Atrial Fibrillation – Part 1 – What is it?

By Julian Booker, MD

Atrial fibrillation, sometimes called a-fib, is the commonest cardiac arrhythmia (abnormal heart rhythm). In contrast to the metronome-like heart rhythm that we are used to, atrial fibrillation is characterized by an irregularly irregular heartbeat. If you were to check your pulse, there would be no pattern. The timing of your heartbeat would almost seem random. The heart rate is usually fast but may be slow. You may experience palpitations or you may be asymptomatic.

What is happening in atrial fibrillation?

Before we go into depth about atrial fibrillation, we should probably discuss normal sinus rhythm which is the heart’s normal rhythm. The normal heart beat requires an amazing coordination between several moving parts. The heart can be thought of as two sets of chambers:

  1. Ventricles – these are the engines that make your body go. They are incredibly muscular and powerful. The right ventricle pumps blood to the lungs to your blood cells can pick up the oxygen that your body needs. The left ventricle delivers that oxygen rich blood to the remainder of the body.
  2. Atria – these chambers that sit atop the heart and serve as reservoirs for blood. Blood collects in the atria and remains there until the ventricles are ready to receive it. The right atrium provides blood to the right ventricle and as you might imagine, the left atrium does the same for the left ventricle.

Your heart has its own pacemaker and specialized electrical wiring that coordinates atrial and ventricular contraction to maximize your hearts effectiveness. The pacemaker for your heart is present in your right atrium so the rhythm of your hearts perpetual dance is choreographed by the atrium.

In atrial fibrillation, there is a short circuit in the electrical system of the atria. Truthfully, short circuit may be too benign a description. During atrial fibrillation, the tissue of the atria is experiencing an electrical storm or seizure.

Atrial fibrillation

Atrial fibrillation (Photo credit: Wikipedia)

This results in a complete discoordinaton of atrial contraction. Instead of generating a good hearty (no pun intended) squeeze, the muscle just rapidly twitches. Because the atria set the pace for the heartbeat, an irregular atrial rhythm means an irregular ventricular rhythm.

The lack of squeeze by the atria has two major effects. The ventricles rely on the atria to help them fill to capacity. Without effective filling, there is potentially less blood flow delivered to the body with each heartbeat. This may result in fatigue, shortness of breath, weakness, leg swelling and a host of other symptoms relating to changes in the volume of circulated blood. The second is that blood has a tendency to stagnate within the atrium. Slow moving blood tends to clot and you don’t have to be a heart doctor to realize that blood clots within your heart are probably bad. These blood clots love visiting your brain and are a leading cause of stroke.

How is it diagnosed?

Atrial fibrillation is diagnosed by electrocardiogram (ECG or EKG). There is a characteristic lack of p-waves seen on the ECG. The p-wave is seen during coordinated electrical activity of the atrium. Since we know that atrial fibrillation is a rapid uncoordinated twitching of atrial muscle, the ECG shows something very similar. The most telling consequence is that the QRS, the ECGs representation of the ventricle doing its job, is also irregular.

Who gets atrial fibrillation?

Atrial fibrillation is more common in men than in women. It becomes more common with increasing age. If you have a strong family history of atrial fibrillation you may be at increased risk to develop the condition. A number of cardiopulmonary conditions such as COPD, hypertension, coronary artery disease, mitral valve disease and heart failure also increase your risk. Other seemingly unrelated conditions like heavy alcohol usage and hyperthyroidism have also been shown to cause atrial fibrillation.

In subsequent posts, I will go into more detail on the evaluation and treatment options so check back soon.

About Julian Booker, MD

I am a noninvasive cardiologist at the University of Alabama at Birmingham specializing in multi-modality cardiovascular imaging and preventative medicine. My training was primarily at Baylor College of Medicine in Houston TX and the National Institutes of Health in Bethesda MD.
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1 Response to Atrial Fibrillation – Part 1 – What is it?

  1. Pingback: Atrial Fibrillation – Part 2 – Blood thinners | MyHeartBlog

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