Transvenous pacing leads were introduced in the 1960s, and the first transvenous implantable cardioverter–defibrillator (ICD) lead (CPI Endotak-C) was introduced in the early 1990s. The Endotak-C was 3.95 mm in diameter (13.2 F) and was introduced through a 14-F sheath. Early bipolar leads were of large diameter Citation[1], but in the 1990s they were downsized to pass through an 8-F sheath. By the 2000s, many leads such as the Medtronic 5076, St. Jude 1388T, and the Boston Scientific Fineline II and Dextrus were introduced through a 7-F sheath. The Medtronic 3830 is a 4.1-F lead delivered through a guiding catheter.
It seems that the electrophysiology community and manufacturers require small-diameter leads. This preference may have a negative impact on lead durability and, possibly, on complications, primarily perforation. Polyurethane, which is used to produce smaller leads, is more likely to degrade prematurely Citation[2]. In this respect, Kleemann et al. in 2007 (before the Sprint Fidelis recall) advocated that the design of smaller leads be re-evaluated Citation[3]. These studies demonstrated that, despite the poor performance of older leads, they had a better survival rate than newer models.
Advantages of small-diameter leads
There are several theoretical advantages of smaller leads: ease of implantation, decrease in axillary/subclavian/innominate vein thrombotic occlusions, easier extraction of chronic leads, a decrease in lead-induced tricuspid insufficiency and a more appropriate size for children and neonates. Ease of implantation is dependent on a physician’s experience and a learning curve with a particular lead. This is quite subjective and has not been systematically studied to date. In addition, there is no evidence that access to the heart for cardiac resynchronization with an ICD is facilitated by three smaller leads, since even the cephalic vein-guidewire technique can accommodate all three of the larger leads, one of which provides defibrillation capability Citation[4–6]. Two studies have evaluated venous occlusion and have shown no relationship between lead size and incidence of occlusion Citation[7,8]. A recent study of 115 consecutive patients with chronic pacing systems found complete occlusion of the subclavian or innominate vein in 38 patients (33%) Citation[7]. There was no relationship seen between venous occlusion and lead diameter, number of leads, duration of implantation, lead insulation type, age or gender of patients. Studies have looked at pacing lead-induced tricuspid insufficiency Citation[9,10]. There is, as yet, no clear consensus that the incidence of severe tricuspid insufficiency is reduced by small-diameter leads. Finally, it seems possible that the only advantage of small-diameter leads is their application in children.
Disadvantages of thin leads
Smaller leads that are coated with polyurethane insulation are associated with an increased incidence of perforation, which may be subacute and relatively late Citation[11]. Perforation affects predominantly active-fixation leads Citation[11–13]. Transmission of greater force per unit area, increased stiffness and increased torque at the tissue-lead interface may result in more frequent perforation. Furthermore, the literature is replete with case reports of small-diameter pacing and ICD leads working their way through the myocardium – especially when implanted at the right ventricular apex Citation[14–16]. There are also the well-publicized lead failures with both the Medtronic Sprint Fidelis and St. Jude Riata ICD leads Citation[17,Citation18]. It seems that decreasing lead stiffness and increasing the size of the distal tip, as in the Fineline leads (Boston Scientific), could reduce the risk of perforation and lead failure while maintaining whatever benefits that smaller-diameter leads might provide.
The design elements that affect lead performance and potential for perforation are as follows:
• Type of lead: passive, fixed screw, extended/retracted helix (fixed screw and passive fixation are less likely to perforate);
• Lead insulation stiffness (choice of materials);
• Lead conductor design (multifilar coils are generally stiffer than single-filar coils for a given wire size; cables can be stiffer than coils);
• Helix factors: tip grind (aggressive/super aggressive helix point vs more benign), helix length, pitch, diameter, helix wire diameter, helix coating versus smooth (uncoated) and helix size versus lead body size;
• Frontal surface area (true effective area);
• Distal stiffness length (many leads are solidly stiff from the helix to some point proximal to the anode electrode). Having a flexible lead body portion between the electrodes reduced the lead’s tendency to wander/penetrate/perforate;
• Choice of stylet – diameter – and amount of tapering at the stylet tip – distance at which the stylet reaches inside of the lead body.
It is time to re-evaluate the clinical usefulness of thin pacing and defibrillator leads as there is accumulating evidence to suggest that the continuing trend to downsize leads may prove counterproductive. Pacing and ICD leads are not simple wires but complex components of cardiac pacing and defibrillation systems. The long-term performance of currently available thin leads should be evaluated according to the variables noted above. At this juncture, there is no doubt that downsizing has increased the incidence of lead perforation mainly affecting extendable helix leads. Such perforations may not be easily recognized and are therefore potentially life-threatening, in part because of their atypical manifestations and later occurrence compared with older and larger more traditional leads.
Financial & competing interests disclosure
The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.
No writing assistance was utilized in the production of this manuscript.
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