.Heart Rhythm. 2008 Mar;5(3)400-5

Relationship between perimitral and peritricuspid conduction timesSébastien Knecht, MD, Matthew Wright, MBBS, PhD, Frederic Sacher, MD, Kang-Teng Lim, MD, Seiichiro Matsuo, MD, Mark D. O’Neill, MBBCh, DPhil, Mélèze Hocini, MD, Pierre Jaïs, MD, Jacques Clémenty, MD, Michel Haïssaguerre, MDFrom the Hôpital Cardiologique du Haut-Lévêque and the Université Victor Segalen Bordeaux II, Bordeaux, France.BACKGROUND Conduction block across the left mitral isthmus (LMI) seems more challenging to achieve and validate compared with the cavotricuspid isthmus (CTI).OBJECTIVE This study sought to investigate the relationship be-tween peritricuspid and perimitral circuit times in the same pa-tient and to compare the difficulty in achieving the CTI and LMI linear lesions.METHODS We retrospectively studied 122 consecutive patients (46 paroxysmal and 76 persistent) admitted for atrial fibrillation ablation or subsequent atrial macroreentry who underwent both CTI and LMI ablation. The peritricuspid and perimitral conduction times were measured after validation of bidirectional block across their respective line by pacing from the septal side of the CTI or LMI and recording of the second late potential on the line of block. Atrial dimensions were measured by standard transthoracic echocardiographic techniques.RESULTS The mean peritricuspid and perimitral times were 180 Ϯ35 ms (range 120 to 300) and 189 Ϯ42 ms (range 120 to 322), respectively, with a mean difference of 7 Ϯ32 ms (Ϫ70 to 95).The correlation between both circuit times was highly significant (r ϭ0.621, P Ͻ.001). In 84 patients (68%), the perimitral time was within 30 ms of the peritricuspid time. In the remaining patients, only 12 (10% of the total patients) had a shorter per-imitral time compared with peritricuspid time. Radiofrequency energy delivered was significantly longer for LMI (15 Ϯ7 min [range 7 to 33]) compared with CTI (7 Ϯ4 min [range 3 to 17]) (P ϭ.005).CONCLUSION The peritricuspid and perimitral circuit times are strongly correlated. In 90% of patients, the perimitral conduction time is within 30 ms or longer than the peritricuspid time. In addition, both circuit times are always Նthan 120 ms. Compared with the left mitral isthmus line, the CTI line is significantly easier to perform.KEYWORDS Catheter ablation; Atrial fibrillation; Linear lesions; Cavotricuspid isthmus; Left mitral isthmus(Heart Rhythm 2008;5:400–405) © 2008 Heart Rhythm Society. All rights reserved.IntroductionSeveral different catheter ablation strategies have been de-scribed to treat atrial fibrillation (AF). In addition to pulmonary vein (PV) isolation1– 8 and ablation based on electrogram anal-ysis,9 –15 linear lesions are frequently needed during AF16 –19 or for subsequent atrial tachycardias (AT).3,20 –22 In the left atrium (LA), the 2 most common linear lesions are the roof line and the left mitral isthmus (LMI) line. The LA roof line joins both superior PVs,23 and the LMI line is from the mitral annulus to the left inferior PV.24 In the right atrium, the cavotricuspid isthmus (CTI) line is the most often performed and joins the tricuspid annulus to the inferior vena cava.25Conduction block at the CTI line seems easier to achieve and to validate than at the LMI line,24 –28 although there are no studies comparing the difficulty of both procedural techniques. When pacing at one side of the completed line, the circuit times for either tricuspid or mitral annuli are related to both conduc-tion velocity and perimeter of the respective annulus. These circuit times are highly variable between patients, precluding the use of specific conduction time as an end point for linear block. However, a close relationship between the perimitral and the formerly determined peritricuspid circuit times within the same patient could be used as a marker for success.This study was conducted to evaluate the relationship between peritricuspid and perimitral circuit times within individual patients, and to compare procedural difficulty in achieving bidirectional block on both CTI and LMI lines during the same electrophysiological procedure. MethodsStudy populationSince May2004,122consecutive patients admitted for drug-refractory symptomatic AF or AT in the context ofDr.Knecht is supported by the Belgian Foundation for CardiacSurgery.Dr.O’Neill is supported by the British Heart Foundation.Drs.Jaïs,Hocini and Haïssaguerre have served on the advisory board of,andreceived lecture fees from,Biosense-Webster.Address reprint re-quests and correspondence:Dr.Sébastien Knecht,Service de Ryth-mologie,Hôpital Cardiologique du Haut-L’évêque,Avenue de Magel-lan, 33604 Bordeaux-Pessac, France. E-mail address: sebastien.knecht@chu-brugmann.be. (Received October 18, 2007; accepted November 30,2007.)1547-5271/$-see front matter©2008Heart Rhythm Society.All rights reserved.doi:10.1016/j.hrthm.2007.11.025prior AF ablation have undergone both CTI and LMI abla-tion,with conduction block achieved and validated by stan-dard criteria during the same procedure. Electrophysiological studyAll patients provided written informed consent.Antiar-rhythmic drugs,with the exception of amiodarone,were ceased at least5half-lives before the study.Oral anticoag-ulation(target International Normalized Ratio2to3)was maintained for at least1month before the procedure,and all patients underwent transesophageal echocardiography within48hours before the procedure to exclude the pres-ence of thrombus.Electrophysiological study was per-formed in the fasting state using mild sedation.The follow-ing catheters were introduced via the right femoral vein:(1) a steerable quadripolar or decapolar catheter(5-mm elec-trode spacing,Xtrem,ELA Medical,Le-Plessis-Robinson, France)was positioned within the coronary sinus(CS);(2) a10-polar circumferential mapping catheter(Lasso,Bio-sense Webster,Diamond Bar,California)was introduced in the LA and stabilized by using a long sheath(SLO,St.Jude Medical,St.Paul,Minnesota)that was continuously per-fused with heparinized glucose;and(3)a3.5-mm externally irrigated-tip ablation catheter(Thermocool,Biosense Web-ster)was used for ablation.Access to the LA was achieved by transseptal puncture,after which a single bolus of50 IU/kg heparin was administered.Surface electrocardio-grams and bipolar endocardial electrograms were continu-ously monitored and stored on a computer-based digital amplifier/recorder system with optical disk storage for off-line analysis(Labsystem Pro,Bard Electrophysiology,Lowell, MA).Intracardiac electrograms werefiltered from30to500 Hz and measured with computer-assisted calipers at a sweep speed of100mm/s.Ablation protocolPulmonary vein isolation was performed using radiofre-quency applications to eliminate electrograms around the ostia and was guided by a circumferential mapping catheter as previously described.4LA ablation was performed at all sites showing any of the following electrogram features potentially representing arrhythmogenic tissue:continuous electrical activity,complex fractionated potentials,sites with a gradient of activation(significant electrogram offset between the distal and proximal recording bipoles on the map electrode)possibly indicating a local rotating wave,or regions with a cycle length shorter than the mean LA ap-pendage(LAA)AF cycle length or showing centrifugal propagation to the surrounding tissue.Ablation at all of these atrial sites was performed for20to60seconds to achieve local prolongation of cycle length.If AF continued after PV isolation and electrogram-based ablation,linear ablation at the most cranial portion of the LA roof was then performed with the end point of elimination of local elec-trograms.Ablation of the LMILinear ablation at the LMI was performed in patients in whom AF persisted after the above steps,or in case of subsequent perimitral AT.During AF,ablation was carried out on an anatomical basis with the end point being elimi-nation of local electrograms using a power between30and 35W.24Radiofrequency applications started at the lateral mitral isthmus(A:V electrogram amplitude ratio of approx-imately1:1)and was extended posteriorly to the ostium of the left inferior PV.During perimitral AT or distal CS pacing,it was often necessary to enlarge the line to the base of the LAA and inside the CS(with power limited to25W) to map and ablate residual gaps.After restoration of sinus rhythm,assessment of bidirectional conduction block was made as previously described.24Briefly,pacing and record-ing were performed as close as possible to each side of the line of block.Electrical block was validated when pacing on the septal side of the line via the CS catheter resulted in late activation on the opposite side,and as the CS pacing site was moved more proximally(toward the septum),the con-duction time to the opposite side shortened.Pacing lateral to the line resulted in a proximal-to-distal activation sequence along the CS.Widely separated local double potentials equidistant along the length of the ablation line were often observed.Ablation of the cavotricuspid isthmusA linear lesion at the CTI was performed in cases of per-sistent AF after LA ablation and in patients with evidence of peritricuspid AT(before or during the procedure).The CTI linear lesion was made by continuously dragging the abla-tion catheter from the ventricular side of the CTI(A:V electrogram amplitude ratio of approximately1:2)toward the inferior vena cava29using a power range between30and 35W.Radiofrequency delivery was executed at the medial part of the CTI(6o’clock in a Left anterior oblique(LAO) position);however,more lateral or septal positions were occasionally used when linear block could not be achieved. During AF,ablation was performed anatomically with the end point of elimination of local electrograms.During peri-tricuspid AT or CS pacing,residual gaps were mapped and targeted.30After restoration of sinus rhythm,bidirectional isthmus block was validated using standard criteria.27 Measurement of the circuit conduction timesThe peritricuspid conduction time was measured after val-idation of the bidirectional block across the CTI.It was made by pacing from the septal side of the CTI approxi-mately1bipole away from the line of block(distance of5 mm)and recording the second late potential on the line of block.Similarly,the perimitral conduction time was evalu-ated after validation of the conduction block across the LMI. It was performed by pacing approximately1bipole septal to the line of block and recording the second late potential on the line of block(Figure1).401Knecht et al Relationship Between Conduction TimesEchocardiographyTwo-dimensional echocardiographic images of the LA and left ventricle were obtained in standard parasternal long-axis and apical 2-chamber and 4-chamber views with sec-ond harmonic and right atrium dimensions (parasternal,transverse,and longitudinal diameters)were measured at end systole in the 3views according to Amer-ican Society of Echocardiography (ASE)guidelines.Left ventricular ejection fraction (LVEF)was assessed by the Simpson method.Statistical analysisFor descriptive statistics,we used the measure of the range,the mean Ϯthe standard deviation (SD)for Gaussian val-ues,and the median ϮSD for non-Gaussian values.For the analysis of the statistical correlation,we used the test of linear regression to compare continuous variables,and Stu-dent t test,Chi-square,and Fisher exact test for nonpara-metric variables.The results were significant if the P value was Ͻ.05.ResultsPatient characteristicsPatient characteristics are summarized in Table 1.There were 122consecutive patients (100male)with a mean ageof 57Ϯ11years (range 26to 78)admitted for drug-refractory symptomatic AF or AT in the context of prior AF ablation.All of them underwent an ablation procedure re-quiring both CTI and LMI ablation with conduction block validated by standard criteria.Forty-six patients (38%)hadFigure 1Measurement of both circuit conduction times.A:Anteroposterior view with a schematic representation of the tricuspid annulus (TA)and the cavotricuspid isthmus (CTI)line (white line).Quadripolar catheter inserted into the coronary sinus and ablation catheter placed on the CTI line.The peritricuspid conduction time (arrow)was measured by pacing from the septal side of the CTI (pacing sign)and recording the second late potential on the line of block (star).B:Anteroposterior view with a schematic representation of the mitral annulus (MA),right and left pulmonary veins (PV),left atrial appendage (LAA),and left mitral isthmus line (white line).Decapolar catheter inserted into the coronary sinus,circumferential catheter placed inside the right atrial appendage,and ablation catheter placed on the LMI line.The perimitral conduction time (arrow)was evaluated by pacing septal to the line of block (pacing sign)and recording the second late potential on the line of block (star).Table 1Patient characteristicsStudied population (n ϭ122)ResultsAge,yrs 57Ϯ11(range 26to 78)Men 100(82%)Paroxysmal AF 46(38%)Persistent AF 76(62%)First procedure 36(30%)Second procedure 46(38%)Third or more procedure 40(33%)LVEF 61%Ϯ10%(range 26to 79)LV diastolic diameter 54Ϯ6mm (range 37to 71)Longitudinal LA 59Ϯ7mm (range 43to 80)Transverse LA 42Ϯ7mm (range 26to 66)Longitudinal RA 55Ϯ6mm (range 39to 71)Transverse RA 38Ϯ8mm (range 21to 65)Peritricuspid conduction time 180Ϯ35ms (range 120to 300)Perimitral conduction time 189Ϯ42ms(range120to 322)AF ϭatrial fibrillation;EF ϭejection fraction;LA ϭleft atrium;LV ϭleft ventricle;RA ϭright atrium.402Heart Rhythm,Vol 5,No 3,March 2008a history of paroxysmal AF,and 76(62%)had a history of persistent AF.Conduction block at both lines was simulta-neously validated during a first ablation procedure for 36patients (30%),a second for 46(38%)and a third or more for 40(32%).LVEF was 61%Ϯ10%(range 27%to 79%)for a left ventricular diastolic diameter of 54Ϯ6mm (range 37to 71).LA diameter was 45Ϯ9mm (range 13to 67)in the parasternal short-axis view.In the apical 4-chamber view,longitudinal dimensions of both right and left atria were 55Ϯ6mm (range 39to 71)and 59Ϯ7mm (range 43to 80)respectively (P ϭNS),whereas transverse dimensions were 38Ϯ8mm (range 21to 65)and 42Ϯ7mm (range 26to 66)respectively (P ϭNS).RA and LA surfaces were 18Ϯ5(range 11to 28)and 22Ϯ5(range 12to 33)respectively (P ϭNS)Perimitral and peritricuspid conduction timeThe mean peritricuspid and perimitral conduction times were 180Ϯ35ms (range 120to 300)and 189Ϯ42ms (range 120to 322),respectively,with a mean difference of 7Ϯ32ms (range Ϫ70to 95).The correlation between both circuit times was highly significant (r ϭ0.622,P ϭ.001)(Figure 2).In 84patients (68%),the perimitral time was within 30ms of the peritricuspid time.In the remaining patients,only 12(32%)had a shorter perimitral time com-pared with peritricuspid time.In total,only 12patients (10%)had a perimitral time shorter than 30ms compared with the peritricuspid time.Furthermore,peritricuspid and perimitral conduction times were always Ն120ms.Difficulty of the linear ablationAmong the 36patients (30%)who underwent a first ablation procedure requiring both LMI and CTI ablation with block on both lines,radiofrequency energy delivered was signif-icantly longer for LMI (15Ϯ7min [range 7to 33])compared with CTI (7Ϯ4min [range 3to 17])(P ϭ.005)(Figure 3).DiscussionThis study highlights the close relationship between the peritricuspid and the perimitral conduction times and con-firms the difficulty in achieving conduction block across the LMI line compared with the CTI line.Relationship between peritricuspid and perimitral conduction timesThere is a strong correlation between peritricuspid and per-imitral conduction times,which may be explained by sim-ilar left and right atrial dimensions,and by implication circuit length in the majority of the patients.In individual patients,peritricuspid conduction time was within 30ms to the perimitral conduction time in 68%of the cases.In the other 32%of the patients,the perimitral conduction time was longer compared with the peritricuspid conduction time in the majority of the cases.The individual differences in conduction times around respective annuli could be ex-plained by the following hypotheses:first,the difference in dimensions between both atria may render electrical prop-agation along the mitral annulus longer than around the tricuspid annulus;secondly,a slower electrical propagation around the mitral annulus may also be observed in case of injury of the LA tissue that occurs spontaneously or because of prior radiofrequency applications (delivered only in the LA in the majority of the cases);and finally,in case of instability at the lateral side of the LMI,the recording catheter was placed within the LAA with a subsequent modification of the perimitral conduction time proportional to the distance between LMI and LAA.Linear lesionsRadiofrequency applications were significantly longer for LMI than CTI while using the same power range.The anatomy of both lines has already been extensively de-scribed 28,31–35and may explain some of the difference.The wall thickness of the LMI ranges from 4to 10mm (withtheFigure 3Duration of radiofrequency applications to obtain bidirectional block across the left mitral isthmus (LMI)and the cavotricuspid isthmus (CTI)lines.SE ϭstandarderror.Figure 2Correlation between peritricuspid and perimitral conductiontimes.403Knecht et al Relationship Between Conduction Timesthickest portion close to the left inferior PV),31whereas the CTI has been shown to be thinner (between 0and 7mm).32,34Recesses and cavities can also greatly prolong the procedure;however,they have been described for both the cavotricuspid and the mitral isthmus.28,33,34Furthermore,some investigators have described that residual conduction gaps at the LMI line may frequently be located at the epicardial side of the line (i.e.,inside the coronary sinus)or between the left inferior PV and the LAA.35Extension of linear ablation to these structures can add time but also risk to the procedure.36Finally,catheter positioning during CTI ablation is often more stable compared with LMI ablation.This difficulty in achieving conduction block at the LMI line raised the question of the timing and overall necessity to perform this linear lesion.The global aim of linear lesions is to reproduce the surgical MAZE procedure,37based on the concept of macroreentrant loop and wandering wavelets participating in the AF process.38–41Several studies have described the additional benefit of the LMI line,particularly for persistent AF,16,17,24,42,43but at the expense of more complications.24,36Importantly,even when not performed during AF,both LMI and CTI lines frequently have to be done after AF termination for subsequent perimitral or peri-tricuspid flutter.12Clinical implicationsWhen both CTI and LMI lines are needed to treat AF or subsequent AT in a patient,the close relationship of both circuit conduction times is useful for the operator.When the patient is in sinus rhythm,the easier CTI line should be achieved and validated first,and the peritricuspid conduc-tion time measured.Then the more difficult LMI line shouldbe attempted or completed during CS pacing.A conduction time 30ms less than the CTI time or Ͻ120ms would suggest that the line is not complete,saving additional time-consuming pacing maneuvers (Figure 4).Study limitationsThe main limitation of this study is that CTI ablation is not routinely performed in all centers in the context of AF ablation.This situation of absence of CTI conduction block obviously precludes the use of the association between the peritricuspid and perimitral times that we have described.Secondly,to evaluate the difficulty in performing linear lesions at the CTI and LMI,only the patients with block of both lines during the first procedure were selected.It was aimed at avoiding bias caused by prior ablation in the vicinity of both lines and to reproduce the same electro-physiological conditions at the time of the conduction block.Finally,there was no measure of the radiation and duration required to obtain block on both lines;however,radiofrequency energy was assumed to be the best param-eter reflecting procedural difficulty given that the same power was used to perform both lines.ConclusionCompared with the LMI line,the CTI line is significantly easier to perform.The peritricuspid and perimitral circuit times are strongly correlated,and in 90%of patients,the perimitral conduction time is within 30ms or longer than the peritricuspid time.In addition,both circuit times are always Նthan 120ms in this cohort of patients ablated for AF.When both lines are necessary,the easier CTI line should be completed before the mitral line,andstandardFigure 4Example of the usefulness of the relationship between both circuit times in one patient.Recording with the ablation (RF)and coronary sinus (CS)catheters.In this patient,the peritricuspid conduction time was calculated at 170ms (A).During ablation of the left mitral isthmus,the perimitral conduction time was first measured at 136ms,suggesting the incompleteness of the line and precluding standard validation maneuvers (B).Further mapping at the epicardial side of the line within the CS (fluoroscopic anteroposterior view)indeed revealed a gap potential (star)(C).Ablation at this 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