Radiofrequency Catheter Ablation for Atrial Fibrillation

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Archibald Higgins
6 years ago
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1 Radiofrequency Catheter Ablation for Atrial Fibrillation Background Atrial fibrillation (AP) is the commonest sustained arrhythmia. It affects around I% of the population, and its incidence is increasing. Its prevalence is higher in the elderly: it affects approximately 5% of patients over the age of 70, and 10% over the age of 80. Although previously considered a "benign" arrhythmia, it is associated with a three- to five-fold increase in the risk of stroke and a 50-90% increase in all-cause mortality 1. Figures from a Scottish population (the Renfrew-Paisley study) have shown that our population has a similar incidence of AF to that reported elsewhere 2, and there are as many general practice consultations in Scotland for atrial fibrillation as there are for. 3 angma. Until recently the only routinely-available non-pharmacological treatment for intractable drug-resistant atrial fibrillation was catheter ablation of atrioventricular conduction and implantation of a permanent pacemaker. Attempts at curative surgery have been developed over the past two decades, the most successful (but most complex) being the Cox Maze Procedure. In the mid-i 990s a number of groups tried to replicate the Maze procedure using linear lesions delivered via an ablation catheter, but with limited success and with a high risk of complications. During these early catheter procedures for atrial fibrillation it was noted by some investigators, particularly Haissaguerre's group in Bordeaux 4, that spontaneous episodes of atrial fibrillation were often triggered by atrial premature beats that originated in one or more of the pulmonary veins. This group started to treat paroxysmal atrial fibrillation by radio frequency ablation of these pulmonary vein ''triggers'', with short-term success rates of 60-70% in highly symptomatic patients. Initial attempts at ablating the sources of atrial ectopy deep within the pulmonary veins were often complicated by pulmonary vein stenosis, and this problem was subsequently addressed by ablating segmentally or circumferentially around the ostium of the pulmonary veins rather than deep within the veins. In the early 2000s, as the procedure became more commonplace, interventional electrophysiologists progressed from isolating only the "target" vein to isolating all four pulmonary veins, in order to eliminate most of the triggers for atrial fibrillation (Pulmonary vein isolation, PVI). Elimination of the triggers that initiate atrial fibrillation is often enough to cure paroxysmal atrial fibrillation. For patients with persistent or permanent atrial fibrillation, the problem lies more in the substrate for perpetuation of atrial fibrillation, and perhaps also in factors such as autonomic tone which modulate the arrhythmia. Other investigators have therefore studied the effects of substrate modification, primarily by creating linear lesions within the left atrium, in addition to a wide encirclement of the pulmonary veins (left atrial catheter ablation, LACA, or wide area catheter ablation, WACA). This technique has been pioneered by Pappone and cqlleagues in Milan. Other groups have shown that, in some cases, persistent atrial fibrillation can be terminated by ablation at sites of ganglionic plexi which innervate the left atrium; still others have

2 concentrated on identifying and ablating areas of complex fractionated atrial electrograms (CFAEs) which are probably due to localised re-entrant circuits or local rapid firing which may contribute to the perpetuation of AF. It is now generally accepted that PVI alone is successful in up to 70% of cases on paroxysmal atrial fibrillation, but a second (or even a third) procedure may be needed to obtain this result. For persistent or "permanent" atrial fibrillation, usually some form of substrate modification (often involving linear lesions across the left atrial roof and/or between the left-sided pulmonary veins and the mitral annulus) is needed in addition to PVI Procedural Techniques and Success Rates The procedures are technically challenging, and the learning curve is long. While an experienced operator might perform a four-vessel PVI in under two hours, more complex procedures involving linear left atrial lesions might take four hours or longer. Cardiac catheterisation is performed with one or two transseptal punctures, the pulmonary veins are identified by angiography, and a circumferential mapping catheter and radiofrequency ablation catheter are positioned in the left atrium. Each vein is targeted in turn, using the mapping catheter to record pulmonary vein potentials (PVPs) from just within the ostium of the vein, and the ablation catheter to bum around the veno-atrial junction and eliminate the PVPs. Once all four veins are electrically isolated, the operator may decide whether or not to deliver further lesions, such as linear ablation between the two superior veins and/or between the left-sided veins and the mitral annulus, or lesions at sites of complex fractionated atrial electrograms. If patients have a history of atrial flutter, cavotricuspid isthmus ablation might be undertaken at the same session. Long-term success rates vary with the procedure used, the operator's expertise, the severity of disease in the patient population, the length of follow-up and the presence or absence of concomitant antiarrhythmic drugs. It is now generally accepted that PVI can be curative in around 70% of patients with paroxysmal AF, and some groups claim success rates of 80-85% after a second or third procedure (with or without medication). For persistent AF, success is more difficult to achieve, and results of between 50% and 70% have been quoted. Complications Serious complications can occur in 2-5% of cases. The commonest is pericardial tamponade (occurring in 1-6%) which is usually treated successfully by pericardiocentesis but may occasionally require surgical intervention. The risk of stroke is 0.5-1%, despite full heparinisation. Pulmonary vein stenosis was a common problem in the past, but in recent times, when lesions are delivered within the left atrium rather than within the veins, the risk of this complication should be 1% or less. Atrio-

3 oesophageal fistula has been reported in a handful of cases, and is almost unifonnly fatal; its incidence is probably 1 in 500 or less. Other complications have been reported, including pneumothorax, haemothorax, pulmonary embolism, air embolism, coronary artery damage, damage to the mitral valve apparatus, atrioventricular block, aorto-atrial fistula, phrenic nerve damage, and Dressler's syndrome Aftercare Patients are usually kept in hospital for at least 24 hours after the procedure; they are treated with heparin after removal of the venous sheaths, and commenced (or recommenced) on warfarin. In some centres, patients are kept in hospital until the INR is :=::2.0;in others, patients are sent home and given instructions to self-inject low molecular weight heparin until the INR is therapeutic. Warfarin is usually continued for at least 3 months after the procedure, and often for 6 months or more, especially if the patient has other risk factors for stroke. Antiarrhythmic drugs are also usually administered for the first 2-3 months post-ablation. Recurrences of atrial fibrillation are not uncommon within the first few weeks; these may be attributable to the irritant effects of the ablation procedure, and are not necessarily a sign of failure. Most publications have discounted recurrences of atrial fibrillation within the first 2-3 months. In most large published series, 30% to 50% of patients require a second ablation procedure, usually 3-6 months after the first procedure. Clinical trials There are few clinical trials reported comparing the results of radiofrequency ablation and antiarrhythmic drug therapy. Several trials are ongoing, and the results of these are expected over the next few years. Wazni et al 5 randomised 70 patients with atrial fibrillation (and no previous antiarrhythmic drugs) to ablation or drug therapy. Patients were followed up for one year, and the primary end-point was recurrence of symptomatic atrial fibrillation or more than 15 seconds of asymptomatic atrial fibrillation. Over one year there were symptomatic recurrences in 22 of the 37 drug-treated patients (63%) and four of the 33 patients treated with ablation (13%). Asymptomatic AF was identified in 16% and 2% respectively. Hospitalisation occurred in 54% and 9% respectively, and quality oflife scores were better in the ablation-treated patients. Stabile et al 6 treated 137 patients with atrial fibrillation (paroxysmal in 67%, persistent in 33%) with antiarrhythmic drugs alone or a combination of drugs and ablation. Amiodarone was used in 64% of cases. The primary end-point was any atrial arrhythmia lasting> 30 seconds. Arrhythmia recurrences were documented in 63 of 69 patients (91.3%) treated with drugs alone, and in 30 of68 patients (44.1%) who underwent ablation. There were three major complications in the ablation group (4.4%): one stroke, one tamponade, and one phrenic nerve paralysis. Pappone et al 7 published a non-randomised comparison of outcomes with ablation in 589 patients versus antiarrhythmic drugs in 582 patients. Over a follow-up period of thee years, AF-free survival was better in the ablation group, and the mortality was lower in

ablated patients than in those treated phannacologically. However, this data in nonrandomised, comes from a single highly specialised centre, and has not yet been reproduced in other series.

4 ablated patients than in those treated phannacologically. However, this data in nonrandomised, comes from a single highly specialised centre, and has not yet been reproduced in other series. A recent randomised trial from the same authors 8 in 198 patients with paroxysmal AF randomised to ablation versus antiarrhythmic drugs showed that 93% of the patients who underwent ablation were free of AF at one year, compared to 35% ofthe drug-treated group Cost-effectiveness There is limited data on the cost-effectiveness of ablation for atrial fibrillation. One study from Bordeaux 9 examined procedure costs in 118 consecutive patients treated with ablation for paroxysmal AF. A mean of 1.52 (range 1-4) procedures were perfonned per patient, and 72% of patients were rendered symptom-free without antiarrhythmic drug.s. The cost of drug treatment pre-ablation was 1590 Euros per patient per year. The -" procedure cost was 4715 Euros initially, then 445 Euros per year. The investigators concluded that after five years, the cost ofrf ablation was less than that of ongoing medical management, and costs continued to diverge thereafter. Patient Selection for Ablation for AF Patient selection is a contentious issue, and there is no doubt that the procedure is driven by patient demand. It is possible to predict to some extent which patients are most likely to be treated successfully by ablation. Expert centres can achieve good results in even the patients with mitt advanced disease 10. However, younger patients, those with paroxysmal AF, and those with structurally nonnal hearts (or mild structural disease) are more likely to have a successful outcome than older patients, those with persistent AF, and those with advanced structural heart disease. On the other hand, "sicker" patients may have more to gain from restoration of sinus rhythm, and in some patients with advanced disease the chance of a major improvement in symptoms (if the procedure works) must be balanced against the lower likelihood of procedural success and perhaps a higher risk of complications. It is generally accepted at the present time that ablation is not yet a "first-line" treatment for paroxysmal atrial fibrillation. In many published series from large centres, patient~~ have been symptomatic despite trials of two or more antiarrhythmic drugs. The most important aspect in patient selection is a full and frank discussion with the patient about the likelihood of success in each individual case, and a full explanation of the risk and severity of complications. Many patients come to the cardiac electrophysiologist with high hopes of a cure for their arrhythmia, envisaging that a quick and simple procedure will result in life-long freedom from symptoms and tennination of all medication. Some will have gleaned misleading infonnation from certain internet sites that quote procedural success rather than long-tenn success. We suggest that the following patients should be considered for radiofrequency ablation: 1. Patients with documented paroxysmal AF, with: symptoms clearly correlated to the documented arrhythmia

5 persistent symptoms resistant to at least two antiarrhythmic drugs (or resistant to one drug, and with a strong contraindication to further drug trials) symptoms occurring at least every three months (for discussion) symptoms that are severe enough to impair quality of life structurally normal heart or mild structural heart disease no contraindication to the catheterisation procedure a full understanding of the risks and benefits of the procedure 2. Patients who have recently progressed from recurrent paroxysmal atrial fibrillation to persistent atrial fibrillation (of less than six months' duration) who fulfil the above criteria. 3. Rarely, patients with persistent atrial fibrillation or "permanent" atrial fibrillation (i.e. patients in whom cardioversion has failed) with: severe symptoms in atrial fibrillation, not due solely to poor rate control persistent symptomatic AF despite cardioversion on antiarrhythmic drugs structurally normal heart or mild structural heart disease no contraindication to the catheterisation procedure a full understanding of the risks and benefits of the procedure a reasonable expectation of a successful outcome (including, in practice, age <70 -for discussion) Service Requirements Techniques for ablation for atrial fibrillation are still developing; however, since atrial fibrillation is the commonest sustained arrhythmia, any centre which offers a service for ablation of this arrhythmia is likely to soon become inundated with referrals. In many large ablation centres in the UK, Europe and North America, AF is now the commonest arrhythmia for which ablation is performed. This is already the case in Glasgow Royal Infirmary (GRI), where the procedure has been performed since January Figures for the first four months of 2007 show that atrial fibrillation is the commonest arrhythmia being treated by catheter ablation in GR!. It is likely that in 2007 we will perform over 300 ablations, of which 100 will be for atrial fibrillation. The service can be led by one highly trained and committed individual, but ideally two consultants should be able to offer the procedure. In addition to the standard electrophysiology laboratory system, a non-fluoroscopic mapping system (either the ESI- NavX system, Endocardial Solutions / St Jude Medical, or the Carto system, Biosense- Webster / Johnson & Johnson) is considered essential to minimise radiation exposure and to assist with the placement of linear lesions. Some of these systems can integrate information from CT or MRI images of the left atrium, if such images are routinely available. The initial consultation with these patients is often time-consuming. It is important for the electrophysiologist to have all the important information about the patient, to avoid

6 unnecessary duplication of investigations and to allow a decision to be made. Cardiologists who refer patients for the procedure should therefore be encouraged to send all necessary documentation when referring patients. This will include: ECG in sinus rhythm ECGs documenting all atrial arrhythmias (e.g. if the patient has had both atrial flutter and atrial fibrillation) Ambulatory ECG recordings, if available, especially if they document the onset of the arrhythmia{s) Results of transthoracic echo (including measurement of left atrial diameter) and transoesophageal echo if this has been done Other relevant results including thyroid function tests Transoesophageal echocardiography (TOE) is often required pre-procedure to rule out thrombus in the left atrium, particularly in patients with persistent AF. TOE is sometimes needed during the procedure if trans septal catheterisation is difficult. Intracardiac echo (ICE), if available, may be better than TOE for guiding difficult transseptal puncture Emergency transthoracic echocardiography may be required during or after the procedure if there is clinical suspicion of tamponade. Cardiothoracic surgery should be available onsite. Likely procedure numbers are difficult to estimate, and may depend on operator experience and ~~threshold"for accepting cases. There are currently no agreed national or international guidelines for "numbers needed to train". However, to develop and maintain competence, it is likely that each centre should perform at least one AF ablation procedure per week on average, and recent international guidelines state that each operator should perform "several procedures per month" 11. The number of AF ablation procedures required for a given population has not been estimated - nor has the number of ablation procedures needed for any other arrhythmia been estimated. However, based on trends in other UK and European centres, most centres developing and offering an AF ablation service find that, within 2-3 years, AF accounts for 30-50% of their ablations. Therefore a centre such as GRI, serving a population of 2.5 million in the west of Scotland and performing around 200 ablations annually for SVT, atrial flutter and other arrhythmias, is now performing around 100 ablations for AF, and the number of AF ablations might be expected to reach 200 per year in the next 3-5 years. Similarly, in the east of Scotland (Edinburgh and Aberdeen combined), the number of AF ablations might be expected to rise gradually to 100 per year over the next 2-3 years as operator experience develops, and to rise further to 200 per year in the east of Scotland over the subsequent few years. More accurate prediction of numbers of procedures required is not possible at the present time, and may depend on the outcome of ongoing long-term clinical trials References

7 I. Benjamin EJ et al. Impact of atrial fibrillation on the risk of death: The Framingham Heart Study. Circulation 1998; 98: Stewart S et al. Population prevalence, incidence and predictors of atrial fibrillation in the Renfrew/Paisley study. Heart 2001; 86: 516~21 3. Murphy NF et al. A national survey of the prevalence, incidence, primary care burden and treatment of atrial fibrillation in Scotland. Heart 2007; 93: Haissaguerre et al Spontaneous initiation of atrial fibrillation by ectopic beats originating in the pulmonary veins. New Engl J Med 1998; 339: Wazni OM et al; Radiofrequency ablation vs antiarrhythmic drugsas first-line treatment of symptomatic atrial fibrillation: a randomized trial. JAMA 2005; 293: Stabile G et at. Catheter ablation treament in patients with drug-refractory atrial fibrillation: a prospective, milticentre, randomized, controlled study (Catheter Ablation for the Cure of Atrial Fibrillation Study) Eur Heart J2006; 27: Pappone C et a1. Mortality, morbidity and quality oflife after circumferential pulmonary vein ablation for atrial fibrillation: outcomes from a controlled nonrandomized long-term study. JACC 2003; 42: Pappone C et al. A randomized trial of circumferential pulmonary vein ablation versus antiarrhythmic drug therapy in paroxysmal atrial fibrillation: the APAF study. JA CC 2006; 48: Weerasooriya R et a1.cost analysis of catheter ablation for paroxysmal atrial fibrillation. PACE 2003; 26: Haissaguerre M et al. Catheter ablation of long-lasting persistent atrial fibrillation: clinical outcome and mechanisms of subsequent arrhythmias. J Cardiovasc Electrophysiol2005; 16: II. Calkins H et al. HRS / EHRA / ECAS expert consensus statement on catheter and surgical ablation of atrial fibrillation. Heart Rhythm 2007; 4: 816~61 DTC June 2007

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