Lead selection and implantation technique for biventricular pacing
a Department of Thoracic and Cardiovascular Surgery, Heart Centre North Rhine-Westphalia, Ruhr University, Bochum, Bad Oeynhausen, Germany
b Department of Cardiololgy, Heart Centre North Rhine-Westphalia, Ruhr University Bochum, Bad Oeynhausen, Germany
Received 3 May 2004; accepted 24 May 2004.
* Bert Hansky, MD, Department of Thoracic and Cardiovascular Surgery, Heart Centre North Rhine-Westphalia, Ruhr University Bochum, 32545 Bad Oeynhausen, Germany. Tel.: +49-5731-970; fax: +49-5731-971820
bhansky{at}hdz-nrw.de
Abstract
Based on the recent experience of 464 patients with left ventricular pacing, we report on specific characteristics of various leads and lead types for left ventricular stimulation. In addition to describing the technique and indications for epicardial lead usage, commercially available coronary vein leads are introduced and discussed. Since there is no universally applicable coronary vein lead, the individually optimal lead choice and the sequelae of an erroneous lead selection are described in typical clinical examples.
Key Words: Cardiac resynchronisation therapy • Biventricular pacing • Implantation technique • Lead selection
Introduction
Electrical stimulation of the left ventricle can be performed by numerous leads1,2 necessitating different technical implantation procedures, but preferably by coronary venous (CV) leads3 requiring an individual lead choice respecting the patient's coronary venous anatomy. Despite a success rate of more than 95% for CV leads, particular indications of epicardial leads persist.
Material and methods
Since 1997, left ventricular stimulation has been applied in 464 patients (122 female and 342 male). Twenty one patients received a transvenous coronary lead after tricuspid valve surgery (tricuspid valve replacement 
, tricuspid valve reconstruction 
) for left ventricular stimulation (VVI: 
, DDD: 
, ICD: ). In 443 patients, cardiac resynchronisation therapy (CRT) by bi-or left ventricular (LV) stimulation was performed. Four hundred and sixteen patients were stimulated at the left ventricle by coronary vein leads (Figs. 1(a)–(d) and 2(a)–(c)), whereas epicardial leads (Medtronic CapsureEpi, Fig. 3) were used in the remaining 27 cases. In the first 13 patients undergoing CRT, epicardial leads were used exclusively. After the introduction of the transvenous approach for LV lead placement, epicardial leads were indicated in only 14 further cases (3.1%).
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In the following, implantation techniques and criteria of various leads are elucidated.
Coronary venous leads: advantages, implantation technique and lead choice
The use of coronary venous leads for left ventricular stimulation provides certain obvious advantages. The transvenous access is by far less traumatising for the patients, who may be mobilised early after surgery. Furthermore, these leads can easily be used in previously cardiotomised patients since electrical stimulation is applied subepicardially via the coronary vein wall (Fig. 4). Therefore, postoperative epicardial adhesions are nearly irrelevant for this mode of stimulation. Increases in threshold occur by far less in CV leads than in epicardial ones. It is most important for preventing postoperative increases in electrical thresholds that CV leads are securely embedded in their target vein since repetitive chronic vein wall injuries by mobile leads result in progressive fibrotic reorganisation of the adjacent vein wall.
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Recent advances in lead technology and progressive experience in our team led to a median X-ray time of 15 min (2.9–68 min) with a mean duration of implantation of 1.5 h (1–3 h), which is lower compared to that of epicardial leads. The surgical implantation of coronary vein leads is technically by far more demanding than the placement of common endocardial leads requiring a most sophisticated X-ray facility.
Various investigation clearly demonstrated the necessity to place CV leads in the lateral or postero-lateral left ventricular vein for CRT.4,5 Lead placement in the anterior or mid-cardiac vein did not result in a persistent haemodynamic improvement and could be regarded as a potential cause for therapy failure.
The choice of the correct CV lead type described by the following three criteria is most important for reaching the target vein and establishing persistent low chronic thresholds (Figs. 1(a)–(d) and 2(a)–(c), chart 1).
(1) Stimulation surface. Leads stimulating by a metal ring adjacent to the lead tip require a stable wedge position in the target vein to achieve adequate constant thresholds (Figs. 1(d) and 2(c)). Leads with microporous tips are prebent in the distal lead segment and achieve constant thresholds in wider or even proximal vein segments (Figs. 1(a)–(c) and 2(b)). These are the leads of choice, if acceptable thresholds in the distal vein cannot be achieved or phrenic nerve stimulation prohibits lead placement.
(2) Technique of coronary vein lead implantation. Leads can either be placed in an "over the wire" fashion (OTW) (Figs. 1(d) and 2(c)) or by a stylet (Figs. 1(b) and (c)). There are some leads in which both techniques can be applied sequentially (Figs. 1(a) and 2(b)): first, the lead is placed into the proximal vein segment using the stylet and is then advanced into the target segment by the OTW technique. The OTW technique, requiring a conventional coronary wire (0.014 mm), is especially favourable in tortuous veins and veins with a sharp-angled course into the coronary sinus.
The calibre of the target vein relative to the diameter of the lead is another important aspect of lead selection. Stiff, thick leads (>1.5 mm) can be placed safely in large straight veins with a diameter of more than 3.5 mm, whereas thin distally prebent leads do not guarantee stabilisation in these vessels (Figs. 1(a)–(d)). These leads (Figs. 2(b) and (c)) are favourable in either very narrow or massively kinked and tortuous veins (Fig. 2(a)). Thick leads might traumatise the venous endothelium with consecutive vessel occlusion (Figs. 5(a) and (b)) by either a thrombus formation or dissection. Lead instability with consecutive malpositioning caused by a diameter discrepancy between lead and vein increases the risk of postoperative dislocation. Furthermore, constant friction of a mobile lead to the endothelium within the vessel by permanent cardiac motion increases the risk of unstable electrical thresholds (Fig. 6). Therefore, an absolutely stable position of the leads is mandatory.
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(3) Lead polarity. Currently available leads are either uni- or bipolar. In comparison to bipolar leads, unipolar ones are of lower diameter facilitating the OTW technique. Bipolar leads are advantageous, if in biventricular ICD patients selective left ventricular pacing is required for haemodynamic reasons or if the interventricular stimulation delay needs to be adjusted. A `pseudobipolar' stimulation is defined as stimulation by the tip of the coronary venous lead and either ring or coil of the right ventricular lead. In our cohort, this pacing mode led to a biventricular depolarisation in 40–50% of all cases at a pacing amplitude of 2.5–3 V (0.5 ms) (Fig. 7). Consequently, only bipolar leads provide a differentiated stimulation of both ventricles independent of the chronic programmed stimulation amplitude.
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Removal of coronary venous leads
Extraction of coronary vein leads (
) did not reveal any problems even in long-term implanted leads (3 months–2 years). Stylet-delivered leads were stabilised after surgical exposure with such a device and removed carefully. The central orifice of OTW leads was frequently occluded in long-term implanted leads, but extraction was successful by means of commercially available tools. `Side–wire' leads (Medtronic Attain 4191) with a sharp-edged metal ring at the lead tip, thicker than the lead body itself, are associated with an increased risk of venous injury including dissection or rupture of the venous wall.6 Therefore, the option of an emergency thoracotomy should be available. We explanted one side-wire lead after stylet stabilisation under continuous rotation without any complication 12 months after the implantation. (see Table 1).
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Epicardial leads
The use of bipolar epicardial leads (Fig. 3) is indicated, if implantation becomes necessary during a cardiosurgical procedure, if transvenous coronary lead placement has failed, or in case of a specific coronary venous anatomy.
Implantation of epicardial leads during cardiac surgery
Patients with high grade mitral valve insufficiency and asynchronous contraction of the papillary muscles achieve a sustained reduction of mitral regurgitation by CRT alone, while additional high-grade aortic valve stenosis requires aortic valve replacement. Epicardial lead placement during open-heart surgery should be performed during the reperfusion period prior to termination of extracorporeal circulation. The heart has to be elevated towards the surgeon to guarantee sufficient surgical exposure for exact lead placement. During this procedure, the relationship of phrenic nerve and epicardial leads cannot be evaluated exactly so that erroneous nerve stimulation has to be ruled out by testing with maximal electrical output with both lungs inflated and a filled heart. In these cases biventricular stimulation can be performed by additional temporary pacing wires at the right atrium and both ventricles. Definitive lead placement in the right atrium and the right ventricle can be performed during a second procedure after recovery from the previous one.
Since epicardial leads have to be placed on native epicardium, their use in patients previously cardiotomised is certainly limited due to epicardial fibrosis and scarring so that screw-in leads are the leads of choice in such cases. Unfortunately, rapid increases in threshold resulting in loss of capture have been observed in this particular lead type.
Implantation of epicardial leads due to a specific coronary venous anatomy
Due to the progress in transvenous lead development, the application of epicardial leads decreased to less than 5%. In our patient cohort, the epicardial approach was chosen on the basis of preoperative venography in 5 patients, because no suitable vein was detected in the target region (
), the venous anatomy was to complex for a transvenous approach (
), or because of an aneurysmatous disease of the target vein (). In 3 further patients transvenous placement of the CV leads failed intraoperatively necessitating a switch to epicardial leads in a second procedure, while 2 further patients were supported by epicardial leads during open heart surgery (Fig. 3). Intractable stimulation of the phrenic nerve in 3 patients led to the explantation of the previously placed CV lead and conversion to an epicardial pacing of the left ventricle instead.
Implantation technique
The main disadvantage of left ventricular epicardial pacing is the necessity to expose the heart surgically resulting in a large surgical trauma compared to the transvenous placement of CV leads. The standard approach for epicardial lead placement is the left lateral thoracotomy. Myocardial injury by bleeding from the stitches itself as well as multiple stitches into the myocardium lead to a rapid massive increase in threshold up to complete loss of capture.
To reach the lateral left ventricular wall, the pericardium has to be incised dorsally to the phrenic nerve before the epicardial leads are fixed by four sutures. To obtain low lead thresholds it is most important to reduce tissue trauma to a minimum.
Videoassisted versus standard thoracotomy
Due to the reduced visibility of the target region dorsally to the phrenic nerve after pericardiotomy, we do not recommend a minimally invasive video assisted procedure3,7,8 for the implantation of epicardial leads. Furthermore, one has to face the risk of multiple implantation attempts at the beating heart with repetitive, threshold-increasing cardiac injuries. Video assisted procedures require single lung ventilation leading to an additional increase of right ventricular afterload that might lead to an acute cardiac decompensation with subsequent cardiopulmonary resuscitation in severely compromised patients. The high risk of inducing ventricular fibrillation while manipulating the beating heart as well as the difficulty of defibrillating these hearts externally have to be taken into account and do not favour the thoracoscopic implantation technique.
Summary
Coronary venous leads are the leads of choice in cardiac resynchronisation therapy. They can be placed with excellent electrical thresholds in previously cardiotomised patients. Due to the enormous morphologic variability of the coronary venous anatomy, the leads have to be selected with respect to each individual case. The use of different leads make a coronary venous approach possible in 95% of all cases which is by far less traumatising than the epicardial one. The removal of even long-term implanted leads does not cause any difficulties.
Epicardial leads should be placed, if the transvenous approach is technically unsuccessful or if cardiotomy is necessary for other reasons. In these cases biventricular stimulation can be performed by additional temporary pacing wires at the right atrium and both ventricles. Definitive right heart lead placement can be performed during a second procedure after recovery from the previous surgery.
References
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