Atrial Fibrillaton
Atrial fibrillation (afib) is the most common abnormal heart rhythm affecting more than 2 million Americans. It is characterized by an irregular heartbeat. Complications from afib can include strokes, weakness in the heart muscle, and congestive heart failure.
Normal Heart and Rhythm
Before we describe atrial fibrillation, we should review the normal heart. Basically, the heart is a muscle that functions as two pumps. The body stimulates muscles to contract (squeeze) by sending electrical signals to the muscle. The heart consists of 4 chambers. The two upper chambers, called atria, receive the blood, and the two lower chambers, called ventricles, pump the blood. The left chambers (left atrium and left ventricle) take oxygen rich blood from the lungs and pump it to the body.
The right chambers (right atrium and right ventricle) take blood from the body and pump it to the lungs to get oxygen. In the normal rhythm, the signal begins in the right atrium at the sinoatrial (SA) node. The electrical signal then progresses down though both right and left atria to the atrioventricular (AV) node. The signal then runs down both left and right bundles to stimulate a contraction of the heart. This electrical pathway results in a coordinated contraction with the right and left atria squeezing first followed by the right and left ventricles squeezing. This coordinated rhythm is called normal sinus rhythm (NSR).
When we look at the electrocardiogram (EKG or ECG) we see the electrical signals of the heart. The initial small wave, called P wave, is the electrical impulse causing the atria to contract. The next larger wave is called the QRS complex which is the larger electrical current causing the ventricles to beat. As we see in the EKG there is a small P wave followed quickly by the QRS complex in every beat. The T wave indicates the recovery period of the heart before the next beat.
So, what is atrial fibrillation?
Essentially, afib is a loss of a coordinated rhythm. The electrical activity in the atria is chaotic. Multiple wavelets or macro reentrant circuits circulate throughout the atria. This results in the atria quivering or fibrillating instead of a coordinated and functional contraction. In addition, since the AV node does not get a consistent signal from the SA node, the ventricles contract at irregular intervals and in some instances the ventricles can contract at rates as high 140-180 beat per minute.
The EKG of atrial fibrillation is characterized by an irregular rhythm. No consistent P wave can be found. The QRS complex occurs at random intervals.
What causes atrial fibrillation?
There are actually many causes of afib. Some of these include diseases of the mitral valve (either leakage or blockage); coronary artery disease (blockages in the arteries; hypertension (high blood pressure); and non-cardiac conditions like thyroid disease; certain tumors; low blood sugar; emotional stresses; extreme pain; and infections. Foods containing MSG, caffeine, tobacco, alcohol, and certain illegal drugs can also cause afib. Atrial fibrillation occurring in people 20 years or younger is often hereditary and is called familial atrial fibrillation.
Primary atrial fibrillation or “lone afib” describes a form of afib without a defined cause. Many patients actually fit into this category. About 50% of cases have no definite cause.
For many years afib was thought to be a completely chaotic rhythm with unorganized electrical signal randomly moving throughout the atria. However, work done in the 1980’s showed that there is a definite pattern to the electrical impulses. This eventually led to the development of the Cox-Maze operation. Essentially, Dr. Cox described a series of incisions in the left and right atria, which turn the heart into a “maze”. This forces the electrical signals to go down only one pathway resulting in a regular or normal sinus rhythm.
Research done in France by Dr. Haissaguerre demonstrated that the majority of atrial fibrillation (90%) originates in an area of the left atrium called the pulmonary veins. These are the vessels that return the oxygen rich blood back to the heart from the lungs. Dr Haissaguerre showed that he could treat these “trigger points” and stop afib.
Doctors frequently break atrial fibrillation into 3 classes. Paroxysmal afib occurs intermittently and will convert back to normal sinus rhythm automatically. This usually progresses into persistent afib, which requires a cardioversion (often an electrical shock) to return to sinus rhythm. Finally, the patient cannot be converted to a normal rhythm. This is called permanent or continuous afib.
Who gets afib?
Men suffer from atrial fibrillation more than women. It occurs more frequently the older you get. Ten percent of people over the age of 60 have atrial fibrillation. Athletes get afib more often because of their enlarged heart and increased vagal tone. Tall people like basketball players have an increased incidence of afib.
Atrial fibrillation can occur in 15-30% of patients undergoing heart surgery. In fact a significant number of patients undergoing any major surgery may have episodes of atrial fibrillation. These cases are typically short term in nature, and often will not return after recovery from surgery is complete.
There is a saying: “afib begets afib”. When a person suffers from afib, their heart begins a process of remodeling. In other words, the heart begins to change. The electrical circuits adapt and the atria enlarge. That is why the longer a patient has afib the more likely they will progress to a continuous or permanent afib. Therefore, treatments for atrial fibrillation are more effective the earlier they are begun.
How does atrial fibrillation make you feel?
Afib is associated with a wide range of symptoms. Some people have no awareness of being in afib while others can tell you the precise moments their heartbeat becomes irregular. Symptoms can vary from mild to severe shortness of breath, fatigue, profuse sweating, and chest pain. Often, they will describe their heart as racing or doing flip-flops in their chest (tachycardia and palpitations). People can experience presyncope (dizziness) and syncope (fainting).
In addition to the physical symptoms, patients can suffer from anxiety and depression. The physical and emotional effects of afib typically worsen with time until a point is reached where patients feel incapable of performing everyday tasks. Co-workers, family, health care providers, and even the patients themselves can be unaware of their slowly decreasing functional status, and will sometimes think, “It’s all in their heads”.
Some patients with afib are in and out of the hospital. This can be for several reasons including control of a fast heart rate, evaluation of chest pain, treatment of complications from afib, and treatment for side effects of medicines used to control afib. Complications from afib include strokes, loss of blood flow to arms and legs, loss of blood flow to organs (intestines, kidneys, etc.), and bleeding from blood thinners. The risk of stroke in patients with afib is 5 times higher than for the general population.
Atrial Fibrillation Treatments
There are three primary goals in the treatment of afib.
1) Controlling the heart rate
2) Prevention of blood clots
3) Re-establishment of normal sinus rhythm
There are three categories of treatment for afib.
1) Medical management
2) Catheter based treatment
3) Surgical treatment
Medical Management of Atrial fibrillation
Medical management of afib consists of two schools of thought. The first tries to restore normal sinus rhythm. Medicines such as procainamide (Pronestyl), propafenone (Rhythmol), and amiodarone (Cordarone) are frequently used to terminate afib and maintain normal sinus rhythm. However, a patient’s ability to tolerate these medicines is quite variable. In addition, the effectiveness of these medications vary widely among patients, and their long-term toxicities are also concerning.
The second type of medical management attempts to control the heart rate, and the patient is allowed to remain in atrial fibrillation. The “flip flopping” that patients complain of comes from the rapid rhythm of the ventricles and not the atrium. Therefore, if the ventricular rate can be controlled, the patients often feel better. Also, when the heart beats very fast for a long period of time, it can cause a deterioration of the heart muscle. Medicines such as digoxin, beta-blockers, and calcium channel blockers slow the signals through the AV node and slow the corresponding ventricular rate.
In addition to controlling heart rate and rhythm, medicines called anticoagulants (blood thinners) are also used to prevent the formation of blood clots. When the atria fibrillate, the blood flow becomes sluggish and pools. This can cause blood clots. Usually in the left atrium, the blood clots form in a small out-pouching called the left atrial appendage. Blood clots in the left atrium can result in strokes, renal failure, and loss of limbs. The most common anticoagulant is warfarin (Coumadin), which must be followed very closely. The dosage is highly individualized, and can change dramatically with new medicines and/or changes in diet. Though warfarin reduces the risks of stroke, it does not eliminate it.
Catheter based treatment of atrial fibrillation uses long flexible tube placed in the blood vessels. The Electrophysiologist (EP – cardiology specialist) threads this catheter into the heart. From there, they can use the catheter to burn (ablate) specific areas inside the heart. These burns form scars, which block the electrical signals. With regards to afib, there are two types of treatment; the EP doctor can perform with ablation catheters.
The first type of ablation therapy is ablation of the AV node. Remember from earlier, the electrical signals run down from the atria into the AV node, which then relays the signal into the ventricles. With ablation of the AV node, the heart can no longer beat rapidly. However, this procedure requires the placement of a permanent pacemaker to insure a safe heart rate. Prevention of a fast heart rate often will reduce the symptoms associated with afib. The patient; however, is still in afib and will have to remain on warfarin to reduce their stroke risk.
Second, catheter ablation therapy can be used to isolate the pulmonary veins. Recall that 90% of atrial fibrillation begins in the pulmonary veins. If these veins can be electrically isolated, then afib can be eliminated. Currently, this is a very difficult procedure with many potential complications. These include injury to structures behind and next to the heart; narrowing of the pulmonary veins from scarring; and perforation of the left atrium. In addition because of method used to deliver the ablation energy, the burn may not be full thickness (go through all the layers of the tissue). Failure to ablate full thickness frequently results in continued atrial fibrillation. The cure rate for catheter ablation ranges from 50-70% depending on the type of afib being treated. Even if cured from afib, there is some debate with regards to anticoagulation therapy because the left atrial appendage still has a potential to form clots.
Surgical treatment of atrial fibrillation originated with the Cox-Maze operation. This surgery requires a large incision down the middle of the chest with the breast bone being separated. The heart lung machine is used while the heart is stopped. Several incisions are made in the heart, which create a maze of scar tissue forcing the electrical signals down a specific path.
After surgery, the patient usually stays 1-2 days in the ICU followed by a total of 7-12 days in the hospital. Because the breast bone is broken, the total recovery time is like any other open heart surgery – about 2-3months. The most common complication following the Maze operation is water retention. Other complications are typical for open heart surgery and include bleeding, infection, stroke, and pneumonia.
The operative mortality for the Maze surgery is about 2%. The success rate for the Maze operation is greater than 95%. Also, the atrial appendage is removed as a part of the operation, so the patients can be taken off warfarin following their recovery.
Recently, several hybrid approaches to the treatment of afib have been developed. These hybrid surgeries use different energy sources to ablate the heart tissue, which eliminates the need to create and close the 10-14 incisions needed to perform the classic Cox-Maze operation. This shortens and simplifies the surgery, and in some cases enables the surgeon to perform the operation though tiny incisions. These energy sources include radiofrequency (electricity), microwave, cryotherapy (cold), Laser, and ultrasound. In addition, the radiofrequency (Rf) source can be delivered in a monopolar and bipolar fashion. Basically monopolar electricity can arc and potentially injure structures next to the heart. On the other hand, bipolar electricity only travels between two wires, so structures near the heart are protected.
We have begun performing a new procedure for atrial fibrillation. This has been termed the “Mini-Maze”. It is a minimally invasive approach to the Cox-Maze operation. We use a clamp device to deliver bipolar radiofrequency energy to perform ablations. Atricure (www.atricure.com), a Cincinnati based company developed the device we use. The system consists of a clamp, which is applied to the left atrium near the pulmonary veins to ablate the tissue. Remember, the pulmonary veins account for 90% of the atrial fibrillation. During the surgery, we use special probes, which help us determine if our burns are complete and full thickness. In addition, we can use these probes to test the nervous system input to the heart and then treat the neurogenic forms of atrial fibrillation as well.
The surgery is performed through 3 small port site incisions on both the left and right sides. The incisions range from 1/2 to 3 inches in size. A lighted scope is used to help us see and provide light: much like the way gall bladder surgeries are often performed today. Typically, most patients go home within 2-3 days and their recovery time at home is often 2–3 weeks.
We, also, remove the left atrial appendage during the surgery to further reduce the stroke risk.
After the surgery, we prefer to keep our patients on their afib medicines and blood thinners for 3 months. About 30% of patients will have brief episodes of afib up to 3 months following the surgery as a result of irritation to the heart muscle. Fortunately, 90-95% of patients are successfully treated and can be removed from their blood thinners and rhythm medicines. Many of the remaining 5-10% of patients can be further treated either with catheter ablation in a very limited manner to fine tune the results of the Mini-Maze or continued on a low dose of rhythm medicines.
The treatment of atrial fibrillation is a complex and evolving process. It requires a close interaction between the primary care doctor, cardiologist, electrophysiologist, surgeon, and patient to determine which mode of treatment is the best choice.
Please realize that ANY interventional therapies are relatively new, and although approved by the FDA as being safe, they may not be successful in all patients. Hopefully this has been informational and helpful to you in making a well-informed decision regarding the treatment of your atrial fibrillation. We look forward to meeting personally with you and to answer any specific questions you may have.