Heart rhythm disorders

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1 Deartment of Cardiac Electrohysiology, St. Mary s Hosital, Imerial College NHS Healthcare Trust, London, UK Corresondence to Piin Kojodjojo, St. Mary s Hosital, Imerial College Healthcare NHS Trust, Praed Street, London W2 1NY, United Kingdom; iin.kojodjojo@imerial.ac.uk Acceted 4 May 2010 This aer is freely available online under the BMJ Journals unlocked scheme, see htt:// heart.bmj.com/site/about/ unlocked.xhtml Pulmonary venous isolation by antral ablation with a large cryoballoon for treatment of aroxysmal and ersistent atrial fibrillation: medium-term outcomes and non-randomised comarison with ulmonary venous isolation by radiofrequency ablation Piin Kojodjojo, Mark D O Neill, Phang Boon Lim, Louisa Malcolm-Lawes, Zachary I Whinnett, Tushar V Salukhe, Nicholas W Linton, David Lefroy, Anthony Mason, Ian Wright, Nicholas S Peters, Praa Kanagaratnam, D Wyn Davies ABSTRACT Background To revent atrial fibrillation (AF) recurrence after catheter ablation, ulmonary venous isolation (PVI) at an antral level is more effective than segmental ostial ablation. around the ulmonary venous (PV) ostia for AF theray is otentially safer comared to radiofrequency ablation (RFA). The aim of this study was to investigate the efficacy of a strategy using a large cryoablation balloon to erform antral cryoablation with touch-u ostial cryoablation for PVI in atients with aroxysmal and ersistent AF. Methods Paroxysmal and ersistent AF atients undergoing their first left atrial ablation were recruited. After cryoballoon theray, each PV was assessed for isolation and if necessary, treated with focal ostial cryoablation until PVI was achieved. Follow-u with Holter monitoring was erformed. Clinical outcomes of the cryoablation rotocol were comared, with consecutive atients undergoing PVI by RFA. Results 124 consecutive atients underwent cryoablation. 77% of aroxysmal and 48% of ersistent AF subjects were free from AF at 12 months after a single rocedure. Over the same time eriod, 53 consecutive aroxysmal AF subjects underwent PVI with RFA and at 12 months, 72% were free from AF at 12 months (¼NS). There were too few ersistent AF subjects (n¼8) undergoing solely PVI by RFA as a comarison grou. Procedural and fluoroscoic times during cryoablation were significantly shorter than RFA. Conclusions PV isolation can be achieved in less than 2 h by a simle cryoablation rotocol with excellent results after a single intervention, articularly for aroxysmal AF. BACKGROUND Pulmonary venous isolation (PVI) remains the cornerstone of most atrial fibrillation (AF) ablation rocedures. On its own, it is successful in reventing recurrence of aroxysmal AF in 60e80% of subjects undergoing PVI after a single rocedure. 1 2 In ablation of ersistent AF, PVI is usually the first ste in a stewise aroach to terminate AF. 3 The shallow learning curve in erforming PVI is artly due to variable PV anatomy, which results in difficulty in areciating the comlex three-dimensional anatomy of the left atrium (LA) and the ulmonary veins and in catheter maniulation around the LA and PV ostia. 4 Pulmonary venous isolation at the antral level is often referred in order to include ostial foci within the level of isolation and minimise the risk of PV stenosis. To this extent, antral ablation has been shown to be more effective than ostial segmental ablation in reventing AF recurrence. 5 With these considerations in mind, ablation technology that could deliver circumferential antral ablation centred on the PV ostia would facilitate AF ablation. Although a range of different ablation energy sources (most commonly radiofrequency energy and cryotheray) are available, cryotheray offers a theoretical advantage in that it does not disrut target tissue architecture and could reduce comlications such as ulmonary venous stenosis and atrio-oeshageal fistulation. 6 7 To date, no case of ulmonary venous stenosis, atrio-oesohageal fistulation or coronary occlusion has been reorted during cryoablation for AF. In this study, results are reorted of a rotocol incororating the use of a large cryoablation balloon to erform antral cryoablation with touch-u focal ostial cryoablation to isolate PVs in atients with aroxysmal and ersistent AF undergoing their index ablation rocedure. In addition, the medium-term results of the large cryoablation balloon rotocol were comared with those from consecutive AF atients undergoing PVI using conventional radiofrequency ablation. (RFA) METHODS Patient selection Patients with symtomatic, medically refractory AF referred for ablation from May 2006 to May 2009 were recruited. Subjects had either aroxysmal AF (defined as self-terminating AF eisodes lasting <7 days) or early ersistent AF (defined as eisodes of AF that lasted >7 days, requiring direct current cardioversion to restore sinus rhythm and transition from a clinical attern of aroxysmal AF in the ast 12 months). All atients were undergoing their first AF ablation rocedure. Informed consent was obtained from all atients rior to the rocedure. All antiarrhythmic agents, Heart 2010;96:1379e1384. doi: /hrt

2 excet amiodarone, were stoed at least 5 half lives before the rocedure. In atients receiving oral anticoagulants, warfarin was stoed 5 days rior to the rocedure with bridging tinzaarin (175 IU/kg). On the day of the rocedure, transoesohageal echocardiograhy excluded intracardiac thrombus. No rerocedural imaging was erformed to assess ulmonary venous anatomy. rotocol Venous access was obtained from the right femoral vein, through which two 8 French sheaths (SR0 sheath, St. Jude Medical, St Paul, Minnesota, USA) were introduced into the left atrium via two searate transetal unctures. A curvilinear maing catheter (Inquiry Otima, St Jude Medical, USA or Lasso, Biosense Webster, Diamond Bar, California, USA) was introduced via one of the transetal sheaths to ma the PV ostia. Contrast ulmonary venograhy was erformed with a 7 French NIH catheter for all targeted PVs and the PV maing catheter was ositioned at every targeted PV ostium to confirm electrical connection of the PV at baseline. Over an exchange length inch guidewire introduced into the left suerior PV, an 8 Fr transetal sheath was exchanged for a 15 Fr deflectable sheath (Flexcath, Medtronic, Minneaolis, Minnesota, USA) to allow introduction of a 28 mm cryoablation balloon (Arctic Front, Medtronic, USA). This was the only cryoballoon used for all cases. The Arctic Front cryoballoon is a deflectable balloon within a balloon catheter, whereby refrigerant is delivered into the inner balloon. A constant vacuum alied between the inner and outer balloon revents the leakage of refrigerant into the circulation in the event of a defect in the inner balloon. Over a guidewire introduced fluoroscoically into each targeted PV, the cryoballoon was inflated in the left atrium before it was advanced into the PV antrum (figure 1). Any oint of contact between the endothelium and balloon was ablated. A deflectable quadriolar catheter was introduced via the left femoral vein for either differential atrial acing or acing in the suerior vena cava to cature the right hrenic nerve. Figure 1 Positions of inflated 28 mm cryoballoon at the four ulmonary venous antra in the same aroxysmal atrial fibrillation (AF) atient. Note the hold-u of contrast in the ulmonary veins due to balloon occlusion of the antra. A quadriolar catheter is ositioned in the suerior vena cava to cature the right hrenic nerve. All four ulmonary veins (PV) were isolated after two cryoballoon alications to each PV. After the introduction of the Arctic Front catheter into each vein sequentially over a inch guidewire, 50% contrast was injected distally via the central lumen to confirm a good seal between the balloon and the ulmonary venous antra. Two 5 min cryoballoon alications were alied to each PV, aiming for a trough temerature of less than 408C. If a good PV seal could not be achieved, the orientation of the Arctic Front catheter was adjusted by either deflecting the catheter and/or Flexcath guidewire or by maniulating the guidewire into a different branch of the PV. The lowest (trough) temerature achieved during each cryoballoon alication was recorded. During cryoballoon alications to the right-sided PVs, the right hrenic nerve was catured by acing (1500 ms CL, 20 ma outut) in the suerior vena cava. The oerator monitored the strength of right hemidiahragmatic contractions by alation in the right hyochondrium to quickly detect injury to the right hrenic nerve. Cryoballoon alications were immediately terminated when any attenuation of the strength of right hemidiahragmatic contractions was felt. After each PV antrum was treated with two cryoballoon alications, the PV ostia were remaed with the curvilinear maing catheter and any residual LAePV connections were treated by focal cryoablation (Freezor Max, Medtronic, USA) to achieve PV isolation. This electrohysiological end oint of entrance block was reconfirmed at the end of the rocedure. In ersistent AF atients, direct current cardioversion was erformed to restore sinus rhythm. If tyical atrial flutter had been reviously documented during electrocardiograhic monitoring, cavotricusid isthmus ablation was erformed using an 8 mm tied radiofrequency catheter (IBI, St Jude Medical, USA) (60W, 608C) until bidirectional isthmus block was achieved. Pulmonary venous isolation by conventional radiofrequency ablation Consecutive atients undergoing PVI using conventional radiofrequency ablation at St Mary s Hosital, London, from May 1380 Heart 2010;96:1379e1384. doi: /hrt

3 2006 to May 2009 were recruited as a comarison grou. The following grous of atients were excluded: A. those undergoing reeat rocedures for recurrent AF (n¼90); B. those undergoing ulmonary venous isolation using other investigational devices such as the Hansen Robotic Catheter system (Hansen Medical, Mountain View, California, USA), MeshAblator (Bard Inc., Lowell, Massachusetts, USA), Ablation Frontiers (Medtronic, USA), etc. (n¼108); C. those who received additional left atrial ablation lesions such as ablation of comlex fractionated atrial electrograms or linear lesions (n¼87). Circumferential antral ablation using a 4 mm cooled tied catheter (Thermocool, Biosense Webster, USA), limited to 25e35W and 17 ml/min flow was erformed around isilateral airs of ulmonary veins, guided by either fluoroscoy or a three-dimensional maing system (Carto, Biosense Webster, USA). Following the creation of two encircling lesion sets, additional ostial segmental ablation guided by a curvilinear maing catheter was carried out until veins were isolated with entrance block set as the same electrohysiological end oint. Similarly, if tyical atrial flutter had been documented during electrocardiograhic monitoring either before or during the rocedure, cavotricusid isthmus ablation was erformed using the same catheter (35W, 17 ml/min), until bidirectional isthmus block was achieved. Postoerative care and follow-u After the rocedure, oral anticoagulation with warfarin was resumed with bridging tinzaarin continued until international normalised ratios (INRs) were theraeutic. All antiarrhythmic agents that were discontinued rior to the rocedure were recommenced, with a view to stoing all antiarrhythmic agents after 3 months if atients remained free from AF. A 3-month blanking eriod was alied such that any AF recurrence during this eriod was not considered as treatment failure. Follow-u was erformed by clinic visits at 1, 3, 6 and subsequently 6 monthly intervals with reeated 24 h Holter monitoring and event recorders. All atients had at least 6 months follow-u. Recurrence was defined as any documented eisode of AF (both symtomatic and asymtomatic) or atrial tachycardia lasting for more than 30 s. Statistical analysis Continuous data are given as mean6standard deviation. Student t test was used to comare differences between grous. Recurrence-free survival over time was calculated by Kalan-Meier method and <0.05 was considered significant. All analyses were erformed using Prism 4.0. (Grahad, USA) RESULTS Patient characteristics In total, 177 atients were recruited in a 3-year eriod from May 2006 to May Of these, 124 atients underwent cryoablation. The mean age of atients undergoing cryoablation was years, with 77% being men. Nearly all subjects had normal left ventricular function. Hyertension was the most common comorbidity. Ten er cent of subjects had reviously undergone cavotricusid isthmus ablation for tyical atrial flutter. The ersistent AF grou was older and had larger left atria comared to the aroxysmal AF grou. Baseline characteristics of aroxysmal and ersistent AF atients undergoing cryoablation are shown in table 1. Over the same eriod, 53 subjects with aroxysmal AF underwent PVI using RFA. Only eight ersistent AF subjects Table 1 Baseline characteristics of aroxysmal and ersistent atrial fibrillation (AF) subjects undergoing cryoablation Paroxysmal AF (n[90) Persistent AF (n[34) Age (years) Men (%) NS Mean LA diameter (mm) LVEDD (mm) NS Ejection fraction (%) NS Duration of AF (years) NS Number of failed antiarrhythmic drugs NS Comorbidities < Hyertension 42 (47%) 20 (59%) < Coronary artery disease requiring 5 (6%) 0 CABG or PCI Prior ablations < Cavotricusid isthmus ablation 10 (11%) 3 (9%) CABG, coronary artery byass graft; LA, left atrium; LVEDD, left ventricular end diastolic diameter; PCI, ercutaneous coronary intervention. had solely PVI as their index rocedure, and this small cohort size recluded any meaningful comarison of outcomes between RFA and cryoablation of ersistent AF. There were no significant differences in baseline characteristics between aroxysmal AF subjects undergoing either cryoablation or RFA (table 2). Acute rocedural results Four-hundred and ninety-two PVs were targeted. Four right inferior ulmonary veins were too small to introduce the PV maing catheter to confirm isolation. Mean rocedural and fluoroscoic times were and min resectively. Although 83% of ulmonary veins were isolated with cryoballoon alications alone, only 40% of atients had all targeted PVs isolated with the use of the cryoballoon alone with two 300 s alications to each PV. Ostial focal cryoablation to a mean of 1.5 PV was required in the remaining 60% of atients. In all PVs excet the left uer ulmonary vein (LUPV), PV isolation was associated with lower mean trough temerature achieved during balloon cryotheray (table 3). All but two ersistent AF subjects required cardioversion at the end of rocedure to restore sinus rhythm. In the two subjects, AF organised into tyical atrial flutter, which terminated into sinus rhythm during cavotricusid isthmus ablation. After left atrial cryotheray, 17 aroxysmal AF Table 2 Comarison between aroxysmal atrial fibrillation (AF) subjects undergoing cryoablation and radiofrequency ablation Paroxysmal AF subjects undergoing (n[90) Conventional Radiofrequency Ablation (n[53) Age (years) NS Men (%) NS Mean LA diameter (mm) NS LVEDD (mm) NS Ejection fraction (%) NS Duration of AF (years) NS Number of failed antiarrhythmic drugs NS Comorbidities < Hyertension 42 (47%) 14 (26%) < Coronary artery disease requiring 5 (6%) 3 (6%) CABG or PCI Prior ablations < Cavotricusid isthmus ablation 10 (11%) 4 (8%) CABG, coronary artery byass graft; LA, left atrium; LVEDD, left ventricular end diastolic diameter; PCI, ercutaneous coronary intervention. Heart 2010;96:1379e1384. doi: /hrt

4 Table 3 Acute success of 28 mm cryoballoon in achieving ulmonary venous isolation Targeted veins subjects and four ersistent AF subjects had cavotricusid isthmus ablation. Radiofrequency ablation In 53 aroxysmal AF subjects, 211 PVs were targeted and 99% (209/211) of PVs were isolated. Six atients had cavotricusid isthmus ablation after PVI. An electroanatomical maing system was used in 51 out of 53 cases. Mean rocedural and fluoroscoic times were and min resectively, which were significantly longer than cryoablation rocedures for aroxysmal AF (<0.001) (table 4). Follow-u Mean follow-u was months, with 644 Holter recordings analysed. Arrhythmia-free survival curves for the entire grou, aroxysmal and ersistent AF subjects are shown in figure 2. At 12 months follow-u, 77% of the aroxysmal AF subjects and 48% of ersistent AF subjects were free from AF recurrence after a single rocedure. There was a significant difference in arrhythmia-free survival between the aroxysmal and ersistent AF grous (¼0.002). Among atients free from AF at 12 months, nine out of 69 aroxysmal AF and two out of 15 ersistent AF subjects were still on antiarrhythmic medication for frequent atrial ectoy. No organised atrial tachycardias were detected during follow-u, with AF being the only recurrent arrhythmia. Radiofrequency ablation At 12 months, 72% of aroxysmal AF subjects who underwent RFA (five on reviously ineffective antiarrhythmics, 27 off antiarrhythmic agents) were free from AF comared to 77% of the aroxysmal AF subjects who underwent cryoablation (nine Table 4 Comarison between aroxysmal atrial fibrillation (AF) subjects undergoing cryoablation and conventional radiofrequency ablation Paroxysmal AF subjects undergoing Isolated with cryoballoon alone (n[90) Mean trough temerature when isolation achieved (8C) Mean trough temerature when isolation not achieved (8C) LUPV 83% NS LLPV 95% <0.01 RUPV 85% RLPV 68% <0.01 All PV 83% All Patients 40% LLPV, left lower ulmonary vein; LUPV, left uer ulmonary vein; RLPV, right lower ulmonary vein; RUPV, right uer ulmonary vein. Conventional radiofrequency ablation (n[53) Follow-u (months) NS Additional 17 (19%) 6 (11%) cavotricusid ablation Procedural time (min) <0.001 Fluoroscoic time (min) <0.001 Comlications One ericardial effusion, two transient hrenic nerve alsies Two ericardial effusion unrelated to transetal uncture requiring drainage Figure 2 Survival curves of subjects undergoing cryoablation. PAF, aroxysmal atrial fibrillation; Per AF, ersistent atrial fibrillation. Comarison between PAF and Per AF curves, ¼ on reviously ineffective antiarrhythmics, 60 off antiarrhythmics). Survival curves are shown in figure 3, with no statistical difference between the two curves. Comlications Five major comlications occurred (table 4). Pericardial effusions requiring drainage occurred in two atients undergoing RFA and one atient undergoing cryoablation, in the latter due to a guidewire erforating the side-branch of the LUPV before any cryoablation was delivered. Uniquely in the cryoablation grou, there were two cases of transient right hrenic nerve alsies, which resolved within 3 and 14 months. The hrenic nerve alsy that took 14 months to recover was caused by unmonitored cryoablation of the right lower PV. As a result of this atient, hrenic nerve monitoring was extended to include cryotheray of the right lower PV, whereas earlier in the series it had only been alied to cryotheray of the right uer PV. Figure 3 Survival curves of aroxysmal atrial fibrillation subjects undergoing cryoablation and conventional radiofrequency ablation. Comarison between conventional radiofrequency ablation and cryoablation survival curves, ¼NS Heart 2010;96:1379e1384. doi: /hrt

5 Reeat ablation During follow-u, 17 (14%) cryoablation atients had reeat ablation for recurrent AF. During their second rocedure, 65 ulmonary veins targeted by cryoballoon ablation during the first rocedure were re-studied. Twenty-seven er cent of PVs remained isolated. Forty-eight PVs demonstrated electrical reconnection (18 LUPV, 15 LLPV, five RUPV, and 10 RLPV). Seventy-four er cent of PVs that demonstrated reconnection were reviously isolated with the cryoballoon alone, whereas 82% of PVs that maintained electrical isolation were reviously isolated with the cryoballoon alone. The mean trough temerature reached during revious cryoballoon theray to reconnected veins was higher comared to the temerature reached during revious cryoballoon theray to ersistently isolated veins ( C versus C, ¼0.03). Radiofrequency ablation During follow-u, 12 (23%) atients who underwent PVI by RFA had a second rocedure for recurrent AF. Out of 47 PVs targeted and isolated during the first rocedure, 11 PVs (23%) remained isolated. All reconnected PVs were re-isolated with RFA. DISCUSSION The resent study is the first to show that a novel, emirical two freeze er vein strategy utilising a large cryoballoon to erform antral cryoablation followed by focal ostial cryoablation to isolate selected ulmonary veins results in medium-term outcomes comarable to RFA; with significantly reduced rocedural and fluoroscoic times. Although the benefits of cryoablation, such as minimal risks of PV stenosis, have long been recognised, an efficient delivery latform to deliver contiguous lesions around PV ostia has been lacking until the introduction of the Arctic Front catheter system. Pulmonary venous isolation using earlier delivery latforms such as 4 mm, 6 mm tied and exandable circular cryoablation catheters required lengthy rocedures of nearly 6 h, and was associated with unsatisfactory clinical outcomes. 8e11 This was thought to be due to the effects of cometitive warming by blood flowing ast the cryocatheter reducing lesion size. The Arctic Front catheter obstructs blood flow from the PV being treated, thereby removing this limitation. Several centres have already reorted on the feasibility of the cryoballoon to isolate PV for treatment of aroxysmal and ersistent atrial fibrillation. 12e16 In the largest series reorted to date, Neumann et al investigated the efficacy of balloon cryoablation in 293 aroxysmal and 53 ersistent AF subjects. 15 Using a subjective grading of 1 to 4 to assess the degree of balloon occlusion during contrast venograhy, a comlete occlusion was associated with an increased robability of PVI with the cryoballoon alone. After a median of 12 months follow-u, 74% of aroxysmal and 42 % of ersistent AF atients were free from AF. Van Belle et al reorted a 73% freedom from recurrent AF, using a 3-month blanking eriod. 17 These results are consistent with the resent findings. In addition, the resent study has shown that a lower trough temerature during cryoballoon alication is also associated with increased likelihood of acute isolation and maintenance of long-lasting electrical disconnection when restudied in atients undergoing reeat ablation rocedures. Some centres have used either rerocedural comuter tomograhy (CT), magnetic resonance imaging or erirocedural fluoroscoy to evaluate the size of the ulmonary venous ostium before choosing to use either a smaller (23 mm) or large (28 mm) cryoballoon. 13e15 It was believed that a closer match between the cryoballoon size and the size of PVostium would allow for better balloon occlusion, and in turn result in more effective lesions. There were two otential disadvantages to this aroach: first, the need for rerocedural CT imaging increased the cumulative radiation dose received by the atients and overall costs, and second, retrosective analysis suggests that the use of a smaller cryoballoon was associated with a higher risk of right hrenic nerve alsy through more distal right PV cryoablation. 15 In two searate small series, detailed electroanatomical maing was used before and after cryoballoon alications to determine the anatomical level at which PVI isolation was achieved. When the 23 mm balloon was used, the veins were found to be isolated at the level of the ostium, whereas use of the 28 mm larger balloon results in the formation of much wider, circumferential and antrally located lesions In cadaveric studies, the right hrenic nerve is not uncommonly less than 2 mm away from the anterior asect of the roximal segment of the right suerior ulmonary vein. 20 Therefore, it would be exected that distal ablation to the right-sided PV (which is more likely with a 23 mm balloon) will result in hrenic nerve injury. This comlication aears to be unique to balloon-based catheter systems delivering cryoenergy, laser or focused ultrasound energy. 21 Chun et al described the feasibility of using only the larger cryoballoon without rerocedural left atrial imaging in 27 aroxysmal AF subjects with the aim of achieving PV isolation at the antral level and minimising the risk of hrenic nerve alsy. 12 Although isolation was achieved in 98% of targeted veins, three cases (11%) of transient hrenic nerve alsy still occurred due to distal PV ablations. Unlike the resent rotocol, a larger number of cryoballoon alications were made articularly for the right inferior PV where a median of u to five 300 s alications were made. In that study, hrenic nerve dysfunction was defined as the loss of reliable cature from acing in the suerior vena cava. The lower rate of hrenic nerve alsy in the resent study (1.6%), the lowest amongst all ublished series, is most likely due to a combination of limiting cryoballoon alications to two er vein, acing the right hrenic nerve at a higher frequency of 40 contractions/min and by alating for a reduction in the strength of diahragmatic contractions in the right hyochondria, which in the authors exerience, recedes the onset of comlete hrenic nerve alsy. The hrenic nerve alsy that took 14 months to recover was caused by unmonitored cryoablation of the right lower PV. As a result of this atient, hrenic nerve monitoring was extended to include cryotheray of the right lower PV, whereas, earlier in the series, it had only been alied to cryotheray of the right uer PV. The clinical outcomes in the resent study are in agreement with revious studies for atients with aroxysmal AF and structurally normal hearts; that PV isolation as the sole rocedure is effective in reventing AF recurrence in the majority of atients. However, in subjects with ersistent AF, additive ablation strategies, combined with PVI, are required to maintain long-term sinus rhythm. The resent definition of ersistent AF was not consistent with those defined in international guidelines, but was chosen arbitrarily with the exectation that atients with a more recent transition from a clinical attern of aroxysmal AF to ersistent AF would exhibit a lesser degree of substrate remodelling and resond more favourably to PV isolation alone. Disaointingly, the medium-term clinical outcome for the ersistent AF grou was significantly lower than aroxysmal AF grou and it is likely that additional ablation lesions will be required during their index rocedure to achieve higher first-rocedural success rates. Heart 2010;96:1379e1384. doi: /hrt

6 Limitations This reort details clinical results of a novel cryoablation rotocol for AF theray. The comarison between RFA and cryoballoon was not randomised, although consecutive atients undergoing PVI by different oerators in the same institution in a real-life clinical setting were recruited. The decision to aly only two cryoballoon alications er vein was based on early exerience with the Arctic Front and ultrasound balloon catheters; and in keeing with other studies whereby a median of two alications was required to isolate all PVs excet the right inferior PV. Only 24 h Holter monitoring was erformed to detect asymtomatic AF and more eisodes may have been detected if longer recording durations were used. Limiting the total number of cryoballoon alications allowed for a shorter rocedural time but did increase rocedural cost, as 60% of the cryoablation cohort required a second catheter to ensure achievement of PV isolation. CONCLUSIONS Pulmonary venous isolation can be achieved in less than 2 h by a simle cryoablation rotocol with excellent results after a single intervention, articularly for aroxysmal AF. Monitoring of hrenic nerve function by continuous acing and alating the vigour of diahragmatic contractions is essential in minimising the risk of hrenic nerve alsy during balloon cryoablation. Funding British Heart Foundation. Dr Piin Kojodjojo is funded by a British Heart Foundation Travel Fellowshi (FS/09/047). Cometing interests None. Ethics aroval This study was conducted with the aroval of St. Mary s Hosital, Imerial College Healthcare NHS Trust. Provenance and eer review Not commissioned; externally eer reviewed. REFERENCES 1. Bhargava M, Di Biase L, Mohanty P, et al. Imact of tye of atrial fibrillation and reeat catheter ablation on long-term freedom from atrial fibrillation: Results from a multicenter study. Heart Rhythm 2009;6:1403e Jais P, Hocini M, Sanders P, et al. 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