●心電學(xué)英語

Lesson Sixty-three The V2transition ratio
——a new electrocardiographic criterion for distinguishing left from right ventricular outflow tract tachycardia origin

Outflow tract ventricular tachycardia(OTVT)represents the most common subgroup of idiopathic ventricular tachycardia(VT).The clinical presentation of OTVT is heterogeneous,ranging from isolated premature ventricular contractions(PVCs)to repetitive nonsustained VT to sustained VT.

Detailedintracardiac electrical mapping has demonstrated that the vast majority of OTVTs originate from the anterior and superior septal aspect of the right ventricular outflow tract(RVOT),just inferior to the pulmonic valve.Less commonly,the site of origin can be localized to the right ventricular(RV)infundibulum,RV free wall,and posterior aspect of the interventricular septum.In approximately 10%to 15%of cases,the arrhythmia originates from the left ventricular outflow tract (LVOT)and can be mapped to the region of the aortic cusps.Rarely,OTVTs can be ablated from within the anterior interventricular vein,aorto-mitral continuity,or the root of the pulmonary artery.

Because OTVT has a focal origin and occurs in patients with structurally normal hearts,it is an arrhythmia that is particularly conducive to localization with the 12-lead electrocardiography(ECG).Typically,OTVT originating in the RV manifests an inferior axis in the frontal plane and left bundle branch block(LBBB)configuration with precordial R/S transition at or after lead V3.By contrast,LVOT VT usually manifests either a right bundle branch block(RBBB)/inferior axis or a LBBB/inferior axis with a precordial R/S-wave transition at or before lead V3.

Criteria to distinguish RVOT from LVOT origin for patients with precordial transition occurring at lead V3have been lacking.The aim of this study was to develop an ECG algorithm for reliably predicting the site of origin of OTVTs with lead V3precordial R/S transition.We hypothesized that comparison of the PVC/VT with the sinus rhythm(SR)QRS morphology would be an effective means of distinguishing LVOT from RVOT VT.

Methods

This study was designed in 2 parts:1)a retrospective review of OTVT ablation cases in order to develop the ECG algorithm;and 2)a prospective assessment of the algorithm on a second group of patients.

Patients with PVCs/VT manifesting a LBBB/inferior axis and a precordial transition(from R/S＜1 to R/S＞1)at lead V3were included.The majority of patients had normal left ventricular function by echocardiography.Patients with ECG evidence of prior myocardial infarction,RBBB during SR,or whose clinical arrhythmia could not be abolished with catheter ablation were excluded.

Mapping and ablation protocol

A standard quadripolar catheter was positioned in the RV apical position,and a 4mm nonirrigated catheter was initially positioned in the RVOT for mapping.In patients with sufficient ectopy,activation mapping wasperformed,recording the earliest local bipolar activation time compared with surface QRS of the clinical PVC. Pace-mapping at a threshold just above local capture was performed in all cases with careful comparison of the paced surface QRS morphology with that of the clinical PVC.All idiopathic PVCs/VT in this series originated from the septal side of the RVOT just beneath the pulmonic valve.

The decision to extend mapping to a LVOT site was made if no adequate RVOT sites were identified or ablation in the RVOT was unsuccessful in abolishing the arrhythmia.The LVOT sites were mapped via a retrograde aortic approach.All mapping was performed after heparin bolus,maintaining an activated clotting time＞250 s.In addition to standard fluoroscopy,a 3-dimensional electroanatomic mapping system and intracardiac echocardiography were used to localize the anatomic position of the ablation catheter within the outflow tract. ECG measurement protocol

Sinus rhythm and VT ECG morphology were measured on the same 12-lead ECG.During the clinical arrhythmia,the following measurements were obtained during both SR and the PVC/VT:1)R-and S-wave amplitudes in leadⅠ,Ⅱ,Ⅲ,aVF,and V1to V3;2) R-wave duration in leads V1to V3;3)QRS duration;and 4)QRS frontal axis(Figure 1).The T-P segment was considered the isoelectric baseline for measurement of R-and S-wave amplitudes.The QRS duration was measured from the site of earliest initial deflection from the isoelectric line in any lead to the time of latest activation in any lead.The R-wave duration was measured from the site of earliest initial deflection from the isoelectric line to the time at which the R-wave intersected the isoelectric line.For all cases,QRS measurements were performed on isolated PVCs representative of the clinical VT before the induction of sustained VT and compared with the SR QRS complex.As a means of accounting for1respiratory variation,we standardized our SR measurements by measuring the largest R-and S-wave over a 10s window at 25mm/s sweep speed.The transition ratio was calculated in leads V2and V3by computing the percentage R-wave during VT(R/R+S) VT divided by the percentage R-wave in SR(R/R+S) SR.

Figure 1Electrocardiographic Measurements.Leads V2and V3of normal sinus beat followed by a premature ventricular contraction (PVC)representative of the clinical outflow tract ventricular tachycardia.Measurements are as follows:A=PVC R-wave duration(ms);B=PVC R-wave amplitude(mV);C=PVC S-wave amplitude(mV);D=PVC QRS duration(ms);E= sinus rhythm R-wave amplitude(mV);and F=sinus rhythm S-wave amplitude(mV).The transition ratio was calculated in each leadwiththefollowingformula:[B/(B+C)VT÷E/(E+F)SR].

We hypothesized that a PVC/VT precordial transition to R＞S at an interspace equal to or earlier than the location of the SR transition would suggest an LVOT origin,whereas a transition at an interspace later than the SR transition would suggest an RVOT origin.The sensitivity and specificity for this measure was assessed.

Results

Retrospective analysis

We identified 40 cases of successful OTVT ablation with lead-V3transition that met our inclusion criteria.The RVOT cohort consisted of 80%anteroseptal sites and 20%posteroseptal sites.The LVOT cohort consisted of 35%LCC,15%RCC,40%left-right coronary cusp junction,and 10%great cardiac vein near the anterior interventricular vein.

The R-wave amplitude was greater for LVOT compared with RVOT PVCs in leads V2(P＜0.001)and V3(P＜0.001).The R-wave duration ratio of the PVC to SR in lead V2(P=0.002)and lead V3(P=0.026)was also significantly greater for LVOT compared with RVOT PVCs.The V2transition ratio was significantly greater for LVOT(range 0.42 to 2.89)compared with RVOT origin(range 0.02 to 0.57)(P＜0.001);however, the V3transition ratio was not significantly different be-tween PVCs of LVOT versus RVOT origin(P=0.093). The overall QRS duration was longer for LVOT compared with RVOT PVCs(P=0.048).

In a multivariate logistic regression,including R-wave duration in leads V1and V2,R-wave amplitude in leads V2and V3,and the R-wave transition ratio in lead V2,the V2R-wave transition ratio was the only independent predictor of PVC origin(P＜0.001,95%CI: 0.01～0.41).

A V2transition ratio≥0.6 predicted an LVOT origin with a sensitivity of 95%and specificity of 100%. This cutoff yielded a positive predictive value of 100% and a negative predictive value of 95%.A more practical cutoff of≥0.5 yields a sensitivity of 95%and specificity of 95%.

The simple qualitative measure of PVC precordial transition(R＞S)occurring at or before the SR transition (R＞S)had a sensitivity of 47%and specificity of 64% for identifying an LVOT origin.However,a PVC precordial transition occurring later than the SR transition had a 19%sensitivity and 100%specificity for RVOT origin. Therefore,a PVC that transitions later than SR effectively rules out an LVOT origin.The surface ECGs of representative PVCs with lead V3R/S transition are illustrated adjacent to2their corresponding sinus beats in Figure 2.

Figure 2Representative Outflow Tract PVC Surface ECG Recordings.The SR QRS and PVC morphologies from the retrospective cohort demonstrating the relatively earlier SR precordial transition in RVOT(left)compared with patients with LVOT PVC origin(right).The ECG speed:25 mm/s.Lead gain standardized to 1/16.

Prospective analysis

The ECG measurements of the ensuing 21 cases of OTVT who underwent successful RF ablation at our institution were performed.The algorithm was able to correctly predict the site of successful ablation(LVOT vs. RVOT)in 91%(19 of 21)of cases.With the simple qualitative measure alone,where LVOT origin is suggested by a PVC transition at or earlier than the SR transition,there was 71%accuracy in diagnosing the PVC origin.On the other hand,when the PVC transition occurred later than the sinus rhythm transition,anLVOT origin could be excluded with 100%accuracy.A proposed algorithm combining the qualitative and quantitative measures is shown in Figure 3.

Conclusions

Figure 3Diagnostic Algorithm for Outflow Tract VT With Lead V3PVC/VT R/S Transition.If the PVC/ventricular tachycardia (VT)transition to an R＞S occurs later than the SR transition (i.e.,SR transition lead V1or V2),then the PVC origin is the RVOT(100%specificity).If the PVC transition occurs at or earlier than the SR transition(i.e.,SR transition lead V3or later),then the V2transition ratio is measured.If the transition ratio is＜0.6,then RVOT origin is likely.If the transition ratio is≥0.6,then LVOT origin is likely(sensitivity 95%, specificity 100%).

We present a novel electrocardiographic measure of the ratio of the VT and SR precordial transition,"the V2transition ratio,"which can reliably distinguish left from right outflow tract PVC/VT origin in patients with OTVT and lead V3precordial R/S transition.A V2transition ratio 0.6 predicts an LVOT origin with high sensitivity and specificity.A precordial transition later than the SR transition excludes an LVOT VT origin.

詞匯

transition n.過渡,臨時轉(zhuǎn)調(diào),轉(zhuǎn)折語

heterogeneous adj.各種各樣的

infundibulum n.漏斗

cusps n.尖,尖點(diǎn),牙尖

conducive adj.有助的

configuration n.配置,構(gòu)形,輪廓

precordial adj.心前的

algorithm n.算法

abolished v.徹底廢除,取消,完全破壞

quadripolar n.四極

ensuing n.接著發(fā)生的，隨后的

注釋

1.accounting for在醫(yī)學(xué)文獻(xiàn)上常表達(dá)“校正”，“應(yīng)對”之意，如Without accounting for stenosis interaction,the value of FFR for each stenosis would have been significantly overestimated.不校正狹窄之間的相互影響，每一狹窄的FFR值將被明顯高估。

2.adjacent to表示“接近”，“近…處”，“與…鄰近”，“毗連…”，當(dāng)修飾名詞時，常放在被修飾名詞的后面，本文中放在句子后面，是因為PVC后有介詞短語修飾；也常放在動詞后面構(gòu)成地點(diǎn)狀語，如Ventricular pacing was performed adjacent to the His bundle and proximal right bundle branch.于希氏束附近和右束支近端實施心室起搏。

參考譯文

第63課V2移行比率——鑒別左右心室流出道心動過速起源的新心電學(xué)標(biāo)準(zhǔn)

流出道室性心動過速（OTVT）是最常見的特發(fā)性室性心動過速（VT）。OTVT臨床表現(xiàn)各異，從單一的室性期前收縮（PVC）到反復(fù)短暫VT及持續(xù)性VT。

精細(xì)的心內(nèi)電標(biāo)測證實大多數(shù)OTVT起源于右室流出道（RVOT）前上間隔，位于肺動脈瓣下方。不常見的起源部位有右心室流出道漏斗部、右心室游離壁和后間隔部位。約10%～15%患者，心律失常起源于左心室流出道（LVOT），并可標(biāo)測到主動脈竇部位。罕見的有經(jīng)前間隔靜脈、主動脈-二尖瓣連接處或肺動脈根部消融的OTVT。

因為OTVT為局灶起源且發(fā)生于心臟結(jié)構(gòu)正?；颊?，因此，這種心律失常特別有利于從12導(dǎo)聯(lián)心電圖定位。起源于右心室的OTVT典型的表現(xiàn)為額面電軸向下、呈左束支傳導(dǎo)阻滯（LBBB）圖形，且心前導(dǎo)聯(lián)R/S移行位于V3或V3以后。相反，LVOT VT通常表現(xiàn)為右束支傳導(dǎo)阻滯（RBBB）/電軸向下或LBBB/電軸向下而R/S移行位于V3或V3以前。

對于心前導(dǎo)聯(lián)移行位于V3的RVOT與LVOT，尚無鑒別標(biāo)準(zhǔn)。本研究目的是建立一種心電圖法則，以便可靠地鑒別移行位于心前導(dǎo)聯(lián)V3的OTVT起源部位。我們假設(shè)比較室性期前收縮/室性心動過速與竇性心律QRS形態(tài)是鑒別LVOT和RVOT VT的有效方法。

方法

本研究分2部分：1）回顧性分析OTVT消融病例，建立心電圖法則；2）應(yīng)用該法則前瞻性分析第2組患者。

納入所有表現(xiàn)為LBBB/電軸向下而心前導(dǎo)聯(lián)移行位于V3的PVC/VT患者。多數(shù)患者超聲心動圖顯示左心室功能正常。心電圖提示有既往心肌梗死、竇性心律RBBB或不能進(jìn)行射頻導(dǎo)管消融的心律失常者排除在外。

標(biāo)測和消融方案

標(biāo)準(zhǔn)四極導(dǎo)管置于右心室心尖部，4mm非灌注導(dǎo)管先在RVOT標(biāo)測。異位搏動足夠多者行激動標(biāo)測，記錄最早的局部雙極激動時間與臨床PVC體表QRS波群作比較。所有患者以略高于局部奪獲的閾值起搏標(biāo)測，仔細(xì)比較起搏時體表QRS波群圖形與臨床PVC圖形。本系列特發(fā)性PVC/VT均起源于肺動脈瓣下ROVT間隔側(cè)。

如果無法確定確切的RVOT部位或RVOT部位不能成功消融心律失常，那么擴(kuò)大標(biāo)測到LVOT部位。通過經(jīng)主動脈逆行方法標(biāo)測LVOT。所有標(biāo)測于彈丸注射肝素后進(jìn)行，維持ACT＞250s。除標(biāo)準(zhǔn)透視外，用三維解剖標(biāo)測和心腔內(nèi)超聲心動圖確定消融導(dǎo)管在流出道的解剖位置。

心電圖測定方案

在同一12導(dǎo)聯(lián)心電圖上測定竇性心律和VT心電圖圖形。在臨床心律失常期間，獲取竇性心律和PVC/VT時的下列數(shù)值：1）導(dǎo)聯(lián)Ⅰ、Ⅱ、Ⅲ、aVF和V1到V3上的R和S波振幅; 2）V1到V3上R波間期；3）QRS間期；和4）QRS額面電軸（圖1）。TP段用作R和S波振幅測量的等電位線。QRS間期測定從任一導(dǎo)聯(lián)的最早轉(zhuǎn)折點(diǎn)到任一導(dǎo)聯(lián)的最遲激動點(diǎn)。R波間期從等電位線的最早轉(zhuǎn)折點(diǎn)到R波與等電位線的相交點(diǎn)。對于所有患者，在誘發(fā)持續(xù)性VT前，測定代表臨床VT的單一PVC QRS波群，并與竇性心律QRS波群比較。為應(yīng)對呼吸變化，我們標(biāo)化SR測定方法，即在25mm/s掃描速度的10s窗口中，測定最大的R和S波。計算VT的（R/R+S）VT QRS波的百分比與SR的（R/R+S）SR QRS波的百分比比值。

我們假設(shè)PVC/VT心前導(dǎo)聯(lián)移行到R＞S的間隙等于或早于SR移行將提示LVOT起源，而遲于SR移行的將提示RVOT起源。分析這一測值的敏感度和特異度。

結(jié)果

回顧性分析

我們確定40例OTVT伴V3移行、并符合納入標(biāo)準(zhǔn)的患者。RVOT組由80%的前間隔和20%的后間隔部位組成。LVOT組包括35%的左冠狀竇，15%的右冠狀竇，40%的左-右冠狀竇連接處，和10%接近前間隔靜脈的心大靜脈。

V2和V3PVC R波振幅LVOT大于RVOT（均P＜0.001）。V2和V3R波間期PVC與SR比率LVOT也顯著大于RVOT（P=0.002，0.026）。V2移行比率LVOT（0.42～2.89）顯著大于RVOT（0.02～0.57）（P＜0.001）；然而，LVOT與RVOT起源的PVC V3的移行比率無顯著差異（P=0.093）?？偟腝RS間期LVOT較RVOT長（P=0.048）。

多變量logistic回歸分析表明，在包括V1和V2的R波間期、V2和V3的R波振幅、及V2R波移行比率眾多因素中，只有V2R波移行比率是獨(dú)立預(yù)測PVC起源的因素（P＜0.001，95%CI:0.01～0.41）。

V2移行比率≥0.6預(yù)測LVOT起源的敏感度95%、特異度100%。此值的陽性預(yù)測值為100%、陰性預(yù)測值為95%。臨床取此值≥0.5，敏感度和特異度均為95%。

單一定量測定PVC心前導(dǎo)聯(lián)移行（R＞S）等于或早于SR移行（R＞S）鑒別LVOT的敏感度47%、特異度64%。然而，PVC心前導(dǎo)聯(lián)移行遲于SR移行診斷RVOT的敏感度和特異度分別為19%和100%。因此，PVC移行遲于SR的明確排除LVOT起源。圖2闡述了與相應(yīng)竇性搏動毗連的典型PVC V3R/S移行體表心電圖。

前瞻性分析

對隨后在本院成功消融的21例OTVT患者行心電圖測定。這一法則能正確預(yù)測91%患者的成功消融部位（19/21）。采用簡單的定性測定方法，即PVC移行等于或早于SR移行提示LVOT，診斷PVC起源的準(zhǔn)確性為71%。另一方面，PVC移行遲于竇性心律移行時，排除LVOT的準(zhǔn)確性達(dá)100%。結(jié)合定性和定量測值構(gòu)建的法則見圖3。

結(jié)論

我們提出VT和SR心前導(dǎo)聯(lián)移行的心電圖測值比率，即V2移行比率，能可靠鑒別V3R/S移行OTVT患者左室或右室流出道PVC/VT起源。V2移行比率≥0.6預(yù)測LVOT起源敏感度和特異度高。心前導(dǎo)聯(lián)移行遲于SR移行排除LOVT VT起源。

圖1心電圖測量。V2和V3正常竇性搏動后為代表臨床流出道室性心動過速的室性期前收縮（PVC）。測量如下：A=PVC R波間期（ms）；B=PVC R波振幅(mV)；C=PVC S波振幅(mV)；D=PVC QRS間期（ms）；E=竇性心律R波振幅（mV）；F=竇性心律S波振幅（mV）。根據(jù)以下公式計算每一導(dǎo)聯(lián)的移行比率：[B/（B+C）VT÷E/（E+F）SR]。

圖2典型流出道PVC體表心電圖記錄。來自回顧性病例的SR QRS和PVC圖形證實，SR心前導(dǎo)聯(lián)移行RVOT（左）早于LVOT（右）PVC起源者。心電圖記錄速度25 mm/s。導(dǎo)聯(lián)增益標(biāo)化至1/16。

圖3V3PVC/VT R/S移行的流出道VT診斷法則。如果PVC/VT移行至R＞S遲于RS移行（例如，SR移行導(dǎo)聯(lián)V1或V2），那么PVC起源在RVOT（特異度100%）。如果PVC移行早于SR移行（例如，SR移行導(dǎo)聯(lián)V3或V4），那么測量V2移行比率。如果移行比率＜0.6，可能為RVOT起源。如果移行比率≥0.6，可能為LVOT起源（敏感度95%,特異度100%）。

[1]Betensky B P,Park R E,Marchlinski F E,et al.The V2Transition Ratio:A New Electrocardiographic Criterion for Distinguishing Left From Right Ventricular Outflow Tract Tachycardia Origin[J].J Am Coll Cardiol,2011,57∶2255-2262.

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