Atrial Fibrillation in a Nutshell

After recently celebrating a holiday festooned with hearts of all shapes and sizes, this first edition of the Cardiac Corner will focus on the most common arrhythmia (i.e. abnormal heart rhythm) that is seen in the United States in 2011, namely Atrial Fibrillation(Afib).

Normally our heart rhythms are formed in a precise and regular fashion by the natural “pacemaker” cells of our heart called the Sinus Node.  Atrial Fibrillation on the other hand is an irregular formation of electrical impulses in the upper chambers of the human heart.  While Afib can be seen in all age groups, as many as 8% of patients over age 80 carry this diagnosis.  As the “Baby Boomer” generation reaches retirement age, Afib is being recognized as a growing epidemic and burden to our already taxed health cares system.

What makes Afib a particularly sneaky problem is that in most patients(>65%), it elicits few if any symptoms.  Most patients are identified during routine physical exams due to irregular pulses, or while receiving an EKG for an unrelated issue.  When symptoms do arise, it is often due to the rapid nature of the heart rate, sometimes causing chest discomfort, shortness of breath, lightheadedness or dizziness.  It is the rarer individual who can sense the subtle irregularities and raise the alarm to their physician that something “isn’t quite right.” Each patient’s burden of Afib is different.  In some patients, Afib comes and goes on its own and is short lasting, in others it will stay until something is done to restore the normal sinus rhythm

The causes of Afib are varied, and include thyroid disease, rheumatic heart disease, hypertension, leaky heart valves and in some patients can be inherited in a genetic fashion.  Age related scar tissue formation is an important reason older individuals are at higher risk for Afib, and rarely does it imply damage as the result of heart attack.  Particularly in younger patients, Obstructive Sleep Apnea places an added stress on the cardiac system when nightime oxygen levels fall, leading to Afib.  Alcohol in excess is clearly toxic to cardiac muscle and can play a role in causing Afib.  The term “Holiday Heart” is a common medical description of patients who show up in the Emergency Room with AFib the day after Christmas, New Years or the 4th of July essentially after having had “one too many”.  At other times of extreme physical stress, such as post-operatively or while acutely suffering from pulmonary infections such as pneumonia Afib is also more likely to occur.  Once Afib has been seen once, it is likely it will return again, whether it be in 5 years, 5 months or 5 days.

Whatever the cause, it is important to recognize that in its own right, AFib is not a life threatening condition.  In general it causes two distinct problems that physicians seek to address.  First, Afib tends to cause rapid heart rates.  The more rapid and the longer lasting the heart rate, the more stress on the heart muscle.  Over a long enough period of time the muscle of the heart can weaken.  Secondly, as the upper chambers of the heart beat irregularly(i.e. fibrillate) these chambers do not squeeze as efficiently.  While this does not affect the force of the main pumping chambers(the ventricles), it does cause blood to move less smoothly through the heart.  When blood pools, it can form blood clot, and blood clots that exit the heart can cause stroke.  Risk of stroke is greatly increased by the history of a previous stroke, Age> 75 or the presence of structural heart disease such as heart failure, valvular disease or hypertension.

Despite its risks, patients with atrial fibrillation on good medical management tend to live as long as patients without afib.  Medical therapy is aimed at preventing rapid arrhythmias, usually with blood pressure medications that slow the heart rate, and also other medications that thin the blood and prevent blood clots that could lead to stroke.  Patients with no risk factors for stroke often are treated with medicines like aspirin.  While easy to take, aspirin is not as effective as medications such as coumadin, also known as warfarin, or the new blood thinner Pradaxa.  In patients with more risk, the benefits of Coumadin are well described over its 40 years of use in the medical field, but so are its difficulties.  Coumadin requires frequent blood tests to follow its effects and its potency is easily affected by foods and other medicines.  Pradaxa, newly approved by the FDA in November 2010, boasts equal efficacy as Coumadin in stroke prevention without the need for blood level monitoring or concerns about dietary or medication interaction.

In some patients, particularly those who are more challenging to manage medically, there is an interest in a more invasive approach to cure Afib.  Over the last 12 years a catheter-based strategy which targets areas in the upper chambers of the heart necessary for afib, has gained popular acceptance as an alternative to medications.  Similar to heart stenting, Afib ablation is a procedure performed without the need for large incisions or general anesthesia.  While carrying a small percentage of procedural risk, even a rare(<1/1000) risk of death, Afib Ablations offer up to 80% chance of permanent cure of afib.  Afib ablation continues to be an area of excitement for Cardiac Arrhythmia specialists who continue their efforts to improve the procedure’s success rate.

In summary, Afib is a growing medical epidemic in the United States, due to the aging of our population.  A thorough medical investigation includes identifying the presence or absence of thyroid disease, coronary disease and obstructive sleep apnea.  Predominantly due to its risks of stroke, blood thinners such as coumadin, or the newly released Pradaxa are our most important tools in its management.  In some, invasive procedures such as Afib ablation can be pursued.

— Dr. George Mark, an Electrophysiologist with the Heart House.