Atrial What?

That was my first reaction when the doctor told me I had atrial fibrillation... atrial what? They gave me a brochure to read in the hospital. It described AF in very clinical terms but the seventies looking cartoon figures and diagrams made me wonder how dated the information was. It wasn't until I got out of the hospital and spent time reading what I could find on the Internet that I got a more current and accurate understanding of AF. I am very thankful for all the doctors who have cared for me but more than once they have disagreed with each other. Having a better understanding and knowing the experience of others has helped me filter the information I was given.

So what is atrial fibrillation? For starters it is the most common form of arrhythmia affecting an estimated 2-5 million people in the U.S. alone. It is common to develop AF after heart surgery or in conjunction with heart valve disorders. There can be other contributing factors but AF can also develop in otherwise healthy hearts with no discernible disease. This is called Lone Atrial Fibrillation (LAF). In my case I would guess that mild hypertension (high blood pressure) and sleep apnea were underlying causes.

To understand AF, you have to understand the normal electrical system of the heart. The top two chambers of the heart are the left and right atria and the bottom two chambers are the right and left ventricles. Each heartbeat originates with an electrical signal from the SA node, located at the top of the right atrium. The SA node is the internal pacemaker of the heart. This signal causes the atria to contract. This is the "lub" of the "lub-dub" heart beat sound. As the electrical signal travels down the atria, it is picked up by the AV node. Think of the AV node as being like a radio receiver that is listening for the signal from the SA node. The AV node delays the signal for a small amount of time before passing it on to the ventricles, causing them to contract. This is the "dub" sound. This sequence is what is considered Normal Sinus Rhythm (NSR).

During AF, the electrical signals in the atria start to recirculate and follow multiple circular paths instead of the normal top to bottom path from the SA node to the AV node. The multiple colliding signals in the atria act more like static that cause the atria to quiver between 300 and 600 times a minute. At this point the atria can no longer pump blood effectively. This is the cause for the most immediate concern for someone with AF, blot clots. Blood can become stagnant in areas of the atria and form blood clots. If a clot breaks loose it can cause problems depending on where it travels in the body. This can include stroke, pulmonary embolism (blood clot in the lungs), or heart attack. Blood clots are generally not a concern unless an AF episode lasts for more than 48 hours. Anti-coagulants drugs (blood thinners) can help minimize the risk.

Now on to the AV node. Remember the AV node is like a radio receiver that is listening for the signal from the SA node. During AF, the AV node ends up receiving a lot of static instead of the steady signal from the SA node. Thankfully the AV node has a safety mechanism built-in that limits how often it will pass on a received signal, kind of like a rev limiter for an engine. For most people this limit is somewhere between 150-180 beats per minute (bpm). It is because of this safety mechanism that AF is not considered life-threatening. The ventricles can still pump blood at rates this high but not efficiently. The resulting ventricular beats also tend to be irregular due to the unorganized character of the signals picked up by the AV node. The high ventricular rates can have some negative long term effects on the heart so drugs to slow down the heart are next on the list.

There seem to be two distinct forms of AF. One is called adrenergic (think adrenaline) where AF episodes are brought on by high stress or physical exertion. The other form is vagal (named after the vagus nerve) where AF starts during rest or sleep, or after a large meal. People who suffer from both forms are considered mixed or dual form. My doctors have yet to recognize these forms but every AF episode I have ever had fits the vagal form mold perfectly. On the flip side, I work with someone who so far has had two AF episodes both occurring during periods of high stress or too much caffeine. My doctors may not be convinced but I am.

Sorry again for the lengthy post. Melinda says I give way too much detail - I guess I just proved it. Next post I'll cover my treatment and experiences since my initial episode.

Dave