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Expert Review: Dr David Heaven. Consultant Cardiologist, Middlemore Hospital
Atrial fibrillation and flutter in primary care
Atrial fibrillation is under-diagnosed and under-treated
|* We have used the abbreviation AF to mean atrial fibrillation or flutter because the principles of antithrombotic therapy and rate control are the same for atrial fibrillation and atrial flutter. However there are some important differences. For example, achieving rate control can be more difficult in flutter than fibrillation, choice of agents for rhythm control are different and people with lone or predominant flutter should be considered for ablation therapy.|
Atrial fibrillation or flutter (AF)* occurs in approximately 1% of the general population. The prevalence doubles with each successive decade over the age of 50 years and it occurs in approximately 10% of people over the age of 80 years. An estimated 30 to 40 thousand people in New Zealand have AF and about one-third of these are unaware of it. Most GPs probably have some patients with undiagnosed AF.
People with AF are at increased risk of stroke, heart failure and other cardiovascular events. AF is associated with doubling of mortality rates, mainly due to ischaemic stroke. Overall the risk of ischaemic stroke in people with AF is approximately 5% per year but this risk is not evenly distributed across people with this arrhythmia. For people at high risk, the benefits of warfarin to lower this risk, outweighs the risks of serious bleeding from warfarin use. Therefore thromboembolic risk assessment is required for all people with AF.
Warfarin is generally considered to be underutilised in the management of AF; it appears that approximately one-third of people with identified AF are taking warfarin. This underutilisation almost certainly results from a cautious approach to avoiding the risks of major bleeding with warfarin. These risks have probably been overstated.
Many people with AF are prescribed digoxin for its beneficial effect of lowering the heart rate. However digoxin does not control the heart rate during exercise. Its use as first-line therapy is limited to people who are unlikely to be active or have overt heart failure.
The New Zealand Guidelines Group guideline ‘The management of people with atrial fibrillation and flutter’ (NZGG, 2005) makes recommendations, which if implemented can be expected to improve the primary care management of people with AF. These recommendations form the basis for this article.
Table 1: People with atrial fibrillation
|Not on warfarin|
|Of the estimated 35,000 people in New Zealand with AF only two thirds are aware of it and only about one-third of those with identified AF are on warfarin.|
Opportunistic screening recommended
Opportunistic screening of the radial pulse for irregularity can help to identify people with asymptomatic atrial fibrillation. The diagnosis needs to be confirmed by ECG, which will also show the heart rate and may suggest underlying cardiac pathology.
Case finding is likely to be higher in older patients or those with cardiac or other conditions often associated with AF. AF appears to occur in Māori people at ages about ten years younger than the general population, probably related to earlier onset of heart disease.
AF is often associated with:
- Cardiac conditions including hypertension
- Alcohol excess
- Severe infection
- Pulmonary pathology
AF results in asynchronous atrial contractions, which reduce cardiac efficiency, and an irregular and usually rapid ventricular rate, which reduces diastolic filling time and coronary perfusion. Most people with AF, but not all, get symptoms from these effects. The most common are palpitations, breathlessness, fatigue, light-headedness and chest discomfort but at times AF can contribute to acute heart failure, myocardial ischaemia and hypotension.
When AF is paroxysmal it may not be present on a standard ECG. Some form of continuous monitoring, such as Holter monitoring or event recording, may be required for people with intermittent symptoms suggestive of paroxysmal AF.
Initial assessment for people with AF
Appropriate initial assessment for all people with AF includes checking for the common causes of AF discussed above, performing a thromboembolic risk assessment and doing any pre-treatment checks necessary before starting particular medications.
Apart from history, examination and ECG the assessment would usually include:
- Transthoracic echocardiogram
- CBC, TSH, renal function, LFTs, INR
- Thromboembolic risk assessment
Transthoracic echocardiography is performed to identify any underlying structural heart disease, which may need further evaluation and information on disorders such as left ventricular hypertrophy, which may impact on thromboembolic risk assessment. When there is likely to be delay in obtaining this examination warfarin therapy does not need to be delayed for people who already meet the criteria for a strategy of rate control and warfarin therapy. Echocardiography is required before a rhythm control strategy is instituted.
Other investigations may also be clinically indicated from this initial assessment.
Antithrombotic therapy and control of rate is the most appropriate strategy for most people with AF. The focus of AF management is to control symptoms and reduce the risk of serious complications such as stroke or heart failure, as well as managing associated pathology. The major components of AF management are antithrombotic therapy, to reduce the risk of stroke, and rate or rhythm control, to reduce haemodynamic disturbance. Antithrombotic therapy and control of rate is the most appropriate strategy for most people with AF.
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