Atrial Tachycardia After Ablation of Persistent Atrial FibrillationCLINICAL PERSPECTIVE
Identification of the Critical Isthmus With a Combination of Multielectrode Activation Mapping and Targeted Entrainment Mapping
Background— Atrial tachycardia (AT) that develops after ablation of atrial fibrillation often poses a more difficult clinical situation than the index arrhythmia. This study details the use of an impedance-based electroanatomic mapping system (Ensite NavX) in concert with a specialized multielectrode mapping catheter for rapid, high-density atrial mapping. In this study, this activation mapping was combined with entrainment mapping to eliminate ATs developing late after atrial fibrillation ablation.
Methods and Results— All study patients developed AT after ablation for atrial fibrillation. The approach to AT ablation consisted of 4 steps: use of a 20-pole penta-array catheter to map the chamber rapidly during the rhythm of interest, analysis of the patterns of atrial activation to identify wave fronts of electric propagation, targeted entrainment at putative channels, and catheter ablation at these “isthmuses.” All ablations were performed with irrigated radiofrequency ablation catheters. Forty-one ATs were identified in 17 patients (2.4±1.6 ATs per patient). Using the multielectrode catheter in conjunction with the Ensite NavX system, we created activation maps of 33 of 41 ATs (81%) (mean cycle length, 284±71 seconds) with a mean of 365±108 points per map and an average mapping time of 8±3 minutes. Of the 33 mapped ATs, 7 terminated either spontaneously or during entrainment maneuvers. Radiofrequency energy was used to attempt ablation of 26 ATs; 25 of 26 of the ATs (96%) were terminated successfully by ablation or catheter pressure.
Conclusions— This study demonstrates a strategy for rapidly defining and eliminating the scar-related ATs typically encountered after ablation of atrial fibrillation.
Received November 5, 2007; accepted January 29, 2008.
Surgical or catheter ablation of atrial fibrillation (AF) is an accepted therapeutic option for drug-refractory, symptomatic AF.1–6 Although patients with paroxysmal AF can be treated successfully with pulmonary vein (PV) isolation alone, additional ablation lesion sets, including linear lesions and ablation at sites of complex fractionated electrograms, are frequently placed to treat patients with persistent AF. One of the most troublesome aspects of the postablation course in this group of patients is the development of atrial tachycardias (ATs). These arrhythmias have a characteristic metronomic 2:1 ventricular response, typically are difficult to manage medically, and frequently recur after cardioversion.7–14 On the other hand, ATs appear to reflect a more organized atrial substrate on the continuum between AF and sinus rhythm, and successful ablation of the AT often is the last hurdle to overcome before sinus rhythm is achieved.
Clinical Perspective p 22
The mechanism of these ATs is typically macroreentry but also sometimes microreentry involving preexisting or iatrogenic ablation-related scar tissue. They typically are challenging to map and ablate because of the unpredictable location and extent of these combined idiopathic/iatrogenic scars. In an effort to efficiently identify the critical isthmuses sustaining postablation ATs, this study evaluated a systematic approach combining rapid high-density activation mapping with a penta-array mapping catheter coupled to an electrical impedance-based electroanatomic mapping system (Ensite NavX, St. Jude Medical, Minneapolis, Minn) and targeted entrainment. This strategy was assessed in a consecutive series of patients who presented with ATs after prior extensive ablation of persistent AF.
The study population consisted of 17 consecutive patients presenting with drug-refractory postablation ATs. All had a history of symptomatic persistent or long-lasting, persistent AF and had undergone at least 1 prior catheter or surgical ablation procedure for AF. The baseline characteristics are described in Table 1.
Previous Ablation Procedure
All patients had at least 1 previous catheter ablation for AF. The catheter ablation procedures involved a combination of extraostial PV isolation, cavotricuspid isthmus (CTI) ablation, left atrial (LA) roof line, mitral isthmus line, and complex fractionated atrial electrogram ablation in the LA, right atrium (RA), and/or the coronary sinus (CS). All patients had ECG documentation of AT refractory to antiarrhythmic drugs. One patient also had initially undergone a surgical maze procedure for AF during concomitant mitral valve replacement surgery.
Electrophysiology Study for AT
For all patients, antiarrhythmic drugs and warfarin sodium were continued up to the day of the ablation. The international normalized ratio was therapeutic (INR 2–3) at the time of the procedure. The surface ECG and bipolar endocardial electrograms were monitored continuously and stored on a computer-based digital amplifier/recorder system (GE Cardiolab, Waukesha, Wis). Intracardiac electrograms were filtered from 30 to 500 Hz and measured at a sweep speed of 100 to 200 mm/s.
A standard decapolar catheter was placed in the CS. A quadripolar reference electrode also was placed in the CS, RA appendage, or aortic root to serve as a location reference for the Ensite NavX mapping system.15 Transseptal access was obtained with contrast, fluoroscopy, and intracardiac echocardiography to place both an Agilis steerable sheath and a Daig SL-1 sheath (St. Jude Medical, St Paul, Minn) in the LA. A circular mapping catheter and either a 3.5-mm-tip Celsius Thermo-Cool (Biosense-Webster, Inc, Diamond Bar, Calif) or Chili (Boston Scientific, Inc, Natick, Mass) ablation catheter were placed through these sheaths into the LA.
In all patients, AT was present at baseline or was induced with rapid atrial pacing from the CS. First, the patients were evaluated for CTI-dependent atrial flutter by entrainment from the distal and proximal CS electrodes and, if suggestive, from the CTI itself.
Using the Ensite NavX system, we acquired separate multicomponent geometries of the LA appendage, left superior PV, left inferior PV, right superior PV, right inferior PV, and LA body with the circular mapping catheter. These were combined into 1 structure as the electroanatomic map of the LA and PVs and then compared alongside a 3-dimensional computed tomography or magnetic resonance of the LA. When ablation was performed in the RA, a separate geometry of the RA was created.
All of the PVs were evaluated for electric disconnection with a multipolar circular mapping catheter (Lasso or Optima catheters; Biosense-Webster, Inc, and St Jude Medical, Inc, respectively). If any reconnection was found, the veins were reisolated, typically requiring only a single ablation lesion at the point of breakthrough. Electric PV isolation was then confirmed with the circular mapping catheter.
The penta-array catheter is a 20-pole steerable mapping catheter arranged in 5 soft radiating spines (1-mm electrodes separated by 4-, 4-, and 4-mm interelectrode spacing) covering a diameter of 3.5 cm (PentaRay, Biosense-Webster, Inc). The penta-array catheter often was manipulated through the steerable sheath to facilitate mapping. Each electrode of this penta-array catheter can be localized by the Ensite NavX system so that the catheter is ultimately visualized as 5 radiating quadripolar splines (Figure 1). After introduction into the LA, activation mapping of the AT was performed. Fifteen bipolar electrograms are acquired simultaneously at each location, thereby allowing rapid creation of activation maps. Potential critical isthmuses were identified as areas of constrained activation (resulting from the idiopathic or iatrogenic scars and anatomic barriers), often also containing fractionated electrograms (Figure 2).
Once these wave fronts of atrial activation and putative isthmus sites were identified, entrainment pacing maneuvers were performed from the ablation catheter at these sites at a cycle length 20 to 30 ms less than the tachycardia cycle length (TCL; Figure 3). The site was considered part of the circuit if the postpacing interval (PPI) measured from the stimulation artifact to the return atrial electrogram on the ablation catheter was within 20 ms of the TCL.
Using the irrigated ablation catheter, we performed radiofrequency ablation with 20 to 50 W of energy and flow rates of 36 and 30 cm3/min, using internal or external irrigation, respectively. Energy was titrated to achieved an ≈10% Ohm impedance drop (Figure 4). If the AT terminated during radiofrequency ablation, rapid atrial pacing was performed to reinduce the arrhythmia. If it remained noninducible, the ablation was considered successful. If another AT was induced, it was then targeted for ablation. When linear ablation was used across an isthmus, activation mapping and/or differential pacing on either side of the ablation line was used to confirm block.
After the procedure, membrane-active antiarrhythmic medications were stopped for all patients. Anticoagulation with warfarin was continued with a target international normalized ratio of 2–3. All patients received routine postprocedure follow-up in the Cardiac Arrhythmia Service clinic at Massachusetts General Hospital, including Holter monitoring. Acute success was monitored at a 6- to 8-week follow-up appointment with an office ECG and instructions for the patient to notify his or her physician with any symptomatic recurrence. Holter recordings were obtained 6 weeks and 6 months after the procedure, or sooner at the discretion of the treating physician.
The authors had full access to and take full responsibility for the integrity of the data. All authors have read and agree to the manuscript as written.
Patient Characteristics and Previous Ablations
Patient characteristics and previous ablation data are listed in Table 1. The mean age of the patients was 62±10 years. The mean left atrial size was 40±5 mm. Two patients had previously documented coronary disease. The mean ejection fraction was 61±14%. One patient (patient 11) had previously undergone mitral valve replacement surgery and had a low ejection fraction (12%) resulting from tachycardia-induced cardiomyopathy. Four patients had undergone 2 previous LA ablation procedures. The second ablation for 3 of those patients was for AT after AF ablation (patients 3, 4, and 16); for 1 patient, it was for AF (patient 11). The mean time from the prior index AF ablation procedure to the “current” AT procedure was 5.8±5.4 months (range, 1 to 21 months).
All patients had AT documented on 12-lead ECG (Table 1). The mean cycle length of the clinical ATs was 266±47 ms (range, 210 to 380 ms). A total of 41 ATs were identified at the electrophysiology study in 17 patients, 1 of whom underwent 2 AT ablation procedures. The mean AT cycle length was 288±76.5 ms (range, 175 to 550 ms). The number of ATs per patient averaged 2.4±1.6 (range, 1 to 6).
Using the Ensite NavX-tracked penta-array mapping catheter, we performed activation maps in 33 of 41 ATs (81%). The characteristics of all ATs for which activation maps were created are summarized in Table 2. Eight ATs were not mapped because they stopped spontaneously before any mapping and did not recur. The mean cycle length of the mapped ATs was 284±71 ms (range, 175 to 550 ms). For 3 of the mapped ATs, detailed mapping data were not available for posthoc analysis. For the other 30 ATs, the activation maps included a mean of 365±108 points, each of which required a mean of 34±14 separate acquisitions with the penta-array catheter. For the macroreentrant ATs, these maps constituted, on average, 96±1% of the TCL. For 14 of the mapped ATs, the time to create an activation map was recorded; the mean time was 8±3 minutes.
Macroreentry versus focal microreentry ATs were defined on the basis of the AT activation map. Unlike macroreentrant ATs, the circuits of which traversed large portions of the atrium, focal ATs clinically mapped to a point source with centrifugal activation from this center. In 25 of 33 (78%), the mechanism was macroreentrant. In 8 of 33 (22%), the mechanism was focal. The most common AT (11 of 33; 33%) was a macroreentrant circuit involving the mitral isthmus (Figures 4 and 5⇓). The next most common location for an AT was a macroreentrant circuit involving the roof (9 of 33; 27%). An AT that involved the septum was the third most common (5 of 33; 15%). There were 2 right-sided ATs, 1 involving the lateral RA (Figure 6) and 1 involving the CTI.
Of the 33 mapped ATs, 7 terminated during entrainment maneuvers or stopped spontaneously and were not reinducible. Radiofrequency energy was used to ablate 26 ATs (Figures 2 and 4⇑), including 2 for which full activation maps were not created. With radiofrequency energy or catheter pressure, 25 (96%) of 26 ATs were terminated successfully. When radiofrequency failed to terminate the tachyarrhythmia, ibutilide was used to attain sinus rhythm. One patient (patient 7) developed AF intraprocedurally after 2 ATs were successfully ablated and then underwent electrical cardioversion to achieve sinus rhythm.
There were no complications in any of the patients undergoing AT ablation, including hematomas, pericardial tamponade, or conduction system damage requiring a permanent pacemaker. After 1.1 procedures per patient and a mean follow-up of 7.0±3.5 months (range, 2 to 14 months), 13 (76%) of 17 patients were free of AT (and AF) recurrences. After electric cardioversion, 3 of the patients have had no further clinical recurrences on antiarrhythmic medications. The final patient had recurrent AT even after cardioversion and is awaiting another ablation procedure.
Iatrogenic ATs have been reported after either surgical or catheter ablation of AF.7–14 After ablation of paroxysmal AF (wherein the initial ablation procedure is predominantly directed to PV isolation), the mechanism of AT is virtually always focal, originating from reconnected PVs.10 However, ablation of persistent AF typically involves LA, and sometimes RA, “substrate” ablation (linear lesions and ablation of sites of complex fractionated electrograms) beyond simple PV isolation. Here, we report a novel approach to mapping these postablation scar-related ATs by using a combination of activation mapping with a multielectrode array mapping catheter and targeted entrainment mapping.
The mechanisms of postablation ATs depend to a large extent on the ablation performed in the index procedure. A segmental approach to PV isolation, confirmed with a circular mapping catheter, resulted in most postablation ATs’ being of a focal mechanism from reconnected PV ostia.10,12 Anatomic approaches have been associated with a much higher prevalence of macroreentrant tachycardias around the mitral isthmus or PV ostia.13,16,17 After a complex fractionated electrogram approach to AF ablation, Nadamanee et al18 reported that 36% of patients had AT, with half having macroreentrant circuits and half having focal mechanisms. It stands to reason that the mechanisms of postablation AT are particularly variable in cases in which multiple strategies are used, as in the present series. The extent of ablation could even be unknown because either the initial strategy was surgical or several ablation procedures had previously been performed.
Haïssaguerre et al19 reported a 40% prevalence of postablation ATs in patients who had undergone catheter ablation of long-lasting persistent AF. Their initial AF ablation strategy included PV isolation, isolation of the superior vena cava, complex fractionated electrogram ablation, LA roof line, mitral isthmus line, CTI line, and CS isolation. The mechanisms of the ATs observed in this series were varied and included focal mechanisms in the anterior LA, CS, LA appendage, and septum.19 The same group reported anterior left AT in patients who had undergone PV isolation combined with LA roof and mitral isthmus lines but no previous anterior LA ablation.20
Catheter ablation of left-sided ATs can be technically challenging. Previous studies evaluating left-sided ATs without prior LA ablation have used a combination of magnetic electroanatomic and entrainment mapping with reasonable success.21,22 Similar approaches have been reported in series of post–AF ablation ATs.10–14,16–18 The usual strategy involves confirmation that the CTI is not part of the circuit and assurance of PV isolation, followed by entrainment mapping at the sites most commonly involved in ATs (septum, LA appendage, mitral isthmus, roof). Activation mapping can then be used as an adjunct when the above strategy is not successful. However, the most commonly used type of activation mapping (with magnetic electroanatomic mapping) is limited by a point-by-point acquisition process that is not always systematic, can be time consuming, and may miss small areas critical to the circuit. Detailed magnetic electroanatomic mapping may require >100 to 200 points, and each flutter circuit can be complex, involving multiple loops and figure-of-8 reentrant circuits. Noncontact mapping of left ATs, in association with AF, also has been described23; however, the accuracy of this mapping system is limited by both the frequently dilated nature of the atrial chamber and the low electrogram voltage amplitudes.
The penta-array catheter has been used to map postablation AT and to identify sources maintaining AF.19,24,25 However, the present series is the first to report its use in activation mapping using an electroanatomic mapping system. This allowed us to perform multielectrode activation mapping and to rapidly create detailed activation maps with relative ease. Almost every map was created in <10 minutes, with some completed in <5 minutes. In particular, when the AT location or cycle length changed in the middle of the procedure, remapping could be repeated expediently. This stands in stark contrast to the point-to-point electroanatomic mapping typically performed with a standard mapping catheter.
The other important advantage of activation mapping with this approach is the opportunity to identify critical isthmuses for these ATs, particularly for the macroreentrant variety. Shah and colleagues26 reported a series of 16 post–AF ablation ATs in which 73% involved a narrow, slowly conducting isthmus in the LA, usually involving the ridge between the left PVs and the LA appendage. When this isthmus was found, the AT usually could be terminated with 1 radiofreqency lesion; otherwise, long linear lesions (mitral isthmus or LA roof) lines had to be performed. With our technique, similar isthmuses can be identified. Figures 4 and 5⇑ show mitral isthmus ATs for which activation mapping identified other areas of activation percolating through scars that could be targeted more easily for ablation. When they are found, a single ablation lesion can terminate the AT, thereby obviating the need for a linear lesion set. When so much ablation has already been performed as part of the previous ablation procedure(s), the ability to substantively limit the extent of ablation may reduce any chance of harm (eg, arterial injury or electric isolation of the LA appendage) and may reduce the potential for additional iatrogenic scar formation.19,27
Our series had a 96% acute success rate; 25 of 26 postablation ATs were terminated with radiofrequency ablation or catheter pressure during the first procedure. Other series have reported similar success rates ranging from 88% to 100%.10,12,13,16,19 Our recurrence rate (5 of 17; 29%) also was similar to other published studies. Recurrence rates in these series ranged from 0% to 47% with mean follow-up ranging from 2 to 16 months.10,12,13,16,19 A higher rate of recurrence tended to occur in series with longer follow-up.
The usefulness of this technique can extend beyond post– AF ablation AT to any tachyarrhythmia in which the circuit is difficult to identify. During a staged ablation procedure to treat persistent AF, it is common for the rhythm to eventually organize to an AT percolating through areas that had been incompletely ablated or areas of chronic scarring. In these cases, the approach described in this study can be used similarly to rapidly identify and ablate isthmuses critical to the tachycardia circuits (Figure 7). In addition, although not specifically evaluated in this study, another approach to consider is multielectrode activation mapping during sinus rhythm to identify putative channels of activation. As previously demonstrated for ATs in the setting of surgically corrected congenital heart disease, systematic ablation of these channels can effectively eliminate clinical ATs.28
This study includes a relatively small cohort of patients. In addition, the follow-up has been based on symptomatic recurrence and periodic Holter monitoring. Although an invasive monitor would be more effective in ruling out asymptomatic recurrences, it should be noted that the 2:1 response frequently observed with these ATs typically renders the patient quite symptomatic as a result of the tachycardia. Furthermore, the possibility of asymptomatic atrial arrhythmia recurrence does not detract from the procedural efficacy in rapidly identifying and terminating the arrhythmias. Another important limitation of this approach is the possibility for the AT to either terminate or change mechanism during entrainment. However, by first performing activation mapping, we could minimize the number of entrainment attempts and thereby minimize the probability of termination. Indeed, termination during entrainment was observed for only 2 of the ATs evaluated in this study. Finally, it may be economically challenging to use the penta-array catheter in addition to the circular mapping catheter during routine clinical procedures as opposed to a limited number of clinical investigational cases as in this study. However, in our more recent experience, we have been able to perform the entire ablation procedure using just the penta-array catheter (without the circular catheter), including creating the LA-PV geometry, performing/verifying electric PV isolation, and mapping/ablating ATs. Alternatively, a circular mapping catheter could be used for mapping; although less effective at conforming to the cardiac anatomy than the penta-array catheter, it nonetheless provides a more rapid means for mapping than does point-to-point mapping with a standard quadripolar mapping catheter.
We report a technique to rapidly identify and eliminate postablation ATs with a high degree of success. In addition, the identification of critical isthmuses may reduce the extent and time needed for radiofrequency ablation. Future studies are needed to fully assess whether this technique may be applied to other scar-related ATs, including those in the setting of prior surgery for congenital heart disease and those in the presence of idiopathic atrial scar.
Source of Funding
This work was supported in part by the Deane Institute for Integrative Research in Atrial Fibrillation and Stroke.
Drs Reddy and Neuzil have received grant support from and served as consultants to Biosense-Webster, Inc, and St. Jude Medical, Inc. Dr d’Avila has served as a consultant to St. Jude Medical, Inc. S. Kim is an employee of St. Jude Medical, Inc. The remaining authors report no potential conflicts.
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Catheter ablation is increasingly being performed to treat drug-refractory, symptomatic atrial fibrillation (AF). One of the more troubling aspects of AF ablation, particularly extensive atrial ablation for persistent AF, is the appearance of atrial tachycardias (ATs) after AF ablation. These arrhythmias often have a metronomic 2:1 ventricular response, typically are difficult to manage medically, and frequently recur after cardioversion. On the other hand, ATs appear to reflect a more organized atrial substrate on the continuum between AF and sinus rhythm; successful ablation of the AT is often the last hurdle to overcome before sinus rhythm is achieved. However, there is no accepted systematic approach to mapping and ablating these arrhythmias. The present article proposes and evaluates a novel method consisting of 4 steps: use of a 20-pole penta-array catheter for rapid mapping of the chamber during the rhythm of interest, analysis of the patterns of atrial activation to identify wave fronts of electrical propagation, targeted entrainment at putative channels, and catheter ablation at these “isthmuses.” The process is useful because it can be performed rapidly and repetitively, especially because these ATs are notoriously transitory and polymorphous. The method also allows identification of critical isthmuses required for macroreentrant AT that may have heretofore gone unnoticed; these areas can then be targeted to terminate the arrhythmia with relatively few radiofrequency applications. In this study, when radiofrequency ablation was attempted, ablation of these ATs resulted in a >95% success rate, and the acute success was durable in follow-up.
Presented in part at the 2007 Annual Sessions of the Heart Rhythm Society, Denver, Colo, May 9–12, 2007, and published in abstract form (Heart Rhythm. 2007;4:S345).
The online Data Supplement can be found with this article at http://circep.ahajournals.org/cgi/content/full/1/1/14/DC1.