Atrial fibrillation (Afib) is the most common heart rhythm
disturbance with about 5.6 million diagnosed cases in the United States. Afib
is a major health problem and a growing epidemic with increased death, stroke
and health care costs associated with it.
Recent studies have advanced our knowledge of the causes of
Afib and have helped direct treatment.
Afib is a rapid, irregular rhythm in the upper chambers of
the heart (the atria). Instead of a
regular, coordinated beat, the atria are rapid and disorganized. When the atria
are not beating in a coordinated fashion, the blood in these chambers does not
drain effectively into the lower chambers of the heart. When blood is not
draining well, it sits in the atria and can form a blood clot. A clot, or a
small part of a clot, can break loose, go to the brain and cause a stroke. Afib is a major cause of stroke. If left
untreated, Afib leads to stroke in 5 out of 100 people per year. To prevent
blood clots and strokes, Coumadin (warfarin) has been prescribed for many
decades. Coumadin will decrease the risk for stroke to less than 1 in 100
patients per year. Coumadin however is difficult to take; requiring frequent
blood draws to ensure that the blood is not “too thin” (leading to bleeding) or
“too thick” (leading to stroke). In addition, eating green leafy foods will
interfere with the level of blood thinning provided by Coumadin (green leafy
foods have Vitamin K which reverses the effect of Coumadin). Many common
medications interfere with Coumadin’s effect as well. Lastly, there is a significant
risk for major bleeding on Coumadin, especially bleeding in the brain. Since 2011, newer blood thinners including
Dabigatran (Pradaxa), Rivaroxaban (Xarelto) and Apixaban (Eliquis) have been
used with increasing frequency. These
newer agents reduce the risk of stroke to a greater degree than Coumadin and
they are generally safer with lower risk for major bleeding and bleeding into
the brain. Other advantages include no dietary restrictions, less interactions
with other medications and a consistent blood thinning effect, so blood drawing
to test levels is not needed. Until recently, one major disadvantage of these
agents had been the lack of an “antidote”, an agent that could reverse the
blood thinning effect if a patient presents with life threatening bleeding or
needed emergency surgery. Fortunately
within the past year, two new reversing medications have been developed, with
one already approved for use. A different approach to preventing blood clots
and strokes is the use of a device called the Watchman, which was recently
approved for use in the U. S. The
Watchman is an umbrella like device that plugs an outpouching in the left
atrium, the left atrial appendage, the most likely source for blood clots. The Watchman is an invasive procedure done in
the heart catheterization lab and may be an alternative for patients who cannot
take blood thinners. Its place in Afib management is evolving as doctors
develop more experience with the device.
Since Afib is a major cause of stroke, can we predict who is
at risk? The risk factors for stroke in Afib patients have been known for a
long time. In 2014, a risk calculator was endorsed by the national guidelines
for Afib. The risk calculator is called CHA2DS2VASc: Congestive heart failure,
Hypertension, Age > 75, Diabetes, Stroke, Vascular disease (ex, heart
attack), Age 65-74 and Sex (female). One
point is assigned for each risk factor except age over 75 and stroke, those
categories are given two points. The
risk for stroke rises with rising risk score (1.3% per year for a score of 1,
2.2% for a score of 2, 4% for a score of
4, etc). In general, blood thinners are
recommended for a score greater than two.
We now know who is at risk for
Afib and how to protect these patients from having a stroke. What about
patients with no history of Afib who present to the hospital with a stroke? There
are several reasons why a patient may have a stroke but even after being
hospitalized and after testing, no cause may be found in 20-30% of stroke
patients. These types of stroke are called cryptogenic, or cause unknown. Afib can cause cryptogenic stroke but
capturing the Afib on a rhythm strip can be difficult. Recently it was shown that long term
monitoring (wearing a heart monitor for one month) increased the ability to
diagnose Afib in cryptogenic stroke patients. Once Afib is diagnosed, blood
thinners can be prescribed and a future stroke prevented.
The management of Afib patients
on Coumadin who need surgery can be a problem. The Coumadin must be held before
surgery, but the proper approach is not known. A recent study looked at two
options: holding Coumadin several days before surgery and exposing the patient
to the risk of a stroke while off the medication or holding Coumadin and
bridging the patient with an injectable blood thinner, holding the injection
12-24 hours before the surgery. The
study found that in low risk patients (those without mechanical heart valves or
a prior stroke) holding the Coumadin and not bridging did not result in an
increase in strokes and was safer with less bleeding during and after the
surgery. These results have greatly
simplified the approach to managing Afib patients who require procedures.
Patients often ask, “What caused
my Afib? What can I do to prevent it from happening again?” Some of the most
exciting new information comes from risk factor modification for Afib. There
are several modifiable risk factors for Afib including hypertension, diabetes,
obesity, sleep apnea, and lack of exercise.
Obesity (body mass index greater than 27 kilograms per meter squared)
can increase the size of the atria and cause scarring in the atria,
predisposing the patient to Afib. In obese Afib patients, it has been shown
that weight loss of 10% of body weight is associated with a six-fold reduction
in Afib. Cardiorespiratory fitness is also a modifiable risk factor. There is a
lower incidence of Afib in patients who regularly perform light to moderate
exercise compared to those who are sedentary.
Afib patients who were entered into a tailored exercise program were
able to dramatically decrease their risk for Afib.
Recent trials, new medications,
devices and risk scores have helped manage the consequences of Afib but the
more we learn about Afib, the more obvious it is that we must treat the risk
factors. If Afib occurs because of hypertension, blood pressure medication
should be given. If Afib occurs due to obesity and low cardiorespiratory
fitness, weight loss and exercise should be prescribed. The best way to prevent
Afib is to identify and treat the underlying causes.
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