Atrial fibrillation (AF or AFib) is the most common irregular heart rhythm that starts in the atria. Instead of the SA node (sinus node) directing the electrical rhythm, many different impulses rapidly fire at once, causing a very fast, chaotic rhythm in the atria. Because the electrical impulses are so fast and chaotic, the atria cannot contract and/or squeeze blood effectively into the ventricle.
Instead of the impulse traveling in an orderly fashion through the heart, many impulses begin at the same time and spread through the atria, competing for a chance to travel through the AV node. The AV node limits the number of impulses that travel to the ventricles, but many impulses get through in a fast and disorganized manner. The ventricles contract irregularly, leading to a rapid and irregular heartbeat. The rate of impulses in the atria can range from 300 to 600 beats per minute.
What are the risk factors for AFib?
The risk for AFib increases with age. High blood pressure, the risk for which also increases with advancing age, accounts for about 1 in 5 cases of AFib.
Risk factors for AFib include
- Advancing age
- High blood pressure
- European ancestry
- Heart failure
- Ischemic heart disease
- Chronic kidney disease
- Moderate to heavy alcohol use
- Enlargement of the chambers on the left side of the heart
How is AFib related to stroke?
AFib increases a person’s risk for stroke. When standard stroke risk factors were accounted for, AFib was associated with an approximately fivefold increased risk of ischemic stroke. AFib causes about 1 in 7 strokes.
Strokes caused by complications from AFib tend to be more severe than strokes with other underlying causes. Strokes happen when blood flow to the brain is blocked by a blood clot or by fatty deposits called plaque in the blood vessel lining.
Symptoms and Signs
Atrial fibrillation itself is rarely life-threatening; however, it can have serious consequences if the ventricular rate is sufficiently rapid to precipitate hypotension, myocardial ischemia, or tachycardia-induced myocardial dysfunction.
Moreover, particularly in patients with risk factors, atrial fibrillation is a major preventable cause of stroke. Although many patients—particularly older or inactive individuals— have relatively few symptoms if the rate is controlled, some patients are aware of the irregular rhythm and may find it very uncomfortable.
Most patients will complain of fatigue whether they experience other symptoms or not. The heart rate may range from quite slow to extremely rapid, but is uniformly irregular unless underlying complete heart block with junctional escape rhythm or a permanent ventricular pacemaker is in place.
Atrial fibrillation is the only common arrhythmia in which the ventricular rate is rapid and the rhythm very irregular. Because of the varying stroke volumes resulting from fluctuating periods of diastolic filling, not all ventricular beats produce a palpable peripheral pulse. The difference between the apical rate and the pulse rate is the “pulse deficit”; this deficit is greater when the ventricular rate is high.
ECG: The surface ECG typically demonstrates erratic, disorganized atrial activity between discrete QRS complexes occurring in an irregular pattern. The atrial activity may be very fine and difficult to detect on the ECG, or quite coarse and often mistaken for atrial flutter.
Echocardiography: Echocardiography provides assessment of chamber volumes, left ventricular size and function, or the presence of concomitant valvular heart disease and should be performed in all patients with a new diagnosis of atrial fibrillation. TEE is the most sensitive imaging modality to identify thrombi in the left atrium or left atrial appendage prior to any attempt at chemical or electrical cardioversion.
Treating atrial fibrillation
Atrial fibrillation is not usually life threatening, but it can be uncomfortable and often requires treatment.
Treatment may involve:
- medicines to prevent a stroke (people with atrial fibrillation are more at risk of having a stroke)
- medicines to control the heart rate or rhythm
- cardioversion – where the heart is given a controlled electric shock to restore normal rhythm
- catheter ablation – where the area inside the heart that’s causing the abnormal heart rhythm is destroyed using radiofrequency energy; afterwards you may then need to have a pacemaker fitted to help your heart beat regularly
Atrial flutter is less common than atrial fibrillation, but shares the same symptoms, causes and possible complications.
Some people with atrial flutter also have atrial fibrillation.
Atrial flutter is similar to atrial fibrillation, but the rhythm in the atria is more organised and less chaotic than the abnormal patterns caused by atrial fibrillation.
Treatment for atrial flutter is also slightly different. Catheter ablation is considered to be the best treatment for atrial flutter, whereas medicine is often the first treatment used for atrial fibrillation.