Current Developments in Atrial Fibrillation

Interview with Theresa Lowry Lehnen, a Clinical Nurse Specialist and Associate Lecturer Institute of Technology Carlow

Characterised by the rapid and irregular beating of the atrial chambers of the heart, episodes of which may become longer or continuous over time, Atrial fibrillation (AF) is the most common cardiac arrhythmia diagnosed in clinical practice. The condition affects more than 33 million people around the world.

In Ireland, 11% of people over the age of 80 have atrial fibrillation and it affects more than 40,000 people in Ireland aged over 50 years.

AF is associated with a significant risk of transient ischemic attack, ischemic stroke, systemic embolism, and death. While not immediately life-threatening, it does carry a five-fold higher risk of stroke caused by the formation of blood clots in the heart and blocked blood vessels in the brain.

According to Theresa Lowry Lehnen, the percentage of people with AF increases with age with 0.1% under 50 years, 4% between 60-70 years and 14% over 80 years of age being affected.

Theresa, who is a Clinical Nurse Specialist and Associate Lecturer Institute of Technology Carlow adds, “Due to increased lifespan, atrial fibrillation is on the rise and predicted to affect 14-17 million people in Europe by 2030, with 120,000-215,000 new cases per year (estimated incidence 0.23–0.41 per 1,000 person/years).

“In particular, 7–8.5 million people will be affected by permanent AF, 3.5–4.2 by persistent AF, and 3.5– 4.2 by paroxysmal atrial fibrillation. A further 280,000–340,000 new ischemic strokes, 3.5–4 million hospitalizations for AF and 100–120 million outpatient visits can also be added to these figures.”

AF constitutes a public health challenge with high comorbidity and increased mortality risk and is a significant cause of increasing health care costs globally. An estimated 1.4% of all adults over 65 years living with undiagnosed AF means more cases of unmanaged atrial fibrillation will create even further economic strain on our healthcare systems.

Aetiology of Atrial Fibrillation

Atrial fibrillation is multi factorial in nature. Abnormalities or damage to the heart’s structure are the most common causes.

“Atrial fibrillation is more common with increased age and affects certain groups of people more than others,” adds Theresa.

“While it can sometimes affect people who are physically very fit, AF is more common in people with other heart conditions such as hypertension, atherosclerosis, cardiomyopathy, pericarditis, heart valve and congenital heart disease. A family history of AF may also increase the risk. AF is also associated with other medical conditions, such as, pneumonia, lung cancer, pulmonary embolism, sarcoidosis, obstructive sleep apnoea, hyperthyroidism and obesity. A number of triggers are associated with the condition including smoking, excessive alcohol and or coffee consumption. When no other medical conditions are associated with it, it is called lone atrial fibrillation.”

Atrial fibrillation is often asymptomatic, especially in the elderly, but many patients experience palpitations, rapid and irregular heartbeat, vague chest discomfort or symptoms of heart failure such as weakness, light-headedness and dyspnoea, particularly when the ventricular rate is very rapid (140 to 160 beats/ minute). Patients may also present with signs and symptoms of acute CVA or other organ damage due to systemic emboli.

Diagnosis and Screening

Theresa explains, “Diagnostic investigation of AF typically includes a complete medical history and physical examination, ECG, full blood count, Urea and Electrolytes and serum thyroid stimulating hormone level. All patients who present with symptoms of AF should have at minimum their pulse checked for irregularities as well as a 12-lead ECG.

“ECG findings for AF indicate the absence of P waves, irregularly irregular R-R intervals and the presence of f (fibrillatory) waves between the QRS complexes. Fibrillatory waves are irregular in timing and morphology with baseline undulations at rates up to or > 300/ minute, best seen in lead V1 and not always apparent in all leads.

“Other diagnostic tests for AF include CXR and echocardiogram. Echocardiography is carried out to assess for structural heart defects such as left atrial enlargement, left ventricular wall motion abnormalities suggesting past or present ischemia, valvular disorders and cardiomyopathy and to identify additional risk factors for stroke such as atrial blood stasis, thrombus or complex aortic plaque. Atrial thrombi are more likely in the atrial appendages, where they are best detected by transoesophageal rather than transthoracic echocardiography.”

Atrial fibrillation is a progressive disorder. The exact electropathological mechanisms underlying persistence of AF are at present unknown and none of the available recording techniques can determine the degree and extensiveness of atrial electropathology or determine the stage of the condition at any time in the process.

Classification of Atrial Fibrillation

The European Society of Cardiology (ESC) distinguishes five types of AF based on presentation and duration of arrhythmia seen in the table at the foot of the page.

Complications

The absence of atrial contractions in atrial fibrillation predisposes the patient to thrombus formation. Theresa says, “Risk of stroke is higher in older patients and in those with mechanical heart valves, rheumatic valvular disease, hyperthyroidism, hypertension, diabetes, left ventricular systolic dysfunction, or previous thromboembolic events. Systemic emboli can also cause malfunction or necrosis of other organs. Atrial fibrillation may impair cardiac output. Loss of atrial contraction can lower cardiac output at normal heart rate by about 10%. Such a decrease is usually well tolerated except when the ventricular rate becomes too fast (> 140 beats/ minute), or when patients already have borderline or low cardiac output. In such cases, cardiac failure may develop.”

Treatment

Treatment of atrial fibrillation varies from person to person and depends on the type of AF, symptoms, treatment of any underlying cause, age, and overall health.

The first step, she notes, is to try to find the cause of the atrial fibrillation. “For example, hyperthyroidism can sometimes be the underlying cause of AF and medication to control the condition can correct the symptoms of atrial fibrillation. If no underlying cause is found, treatment of AF is usually aimed at either rhythm or rate control. Since AF induces electrical, structural, and contractile remodelling, therapy aimed at prevention or restoration of remodelling and consequently restoration of sinus rhythm should be the first choice strategy. The different AF treatment modalities include pharmacological therapy, electrical cardioversion, pacemaker implantation combined with His bundle ablation or surgical isolation of the pulmonary veins with or without additional linear lesions/ substrate modification.

“Anti-arrhythmic medication can control atrial fibrillation by restoring normal heart rhythm and controlling the rate at which the heart beats. The choice of anti-arrhythmic depends on the type of AF, comorbidities, side effects of the medicine chosen and response to therapy. Some patients may need more than one anti-arrhythmic to control atrial fibrillation and a variety of medications are available to restore normal heart rhythm. The aim is to reduce the resting heart rate to < 90 beats per minute, however, in some people the target is < 110 bpm.

“First line drugs include beta blockers such as propranolol or atenolol and nonhydropyridine calcium channel blockers such as diltiazem or verapamil, which slows the conduction of impulses to the ventricles. Digoxin may be added to control the heart rate further. Digoxin is usually only effective for controlling the ventricular rate at rest and should therefore only be used as a monotherapy in predominantly sedentary patients.

“Anti-arrhythmic drugs can be classified clinically into those that act on supraventricular arrhythmias (example verapamil), both supraventricular and ventricular arrhythmias (example amiodarone) and those that act on ventricular arrhythmias (example lidocaine). They can also be classified according to their effect on the electrical behaviour of myocardial cells during activity (Vaughan Williams Classification). Class I antiarrhythmic medications are membrane stabilising drugs example lidocaine and flecanide. Class II are beta blockers. Class III include amiodarone and sotalol and Class IV are calcium channel blockers, including verapamil, but not dihydropyridines.

“The negative inotropic effects of antiarrhythmic drugs tend to be additive. Special care should be taken if two or more are used, especially if myocardial function is impaired. Many medications that are effective in countering arrhythmias can also provoke them in some instances. Patients must be monitored closely as common side effects of anti-arrhythmic medications include, hypotension, fatigue, nausea, vomiting, possible issues with liver, kidneys, thyroid or lungs and heart rhythm disorders. Amiodarone causes sensitivity to sunlight and skin changes are common, therefore, sun protection is important when taking this medication.”

Aspirin is not recommended to prevent strokes caused by atrial fibrillation. Theresa explains, “Patients with a high or moderate level of risk of stroke or thrombus formation due to atrial fibrillation, are usually prescribed an anticoagulant such as warfarin or a newer type of anticoagulant-novel oral anticoagulants (NOACs) also called direct oral anticoagulants (DOACs), such as dabigatran, rivaroxaban, apixaben or edoxaben. There are fewer dietary and medication interactions with the newer agents, and less need for monitoring. NOACs are at least as effective or superior to warfarin for stroke prevention in patients with non-valvular atrial fibrillation, and are at least as safe or safer in terms of bleeding risk, according to three large clinical trials.

“NOACs have major pharmacologic advantages over warfarin, which is a vitamin K antagonist, including rapid onset/offset of action, few drug interactions and predictable pharmacokinetics. Practical advantages of novel oral anticoagulants over warfarin include fixed once or twice-daily oral dosing without the need for coagulation monitoring. Potential drawbacks include a risk of bleeding that might be increased in patients over 75 years of age, the lack of a routine laboratory test to reliably measure anticoagulant effect and previously, the lack of an antidote for reversal.

“Choice of NOAC is influenced by the patients individual characteristics, including risk of stroke or VTE, risk of bleeding and comorbidity, in particular renal dysfunction. It is also recommended that one of the bleeding risk scores, such as the HAS-BLED score, be used to help risk-assess patients. The choice of agent should take into consideration the patient’s age, weight and creatinine clearance, as dose adjustment may be required.”

Pharmacologic cardioversion, also referred to as chemical cardioversion, uses anti-arrhythmic medication instead of an electrical shock. Pharmacological cardioversion is often used for the treatment of atrial fibrillation of recent onset. Flecainide, ibutilide, propafenone and vernakalant can be used in patients with no structural heart disease. Where structural heart disease is present, intravenous amiodarone is the drug of choice. Flecainide administered intravenously in patients with AF of recent onset has been shown to restore sinus rhythm in 72-95 % of patients, with greatest success rates in those who receive treatment within 24 hours of atrial fibrillation onset. When AF has persisted for >48 hours, pharmacological cardioversion is much less likely to be effective. Amiodarone appears to be the most effective agent for restoring sinus rhythm in patients with persistent atrial fibrillation.

For patients who have been in AF for longer than 12-24 hours, or in whom the duration of the arrhythmia is not clear, a minimum period of anticoagulation of three weeks is recommended before cardioversion. “Even if echocardiography has demonstrated no thrombus before cardioversion, patients should be anticoagulated for at least one month post cardioversion, since mechanical atrial function may return slowly after cardioversion,” Theresa adds.

Differentiation between Atrial Flutter and Atrial Fibrillation

“Atrial flutter is much less common than atrial fibrillation but its causes and hemodynamic consequences are similar,” she says.

About a third of people with atrial flutter also have atrial fibrillation.

“Both conditions carry increased risk of stroke. In atrial fibrillation, the atria beat irregularly. In atrial flutter, the atria beat regularly, but faster than usual and more often than the ventricles, and there may be four atrial beats to every one ventricular beat. During atrial flutter, unlike atrial fibrillation, electrical activity in the atria is coordinated. The atria do contract, but at a very rapid rate of 250 to 350 times per minute. This rate is too fast to allow every impulse to be conducted through the atrioventricular node to the ventricles. Because the AV node cannot usually conduct at this rate, typically half of the impulses get through (2:1 block), resulting in a regular ventricular rate of 150 beats/minute. The diagnosis of atrial flutter is by electrocardiography. In typical flutter, ECG shows continuous and regular atrial activation with a saw tooth pattern, most obvious in leads II, III, and aVF.

“Carotid sinus massage can increase AV block and better expose the typical flutter waves. A similar response may follow pharmacologic AV nodal blockade, example with adenosine, but such therapy does not terminate atrial flutter. Treatment of atrial flutter focuses on ventricular rate control, rhythm control, and prevention of thromboembolism. Patients with chronic or recurrent atrial flutter require an oral anticoagulant. The choice among the therapies is based on the same considerations as for atrial fibrillation. Patients often require cardioversion or atrial flutter substrate ablation.”

Atrial Fibrillation is the most common cardiac arrhythmia affecting at least 3% of Irish adults over 60 and is associated with almost one in three strokes in Ireland. Globally the prevalence of AF is rising and approximately 600 men and 375 women per 100,000 population are affected. In the 2017 report “Burden of Stroke in Europe” the Stroke Alliance for Europe signalled a possible 58% increase in the absolute number of strokes in Ireland over the next decade.

Screening for Atrial Fibrillation in General Practice

Projections show that the number of people living with stroke as a chronic condition will rise from 3,718,785 in 2015 to 4,631,050 in 2035, representing an increase of 25% or almost one million people across Europe. There are approximately 8,000 strokes in Ireland annually, a third of which are associated with atrial fibrillation.

In 2015, HIQA published a ‘Health technology assessment (HTA) of a national screening programme for atrial fibrillation in primary care’. The HTA announced that a national screening programme for atrial fibrillation for over 65s in primary care would be cost-effective.

HIQA’s Director of Health Technology Assessment Dr Máirín Ryan, said; “Based on the best available evidence, annual opportunistic pulse palpation for those aged 65 and older is expected to lead to reductions in the incidence and severity of atrial fibrillation-related strokes assuming that those detected by screening have a comparable risk of stroke as those detected through routine care.”

Almost 11% of Irish adults aged 65 years and over attending general practice have atrial fibrillation. The HSE (2015) study ‘Atrial Fibrillation Screening in General Practice’ concluded that “opportunistic screening for an irregular pulse in General Practice to assist in the detection of AF is both feasible and beneficial”.

Theresa concludes, “General practices are well placed to opportunistically screen older patients and are ideal in terms of the pathway for treatment for those identified. Opportunistic screening for an irregular pulse carried out by GPs and GPNs “has the potential to be an extremely important stroke prevention strategy, capable of saving society and the health service significant social and economic costs”.

References available on request

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