Entrainment Mapping for Rapid Distinction of Left and Right Atrial Tachycardias (PDF)

Entrainment mapping for rapid distinction of left and right atrial tachycardias Hidekazu Miyazaki, MD,a William G. Stevenson, MD,a Kent Stephenson, MD,a Kyoko Soejima, MD,b Laurence M. Epstein, MDa From the aCardiovascular Division, Department of Internal Medicine, Brigham and Women’s Hospital, Har...

Entrainment mapping for rapid distinction of left and right atrial tachycardias Hidekazu Miyazaki, MD,a William G. Stevenson, MD,a Kent Stephenson, MD,a Kyoko Soejima, MD,b Laurence M. Epstein, MDa From the aCardiovascular Division, Department of Internal Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts, and b Cardiovascular Division, Department of Internal Medicine, Keio University, Tokyo, Japan. BACKGROUND Distinguishing left from right atrial tachycardia is a critical step for guiding ablation. OBJECTIVES The purpose of this study was to develop and validate a simple algorithm predicting the location of macroreentrant atrial tachycardia (AT) circuits from limited entrainment mapping in right atrium (RA) and coronary sinus (CS). METHODS In 180 patients with organized reentrant AT, entrainment was performed at the high RA, proximal CS, and distal CS. The difference between the postpacing interval (PPI) and tachycardia cycle length (TCL) was calculated at each site. The location of the AT reentrant circuit was determined by mapping and ablation. An algorithm predicting AT regions was developed from 104 ATs in the first 90 patients (group I) and prospectively evaluated in a validation cohort of 106 ATs in the second 90 patients (group II). RESULTS In group I, PPI-TCL difference ⬍50 or ⬎50 ms at the high RA distinguished RA from LA reentrant circuits. For RA tachycardias, PPI-TCL difference at the proximal CS distinguished common flutter from lateral RA circuits. For LA circuits, PPI-TCL difference at the proximal and distal CS distinguished perimitral reentry from reentry involving the right pulmonary veins and septum. In group II, an algorithm based on PPI-TCL difference ⬎50 or ⬍50 ms at the high RA, proximal CS, or distal CS had sensitivity of 94%, specificity of 88%, and predictive accuracy of 93% for predicting the successful ablation region. CONCLUSION Limited entrainment from sites accessible from the RA can expeditiously suggest the AT location to guide more detailed mapping and potentially avoid unnecessary transseptal punctures in some patients. KEYWORDS Atrial tachycardia; Macroreentry; Postpacing interval (Heart Rhythm 2006;3:516 –523) © 2006 Heart Rhythm Society. All rights reserved. Introduction of the likely region of interest would facilitate the map- ping and ablation procedure, particularly if those tachy- Reentrant atrial tachycardias (ATs) usually are associated cardias that require LA mapping and ablation can be with atrial scars or incisions from prior surgery1,2 or rapidly identified. During entrainment, the difference be- catheter ablation.3,4 These ATs can be located in the left tween the postpacing interval (PPI) and the tachycardia atrium (LA) or right atrium (RA) and localization can be cycle length (TCL) is an indication of the conduction challenging, often requiring extensive activation se- time between the pacing site and the reentrant circuit. We quence and entrainment mapping.5,6 Rapid identification hypothesized that entrainment mapping from three sites accessible from the RA could be used for rapid identifi- Dr. Miyazaki is supported by the Jikei University School of Medicine, cation of the likely region (RA, anterior LA, and poste- Tokyo, Japan. rior LA) containing the reentrant circuit. Address reprint requests and correspondence: Dr. William G. The purpose of this study was to develop and validate Stevenson, Cardiovascular Division, Brigham and Women’s Hospital, 75 a simple algorithm predicting the location of ATs by Francis Street, Boston, Massachusetts 02115. E-mail address: [email protected]. using limited entrainment mapping in the RA and coro- (Received September 28, 2005; accepted January 12, 2006.) nary sinus (CS). 1547-5271/$ -see front matter © 2006 Heart Rhythm Society. All rights reserved. doi:10.1016/j.hrthm.2006.01.014 Miyazaki et al Rapid Distinction of Regionalization of Atrial Circuit 517 Methods fluoroscopic projection), and mid to distal CS (⬎3 cm from the CS orifice). A train of atrial stimuli (10 mA, 2-ms pulse width, either unipolar or bipolar) was performed at a cycle length 10 Study population to 30 ms shorter than TCL for a sufficient duration to accel- erate all recorded electrograms to the pacing cycle length. PPI Patients who underwent catheter mapping and ablation was measured from the last stimulus to the first peak of the were included in the study if they had an organized next electrogram recorded from the pacing site (Figures 1 regular AT (⬍20 ms of A-A interval variability) that through 3). If saturation of the recording amplifier obscured satisfied the following conditions: (1) determined to be that signal, the electrogram recorded from the adjacent proxi- macroreentrant based on a combination of activation se- mal recording electrodes was used for the PPI measurement, quence and entrainment mapping that indicated relatively provided this electrogram was synchronous with that observed widely separated sites (such as the atrial roof and floor) at the distal electrode in the absence of pacing. When the were in the reentrant circuit (Figure 1D); and (2) location electrogram at the distal electrode was not simultaneous with of the reentrant circuit was further supported by success- that of the adjacent proximal electrode, PPI-TCL difference ful ablation defined as termination and suppression of was calculated from the conduction time between the last reinitiation by ablation. stimulus that entrained tachycardia and the second beat after A total of 180 consecutive patients (135 men and 45 the stimulus (N ⫹ 1 beat) as described previously.7 women; mean age 56 ⫾ 11 years, range 20 – 85 years) with Activation sequence mapping was aided by electroanatomic 210 ATs who met the inclusion criteria were included. A mapping system (CARTO, Biosense-Webster Inc.) using 7Fr total of 84 of the ATs that were not due to reentry through quadripolar catheters with a 4- or 8-mm distal electrode. LA the subeustachian isthmus occurred in 74 patients who had mapping was performed via transseptal catheterization. Sys- a history of atrial fibrillation and had a prior ablation pro- temic anticoagulation was achieved with intravenous heparin cedure for atrial fibrillation (37 patients) or were undergoing to maintain an activated clotting time of 250 to 350 seconds for a first procedure for presumed atrial fibrillation (37 patients) LA mapping and ablation. Radiofrequency catheter ablation (Table 1). The relationship of entrainment mapping to AT was performed to transect a portion of the path of a macro- location was assessed in the first 90 consecutive patients reentrant circuit by connecting anatomic barriers or areas of (group I) and an algorithm for AT location developed from conduction block. In patients who had prior surgery or ablation this group. The algorithm was tested in the second 90 for atrial fibrillation, potential gaps in prior ablation lines were consecutive patients (group II). Patient characteristics were targeted. For ATs involving the isthmus between the left pul- similar in the two groups (Table 1). monary veins and the mitral isthmus, ablation lesions were placed across the isthmus with ablation in the CS if conduction Mapping and catheter ablation procedure block was not achieved across the line. For ATs involving the right veins, a line of lesions was placed from the right to left Electrophysiologic study was performed after written informed superior pulmonary veins or, when the septum was involved, consent was obtained. Data collection was performed accord- across the septum to the fossa ovalis and/or mitral annulus. For ing to the protocol approved by the Institutional Human Sub- ATs involving the RA lateral or posterior wall, a line of ject Protection Committee. RA recording and stimulation was ablation lesions was placed connecting an area of scar or performed from either a 20-pole electrode catheter with 2-12- conduction block with an anatomic obstacle the inferior vena 2-mm interelectrode spacing (Biosense-Webster Inc., Dia- cava, tricuspid annulus, or fossa ovalis. Conduction block mond Bar, CA, USA) placed parallel to the tricuspid annulus across a line was assessed from absence of electrograms, in- with its tip advanced into the CS or a quadripolar catheter ability to capture with pacing, or double potentials along the positioned at the high RA. When the proximal electrodes on course of the line. Radiofrequency energy was delivered start- the 20-pole catheter were used for stimulation, they were ing at 20 to 30 W and increased to a maximum power output generally above the fluoroscopic midpoint of the RA on its of 50 W and temperature of 60°C for the 4-mm electrode lateral wall as viewed in the left anterior oblique (LAO) pro- catheter (in 36 patients) and 70 W with a target temperature of jection. If the 20-pole catheter electrodes did not provide pac- 50° to 56°C for the 8-mm electrode catheter (144 patients). ing in that region, the roving catheter was placed at that region for pacing. CS recording and stimulation was performed from Classification of anatomic location the electrodes of the 20-pole catheter in the CS or from a steerable multielectrode catheter. Induction of ATs was per- The AT reentrant region was anatomically classified into six formed from the RA and/or CS at two drive cycle lengths with divisions based on the location where it was interrupted by up to two extrastimuli and burst pacing. If the clinical arrhyth- ablation: (1) lateral or posterior wall of RA, (2) subeusta- mia did not occur spontaneously and was not induced in the chian isthmus used for common RA flutter, (3) atrial sep- baseline state, stimulation was repeated during administration tum, (4) adjacent to the right pulmonary veins, (5) involving of intravenous isoproterenol (1– 6 ␮g/min). the isthmus between the mitral annulus and the left inferior Entrainment was performed at the high RA, proximal CS pulmonary vein, and (6) adjacent to the left pulmonary veins (within 1 cm of the CS orifice as assessed from the LAO but not involving the mitral isthmus. 518 Heart Rhythm, Vol 3, No 5, May 2006 Figure 1 Tracings from a patient who had prior circumferential pulmonary vein isolation and linear lesions in the subeustachian and mitral isthmuses. The sequence of activation is indicated by the long diagonal arrows. Tachycardia cycle length (TCL) is 220 to 230 ms. Shown from top to bottom are surface ECG leads and bipolar intracardiac recordings from a 20-pole catheter with electrodes 17/18 at the high right atrium (RA), electrodes 5-6 at the coronary sinus (CS) orifice, and electrodes 1-2 in the distal CS. A: Entrainment from the high RA (TA 17/18). The postpacing interval (PPI) is 445 ms and the difference between PPI and TCL is 225 ms, confirming that the high RA is out of the circuit and indicating likely left atrial (LA) origin of the tachycardia. B: Entrainment performed from the proximal CS (CS prox). PPI is 255 ms, and the PPI-TCL difference is 35 ms, confirming that the proximal CS is in or near the circuit. C: Entrainment from the distal CS (CS dis). PPI is 250 ms, and the PPI-TCL difference is 20 ms, confirming that the distal CS is in or near the circuit. D: Activation mapping and entrainment at additional left atrial sites was consistent with reentry around the mitral annulus. Ablation at a gap in the prior ablation line between left inferior pulmonary vein and mitral annulus abolished this tachycardia. Miyazaki et al Rapid Distinction of Regionalization of Atrial Circuit 519 Table 1 Baseline characteristics of the patients Data analysis Group I Group II Characteristics (n ⫽ 90) (n ⫽ 90) The PPI-TCL difference at the high RA, proximal CS, and distal CS was measured for all tachycardias (Figures 1 Age (yr) 55 ⫾ 11 57 ⫾ 11 through 3). Continuous data are expressed as mean ⫾ SD. Male sex (%) 64 (71) 68 (75) Hypertension (%) 36 (40) 30 (33) Generalized estimating equations were used to adjust for Coronary heart disease (%) 16 (18) 10 (11) multiple observations in individual patients. Categorical Valvular heart disease (%) 6 (7) 6 (7) variables were compared by Chi-square analysis. Data anal- Cardiomyopathy (%) 0 (0) 3 (3) ysis was performed with STATA software package (Stata Atrial septal defect (%) 2 (2) 1 (1) Prior cardiovascular surgery Corp., Texas, CA, USA). Two-sided P ⬍.05 were consid- Coronary artery bypass 5 (6) 3 (3) ered significant. graft (%) Mitral or aortic valve 3 (3) 5 (6) surgery (%) Closure for atrial septal 3 (3) 1 (1) Results defect (%) Atrial maze procedure (%) 1 (1) 1 (1) Prior Catheter Ablation Retrospective evaluation cohort Atrial fibrillation (%) 14 (16) 23 (25) Atrial flutter (%) 7 (8) 8 (9) In group I, a total of 104 ATs were examined, including 47 Concomitant atrial 15 (17) 22 (24) common RA flutters, 10 ATs from the RA lateral region, 10 fibrillation ablation from the atrial septum (five ablated from the right side and Left ventricular ejection 0.65 ⫾ 0.16 0.66 ⫾ 0.16 five ablated from the left side of the septum), 7 from the fraction Left atrial size (mm) 43.0 ⫾ 6.6 42.7 ⫾ 7.7 right pulmonary vein region, 15 involving the isthmus be- tween the mitral annulus and left inferior pulmonary vein, and 15 from the left pulmonary vein region (Table 2). The PPI-TCL difference at the high RA was significantly shorter Figure 2 Tracings from a patient with prior circumferential pulmonary vein isolation and linear lesions in subeustachian and mitral isthmuses and at the roof of the left atrium (LA). The sequence of activation is indicated by the long diagonal arrows. Tachycardia cycle length (TCL) is 240 to 250 ms. The catheter location is approximately the same as the case shown in Figure 1 (electrodes 19/20 at the high right atrium [RA], 5/6 at the coronary sinus [CS] orifice, and 1/2 at the middle CS). A: Entrainment from the high RA (TA 19/20). The postpacing interval (PPI) is 380 ms, and the PPI-TCL difference is 140 ms, confirming that the high RA is out of the circuit and indicating likely an LA origin of tachycardia. B: Entrainment is performed from the proximal CS (CS os). PPI is 285 ms, and the PPI-TCL difference is 35 ms, confirming that the proximal CS is close to the circuit. C: Entrainment from the middle CS (CS mid). PPI is 320 ms, and the PPI-TCL difference is 90 ms, confirming that the middle CS is out of the circuit. Activation mapping was consistent with reentry around right pulmonary veins. Ablation at a gap on the superior aspect of the line encircling of right pulmonary veins abolished this tachycardia. 520 Heart Rhythm, Vol 3, No 5, May 2006 Figure 3 Tracings from patient 84, who had a history of atrial septal defect closure and mitral and aortic valve replacement. Tachycardia cycle length (TCL) is 410 to 420 ms. The sequence of activation is indicated by the long diagonal arrows. Shown from top to bottom are surface ECG leads and bipolar intracardiac recordings from a 20-pole catheter with electrodes 17/18 at the high right atrium (TA) and electrodes 1-2 at the coronary sinus (CS) orifice. A: Entrainment from the roving ablation catheter (ROV) at the high RA. The postpacing interval (PPI) is 460 ms, and the PPI-TCL difference is 40 ms, confirming that the high RA is close to the circuit and indicating likely RA origin of tachycardia. B: Entrainment is performed from the proximal CS (CS os). PPI is 500 ms, and the PPI-TCL difference is 80 ms, confirming that the proximal CS is out of the circuit. C: Entrainment from the roving ablation catheter at the distal CS. PPI is 540 ms, and the PPI-TCL difference is 120 ms, confirming that the distal CS is remote from the circuit. Further activation and entrainment mapping demonstrated the scar-related reentry in lower part of lateral and inferior wall of the right atrium. Ablation between the lower anterior aspect of the scar and the tricuspid annulus abolished this tachycardia. during RA tachycardias (25 ⫾ 14 ms) than for either septal vein region and right lateral atrial region (Figure 4B) and was (81 ⫾ 24 ms) or LA tachycardias (105 ⫾ 25 ms, P ⬍.001; significantly longer for these ATs than ATs at other locations. Figure 4A). All LA tachycardias had PPI-TCL differences For LA tachycardias, entrainment from the proximal CS re- ⬎50 ms during high RA entrainment. In contrast, only two sulted in significantly longer PPI-TCL difference during AT RA tachycardias had PPI-TCL differences ⬎50 ms at the involving the left pulmonary vein region than for the mitral high RA, both with scar-related lateral wall reentry. isthmus or right pulmonary vein region (85 ⫾ 20 ms vs 32 ⫾ The PPI-TCL difference during entrainment at the proximal 10 ms and 34 ⫾ 18 ms, P ⬍.001, respectively). During en- CS was ⬎50 ms for 23 of 25 ATs ablated at the left pulmonary trainment from the distal CS, the PPI-TCL difference was Table 2 Relationship between predicted site of atrial tachycardia origin (algorithm) and actual location based on ablation site in group I Predicted location Successful RA Common Septum or Mitral Left Sens Spec PPV NPV ablation site n TCL (ms) lateral AFL right PVs annulus PVs (%) (%) (%) (%) RA 57 8 47 2 96 100 100 96 RA lateral 10 417 ⫾ 100 8 2 80 100 100 98 Common AFL 47 261 ⫾ 41 47 100 100 100 100 Left atrium 37 7 14 16 100 82 76 100 Left PVs 15 235 ⫾ 68 1 14 93 98 88 99 Mitral annulus 15 245 ⫾ 59 1 13 1 87 99 93 98 Right PVs 7 234 ⫾ 65 6 1 88 97 83 98 Septum 10 355 ⫾ 101 9 1 Total 104 8 47 18 14 17 94 88 98 75 Data were obtained from initial 90 patients (retrospective analysis). AFL ⫽ atrial flutter; NPV ⫽ negative predictive value; PPV ⫽ positive predictive value; PVs ⫽ pulmonary veins; RA ⫽ right atrium; RA lateral ⫽ RA lateral wall; Sens ⫽ sensitivity; Spec ⫽ specificity; TCL ⫽ tachycardia cycle length. Miyazaki et al Rapid Distinction of Regionalization of Atrial Circuit 521 Figure 4 Comparisons of the difference between the postpacing interval (PPI) and tachycardia cycle length (TCL) at the high right atrium (RA) (A), proximal coronary sinus (CS) (B), and distal CS for atrial tachycardias (ATs) ablated from the six different regions (x-axis) in group I. Lateral RAT is atrial tachycardia (AT) involv- ing the lateral region in the RA; septal AT is AT involving the atrial septum; RPV AT is AT with circuit adjacent to the right pulmonary veins (PVs); mitral AT is AT with circuit adjacent to mitral annulus involving isthmus between the mitral annulus and left PVs; LPV AT is AT with circuit adjacent to the left PVs but not involving the mitral isthmus. significantly shorter during AT involving the mitral isthmus or from the atrial septum, 18 from right pulmonary vein re- left pulmonary vein region than for the right pulmonary vein gion, 19 from the mitral annulus involving the isthmus region (31 ⫾ 21 ms and 37 ⫾ 15 ms vs 84 ⫾ 26 ms, P ⬍.001, between the mitral annulus and left inferior pulmonary vein, respectively; Figure 4C). and 21 from the left pulmonary vein region (Table 3). The Based on the group I data, an algorithm was developed algorithm correctly localized the region involved in 93% of for identifying the successful ablation region (Figure 5). First entrainment at the high RA is assessed. A PPI-TCL difference ⱕ50 ms indicates an RA tachycardia. A PPI-TCL difference ⱕ50 ms at the proximal CS then discriminates between common RA flutter and AT from lateral RA. If entrainment at the high RA has a PPI-TCL difference ⬎50 ms, an LA tachycardia is likely. A PPI-TCL difference ⱕ50 ms at the proximal CS then suggests AT involving the right pulmonary vein region or mitral annular region. A PPI-TCL difference ⱕ50 ms at the distal CS indicates involvement of the atria adjacent to mitral annulus. In group I, this algorithm correctly identified LA compared with RA origin with a sensitivity of 89%, specificity of 100%, positive predictive value of 100%, negative predictive value of 86%, and predictive accuracy 93% (Table 2). Overall for predicting the correct ablation region, the sensitivity was 94%, specificity 88%, positive predictive value 98%, negative pre- Figure 5 Stepwise algorithm for determining the location of dictive value 75%, and predictive accuracy 93%. atrial tachycardia (AT) circuits. See text for discussion. DCS ⫽ distal coronary sinus; HLRA ⫽ high lateral right atrium; Lateral Prospective validation cohort RAT ⫽ AT involving the lateral region in the RA; LPV ⫽ left pulmonary vein; PCS ⫽ proximal coronary sinus; PPI-TCL ⫽ In group II, a total of 106 ATs were examined, including 32 difference between postpacing interval and tachycardia cycle common RA flutters, 10 ATs from the RA lateral region, 6 length; RA ⫽ right atrium; RPV ⫽ right pulmonary vein. 522 Heart Rhythm, Vol 3, No 5, May 2006 Table 3 Relationship between predicted site of atrial tachycardia origin (algorithm) and actual location based on ablation site in group II Predicted location Successful RA Common Septum or Mitral Left Sens Spec PPV NPV ablation site n TCL (ms) lateral AFL right PVs annulus PVs (%) (%) (%) (%) RA 42 8 32 2 95 100 100 97 RA lateral 10 416 ⫾ 110 8 2 80 100 100 98 Common AFL 32 256 ⫾ 65 32 100 100 100 100 Left atrium 58 17 17 24 93 83 87 91 Left PVs 21 230 ⫾ 61 21 100 95 84 100 Mitral annulus 19 246 ⫾ 35 1 17 1 89 99 94 98 Right PVs 18 236 ⫾ 70 16 2 88 96 88 96 Septum 6 401 ⫾ 118 5 1 Total 106 8 32 24 17 25 95 88 96 85 Data were obtained from second 90 patients (prospective analysis). Abbreviations as in Table 1 AT circuits. Predictive accuracy for ATs involving the tri- dia. Electrodes arrays may shorten mapping time but require cuspid annular, mitral annular, or left pulmonary vein re- deployment in the chamber of interest and are associated gion was somewhat better than for ATs at other atrial with some risk. Predicting the likely origin of AT should regions (97% vs 85%, P ⫽.021). facilitate use of activation mapping and more detailed en- trainment mapping to identify critical reentrant circuit re- gions for ablation. The P-wave morphology during AT can Discussion also suggest the AT region.8,9 P waves often are low am- plitude and superimposed on T waves, making their assess- The response to entrainment indicates the proximity of the ment difficult. pacing site to a reentrant circuit. The PPI-TCL difference Other studies have used entrainment mapping for iden- reflects the conduction time between the pacing site and the tifying critical AT circuit sites.1,5,6,8,10,11 However, this is tachycardia circuit. In patients with organized reentrant AT, the the first study to show that entrainment at limited atrial sites present study systematically analyzed the relationship between accessible from the RA can be used for estimating the anatomic location of AT reentrant circuit and PPI-TCL differ- location of AT circuits. The location of the RA pacing site ence at three different atrial sites that were accessible from the has an important influence on the PPI for LA tachycardias. RA. The following key findings were demonstrated. (1) During Pacing from posterior RA sites at high output theoretically entrainment from the high RA, a PPI-TCL difference ⬎50 ms could capture the LA and falsely suggest that the tachycar- strongly suggests an LA tachycardia. Exceptions do occur with dia was in the RA. RA scars, likely due to the potential for a long conduction time between the high RA and a circuit on the other side of a region Study limitations of conduction block in the low RA. Entrainment from the low RA should identify these circuits. (2) The combination of There are important caveats and limitations of our approach. PPI-TCL difference (⬍50 ms) at the high RA and proximal CS We defined the reentrant circuit location based on where the distinguishes common RA flutter from a reentry elsewhere in tachycardia was interrupted with ablation. These circuits the RA. (3) Entrainment from the high RA and two CS sites can be large, and it is possible that the circuits could be allows excellent prediction of the general region contributing interrupted by ablation in other locations. After entrainment, to LA reentrant tachycardias. we attempted to identify narrow isthmuses for ablation based largely on entrainment and anatomic considerations. Entrainment mapping and other methods We did not perform a complete activation sequence map before ablating an isthmus in the circuit; therefore, for many Reentrant circuits causing macroreentrant ATs can be de- tachycardias, we cannot be more specific regarding the fined by extensive activation sequence mapping.5,6 Defining types of reentrant circuits in the study. Additional entrain- an unknown macroreentrant circuit, however, can be diffi- ment sites potentially could provide more detailed charac- cult, particularly in patients with prior extensive linear ab- terization, as shown in Figure 1D, but are not necessary for lation or surgery. Low-amplitude and fractionated electro- success when an isthmus is identified. This selection of grams can make assignment of an activation time difficult. ablation sites likely introduces some bias into the assign- Point-by-point activation mapping requires some time, and ment of reentrant circuit locations, and it may have been there is the risk that catheter manipulation will terminate the possible to ablate some ATs at more than one region. It tachycardia or change the tachycardia to another tachycar- seems unlikely that this source of classification bias would Miyazaki et al Rapid Distinction of Regionalization of Atrial Circuit 523 have a significant effect on distinguishing RA from LA cess should facilitate planning for transseptal catheterization circuits. Multiloop and biatrial circuits have been described, and allow more focused, detailed mapping. but we included for analysis only ATs for which a success- ful ablation site was identified. The algorithm does not adequately distinguish ATs that References can be ablated from the region adjacent to the right pulmo- nary veins from those that require ablation in the septum 1. Kalman JM, van Hare GF, Olgin JE, Saxon LA, Stark SI, Lesh MD. Ablation of “incisional” reentrant atrial tachycardia complicating sur- more distant from the right pulmonary veins. The location gery for congenital heart disease. Use of entrainment to define a of the RA pacing site has an important influence on the PPI critical isthmus of conduction. Circulation 1996;93:502–512. for LA tachycardias. If the pacing site is at the posterior RA, 2. Ishii Y, Gleva MJ, Gamache MC, Schuessler RB, Boineau JP, Bailey it may be possible for pacing to capture the LA and falsely MS, Damiano RJ, Jr. Atrial tachyarrhythmias after the maze proce- dure: incidence and prognosis. Circulation 2004;110:II-164 –II-168. suggest that an LA tachycardia is in the RA. 3. 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Characterization of reentrant In some cases, whether AT is focal or macroreentrant circuit in macro-reentrant right atrial tachycardia after surgical repair cannot be easily determined without extensive mapping. We of congenital heart disease: isolated channels between scars allow “focal” ablation. Circulation 2001;103:699 –709. expect this method will be useful for any reentrant arrhyth- 7. Soejima K, Stevenson WG, Maisel WH, Delacretaz E, Brunckhorst mia, provided pacing does not alter the tachycardia. It could CB, Ellison KE, Friedman PL. The N ⫹ 1 difference: a new measure be misleading with automatic tachycardias, although the for entrainment mapping. J Am Coll Cardiol 2001;37:1386 –1394. PPI would be expected to be shorter at sites close to the 8. Kalman JM, Olgin JE, Saxon LA, Lee RJ, Scheinman MM, Lesh MD. Electrocardiographic and electrophysiologic characterization of atyp- focus compared with distant sites. 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