2

Standard Right Atrial Ablation is Effective for AtrioventricularNodal Reentry with Earliest Activation in the Coronary Sinus

JANE CHEN, M.D., FREDERIC ANSELME, M.D.,∗ TIMOTHY W. SMITH, D.PHIL., M.D.,PETER ZIMETBAUM, M.D.,‡ LAURENCE M. EPSTEIN, M.D.,†

PANOS PAPAGEORGIOU, M.D., PH.D.,‡ and MARK E. JOSEPHSON, M.D.‡From the Washington University School of Medicine, St. Louis, Missouri, USA; ∗Service de Cardiologie, Hopital Charles Nicolle, Rouen,

France; †Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts, USA; and ‡Beth Israel Deaconess MedicalCenter, Harvard Medical School, Boston, Massachusetts, USA

Ablation of AVNRT with Earliest CS Activation. Introduction: Reports suggest that coronary sinus(CS) or left atrial ablations may be necessary for treatment of AV nodal reentrant tachycardia (AVNRT)with earliest retrograde atrial activation in the CS. We assessed the efficacy of standard right atrial catheterablation approaches in these tachycardias and determined the incidence of earliest activation in the CS inAVNRT.

Methods and Results: We retrospectively evaluated intracardiac recordings from 225 consecutive patientswho underwent electrophysiologic studies and radiofrequency (RF) ablation for AVNRT in two institutions.Atrial activation during AVNRT was evaluated using multiple catheters according to standard protocol usedin our laboratories. RF ablations in the triangle of Koch were performed in all patients. Eighteen of 225patients (8%) had earliest activation in one of the CS poles. The demographics and AVNRT characteristicsof these 18 patients were similar to those of the other 207 patients who did not have CS as earliest activationsite and included both typical and atypical AVNRT. Following RF ablation, none of the 18 patients hadinducible AVNRT.

Conclusion: Successful RF ablation can be performed at standard sites in the triangle of Koch regardlessof earliest site of atrial activation. The incidence of CS as earliest retrograde atrial activation site in AVNRTis 8%. (J Cardiovasc Electrophysiol, Vol. 15, pp. 2-7, January 2004)

tachycardia, atrioventricular node, reentry, ablation

Introduction

The traditional view of atrioventricular nodal reentranttachycardia (AVNRT) is that of a circuit involving the func-tional dissociation of two pathways.1,2 It has been suggestedthat these pathways are anatomically distinct as well.3 Pre-vious observations have shown the initial site of retrogradeatrial activation via the fast pathway to be in the His-bundleelectrogram (HBE) in the apex of the triangle of Koch, fol-lowed 10 to 55 ms later by activation of the coronary sinus(CS).4,5 In contrast, the earliest site of retrograde atrial ac-tivation via the “slow pathway” in atypical AVNRT is nearthe os of the CS, at the base of the triangle of Koch, andprecedes the low septal right atrium by 5 to 20 ms.6,7 Inrecent years, however, the concept of anatomically distinctpathways has been challenged. Multiple simultaneous sitesof retrograde atrial activation have been reported, as well asretrograde atrial activation patterns that are inconsistent withan anatomic circuit involving sequential activation of distinctpathways.8,9 Retrograde activation in the CS that is too earlyto have been a consequence of sequential activation from theapex of the triangle of Koch (“CS breakthrough”) is noted in

Address for correspondence: Jane Chen, M.D., Cardiovascular Divi-sion, Washington University School of Medicine, 660 S. Euclid Avenue,Campus Box 8086, St. Louis, MO 63110. Fax: 314-454-8250; E-mail:janechen@im.wustl.edu

Manuscript received 19 June 2003; Accepted for publication 3 September2003.

doi: 10.1046/j.1540-8167.2004.03299.x

>50% of patients,9 suggesting not only that atrial activationis heterogeneous but that connections between the AV nodeand the left atrium may exist. Cases of eccentric retrogradeleft-sided atrial activation patterns have been described,10,11

although the actual incidence is unknown. Left-sided abla-tions for AVNRT also have been reported in the literature,12,13

suggesting that left-sided connections may be a critical com-ponent of the tachycardia circuit. However, the significanceof earliest atrial activation in the CS as an indication that left-sided ablations may be required is unclear. Preliminary datafrom Tondo et al.14 suggest that the presence of an earliest siteof retrograde atrial activation recorded along the CS cathetermay indicate that left-sided ablations along the mitral annulusare required for successful treatment.

The aim of the present study was to determine the inci-dence of CS as earliest site of retrograde atrial activation andto assess whether left-sided ablations are necessary to curesuch arrhythmias. Our working hypothesis is that atrial acti-vation during AVNRT is heterogeneous and that sites of earli-est retrograde atrial activation, whether right or left sided, areepiphenomena of a subatrial circuit. As such, standard right-sided ablation in the triangle of Koch should be an effectiveinitial approach even when the retrograde atrial activation isin the left atrium.

Methods

Study Population

We retrospectively assessed the results of radiofrequency(RF) ablation in 225 consecutive patients with inducible

Chen et al. Ablation of AVNRT with Earliest CS Activation 3

AVNRT and evaluated intracardiac recordings from thesepatients in order to determine the incidence of CS as theearliest site of retrograde atrial activation. The diagnosis ofAVNRT was made based on previously published standardcriteria15-17 and included septal V-A time <55 ms in typicalAVNRT; introduction of single premature ventricular depo-larizations during the His refractory period that did not ad-vance atrial activation or terminate the tachycardia; presenceof bundle branch block that did not alter the V-A interval18-20;and V-A time with right ventricular base pacing greater thanthe V-A time with right ventricular apex pacing.

Statistical Analysis

Continuous variables are expressed as mean ± SD andcompared using Student’s t-test (unpaired). Categorical vari-ables were compared using Fisher’s exact test. P < 0.05 wasconsidered statistically significant, and all tests were two-tailed.

Catheter Recording Sites

Transvenous intracardiac recordings using multielectrodecatheters were used according to standard protocol in ourlaboratory. Quadripolar catheters with 5-mm interelectrodespacing were positioned in the high right atrium (HRA) andright ventricular apex (RVA). A quadripolar, hexapolar, ordecapolar catheter with 2-mm interelectrode distance wasplaced across the tricuspid valve and positioned so that thelargest His electrogram was seen in the distal electrode pair,and the remaining electrodes were in contact with the atriumalong the tendon of Todaro (HBE catheter). Efforts were madeto ensure that atrial potentials were seen in each electrodepair during sinus rhythm and during AVNRT. A steerablequadripolar catheter with 2-5-2 mm interelectrode distances,or an ablation catheter with a large distal electrode, was posi-tioned along the tricuspid annulus just anterior to the os of theCS, with the ratio of atrial to ventricular electrogram ampli-tudes at the distal pair less than 1:3 during sinus rhythm (slowpathway [SP] catheter). The SP catheter was positioned ac-cording to electrogram signals in order to standardize record-ings for all patients and was not dictated by the presence orabsence of an SP potential. A decapolar catheter with 5-mminterelectrode distance was placed in the CS. The CS catheterwas positioned so that the proximal pole was always medial tothe HBE catheter in the left anterior oblique projection withthe HBE perpendicular to the screen. Data were analyzedfrom the HRA, SP, HBE, and CS catheters, and the bipolarrecording with the earliest retrograde atrial electrogram wasdesignated as time zero.

Measurement of Atrial Activation

Electrograms were filtered at 40 to 400 Hz. Measure-ments of atrial activation were made at a sweep speed of200 mm/s by the use of computer-based or hand-held calipersfrom recordings that showed the most visible atrial electro-grams in all poles during AVNRT. Whenever possible, thegain was kept the same among the recordings during anal-ysis. When atrial and ventricular electrograms occurred si-multaneously during AVNRT, intracardiac recordings duringdelivery of single or double ventricular premature depolar-izations to separate atrial from ventricular electrograms wereused for analysis. These recordings were carefully analyzedto ensure that the ventricular premature depolarizations did

not affect the tachycardia circuit (no resetting). The timing ofall other atrial electrograms were measured in millisecondsrelative to time zero.

Ablations

Catheter ablations were performed using a combinationof anatomic and electrophysiologic markers. The ablationcatheter initially was placed in the inferior posterior triangleof Koch (between the inferior edge of the os of the CS andthe tricuspid valve on the right anterior oblique projection)or the midseptal region, at the discretion of the operator. Thecatheter was rotated clockwise to obtain good contact withthe septum on the left anterior oblique projection. Atrial andventricular electrograms were verified so that the ratio of theiramplitudes was less than 1:3. The presence of SP potentials asdescribed by Jackman et al.21 was not required for selectionof the ablation site. If the ablation was initially unsuccessful,then the tip of the ablation catheter was moved in small (<0.5cm) increments anteriorly along the right atrial septum. Pro-grammed stimulation was repeated after RF ablations, andisoproterenol and/or atropine were administered after abla-tions to assess the reinducibility of AVNRT. The endpoint ofall procedures was the inability to induce sustained AVNRT.Abolition of the SP potential, if present, was not an endpoint.

Results

An example of earliest atrial activation in the CS in apatient with typical AVNRT is shown in Figure 1 and anexample in a patient with atypical AVNRT is shown inFigure 2.

Patient characteristics, as well as measurements of ret-rograde atrial activation times during AVNRT, are given inTable 1. Earliest retrograde atrial activation was recorded inthe CS in 18 (8%) of 225 patients. Thirteen patients had a sin-gle earliest site of retrograde atrial activation in the CS. Theremaining 5 patients had earliest activation in the CS as wellas an early site at another catheter occurring within 5 ms ofthe early CS site. Four of the 18 patients had earliest atrial ac-tivation near the os of the CS, and all four had typical AVNRT.The remaining 14 patients had earliest sites well within theCS. The demographics of the 18 patients with earliest CSactivation were similar in those of the other AVNRT patientswho did not have CS as earliest activation site (Table 2).There was no significant difference in the proportion of fe-males, presence of heart disease, and mean age between thetwo groups. Similarly, there was no significant difference inthe mean cycle lengths of AVNRT between the two groups.

Of the 225 patients analyzed, 211 patients (93.8%) hadtypical (slow-fast) AVNRT. Fourteen patients (6.2%) hadatypical (fast-slow) AVNRT. Three of the 225 patients hadboth typical and atypical AVNRT and were counted in theatypical AVNRT group. Of the 18 patients with earliest ac-tivation in the CS, 16 patients had typical AVNRT (7.6% of211 patients with typical AVNRT), and 2 had atypical AVNRT(14.3% of 14 patients with atypical AVNRT). There was nostatistically significant difference between the proportions ofpatients with earliest activation in the CS when the atypicalAVNRT group was compared to the typical AVNRT group(P = 0.31, Table 3).

All 18 patients with CS as earliest activation site un-derwent successful ablation with RF energy in the mid to

4 Journal of Cardiovascular Electrophysiology Vol. 15, No. 1, January 2004

Figure 1. Example of retrograde atrial activation pattern in typical AV nodal reentrant tachycardia in patient 5. A single ventricular premature stimulus wasdelivered to separate atrial and ventricular electrograms without resetting the tachycardia. The earliest retrograde atrial activation is seen in the coronarysinus (CS) 7/8 bipolar electrogram, followed by activation of the distal CS poles and His-bundle electrograms (HBE). The ablation catheter (Abl) distal (d)and proximal (p) is positioned in the slow pathway region. Surface leads I, II, III, and V1 are shown at the top of the tracing. A = atrial electrograms; ds =distal; HRA = high right atrium; px = proximal; RV = right ventricle.

posterior triangle of Koch, with no inducible AVNRT at theend of the procedure. In the group of patients who did not haveCS as earliest activation site, 4 patients (2.3%) had persistentAVNRT at the end of the study: 2 patients had transient heartblock after which the procedures were terminated; 1 patienthad residual nonsustained AVNRT after ablation, but the pro-cedure was aborted due to worsening congestive heart failure;and 1 patient with residual nonsustained AVNRT in whomwe believed that further ablations would have been associ-ated with high risk of complete heart block. There were nosignificant differences in the mean number of RF energy ap-plications between the two groups, nor were there significantdifferences in the percentage of patients with residual dualAV nodal physiology or single AV nodal echos after ablations(Table 2).

Discussion

The major findings in this study are as follows: (1) theincidence of earliest retrograde atrial activation in the CS is8% in this study group; and (2) standard right-sided ablationin the triangle of Koch is an effective initial approach toeliminating AVNRT, regardless of the site of earliest atrialactivation.

Although single early breakthrough sites in the CS havebeen reported, they were previously thought to be rare andwere observed mostly in patients with atypical AVNRT.Hwang et al.22 found that 6% (20/356) of the patients with

AVNRT they studied had earliest retrograde atrial activationin either the lateral (8/20) or posterior (12/20) CS poles. All ofthese patients had atypical AVNRT and were initially thoughtto have orthodromic AV reentrant tachycardia involving left-sided bypass tracts. Anselme et al.9 reported 4 patients (8.7%)with earliest CS activation from a group of 46 patients withtypical AVNRT. All 4 patients, however, also had simultane-ous earliest activation in the HBE. In the current study, wefound earliest atrial activations in the CS in typical as wellas atypical AVNRT. The proportion of patients with earliestCS breakthrough site is higher in atypical AVNRT (14.3%)compared with typical AVNRT (7.6%), although this was notstatistically significant. Fourteen of our patients had earliestactivation well within the CS, with the os of the CS acti-vated later. Earliest retrograde atrial activation in the CS mayrepresent propagation of the impulse over a left-sided ex-tension of the AV node to the left atrium. The significanceof these extensions as critical components of the reentrantcircuit, however, is unclear. Previous studies have shown nocorrelation between the His-to-earliest CS electrogram inter-val and the AVNRT cycle length, which would be expectedif these left-sided atrionodal connections were crucial partsof the reentrant circuit.23

The significance of earliest CS atrial activation with re-gard to the site of ablation is unknown. Reports in the lit-erature show that left-sided ablations for AVNRT, althoughuncommon, sometimes are necessary for cure of the tachy-cardia. Sorbera et al.13 used the transseptal approach to ablate

Chen et al. Ablation of AVNRT with Earliest CS Activation 5

Figure 2. Example of retrograde atrial activation pattern in atypical atrioventricular nodal reentrant tachycardia in patient 13. Earliest retrograde atrialactivation is seen in the coronary sinus (CS) 5/6 bipolar electrogram. The ablation catheter (Abl) distal (d) and proximal (p) is positioned in the slow pathwayregion. Surface leads I, II, III, and V1 are shown at the top of the tracing. A = atrial electrograms; ds = distal; HRA = high right atrium; px = proximal;RV = right ventricle.

3 patients with typical AVNRT in whom right-sided ablationspreviously had failed. Ablation targets on the left side werebased on the ratio of atrial to ventricular electrograms, andthere was no mention of earliest sites in the CS. Jaıs et al.12

also reported a case of left-sided ablation for typical AVNRT

TABLE 1

Patient Data

Sites of Atrial Recording (ms)

Patient No. Age (years) Sex Heart Disease CL (ms) HRA SP HBE CS

1‡ 71 M N 550 30 20,25 2,0,2,6,10 10,0,7,10,202 42 M Y∗ 380 120 N/A 58,59,61,60,60 35,25,12,0,203‡ 61 F N 320 50 26,30 5,0,0,–,– 29,7,0,10,124§ 26 F N 470 57 N/A 10,10,8,12,– 0,0,20,30,05 20 M N 560 72 –, 32 12,12,18,20,32 20,0,4,10,186∗∗ 45 F N 370 145 –, 25 28,15,20,15,– 5,2,0,34,507 33 F N 475 32 10,20 5,2,5,10,10 2,0,10,20,308 49 F N 270 35 50,– 40,45 40,25,0,34,359§ 74 F N 285 30 –,49 33 0,15,20,25,32,3,42,45,49†

10 34 F N 330 38 27,24 5,5,25,26,35 20,0,4,15,2111 33 F N 300 65 40,52 15,32,30,28,35 18,0,5,25,2812 45 F N 450 55 58,– 32,30,35,25,20 18,4,0,5,3013∗∗ 30 M N 440 98 11,10 18,20,30,40,45 40,38,0,12,2814 62 F N 429 35 18,20 14,8,6 10,0,7,18,2815 61 F N 480 N/A N/A 60,33,55 20,15,0,5,2016§ 72 M N 488 66 N/A 40,35 0,0,10,15,2017 65 F N 318 N/A N/A 5,2,5 8,0,8,1518§ 19 F N 320 N/A 13,18 21,17,9 0,0,9,28∗Valvular heart disease; ∗∗atypical AV nodal reentrant tachycardia; †unipolar recordings; ‡simultaneous early activation in HBE; §earliest activation at CS os.CL = cycle length; CS = coronary sinus (proximal to distal) (when only four measurements are listed, the first is recorded at the CS ostium); HBE =His-bundle electrogram (distal to proximal); HRA = high right atrium; SP = slow pathway from distal to proximal.

in a patient who had failed multiple prior ablations from theright side, although the earliest site of atrial activation wasnot reported. A study by Landolina et al.24 showed that in41 patients with typical AVNRT, 6 (15%) had earliest atrialactivation within the CS. Although ablation within the CS

6 Journal of Cardiovascular Electrophysiology Vol. 15, No. 1, January 2004

TABLE 2

Patient Characteristics

Patients with Patients with EarliestEarliest Atrial Atrial Electrogram

Electrogram in CS Elsewhere

No. of patients (%) 18 (8%) 207 (92%)Percent female 72 70Age (years) 47 ± 18 51 ± 18Percent with heart disease 5.6% 15.6%AVNRT cycle length (ms) 402 ± 92 359 ± 69No. of radiofrequency

energy applications7 ± 6 6 ± 6

Percent with AVNRTafter ablation

0 2.3%

Percent with dual AVnodal physiology afterablation

50% 44%

Percent with AV nodalechos after ablation

38% 35%

No significant differences were found between the two groups for any ofthe listed variables.AVNRT = atrioventricular nodal reentrant tachycardia; CS = coronary sinus.

and along the mitral annulus was necessary in 2 patients, itwas not reported that these two patients had earliest activa-tion sites within the CS. Tondo et al.25 reported a group of 50patients in whom 14 had earliest atrial activation site withinthe CS. RF energy applications targeted at these earliest siteseliminated the SP in 6 of these 14 patients. In the same study,a line of block created in the remaining 36 patients betweenthe tricuspid valve and the os of the CS did not eliminateAVNRT, whereas ablation at different sites within the CSwas successful, even though these 36 patients did nothaveearliest activation sites within the CS. The same investiga-tors also reported 4 patients with earliest CS activation sites,3 with typical AVNRT and 1 with atypical AVNRT.14 In thesepatients, standard sites of ablation for AVNRT failed to elim-inate AVNRT, whereas left-sided ablations along the mitralannulus, via the transseptal or aortic approach, successfullyeliminated AVNRT. In 2 of their patients, a high-frequencypotential following a local atrial potential in sinus rhythm,similar to SP potentials, was recorded at the mitral annulus atthe sites of ablation. In the other 2 patients, however, SP po-tentials were not recorded, and ablations were directed at thesites of earliest atrial activation, with successful eliminationof AVNRT. Successful ablation of AVNRT by targeting sitesof earliest atrial activation in the CS may suggest that sepa-rate nodo-atrial pathways linking parts of the left atrium to the

TABLE 3

Comparison of CS Earliest versus CS Not Earliest in Typicaland Atypical AVNRT

Typical AVNRT Atypical AVNRT n P Value

CS earliest 16 2 18CS not earliest 195 12 207n 211 14 225

0.31

No statistically significant difference was found between the proportion ofpatients with earliest activation in the CS when the atypical AVNRT groupwas compared to the typical AVNRT group.AVNRT = atrioventricular nodal reentrant tachycardia; CS = coronary sinus.

AVNRT reentrant circuit exist, and that left-sided ablationsmay be necessary for ablating these tachycardias.

In the present study, we found no evidence suggesting thatan earliest atrial activation site in the CS is a predictor thatleft-sided ablations are necessary. Although the success ofablations in the mid-to-posterior region of triangle of Kochdoes not elucidate the mechanism of the AVNRT reentrantcircuit, a critical part of the circuit appears to involve or beinfluenced by a region in the mid-posterior triangle of Koch,because ablation in this region can successfully eliminateAVNRT in >90% of patients.3,21,26-28 Earliest atrial activa-tions in the CS may represent a link between the AV nodalcircuit and the left atrium, and this phenomenon is observedin 8% of the patients in our series. Standard right-sided abla-tions are an effective initial approach to cure the tachycardia.Left-sided ablations should be reserved for patients who havefailed right-sided ablations. The presence of earliest activa-tion in the CS, however, does not predict the failure of right-sided approach or the requirement for subsequent left-sidedablations.

Study Limitations

The main limitation of this study is the potential vari-ability of catheter position, particularly of the CS catheter.Malposition of catheters could give rise to inaccurate resultsin the measurement of atrial activation timing and pattern.All catheters were placed using fluoroscopic guidance in thestandardized fashion according to laboratory protocol, whichdoes not include routine injection of radiographic contrastinto the CS to verify the location of the os. Rather, to as-sure that the proximal poles were just inside the CS os, theCS catheter was always placed with the proximal poles to theleft of the HBE catheter in the left anterior oblique projection.Because the majority of patients with earliest CS activationhad earliest sites distal to the proximal CS pole, we believethat these activation sites are well within the CS. A secondlimitation is the measurement of intracardiac electrograms,where atrial activation pattern may not be clearly discernible,especially in typical AVNRT where there may be apparentsimultaneous activations of the atrium and ventricle. Prema-ture ventricular depolarizations were delivered when neces-sary to better analyze the atrial electrograms, without reset-ting the tachycardia. Our 18 patients were selected becausethe electrograms clearly showed that the earliest retrogradeatrial activation occurred in the CS poles. A third limitationis that a limited number of catheters was used. In contrast toprior surgical studies with high-resolution mapping of the AVjunction, the areas mapped by our catheters were relativelysmall and limits the accuracy of our “earliest site.” Detailedmapping, however, is not the goal of this study. Rather, weaimed to assess atrial activation patterns in the practical set-ting, with methods and catheters that are commonly usedduring an electrophysiologic study for AVNRT. Clinical de-cisions, such as determining the site of ablation, are madeduring a study based on the available catheters and the bestassumptions as to the positions of the catheters. Finally, thepatients reported in prior studies in whom left-sided ablationswere necessary had previously unsuccessful ablation at theright posteroseptal region, whereas our patients did not haveprior ablations. This may explain the differences in successfulablation sites.

Chen et al. Ablation of AVNRT with Earliest CS Activation 7

Conclusion

The incidence of CS as earliest retrograde atrial activationin AVNRT is 8% and includes both typical and atypical pat-terns. Although these early sites are likely the consequenceof conduction over left-sided atrionodal extensions, standardright-sided ablations guided by anatomic position and intrac-ardiac electrograms are effective in treating these patients,suggesting that these left atrial inputs are not crucial to theAVNRT reentrant circuit. Left-sided ablations are thereforenot routinely necessary for the successful treatment of thesetachycardias.

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