Lesson Eighty-five Electrocardiographic and electrophysiological characteristics of atrial tachycardia with early activation close to the his-bundle

Atrial tachycardia（AT）with earliest activation in the area of the His-bundle,suggesting an origin from the superior paraseptal area of the atria,in the space delineated between the anterior supero-septal right atrium （RA）,the anterior supero-septal left atrium（LA）,and the noncoronary aortic cusp1（NCC）,is relatively rare,and successfulablation hasbeen achieved from the NCC,the supero-septal aspect of the RA,posterior to the His-bundle,or from the antero-septal part of the LA.However,a specific P-wave morphology for this group of AT has not been described in the established ECG algorithms.Therefore,the aims of this study were（1）to determine the P-wave morphology in the 12-lead ECG and（2）to analyze the intracardiac electrograms in AT with earliest activation in the area of the His-bundle.

33 patients had AT with earliest activation in the region of the His-bundle constitute the population of the current study. They all underwent successful radiofrequency（RF）ablation.

Analysis of the 12-Lead Electrocardiogram

The 12-lead ECG during arrhythmia was obtained during the electrophysiological study,the morphology assessments were performed in all leads with a speed of 25 or 50 mm/s,and the timing measurements were done ataspeed of100 mm/s.In caseofT-wave superimposition,analysis of the P-wave was performed during periods of AV block or facilitated by ventricular pacing as previously described.P-wave duration and morphology in all 12-leads as well as the PR-interval were analyzed.The P-waves were assessed on the basis of the deviation from baseline and classified as positive（+）,negative （-）,flat,biphasic （-/+or+/-）,and triphasic（+/-/+or-/+/-）.All ECGs were evaluated by 3 experienced electrophysiologists.

Analysis of the Intracardiac Electrograms

During arrhythmia,the following parameters were assessed:

（1）the timing of the earliest atrial bipolar signal in the RA,in the aorta,and,when available,in the LA,with respect to the beginning of the P-wave in the surface ECG;

（2）the timing of the local bipolar signal at the successful ablation site with respect to the beginning of the P-wave（Fig 1）;

（3）the difference between the atrial activation timing at the site of successful ablation and the bipolar atrial signal recorded in the His catheter.

General Electrophysiological Characteristics

During the electrophysiology study,sustained AT either started spontaneously or was induced with programmed and/or burst atrial pacing in 29 patients;in 4 patients despite pharmacologic provocation only frequent atrial premature contractions （PACs） were induced.The cycle length of the AT was 460±88（range 360-670）milliseconds.Among the patients with AT,AV conduction was 1:1 in 23 cases,and in 6 there was a Wenckebach periodism2.The tachycardia was not inducible by ventricular stimulation,and there was no evidence of an accessory pathway in any patient.In 23 patients,the NavX system （St.Jude Medical Inc.）and in 10 patients,the LocaLisa system（Medtronic Inc.）was used for mapping.

Figure 1 Intracardiac electrograms during para-Hisian AT.Tracings are ECG leadsⅡ,V1,V2,and intracardiac electrograms recorded from a mapping catheter at the NCC,a catheter at the high right atrium,a catheter at the His-bundle,and a catheter within the coronary sinus during para-Hisian AT.

12-Lead Electrocardiogram Characteristics

In all patients,the P-wave during AT/PACs was significantly shorter compared to the sinus rhythm（87±18 vs.117±23 milliseconds,P＜0.001）.In patients with 1∶1 AV conduction,the PR-interval during tachycardia was significantly shorter than in sinus rhythm（131±37 vs.170±47 milliseconds,P＜0.01）.

Examples of the P-wave morphology during tachycardia are shown in Figure 2.The most prominent features were a narrow P-wave and biphasic（-/+,n=23） or triphasic （+/-/+,n=5） morphology in the precordial leads,particularly in V4-V6,and a biphasic（-/+,n=13;40%） ortriphasic （+/-/+,n=12）morphology in the inferior leads.In aVR,a biphasic（+/-）aspect was observed in 18 patients and a triphasic（-/+/-） P-wave morphology in 5.Furthermore,P-waves were biphasic（-/+）in both the inferior and in the precordial leads in 11 patients,whereas in 8 patients they were biphasic（-/+）in the precordial and triphasic（+/-/+）in the inferior leads,and in 5 patients they were triphasic（+/-/+）in both the inferior and the precordial leads.Leads I,aVL,and V1were not useful to characterize the pattern.

Although these distinctive P-wave characteristics were reliably associated with earliest activation in the region of the His-bundle,they did not accurately identify the exact successful ablation site（e.g.,right vs.left atrial septum vs.noncoronary cusp）.

Figure 2 Representative examples of the P-waves morphology during para-Hisian AT.The 2 cases on the left have the characteristic narrow P-wave and biphasic（-/+）aspect in the precordial and inferior leads.On the right,2 examples of a triphasic （+/-/+） P-wave morphology in the inferior leads are shown.

Characteristics of the Intracardiac Electrograms and Catheter Ablation

The atrial bipolar signal preceded the P-wave by 31± 12（range 12-54）,37±10（range 22-50）and 39±11 （range 28-60）milliseconds in the supero-septal aspect of the RA,in the aorta and in the antero-septal aspect of the LA,respectively（Fig.3）.The difference in the earliest activation time between the 3 chambers was not significant.However,activation mapping during AT wasperformedintheLAinonly8patients.

During AT/PACs,the atrial potential at the site of successful ablation preceded the beginning of the P-wave by a mean of 38±11 （range 10-60）milliseconds and atrial activation at the His-bundle by 8± 6（range 0-22）milliseconds.

Figure 3 Fluoroscopic images during mapping of both the right and left side of the interatrial septum and the aortic root.Right（30°,left panel）and left（50°,right panel）anterior oblique radiographic views show a multipolar catheter inside the coronary sinus,a multipolar catheter at the His-bundle,a mapping catheter in the noncoronary aortic sinus,a mapping catheter at the left antero-septalaspectofthe interatrial septum.

The site of successful ablation was:NCC in 24 patients;antero-septalin theLA in 4 patients;superoseptal in the RA in 3 patients;left coronary cusp in the patient with a bicuspid aortic valve and between the right coronary cusp and the NCC in 1 patient.

The initial ablation site was guided by the earliest activation.If there was no difference in the activation time between the supero-septal RA or the antero-septal LA and the aorta,ablation was started in the aorta because of the presumed lower risk of AV block.

In 26 patients,the site of earliest activation corresponded with the site of successful ablation:RF application in the aorta eliminated the AT/PACs in 24 cases（5 patients with similar activation times in the aorta and in the RA）,and in the antero-septal LA in 2 cases.In 2 cases with similar activation timing in the aorta and supero-septal RA and in the aorta and in the antero-septal LA,respectively,RF application in the RA and in the LA was needed to eliminate the AT after unsuccessful ablation in the aorta.

In 3 patients,despite earliest activation in the aorta,RF application here was not successful,and ablation on the right side of the septum in 2 cases and on the left side in 1 case was required.In 1 patient,despite earliest activation at the left septum（44 milliseconds earlier than the P-wave）,ablation was not successful here,and RF application in the aorta（43milliseconds earlier than the P-wave） eliminated the AT.In another patient,the earliest activation was observed at the right septum（42 milliseconds in front of the P-wave）;however,RF application here did not eliminate the AT but caused first degree AV block,and additional ablation in the aorta（38 milliseconds in front of the P-wave）eliminated the AT.

Main Findings

The present study represents one of the largest experiences in patients with focal AT and earliest activation at the His bundle undergoing successful ablation.The principal findings of the study are that（1）this kind of AT shows a very characteristic narrow and biphasic（-/+）or triphasic（+/-/+）P-wave morphology in the precordial leads,especially in V4 to V6,and in the inferior leads;（2）because the activation of the para-Hisian RA,the antero-septal LA and the NCC is almost simultaneous,the P-wave morphology reliably identifies a para-Hisian origin but it does not predict the successful ablation site（i.e.,NCC vs.either side of the interatrial septum）.

Anatomical Considerations

The propagation of atrial depolarization and the resulting P-wave morphology of AT with earliestactivation close to the His-bundle are directly related to the complex anatomical configuration of the paraseptal region,with the aortic root centrally located and the NCC abutting the superior paraseptal region between the RA and the LA （Fig.4）.As shown by Yanni et al.,groups of cells of conduction tissue are located within the AV junction as well as in the right and left paraseptal region,immediately dorsal to the aortic root.Although their function is not yet clarified,this structure is probably originating from the（inferior）extension of the AV node and,intriguingly,AT originating from this region present"nodal-like"response3.

During para-Hisian AT,the activation area within the first milliseconds of atrial depolarization is a diffuse zone in the superior paraseptal area of the atria,and activation occurs almost simultaneously on both sides of the septum.Thus,it is unlikely that such a diffuse initial activation,involving the aorta,the right and the left atrium,occurs by the conduction of an impulse across the interatrial septum,with the focus located in one of these structures.Most likely,this activation pattern suggests propagation from an intermediate focus located epicardially in the paraseptal region,between the aorta,the right and the left atrium.

Based on these considerations and on those of previous studies,ATs arising from the supero-septal RA as well as from the NCC,the antero-septal LA or mitro-aortic continuity may all represent the same entity.Therefore,it would seem to be more appropriate to define them in a nonequivocal way as para-Hisian AT or AT with early activation close to the His-bundle because the universal finding is earliest activation in the region where a His-bundle potential is registered.

詞 匯

delineate v.描繪，描述，刻畫，繪出…的輪廓

constitute v.組成，構(gòu)成，設(shè)立，制定

superimposition n.疊加，疊置，被覆

biphasic adj.雙相的，兩階段的

triphasic adj.三相的，三個階段的

sustain v.支撐，支持，支援，維持，供養(yǎng)

millisecond n.毫秒

prominent adj.突起的，引人注目的，突出的，杰出的

Figure4 Computed tomography scan of right and left atria and of the aortic root.The para-Hisian region lies between the right and left interatrial septum and the aortic root,in particularthe noncoronary aortic cusp.The anatomical scan shows the close relationship between these 3 structures.On the left panel a sagittal and on the right one an axial view is showed.

distinctive adj.特殊的，特別的，區(qū)別性的

interatrial adj.心房之間的

abut v.鄰接，與…鄰接，使…緊靠

nonequivocal adj.無疑的，無歧義的，確定的

注 釋

1.cusp是通常譯成“尖，尖點，牙尖”，如bicuspid二尖的，tricuspid三尖的，但也可以解釋為“竇”，如本文中的“noncoronary aortic cusp”即指“無冠竇”，right coronary cusp 右冠竇，left coronary cusp左冠竇。

2.Wenckebach periodism譯成“文氏周期現(xiàn)象”，因心臟傳導(dǎo)系統(tǒng)某個部位傳導(dǎo)功能下降，表現(xiàn)為傳導(dǎo)逐漸（搏）減慢，最后傳導(dǎo)中斷。醫(yī)學(xué)文獻(xiàn)中通常用Wenckebach phenomenon表達(dá)傳導(dǎo)的文氏現(xiàn)象。

3.nodal-like response...譯成“結(jié)樣反應(yīng)”，是指反應(yīng)特性類似房室結(jié)，如：受迷走神經(jīng)影響；快頻率依賴傳導(dǎo)文氏現(xiàn)象；倍他受體阻斷劑和異搏定可延緩及阻滯傳導(dǎo)；縱向分離特性。

參考譯文

第85課最早激動緊鄰希氏束的房性心動過速心電圖和電生理特征

最早激動位于希氏束區(qū)的房性心動過速，起源于心房間隔旁區(qū)上方，即位于前上間隔右心房側(cè)、前上間隔左心房側(cè)和主動脈無冠竇之間的空間，相對罕見，已有經(jīng)主動脈無冠竇、右心房上間隔、希氏束后方、或左心房前間隔的成功消融。然而，在現(xiàn)有的心電圖診斷規(guī)則上，缺乏有關(guān)這組房性心動過速特異P波形態(tài)的闡述。因此，本研究的目的是：（1）確定12導(dǎo)聯(lián)心電圖上的P波形態(tài)；（2）分析最早激動位于希氏束區(qū)的房性心動過速的腔內(nèi)電圖。

33例最早激動位于希氏束區(qū)的房性心動過速患者構(gòu)成了本研究的人群，他們均成功實施了射頻消融術(shù)。

12導(dǎo)聯(lián)心電圖分析

電生理檢查過程中獲取心律失常發(fā)作時的12導(dǎo)聯(lián)心電圖，對所有導(dǎo)聯(lián)進(jìn)行形態(tài)分析，走速25 or 50 mm/s,而時間測定時的走速為100 mm/s。當(dāng)存在T波重疊時，于房室傳導(dǎo)阻滯時，或通過以前描述的心室起搏方法協(xié)助分析P波。分析所有12導(dǎo)聯(lián)上的P波間期、形態(tài)以及PR間期。根據(jù)偏離基線情況判讀P波，分為正向波（+）、負(fù)向波（-），平直、雙相波（-/+或+/-）,和三相波 （+/-/+或-/+/-）。所有心電圖由三位有經(jīng)驗的電生理專家評估。

腔內(nèi)電圖分析

心律失常期間對以下參數(shù)進(jìn)行分析：

（1）右心房、主動脈，有可能左心房中最早心房雙極信號到體表心電圖P波起始的時間;

（2）消融成功部位局部雙極信號到P波起始的時間（圖1）；

（3）成功消融部位心房激動時間與希氏束電極記錄到的雙極心房信號之間的時差。

總體電生理特征

電生理檢查期間，29例發(fā)生自發(fā)的或程控或觸發(fā)心房起搏誘發(fā)的持續(xù)性房性心動過速；4例患者在藥物激發(fā)下只能誘發(fā)出頻發(fā)的房性期前搏動。房性心動過速的周長為460±88（360～670）ms。房性心動過速患者中，23例呈1∶1房室傳導(dǎo)，6例呈文氏周期現(xiàn)象。心室刺激不能誘發(fā)心動過速，均無旁道跡象。23例采用NavX系統(tǒng)標(biāo)測 （St.Jude Medical Inc.），10 例采用 LocaLisa系統(tǒng)標(biāo)測（Medtronic Inc.）。

12導(dǎo)聯(lián)心電圖特征

所有患者房性心動過速或房性期前收縮時的P波時程顯著短于竇律P波時程[（87±18）ms vs.（117±23）ms,P＜0.001].1∶1房室傳導(dǎo)的患者，心動過速時的PR間期顯著短于竇性心律的[（131±37）ms vs.（170±47）ms,P＜0.01]。

心動過速氏的P波圖例見圖2。最突出的特征是胸導(dǎo)聯(lián)特別是 V4～V6，P 波狹窄并呈雙相（-/+,n=23）或三相（+/-/+,n=5）圖形，下壁導(dǎo)聯(lián)呈雙相（-/+,n=13）或三相（+/-/+,n=12）圖形。18例見到aVR雙相（+/-）P波，5例見到三相（-/+/-）P波。此外，11例下壁和胸導(dǎo)聯(lián)均見到雙相（-/+）P波，而8例胸導(dǎo)聯(lián)呈雙相（-/+）P波，下壁導(dǎo)聯(lián)呈三相（+/-/+）P波，5例下壁導(dǎo)聯(lián)和胸導(dǎo)聯(lián)均呈三相（+/-/+）P波（見圖3）。Ⅰ、aVL和V1無助于描述圖形特征。

雖然這些特征的P波與希氏束區(qū)的最早激動明確相關(guān)，但它們不能精確定位實際的成功消融部位（即右心房間隔、左心房間隔和無冠竇）

腔內(nèi)電圖特征和導(dǎo)管消融

右心房上間隔部位、主動脈竇部位和左心房前間隔部位的心房雙極信號較P波提前程度分別為31±12（12～54）,37±10（22～50）和 39±11（28～60）ms（圖 3）。3 個腔室之間的最早激動時間差異不明顯。然而，在左心房進(jìn)行房性心動過速激動標(biāo)測的只有8例。

房性心動過速/心房期前收縮期間，成功消融部位的心房電位較P波起始提前平均38±11（10～60）ms，而較希氏部位心房激動提前8±6（0～22）ms。

成功消融部位：無冠竇24例，左心房前間隔4例，右心房上間隔3例，主動脈二葉瓣的左冠竇1例，右冠竇與無冠竇之間1例。根據(jù)最早激動確定最初消融部位。當(dāng)右心房上間隔或左心房前間隔與主動脈竇之間的激動時間無異時，從主動脈竇開始消融，因為常認(rèn)定該部位發(fā)生房室阻滯的風(fēng)險較低。

26例最早激動與成功消融部位相一致：24例于主動脈竇射頻消融消除房性心動過速/房性期前收縮（其中5例主動脈竇與右心房的激動時間相似），2例位于左心房前間隔。有2例主動脈竇與右心房上間隔、主動脈竇與左心房前間隔之間的激動時間類似，在主動脈竇消融失敗后，需在右心房和左心房射頻消融消除房性心動過速。

3例盡管最早激動位于主動脈竇，射頻消融無效，需行間隔右側(cè)（2例）和間隔左側(cè)（1例）消融。1例盡管最早激動位于左間隔（較P波提前44ms），此處消融失敗，于主動脈竇（較P波提前43ms）消除房性心動過速。另1例最早激動在右間隔（較P波提前42ms），但此處射頻消融不能消除房性心動過速，卻導(dǎo)致一度房室傳導(dǎo)阻滯，外加主動脈竇消融（較P波提前38ms）消除房性心動過速。

主要發(fā)現(xiàn)

本研究是目前對局灶性房性心動過速且最早激動位于希氏束的患者實施成功消融的最大經(jīng)治之一。主要發(fā)現(xiàn)如下：（1）這一類型的房性心動過速表現(xiàn)為胸導(dǎo)聯(lián)、特別是V4～V6，和下壁導(dǎo)聯(lián)上非常特征的狹窄且雙相（-/+）或三相（+/-/+）P波圖形；（2）由于右心房希氏束旁，左心房前間隔和無冠竇幾乎同時激動，P波形態(tài)能可靠鑒別希氏束旁起源，但不能預(yù)測成功消融部位（即無冠竇或房間隔兩側(cè)）。

解剖考量

最早激動接近希氏束的房性心動過速的除極傳導(dǎo)及所導(dǎo)致的P波形態(tài)與間隔旁區(qū)的復(fù)雜構(gòu)形直接相關(guān)，主動脈根部位于中心，無冠竇鄰接左右心房之間的上間隔旁區(qū)（圖4）。正如Yanni等研究表明，集群的傳導(dǎo)組織細(xì)胞位于房室交接區(qū)以及左右側(cè)間隔旁區(qū)，緊挨主動脈根部背側(cè)。雖然它們的功能尚未明晰，這一結(jié)構(gòu)可能源于房室結(jié)的向下延伸，令人驚奇的是該區(qū)域起源的房性心動過速呈現(xiàn)“結(jié)樣”反應(yīng)。

在希氏束旁區(qū)房性心動過速發(fā)作時，最初幾秒內(nèi)的激動區(qū)域是位于心房上間隔旁區(qū)的彌漫區(qū)帶，間隔的兩側(cè)幾乎同時發(fā)生激動。因此，這種彌漫的初始激動，涉及主動脈與左右心房，不太可能由位于這些結(jié)構(gòu)之一處的起搏點，通過跨房間隔傳導(dǎo)而發(fā)生。

最有可能的是這種激動模式表明傳導(dǎo)來自位于心外膜主動脈與左右心房之間的間隔旁區(qū)的中間點?；谶@些考量以及既往的研究，源于右心房上間隔以及無冠竇、左心房前間隔或二尖瓣-主動脈連接處的房性心動過速可能都代表同一實質(zhì)。因此，將它們定義為希氏束旁房性心動過速或最早激動接近希氏束的房性心動過速較為恰當(dāng)，因為普遍的表現(xiàn)是最早激動的區(qū)域即是標(biāo)測到希氏束電位的部位。

圖1 希氏束旁房性心動過速時的心腔內(nèi)電圖 描記的是希氏束旁房性心動過速時體表Ⅱ、V1、V2心電圖和分別由位于無冠竇的標(biāo)測電極和高位右心房、希氏束及冠狀竇內(nèi)電極記錄到的腔內(nèi)電圖。

圖2 希氏束旁房性心動過速時P波形態(tài)圖例 左側(cè)2例顯示胸導(dǎo)聯(lián)和下壁導(dǎo)聯(lián)特征性窄而負(fù)正雙相的P波。右側(cè)2例顯示下壁導(dǎo)聯(lián)負(fù)正負(fù)三相P波。

圖3 房間隔左、右側(cè)和主動脈根部標(biāo)測時的X線圖像右前斜位（30°）和左前斜位（50°）X線透視顯示一根多極電極位于冠狀竇內(nèi)，一根多極電極位于希氏束，一根標(biāo)測電極位于無冠竇，一根標(biāo)測電極位于房間隔的左前隔面。

圖4 左右心房和主動脈根部CT圖像 希氏束旁區(qū)位于左右心房間隔和主動脈根部，特別是無冠竇之間。解剖掃描顯示此三種結(jié)構(gòu)的緊密關(guān)系。左列是矢壯面觀，右列是軸位觀。