Connecting the Cardiac Cousins
The Relationship Between Afib and Heart Failure
It's a "chicken or the egg" conundrum: Does
atrial fibrillation (AFib), a disorder affecting the heart's rhythm, lead to
congestive heart failure (CHF) and vice versa?
"AFib and heart failure have emerged as the new cardiovascular epidemics," says
Elad Anter, MD, a cardiac electrophysiologist at the
CardioVascular Institute at BIDMC. "AFib and heart failure often occur together, and their combination is associated with increased complications and death compared with each disorder alone."
The association between AFib and heart failure is well established: about 25% percent of patients with heart failure also have AFib and this association increases to as much as 50% when the heart failure is severe.
Although researchers do not fully understand the causative relationship between the two conditions, their coexistence can be explained by the risk factors they share, including increased age, hypertension, diabetes, obesity and existing heart disease.
Two Serious Conditions
AFib, the most common abnormal heart rhythm (or cardiac arrhythmia), affects the upper two chambers (or atria) of the heart. Its name comes from the fibrillating or quivering activity of the heart muscle, which replaces the normal, coordinated contraction (also called sinus rhythm). Common symptoms are palpitations, shortness of breath, exercise intolerance and chest pain. The most fearful consequence of AFib is the risk of stroke, which increases because blood can pool and clot in the poorly contracting atria.
Heart failure occurs when the heart becomes too weak to pump enough blood to meet the body's needs. As a result, fluid tends to build up in the lungs and other parts of the body. Although severe heart failure can be life-threatening, in most cases it is a chronic condition that can be treated and managed, and sometimes cured. The most common symptoms are shortness of breath, swelling of the feet and legs, and fatigue.
AFib and Heart Failure
The relationship between AFib and heart failure has been the subject of vibrant research. AFib facilitates the development and progression of heart failure in several ways, according to Anter:
- AFib leads to an increase in the heart rate (the number of beats per minute), in turn shortening the time it takes to fill the heart with blood. This reduces the effectiveness of the heart function. For this reason, a goal for all patients with AFib is to adequately control the heart rate. The optimal rate in patients with AFib is 60 to 80 beats per minute at rest and up to 110 beats per minute during moderate exertion.
- AFib is also associated with a loss of the atria's ability to contract, which means an overall loss of 10 to 15 percent of the heart's ability to pump blood. This is of particular importance in patients with heart failure. Several studies have shown that this effect alone can lead to significant and immediate worsening of the heart failure condition.
- The quivering activity of the atria is associated with an increased metabolic demand on the heart compared with normal rhythm. In other words, the heart requires more energy (calories) to function. Restoration of normal rhythm has been shown to improve the energetic and metabolic state of the heart.
Similarly, heart failure increases the risk of developing AFib in several ways, by:
- stretching heart muscle fibers.
- disrupting calcium levels.
- impacting the autonomic nervous system, which controls basic bodily functions like the heart rate, digestion and breathing.
Treating AFib in Heart Failure Patients
The main reason to treat AFib in patients with heart failure is to control their symptoms and to stop the progression of their heart failure.
"Patients with AFib exhibit a wide variety of clinical symptoms, ranging from none to disabling symptoms," Anter said. "Subtler symptoms such as fatigue, lack of energy and anxiety are common and can remain undetected."
Many patients with so-called "asymptomatic" AFib feel much better after successful conversion to normal rhythm, which can be accomplished with medication or electrical cardioversion. This is a brief and safe outpatient procedure done under sedation. An electrical shock is delivered to the heart through patches placed on the chest.
"I attempt to restore normal sinus rhythm in most patients, even if it is for a short period of time, to determine their true symptoms," he said. "Restoration of sinus rhythm can slow the progression of heart failure, and at times reverse it."
AFib remodels the electrical and mechanical functions of the heart, damaging its structural and molecular integrity. Luckily, these destructive processes and the progression to heart failure can be reversed if AFib is treated early.
The two mainstay strategies for treating AFib are rhythm and rate control therapies. In the rhythm-control strategy, the normal, organized rhythm is restored. In the rate-control strategy, the abnormal AFib rhythm is maintained, but the heart rate is slowed to a safe range. In both strategies, patients take a blood-thinner medication, most commonly warfarin (Coumadin®) or the newer dabigatran (Pradaxa®) to reduce the risk of stroke.
"One of the most exciting and promising therapeutic options for AFib is a curative catheter ablation," says Dr. Anter.
The observation that AFib is initiated by extra beats originating in the pulmonary veins led to the development of catheter-based techniques to isolate the pulmonary veins from the rest of the heart and thus eliminate the source of AFib.
Catheter-based ablation of AFib is currently a widely accepted solution for patients with symptomatic AFib and has been successfully done on tens of thousands of patients in the United States. Catheter ablation of AFib also has been shown to be effective in patients with heart failure.
The non-surgical ablation procedure is done through catheters (long, narrow tubes) that are inserted to the heart through the groin vessels. The ablation is performed by applying a source of energy such as radio frequency to the heart, achieving carefully controlled scarring that blocks the abnormal electrical impulses and reduces or even eliminates arrhythmia.
In a recent analysis of studies comparing catheter ablation with anti-arrhythmic drug therapy for AFib, catheter ablation was associated with a 75 to 80 percent success rate as compared with 25 percent for drug therapy - a track record consistent with experience at the CardioVascular Institute.
Furthermore, Dr. Anter said, "Catheter ablation for AFib has been shown to be effective in patients with heart failure. It is a very appealing therapeutic option for these patients, because they are typically intolerant to the commonly used anti-arrhythmic drugs."
Window of Opportunity
AFib is a dynamic disease, with a well-characterized pattern of progression that can culminate in stroke, heart failure or both.
"The natural history of AFib suggests there is a window in which therapy can yield substantial benefit," says Anter. "Prevention is the best approach, through managing heart failure, hypertension and diabetes. Once AFib occurs, active treatment to restore normal rhythm can halt and even reverse the disease."
Above content provided by the CardioVascular Institute at Beth Israel Deaconess Medical Center. For advice about your medical care, consult your doctor.
Posted December 2011