ASK DR. BAUGHAN                                             March 17, 2000

ATRIAL FIBBING

With Bill Bradley out of the Presidential race, I can now review atrial fibrillation without seeming partisan.  Atrial fibrillation is a fairly common problem of an irregular heartbeat that affects about 2.5 million Americans, including 5% of people over 65.  The atrium is the entry chamber of the heart.  It is where our “natural” pacemaker cells reside, the cells that initiate the heartbeat.  Ordinarily this pacemaker (the sinus node) sends out an impulse 60-100 times a minute when the person is at rest.  The impulse travels to a way station at the junction of the atria and the ventricles (the main pumping chambers of the heart) called the atrio-ventricular node (A-V node) before continuing on to the ventricles.

In atrial fibrillation, many cells in the atrium start acting like pacemaker cells, sending up to 300 signals per minute.  The A-V node acts like a filter, only letting some of them through.  Still, the heart may beat 140-300 times a minute.  This may happen episodically for a few minutes or hours (Intermittent Atrial Fibrillation) or it may happen all the time (Chronic Atrial Fibrillation).

Two effects of atrial fibrillation (AF) cause health concern.  First, the speed of the heartbeat.  If your heart is beating 160 times a minute for very long, you will feel like you are running a race and cannot stop.  You may feel tired, weak and short of breath.  If you have angina or have had heart attacks, this may aggravate  those problems because each heartbeat does not have the time to fully fill and pump the oxygen your heart needs.  Similarly, if you have chronic lung disease, anything that worsens the blood’s ability to carry oxygen will aggravate shortness of breath.  So the first order of business is to slow the heartbeat.  Ideally, medicines or an electrical stimulus to the heart can get the wannabee pacemaker cells to shut up and let the rightful pacemaker run the show.  If that cannot be achieved, medicines can help the filtering action of the A-V node keep the heartbeat to 60-100.

The second concern is the blood flow effects of “fibrillation.”  Fibrillation refers to the wriggling action of the atrial walls when many cells are sending out impulses chaotically.  This sets up turbulent blood flow in the atrium, with eddy currents in the corners. (Imagine the flow of people in the waiting lines at the rides in Disney World if they removed the guide rails).  Stagnant blood flow or eddy currents gives the opportunity for clots to form.  If these clots then drift back into the main stream, they can get pumped out to the lungs, heart or brain, causing pulmonary emboli, heart attacks, but most commonly, strokes.  If a person has chronic atrial fibrillation, they have a 6% risk of having a stroke each year if they do not take blood thinners.  If they take aspirin, that reduces the risk to 3-4% per year.  If they take Coumadin (Warfarin) in proper doses, the risk is reduced to 1-2% per year.

Getting people to seek medical attention when their heart is beating too fast is no problem because they feel lousy.  Getting people (and doctors) to monitor the dosing of Coumadin is an on-going challenge.  Coumadin interacts with many other medicines and can be affected by various foods.  If there is too much Coumadin on board, the person is at risk for bleeding problems, internal or external.  If they don’t have enough Coumadin effect, the medicine is not giving any protection against strokes.  If people have Chronic Atrial Fibrillation and are taking Coumadin long term, even if they feel fine, they should be checking a blood test (called the Prothrombin Time - Pro-time, PT, or INR) at least monthly.  The dose of Coumadin often needs tweaking to keep it effective and safe.

Sometimes we find conditions that set off AF, such as thyroid problems, and we can correct the underlying cause.  Most often, however, we do not know why the natural pacemaker gets superseded by the other rowdy atrial cells.  However, with heart rate control and adequate anti-coagulation, people with atrial fibrillation can expect a normal lifespan and be able to live normally active lives.