Understanding atrial fibrillation

Atrial fibrillation is a type of heart rhythm disturbance or ‘arrhythmia’. In this article, consultant cardiologist Dr John Whitaker explains what causes atrial fibrillation and how it can be addressed.

What is atrial fibrillation?

Atrial fibrillation (AFib) is the most common type of abnormal heart rhythm and is characterised by an irregular and often fast heartbeat. It originates from the top left chamber of the heart, called the left atrium. During atrial fibrillation, there is a loss of synchronised electrical activity in the left atrium which results in irregular and rapid signals being sent to the main pumping chambers of the heart (the ventricles).

A normal resting heartrate is usually around 60-100 beats per minute (bpm), but with atrial fibrillation, patients often experience a much faster heart rate even while at rest and it is not unusual for patients heart rate to be 140 - 160bpm and can sometimes reach even higher rates up to 200bpm.

What are the symptoms of atrial fibrillation?

AFib can occur in short and self-terminating episodes (paroxysmal AF, which are episodes that last less than 7 days and most commonly less than 48 hours), or persistent episodes that carry on for longer than this. The characteristic symptom is that of palpitations, which are a consequence of the fast, irregular heartbeat, but there may be other accompanying symptoms such as:

• Dizziness
• Chest pain
• Shortness of breath
• Exercise intolerance

What are the risk factors for atrial fibrillation?

AFib is more likely to develop in older individuals, or those with a past history of other cardiac problems, but anyone can develop it regardless of age or gender. In the event that AFib is identified, this would normally prompt a careful assessment for any other coexisting cardiac disease which may be important to identify.

Conditions such as high blood pressure, obesity, hyperthyroidism, sleep apnoea, and excess alcohol intake are also associated with a higher incidence of AFib, and management of these conditions alongside any specific intervention for the heart rhythm will form an important aspect of care for any patient with AFib.

Some patients with AFib identify specific triggers that may make them more likely to experience an episode. These can include large meals, taking alcohol or caffeine, stress or sleep disturbance. However, such triggers are very specific to an individual patient and the majority of patients do not clearly identify them. Importantly, most episodes of AFib come on without any clear trigger.

Is atrial fibrillation dangerous?

AFib is not necessarily dangerous, and some patients may not feel that it has a significant impact on their quality of life. However, of critical importance AFib is associated with an increased risk of stroke and assessment and management of this risk is a crucial part of managing Afib. In addition to the risk of stroke, in some patients AFib may cause heart failure and both of these conditions can be fatal if unaddressed.  

How is atrial fibrillation diagnosed?

The main method for diagnosing AFib and other heart arrhythmias is by performing an electrocardiogram, which records the electrical activity of the heart. These come in the form of hospital-grade devices which are typically acquired while the patient is at rest, ‘ambulatory ECG' monitoring systems, which are worn outside the hospital to provide an assessment of the heart rhythm during normal activity or, increasingly, personal ‘wearable’ devices that are available and include certain smartwatches and other small commercially available portable devices. Acquiring some form of heart rhythm monitoring during an episode of arrhythmia is necessary to make a diagnosis of AFib.

How is atrial fibrillation treated?

Treatment differs from case to case, and there are a variety of options a patient and their cardiologist may need to explore.

The stroke risk associated with AFib may be very powerfully reduced in some patients through the use of blood thinning medications which are effective and safe drugs in many patients.

Medications to slow the heart rate such beta-blockers and calcium channel blockers may be helpful for some patients in either the short or the longer term to provide ‘rate control’. These medications are unlikely to make the AFib stop and in some patients are limited because of periods whe the heart rate is low.

For those who have persistent AFib, a procedure called a direct current cardioversion (DCCV), during which an electric shock is applied under anaesthesia in an attempt to reset the rhythm, may be helpful. While a DCCVis often effective in restoring the normal heart rhythm, it will not prevent a recurrence of AFib. DCCV can be a useful test to see how long it restores a normal heart rhythm for and how much (if at all) it improves symptoms.

A further option for managing AFib is a procedure called a catheter ablation. This is an invasive procedure, typically performed under general anaesthesia or sedation, in which catheters are passed into veins, most commonly at the top of the leg, through which they are moved to the heart. Treatment, in the form of heating or freezing energy is applied to specific areas in the heart with the goal of eliminating the tissue responsible for initiating and maintaining the episodes of AFib. AFib ablation may be performed as a day case or with an overnight stay, and in many patients represents the strategy with the best chance of restoring and maintaining a normal heart rhythm.