Atrial Fibrillation

Dr. Terry Murphy

ED Medical Director

Samaritan Hospital

Atrial Fibrillation is the most common heart rhythm abnormality suffered by older Americans; it afflicts more than 2 million people in the United States. Atrial Fibrillation usually has a sudden onset, often without warning.  In some situations, the illness can be sporadic (paroxysmal); but in most situations it remains constant (chronic).

The symptoms most people notice with Atrial Fibrillation are:

Irregular heartbeat/palpitations/fluttering in their chest

Lightheadedness, dizziness or weakness

Chest pain or discomfort

Shortness of breath

Confusion

In order to understand the condition of Atrial Fibrillation, you first have to understand some of the heart’s anatomy and physiology.  The first is to remember that the heart has four separate chambers – two atria and two ventricles.  Blood returns from the body into the right atrium, which when it contracts, opens the valve that separates it from the right ventricle, and squeezes blood into the right ventricle.  Blood is then ejected from the right ventricle into the lungs when the muscle cells of the right ventricle contract to open the valve.  This process is repeated in the left atrium and left ventricle when blood returns from the lungs. The left ventricle, which ejects blood to the body, comprises the vast majority of the muscle of the heart.

Second, there are two types of muscle cells of the heart.  One type functions like regular muscle, that is, it contracts to open valves and eject blood from one chamber to another (atria to ventricles), or out to the lungs (right ventricle) or body (left ventricle).  The other type of muscle cells, are really “electrical” cells, as they spontaneously produce and then spread a small electrical current that causes the other muscle cells to contract.  While any of the special “electrical” cells has the ability to spontaneously produce an electrical current, in normal health, a group of cells in the right atrium initiates the current. This group of cells is called the sinoatrial node (SA node) or “pacemaker” cells.

After a spontaneous electrical current has been generated in the SA node, the current spreads along the course of other “electrical” cells (sort of like conduit) proceeding from the atria down to the ventricles in a very precisely orchestrated fashion.  It is very important that the atria contract first so that they empty into and fill the ventricles before the ventricles contract. 

Analogize this wave of electrical spread and the subsequent coordinated muscle contraction that it causes, to the SA node being the conductor of an orchestra – initiating the music and then making sure everyone plays his/her instrument at the correct time to make beautiful music rather than random, uncoordinated, meaningless sounds.  Atrial Fibrillation is sort of like an orchestra without a conductor, where everyone plays their instrument in a completely chaotic fashion.  That is the “electrical’ cells, in both the right and left atria, are firing at random and extremely rapidly, so there is no effective contraction of the atrial muscles.  Fortunately, this chaotic action is limited to the atria – the “electrical” system of the ventricles is protected from spread of this chaos by a structure between the atria and ventricles called the AV node.  Therefore, the ventricles continue to contract, but not as efficiently as with a coordinated contraction of the atria.

The most common causes of Atrial Fibrillation are structural change in the heart’s anatomy – most commonly, enlargement (dilatation) of the atria.  These structural changes occur most frequently because of high blood pressure, abnormal heart valves or lack of adequate blood supply to the area of the SA node.  Other illnesses such as COPD (chronic obstructive pulmonary disease – emphysema or chronic bronchitis), an overactive thyroid, pneumonia or congenital heart defects are often causally related.  Additionally, exposures to stimulants such as caffeine or nicotine, excess alcohol consumption, viral infections, heart surgery or sleep apnea are known to have caused Atrial Fibrillation.

Risk factors for developing Atrial Fibrillation include:

Age – the older you get the more likely your heart will undergo the abnormal structural changes that can cause Atrial Fibrillation.

Heart disease – valve malformations or infections, heart attacks or heart surgery, or high blood pressure all increase the risk.

Family history – specific genes for the transmission of Atrial Fibrillation genetically have been identified.

Excessive alcohol, caffeine or nicotine use – especially binge drinking of alcohol, can trigger Atrial Fibrillation.

Several complications can occur because of Atrial Fibrillation:

Because the atria contract chaotically, blood is not effectively emptied out of the atria and the blood that does not empty can form into small blood clots.  These blood clots can then enter either ventricle and be ejected out (embolize) to the lungs, brain, intestines or extremities causing blockage of the blood supply to those (or other) organs.

Because the atria contract rapidly (often up to 300 times a minute), the ventricles usually contract rapidly also – from 120 to 300 times a minute.  Ventricles that contract too rapidly do not have adequate time to fill with blood and therefore they do not deliver enough blood to the lungs, brain, heart and other organs when they contract. The lack of enough blood causes to low of a blood pressure and inadequate function of the organs.  Also because the ventricles contract so rapidly, the muscle requires additional oxygen to supply the extra needs – too rapid of a rate may exceed the body’s ability to supply those needs.

Because the atria are beating rapidly and chaotically, people often feel palpitations or irregular contractions of their heart.

Anyone who has the onset of palpitations, especially when associated with either a rapid heart rate, chest pain or shortness of breath, or dizziness or weakness should seek prompt medical attention.  Everyone newly diagnosed with Atrial Fibrillation should be evaluated by a physician in an attempt to determine and treat the cause of their Atrial Fibrillation, or manage the rate and risk of blood clotting/embolizing.

Treatment of people who have Atrial Fibrillation involves deciding whether (and how) to convert the heart’s rhythm back to normal; trying to prevent blood clots from forming so there are no emboli; and controlling the ventricular rate of contraction if a normal rhythm cannot be established.

Converting the heart’s rhythm back to normal.  This occurs spontaneously in some instances, especially if the underlying cause can be removed – e.g. alcohol binge drinking, exposure to stimulants, correction of excessive thyroid hormone production, correction of blood electrolyte imbalances.  In some instances when the atrial fibrillation persists despite correction of an underlying condition or if the person is very young, and especially when there is no demonstrated structural abnormality, an effort will be made to convert the rhythm with either an electric shock or medication administration.

Controlling the heart rate of ventricular contraction. Unfortunately most of the time an underlying structural abnormality (e. g. dilatation of the atria, disease of the “electrical” system, or a heart valve defect) or other illness that cannot be reversed (COPD or prior heart surgery) exists that causes the Atrial Fibrillation.  In these instances, converting the Atrial Fibrillation back to a normal rhythm has a very high rate of failure.  In these circumstances, a class of medications called beta blockers is used to keep the ventricles from contracting too rapidly. Commonly prescribed medications include amiodarone (Cordarone, Pacerone), propafenone (Rythmol), procaineamide (Procambid, Pronestyl) or dofetclide (Tikosyn). 

Preventing blood clots that can embolize – almost universally people with chronic Atrial Fibrillation are prescribed warfarin (Coumadin) to decrease the ability of blood to clot.  People who take Coumadin must take it daily and monitor blood levels (INR) to be certain they stay in a therapeutic range, without being too low (clot) or too high (at a risk for bleeding).

Newer, less invasive, surgical techniques such as ablating the site of abnormal electrical cells by cauterizing them through a catheter passed up through the groin to the heart or laparoscopic ablation, through the chest, are ideal for young, otherwise healthy, adults who are carefully selected by their physician(s).

Lastly, self care for patients with controlled Atrial Fibrillation includes:

Judicious alcohol and caffeine consumption

Cessation of cigarette smoking

Moderate physical exercise to maintain good cardiovascular health

Managing co-existing diseases such as high blood pressure or COPD.

This article is intended to provide useful information, not medical advice. This information cannot, and is not meant to, replace consultation with your physician regarding your individual circumstances.