John Radcliffe Hospital, Oxford, UK
* Correspondence to: Dr A. J. Mitchell, Department of Cardiac Rhythm Management, John Radcliffe Hospital, Oxford OX3 9DU, UK. Tel: +44 1865 220891; fax: +44 1865 221432
E-mail address: mitcharj{at}doctors.org.uk
Received 11 September 2003; accepted 19 September 2003
See doi:10.1016/j.ehj.2003.09.033for the article to which this editorial refers
Atrial fibrillation (AF) is an increasing cause of both morbidity and mortality and over recent years hospitalizations due to the arrhythmia have risen dramatically.1For elderly patients with asymptomatic persistent AF, both rate control and rhythm control have been shown to be effective strategies.2For the younger or more symptomatic patient however, the main objectives remain the restoration and maintenance of sinus rhythm. Cardioversion of AF restores sinus rhythm in 8590% of patients, yet there is a high relapse rate, with only a quarter of patients maintaining sinus rhythm at 1 year without the continued use of antiarrhythmic drugs. The inherent delay between relapse to AF and scheduling of repeat external cardioversion allows atrial electrical and structural remodelling to occur, promoting the persistence of AF (AF begets AF). As a consequence of this, the atrial defibrillator has become an exciting prospect for patients with recurrent AF. Self-activated atrial defibrillation can be performed quickly after recurrence of the arrhythmia, avoiding hospitalization and with the expectation that sinus rhythm will beget sinus rhythm.
Over the last few years there has been rapid growth in the development of implantable pacemaker and defibrillator technology for AF and third generation atrial defibrillators are currently under investigation. The first atrial defibrillator was the Metrix device manufactured by InControl (Redmond, Washington, USA) and the long-term use of the device is discussed in this month's Journal.3The Metrix atrial defibrillator was implanted with shocking coils situated in the right atrium and coronary sinus, and could deliver a maximum of six Joules synchronized to the R wave using a ventricular pace/sense lead. The Jewel AF (Medtronic, Minneapolis, USA) was a dual-chamber defibrillator that also offered back up ventricular defibrillation. The device had a number of advantages over the Metrix including improved programmability and enhanced diagnostic capabilities. Automatic atrial anti-tachycardia pacing therapies could be enabled to painlessly terminate atrial arrhythmias. Atrial preventative pacing algorithms were also available. The Medtronic GEM III AT dual-chamber defibrillator and Guidant (Indianapolis, USA) Prizm AVT are newer dual chamber defibrillators with atrial preventative and anti-tachycardia pacing algorithms in addition to atrial shock therapies.
Concerns about atrial defibrillator therapy have focused on the immediate discomfort from the shock and the long-term tolerability of repeated self-cardioversion. Efforts to improve shock tolerability have been directed at trying to reduce the atrial defibrillation threshold below the pain threshold. However even with optimal lead configurations, shock waveforms and synergistic drug therapy this is unlikely to be achieved as patients feel discomfort with energy levels as low as one Joule. There has been more success with the use of medication to improve shock tolerability, with either inhaled narcotic analgesics or orally active benzodiazepines. Interestingly, it has become apparent that the sensation from the shock is a short-lived discomfort rather than a pain and that sedative anxiolytics may have a larger role to play. Research is ongoing into ways to facilitate rapid and safe drug delivery. Short-term (6 month) use of the Jewel AF device for AF recurrences has recently been shown to improve quality of life with an associated improvement in symptom frequency and severity.4The longer use of the Jewel AF defibrillator in a group of patients performing frequent manual cardioversions of AF at home had no effect on levels of anxiety or depression.5
In this month's Journal, Geller and colleagues present long-term outcome data from the Metrix group of patients.3These were a young group of patients and most did not have structural heart disease. One hundred and six patients were identified nearly 3 years after device implantation. Forty-five patients had been chosen to use the device to actively treat AF. The device was turned off or explanted in half of the recipients and the remaining few used it as a monitoring tool. Of the 45 patients who were chosen to use the device to treat AF recurrences, 38 continued to perform manual cardioversion at long term follow-up and one patient had the device programmed to treat AF automatically. The investigators comment that the reasons for shock intolerance were frequent early recurrence of atrial fibrillation (ERAF) necessitating repeat cardioversion and frequent shocks. We know that ERAF particularly occurs in patients with paroxysmal AF (who represented more than half of the study population) and after short durations of AF.6Though cardioversion may technically have been successful with a few beats of sinus rhythm restored, from the patient's perspective it would have been unsuccessful as they would still be aware of AF after the procedure. Unfortunately methods to prevent ERAF with overdrive pacing have largely been unsuccessful though there are some data supporting the role of drug therapy for ERAF suppression.
What does this study tell us? It tells us that in selected patients with recurrent AF, repeated self-defibrillation using an implanted atrial defibrillator is an acceptable form of therapy. It also indicates that in spite of the resilient nature of AF, the majority of patients can be maintained in sinus rhythm, several years after device implantation. Choosing the right patient for the atrial defibrillator is vital for long-term success. The ideal patient appears to be a motivated patient with recurrent drug-resistant, highly symptomatic persistent AF that requires frequent hospitalization for cardioversion. Patients with paroxysmal AF are not suitable due to the high ERAF rate and also the small benefit from cardioversion-why cardiovert yourself when the rhythm will eventually stop itself? Furthermore, these patients may be better served with ablative procedures. Analysis of the shock data from the Eastbourne atrial defibrillator group reveals that a shock frequency of once per month is acceptable to most patients and that those patients who are on antiarrhythmic drug therapy are more likely to develop prolonging sinus rhythm duration.7
The future of the atrial defibrillator appears to be as an implantable device for patients with symptomatic persistent AF who have failed drug therapy. It is also likely that atrial pacing algorithms and atrial shock therapy will be rapidly incorporated into standarddefibrillator devices. With the high incidence of atrial arrhythmias observed in recipients of implantable cardioverter defibrillators for ventricular arrhythmias, such devices are under development by most large device companies. Short-lasting drug therapy may reduce the discomfort from shock therapy and continued improvements to atrial pacing algorithms may reduce the number of AF episodes requiring cardioversion. With careful patient selection, the use of the atrial defibrillator empower patients to take charge of their condition and liberate them from the fear of recurrent hospitalization.
References
Related articles in EHJ: