After a person has suffered a stroke, identifying the root cause of the stroke becomes an essential part of preventing it from happening again, especially if the stroke was caused by atrial fibrillation (AF). Unfortunately, asymptomatic AF can be difficult to detect by standard methods and some doctors believe it may be an under-recognized cause of cryptogenic stroke (of unknown origin).

Transoma Medical (St. Paul, Minnesota) believes its Sleuth AT implantable cardiac monitoring system may help physicians identify AF in as many as 40% of cryptogenic stroke patients. Studies using external monitors have only found about 10% to 20% of those patients to have AF, Brian Brockway, Transoma's founder and CEO, told Diagnostics & Imaging Week. That's why the company has initiated a long-term study to monitor cryptogenic stroke patients for AF.

The company said that Emile Daoud, MD, an electrophysiologist, performed the first implant in the study Friday at Ohio State University Medical Center (Columbus). Transoma received FDA 510(k) clearance for the Sleuth AT, its next-generation product, in February. According to the company, the Sleuth AT is the only wireless, automated implantable cardiac monitoring system with programmable and frequent electrocardiogram (ECG) sampling.

With long-term continuous monitoring using an implantable device like the Sleuth AF, physicians anticipate that as many as 30% to 40% of cryptogenic stroke patients are going to be diagnosed with AF, Brockway said. He noted that identifying AF as the cause of the stroke is important to the patient's therapy because it means the difference between being prescribed aspirin (if AF is not present) or an anticoagulant like Coumadin (if AF is present).

"With Sleuth AT, we can continuously monitor the patient for AF over a prolonged period to determine if, when and for how long AF is present," Daoud said.

The Long-Term Cardiac Monitoring for Detection of Atrial Fibrillation after Cryptogenic Stroke is a pilot study involving five centers in Canada and the U.S. The investigators driving this study are Daoud and Andrew Krahn, MD, from the London Health Sciences Center at University Hospital (London, Ontario). The primary endpoint of the study is to determine the incidence of AF at one year from Sleuth AT implantation in patients who have had cryptogenic stroke.

According to Transoma, Sleuth AT allows physicians to program the capture of high-quality ECG strips at frequent intervals, providing a new level of insight into complex arrhythmias, which are often asymptomatic and frequently changing. These captured ECG strips are automatically transferred to a 24/7 monitoring center, staffed by certified cardiac technicians, who classify and notify physicians of the presence of a wide variety of cardiac arrhythmias such as ventricular tachycardia, bradycardia, supraventricular tachycardia and AF.

"It will be very interesting to see the results that come out of this study," said Geoff Eubank, MD, a neurologist at Neurological Associates (Columbus, Ohio), who frequently treats cryptogenic stroke patients and partners with Daoud for evaluation of these patients. "Monitoring and diagnostic technology up until now has been limited and sporadic in providing data. I'm hopeful that the long-term, continuous and automated nature of this system will prove more effective in delivering the information we need to effectively treat these patients and prevent future strokes."

If the study reveals what physicians are hypothesizing, Brockway said, it will be important for Transoma because the company expects that the use of implantable monitors like the Sleuth AT will become commonly used to identify AF.

"Having this study underway is a milestone because AF could be the cause of a large number of cryptogenic strokes," Brockway said. "AF is a common cardiac arrhythmia that is challenging to manage. However, we believe Sleuth AT is a unique and superior method for monitoring AF and the effects of current and future therapies."

Stroke without an obvious explanation constitutes 30% to 40% of all ischemic strokes, Transoma said. AF is the most common form of cardiac arrhythmia, and a strong independent risk factor for patients predisposed for stroke, heart failure and all-cause mortality. The incidence of ischemic stroke in patients with AF is 2 to 7 times greater than that of people without AF, the company noted. In an ischemic stroke, blood supply to part of the brain is decreased. This may lead to malfunction of the brain tissue in that area.

"It's a significant market, we estimate that in the U.S. 150,000 to 175,000 patients would be candidates for monitoring who have had a stroke, don't have a PFO, and the cause is unknown," Brockway told MDD.

According to the company, earlier studies have shown that with conventional methods, AF cannot be detected in all cases, and that a prolonged duration of monitoring may be required to effectively manage stroke patients. Due to the asymptomatic and transient nature, paroxysmal (sudden onset) AF detection does not often occur within the bounds of the admission ECG or 24-hour Holter monitoring, Transoma said.

The Sleuth AT cardiac monitoring system includes the implanted monitoring device, the personal diagnostic manager (PDM), the base station and a 24/7 monitoring center operated by Medicomp. Transoma describes the implantable cardiac monitor as a small, thin device, about the size of a 50-cent piece (or the size of the smallest pacemakers), which continuously monitors the electrical activity of the heart, the ECG. The cardiac monitor is implanted under the skin during a brief, simple, outpatient procedure, the company said.

The PDM is a hand-held, multipurpose device that automatically retrieves and stores relevant ECG data from the implanted cardiac monitor, securely relays the information to the base station and then to the monitoring center. The PDM is also used by the physician to program the implanted cardiac monitor, the company noted.

Data are collected in three ways: Patients who experience symptoms, such as lightheadedness, can press a button on the PDM which tells the system to store the patient's ECG strip during the time of the symptom; the system automatically captures and stores the ECG strip when the patient's heart rate is above or below physician-programmed limits; and the system can be programmed to capture regular ECG strips every 4 hours, 15 minutes or 7.5 minutes.

At the third-party monitoring center, certified cardiac technicians review the patient's ECG data and provide information to the physician to aid in diagnosis and ongoing treatment. Physicians can access this information via a secure Web portal, and have the reports faxed or e-mailed to them as they prefer.

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