Atrial fibrillation natural history

Overview
Atrial fibrillation can be complicated by embolic events including stroke and systemic embolization. The atrial kick (active filling of the left ventricle by atrial contraction) often contributes importantly to the filling of the left ventricle, and the loss of the atrial kick can be associated with the development of congestive heart failure.

Complications
Due to the lack of coordination of atrial activation, there is a decline in the mechanical pumping action of the atrium. The decline in mechanical function of the atrium may or may not lead to inadequate filling of the ventricle(s) depending upon the importance of the atrial "kick" or atrial contribution to ventricular filling in a given patient. In patients with a stiff left ventricle (such as patients with hypertension), the atrial kick may be critical to achieve adequate ventricular filling. In addition, atrial fibrillation may worsen the signs and symptoms of congestive heart failure, particularly among those patients with valvular heart disease, due to a reduction in the atrial kick needed to fill the left ventricle.

Patients with atrial fibrillation usually have a significantly increased risk of stroke (up to 7 times that of the general population). Stroke risk increases during AF because blood may pool and form clots in the poorly contracting atria and especially in the left atrial appendage (LAA). The level of increased risk of stroke depends on the number of additional risk factors. If the AF patient has none, the risk of stroke is similar to that of the general population. However, many patients do have additional risk factors and AF is a leading cause of stroke.

Chronic AF is associated with a 1.5 to 1.9 fold increased risk of death, often times due to thromboembolic events.

If left untreated, the chronic tachycardia associated with atrial fibrillation may result in a tachycardia mediated cardiomyopathy.

Natural History
Atrial fibrillation may be continuous (persistent or permanent AF) or alternating between periods of a normal heart rhythm (paroxysmal AF). The natural tendency of atrial fibrillation is to become a chronic condition. Chronic AF leads to a small increase in the risk of death.

Prognosis
The rate of ischemic stroke among nonrheumatic atrial fibrillation patients averages over 5% per year, a rate that is between 2 and 7 times that of non-AF patients. The CHADS Score can estimate this rate with greater certainty.

HAS-BLED score

 * One in every 6 strokes occurs in atrial fibrillation patients.
 * The rate of brain ischemia in conjunction with nonvalvular atrial fibrillation exceeds 7% per year. * Patients with both rheumatic heart disease and atrial fibrillation have an 17-fold risk increase when compared to age-matched controls and an attributable risk of 5 times greater than those with nonrheumatic atrial fibrillation.

Observational Studies

 * The Framingham Heart Study also found that the annual risk of stroke attributable to atrial fibrillation increased from 1.5% in those aged 50-59 years to 23.5% for those aged 80-89 years.
 * In the Manitoba Follow-up Study, atrial fibrillation doubled the risk of stroke independently of other risk factors.
 * The relative risk for stroke in the Whitehall study was 6.99%.
 * Relative risk in the Regional Heart study was 2.3%.
 * In the ALFA study follow up, patients wwith atrial fibrillation were found to have a 2.4% incidence of thromboembolism with the mean being 8.6 months of follow-up time.

Atrial Fibrillation in the Setting of STEMI
The occurrence of atrial fibrillation in the setting of ST elevation MI is associated with a poor prognosis including a 40% rise in the risk of mortality in meta-analyses The basis for thisincrease risk of mortality is not clear. Most likely it reflects the fact that atrial fibrillation is a marker of impaired LV function, but it may also reflect the loss of the atrial kick or the hazard associated with triple therapy with aspirin, clopidogrel, and coumadin.

Mortality
Atrial fibrillation is associated with a 1.5 to 1.9 fold increase in the risk of death. The mortality rate of patients with atrial fibrillation is nearly double that of patients with normal sinus rhythm. This increase is due not only to atrial fibrillation but this also associated with the severity of the underlying disease, and is often due to thromboembolic events. The administration of drugs aimed at rate control alone offers no survival advantage over the use of rate control along with anticoagulation as demonstrated in the AFFIRM trial.