Lesson Eighty-eight How to perform permanentHis bundle pacing in routine clinical practice

Clinical permanent His bundle pacing（PHBP）was first described in 2000.Since then,several investigators acrossthe world have published the safety and feasibility of PHBP.Benefits include ability to achieve physiological pacing by recruiting the native His Purkinje system and avoiding electrical dyssynchrony,potentially translating into reduced HF incidence.Also,limited clinical observations have demonstrated that the lead does not cross the tricuspid valve and this may result in lower incidence of valvular regurgitation.

Equipment requirements

Following are the equipment requirements:

1.Medtronic（Minneapolis,MN）383069-cm His lead with 1.8-mm exposed helix,lead outer diameter（OD）4.2F（Figure 1A）.It is a solid core pacing lead with no central lumen to deliver a stylet,requiring a long sheath for delivery.

2.Medtronic C315 His nondeflectable sheath（43cm）,inner diameter（ID） 5.5F,OD 7.0F（see asterisk in Figure1B）,primary curve to reach the superior aspect of the tricuspid annulus,secondary curve to reach the septum.A Medtronic deflectable sheath （C304-69;ID5.7F and OD 8.4F） is also available with unidirectional deflection（Figure1C）;it can be helpful in challenging anatomical situations（dilated right atrium[RA] ,an inferiorly displaced His bundle[HB] ,etc.）.

3.Short 7F peel-away sheath to place the C315 His sheath through it.It allows continued vascular access after the His sheath is split（guide wire can be retained as well）.

4.Pace-sense analyzer（PSA）to record intracardiac electrograms（EGMs）.Because of the inherent sensing algorithms built into the Medtronic PSA,we usually connect the pacing lead to the atrial channel（higher gain setting of 0.05 mV/mm）.For PSAs of other manufacturers,the lead can be connected to the ventricular channel.

5.Unipolar connection to map the HB EGMs with the pacing lead.We use the pacing lead to map the HB with PSA EGMs,without the need for a mapping catheter.Also,an electrophysiology（EP） recording system can be used（PSA EGMs are adequate）.

6.Twelve-lead electrocardiogram for the procedure（critical to analyze pacing morphologies to confirm recruitment of the HB）.

Figure 1 A:Select Secure 3830 lead.B:Several nondeflectable sheaths used for the 3830 lead.The first sheath marked by the asterisk is a C315 His nondeflectable sheath used for His bundle mapping and lead placement.All other sheaths are used for either right atrialor rightventricular lead placement.C:Deflectable sheath used occasionally to place the His bundle lead

Procedure description

Once vascular access is obtained（cephalic,axillary,or subclavian vein）,a guidewire is advanced into the RA or RV.A short 7F sheath can be advanced over the wire to retain access.Otherwise,the C315 His sheath is advanced into the RA or RV and the guidewire removed.The pacing lead is advanced to the tip of the sheath,with the distal tip of the lead exposed minimally.Unipolar connections are made with the tip of the lead and cardiac tissue.

If the sheath and the lead tip are in the RV,the apparatus is gently pulled back to the atrioventricular grove with minimal counterclockwise rotation to ensure that the lead tip is abutting the septum.If the sheath and the lead are in the RA,gentle forward clockwise rotation tends to move the apparatus to the summit of the tricuspid annulus.

While this is being performed,it is important for both the operator and the person operating the PSA to pay careful attention to intracardiac EGMs.Small movements are encouraged as HB deflections can be easily missed.We usually set the sweep speed to 50 or 100 mm/s to allow better separation of atrial,HB,and local ventricular EGMs.

Once HB EGMs are obtained,unipolar pacing is performed since the proximal pole of the lead is within the sheath.We start pacing at 5 V@1 ms and assess 12-lead QRS morphologies.The following patterns can be observed:

1.Pure HB pacing where stimulus to ventricular activation is equal to the intrinsic HV interval and paced QRS morphology is identical to the intrinsic QRS complex.We term this as selective HB pacing（Figure 2,Figure 3）.

2.HB capture with local ventricular fusion:stimulus-ventricular capture is shorter than the HV interval.The pacing output is decremented to assess the changing QRS morphologies（akin to para-His pacing performed to assess septal accessory pathways）.We term this as nonselective HB pacing（Figure 2,Figure 3）.Various responses can be observed:

（a）At high output,the HB is preferentially recruited with progressive widening as output is reduced,resulting in more local ventricular capture.

（b）At high output,more fusion is encountered because of local ventricular capture,and at lower output,HB is preferentially activated,resulting in less fusion（Figure 2,Figure 3）.

（c）Sometimes just before loss of capture,pure HB pacing can be seen.Also,selective RBB or left bundle branch（LBB）capture can be demonstrated（Figure 3）.

（d）Sometimes because of the proximity of RBB and more ventricular placement of the lead,RBB capture can occur.This results in an LBB block pattern-wide QRS complex.It may be difficult to determine whether local myocardial capture occurs along with RBB capture.If intrinsic conduction is present,measuring the HV interval can help determine RBB capture.Typically,a local HV interval would be short（＜30 ms）,with no far-field atrial EGM seen on the PSA.

We believe that these responses are due to anatomical and functional aspects of the HB system.Anatomy of the HB has been well characterized.Preferential pacing of RBB and LBB can be explained in part by the phenomenon of longitudinal dissociation of the His-Purkinje conduction system.Other properties such as favorable source-sink1ratios and virtual electrode polarization may play a part as well.

Once HB capture is ascertained,the lead is turned 4-5 times in a clockwise direction.Usually,torque is built up and transmitted to the end of the lead.Once it is released,the lead may unwind 1-2 rotations.It is important to use the sheath to support the lead and make good contact with the septum.The sheath is pulled back,and the lead is advanced to allow for slack.Current of injury,either of the HB or local ventricular tissue,is usually seen（Figure 4）.However,there are cases where the lead is well affixed with good pacing thresholds and minimal local tissue injury.Testing is performed in both unipolar and bipolar configurations.Starting at 5V@1 ms,output is decremented to assess response to pacing.Either selective or nonselective HB pacing is accepted,and pacing thresholds less than 2V@1 ms are deemed acceptable.If the patient is pacemaker dependent,lower pacing thresholds are sought after before accepting the final lead position.If the pacing threshold margins are not deemed acceptable by the operator after multiple attempts,the lead is placed slightly more anteriorly,with largerventricularsensingand pacingmorphology consistent with septal pacing.

Figure 2 At pacing outputs above 2V@0.5ms,there is fusion with His bundle（HB）and local ventricular capture（nonselective HB capture）.Below 2V@0.5ms,there is pure HB capture with paced QRS morphology identical to the native QRS complex（selective HB pacing）.Note that once pure His capture is obtained as the pacing threshold,inter-mittent fusion is still high enough to intermittently recruit the local venticular myocardium.ECG=electrocardiogram.

Figure 3 At higher output（up to 1.5V@1 ms）,there is fusion between His bundle and local myocardial capture（nonselective response）.At lower outputs（up to 0.5 V@1ms）,there is pure His bundle capture with stimulus to QRS onset（S-QRS）equal to the native HV interval（selective response,*）.Below this output,there is selective right bundle branch（RBB）capture.

Figure 4 A:Ten-lead electrocardiogram of a 74-year-old man with permanent AF,incomplete left bundle branch block pattern,and bradycardia.B:Pace-sense analyzer electrograms as the His bundle is mapped in a unipolar configuration （connected to the atrial channel）.C:Current of injury of the His bundle as the lead is screwed into place.Asterisk denotes current of injury of the His bundle as the lead is screwed into place.

Acute ventricular sensing issues

Because of the location of the lead tip,we see a wide range of ventricular sensing values（1.2-10 mV）.We compare ventricular EGMs with atrial EGMs to assess sensing margins.Typically,the lead tip records small atrial EGMs and atrial oversensing is not a major issue.Unipolar and bipolar sensing is assessed,and if no far-field sensing is seen,unipolar sensing can be used if it offers better sensing safety margins.However,it is rare that we program unipolar ventricular sensing.In patients who are pacemaker dependent,we do not use unipolar sensing and ventricular sensitivity is usually set to＞1.2 mV on the basis of measured values and care is taken to assess far-field atrial sensing before accepting the final location of the ventricular lead.

Acute pacing issues

The HB is encased in a fibrous sheath with various anatomical variations.Pacing thresholds are expected to be inherently higherbecause ofthe lead-tissue interface.Therefore,if pacing thresholds are lower than 2V@1 ms at implantation with good HB recruitment,we accept the lead position.Typically,as the pacing output decreases,there is more fusion with ventricular capture,thereby providing good safety margins（nonselective HB pacing cases only）.The pacing output is set to 5V@1 ms at implantation and decreased at

2-month check.In dependent patients,we look for at least 2-3 times safety margin.We aim for nonselective HB pacing in such cases and determine safety margins from the lowest output capture of either the HB or local ventricular tissue.If selective HB pacing is desired in the setting of higher pacing thresholds,we place a backup lead in the RV.This necessitates placement of a BiV pacemaker with the HB lead plugged into the LV port.We program an LV to RV offset of 80 ms.If HB capture occurs,the RV stimulus falls in the refractory period,resulting in functional noncapture.If HB capture does not occur,the RV stimulus acts as safety pacing.

詞 匯

recruit n.&v.新兵、心成員、新手；招募、組織、雇傭

dyssynchrony n.非同時(shí)、非同步、非共時(shí)性

helix n.螺旋、耳輪

unidirectional adj.單向的

inherent adj.內(nèi)在的

algorithms adj.算法

grove n.溝、樹叢、果樹林

abut v.鄰接、與 鄰接，與 緊靠

intrinsic adj.固有的、內(nèi)部的、內(nèi)在的

decrement n.&v.減少、減量、減縮兩；減少，減縮

akin adj.同類的、同族的、同源的

torque n.&v.扭轉(zhuǎn)力、金屬飾環(huán)、轉(zhuǎn)距；加轉(zhuǎn)距于

slack n.&adj.&adv.&v.松弛、蕭條；松弛的、懈怠的、松閑

的；松弛地、松閑地；放松、懈怠、減緩

affix n.&v.附加物、詞綴；黏上、蓋、添上

deem n.&v.評(píng)價(jià)；認(rèn)為、認(rèn)為 是

margin n.&v.邊緣、邊、利潤(rùn)額、余地；加邊于

encase v.把 裝入箱子、圍住、包裝

offset n.&adj.&v.補(bǔ)償、支管；補(bǔ)償?shù)摹㈠e(cuò)斷的、膠印的；補(bǔ)

償、把 并列

注 釋

1.source-sink（ratio）指“源 -庫(kù)（比）”，最初用于描述生物物種的遷移現(xiàn)象。心臟電生理學(xué)上用source-sink來闡述一些心臟傳現(xiàn)象，在此，source-sink指的是電流負(fù)荷（current-load），傳導(dǎo)系統(tǒng)局部的容量變化可加快或減慢激動(dòng)傳導(dǎo)速度。When the source volume is larger compared with the sink volume,activation proceeds because there is sufficient electrical current to activate myocardial cells in the distal direction.當(dāng)源容量大于庫(kù)容量時(shí)激動(dòng)進(jìn)展，因有足夠的電流激動(dòng)遠(yuǎn)端心肌細(xì)胞。Local source-sink relationships determine the formation of conduction heterogeneities and provide conditions for the development of slow conduction,unidirectional block,and reentry.局部源-庫(kù)關(guān)系決定傳導(dǎo)異質(zhì)性并提供發(fā)生慢傳導(dǎo)、單向阻滯和折返的條件。

參考譯文

第88課 臨床實(shí)踐中如何實(shí)施希氏束起搏

2000年首次提出希氏束起搏，自那以后，國(guó)際上多位研究者發(fā)表了希氏束起搏的安全性和可行性的報(bào)道。希氏束起搏的優(yōu)點(diǎn)在于通過自身的希氏束系統(tǒng)達(dá)到生理性起搏，避免電不同步，從而減少心力衰竭的發(fā)生率。另外，有限的臨床觀察證實(shí)電極不跨過三尖瓣，三尖瓣反流的發(fā)生率較低。

設(shè)備要求

1.美敦力（Minneapolis，M）383069-cm 希氏束電極，突出的螺旋1.8-mm，電極外徑（OD）4.2F（圖1A）是一無實(shí)心起搏電極，無內(nèi)腔供定型鋼絲通過，而需長(zhǎng)鞘輸送。

2.美敦力C315希氏束非可調(diào)彎鞘（43cm），內(nèi)徑（ID）5.5F，OD 7.0F（見圖1B星標(biāo)），第一彎到達(dá)三尖瓣環(huán)上方，第二彎到達(dá)間隔。美敦力可調(diào)彎鞘（C304-69；ID 5.7F和OD 8.4F）可做單向偏彎（圖1C）；有助于挑戰(zhàn)性的解剖情況[擴(kuò)大的右心房，下移的希氏束等] 。

3.短7F撕開鞘用于輸送C315希氏束鞘。它使得希氏束鞘撕開后保持血管通路（也可保留指引導(dǎo)絲）。

4.起搏-感知分析儀（PSA）用于記錄腔內(nèi)電圖（EGMs）。鑒于整合到PSA中的內(nèi)在感知算法，我們通常將起搏電極連接到心房通道（設(shè)置較高的增益，0.05mV/mm）。對(duì)于其他廠商的PSAs，電極可連接到心室通道。

5.電極連接起搏電極標(biāo)測(cè)希氏束EGMs。我們用起搏電極標(biāo)測(cè)希氏束和PSA EGMs，無需標(biāo)測(cè)電極。也可用電生理（EP）記錄系統(tǒng)（PSA EGMs足夠的）。

6.手術(shù)過程需12導(dǎo)聯(lián)心電圖（對(duì)于分析起搏圖形確定奪獲希氏束至關(guān)重要）。

手術(shù)過程闡述

一旦建立血管通路（頭靜脈、腋靜脈、鎖骨下靜脈），指引導(dǎo)絲送入至心房或心室。短7F鞘沿導(dǎo)絲送入以保留通路，或者送入C315希氏束鞘到心房或心室而拔出指引導(dǎo)絲。起搏電極送入至鞘的頂端，盡可能少的露出電極遠(yuǎn)端。電極頂端與心臟組織采用單極連接。

如鞘和電極頂端位于右心室內(nèi)，輕輕回撤器械到房室溝，略作逆種向旋轉(zhuǎn)以保證電極頂端緊密接觸間隔。如鞘和電極位于右心房?jī)?nèi)，輕輕順種向推送器械到三尖瓣環(huán)的最高點(diǎn)。

在這一操作過程，術(shù)者和PSA操作者都應(yīng)注意腔內(nèi)電圖。建議小幅移動(dòng)，因?yàn)橄Ｊ鲜ㄒ妆贿z漏。我們通常設(shè)置屏掃速度為50或100mm/s，以便分開心房、希氏束和局部心室EGMs。

一旦獲得希氏束EGMs，實(shí)施單極起搏，因?yàn)殡姌O的近端電極位于鞘內(nèi)。我們以5V@1ms開始起搏并分析12導(dǎo)聯(lián)QRS波群?？梢杂^察到以下類型：

1.純希氏束起搏時(shí)起搏信號(hào)到心室激動(dòng)的間期與自身的HV間期相同，起搏的QRS形態(tài)與自身的QRS形態(tài)一致。我們稱這種起搏為選擇性希氏束起搏（圖2-3）。

2.希氏束奪獲融合局部心室激動(dòng)：起搏信號(hào)-心室奪獲間期短于自身HV間期。降低起搏輸出來分析QRS形態(tài)變化（類似實(shí)施希氏束旁起搏分析間隔旁路）。我們稱其為非選擇性起搏（圖2-3）?？梢杂^察到不同的反應(yīng)：

（a）高輸出下，希氏束優(yōu)先被激動(dòng)并隨輸出減少而進(jìn)行性增寬，導(dǎo)致較明顯的局部心室奪獲。

（b）高輸出下，因?yàn)榫植啃氖业膴Z獲而呈明顯融合，低輸出下，希氏束優(yōu)先激動(dòng)，以致融合少。（圖2-3）。

（c）有時(shí)在喪失奪獲前可見到純希氏束起搏。也可見到選擇性RBB或LBB奪獲（圖3）。

（d）有時(shí)因?yàn)殡姌O更接近RBB和心室，可發(fā)生RBB奪獲。這導(dǎo)致LBB阻滯的寬QRS波群。這難以確定局部心室奪獲時(shí)是否伴隨RBB奪獲。如存在自身的傳導(dǎo)，測(cè)定HV間期有助于確定RBB奪獲。典型的表現(xiàn)是局部HV縮短（＜30ms）而PSA上無遠(yuǎn)場(chǎng)心房EGMs。

我們相信這些反應(yīng)與希氏束系統(tǒng)的解剖和功能有關(guān)。希氏束的解剖特征明確。優(yōu)先起搏RBB和LBB可用希氏束-普肯氏傳導(dǎo)系統(tǒng)的縱向分離現(xiàn)象加以部分解釋。其他特性如正向源-庫(kù)比和虛擬電極極化也可起到部分作用。

一旦確定希氏束奪獲，電極順鐘向旋轉(zhuǎn)4～5圈。通常情況下扭力會(huì)傳遞到電極末端。一旦松開，電極會(huì)回轉(zhuǎn)1～2圈。重要的是利用鞘支撐電極并緊密接觸間隔?；爻非使埽瑫r(shí)推送電極使其呈松弛狀態(tài)。通?？梢姷较Ｊ鲜蚓植啃氖医M織的損傷電流（圖4）。然而，有時(shí)電極固定好且起搏閾值理想但局部組織損傷微小。在單極和雙極情況下測(cè)試。起始為5V@1ms，降低輸出來分析對(duì)起搏的反應(yīng)。選擇性或非選擇性起搏是可接受的，起搏閾值低于2V@1 ms認(rèn)為是可行的。如患者是起搏依賴的，在接受最好的電極位置前應(yīng)尋求更低的起搏閾值。如經(jīng)過術(shù)者多次努力，起搏閾值不能被接受，應(yīng)將起搏電極略前移，有較大的心室感知和起搏圖形，與間隔起搏相一致。

急性心室感知問題

鑒于電極端的位置不同，我們見到寬泛的心室感知值（1.2～10mV）。我們比較心室的EGMs和心房的EGMs分析感知臨界值。典型的是電極端記錄到小的心房EGMs和心房過感知不成為一個(gè)大的問題。分析單極和雙極感知，如無遠(yuǎn)場(chǎng)感知且能提供良好的感知安全范圍，可選用單極感知。然而，我們極少設(shè)置單極心室感知。對(duì)于起搏器依賴者，我們不選用單極感知，根據(jù)測(cè)定的基礎(chǔ)值，心室感知設(shè)置通常＞1.2mV，在接受最后的心室電極位置前注意分析遠(yuǎn)場(chǎng)心房感知。

急性起搏問題

希氏束被包繞于纖維鞘中，有著多種多樣的解剖變化。因?yàn)殡姌O-組織的界面關(guān)系，起搏閾值自然較高。因此，植入時(shí)如起搏閾值低于2V@1ms時(shí)能良好激動(dòng)希氏束，我們接受電極的位置。典型的是當(dāng)輸出降低時(shí)，更多融合心室奪獲，因此提供良好的安全界限（僅為非選擇性希氏束起搏病例）。植入時(shí)將起搏輸出設(shè)在5V@1ms，兩個(gè)月隨訪時(shí)降低。對(duì)于依賴者，我們尋求2～3倍的安全界限。此類患者我們的目標(biāo)是非選擇性希氏束起搏，從希氏束或局部心室組織確定最低的輸出奪獲。如需在起搏閾值較高的情況下尋求選擇性希氏束起搏，我們?cè)谟倚氖抑踩雮浞蓦姌O。這使得有必要選擇雙室起搏器，將希氏束電極插入左心室接口。我們程控左心室向右心室補(bǔ)償80ms。如希氏束發(fā)生奪獲，右心室的刺激落在不應(yīng)期內(nèi)，導(dǎo)致功能性失奪獲。如希氏束無奪獲，右心室刺激充當(dāng)安全起搏。

圖1A：選擇安全的3830電極。B：幾種用于3830電極的非調(diào)彎鞘。第一根標(biāo)記星號(hào)的為C315希氏束非調(diào)彎鞘，用于希氏束標(biāo)測(cè)和電極放置。所有其他鞘用于右心房或右心室電極放置。C：偶爾用于希氏束電極放置的可調(diào)彎鞘。

圖2起搏輸出2V@0.5ms以上時(shí)，出現(xiàn)希氏束與局部心室奪獲的融合（非選擇性希氏束奪獲）。輸出低于2V@0.5ms時(shí)，純希氏束奪獲的起搏QRS形態(tài)與自身QRS波相一致（選擇性希氏束起搏）。注意一旦純希氏束奪獲作為起搏閾值，間歇性融合仍然足可間隙地激動(dòng)局部心肌。ECG=心電圖。

圖3較高輸出下（up to 1.5V@1ms），希氏束與局部心肌奪獲之間融合（非選擇性反應(yīng)）。較低輸出下（up to 0.5 V@1ms），呈單純希氏束奪獲，起搏信號(hào)與QRS波群起始點(diǎn)之間的間期（S-QRS）與自身HV間期一致（選擇性反應(yīng)，*）。低于該輸出時(shí)，呈選擇性RBB奪獲。

圖4A：74歲男性持續(xù)性心房顫動(dòng)伴不完全性左束支和心動(dòng)過緩的十導(dǎo)聯(lián)心電圖。B：起搏-感知分析儀電圖顯示的希氏束標(biāo)測(cè)單極圖形（與心房通道連接）。C：電極旋入后的希氏束損傷電流。星號(hào)標(biāo)注電極旋入后的希氏束損傷電流。