Download atrial fibrillation

JULY 2011
A
ATRIAL FIBRILLATION
trial fibrillation (AF) is the most common sustained Symptoms
cardiac arrhythmia. The incidence is increasing In some cases AF can be completely without symptoms.
in Australia due to the ageing population. It is
estimated that 10% of the population older than 75 years Symptoms can range from none to severe:
have atrial fibrillation. AF is more common in males than
■■ Fatigue
females.
■■ Palpitations (irregular heart rate)
■■ Shortness of breath
■■ Angina-like chest pain
Definition
■■ Decreased exercise tolerance
Atrial fibrillation is an abnormal irregular heart rhythm
■■ Heart failure
(arrhythmia) with uncoordinated generation of electrical
■■ Presyncope or lightheadedness
signals in the atria of the heart.
(and rarely syncope) There are a number of different classifications of atrial
AF has a negative impact of quality of life and carries a
fibrillation:
high risk of morbidity and mortality. AF increases the risk
■■ Paroxysmal
of embolic stroke.
■■ Persistent
■■ Permanent
Paroxysmal atrial fibrillation is defined as episodes
of AF that revert to normal sinus rhythm within one
week. Persistent AF lasts more than one week and can
be converted to sinus rhythm with cardioconversion.
Permanent AF lasts indefinitely and cannot be converted
to sinus rhythm.
Treatment
Current treatment strategies aim at controlling the risks
of adverse events from the abnormal rhythm, rather than
curing the condition.
Long-term management of atrial fibrillation follows
two strategies: controlling rate and rhythm. The aim of
treatment is to either restore and maintain sinus rhythm
Atrial fibrillation often begins with paroxysmal episodes (rhythm control) or to control the rate while allowing the
but usually becomes more frequent and sustained until it arrhythmia to continue (rate control).
becomes permanent. It is a progressive condition.
The decision to use a rhythm-control or rate-control
strategy is based on clinical factors and primarily aimed at
Causes
improving the patient’s quality of life.
Some causes of atrial fibrillation include:
■■ Rheumatic heart disease
Rhythm control
■■ Mitral valve disease
Recurrent use of electrical cardioconversion restores
■■ Non-rheumatic mitral valve disease
rhythm control.
■■ Chronic lung disease
■■ Hypertension
Medications used to control rhythm include:
■■ Coronary artery disease (CAD)
■■ Amiodarone (Aratac, Cordarone X)
■■ Hyperthyroidism
■■ Disopyramide (Rythmodan)
■■ Acute alcohol intoxication or alcohol withdrawal
■■ Dronedarone (Multaq)
■■ Sotalol (Solavert, Sotacor, Cardol)
Subclinical hyperthyroidism (normal T3 and T4 with
■■ Flecainide (Tambocor)
low TSH) causes a 3-fold increase in the risk of atrial
fibrillation.
Amiodarone is considered the safest agent in patients
AF is extremely common after all forms of cardiac surgery, with heart failure. Digoxin does not restore sinus rhythm.
such as coronary artery bypass graft surgery (CABG) or
Rate control
valvular surgery.
The main medications used for rate control are the
calcium channel blockers, verapamil and diltiazem, or
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Atrial Fibrillation update, continued
the beta-blockers. In general, a beta-blocker should not
be prescribed with verapamil or diltiazem, due to risk of
profound bradycardia.
Digoxin is often prescribed but usually in conjunction
with a beta-blocker, verapamil or diltiazem as it does not
adequately control exercise-induced tachycardia on its
own.
Anticoagulation
One of the most important complications of atrial
fibrillation is the increased risk of embolus or clot. The
annual risk of stroke in patients with AF is 1.5% in people
aged 50 to 59 and almost 25% in those aged 80 to 89 years.
Therefore anticoagulation is an integral component of
management of atrial fibrillation. Anticoagulation should
be considered regardless of which management strategy
(rhythm or rate control) is followed.
Warfarin
Warfarin reduces the relative risk of stroke in nonvalvular AF by 64% compared with placebo or no
treatment. Even among very elderly patients with AF,
anticoagulation with warfarin is superior to aspirin for
primary stroke prevention. The risk of major bleeds with
warfarin use is no greater than aspirin use.
Current recommendations suggest aiming for an INR of
2 to 3 in all patients with atrial fibrillation and risk factors
for stroke. Many drugs including herbs and vitamins
interact with warfarin.
Dabigatran
Dabigatran (Pradaxa) is a new anticoagulant drug,
indicated in Australia for prevention of venous
thromboembolism (VTE) after total hip or knee
replacement surgery and recently approved for use in
patients with atrial fibrillation. Studies suggest it is
more effective than warfarin with a similar rate of major
bleeding and significantly reduced risk of intracranial
haemorrhage (by 60%).
Dabigatran has significant advantages over warfarin
with need for anticoagulant monitoring and fewer drug
interactions. However, it has a considerably higher
cost. Dabigatran is currently not on the Pharmaceutical
Benefits Scheme (PBS).
Aspirin
In patients with a low risk of stroke or where warfarin is
contraindicated, aspirin can be used. Aspirin is about half
as effective as warfarin for stroke prevention in AF.
Clopidogrel
The combination of aspirin and clopidogrel (Iscover,
Plavix) is not as effective as warfarin protecting against
stroke in patients with AF. Clopidogrel may be used in
© Manrex Pty Ltd (ABN: 63 074 388 088) t/as Webstercare - 2011
conjunction with warfarin patients with a drug-eluting
stent.
CHADS2
The CHADS2 risk score is a validated tool that can be used
to determine the most appropriate medication - warfarin
or aspirin - depending on the patient’s risk factors. The
potential benefit of warfarin needs to be assessed against
the potential for a major bleeding episode.
The CHADS2 criteria (with the number of points) are:
■■ Congestive heart failure (1)
■■ Hypertension (1)
■■ Age ≥ 75 years (1)
■■ Diabetes mellitus (1)
■■ Previous Stroke or TIA (2)
Recommended therapy for patients at high risk (score of
2 to 6) is warfarin. Warfarin or aspirin is recommended
for those at moderate risk (score of 1); and aspirin for low
risk patients (score 0).
Choice of therapy is based on this risk score as well as
assessment of relative benefits and harms, frailty, patient
preference, falls risk and other factors such as drug
interactions.
Summary
Atrial fibrillation is a common condition in the older
person, especially those over 80 years of age. Management
is aimed at improving quality of life. Medications are
used to control rate or rhythm. Anticoagulation with
warfarin is recommended due to the high risk of stroke.
Warfarin is often underused due to an overestimation of
bleeding risks.
References
Clinical Geriatrics 2011;19:34-40.
NPS News 92
Australian Medicines Handbook