What is atrial flutter?
Atrial flutter is a common fast heart rhythm that affects the top chambers of the heart (called the atria). It is due to a single circuit of electrical activity that rapidly travels around a part of one or both of the atria. This has several effects. First, that rapid electrical activity is transmitted to the lower chambers of the heart (called the ventricles), which pump blood to the lungs and the rest of the body, via a structure called the atrioventricular node, or AV node. The AV node generally does not transmit every impulse, and therefore slows the lower chambers’ response to this rapid atrial activity. However, the ventricles, which are responsible for the pulse, will generally beat at a faster rate than usual. The rhythm of the ventricles and the pulse may beat in either a regular or irregular fashion.
Symptoms that result from Atrial Flutter
Due to the loss of the normal contraction of the atria and the fast and sometimes irregular ventricular rate, patients with atrial flutter may feel fatigued, short of breath or faint, or may experience palpitations (heart racing or pounding). Some patients have none of these symptoms. Because atrial flutter episodes may be transient or last for days, weeks or even months at a time, the duration of these symptoms may also vary. Rarely, when a patient does not feel the atrial flutter, but the rhythm results in an abnormally fast ventricular rate over a long period of time, the ventricles may weaken and the patient may develop severe shortness of breath and another condition called congestive heart failure.
Atrial Flutter and Stroke
Because the top chambers of the heart do not move well during rapid activity, blood can stagnate. Whenever blood stagnates, it can form a blood clot. In atrial flutter (as in the closely related rhythm, atrial fibrillation), blood stagnation and blood clot formation most commonly occurs in an outpouching off the left atrium called the left atrial appendage. When a blood clot forms, it can break off and travel to another part of the body (becoming an embolism) and potentially block or occlude blood vessels, therefore reducing or eliminating blood flow to the organ those blood vessels supply. When the occluded blood vessel supplies blood to the brain, a stroke results. Although this is generally the most concerning complication, occlusion of other blood vessels can also cause other problems. For example, if the occluded blood vessel supplies the heart, a heart attack may result.
Atrial Flutter and Atrial Fibrillation
Please see the separate section on atrial fibrillation. Patients with atrial flutter often also have atrial fibrillation, and the two arrhythmias are similar in several ways. In addition, it is important to understand that even if a patient is successfully treated or even “cured” of atrial flutter (such as with ablation as described below), that patient may still be at risk for atrial fibrillation. Atrial flutter is generally more difficult to control with medicines than atrial fibrillation, but ablation is generally simpler and more successful for atrial flutter.
Treatment of Atrial Flutter
- Curative ablation: The most common type of atrial flutter, called typical atrial flutter, is responsible for the great majority of these abnormal heart rhythms. Typical atrial flutter is a circuit around the right atrium; the details of this circuit were first discovered and described by UCSF researchers. Ablation is a straightforward, highly successful, and low-risk procedure that can be employed to cure this rhythm. Ablation involves advancing thin catheters through small incisions in the leg(s) and sometimes the neck, which are then placed into different part of the heart under X-ray guidance. Using those catheters, the exact nature and location of the rhythm can be determined. Using a special catheter that delivers energy, the critical part of the electrical conduction responsible for the fast rhythm is eliminated. For ablation of atrial flutter, the success rate is about 97%.
Atypical flutter can sometimes develop either spontaneously or, more often, when the patient has had previous heart procedures. While the success rate of curing these flutters with ablation is usually not as high as it is for typical flutter, such atypical flutters are generally very amenable to ablation procedures.
- Cardioversion: Cardioversion involves administering medication or an electric shock to the heart to convert the atrial flutter to a normal rhythm. While this can be effective in restoring the normal rhythm, cardioversion does not prevent the abnormal rhythm from returning. Medications may decrease the likelihood that atrial flutter will return. If atrial flutter recurs after cardioversion, options include another cardioversion or catheter ablation.
- Stroke prevention: The formation of clots that result in strokes and other complications can be prevented by using medicines that thin the blood. A variety of such drugs are now available, and the choice of the particular drug depends on the specific characteristics of the particular patient. Because of the known risk of recurrence of atrial flutter after cardioversion, even a successful cardioversion does not negate the need for these blood-thinning drugs. However, after a patient undergoes a successful atrial flutter ablation, blood thinning agents may no longer be needed. Typically, whether a blood thinning drug is needed after a successful ablation depends on whether or not the patient has a history of atrial fibrillation, and the perceived risk of subsequent atrial fibrillation.
Whether a normal rhythm is achieved by ablation or electrical or pharmacologic cardioversion, the transition from being in atrial flutter to normal rhythm can temporarily increase the risk of stroke. There are two ways this can be addressed. These are most relevant to patients who undergo their ablation or cardioversion procedure while in atrial flutter:
- The patient can undergo at least three weeks of blood thinning medical therapy (depending on the drug that is prescribed, this may need to be documented with serial blood tests during those three weeks); or, just prior to the ablation or cardioversion, a patient can undergo a transesophageal echocardiogram. This is a special cardiac imaging procedure in which an ultrasound probe is advanced down the swallowing tube (the esophagus) under sedation, and in this case can be used to rule out the presence of a pre-existing blood clot in the heart.
- Because the transition from atrial flutter to normal rhythm (whether achieved with ablation, electricity or a medicine) can result in a temporary deterioration in atrial function (and therefore a transient higher risk of blood clot formation), blood thinning drugs are generally prescribed for at least one month after these procedures.
- Other medical treatments: Medicines can also play a role in helping atrial flutter patients with their symptoms. Some drugs can slow down the heart rate during atrial flutter. However, the effectiveness of these medicines is often limited, particularly when patients exercise or even walk. In addition, the dose of these drugs can sometimes be limited by the fact that they lower the blood pressure. Other medicines that actually prevent atrial flutter from occurring can also be prescribed. However, each of these medicines has its own potential side effects, with the risk of the drugs varying with a patient’s other diseases and general status of the patient’s heart.
Atrial Flutter Research at UCSF
Previous research at UCSF has been critical in understanding and curing patients with atrial flutter. From the first ablation ever performed to describing the typical atrial flutter circuit itself, UCSF researchers have contributed significantly to advancing the treatment of this disease. More recent research has described new variants of the disease, helping electrophysiologists around the world properly study and treat atrial flutter patients.
As part of the ongoing electrophysiology cohort study, Dr. Gregory Marcus is now collecting blood for DNA in atrial flutter patients. This collection now includes more than 150 patients. This effort has already resulted in several publications in peer-reviewed journals, and will help us understand the basic reasons that patients develop atrial flutter. The data obtained from this effort may also help to identify patients at risk and, by revealing the underlying causes, will be important in developing novel therapies to treat and ultimately even prevent this disease.