What is atrial fibrillation?

by | Aug 29, 2015 | Cardiac Electrophysiology, Cardiology, General Public |

What is Atrial Fibrillation?

 

Atrial fibrillation is the most common sustained arrhythmia in the human heart (1).  In the United States today, over 5.6 million patients have been diagnosed with atrial fibrillation and this number is growing; by the year 2030 it is estimated that this diagnosis will extend to 12.1 million Americans (2).  Atrial fibrillation is a disease of rapid, chaotic electrical activity in the upper chambers of the heart, the left and right atria (3).  Normally, each heartbeat starts in the normal, natural pacemaker of the heart, the sinoatrial (SA) node which lies in the right atrium.  A normal heartbeat depends on an electrical wave that begins in the SA node and travels out from this node to first cover both atria, then traverses the AV node, which is a bridge to the ventricles, and finally to the ventricles, the main pumping chambers of the heart.  When atrial fibrillation starts, rapid irregular electrical signals occur in the atria apart from the SA node and “take over” the heart rhythm from the top down.  In other words, these rapid chaotic electrical impulses suppress the normal “sinus” rhythm of the heart, and create a chaotic irregular heart rhythm.

 

One analogy for atrial fibrillation is a fireworks show.  If you were listening to your favorite song, and really wanted to focus listening to the song’s rhythm, it would be simple if you were sitting in your room quietly with your headphones on.  However, try listening to the rhythm outdoors at a fireworks show, for example on the 4th of July, and it would be an entirely different experience.  The rapid chaotic popping of the fireworks would make it difficult to appreciate your music, let alone determine the drum rhythm.  In the same way, extra electrical signals in the heart’s atrial chambers can  “drown-out”and may suppress your normal heartbeat, and contribute to the feeling of heart palpitations, fatigue, and dizziness.

 

Aside from the discomfort of heart palpitations and dizziness, atrial fibrillation may be life-threatening, in that it increases the risk of stroke by 500%.  Because atrial fibrillation causes chaotic, uncoordinated electrical activity in the atria, the muscular contraction of the atria is also chaotic, uncoordinated and weak.  The weakness of atrial pumping in atrial fibrillation is called stunning, and it increases the formation of blood clots within the heart (4).  These blood clots can travel, or embolize, to the brain where they cause stroke, and can embolize to other areas of the body, including the eyes, kidneys, abdominal blood vessels, and toes.  To prevent stroke and other blood coagulation, anti-coagulants such as warfarin (coumadin) or newer anti-coagulants such as Apixaban (Eliquis), Rivaroxaban (Xarelto), and Dabigatran (Pradaxa) are prescribed.  The benefit of using these anticoagulants in atrial fibrillation is a reduction in stroke risk; however, the very real side effect of major bleeding is common and can limit the use of anticoagulants in some situations.  There are newer therapies to exclude or “pinch off” the major offender of blood clots in atrial fibrillation, the left atrial appendage; however, there is also risk of damaging the heart or bleeding with this approach as well.  A major portion of my research is looking into the biology of why atrial stunning in atrial fibrillation happens, and to try to reverse this effect without having to use blood thinners and anticoagulants.  As more develops with this research, I will post some updates on the progress we’ve made in reducing stroke risks in atrial fibrillation.

 

Another approach to treating atrial fibrillation is ablation, where a catheter is placed inside the heart and delivers energy to a small area of the atria that are causing the electrical chaos behind atrial fibrillation.  Ablation is not a cure for atrial fibrillation per se, but is an effective adjunct to medications that control heart rhythm, rate, and anticoagulation.  Ablation is approximately 70% effective for reducing atrial fibrillation over 1-2 years, however, atrial fibrillation can always come back.  This is because a catheter cannot change underlying risk factors for AF (such as age, hypertension, heart failure, etc.), and atrial remodeling is an ongoing lifelong process of a heart’s reaction to its environment.  Thus, atrial fibrillation is a disease of the upper atrial chambers of the heart, with significant symptoms including palpitations, and that increases stroke risk.  Atrial fibrillation has no permanent cures, but lifestyle modifications, medical therapy with rate/rhythm control drugs, anticoagulants, and sometimes catheter ablation, can help in reducing burden of AF, reducing symptoms, and reducing stroke risk.

 

For more information on atrial fibrillation, see the links below:

 

 

References:

1.  Lip GY, Tse HF, Lane DA. Atrial fibrillation. Lancet. 2012 Feb 18;379(9816):648-61. doi: 10.1016/S0140-6736(11)61514-6. Epub 2011 Dec 11. Review.

2. Colilla S, Crow A, Petkun W, Singer DE, Simon T, Liu X. Estimates of current and future incidence and prevalence of atrial fibrillation in the U.S. adult population. Am J Cardiol. 2013 Oct 15;112(8):1142-7.

3. Savage N.  Beating Stroke.  Nature.  2013 Jan 31;493(7434):S12-3.

4. Watson T, Shantsila E, Lip GY.  Mechanisms of thrombogenesis in atrial fibrillation:  Virchow’s triad revisited.  Lancet.  2009 Jan 10;373(9658):155-66.