who are seeking an alternative to the risks of warfarin.
Massachusetts General Hospital Heart Center
The Massachusetts General Hospital Heart Center is a multidisciplinary program that integrates the experts and services of the divisions of Cardiology, Cardiac Surgery, Cardiac Anesthesia, Cardiac Imaging, and Cardiac Nursing to provide state-of-the-art care for patients with all types of cardiac disorders. Continuing its legacy as a pioneer in cardiac research, the Heart Center also conducts bench-to-bedside research aimed at improving the prevention, diagnosis, and treatment of heart disease worldwide.
For more information about the Massachusetts General Hospital Heart Center or to refer a patient, please call 866-MGH-8910 (866-644-8910) or visit the Heart Center website
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