Resultsof cryoenergy andradiofrequency-based catheterablation for treating ventricular arrhythmias arising from the papillary muscles of the left ventricle, guided by intracardiac echocardiography and image integration

The papillary muscles(PMs)from the left ventricle (LV)have been shown to be a potential site of origin of ventricular arrhythmias(VAs)in patients with and without structural heart disease.Catheter ablation has been described as an effective treatment for these arrhythmias,although radiofrequency delivery at these regions has been associated with poor manipulation and catheter stability compared with other VAs.This study compares procedural outcomes and recurrence rate after catheter cryoablation or radiofrequency ablation for the treatment of ventricular tachycardia(VT)and premature ventricular complexes(PVCs)localized at the PMs of the LV,with the aid of intracardiac echocardiography(ICE) and image integration.

A total of 21 patients with recurrent VAs originating at the PMs of the LV were identified from retrospective review of 189 consecutive patients with symptomatic sustained VT,nonsustained VT,or PVC referred for catheter ablation.The sites of origin of idiopathic VAs included the posteromedial PM(PMPM) in 19(10％)，and anterolateral PM(ALPM)in 3(1.5％).

One operator treated the first 12 patients with cryoenergy,and a different operator treated the following 9 patients,using radiofrequency energy.Procedural outcomes suchas catheterstability,incidence of multiple VAs morphologies during energy delivery, acute success rate,and long-term recurrence rate were comparedbetweenthosepatientstreatedwith cryoenergy and those with radiofrequency.For mapping and pacing,standard multielectrode catheters were placed in the coronary sinus(CS),His bundle region, and RV apex through the right femoral vein.Arrhythmia inductionwasattemptedbyprogrammedelectric stimulation from the RV apex,RV outflow tract,and CS, with 1,2,and 3 extrastimuli introduced after an 8-beat drive train,if necessary,with the addition of an isoproterenol infusion.

Imaging

A 2-dimensional ICE probe was positioned toward the RV outflow tract and RV inflow tract to visualize the different LV structures,as shown in Figure 1.To specify VAs origin and catheter position,3 segments were attributed to each PM:the apex,at the point of insertion of the chords(distal third of the PM);the body(middle portion of the PM);and the base,at the LV wall insertion. Catheter position,contact,and stability were assessed through this method.Catheter stability was defined asthe absence of back and forth movement of the catheter during energy delivery at the effective lesion site.

Multidetector computed tomography(MDCT)was performed with a 64-detector＜15 days before catheter ablation.No ionic contrast material was used and scanningwasperformedwithacollimatedslice thickness of 0.9 mm.

Figure 1A,Intracardiac echocardiography(ICE)image of the posteromedial papillary muscle(PMPM).A multipolar catheter is placed over the PMPM,for mapping the clinical arrhythmia.B,ICE image showing the Freezor Max 8 mm cryoablation catheter delivering cryoenergy at the base of the PMPM.C,Clinical ventricular tachycardia.D,Pace-mapping score of 24 at the site of effective lesion.E,Left anterior oblique and(F)right anterior oblique fluoroscopic projection of the cryocatheter at the effective lesion site.

Cryoablation

Cryoenergy was delivered at myocardial sites exhibiting the earliest bipolar activity or local unipolar QS pattern or at a Purkinje network with an early activity preceding the QRS onset for≥25 ms during the VA(Figure 2)at pace-mapping areas exhibiting QRS match of≥11 of 12.Focal ablation was performed with a 9-Fr/8-mm cryoablation catheter through a transeptal and transmitral approach.Transeptal access was obtained by performing a transeptal puncture with a Brockenbrough needle.Special attention was given to catheter manipulation inside the LV to avoid damage to the chords because the cryocatheter is stiffer than the radiofrequency catheter.This was continuously assessed by ICE.When a reduction in the incidence of VT or PVCs was observed,cryoenergy was delivered for≤240s with 2 freeze-thaw-freeze1cycles; otherwise,cryoenergy delivery was terminated,and the catheter was repositioned.

Figure 2Cryoablation.A,Activation map of the clinical arrhythmia at the body of the anterolateral papillary muscle(ALPM),in the 3-dimensional integrated left ventricle(LV)multidetector computed tomography model.The cryocatheter is positioned at the earliest activation site.B,Intracardiac echocardiography(ICE)visualization of the cryocatheter at the body of the ALPM.C,Melt-down effect during cryoenergy delivery at the ALPM. This corresponds to an artifact generated by the cryoenergy over the mapping system.The movement of the catheter is only apparent and continuous assessment of catheter position and stability during energy delivery is achieved by ICE.D,Clinical premature ventricular complex mapped at the body of the ALPM.The VEGM-QRS interval was measured to 35 ms.E,Pace mapping at the site of earliest activation,accounting for a score of 24.

Radiofrequency Ablation

Radiofrequency energy was delivered using the same criteria previously described.Focal ablation was performed with a 4-mm open irrigated radiofrequency ablation catheter through a transmitral or transaortic approach.When a reduction in the incidence of VT or PVCs was observed radiofrequency was delivered for≤90 s,with 2 posterior 45-s consolidation lesions at the same area;otherwise,radiofrequency delivery was terminated,and the catheter was repositioned.

The end point of catheter ablation was the eliminationandnoninducibilityofVAsduring isoproterenol infusion(2-10 μg/min)and burst pacing from the RV to a cycle length as short as 300 ms. Procedural acute success was defined as abolition of inducible or spontaneous VA.

Procedural Outcomes

Termination of the arrhythmia was observed in 19 patients without further inducibility.There were no intraoperativecomplications.Patientstreatedwith cryoenergy(n=12)showed a 100％acute success rate, whereasthosetreatedwithradiofrequency(n=9) presented a 78％success rate.Catheter stability was achieved in all patients treated with cryoenergy and only in 2 patients treated with radiofrequency.Incidence of multiple VA morphologies was observed in 7 patients treated with radiofrequency(77.7％),whereas none was observed in those treated with cryoenergy.All patients included in this study had single VA morphology before catheter ablation.

In the cryoablation group,VAs originating from the base of the PM were observed in 6 patients,the apex in3 patients,and the body in 3 patients.In the radiofrequency group,VAs originating from the base of the PM were observed in 6 patients,and 3 patients showed VAs from the body.Pace mapping showed≥11 of 12 match in all treated PMs at the site of effective lesion.Purkinje potentials(PP)were observed in 13 (62％)patients,mainly in VAs with origin at the base of the PM(base 100％versus body 16 versus apex 0％).

Follow-Up Outcomes

Median follow-up was 360 days(interquartile range,116-365)forcryoablationand87days (interquartile range,65-148)for radiofrequency.There was no increase in the incidence of mitral valve regurgitation,or an increase of MR severity after ablation,using either method.None of the patient treated with cryoablation showed VA recurrence during follow-up(recurrence rate of 0％).One patient from the cryoablation group showed a 50％VA Holter burden reduction,from 40％to 19％,during the first month. After 6 months,Holter burden was＜5％and the patient remained asymptomatic,without the use of antiarrhythmic drugs.Four patients(44％)presented VA recurrence during follow-up in the radiofrequency group(P=0.03).VA Holter burden was decreased from 20±15％to 2.8±5％in the cryoablation group and from 21±12％to 11±8％in the radiofrequency group.

Discussion

Catheter irrigation is often used to cool the ablation electrode such that more power can be delivered without being limited by the formation of thrombus at the catheter-tissue interface.Amajorconcernduring radiofrequency ablation is mitral valve dysfunction by injury or rupture of the PMs,specially when using irrigated tip ablation catheters,although this has not yet been reported.Excessive intramyocardial heating can produce steam formation and abrupt volume expansion, which may be audible as steam pops.Pops are capable ofcausingdeeptissuetears,andpatientswith ventricular perforations are more likely to require surgical repair.

Catheter cryoablation was introduced into clinical electrophysiologyin1998.Cryoablationhasbeen reported as a safe alternative for catheter ablation in idiopathic VT arising from the RV outflow tract,aortic cusps,and epicardium.Cryothermal safety profile is attributed to the mechanism of tissue destruction. Histology of chronic lesions shows well-demarcated2lesions with minimal tissue disruption and preserved underlying architecture.Catheter stabilization during ablation at the PMs is a major consideration.Stabilization is achieved because of catheter-tissue adherence after reaching temperatures of-80℃.

詞匯

integration n.整合,融合，集成

cryoablation n.冷凍消融

cryoenergy n.冷凍能量

probe n.&v.探測器,探針,探頭；探索

specify v.具體指定,詳細說明，列舉

collimate v.使...平行,校準

thaw v,&n,融化,使...融化,變暖和；融化,緩和

consolidation n.鞏固,合并,聯(lián)合

pop adj.&v.&n.&adv.通俗的，流行的；敲擊，取出；流行音樂，汽水，砰然聲，槍擊；突然地，砰地

cryothermal adj.冰凍的，冷凍的，冰溫的

disruption n.破裂,混亂

architecture n.建筑學，建筑風格，架構(gòu)

注釋

1.freeze-thaw-freeze指“冷凍-融化-冷凍”過程，冷凍導管消融過程中常采用此方法，可擴大消融的創(chuàng)面，如Data in hepatocellular ablation show that repetitive freezethaw cycles create larger lesions than those obtainedby longer freezing at a certain temperature.肝細胞消融資料顯示，在特定的溫度下，重復冷凍-融化周期與較長時間的冷凍比較，能產(chǎn)生較大的病損。

2.well-demarcated指“界限明晰的”，如Histological analysisagainrevealedhomogeneouslesionswithwelldemarcated borders.組織學分析再次揭示有著界限明晰邊緣的均質(zhì)病損。

參考譯文

第71課腔內(nèi)心臟超聲和圖形整合指導下的左心室乳頭肌起源室性心律失常的冷凍和射頻消融

業(yè)已顯示左心室乳頭肌是伴或不伴心臟結(jié)構(gòu)異?；颊咝穆墒С５臐撛谄鹪床课?。與其他部位室性心律失常比較，這些區(qū)域的心律失常消融操作困難、導管穩(wěn)定性差，但已有導管消融有效的報道。本研究借助心腔內(nèi)心臟超聲和圖像整合，比較左心室乳頭肌起源室性心動過速或期前搏動的冷凍和射頻消融手術(shù)結(jié)果及復發(fā)率。

回顧性分析連續(xù)189例因癥狀性持續(xù)性室性心動過速、陣發(fā)性室性心動過速或室性期前搏動接受射頻導管消融的患者，確定21例為左心室乳頭肌起源的反復發(fā)作室性心律失常。這一特發(fā)性室性心律失常的起源部位包括后內(nèi)側(cè)乳頭?。?9例）和前外側(cè)乳頭?。?例）。

一位術(shù)者對最初12例患者行冷凍消融術(shù)，另一位術(shù)者對隨后的9例患者行射頻消融術(shù)。將冷凍消融術(shù)和射頻消融術(shù)結(jié)果進行對比，內(nèi)容涉及導管穩(wěn)定性、消融過程中多種形態(tài)室性心律失常的發(fā)生率、即刻成功率和長期復發(fā)率。經(jīng)右股靜脈途徑將標準多極導管放置到冠狀竇、希氏束和右心室心尖，用于標測和起搏。經(jīng)右心室心尖部、右心室流出道和冠狀竇發(fā)放8次短陣刺激加1、2、3個額外刺激，誘發(fā)心律失常，必要時加用異丙腎上腺素滴注。

顯像

二維心腔內(nèi)心臟超聲探頭抵近右心室流出道和流入道，以便顯示左心室不同結(jié)構(gòu)，如圖1所示。為闡述室性心律失常起源部位和導管位置，將每一乳頭肌分成3個節(jié)段：尖部，腱索插入點（乳頭肌遠端1/3）；體部（乳頭肌中部）；基部，左心室壁插入部。通過這種方法對導管的位置、接觸和穩(wěn)定性進行評估。導管的穩(wěn)定性是指在有效靶點能量釋放過程中導管無前后向移動。

于導管消融前15d內(nèi)做64排CT檢查。使用非離子對比劑，掃描層厚0.9mm。

冷凍消融

在起搏標測到QRS波群圖形匹配≥11/12的區(qū)域，于呈現(xiàn)最早雙極激動或局部單極QS圖形的心肌部位、或在較室性心律失常QRS群起點提前≥25ms的浦肯氏網(wǎng)部位釋放冷凍能量（圖2）。采用9-Fr/8-mm冷凍消融導管跨間隔和跨二尖瓣方法進行冷凍消融。用Brockenbrough穿間隔針建立跨間隔通路。導管進入左心室的操作應(yīng)特別小心，以免損傷腱索，因為冷凍導管比射頻消融導管硬。心腔內(nèi)心臟超聲連續(xù)評估此過程。當觀察到室性心動過速或室性期前搏動減少時，繼續(xù)釋放冷凍能量，不超過240s，重復冷凍-融化-冷凍兩輪，否則，停止冷凍，調(diào)整導管位置。

射頻消融

按照之前描述的同一標準釋放射頻能量。采用4mm開放式灌注射頻消融導管經(jīng)跨二尖瓣或主動脈瓣途徑作病灶消融。當觀察到室性心動過速或室性期前搏動減少時，繼續(xù)釋放射頻能量，不超過90s，對同一區(qū)域追加2次45s的鞏固消融；否則，停止消融，調(diào)整導管位置。

導管消融的終點是消除室性心律失常，且靜脈滴注異丙腎上腺素(2～10μg/min）及右心室猝發(fā)起搏周長短至300ms下，不能誘發(fā)室性心律失常。手術(shù)即刻成功率定義為消除誘發(fā)的或自發(fā)的室性心律失常。

手術(shù)結(jié)果

19例患者心律失常得到中止且不能被進一步誘發(fā)。術(shù)中無并發(fā)癥。冷凍治療組（12例）手術(shù)即刻成功率100％，而射頻治療組（9例）成功率78％。冷凍治療組所有患者導管穩(wěn)定性好，而射頻治療組導管穩(wěn)定性好的只有2例。射頻治療組7例（77.7％）發(fā)生多形室性心律失常，而冷凍治療組無多形室性心律失常發(fā)生。本研究中所有患者消融前均呈單一形態(tài)的室性心律失常。

在冷凍消融組，室性心律失常起源于乳頭肌基部6例，體部和尖部各3例。射頻消融組，室性心律失常起源于乳頭肌基部6例，體部3例。所有乳頭肌有效部位起搏標測顯示匹配達≥11/12。浦肯野電位見于13例（62％），主要見于乳頭肌基部起源的室性心律失常（基部100％、體部16％、尖部0％）。

隨訪結(jié)果

冷凍消融組隨訪時間中位數(shù)360d，射頻消融組87d。兩組消融后均無增加二尖瓣脫垂的發(fā)生率或增加二尖瓣反流嚴重性。隨訪期間冷凍消融組無室性心律失常復發(fā)。冷凍消融組1例隨訪第1個月24h動態(tài)心電圖即顯示室性心律失常負荷下降50％，從40％下降到19％。6個月后，動態(tài)心電圖負荷＜5％，無癥狀，未服用抗心律失常藥物。隨訪中射頻消融組4例（44％）出現(xiàn)室性心律失常復發(fā)。動態(tài)心電圖負荷冷凍消融組從（20±15）％降至（2.8±5）％，射頻消融組從（21± 12）％降至（11±8）％。

討論

導管灌注常用于冷卻消融電極，有利于釋放更大的能量，而不受導管-組織接觸界面血栓形成的限制。射頻消融中主要關(guān)注的是乳頭肌損傷或斷裂而導致二尖瓣功能不全，特別在使用灌注消融導管時，盡管尚未見報道。心肌內(nèi)加熱可產(chǎn)生蒸汽和突發(fā)容量膨脹，這可聽到蒸汽爆破聲。爆破可引起深部組織撕裂，心室穿孔的患者更多需要外科修補。

導管冷凍消融于1998年用于臨床電生理學。有報告認為冷凍消融是右心室流出道、主動脈竇和心外膜起源特發(fā)性室性心動過速導管消融的安全替代方法。冷凍安全性取決于組織破壞的機制。慢性病損的組織學檢查顯示病損界限明晰，組織斷裂小，保留基本架構(gòu)。乳頭肌部位消融主要關(guān)注的是導管穩(wěn)定性。當溫度達到-80℃時，導管-組織粘著而達到穩(wěn)定。

圖1A.后內(nèi)測乳頭?。≒MPM）心腔內(nèi)心臟超聲顯像（ICE）。多極導管置于PMPM表面，用于標測臨床心律失常。B.ICE顯示Freezor Max 8 mm冷凍導管于PMPM基部釋放冷凍能量。C.臨床室性心動過速。D.有效部位起搏標測評分24分。E.有效部位冷凍導管左前斜位。F.右前斜位透視投照位。

圖2冷凍消融。A.三維整合左心室多排CT模型中，于前外側(cè)乳頭?。ˋLPM）體部激動標測臨床心律失常。冷凍導管位于最早激動部位。B.ICE顯示冷凍導管位于ALPM體部。C.ALPM部位冷凍消融過程中融化效應(yīng)。這與標測系統(tǒng)上冷凍能量產(chǎn)生的偽影相一致。唯一明顯的是導管移動，通過ICE連續(xù)評估能量釋放過程中導管的位置和穩(wěn)定性。D.ALPM體部標測到臨床期前室性搏動。測得VEGM-QRS間期達35ms.E.最早激動部位起搏標測，評分24分。

[1]Rivera S,Ricapito Mde L,Tomas L,et al.Results of Cryoenergy and Radiofrequency-Based Catheter Ablation for Treating Ventricular Arrhythmias Arising From the Papillary Muscles of the Left Ventricle, Guided by Intracardiac Echocardiography and Image Integration[J]. Circ Arrhythm Electrophysiol,2016,9（4）∶e003874.

（童鴻）

《食管心臟電生理技術(shù)快速參考》由浙江省人民醫(yī)院蔡衛(wèi)勛、李忠杰主編，已于近期發(fā)行。本書重點介紹了食管心臟電生理技術(shù)的方法、技巧，并對可能遇到的診斷、操作等問題作整理解答。全書共5章，100個問答，便于電生理初學者快速參考。定價15元。購書請聯(lián)系浙江省人民醫(yī)院心電功能科蔡老師（0571-85893072）。

Lesson Seventy-one