Management of atrial fibrillation in heart failure

Introduction

Congestive heart failure (CHF) and atrial fibrillation (AF) affect about 1-2% of the population, and their prevalence progressively increases with age. Risk factors for each condition are similar and both frequently coexist. CHF affects overall more than 50% of patients with AF, whilst the prevalence of AF increases proportionally with the severity of the CHF, reaching as much as 40-50% of patients in NYHA functional class IV. AF is related to an increase in global and cardiovascular mortality, and to an increased risk of a cerebrovascular accident. Occurrence of AF frequently causes acute CHF or deterioration of a previous one. Reciprocally, CHF is one of the most potent predictors of AF, as it increases in the risk of AF up to 6 times, even in cases of asymptomatic left ventricular dysfunction.

Treatment

The clinical consequences of AF are well-known: loss of the atrioventricular synchronism, subjective sensation of an irregular beat, haemodynamic deterioration as a consequence of the loss of the atrial contractile function, risk of thromboembolism due to the presence of blood clots in the atria, development of a tachycardiomyopathy and a decrease in the quality of life and life expectancy. The objectives of AF treatment include rate control, AF prevention, maintenance of sinus rhythm and prevention of embolic events.
From a clinical point of view, it would be useful to classify our patients in terms of the therapeutic options. When approaching the treatment of AF, the first question we must ask ourselves is whether our objective is rhythm control or rate control. In the light of recently published works any one of these options is equally valid, and the decision to adopt one or another depends on the existence or not of cardiopathy, age of the patient, symptomatology, duration of the AF, risk of cardioversion and secondary effects of the antiarrhythmic drugs used to maintain the sinus rhythm. Thus, in the AFFIRM trial, it was demonstrated that the non-existence of CHF favoured the rate control strategy, but no differences were seen in patients with CHF. Regardless of the strategy employed, pharmacological and non-pharmacological measures can be employed in both options.
It is essential when approaching the treatment of AF within CHF, not to obviate the treatment of provoking factors and of the underlying aetiology. It is practically impossible to achieve an adequate heart rate control during an acute episode of CHF until hemodynamic stabilization has been achieved. Another example of interaction is treatment with ACE inhibitors or ARA II, pillars in tackling CHF and ventricular dysfunction and that have been related with a decrease in the rate of AF, probably through a decrease of interstitial fibrosis and improvement in wall stress, reducing auricular dilation and acting on the remodelled atrium.

Rhythm control (maintenance of sinus rhythm)

• Drugs

The recurrence rate of AF is high. Antiarrhythmic drugs can prevent recurrences, but their effectiveness is incomplete and the potential risks, some of them fatal, are a serious concern. For this reason the selection of a drug must always be based on safety. Demonstration of an increase in mortality associated with the use of class I drugs and the increased risk of proarrhythmia in patients with CHF have led to a shift towards class III drugs like Amiodarone and Dofetilide. The effectiveness of amiodarone and its potential benefit regarding mortality in CHF or, at least, the absence of deleterious effect, transform it into the drug of choice for most patients in AF.
Heart rate control, anticoagulation and treatment of CHF must be done simultaneously and before considering a cardioversion.

• Non-pharmacological strategies

- Electrical cardioversion is more effective than pharmacological cardioversion in the reversion to sinus rhythm. It must be immediately considered in case of severe CHF.
- Catheter ablation: It has been proposed that catheter ablation, creating linear lesions in the atria would emulate the results of the surgical Maze procedure, avoiding the extensive surgical morbi-mortality, especially in patients with CHF. Initial studies of linear ablation for the treatment of AF proposed acting on both atria. Isolated lesions in the right atrium proved to be safe but ineffective and lesions in the left atrium, although improving the success rate, did so at the cost of significant morbidity, including the possibility of proarrhythmia by re-entry in the left atrium. At present ablation of arrhythmogenic sources in pulmonary veins or the isolation of these constitute curative strategies in a significant percentage of patients.
- The implantable auricular cardioversor (Atrioverter) was developed and tested in a multicentric trial, and demonstrated its effectiveness and safety. However, the fact that the discharge is painful in a high percentage of cases, as well as the potential risk of inducing ventricular arrhythmias, have led to the abandonment of this idea. On the other hand and given that atrial arrhythmias are a frequent problem in patients wearing an ICD for ventricular arrhythmia, devices have been developed capable of managing episodes of AF, by combining over-stimulation therapies (bursts, ramps, stimulation at 50 Hz) and cardioversion both in the atria and in the ventricles. An atrial shock can be administered either by means of the same configuration as for the ventricle, or by implanting an additional lead in the coronary sinus, which allows lower thresholds of atrial defibrillation. Because the discharge is painful, this can be programmed independently of other therapies in the atrium. It can also be activated in a semiautomatic manner by the patient or programmed in a nocturnal schedule to reduce symptoms.
- The concept of the stimulation for the prevention of AF is relatively recent. New algorithms of AF prevention have been developed, as well as systems for bi-atrial stimulation, double stimulation in the right atrium, stimulation in the interatrial septum, etc. More controlled studies and a long term follow-up of the patients are needed to better understand the benefit of this type of device, as well as the potential role of bi-ventricular stimulation in patients with CHF when preventing episodes of AF or improving the effectiveness of atrial therapies, through improvement of the haemodynamic profile and reduction of the wall stress and atrial distension.

Control of heart rate

• Pharmacological treatments

Digoxin is the most frequently employed drug and is particularly useful in CHF for its positive inotropic effect. However, its control during physical activity is poor, frequently requiring its association with beta-blockers or calcium antagonists. The latter, applied intravenously, are specially useful in acute control of fast rates, provided the patient's clinical condition allows it. Amiodarone constitutes a potential alternative in controlling heart rate, specially in association with Digoxin in cases of acute deterioration of CHF which impedes the use of other therapeutic options. We can consider a good control when the resting ventricular rate is less than 90 bpm and less than 150 bpm during exercise, according to some authors.

• Non-pharmacological strategies

In 10-15% of the patients, control of ventricular response during AF is impossible to achieve with pharmacological measures. In these cases radiofrequency ablation of the AV node and permanent implantation of a pacemaker can be used. Using this technique rate control is achieved, and an improvement in the quality of life, functional degree of the patients, left ventricular ejection fraction and exercise capacity, as well as a reduction in the number of hospitalisations has been demonstrated. The possibility of implanting biventricular stimulation devices after AV node ablation in patients with ventricular dysfunction, bundle branch block and permanent AF is a strategy still to be evaluated.

Conclusion

Few data are available from controlled clinical trials in relation to AF management in patients with CHF. The interaction between AF and CHF means that neither of them can be properly managed without treating both. Prospective, randomised trials to determine the benefit of maintaining sinus rhythm in patients with CHF and AF are urgently needed. Since AF has been associated with an increase in mortality in patients with CHF in non-randomised trials, the primary objective is to determine whether rhythm control in patients with AF and CHF reduces cardiovascular mortality in comparison with rate control, and thereby determine the optimal strategy in dealing with these patients.

The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.