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Dr Diana R Holdright
MD, FRCP, FESC, FACC, MBBS, DA, BSc

Consultant Cardiologist

Dr Diana Holdright
 
 

Cardiac Conditions - Atrial Fibrillation

Atrial fibrillation is the most common heart rhythm disturbance, affecting 1% of the general population, increasing with age to around 17% in octogenarians. About two thirds of patients have symptoms associated with this, including palpitations, dizziness, breathlessness, and fatigue; the remainder feel well and atrial fibrillation is a coincidental finding.

Atrial fibrillation results from loss of the normal organised propogation of electrical activity through the heart; instead, there is chaotic electrical activity within the two upper collecting chambers of the heart, the atria.  When the atria fibrillate, they no longer contract in a mechanically useful way, causing a degree of stasis to blood flow and predisposing to clot (thrombus) formation within the chambers, and in particular within a finger-like projection called the left atrial appendage.

atrial fibrillation

Although thrombus within the heart is generally asymptomatic, it may fragment and break loose (embolise) into the circulation; if the thrombus reaches the brain, in many instances it will cause a stroke. As such, although some patients have few or even no symptoms at all, atrial fibrillation should not be considered a benign condition: irrespective of symptomatic status, atrial fibrillation increases the risk of stroke sixfold, and mortality is doubled compared with patients of a similar age but in a normal heart rhythm. This risk can be reduced by taking a drug such as warfarin (see below), which “thins” the blood and therefore decreases the likelihood of thrombus forming in the first place, but it is important to note that patients with paroxysmal (self-limiting) atrial fibrillation actually have a stroke risk similar to those in persistent or permanent atrial fibrillation.

Whether aspirin or the more effective drug, warfarin, is prescribed will depend on an individual patient’s risk of stroke, which is determined using the CHA2DS2VaSc scoring system, whereby presence of a recognised risk factor is acknowledged with points as indicated below:

Congestive Heart Failure 1
Hypertension 1
Age 75+ 2
Age 65-74 1
Diabetes 1
Prior stroke/TIA/thromboembolic event 2
Vascular Disease 1
Gender (female) 1

A total score of 2 or more indicates that formal anticoagulation, i.e. warfarin therapy, would be of greater benefit than aspirin. There is currently considerable research being undertaken into new drugs to replace warfarin, such as dabigatran and rivaroxaban, which do not require such rigorous monitoring with blood tests.

Atrial fibrillation may be paroxysmal, sustained (lasting more than 7 days) or permanent; over time episodes of paroxysmal atrial fibrillation typically become more frequent and protracted, and may ultimately become permanent. Atrial fibrillation is usually associated with other cardiac conditions such as high blood pressure, coronary artery disease, heart muscle and valve disease but occasionally it occurs in isolation (lone atrial fibrillation). Coexisting conditions of course need investigation and treatment in their own right.

In patients who are diagnosed in the outpatient setting and are not greatly compromised, the aims of treatment are to slow the heart rate (since the heart rate in atrial fibrillation is usually considerably higher than it should be), to consider whether or not to attempt to restore normal rhythm, and to determine who should be offered medication such as warfarin or dabigatran to reduce the likelihood of thrombus formation and subsequent embolism. There are a numbers of drugs, for example, beta blockers and calcium antagonists, which are used to slow the heart rate. In certain patients it is appropriate to try to restore normal heart rhythm, either with anti-arrhythmic drugs, such as sotalol, flecainide and dronedarone, or with electrical cardioversion, whereby a low voltage electric current is delivered through pads applied to the chest wall under general anaesthesia or sedation. Highly symptomatic patients might benefit from AV nodal ablation, to slow the heart rate, or pulmonary vein isolation and atrial substrate modification, to prevent a recurrence of atrial fibrillation.

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Related pages:

News - March 2013 - Three new alternatives to warfarin for atrial fibrillation - which to choose?

News - October 2012 - Yet another alternative to warfarin on its way in patients with atrial fibrillation

News - November 2011 - Dabigatran treatment in atrial fibrillation