The course of the sinus node artery and its impact on achievinglinear block at the left atrial roof in patients with persistentatrial fibrillationMiki Yokokawa, MD,* Baskaran Sundaram, MD,† Hakan Oral, MD,* Fred Morady, MD,*man Chugh, MD*
From the *Divisions of Cardiovascular Medicine and †Cardiothoracic Radiology, University of Michigan, Ann Arbor,Michigan.
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BACKGROUND Linear block at the left atrial (LA) roof may bechallenging in some patients undergoing an ablation procedure foratrial fibrillation.
OBJECTIVE To identify factors that may influence the likelihoodof achieving roof block.
METHODS Seventy-four patients (61 � 10 years; 59 men [80%);LA diameter, 46 � 6 mm; ejection fraction 0.55 � 0.10) under-went linear ablation at the LA roof for persistent atrial fibrillation.The morphology of the roof and its anatomical relationship toadjacent structures were analyzed on a preprocedure computedtomography scan.
RESULTS Complete block along the LA roof was achieved in 61 ofthe 74 patients (82%). There was no significant difference in themyocardial thickness, length, or other morphological aspects ofthe LA roof between patients with and without complete block.The sinus node artery (SNA) originated from the right coronary
atients (30%). The prevalence of a left SNA (from the circumflex)mong patients with and without linear block at the roof was 21%nd 69%, respectively (P � .001). On multivariate analysis, a leftNA was the only independent predictor of incomplete conductionlock at the LA roof (odds ratio 6.8; 95% confidence interval.7–28; P � .007).
CONCLUSIONS A left SNA identifies patients in whom conductionblock at the roof is more difficult to achieve. A left SNA may actas an epicardial heat sink, preventing adequate heating of the LAroof during linear ablation.
artery in 52 patients (70%) and the left circumflex artery in 22 All rights reserved.
IntroductionLinear ablation at the left atrial (LA) roof has been shown toimprove outcomes in patients with paroxysmal atrial fibril-lation (AF)1 and also has a critical role in patients withersistent AF.2 Linear block at the LA roof can be achieved
in most patients but may be challenging in some patients.The clinical and/or anatomic factors that may affect thelikelihood of achieving linear block at the LA roof have notbeen analyzed in detail. The purpose of this study was toidentify morphological characteristics of the LA roof andthe adjacent vasculature that may influence the acute effi-cacy of linear ablation at the LA roof.
MethodsThe subjects of this study were 74 consecutive patients whounderwent linear ablation at the LA roof during an initial
This work was supported in part by a grant from the Leducq Transat-lantic Network. Address for reprint requests and correspondence: Dr
man Chugh, MD, Division of Cardiovascular Medicine, Cardiovascularenter, University of Michigan, SPC 5853, 1500 E Medical Center Dr,
ablation procedure for persistent AF between February 2007and October 2009 and in whom multislice computed tomog-raphy (CT) had been performed prior to the procedure.
CT with 3-dimensional reconstructionEach patient underwent contrast-enhanced scanning with a64-slice CT scanner 1–4 weeks before the ablation procedure(GE Medical Imaging, Waukesha, WI). CT imaging was per-formed to evaluate for variant pulmonary vein (PV) anatomyand not for analysis of the LA roof, which was done retrospec-tively, after the ablation procedure. Following initial antero-posterior and lateral planning images, the LA was identified byusing a few limited 5-mm axial noncontrast images, scanningcaudally from the aortic root region to the cardiac apex. Theoptimal time to opacify the left atrium was calculated by usingthe time-density curve obtained by placing a region of interestin the middle of the left atrium and continuously scanningimmediately after injecting a small amount of contrast material(15 mL of Iopamidol at 4 mL/s followed by 20 mL of saline at4 mL/s). Subsequently, PV-CT protocol images were obtained
by scanning in the caudocranial direction (from 2 cm below the
cardiac apex to lung apices) in a single end-inspiratory breathhold. During this scan, contrast material was injected (100 mLof contrast at 4 mL/s followed by 50 mL of saline at 4 mL/s;Iopamidol-370, Bracco Diagnostics, Inc, Princeton, NJ).
Analysis of the LA roofThe CT analysis of the LA roof was performed 26 � 8 monthsafter the ablation procedure. The analysis was performed by 2of the investigators (M.Y. and B.S.) who were blinded to theresults of the ablation procedure. End-diastolic phase images ofthe left atrium were analyzed in both 2 and 3 dimensions byusing commercially available viewing and postprocessingworkstation (Vital Images, Inc, Minnetonka, MN).
The LA roof was defined as the region between the rightsuperior PV ostium and the left superior PV ostium (Figure 1).The anterior extent was defined by a straight line between themid-anterior aspect of the upper PVs. The posterior extent wasdefined by a straight line between the mid-posterior aspect ofthe upper PVs. The morphology of the LA roof and its ana-tomical relationship to adjacent structures were analyzed. Thecurvilinear length was obtained by measuring the length of theendocardial surface of the LA roof. The length was obtained bymeasuring the endocardial distance in a straight line from thesuperior aspect of the right superior PV ostium to the superioraspect of the left superior PV ostium. The “depth” was definedas the distance from that straight line to the most cranial aspectof the endocardial surface of the LA roof. The morphology ofthe LA roof was classified as flat, concave, convex, or pouch-like.3 The angulation of the upper veins with respect to the LAoof was also measured.
Analysis of the coronary vasculatureAll coronary vessels were identified from their origins andfollowed to their destinations. The sinus node artery (SNA)was defined as the artery that supplies the sinoatrial node,
Figure 1 The LA roof region in a cranial view. The solid lines representextents of possible anterior or posterior approaches during the linearablation of the LA roof. LA � left atrial; LAA � left atrial appendage;
IPV � left inferior pulmonary vein; LSPV � left superior pulmonaryein; RIPV � right inferior pulmonary vein; RSPV � right superior
ulmonary vein.
located at the cavoatrial junction. The findings were verifiedby using transaxial images, multiplanar reformatted images,angiographic views (long and short axial planes), and sur-face-rendering 3-dimensional (3-D) images. Following ves-sel tracing, the SNA was overlaid on the LA surface-ren-dered images to discern its relationship to the roof. Theorigin of the SNA, its epicardial course, and its relationshipto the surrounding cardiovascular structures were noted. Ifthe SNA originated from the proximal portion of the rightcoronary artery, it was termed as a right SNA. If the SNAoriginated from the proximal portion of the left circumflexcoronary artery, it was designated as a left SNA. If the SNAoriginated from both coronary circulations, it was termed adual SNA. Various courses of the left SNA, designated L1,L2, or L3,3,4 were also described. The L1 type is a branchof the left anterior atrial artery that originates from thecircumflex artery proximal and anterior to the LA append-age and describes the course of the left SNA as it traversesthe high anterior wall of the left atrium before reaching thecavoatrial junction in the high right atrium. The L2 type isa branch of the left lateral atrial artery that originates fromthe circumflex artery posterior to the LA appendage anddescribes the path of the left SNA as it emerges at the lateralleft atrium near the mitral isthmus and courses anterior tothe left PVs before emerging at the LA roof. The L3 varietyalso arises near the mitral isthmus but then ascends posteriorto the left PVs before reaching the roof. The maximumdiameter of the SNA was also measured.
Electrophysiologic studyAntiarrhythmic drug therapy was discontinued �5 half-ives before the electrophysiologic study, except for amio-arone that was discontinued �8 weeks before the proce-ure. The electrophysiological study was performed in theasting state under conscious sedation. Immediately afterhe transseptal puncture, systemic anticoagulation waschieved with intravenous heparin and the activated clottingime was maintained between 300 and 350 seconds through-ut the procedure. Mapping and ablation were performedith a 3.5-mm, open-irrigation-tip catheter (Thermocoolavistar, Biosense Webster, Diamond Bar, CA). Bipolar
lectrograms were displayed and recorded at filter settingsf 30–500 Hz during the procedure (EPMed Systems, Westerlin, NJ).
Catheter navigation and ablation were performed withhe guidance of an electroanatomical mapping systemCARTO, Biosense Webster). The esophagus was visual-zed by the administration of barium5 or the insertion of a
radiopaque marker, and its course was tagged on the elec-troanatomic map.
Ablation strategyAll patients presented to the laboratory in AF, and ablationwas performed during AF. Linear ablation was performedalong the LA roof (using 25–30 W) in all the 74 patients andmitral isthmus in 54 of the 74 patients (73%) who remained
in AF after antral PV isolation and ablation of complex,
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1397Yokokawa et al Left Atrial Roof and Linear Block
fractionated atrial electrograms. Ablation of the LA roofwas performed during AF in 68 patients (92%), for roof-dependent atrial tachycardia (AT) after AF termination in 4patients (5%), and for the prevention of roof-dependent ATin 2 patients (3%) during sinus rhythm.
Sinus rhythm was restored by transthoracic cardiover-sion in patients who remained in AF after the ablationprotocol. After sinus rhythm was restored, conductionblock across the LA roof was assessed. If the initial linefailed to yield conduction block, ablation was performedslightly anterior or posterior to the initial linear lesion.The presence of a linear block at the roof was determinedduring pacing from the LA appendage. The linear blockwas confirmed by documenting a corridor of double po-tentials on the line and an ascending activation sequenceof the posterior LA during LA appendage pacing.1 Theonduction delay at the LA roof was defined as thetimulus-to-electrogram interval recorded on the line dur-ng pacing from the LA appendage.
Also, for each patient, the course of the SNA (on CT)as compared with the location of the roof line on the-D map to determine whether the artery “crossed” theoof line.
Postablation follow-upAfter the ablation procedure, the patients were hospitalizedovernight and anticoagulated with intravenous heparin.They were prescribed oral anticoagulation and dischargedon the following day. Patients were seen in an outpatientclinic 3 months after the procedure and every 3–6 monthsthereafter. They were instructed to call a nurse coordinatorif they experienced symptoms suggestive of arrhythmia andwere provided with an event monitor. If antiarrhythmicmedications were prescribed at discharge, they were discon-tinued at the 3-month office visit. All patients were providedwith a 30-day, autotrigger (Lifestar AF Express; LifeWatch, Inc, Buffalo Grove, IL) event monitor at 12 monthsafter the ablation procedure. Recurrence was defined assymptomatic or asymptomatic AF/AT after the 3-monthblinding period.
Statistical analysisContinuous variables are expressed as mean � standarddeviation and were compared by using the Student t test or
Table 1 Patient characteristics
All (N � 74) Com
Age (y) 61 � 10 6ex: Man, n (%) 59 (80) 48A diameter (mm) 46 � 6 4eft ventricular ejection fraction 0.55 � 0.10 0.5tructural heart disease, n (%) 20 (27) 17ypertension, n (%) 48 (65) 39ody mass index (kg/m2) 33 � 8 3
Data are shown as mean � standard deviation. Percentage values areLA � left atrium.
paired t test, as appropriate. Categorical variables were
compared by using �2 analysis or with Fisher exact test, asppropriate. A logistic regression analysis was performed todentify the predictors of incomplete conduction blocklong the LA roof. A P value of �.05 indicated statisticalignificance.
ResultsPatientsThere were 59 men and 15 women, and the mean age of thepatients was 61 � 10 years (range, 27–82 years). The meaneft ventricular ejection fraction was 0.55 � 0.10, and the
ean LA diameter by transthoracic echocardiography was6 � 6 mm (Table 1). AF was first diagnosed for 3 yearsefore presentation. Eleven patients (15%) had coronaryrtery disease, 24 (32%) had left ventricular hypertrophy, 45%) had dilated cardiomyopathy, 2 (3%) had valvular heartisease, 1 (2%) had hypertrophic cardiomyopathy, and 12%) had congenital heart disease.
Conduction block at the LA roofComplete conduction block along the LA roof was achievedin 61 of the 74 patients (82%). Patients with incompleteconduction block tended to require more radiofrequency(RF) energy delivery at the roof than did those with com-plete block (12 � 6 minutes vs 9 � 5 minutes, respectively;
� .12). Except for a larger LA diameter on transthoracicchocardiography in patients without complete block (49 �mm vs 46 � 6 mm; P � .046), the baseline characteristicsf the 2 groups were similar (Table 1). The postablationonduction delay across the LA roof was 171 � 34 ms inatients with block as compared with 123 � 9 ms in thoseithout complete block (P � .002).
Morphology of the LA roof and its relationship toadjacent structuresA pouch was present at the LA roof in 2 patients (3%). Thelength and the curvilinear length of the LA roof were similarbetween patients with and without complete block along theLA roof (length: 38 � 8 mm vs 40 � 10 mm; P � .38;curvilinear length: 40 � 9 mm vs 42 � 10 mm; P � .39).There was also no difference in the length of the roof line(per the 3-D map) in patients with and without conductionblock (40 � 7 mm vs 41 � 8 mm, respectively; P � .60).The depth and the maximum myocardial thickness of the
block (n � 61) Incomplete block (n � 13) P
58 � 7 .2511 (85) 1.0
49 � 6 .04608 0.55 � 0.10 .96
3 (23) 1.09 (69) 1.035 � 7 .38
in parentheses.
plete
2 � 10(79)6 � 65 � 0.(28)(64)3 � 8
shown
LA roof were also similar between patients with and with-
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1398 Heart Rhythm, Vol 9, No 9, September 2012
out conduction block at the roof (depth: 3.0 � 2.1 mm vs3.2 � 2.4 mm; P � .81; maximum thickness: 2.4 � 0.6 mms 2.3 � 0.6 mm; P � .86) (Table 2).
There was no difference in the angulation of the LA roofith respect to the right superior or the left superior PVs inatients with and without linear block at the roof (rightuperior PV: 143° � 16° vs 149° � 14°; P � .18, left
superior PV: 155° � 23° vs 151° � 17°; P � .53). Theminimum distance from the LA roof to the right pulmonaryartery was similar between the 2 groups (3.8 � 1.4 mm vs3.9 � 2.1 mm; P � .89). LA volume was larger in patientswithout conduction block at the roof as compared with thatin patients with block (168 � 54 mL vs 135 � 43 mL; P �.02).
Vasculature at the LA roofA left SNA was observed in 22 of the 74 patients (30%;Table 2). In the remaining 52 patients (70%), the SNAoriginated from the right coronary artery. The mean diam-eter of the SNA was 1.4 � 0.2 mm, and was similar inpatients with and without conduction block (1.4 � 0.2 vs1.4 � 0.3; P � .96). There were 2 distinct patterns of theleft SNA: coursing at the high anterior LA in 14 patients(64%) (L1 type; Figure 2), and overlying the roof, afterpassing over the ridge between the LA appendage and theleft PVs in 8 patients (36%) (L2 type; Figures 3 and 4). Nopatient demonstrated the L3 pattern. The mean diameters ofthe L1 type and L2 type were 1.4 � 0.3 and 1.4 � 0.2 mm,respectively (P � .68). In 4 patients (5%), the sinus nodewas supplied by branches of both the right coronary andcircumflex arteries. In patients with a right SNA, the artery
Table 2 Computed tomography characteristics of the LA roof
All (
Curvilinear length (mm) 40ength (mm) 38epth (mm) 3.1aximum thickness (mm) 2.4orphologyStraight type, n 32 (Concave type, n 25 (Convex type, n 15 (Pouch type, n 2 (
ngulation of the LA roof with the PV (deg)Right superior PV 144Left superior PV 155
inimum distance from right pulmonary artery (mm) 3.9eft SNA, n 22 (ual SNA 4 (NA diameter (mm) 1.4A dimension (mm)Anterior-posterior 47Transverse 65Superior-inferior 70
A volume (mL) 140
Data are shown as mean � standard deviation. Percentage values areLA � left atrial/atrium; PV � pulmonary vein; SNA � sinus node arte
had no relationship to the LA roof (Figure 5).
The prevalence of a left SNA was higher in patients withincomplete conduction block at the roof than in patientswith complete block (69% vs 21%; P � .001). The SNA didnot “cross” the roof line (as determined by a side-by-sidecomparison of CT and the 3-D map) in any of the 60patients with roof block. On the other hand, the SNA didcross the roof line in 5 of the 12 (42%) patients without roofblock (P �.0001). In the remaining 2 patients, it could notbe determined whether the SNA crossed the roof line on the3-D map. There was no significant difference in the maxi-mum myocardial thickness at the LA roof in patients withand without left-sided SNA (2.4 � 0.5 mm vs 2.3 � 0.6
m; P � .66).
Predictors of incomplete conduction block alongthe LA roofBy multivariate analysis, among the variables of LA diam-eter on transthoracic echocardiography, anterior-posteriordimension and superior-inferior dimensions of the leftatrium on CT, LA volume, and a left SNA, the presence ofa left SNA was the only independent predictor of incom-plete block along the LA roof (odds ratio 6.8; 95% confi-dence interval 1.7–28; P � .007) (Table 3).
OutcomesIn 1 patient undergoing a repeat procedure for AT, acutesinus node dysfunction occurred, manifested as junctionalrhythm, during RF ablation at the high anterior wall of theleft atrium. High power (40 W) was required to terminatethe tachycardia as ablation with lower power settings wasunsuccessful. The presence of an L1-type SNA was con-
firmed on CT, which was running precisely at the region
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1399Yokokawa et al Left Atrial Roof and Linear Block
where RF ablation was performed. Because of persistentbradycardia and new-onset congestive heart failure, a per-manent dual-chamber pacemaker was implanted within aweek of the ablation procedure, with resolution ofsymptoms.
Another patient presented for a repeat procedure for aroof-dependent macro-reentrant AT that could not be elim-inated despite multiple attempts anterior and posterior to theinitial roof line. The tachycardia was finally eliminatedduring RF ablation of the inferoposterior left atrium outsidethe right inferior PV.
A repeat ablation procedure was required in 46 of the 74patients (62%). Thirty-six of 61 patients (59%) with com-plete block and 10 of 13 patients (77%) without completeblock required a repeat procedure (P � .35). Among the 36patients with complete block who required a repeat proce-dure, resumption of conduction across the LA roof wasfound in 23 patients (64%). The prevalence of a left SNAwas similar among patients with and without resumption ofconduction across the LA roof (7 of 23 [30%] vs 2 of 13[15%]; P � .32). After a mean of 2 � 1 procedures, and23 � 10 months of follow-up since the last procedure, 54 ofhe 74 patients (73%) remain arrhythmia-free without anti-
Figure 2 An example of an L1 course of the left SNA. As shown in (Aanterior LA. In (B), the course of the SNA has been superimposed (in redLAA � left atrial appendage; LCx � left circumflex artery; LIPV � leftnferior pulmonary vein; RSPV � right superior pulmonary vein; SNA �
rrhythmic medications.
DiscussionMajor findingsIn this study, the presence of a left SNA was associated withunsuccessful linear ablation at the LA roof. This findingsuggests that the heat-sink effect of blood flow in the SNAmay prevent adequate heating of the atrial myocardium atthe LA roof during RF ablation. Preprocedural imaging canreadily identify patients with a left SNA, and this findingmay influence the operator’s decision to perform ablation atthe LA roof since an incomplete line may be associated withproarrhythmia.6
Convective cooling during LA roof ablationThe mean diameter of the left-sided SNA was 1.4 mm inthis study. It may be difficult to conceive that small atrialbranches could exert a significant heat-sink effect and hin-der linear ablation at the roof. However, a prior experimen-tal study showed that flow through arteries as small as �0.3
m can prevent transmural lesion formation.7 Furthermore,perfusion rates as low as 1 mL/min through these smallarteries were sufficient to impede adequate heating of themyocardium. During a case of difficult linear ablation at theLA roof, one might be tempted to use higher power toovercome the cooling effect of arterial blood flow through
NA (arrows) originates anterior to the LAA and then courses at the highe 3-dimensional reconstruction of the LA. Ao � aorta; LA � left atrium;r pulmonary vein; LSPV � left superior pulmonary vein; RIPV � rightnode artery.
), the S) on thinferiosinus
the SNA. However, this must be tempered against the risk
1400 Heart Rhythm, Vol 9, No 9, September 2012
of perforation and arterial injury (see below). In fact, ex-tremely high tissue temperatures (�93°C) were required toovercome the heat-sink effect in an experimental study.7
Course of the SNAThere were 2 distinct courses of the left-sided SNA over theleft atrium before the artery reached the sinus node in the
Figure 3 L2-type SNA. In this case, the SNA originates from the LCx pis shown to be coursing over the LA roof. Ao � aorta; LA � left atrial; Lpulmonary vein; LSPV � left superior pulmonary vein; RIPV � right inpulmonary vein; SNA � sinus node artery.
Figure 4 A: The course of a left-sided SNA (in red) superimposed3. B: The 3-D electroanatomic map (cranial view) from the same paradiofrequency energy was delivered in a linear fashion at the roof. NoSNA shown in (A). Linear block across the LA roof could not be obtaleft inferior pulmonary vein; LSPV � left superior pulmonary vein; RI
SNA � sinus node artery; 3-D � 3-dimensional.
right atrium. In the majority of patients with a left SNA, theartery ran over the high anterior left atrium. In the remain-ing, it meandered anterior to the left-sided PVs beforereaching the LA roof. The hypothesis that a left SNA acts asa heat sink at the LA roof may be questioned since in themajority of cases, the artery runs slightly anterior and caudalto an idealized “roof line” connecting the superior PVs.
to the LAA (A) before emerging at the LA roof. In (B), the SNA (arrow)left atrial appendage; LCx � left circumflex artery; LIPV � left inferiorulmonary vein; RPA � right pulmonary artery; RSPV � right superior
D reconstruction of the left atrium from the same patient as in Figureho underwent linear ablation at the LA roof. Red tags show wherethe “roof line” corresponds very closely to the extent of the left-sidedthis patient. LA � left atrial; LAA � left atrial appendage; LIPV �
ight inferior pulmonary vein; RSPV � right superior pulmonary vein;
osteriorAA �ferior p
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1401Yokokawa et al Left Atrial Roof and Linear Block
However, the roof as an isthmus is not defined as a discreteline at the most cranial aspect of the roof. Analogous toablation at the cavotricuspid isthmus where energy deliverymay be required lateral or septal to the initial line, linearblock at the roof may require energy delivery posterior oranterior to the initial line deployed at its most cranial aspect.Because the voltage at the posterior LA is often quite lowafter extensive ablation, and because of the potential foresophageal injury with a posterior approach, additional lin-ear ablation is frequently performed anterior (ie, at the highanterior left atrium) to the initial roof line. Thus, it isplausible that blood flow through an L1-type SNA may act
Figure 5 A: An example of a right-sided SNA originating from the RCAegion. Ao � aorta; LA � left atrial; LAA � left atrial appendage; LIPV �
atrium; RAA � right atrial appendage; RCA � right coronary artery; RIPVsinus node artery; SVC � superior vena cava.
Table 3 Multivariate predictors of incomplete LA roof block
VariablesOdd ratio (95%confidence interval) P
LA diameter by echocardiography 1.0 (0.91–1.2) .54Anterior-posterior dimension (CT) 1.0 (0.84–1.2) .85Superior-inferior dimension (CT) 1.0 (0.88–1.2) .94LA volume (CT) 1.0 (0.98–1.0) .50Length of roof line (3-D map) 1.0 (0.90–1.1) .96Left SNA 6.8 (1.7–28) .007
3-D � 3-dimensional; CT � computed tomography; LA � left atrial/
atrium; SNA � sinus node artery.
as a heat sink and prevent adequate heating of the myocar-dium at the roof region. Furthermore, as stated above, arte-rial branches with a fraction of the diameter of the left-sidedSNA have been shown to prevent successful linear abla-tion.7 It is also possible that small branches of the L1-typeSNA that subtend the roof region but cannot be visualizedon CT play a role in preventing successful ablation at theLA roof.
Injury to the SNA during LA ablationDespite an increase in the number of procedures incorpo-rating linear ablation in patients with persistent AF, arterialinjury during linear ablation at the anterior LA or the LAroof has not been described. One of the patients in thecurrent study experienced acute sinus node dysfunction dur-ing ablation of an AT originating from the high anteriorwall. The rarity of the complication may be due to severalfactors. First, the blood flow through the SNA may beprotective against arterial injury. Catheter contact in thisregion may be poor, which may further protect the vesselfrom prolonged heating. A dual supply to the sinus nodemay also be protective. Last, lower power (25–30 W) istypically used during roof or anterior wall ablation. In this
s). B: The right SNA (white arrow) has no relationship with the LA roofferior pulmonary vein; LSPV � left superior pulmonary vein; RA � rightt inferior pulmonary vein; RSPV � right superior pulmonary vein; SNA �
(arrowleft in
� righ
case, 40 W was used because of inefficacy with the lower
cs
1402 Heart Rhythm, Vol 9, No 9, September 2012
power settings, which may have contributed to arterialinjury.
Morphology of the LA roofConventional parameters such as tissue thickness and mor-phology were not associated with the efficacy of LA roofablation in this study. Other morphological characteristics,such as recesses or pouches, also were not found to beassociated with outcome. In fact, the prevalence of a pouchat the roof in this study (3%) was lower than at the mitral(20%)8 and cavotricuspid isthmus (13%)9 reported in priorstudies. Less obvious factors such as angulation of the upperveins at the roof, which may have an impact on catheterstability, were also evaluated but were not found to beassociated with acute outcome. It is noteworthy that akin toablation at the mitral isthmus,9 only the presence of aoronary artery branch was found to be independently as-ociated with the outcome of linear ablation at the roof.
Alternatives to linear ablation at the roofLinear ablation at the LA roof may be performed to eithermodify the atrial substrate in patients with persistent AF orto eliminate macro-reentrant AT around the left- or right-sided PVs. If bidirectional block cannot be obtained in areasonable amount of time in the former situation, the leftSNA may be playing a role, and it may be best to forgofurther ablation, hoping that the patient does not develop aroof-dependent AT as a consequence. However, if a roof-dependent AT cannot be eliminated despite multiple lines atthe LA roof, then the operator needs to consider a differentstrategy to prevent arrhythmia recurrence. One possibleapproach is to target the AT at a different point along themacro-reentrant loop, as was done in one of the patients inthis study. During roof-dependent AT, the wave front mustpivot at the inferior left atrium, that is, around one of theinferior PVs. Since the voltage at the antrum around theinferior PVs is frequently of very low amplitude, owing toPV isolation and substrate ablation, a slowly conductingcorridor may be found at the inferoposterior left atriumbetween the 2 lower PV antra. In the aforementioned pa-tient, RF energy was delivered at this point and extended tothe right PV antrum, terminating the tachycardia. Althoughsuch an approach may not be generalizable to all patients, itmay offer the operator an alternative in difficult cases.
Prior studiesPrevious studies have reported acute1,10 and long-term clin-ical outcomes1 following linear ablation at the roof. Otherstudies have analyzed the anatomy of the LA roof in pa-tients undergoing catheter ablation of AF.11–13 However,the current study is the first to demonstrate a correlationbetween anatomic characteristics at the LA roof and acute
electrophysiologic outcomes.
LimitationsConduction block across the roof was determined by pub-lished criteria as described above. However, in some cases,it may be difficult to be certain whether conduction blockacross the roof has been achieved. We should also note thatthis study evaluated only the role of the SNA in influencingthe likelihood of acute conduction block at the roof.Whether the SNA also plays a role in lesion recovery duringfollow-up is unknown.
Clinical implications and conclusionsThe presence of a left SNA may make it more difficult toachieve complete conduction block at the LA roof, probablybecause of convective heat loss. Identification of a left SNAon preprocedure imaging may influence the electrophysi-ologist’s decision to perform linear ablation at the LA roofin patients with persistent AF. Since the SNA may beinjured during RF ablation, it is best to avoid high powerdelivery in the region of the high anterior left atrium and theLA roof.
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