Reducing Stroke in Atrial Fibrillation
By Gregory A. Cogert, MD, FACC, FHRS
WHAT IS ATRIAL FIBRILLATION?
Atrial fibrillation (AF) is the most common heart rhythm problem in America, with over 4 million people who carry the diagnosis of AF and many more yet to be diagnosed. Normally, every beat of the heart is initiated by the upper chamber (atrium) contracting. This atrial impulse sets the heart rate and facilitates the flow of blood in the heart. With atrial fibrillation, there is continuous chaotic electrical activity in the atrium with no atrial contraction and no atrial control of the heart rate. The loss of normal atrial blood flow can result in clotting of blood in the heart. The loss of heart rate control can result in symptoms of fatigue, weakness, loss of exercise tolerance, and potentially a dangerously fast or slow heart rate.
Atrial fibrillation can result in a dramatic reduction in quality of life, physical condition, mental health, and social functioning, as well as cause congestive heart failure, stroke, dementia and death.
WHO IS AT RISK FOR ATRIAL FIBRILLATION?
There is an increasing incidence with age and it is estimated that 25% of adults over 40 will develop AF during their lifetime. In addition to age, common risk factors for AF include high blood pressure, obesity, and obstructive sleep apnea. Patients with any chronic medical problem are also at an increased risk for AF, especially problems of the heart, lungs, kidney, thyroid and diabetes.
HOW IS ATRIAL FIBRILLATION TREATED?
The first step in the treatment of AF is to evaluate the risk of stroke and initiate a treatment plan to minimize that risk. There are 5 classic risk factors for stroke in AF. They are the “CHADS risk factors”
C = Congestive Heart Failure
H= Hypertension
A= Age over 75 years old
D= Diabetes
S= prior Stroke or TIA
The risk for stroke in AF with none of these risk factors is under 2%, whereas, in the presence of all 5, the annual stroke rate approaches 20%. Stroke risk is also increased in women, patients over 65 years old, and the presence of vascular disease.
There are currently four approved anticoagulant medications (blood thinners) used to minimize stroke in AF:
Coumadin (warfarin): Blocks the liver’s production of clotting factors. Warfarin was the only option prior to 2010. Warfarin is a once daily medication that is affordable. An individual’s dose is highly variable and frequent blood tests are required to confirm the correct dosing. Negatives include multiple food and drug interactions resulting in frequent dose changes and blood tests.
Pradaxa (dabigatran): Direct Thrombin Inhibitor. Approved by the FDA in October, 2010. In a large research trial it was found to be superior to warfarin. If kidney function is stable, the dosing is reliable and no blood tests are required. There are significantly less food and drug interactions than with warfarin. It is more expensive and there are less long-term safety data than warfarin. Negatives include the cost, twice daily dosing, and >10% of patients do not tolerate due to stomach irritation.
Xarelto (rivaroxaban): Clotting factor (Xa) inhibitor. Approved for treatment of AF in November, 2011. Similar to dabigatran with stable dosing and minimal food and drug interactions negating the need for frequent blood tests in patients with stable kidney function. Cost is similar to dabigatran. In the large research trial that led to approval, its effectiveness was found to be equivalent to warfarin (as opposed to superiority seen with dabigatran). Advantages include once daily dosing and an improved side effect profile.
Eliquis (apixaban): Clotting factor (Xa) inhibitor. Approved for treatment of AF in December, 2012. Similar to rivaroxaban with stable dosing and minimal food and drug interactions negating the need for frequent blood tests in patients with stable kidney function. In the large research trials that led to approval, its safety and effectiveness was found to be superior to warfarin with a bleeding profile comparable to aspirin. Disadvantages include twice daily dosing.
BLOOD THINNERS FOR EVERYONE?
In all but the lowest risk for stroke patients (CHADS>2), anticoagulant medications have shown clear superiority in reducing the risk for stroke in AF. This conclusion has been validated in long-term research studies of over 100,000 patients. Importantly, the risk for stroke does not follow the quantity of AF a patient has, and even patients who spend the majority of time in normal rhythm warrant the same treatment as those in continuous atrial fibrillation.
There is, however, a subgroup of patients in whom the risk of bleeding conferred by taking blood thinners outweighs their benefits. These are patients who are at a high risk for bleeding, many of whom have had previous life threatening bleeding in the head or have required blood transfusion. In this subgroup of patients who cannot safely take blood thinners, we consider an invasive approach to stroke reduction.
Over 90% of strokes in AF are felt to originate from the left atrial appendage (LAA). For years cardiac surgeons have sought to mitigate stroke risk in patients undergoing cardiac surgery by removing the LAA. The AtriClip was approved in 2010 for surgical closure of the LAA to prevent stroke in AF. Less invasive procedures to exclude the LAA from the circulation without heart surgery are currently being developed.
The best-studied implantable device to occlude the LAA is the Watchman device. The Watchman is a plug inserted from within the heart to occlude the LAA without requiring heart surgery. This device remains under active investigation, but is yet to be approved by the FDA.
Recently the FDA has approved the LARIAT suture delivery device to close the LAA. The LARIAT procedure is performed under general anesthesia. The LARIAT is a pre-tied suture that is delivered from one puncture in the right groin and another below the rib cage. Once the suture is advanced to the base of the LAA, the loop is tightened down permanently, sealing the LAA off from the rest of the heart. Once tied off, the appendage shrivels into scar tissue. A successful LARIAT eliminates the main source of stroke in AF, while avoiding the potentially serious bleeding risks of blood thinners, as well as the need for heart surgery. In the trial that led to its approval, the LARIAT procedure took on average 45 minutes to complete and had a 95% success rate at 3 months of follow up. Although this is a new technology lacking long-term results, surgical research has not found any negative effects from removing the LAA. While the preponderance of research data currently supports taking lifelong blood thinners, the hope is that future studies will show that procedures like LARIAT will eliminate the need for blood thinners.
SUMMARY
Atrial fibrillation is the most common heart rhythm problem in America. In addition to its known associations with decreased quality of life, congestive heart failure, dementia, and death, AF confers a 5x increased risk for stroke. The first step in the management of AF is to minimize stroke risk. This is done primarily by taking one of the four approved blood thinners: Coumadin (warfarin), Pradaxa (dabigatran), Xarelto (rivaroxiban), or Eliquis (apixaban). In patients who are unable to tolerate blood thinners due to bleeding risk, the left atrial appendage is targeted as the culprit for over 90% of stokes in AF. Cardiac surgery and LARIAT suture delivery are the two approved methods to seal off the LAA from the rest of the heart.