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Atrial fibrillation.

March 30, 2013

Continuing my series on dysrhythmias, today I will discuss atrial fibrillation and atrial flutter (AF).  These conditions exist when electrical impulses originate in places other than the sinoatrial (SA) node, such as in the pulmonary veins or other foci in the atria, Heart-Electrical-Systemcausing irregular contraction of the atria.  The National Heart, Lung, and Blood Institute has a good webpage describing atrial fibrillation in detail, including a great animation at the bottom of the page.

According to the Centers for Disease Control and Prevention (CDC), atrial fibrillation is the most common arrhythmia, affecting 2.66 million people as of 2010.  Incidence rises with age, so the older you get the more likely you are to experience this arrhythmia.  AF occurs more often in white people than African-Americans.  The risk factors for AF include  uncontrolled high blood pressure, heart failure and other heart disease, diabetes, hyperthyroidism, and advancing age.

Symptoms of atrial fibrillation include palpitations, shortness of breath, chest pain, and fatigue or weakness.  How symptomatic a person will be depends on how many of the aberrant impulses are transmitted from the atria to the ventricles.  If many of the signals are transmitted through the AV node to the ventricles, the heart rate may rise into the 150’s or higher.  This is called atrial fibrillation with rapid ventricular response (A Fib with RVR).  Patients having rapid ventricular response typically have chest pain, shortness of breath, and other symptoms of poor perfusion such as dizziness and fainting.  This is a medical emergency which must be treated at a hospital.  Some people have slower conduction through the AV node, keeping the overall heart rate below 100 beats per minute.  This situation is not as dangerous, but still merits expeditious treatment.

Cardioversion, putting the heart back into a normal sinus rhythm with either medication or defibrillation, is usually the goal of treatment.  Much depends on how long the patient has been in A Fib.  When the atria do not contract as they are supposed to, clots imagescan form in the left atrium, especially in the left atrial appendage.  This is an outpouching of the left atrium (LA) that forms a natural little corner that anything sticky can collect in.  The danger of clot formation in the LA is that pieces of clot may break off and be pumped with the blood into the left ventricle and then into the systemic circulation.  The biggest risk is that these emboli will end up lodging in one of the arteries of the brain, causing a stroke.  Cardioverting a patient who has significant mural thrombus (clot along the wall of the atrium) may cause catastrophic stroke as the clot is suddenly squeezed and breaks off.  To prevent this, doctors often perform a transesophageal echocardiogram (TEE) prior to cardioversion.  TEE is an ultrasound of the heart performed with an ultrasound probe placed in the esophagus.  Patients must be sedated for this procedure, otherwise the probe would never get past the gag reflex.  If significant clot is seen, then the patient is started on anticoagulant drugs that will be continued after going home for several weeks before cardioversion is attempted.  Heart rate will be controlled with medication in the meantime.  This gives time for the clot to dissolve and the anticoagulants prevent new clot from forming.  If there is not clot in the atrium, then cardioversion will be attempted at once.  If the patient has not already converted spontaneously with the medications given in the hospital, electrical shock will be used.  Again, for this procedure the patient is sedated and given pain medication.  Defibrillator pads are applied to the chest and electrical current is applied (shock) to reset the heart’s rhythm.  After a successful cardioversion, the patient is generally sent home on an antiarrhythmic drug to prevent recurrence.  If unsuccessful, anticoagulant drugs are started, usually Coumadin (warfarin) by mouth and heparin in shots or IV until Coumadin reaches a therapeutic level.  This takes several days.  Sometimes patients go home before reaching theraputic levels and need to continue injecting heparin at home for a few more days.

So, I’ve been talking about A Fib for a while here.  Atrial flutter (A flutter or AF) is similar to A Fib in that the atria are not beating properly.  In flutter, there is a rapid atrial rate but the firing of the cells in the atria are still coordinated with each other.  Thus there is still the regular squeeze of the beats rather than the quivering seen in A Fib.  The atrial beats are transmitted through the AV node to the ventricles at a ratio of 2:1, 3:1, or 4:1.images-1Treatment of atrial flutter is essentially the same as for atrial fibrillation.  Often a patient will switch back and forth between these patterns, hence the term A Fib/Flutter.

A patient who has had one episode of A Fib or Flutter is likely to have another episode sometime during their life.  Often these recurrences are asymptomatic.  You should see a doctor regularly to monitor your condition.  These recurrences may be prevented or controlled with medications.  In patients with frequent recurrences, ablation may be an option.  In this procedure, an electrophysiologist (specialist in the electrical system of the heart) finds and burns or freezes sources of aberrant signals in the atria.  See the link above for a detailed explanation.

I found an excellent FAQ sheet on the American Heart Association website which explains this topic in easy to understand language.  Other resources include the Heart Rhythm Society, the National Stroke Association, WebMD Atrial Fibrillation Health Center, and

More later on antiarrhythmic drugs used to treat A Fib/Flutter.


2 Comments leave one →
  1. Paul Catum permalink
    June 9, 2013 10:19 pm

    Thanks for your post. This is a great summary of atrial fibrillation and flutter for the lay reader! Often, physicians will need to look at a 12-lead ECG to make a precise diagnosis, especially to distinguish between atrial fibrillation with moderate or rapid ventricular response. There are some good examples at this site:

    • June 10, 2013 9:50 am

      Thanks for the link. The examples on that page are interesting. Can you explain to me why the A flutter was so clear in lead 2 but not in the V leads?

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