Stroke is the fourth leading cause of death in the United States and the leading cause of disability. Fortunately, innovations in technology and medicine are making prevention more attainable than ever before in high-risk patient groups.
AFib & Stroke Risk
Christopher Ellis, MD, cardiac electrophysiologist at Vanderbilt Heart and Vascular Institute, said atrial fibrillation makes patients five times more likely to have a stroke. In AFib, which affects an estimated 3 million Americans, the irregular heartbeat makes it harder for the upper and lower chambers to work together, leading to an increased likelihood that blood will pool and clots will form.
“When it comes to AFib management, the most important thing in my mind is how I can prevent stroke,” said Ellis, who specializes in invasive atrial fibrillation therapies. “A lot of people think if you have a history of AFib but aren’t currently in AFib, you don’t need treatment, but it doesn’t take long for it to flip in and throw a clot. The risk of stroke is the same for patients with intermittent or chronic AFib.”
According to national research, AFib is responsible for approximately 25 percent of all ischemic strokes, and AFib resulting in cardioembolic stroke is associated with a mortality rate of 30 percent at one year.
Stroke Risk Factors
Ellis said the most current risk predictor for stroke is the CHA2DS2-VASc score. A modification to the earlier CHADS2 score, the newer iteration adds three additional risk factors. Patients are assigned points for each risk factor, with a maximum score of 9. Factoring into the equation are Congestive heart failure, Hypertension (consistently above 140/90 mmHG), Age (≥ 75), Diabetes and prior Stroke (or TIA or thromboembolism) plus Vascular disease, Age (65-74) and Sex (gender).
The score is calculated by allotting one point to each item except stroke and age. Prior stroke, TIA or thromboembolism is weighted at two points, and age is either scored at one point from 65-74 or two points at age 75 and above.
Medication & Stroke Prevention
While a score of zero indicates low risk for patients, scoring a single point moves a person into the moderate risk category. For these patients, physicians often prescribe a daily aspirin regimen. A score of two to three could be a medical therapy ring toss, Ellis said, with some physicians opting for aspirin and others a prescription blood thinner.
“Blood thinners like warfarin are proven more effective head-to-head against aspirin but require blood tests and dietary restrictions,” Ellis noted. While warfarin is among the most widely prescribed drugs in the U.S., the anticoagulant also puts patients at increased risk of internal bleeding, mandating frequent monitoring.
However, a new class of blood thinners – novel oral anticoagulants (NOACs) – are promising better results with less complications. The U.S. Food and Drug Administration recently approved three new oral anticoagulants – dabigatran, rivaroxaban and apixaban – for stroke prevention in patients with atrial fibrillation. These new anticoagulants do not require strict and frequent lab monitoring, or dietary restrictions, and incur fewer drug interactions than warfarin. Dosing may be adjusted based on kidney function. Still, lack of a specific reversal agent and clinical data regarding their long-term safety could keep warfarin in the game for years to come.
“There are two ways to get off blood thinners,” Ellis continued. “Your risk for stroke changes, or something bad happens while on blood thinners.”
Bleeding, bone breaks or stroke make some warfarin patients ideal candidates for procedural treatment to lower stroke risk. Two novel procedures, now available at Vanderbilt, focus on closing the left atrial appendage (LAA), to eliminate the risk of bleeding.
“When we find a clot in patients who’ve had a stroke and AFib, it’s almost always in the left atrial appendage,” Ellis explained. “If we can shut the appendage off, we can typically prevent stroke without the bleeding risks associated with blood thinners.”
Anatomy of the LAA holds clues, as well. Cardiologists have identified four consistent shapes of left atrial appendages, and Ellis said identifying structural consistencies in stroke patients could help predict the best candidates for procedural treatment.
LARIAT™ Suture Delivery Device
Ellis was the first … and currently only … cardiologist to use the LARIAT™ Suture Delivery Device at Vanderbilt Heart, and he has seen positive results since debuting the procedure in July.
Performed under general anesthesia, the LARIAT procedure places one catheter under the patient’s rib cage with another guiding it into place. The catheter is sent to the heart's LAA and places and tightens a loop stitch around the base of the appendage, sealing it off from the rest of the heart and blocking clots from traveling to the brain. LARIAT patients typically spend two days in the hospital for follow-up.
AtriCure® AtriClip PRO
A second option available to patients is the AtriCure® AtriClip PRO, offered at Vanderbilt as part of a six-site clinical trial. Working through a small incision, surgeons use a barrette-like device to clamp off the LAA. “First we look at the size and shape of an appendage, and if it’s too big or pointing the wrong way for the LARIAT, we use the AtriClip,” Ellis said. The procedure is more invasive than the LARIAT and typically requires three to four days of hospitalization.
Watchman™ LAA Closure Device
A third option cardiologists hope to see widely available soon is the Watchman™ Left Atrial Appendage Closure Device, now in its final stage of FDA approval. In 2011, Saint Thomas Heart at Baptist Hospital (now Saint Thomas Midtown) became the first hospital in Tennessee to implant the Watchman as part of a clinical trial. The device is introduced into the heart via a catheter through a vein in the upper leg or groin and captures clots that might form in that area of the heart.
“The concept of closing the appendage has been around for many years but was only done during major heart surgery,” Ellis said. “Now it’s a stand-alone procedure with minimally invasive complications.”
Reveal® Insertable Cardiac MonitorAccording to Christopher Conley, MD, cardiologist with Centennial Heart at Skyline, the cause for stroke goes unidentified in 30 percent of patients. He and other cardiologists nationwide are using the Reveal Insertable Cardiac Monitor by Medtronic as part of a stroke workup to help detect irregular heart rhythm. Smaller than a pack of gum, the monitor is inserted just beneath the skin in the upper chest area.
“When someone is hospitalized and no source is found, neurologists are asking for long-term heart rhythm monitoring to try to find undetectable AFib,” Conley explained. “It’s the same technology we’ve used for years to look for other conditions like unexplained fainting but going in a new direction.”