Septal Implantation of Right Ventricular Lead : Technique
The author’s default preferred method is septal pacing.
The technique described here is what the author has learned and practiced at this training institution. It is based on the method described and advocated by Harry G Mond using a three dimensional stylet. The end goal is to pace the lead at the inter-ventricular septum at its mid point to ensure a narrow as possible paced QRS complex by delivering the impulse near simultaneously to the RV and LV
The “mid-septal position” needs further emphasis : This location is the ideal place to capture both ventricles at the same time (hence narrow QRS complex). Too anterior (towards the apex) could lead to capture similar to RV apcial capture. Too proximal (i.e. just beyond the tricuspid valve annulus), may have lead stability issues or may entrap a tricuspid leaflet leading to significant regurgitation. If it is too high, it will predominantly pace the RVOT with delayed exit to the LV and sometimes causing symptoms of palpitations similar to RVOT ectopics. If it is too low, it will be similar to RV apical pacing with basal to top activation
The goal is to achieve a narrowest possible paced QRS complex with acceptable lead parameters. Therefore a combination of radiographic and paced ECG mapping is utilized to get to the ideal mid-septal position.
- Crossing the tricuspid valve (and ideally drag down the lead from the RV outflow tract)
- Placing the lead tip opposed to mid portion of the interventricular septum using the 3D stylet and radiologic guidance
- Confirming position and parameters electrically (ECG morphology)
- Deployment of the screw to fix the lead & reconfirm parameters
Although the lead is usually 6Fr thick, it is an extremely floppy structure compared to other coronary and vascular catheters. This floppiness facilitates placement of the lead in challenging positions during implantation and after implantation free movement of its body within the vascular space. The downside of this floppiness is that, lead placement requires the use of stiff metal stylets to guide the lead to the desired position.
The active fixation ventricular lead pack comes with several metal stylets of varying hardness and they are usually straight ones but some contain a J shaped stylet in addition to straight ones. This J curved stylet can be used to facilitate lead crossing through the tricuspid valve.
Manipulating the RV lead through the tricuspid annulus requires dexterity, thoughtful approach and most importantly patience.
A gently curved stylet as follows which conforms to the RV cavity can facilitate crossing the TV. Our preferred approach is to make a three dimensionally curved stylet and use it to guide the lead because in vast majority of cases valve crossing and correct lead placement can be achieved in a single pass using this stylet.
Shaping the 3 Dimensional Stylet
If one takes time to appreciate the shape of the stylet in anatomical orientation it’s extremely easy to figure out its usefulness.
The curves are constructed by drawing a pre-wetted (heparinized saline) straight stylet over wet gauze swab or artery forceps as demonstrated below.
Video : Creation of the 3 Dimensional Stylet : The stylet has two curves – large curve and small curve. The large curve facilitates crossing of the tricuspid valve and small distal curve facilitates septal pacing. All curves should be made without kinking (acute bends) the stylet as kinks (even if they are subsequently straitened out) will impair the smooth gliding of the lead over the stylet
Inserting the lead through the sheath
Once you are ready with a curved stylet, the lead implantation can begin. The foremost step is the insertion of the lead via the sheath. For this, the sheath dilator and guide-wire are gently pulled out and the lead is inserted through the lumen of the sheath.The lead should go in about 1/3 of its length without any resistance but its always better to check furoscopically as to where the lead is. It is very important that the lead be advanced slowly and not forcibly.
Never pull out the guidewire blindly (without looking through fluro) if there is a temporary pacing wire giving critical pacing support. The distal curved part of the guide-wire can get entangled in the temporary wire and dislodge it from the RV leading to loss of capture.
One potential place where brisk forcible insertion might cause problems is the SVC free wall: If the sheath is too much in, the tip will lie against the free wall of the SVC and the lead coming out of it will impinge on the wall creating a resistance. Therefore it is imperative that fluroscopic screening is done at the slightest resistance without pushing the lead blindly. If impinging, the whole sheath should be slightly withdrawn and the lead marched forward with about inch of stylet pulled out to make it floppy and fall down
Crossing the Tricuspid Valve
After parking the lead in the RA, the straight stylet is withdrawn and the curved 3D stylet is inserted. One must keep hands free of blood and the stylets wet with heparinized saline during stylet exchanges. With the 3D stylet fully in, now the whole stylet – lead assembly is advanced in an attempt to cross the tricuspid valve. Most of the time with the assistance of the large curve of the stylet, the lead crosses the valve. The stiffness of the stylet determines the large curve and if the lead is heavy (e.g. an ICD lead) or the stylet is soft the curve may open up when inside the heart – impeding crossing. In such situation, the large curve has to be made more acute or a stiffer stylet has to be used. Monitoring the ECG is helpful as when the lead seems to enter the RV, occurrence ventricular ectopics confirm that the lead is indeed in the RV
Occasionally though the lead fails to cross the valve and one must resort to various tricks to cross the valve. It’s a fine balance between the floppiness of the lead and the support given by the stylet. If one withdraws the stylet one or two inches the lead tip segment becomes floppy enabling it to be “wriggled” in through the valve. The core principle is to not push the lead forcibly with the stylet fully inside in it – especially when the lead is impinging on an undetermined obstacle
Placing in the Mid-septal Position
In AP projection the RV free wall is most anterior and the septum lies behind it with RV cavity separating the two. Because of the oblique rotation of the heart, it is necessary to appreciate that the inter-ventricular septum seen in AP projection is actually foreshortened and one cannot get an accurate idea of the distance from the tricuspid valve to the Apex (i. e. the horizontal length of the septum) – Therefore we need the right – anterior – oblique (RAO) view to get an idea of the true longitudinal width of the inter-ventricular septum. At RAO 30 degrees, the shadow that we see is a good projection of the septum. Therefore the mid-septal position where we place the lead is decided while viewing in RAO 30.
At times, it is difficult to get to the mid septal position as the lead tends to gravitate into the apex. In such instances, the RVOT drop-down method can be utilized facilitate septal positioning. With the straight stylet almost halfway withdrawn, the operator can try to wriggle the floppy lead into the right ventricular outflow tract (which is aided by the blood flow). Once well in the RVOT, the straight stylet is exchanged with the 3D stylet and the lead is slowly withdrawn under fluroscopy until the tip “drops” to the septum.
The second situation where low septal pacing is preferred over mid septal, is when implanting ICD leads. If there is no long-term pacing need its better to implant in low septum as ICD leads are heavy and hence prone to more early dislodgement. It is also assumed that low septal position give more coverage for the shocking vector of the RV coil. However in CRTDs, mid-septal pacing may provide better axis separation for optimal CRT response compared to low septal position.
At times, anterior septum is better electrically rather than mid-septal position. Occasionally, despite good radiographic position – one finds that the QRS complex is not narrow (aka ugly !) in the mid septum. Electrical mapping may show that the best site is way more anterior in the septum. If this is the case, that location should be chosen.
As demonstrated above, if the tip is apposed against the mid-line, then we are sure that it’s pacing the septum – not the free wall. Its best practice to confirm this view before deploying the active fix screw as a free wall fix can lead to a perforation. If the lead is seen taking curve along the inferior aspect of the cardiac silhouette (crossing the mid-line), then it has gone in to the coronary sinus and needs re-positioning.
Note : A recent retrospective study (here) showed disproportionately large number of children developing dilated cardiomyoaphthy after RV inlet pacing – it had not been defined as to what RV inlet is but it is assumed that its the proximal (~mid) septal position. How ever the numbers are small for a definitive conclusion. The paediatric pacing done at LRH, Colombo is being retrospectively analyzed for this problem and should shed some light as ALL trans-venous pacing done since 2007 (and being done) have been mid septal pacing. Although it has not been systematically studied so far in the LRH pacemaker recipients the problem should have manifested as the pacemaker children are regularly followed up and because nearly half in the above study population had developed DCM !!!
Despite optimal limb lead QRS complex, most of the time the precordial leads do show some hint of LBBB. This is because the although septal, the initial activation is from the RV. However this LBBB like look is very narrow when compared with the ugly LBBB resulting from apical pacing.
Once radiographically and electrically satisfactory result has been achieved, the active fix screw should be deployed to fix the lead. For details on testing lead parameters please see here
Deployment of Active Fixation
Active fix lead deployment must be done meticulously and not hurried. The screw in mechanism must enter the myocardium in a similar fashion that a cork screw enters the cork.
If one tests the screwing mechanism in vitro, it would be noted that the screw abruptly comes out after few rotations and therefore if deployed rapidly, the screw will stab into the myocardium – not screw in. Stabbing will lead to more tissue damage and may increase chance of short term lead dislodgment. Another pointer is that over-screwing also must be avoided as once the screw comes out, it achieves a relatively fixed length – it does not keep on lengthening. In standard leads this is occurs about after 10-15 turns. Over-screwing builds up torque in the screw which is released in the opposite direction when the screwing clip is released – this increases the chance of lead dislodgement.
If the fluoroscopic system supports high magnification, one can visualize the screw being deployed but it’s not a must if you count the number of turns. The recommended number of turns for a RV lead is 10-15 but depends on the lead manufacturer.
Once the screw has been deployed, the curved stylet can be taken out. The stylet should be gently but firmly pulled out – rapid pull must be avoided as that may dislodge the lead. Removal of the stylet should be done under continuous fluroscopy as the wriggling movement of the lead during pull out is a surrogate marker for lead stability.
Thereafter a straight stylet is placed in halfway along the lead. It’s imperative that only half of the stylet is put it – if full length is inserted, the distal part of the lead may straighten out and get dislodged. The sole propose of this stylet is to provide support of lead anchorage at the pocket.
With the straight stylet is in place, the parameters are checked again for confirmation. Once the parameters are deemed suitable, the peel-away sheath can be now removed by pulling apart from its two “ears”.