ATRIAL fibrillation, commonly referred to as AFIB, is the most common sustained cardiac arrhythmia (abnormality of heart rhythm) worldwide.

AFIB accounts for a significant burden of symptoms, complications, and death, particularly in an aging population. In order to understand atrial fibrillation, we first must understand how the heart beats. Each heartbeat is a result of an electric current running through the heart muscle, usually at regular intervals of 60-100 beats per minute. This electrical current stimulates heart contraction. The heart, much like a house, has an electrical system. This system has a current generator “the sinus node” and “wires” which are really specialised muscle fibres. The sinus node serves to initiate an electrical current which travels along the wires (muscle fibres) and is distributed throughout the heart.

Normally, the electrical current starts in the right upper chamber of the heart (right atrium) in the region of the sinus node and then spreads initially to the left upper chamber of the heart (left atrium). The upper chamber of the heart comprising of the two atria thus contract first, followed by the current spreading to the lower chamber ventricles “the pumping chambers” which then contract together after the atria.

AFIB is a disturbance in the electrical activity of the atria so that instead of a coordinated flow of current in the atria, there is a chaotic flow of waves of electricity moving in different directions and speeds resulting in the absence of atrial contraction and rapid irregular contraction of the ventricles.

What causes AFIB?

Atrial fibrillation, whatever the underlying cause, results from disruption of the normal electrical activity of the atria. What then leads to this disruption? For many patients, the answer is as simple as getting older. An aging heart is associated with replacement of some muscle tissue in the atria by scar tissue. Unfortunately, scar tissue does not have similar properties as normal muscle tissue and so does not conduct electricity as well as muscle tissue. The presence of scar tissue can thus make an older heart more susceptible to the development of atrial fibrillation.

It is estimated that in the United States the prevalence of atrial fibrillation in the population above the age of 80 is around 11 per cent. The true prevalence of AFIB in Jamaica is not well known. Aside from aging, any disease process that results in either stretching or high pressures in the atria will predispose one to atrial fibrillation. Given this, atrial fibrillation occurs frequently with many other cardiac diseases. Any cardiac disease process that affects heart structure or pressures can lead to the development of atrial fibrillation. This includes hypertension, coronary artery disease, valvular heart disease, congestive heart failure etc. Less commonly, we can see atrial fibrillation in non-cardiac disease where the heart is secondarily involved, eg thyroid disease.

How can you tell if your symptoms are due to atrial fibrillation?

Patients with atrial fibrillation can have a variety of symptoms. The most common symptom is a result of the chaotic atrial activity which often leads to rapid and irregular beating of the ventricles. Patients will often notice a rapid heartbeat which often will worsen with any attempt at exertion. Atrial fibrillation also results in a reduced efficiency of heart function. The atria normally act to help fill the ventricles prior to ventricular contraction. In atrial fibrillation the atria stop contracting and thus the ventricles must fill passively that is, by the pressure of blood flow only without the benefit of contraction. This leads to increased pressure in heart chambers and in the lungs. Higher pressures in the heart and lungs can result in shortness of breath and a reduced ability to exercise or indeed complete activities of daily living. Atrial fibrillation, however, does not only result in symptoms but has other significant clinical consequences, particularly the risk of stroke and heart muscle damage.

How dangerous is atrial fibrillation?

As noted above, in atrial fibrillation the atrial chambers do not contract. As a result of this, stasis of blood can occur in the atria, particularly on the left side. Blood clots can form in the atrial chambers and be carried by normal blood flow to different areas of the body. As clots reach smaller branch vessels they can obstruct blood flow, leading to tissue death. The most devastating consequence of this obstruction is stroke. The risk of stroke in a patient with atrial fibrillation varies significantly depending on factors such as age, sex, diabetes, hypertension, a history of cholesterol deposition and a prior history of stroke. In patients at highest risk, the risk of stroke can be over 20 per cent per year. Clots can end up in other areas of the body leading to other clinical syndromes, example damage to bowel or kidneys.

Another consequence of untreated atrial fibrillation is the occurrence of damage to the muscle of the heart itself resulting in a condition referred to as cardiomyopathy. Atrial fibrillation that is not appropriately treated can result in the heart rate at rest being quite fast. In many cases this may lead to resting heart rates of 150 to 200 beats per minute. If the heart is made to work at these speeds for days to weeks, damage to the structure and function of the pumping chambers can occur. The ventricles can enlarge and be unable to pump blood as normal. This condition is known as Tachycardia Mediated Cardiomyopathy (or in layman’s terms heart muscle damage from a fast heart rate). If identified early, the condition is reversible if the heart rate is slowed down but permanent heart muscle damage and congestive heart failure can be the long-term result if treatment is delayed.

Clinical presentation

Atrial fibrillation can present in several different ways. Many patients present to their physicians with a history of palpitations. In the elderly, palpitations may be less prominent as symptoms. Others can present with symptoms of exertional intolerance, fatigue, shortness of breath, heart failure or sometimes, unfortunately, with a stroke or other conditions related to obstruction of blood flow. The diagnosis of atrial fibrillation can, however, be challenging given its natural history.

As noted above, changes in the structure and electrical properties of the atria underly the development of atrial fibrillation, and these changes occur gradually over time. As time goes by, the predisposition for the heart to go into atrial fibrillation increases. Given this, many patients will start out by having brief, intermittent episodes of palpitations that may last a short time. The frequency and length of these episodes tend to increase over time. However, in the early stages it can be quite difficult to document these episodes and make a diagnosis. A standard ECG has a recording duration of six seconds and thus can be normal in many patients in whom episodes are occurring for only a few seconds every day. There are, however, methods that allow us to monitor patients for longer periods of time at home which we will discuss further.

In a subsequent article we will discuss diagnosis, treatment, prevention, and prognosis.

Dr Ernest Madu MD, FACC, and Dr Paul Edwards MD, FACC are consultant cardiologists at Heart Institute of the Caribbean (HIC) and HIC Heart Hospital. HIC is the regional centre of excellence for cardiovascular care in the English-speaking Caribbean and has pioneered a transformation in the way cardiovascular care is delivered in the region.

Dr Madu is a main TED Speaker whose TED talk has been translated into 19 languages, seen, and shared by more than 500,000 viewers. He has received the Distinguished Cardiologist Award, the highest award from the American College of Cardiology and has been named among the 100 most influential people in health care and among the 30 most influential in public health. Dr Madu is also a recipient of the Global Health Champion Award from the University of Pennsylvania. Dr Madu was past CEO of HIC and is currently the chairman of IHS Holdings Ltd, an asset management company with interests in the USA, Africa, and the Caribbean.

Correspondence to info@caribbeanheart.com or call 876-906-2107.