Lesson Sixty-six "Classical"response in a pre-excited tachycardia:What are the pathways involved?

●心電學英語

Lesson Sixty-six "Classical"response in a pre-excited tachycardia:What are the pathways involved?

Introduction

A 24-year-old patient presented with history of recurrent palpitation and was diagnosed as wide QRS tachycardia which was cardioverted.The sinus rhythm ECG and the tachycardia ECG are shown in Figure 1. During the electrophysiological study,2 morphologies of tachycardia were inducible,1 with right bundle branch block（RBBB）morphology（Figure 2A）and another with left bundle branch block（LBBB）morphology（Figure 2B）,which was her clinical tachycardia.The LBBB type wide QRS tachycardia was faster（Figure 2B）.DuringtheRBBBmorphologytachycardia, ventricular entrainment showed a V-A-V response and a His refractory ventricular extrastimulation1advanced the retrograde atrial activation,resetting the tachycardia.

TheLBBBmorphologytachycardiashowed variation in cycle length with a constant Ventriculo-Atrial（VA）interval.Atrial entrainment did not change the QRS morphology or VA relationship.An early premature atrial extrastimulation from the lateral right atrium showed an interesting finding（Figure 3）.Very late atrial extrastimulus from the same location did not advance the V without affecting the septal A.What are the mechanisms of the two tachycardias?

Commentary

The baseline ECG showed features typical of an accessory pathway,in the right posterior location.The clinical tachycardia was a regular wide QRS tachycardia（Figure 1B）,with LBBB morphology and left axis deviation.The 12-lead ECG of the tachycardia gives certain clues to the underlying pathways.The typical antidromic tachycardia would have resulted in a wider QRS and predominantly positive complexes in the lateral precordial leads because of ventricular activation solely through the accessory pathway.A fast conducting AVN-His bundle may,however,result in relatively narrower QRS.When the tachycardia morphology does not correspond to the pre-excitation pattern in sinus rhythm,multiple pathways should be considered.The wide QRS tachycardia shows left axis deviation and LBBB and has a sharp rapid component of the initial part and has no precordial transition.These features are moretypicalofanatriofascicular（Mahaim）tachycardia,although the sinus rhythm ECG is not typical for a Mahaim fiber.

Intracardiac recording in Figure 2shows an orthodromic tachycardia（[ORT]with RBBB aberrancy）with antegrade conduction through the His bundle,and retrograde conduction through a right-sided pathway（Figure 2A）;earliest atrial activity was noted in the distal HALO electrodes in the posterolateral tricuspid annulus.An atrial tachycardia with aberrancy was ruled out by a VAV response to ventricular entrainment.A short postpacing interval and atrial pre-excitation2by a Hisrefractoryventricularstimulusconfirmedthe diagnosis.

Figure 1Twelve-lead electrocardiograms of the patient in sinus rhythm（A）and during clinical tachycardia（B）.

The wide QRS tachycardia with LBBB morphology（Figure 2B）has a shorter cycle length but has the same eccentric retrograde activation sequence.It was initiated by catheter-induced ventricular ectopics during the ORT.The HV was negative（ventricular-His[VH] =80ms）showing that it is a truly pre-excited long VH tachycardia.At this point,it can be assumed that the H is a retrograde H（further confirmed by observations mentioned below）.Two additional points should be noted in Figure 2B∶（1）the retrograde activation sequence is same as during the ORT（tachycardia 1）and（2）the cycle length is considerably shorter during the wide QRS LBBB morphology rhythm.These essentially rule out a classic antidromic tachycardia mediated by the same AV connection.However,thepresenceofRBBBor incorporation of the slow pathway during the ORT alone may cause it to be slower than antidromic tachycardia. Orthodromic reentry with aberrancy is ruled out by the negative HV.AVNRT with bystander accessory pathway is excluded because of eccentric atrial activation and because the retrograde activation did not change between the tachycardias.Further,in AVNRT with bystander activation,the VH is usually short and the H recorded is an antegrade H.A late atrial extrastimulus during the tachycardia when the AV junction is refractory can be used to diagnose AVNRT with bystander pathway（see below）.A His refractory ventricular stimulus can also exclude AVNRT if it resets the tachycardia with the same activation sequence in atria-this was demonstrated in this case.The possibility then we have to consider is thatthesecondtachycardiaisbecauseofa pathway-to-pathway conduction-antegrade conduction through a right-sided accessory pathway（LBBB,left axis）,with a negative VH as noted in the figure and retrogradeconductionthroughthesameright posterolateral pathway mediating the ORT,with earliest atrial activation in HALO 1,2.Pathway-to-pathway tachycardia are usually possible only when the pathways are at a considerable distance anatomically.When 2 pathways are close by,like in this case,tachycardia can be sustained more easily if at least one of the pathways has decremental conduction property.In such a scenario, the AVN can conduct retrogradely and activate part of the atria.The rare possibility of ORT with bystander pathway was previously reported;however,they are associated with minimal QRS widening and a short rather than negative HV.

Figure 2Surface leadsⅠ,Ⅲ,and V1and intracardiac electrograms from right atrium（HALO 1,2 at lateral right atrium to HALO 17,18）,His bundle（His bundle distal[HBED]and His bundle middle[HBEm]）,the coronary sinus（coronary sinus distal[CSD]and coronary sinus proximal [CSP]）and right ventricular apex（RVA）.A,The orthodromic tachycardia with right bundle branch block aberrancy.B,The left bundle branch block tachycardia of shorter cycle length and long ventricular-His of 80 ms with the same retrograde eccentric atrial activation as in the initial tachycardia.

Atrialentrainmentshowedresettingofthe tachycardia without alteration of the QRS morphology or VH interval,thus confirming atria as necessary part of the circuit and also making AVNRT or ORT with bystanderpathwayunlikely.Iftheatriofascicular pathway was merely a bystander,QRS morphology and the VH relationship would change with resetting of the tachycardia.This also rules out a myocardial VT. Coupled atrial premature stimuli also showed advancing of the V.A relatively early coupled atrial stimulus produced an interesting finding as noted in Figure 3, which shows a coupled atrial extrastimuli during the pre-excited rhythm,which delayed the ventricular activation through the pathway and reset the tachycardia withoutchangingtheVHorVAinterval.This demonstrates the decremental nature of the anterograde pathway during tachycardia.It also demonstrates that the H is a retrograde H related to V.If His bundle activation contributed to activation of septal atrium,this resetting would have been expected to at least slightly alter the atrial activation pattern.Even very late atrial extrastimuli（delivered from the presumed site of antegrade pathway）advanced the septal A making it likely that atrium in the vicinity of the His is activated through the retrograde accessory pathway and there is Hto A block during the LBBB tachycardia.Further,the atrialactivationduringboththeORTandthe pre-excited tachycardia is the same showing that there is no retrograde activation of atrium through the AVN. During cycle length changes in the LBBB tachycardia the VH and VA interval remained constant.Thus,a diagnosis of pathway-to-pathway tachycardia,mediated by a Mahaim fiber and a closely located nondecremental pathway was made.

Patientsubsequentlydevelopedanatrial tachycardia with 2∶1 AV conduction through both accessory AV connection（Figure 4A）.Figure 4A shows thecharacteristicMahaimpotentialat9o′clocktricuspid location with a short M to QRS interval.This short M to QRS interval is not typical for Mahaim conduction.It shows that the QRS is also contributed by antegrade conduction through the right posterior nondecremental pathway-a case of pre-excited Mahaim conduction. Successful ablation of the Mahaim fiber resulted in change in QRS morphology.The right posterior pathway was mapped during ORT and successfully ablated at the posterior tricuspid annulus region（Figure 4B）.Post ablation of both pathways there was persistent RBBB and no VA conduction at 500 ms showing a poor retrograde conduction through the AV node.

Figure 3Surface leadsⅠ,Ⅲ,and V1and intracardiac electrograms from right atrium,His bundle,the coronary sinus and right ventricular apex.The effect of an early coupled atrial stimulus（asterisk）during tachycardia is shown.CI indicates coupling interval of atrial stimulus;TCL,tachycardia cycle length;and V-V',interval between surface QRS following the extrastimulus.

詞匯

aberrancy n.偏離正路，差異

eccentric adj.&n.古怪,古怪的,偏心;偏心輪,偏心圓

incorporation n.包含,公司,混合

anatomically adv.在解剖學上

decremental adj.減少的，遞減的

注釋

1.His refractory ventricular extrastimulation指“希氏束不應期間的心室期外刺激”，通常在室上性心動過速時，略短于心動過速周長（＜40ms）的心室起搏即是。2.atrial pre-excitation指“心房提前激動”或“心房預激”。室上性心動過速時心室起搏，使得心房頻率加快，心動周期縮短15ms或以上，即為心房預激。希氏束不應期間心室起搏引起心房預激，要考慮順傳型房室折返性心動過速。

Figure 4Fluoroscopic left anterior oblique projections of location and electrograms from the following catheters∶the duo-decapolar catheter along the tricuspid annulus（HALO 1,2 to 17,18）,the decapolar coronary sinus（CS）,the mapping and ablation catheter（shown with asterisk.RFd and RFp）and quadripolar catheters in the His（His bundle distal[HBED],His bundle middle[HBEm],and His bundle proximal[HBEp]）and right ventricular apex（RVA）.A.Atrial tachycardia with 2∶1 conduction and M potentials at the ablation catheter at the site of successful ablation of the Mahaim fiber.Note the short M-Local V interval and simultaneous activation of the RVA and ventricular annulus（RFd）because of antegrade conduction through both pathways.B.The recording during orthodromic tachycardia,ablation at the posterolateral tricuspid annulus results in local separation of VA and termination of tachycardia（solid down arrow）.

參考譯文

第66課預激心動過速的“經(jīng)典”反應——涉及哪些旁道？

購買蔬菜、水果時，不買異常氣味的蔬菜和水果。有些商販為了蔬菜更好看，用化學藥劑進行浸泡，這些物質有異味，不容易被沖洗掉。不買顏色異常的蔬菜和水果，不買形狀異常的蔬菜和水果。有的蔬菜使用了激素物質，會長成畸形。盡量不要食用“新奇”“野味”等不常食用或從未食用過的食物。

患者女性，24歲，因反復心悸而就診，診斷為寬QRS波群心動過速并得到復律。圖1為竇性節(jié)律心電圖和心動過速心電圖。電生理檢查中，誘發(fā)出兩種形態(tài)的心動過速，一為右束支傳導阻滯（RBBB）圖形（圖2A），另一為左束支傳導阻滯（LBBB）圖形（圖2B），與她臨床發(fā)作的心動過速一樣。LBBB型寬QRS波群心動過速較快（圖2B）。RBBB圖形心動過速時，心室拖帶顯示V-A-V反應，希氏束不應期心室期外刺激使逆?zhèn)餍姆考犹崆?，重整心動過速。

LBBB圖形心動過速顯示周長變化而室-房（VA）間期恒定。心房拖帶不能改變QRS形態(tài)或VA關系。右心房外側壁早期房性期外刺激顯示令人感興趣的發(fā)現(xiàn)（圖3）?！?br>