Ventricular Leads
S. B
OVEDACoronary Sinus and Target Vein Anatomy
It is now well known that cardiac resynchronisation therapy (CRT) achieved by biventricular pacing improves haemodynamics in advanced heart failure patients with interventricular and/or intraventricular dyssynchrony. The delivery of CRT is still challenging, as transvenous access to the left ventricle through the coronary sinus tributaries is required. When this technique was first introduced, stylet-delivered shaped leads were used for the left ventricu- lar pacing, but the implantation success rate (around 90%) was very depen- dent on the coronary sinus anatomy, and on the access to and diameter of the lateral vein.
The usual anatomy of the coronary sinus consists of three groups of veins, designated according to their localisation along the left ventricle as posterior, lateral, and anterior. In fact, the coronary sinus configuration varies greatly from patient to patient. In some, there is no lateral vein.
Sometimes, there is only a posterolateral or an anterolateral vein. Vessels may be large, medium-sized, or very small. In addition, left ventricular lead placement is performed by a retrograde approach, and the presence of venous valves or spasm phenomenon can make the progression very diffi- cult.
For all these reasons, the left ventricular lead should be selected after a venogram has been performed, since the choice will depend on the size, tor- tuosity, and angulation of the target vein with the coronary sinus. To improve the implantation success rate, the industry proposes a range of stylet- and over-the-wire-guided leads to suit all venous anatomies [1]. Over- the-wire leads will be used in the case of small or medium-calibre tortuous
Cardiology Department, Clinique Pasteur, Toulouse, France
veins or when there is acute angulation with the coronary sinus. By contrast, stylet leads will be more appropriate for medium-sized and large straight veins and an open angle with the coronary sinus.
Angioplasty Technology: Over-the-Wire LV Leads
This great variability of the coronary sinus anatomy led to the development of a novel ‘over-the-wire’ approach, combining a standard pacing lead and angioplasty technology. The technique is based on shaped sheaths for coro- nary sinus catheterisation and angiography, and guide wires for the left ven- tricular lead [1]. The sheaths must be smooth and flexible, to avoid coronary sinus dissection. A special venography balloon catheter is inserted into the sheath to perform a coronary sinus angiogram that will help in identification of the target vein and thus in the selection of the most appropriate left ven- tricular lead. Then, using angioplasty techniques and tools, the left ventricu- lar lead will be driven to the target vein using the inner stylet for a classical shaped lead, or a special guide wire for an over-the-wire left ventricular lead.
After placement of the left ventricular lead, the sheath is removed by cutting (Medtronic, Biotronik), peeling (St. Jude Medical), or just dragging it away (Guidant, Ela Médical) all along the lead.
This logical approach to reaching the target vessel in the coronary sinus has interested many interventional cardiologists specialising in coronary angioplasty. They have adapted their skill, performing coronary vein balloon angioplasty and evolving new solutions for difficult cases.
Over-the-Wire/Stylet LV Leads
These over-the-wire systems have been improved more recently with new active fixation mechanisms and steroid-eluting leads to provide better pac- ing thresholds [2]. Among the recent advancements may be mentioned the distal tip silicone seal designed to reduce blood ingress into the lumen.
Some over-the-wire leads have no shape and a passive classical (Guidant Easytrak 1 and 2) [3] or active silicone screw (Ela Médical) fixation system on the distal tip. In many cases (Medtronic, Biotronik, St. Jude Medical, Guidant Easytrak 3) the leads have an angled lead body with two or more distal curves (Medtronic, St. Jude Medical) or a helix (Biotronik, Guidant Easytrak 3) for a better stability inside the vein.
Many over-the-wire leads can also be stylet-delivered (Medtronic, St. Jude
Medical, Biotronik), depending on the configuration of the target vein. The
Medtronic 4193 lead has a 4F flexible lead body for easier implantation in the
small veins. One of the problems of these over-the-wire thin leads is the risk
of phrenic nerve stimulation because of their placement in the distal part of the vein. In this situation, it is necessary to withdraw the lead until phrenic nerve stimulation stops.
Finally, all left ventricular leads have the standard IS-1 connection, except the Guidant Easytrak leads (original LV1 connection) [3].
Results
As has been demonstrated by Boriani et al. [4], it is obvious that CRT proce- dures require a learning curve, and the implant success rate increases dra- matically from 52% in inexperienced hands to more than 90% in trained teams. There is also an improvement in the success rate when the implanter uses the complementarity of the left ventricular lead range: from 91.6% with over-the-wire leads only, up to 94.1% success when stylet and/or over-the- wire leads are used. This means that comprehensive knowledge of CRT tools and leads is necessary to achieve a success rate of 90% or more, which seems to be the goal at present. However, despite this, experience remains the most important factor of success.
Unfortunately, we know that in a small group of patients (around 5%) CRT is impossible to achieve. Peculiarities of anatomy are the main reasons for unsuccessful attempts, leading to inability to access the coronary sinus ostium or the coronary vein, or dislodgement or unstable positioning of the lead.
The electrical performances of over-the-wire left ventricular leads are similar to those observed for right ventricular leads, except for the pacing threshold, which is usually higher, around 1.5 V in our experience (Table 1).
In addition, left ventricular pacing thresholds are not significantly different between over-the-wire- and stylet-delivered leads [5].
We compared the data of the MIRACLE [6] and InSync III [7] studies to assess whether there was an improvement in implantation success rates and complication rates with increased experience and the introduction of new left ventricular lead technologies. In each study, investigators were asked to first attempt the implant with a selected lead: the Attain 2187 (stylet-deliv- ered) for the MIRACLE and the Attain 4193 (over-the-wire-guided) for the InSync III study. If unsuccessful, they could use other leads included in the protocols. Performance comparisons were made between the MIRACLE and the InSync III studies, both of which used CRT-only devices (Table 2). It is very interesting to observe that implantation success rate improved with experience. However, there was a highly significant decrease in implantation time and fluoroscopy time with the InSync III study which can be attributed to implanter experience and the addition of the over-the-wire lead (Fig. 1).
Finally, perioperative complications decreased significantly with the addition
of the Attain over-the-wire lead in InSync III (Table 3). These data suggest that an over-the-wire lead should be implanted primarily in order to signifi- cantly reduce procedure duration, fluoroscopy time, and the risk of perioper- ative complications.
It seems likely that implanter experience and coronary sinus anatomy have a strong impact on procedure times and outcomes.
Fig. 1. Median implantation time with interquartile range Figure 1 : Median Implant Time with Interquartile Range
2.7 2.3
1.0 2.0 3.0 4.0 5.0
MIRACLE InSync III
Hours
P < 0.0001 Table 1. Experience at the Clinique Pasteur, 2003-2004
CRT implants 2003-2004
Enrollment period January 2003 – December 2004
OTW vs stylet LV leads (%) 100% vs 0%
Implant attempts 128
Successful implants (% success rate) 122 (95%) Number of patients needing 2 procedures 5 (4%)
Mean procedure time (min) 92 ± 53
Complications
a14 (11%)
Mean LV pacing thresholds (V) 1.53
a
