Lesson Eighty-six Slow/fast atrioventricular nodal reentrant tachycardia using the inferolateral left atrial slow pathway-role of the resetting response to select the ablation target

In the majority of cases of slow/fast Atrioventricular nodal reentrant tachycardia（AVNRT）,which occurs in≈90%of the patients,the anterograde slow pathway is formed by the rightward inferior extension of the atrioventricular node,which can be targeted for ablation with a low risk of atrioventricular block at the inferior triangle of Koch.In a smaller number of patients,the anterograde limb of the slow/fast AVNRT circuit is formed by the leftward inferiorextension of the atrioventricular node,which can be targeted at the roof of the coronary sinus,≈1 to 3cm from the coronary sinus ostium or from the inferior paraseptal mitral annulus.On rare occasions,the slow pathway participating in AVNRT may connect to the basal inferolateral left atrium （IL-LA）,near the mitral annulus.we refer to it as IL-LA slow pathway.Because most of these patients do not exhibit retrograde conduction over the IL-LA slow pathway,and anterograde slow pathway conduction cannotbe recorded for localization,a different approach must be used to identify a safe and successful site for ablation.The aim of this study was to describe a technique to identify the ablation target by using the resetting response1elicited by delivering late atrial extrastimuli along the basal IL-LA,near the mitral annulus,to localize the atrial end of the anterograde slow pathway participating in the tachycardia.

Slow/Fast AVNRT Ablation Procedure

In patients with slow/fast AVNRT and no prior failed ablation procedure,the slow pathway at the inferior triangle of Koch was empirically targeted for ablation.Ablation sites always remained below the level of the roof of the coronary sinus ostium.When ablation at the inferior triangle of Koch failed to eliminate the tachycardia,the leftward inferior extension of the atrioventricular node was targeted by delivering a radiofrequency application along the roofofthe coronary,1 to 3cm from the coronary sinus ostium.In cases where ablation,which targeted both the rightward and leftward inferior extensions of the atrioventricular node,failed to eliminate the tachycardia,we considered that the IL-LA slow pathway may form the anterograde limb of the AVNRT circuit.Transseptal puncture was performed,and the resetting response to late extrastimuli during AVNRT was used to select the ablation target.

Radiofrequency applications（15-30 Watts with a nonirrigated catheter and 30-35 Watts with an irrigated catheter）were delivered to that site.When accelerated junctional rhythm occurred, the radiofrequency application was maintained until 15 to 30 seconds after cessation （or marked slowing） of the accelerated junctional rhythm.The end point of ablation was elimination of 1:1 anterograde slow pathway conduction during decremental atrial pacing and noninducibility of the tachycardia for 1 hour in both the baseline state and during isoproterenol administration（2-4μg/min）.

Resetting Technique to Localize the Atrial End of IL-LA Slow Pathway

The mapping/ablation catheter was positioned at the basal IL-LA,near the mitral annulus,at≈4:00 to 5:30 o'clock in the leftanterior oblique（LAO）projection（Figure 1）.During stable slow/fast AVNRT（with minimal or no cycle length variation）,a single late atrial extrastimulus was delivered to the test site,beginning near the timing of the end of the QRS complex and shortening the coupling interval in 5 or 10ms decrements,as long as the timing and morphology of the retrograde atrial potential in the His bundle electrogram were unchanged,indicating that the retrograde fast pathway was not engaged（Figure 2）.A reproducible advancement of the next His bundle potential by at least 5ms,followed by resetting of the tachycardia cycle length,indicated that the atrial extrastimulus engaged the anterograde slow pathway（Figure 2）.The lateness of the extrastimulus was measured from the onset of the His bundle potential for comparison between sites （Figure 2）.Multiple sites were tested near the inferolateral mitral annulus.The site where the latest atrial extrastimulus advanced the next His bundle potential and reset the tachycardia was considered closest to the atrial end of the anterograde slow pathway participating in the tachycardia and was selected as the target for ablation.

In patients with a prior failed ablation procedure,we generally used the resetting response during AVNRT to identify the anterograde slow pathway participating in the AVNRT circuit.Resetting was sequentially tested at the inferior triangle of Koch,the roof of the proximal coronary sinus,and the basal IL-LA.

The clinical and electrophysiological characteristics

The resetting response to extrastimuli and the response to ablation indicate that the IL-LA slow pathway formed the anterograde limb of the reentrant circuit in 10（1.2%）of 843 patients with slow/fast AVNRT.These 10 patients include 7 of 148（4.7%）patients who had a prior failed ablation procedure.

Figure 1 Radiographs in the right anterior oblique（RAO;A）and left anterior oblique（LAO;B）projections show the mapping catheter positioned at the basal inferolateral left atrium,close to mitral annulus（arrow,inferolat LA）,at the site of resetting with the latest extrastimulus and successful ablation of the IL-LA slow pathway.Other catheters are positioned at the right atrial appendage （RAA）,His bundle region（HB）,anterobasal right ventricle（RV）,and coronary sinus（CS）.

There were one or both of 2 unusual characteristics noted in 5 of the patients using the IL-LA slow pathway in slow/fastAVNRT.The H-A intervalduring tachycardia was short（＜30 ms）in 4 （40%）patients.The 2 for 1 response（an atrial extrastimulus resulting in simultaneous conduction over the fast atrioventricular nodal pathway and a slow pathway producing 2 His bundle/ventricular potentials）was observed in 3（30%）patients.Two patients exhibited both the shortest H-A intervals during tachycardia（0 and 15 ms）and the 2 for 1 response.Notably,these were the only 3 patients exhibiting the 2 for 1 response in the entire cohort of 843 patients with slow/fast AVNRT.

Resetting of AVNRT was initially tested at the inferior triangle of Koch in 2 of the 10 patients and along the roof of the coronary sinus in 6 of the 10 patients using the IL-LA slow pathway in slow/fast AVNRT.Extrastimuli at the inferior triangle of Koch failed to advance the His bundle potential and reset the AVNRT cycle length in both of the 2 patients,whereas extrastimuli at the roof of the coronary sinus reset the tachycardia in 3（50%）of the 6 patients.However,when successful,resetting from the roof of the coronary sinus required a relatively early extrastimulus（extrastimulus timing ＜35 ms after the His bundle potential）compared with the successful ablation site at the basal IL-LA（≥35ms;Figure 2）.Ablation was initially performed unsuccessfully at the inferior triangle of Koch in 9 patients and in the roof of the coronary sinus in 4 patients,including the 3 patients with successful resetting from the roof of the coronary sinus.Junctional automaticity was elicited when radiofrequency current was applied to the inferior triangle of Koch,indicating injury of the rightward inferiorextension of the atrioventricular node,but neither anterograde slow pathway conduction nor the tachycardia cycle length was affected.

Figure2 Resetting technique for localizing the atrial end of the inferolateral left atrial slow pathway forming the anterograde limb of the slow/fast reentrant circuit.A,During slow/fast atrioventricular nodal reentrant tachycardia with constant cycle length 395ms,an atrial extrastimulus was delivered to the mapping catheter（roof coronary sinus[CS]） at the roof of the coronary sinus,4cm from the ostium,340ms after the right atrial appendage（RAA） potential,and 20 ms after the His bundle（HB） potential.The extrastimulus did not prevent retrograde activation of the fast pathway as the timing and morphology of atrial activation in the His bundle electrogram were not changed（A-A=395ms in the HBp electrogram）.The atrial extrastimulus advanced the next His bundle potential（H2） by 10 ms （H-H2=385ms in the HBd electrogram）.The advanced His Bundle potential（H2） was followed by a similar 10ms advance in atrial activation and a subsequent H2-H interval equal to the tachycardia cycle length（395ms in the HBd electrogram）,indicating resetting of the tachycardia cycle length （ie , resetting the tachycardia）. B, When a later atrial extrastimulus （360ms after the RAA potential and 40ms after the HB potential） was delivered from the mapping catheter in the inferolateral left atrium （LA） close to the mitral annulus（arrow,S2）,after retrograde atrial activation had occurred（A-A=395ms in the HBp electrogram）,the next His bundle potential（H2） was advanced by 10ms（H-H2=385ms in the HBd electrogram）,thus resetting the tachycardia（10ms advance in atrial activation and a subsequent H2-H interval equal to the tachycardia cycle length of 395ms）.The resetting of the tachycardia with such a late atrial extrastimulus suggests this site is located close to the atrial end of the slow pathway forming the anterograde limb of the reentrant circuit.II,V1indicates electrocardiographic leads II and V1;d,distal;and p,proximal.

Extrastimuli delivered to the basal IL-LA（Figure 1）advanced the His bundle potential by ≥10 ms and reset slow/fast AVNRT in all 10 patients（Figure 2）.A median of 4 left atrial sites was evaluated in each patient.The latest atrial extrastimulus eliciting a positive resetting response was delivered at least 35ms（mean,49 ±12ms;range,35-65ms） after the timing of the onset of the His bundle potential（Figure 2）.Ablation was targeted at the site of resetting by the latest extrastimulus as this was interpreted as being closest to the atrial end of the anterograde slow pathway in the reentrant circuit.A median of1 radiofrequency application eliminated slow pathway conduction and terminated the tachycardia in allpatients.The successful ablation site was located at the basal IL-LA,near the mitral annulus.Accelerated junctional rhythm with retrograde conduction over the fast pathway（IL-LA slow pathway automaticity）occurred during the successful radiofrequency application in 9 of 10（90%）patients.Anterograde fast atrioventricular nodal pathway conduction remained intact in allpatients.No procedural complications were observed in any patient.

詞 匯

participate v.參與，分享，含有

empirically adj.經驗性地，憑經驗地

triangle n.三角形，三角，三角鐵

oblique n.&adj.&v.傾斜物，斜肌;斜的;傾斜,斜行進prior adj.在先的，優(yōu)先的，更早，更重要

注 釋

1.resetting response指“重整反應”，是緊接重整刺激后首個心動過速激動的時間與引起重整的期前刺激聯(lián)律間期之間的關系，通常有3種類型，分別是遞增型、遞減型和平坦型。

參考譯文

第86課 基于左心房下外側慢徑路的慢快型房室結折返型心動過速：重整反應在選擇消融靶點中的作用

房室結折返型心動過速（AVNRT）中的近90%為慢快型，其順向慢徑主要由房室結向右下延伸形成，位于Koch三角下方，消融此處發(fā)生房室傳導阻滯的風險低。少數(shù)患者的慢快型AVNRT折返環(huán)前傳支由房室結向左下延伸形成，距冠狀竇口1～3cm的冠狀竇頂部或二尖瓣環(huán)下間隔旁可成為靶點。極少數(shù)情況下，參與AVNRT的慢徑與鄰近二尖瓣環(huán)的左心房下外側（IL-LA）基部相連接。我們稱之為IL-LA慢徑。由于多數(shù)患者并不表現(xiàn)經IL-LA慢徑的逆?zhèn)鳎覠o法記錄順傳慢徑來定位，因此需用不同的方法來確定安全和成功的消融部位。本研究的目的是闡述一種利用沿IL-LA基部的晚期心房刺激引發(fā)的重整反應技術，來定位參與心動過速順傳慢徑的心房端，從而確定消融部位。

慢快型AVNRT的消融手術

對于既往無消融失敗史的慢快型AVNRT患者，于Koch三角下方行經驗性消融。消融部位總是位于冠狀竇口頂部水平下方。當在Koch三角下方消融失敗時，選擇房室結左下延伸部位為靶點，沿距冠狀竇口1～3cm的冠狀竇頂部進行消融。對于房室結左右側延伸部消融均失敗者，我們考慮IL-LA慢徑構成AVNRT折返環(huán)的前向支。行房間隔穿刺，利用于AVNRT發(fā)作期間對晚期期外刺激的重整反應選擇消融靶點。

對該部位進行射頻消融（非灌注導管15～30W，灌注導管30～35W）。當出現(xiàn)加速性交界性節(jié)律時，維持消融直至加速性節(jié)律停止或明顯減慢后15～30s。消融終點是在基礎狀態(tài)下或異丙腎上腺素激發(fā)下（2～4 μg/min）進行遞減性心房起搏時無1:1慢徑前傳且無法誘發(fā)心動過速，達1h。

重整技術定位IL-LA慢徑心房端

標測/消融導管位于近二尖瓣環(huán)的IL-LA基部，相當于左前斜位（LAO）上4:00～5:30鐘點的位置（圖1）。于穩(wěn)定的慢快型AVNRT發(fā)作期間（周長微小變化或不變），發(fā)放單一晚期心房期外刺激，從接近QRS波群終點時間開始，以5或10ms的遞減縮短聯(lián)律間期，只要希氏束電圖上的逆?zhèn)鞣坎〞r間與形態(tài)不變，表明未侵入逆?zhèn)骺鞆剑▓D2）。下一希氏束電位的可重復性提前至少5 ms，隨后是心動過速周長的重整，表明房性期外刺激侵入順傳的慢徑（圖2）。從希氏束起始開始測定期外刺激的延后時間用于不同部位的比較（圖2）。對接近下外側二尖瓣環(huán)的多個部位進行測試，能使希氏束電位前移并且重整心動過速的最晚心房期外刺激部位，認為是參與心動過速的順傳慢徑心房端并確定為消融靶點。

對既往有過消融失敗的患者，我們通常于AVNRT期間利用重整反應去鑒別參與心動過速的順傳慢徑。于Koch三角下方、冠狀竇近端頂部和IL-LA基部進行連續(xù)重整測試。

臨床和電生理特征

對期外刺激的重整反應和對消融的反應表明，843例慢快型AVNRT患者中的10例（1.2%），IL-LA慢徑形成折返環(huán)的前傳支。這10例包含了既往有過消融失敗的148例患者中的7例（4.7%）。

5例利用IL-LA慢徑的慢快型AVNRT患者具有兩種不同尋常特征的一種或兩種表現(xiàn)。4例（40%）心動過速時H-A間期短（＜30 ms）。3例（30%）表現(xiàn)為1:2反應（一次心房期外刺激同時經房室結快徑和慢徑傳導產生2個希氏束電位/心室波）。2例同時具備心動過速時最短的H-A間期（0 and 15 ms）和1:2反應。值得注意的是這是843例慢快型AVNRT患者中僅有的表現(xiàn)為1:2反應的3例。

10例利用IL-LA慢徑的慢快型AVNRT患者的AVNRT重整，2例開始于Koch三角下方，6例沿著冠狀竇頂部。2例Koch三角下方的期外刺激均不能使希氏束電位前移和重整AVNRT周長，而6例冠狀竇頂部期外刺激中的3例（50%）重整了心動過速。然而，其時的成功，與在IL-LA基部成功消融的部位比較，冠狀竇頂部的重整需要相對較早的期外刺激（希氏束電位后＜35ms比＞35ms，圖2）。9例Koch三角下方消融失敗，4例冠狀竇頂部消融失敗，包括冠狀竇頂部成功重整的3例，當對Koch三角下方消融時出現(xiàn)交界性節(jié)律，提示損傷到房室結右下延伸部，但慢徑前傳與心動過速周長均未受到影響。

所有10例IL-LA基部的期外刺激（圖1）均使希氏束電位前移≥10 ms并重整慢快型AVNRT（圖2）。每例患者左心房評估部位的中位數(shù)是4個。引發(fā)陽性重整的最晚房性期外刺激至少在希氏束電位起始點后35ms，平均（49±12）ms，從35～65 ms（圖2）。消融靶點位于最晚期外刺激重整的部位，因為該處最接近折返環(huán)前傳慢徑的心房端。所有患者阻斷慢徑傳導和中止心動過速的射頻消融次數(shù)中位數(shù)是1次。成功消融部位位于近二尖瓣環(huán)的IL-LA基部。10例中的9例（90%）成功消融過程中發(fā)生加速性交界性節(jié)律通過快徑逆?zhèn)鳎↖L-LA慢徑自律性）。所有患者房室結快徑前傳無損。無并發(fā)癥發(fā)生。

圖1右前斜位（RAO，A）與左前斜位（LAO，B）射線照相顯示標測導管位于左心房基部下外側，接近二尖瓣環(huán)（箭標，左心房下外側），位于最晚期外刺激和成功消融IL-LA慢徑的部位。其他導管位于右心耳（RAA），希氏束區(qū)（HB），右心室前基底部（RV），和冠狀竇（CS）。

圖2用于定位形成慢快型折返環(huán)前傳支的左心房下外側慢徑心房端的重整技術

A：在恒定周長395ms的慢快型房室結折返型心動過速期間，于距冠狀竇口4cm的冠狀竇（CS）頂部、右心耳（RAA）電位后340ms、希氏束（HB）電位20ms后發(fā)放心房期外刺激至標測電極。期外刺激不影響快徑逆?zhèn)?，因希氏束電圖上的心房激動時間和形態(tài)不變（希氏束近端電圖A-A=395ms）。心房刺激使下一希氏束電位（H2）提前10ms（希氏束遠端電圖H-H2=385ms）。提前的希氏束電位（H2）尾隨著相同10ms提前的心房激動，其后的H2-H間期與心動過速周長相同（希氏束遠端電圖395 ms），提示心動過速周長重整（即心動過速重整）。B：當從位于接近二尖瓣環(huán)（箭標，S2）的下外側左心房（LA）標測導管發(fā)放較晚的心房期外刺激（RAA電位后360 ms、HB電位后40ms），在逆?zhèn)餍姆考雍螅ㄏＪ鲜穗妶DA-A=395ms），下一希氏束電位（H2）提前 10ms（希氏束遠端電圖H-H2=385 ms），重整了心動過速（心房激動提前10ms，隨后的H2-H間期與心動過速周長395ms相同）。在這一晚期心房期外刺激下心動過速重整，提示該部位接近形成折返環(huán)前傳支的心房端。Ⅱ，V1指心電圖Ⅱ和V1；d，遠端；和p，近端。