Dr Arvind Vasudeva Consultant Cardiologist Atrial Fibrillation An update on diagnosis and management Atrial fibrillation (AF) remains the commonest disturbance of cardiac rhythm seen in clinical practice. Approximately 1 in 4 adults will experience AF at some time, and the prevalence is around 2%, rising to more than 6% in the over 80s. Untreated, AF will confer a 5% risk of ischaemic stroke per year, and the treatment priorities are therefore to prevent complications as well as control symptoms. Early and accurate diagnosis is crucial, followed by an assessment of stroke risk. A patient-centred approach is vital to effective management. Patho-physiology AF is characterised by chaotic electrical activation within the atria, with the loss of effective atrial mechanical contraction. Recognised drivers for this activity are often within the pulmonary veins. The ventricular rate is usually rapid and irregular. The key consequences of the change in rhythm are; 1. Reduction in cardiac output due to loss of a trial contraction. This is most likely to cause decompensation in those with underlying valve pathology or left ventricular dysfunction 2. Stasis in the left atrium resulting in thromboembolism 3. Impaired flow in coronary arteries AF can be; 1. Paroxysmal (self-terminates within 7 days) 2. Persistent (requires cardioversion) 3. Permanent It is thought that many patients progress from the paroxysmal to permanent form due to the progressive remodelling of the left atrium (comprising both structural and electrical changes).
Diagnosis The diagnosis of AF should be considered in any patients presenting with palpitations, breathlessness, syncope/dizziness, or chest discomfort. It should also be considered in any patient with a TIA or stroke. It should be remembered that many patients with AF are asymptomatic, and it should be actively sought in those with significant risk factors (hypertension, diabetes, obesity, sleep apnoea, heavy drinkers etc.). Palpation of the pulse remains a useful, if non-specific tool. A 12 lead ECG should be undertaken in anyone in whom AF is suspected. In patients with paroxysmal AF the confirmation by ECG can be more elusive. Many episodes can be asymptomatic so a 24 hour ECG monitor can be useful even if the symptoms are less frequent. However many patients require longer periods of monitoring and many options are now available. These include 7-day event monitors, implantable loop recorders, hand-held ECG recorders, the Zio patch (an external recording device) and even smartphone linked recorders. It is crucial that the raw data is analysed to avoid mis-diagnosis (be very careful with the machine analysis!), and it should always be remembered that AF should only be diagnosed if the arrhythmia lasts at least 30 seconds. Incorrect diagnosis of AF by ECG machine Palpation of the pulse remains a useful, if non-specific tool! www.parkside-hospital.co.uk
Further Investigation Echocardiography will invariably be useful in planning management in the AF population. It is important to rule out any treatable underlying causes of AF, as well as assessing left ventricular function. The left atrial dimension (>50 mm) is a key predictor of the frequency and duration of episodes of paroxysmal AF. The size of the left atrium is also a useful predictor of the maintenance of sinus rhythm post cardioversion. Indications for Echocardiography in AF The baseline echo is important for long-term management When a rhythm control strategy (including cardioversion) is being considered High risk of underlying structural/functional disease which would alter management To assess response to treatment Additional investigations may be required depending on the assessment of the possible causes of AF, or to assess co-existing cardiac conditions. These could include CT coronary angiography (if chest pain is a symptom or there is a suspicion of underlying coronary disease), cardiac MRI, and ambulatory BP monitoring. Assessment of Stroke Risk AF increases the risk of stroke by 5-fold but this risk is not homogenous. Various clinical risk factors are important and have been developed into risk assessment tools. The best known are the CHA 2 DS 2 and CHA 2 DS 2 -VASc tools. There has been a change in emphasis to try and more accurately stratify those at very low risk in whom antithrombotic therapy is not needed, and the CHA 2 DS 2 -VASc tool is more accurately able to discriminate amongst the lowest risk groups. Risk Factors for Stroke in AF Left Atrium Major Risk Factors Previous stroke TIA or systemic embolism Age >75 years Clinically Relevant Risk Factors Congestive cardiac failure or LVEF <40% Hypertension Diabetes Mellitus Vascular Disease Age 65-74 Female gender CHA 2 DS 2 -VASc Stroke Risk Tool Risk Factor Score CHF or LVEF < 40% 1 Hypertension 1 Age >75 years 2 Diabetes Mellitus 1 Stroke/TIA/ Thromboembolism 2 Vascular Disease 1 Age 65-74 years 1 Female Gender 1
The CHA 2 DS 2 -VASc tool should be used to assess the stroke risk in patients with; 1. Symptomatic or asymptomatic paroxysmal, persistent or permanent AF 2. Atrial flutter 3. A continuing risk of arrhythmia after cardioversion of AF to sinus rhythm In all cases the bleeding risk should be assessed, and the risk factors modified as far as possible. The HASBLED scoring system seems to have the best predictive value. A HASBLED score of above 3 seems to indicate a high risk of bleeding and anticoagulation should be undertaken with caution. However these risk factors are modifiable. Falls are often used as a reason for not offering anticoagulation, particularly to the elderly, but studies have not borne this out, and the benefits of anticoagulation in this high risk group far outweigh the risks. The final group is one that is difficult to define, and requires careful consideration of risk factors, echocardiographic findings and patient preference. It is also clear that there is little evidence to help decide on the optimal approach in patients following ablation, and at present the general approach is to continue to treat as per the pre-ablation score. Who and How to Anticoagulate Anticoagulation should be offered to all those with a CHA 2 DS 2 -VASc score of 2 or above, and should be considered for men with a score of 1. Those with a low score (1 for women, or 0 for men) do not need to be offered stroke prevention treatment. There is no longer a role for aspirin monotherapy as there is no convincing evidence for its efficacy. Letter Clinical Characteristic Points H Hypertension 1 A Abnormal liver or renal function 1 or 2 S Stroke 1 B Bleeding 1 L Labile INRs 1 E Elderly (>65 yrs) 1 Warfarin has for many years been the main method of anticoagulation. However it requires careful monitoring, has a narrow therapeutic window and can be unreliable because of its many interactions. If patients are treated with warfarin we should now regularly assess the time in therapeutic range (TTR). Patients with a TTR of less than 40% are actually at higher risk of stroke than those untreated. The new anticoagulant drugs (NOACS) have the advantage of not requiring regular monitoring, and have been proven to be at least as good as warfarin in stroke protection. They should now be considered as an alternative to warfarin in all new patients requiring anticoagulation, and those with a TTR of <65% if already taking warfarin. The majority of thrombus formation in AF is in the left atrial appendage, which is a blind pocket arising from the left atrium. Left atrial occlusion devices have been shown to be an effective alternative approach in those patients who have a high thromboembolic risk, but cannot be anticoagulated. The appendage can also be removed or obliterated during cardiac surgery for other indications. D Drugs or Alcohol 1 or 2 1 Female Gender 1 The HASBLED scoring system seems to have the best predictive value.
Rate or Rhythm Control Strategies The goal of treatment is to control symptoms, as numerous studies have shown no significant mortality benefits in restoration of sinus rhythm. There is also no reduction in stroke risk with the rhythm control strategy. Moreover many of the drugs used to restore and maintain sinus rhythm have a number of important side effects. Rate control is therefore first line therapy for most patients, and can include drugs such a beta-blockers, calcium antagonists and digoxin. In some patients a back up pacemaker may be required. Rhythm control may be appropriate for; 1. Those with a reversible cause 2. Those who develop heart failure as a result of AF 3. Those who have very recent onset AF 4. Those who remain symptomatic despite treatment The rhythm control pathway may include pharmacological cardioversion (with amiodarone or sotalol) or electrical cardioversion, followed by attempts to maintain sinus rhythm with drugs such as amiodarone or flecainide. Although these drugs may be effective at reducing the future burden of AF they do not reduce mortality and may have considerable side effects. Patients with paroxysmal AF, relatively infrequent episodes, and known to have normal left ventricular function, can be managed with the pill in the pocket approach. This approach should be reserved for those patients with a reasonable understanding of the condition and when to take the medication. The pulmonary veins thus become isolated from the left atrium. This is a minimally invasive procedure that can be performed under local or general anaesthesia. In patients with paroxysmal AF, ablation can now be considered a first-line option with a high success rate. Occasionally a second procedure is required. However ablation has been shown to reduce the burden of AF, and improve quality of life, compared to anti-arrhythmic drug therapy in those with paroxysmal AF. In persistent AF the situation is different. Due to the electrical and structural remodelling that has taken place the pulmonary vein triggers are no longer solely responsible for the AF, and additional ablation in other areas of the atrium is required. The success rates are therefore reduced, and repeat procedures are often required. Ablation should therefore only be considered when medical therapy has proved ineffective, and after discussion of the risks and benefits with the patient. Summary; AF remains a common and important dysrhythmia with important sequelae Priorities are to control symptoms and assess stroke risk Where the stroke risk is significant anti-coagulation should be considered, and the benefits and risks discussed with the patient Rhythm control should be considered when patients remain symptomatic despite medical therapy, when the AF has a reversible cause, or if the AF is of recent onset Left atrial ablation is an effective tool in paroxysmal AF but less likely to be successful if AF is persistent Left atrial ablation is a technique designed to deliberately damage discrete areas of tissue in the pulmonary veins that seem to house the drivers in most patients with AF.