Implant Experience with Unipolar Polyurethane Pacing Leads

Abstract

A total of 905 unipolar polyurethane pacing leads have been implanted by the first author's group, between April 1978 and February 1982, with a mean implant time of 1.4 years. Twelve leads were explanled and analyzed. Eleven of the explanled leads exhibited some degree of surface damage or “frosting.” Of the 11, five atrial (Medtronic 6991 U) and one ventricular (Medtronic 6971) lead suffered complete insulation failure. One lead was completely free from surface damage, Clinically, insulation failure presented as muscie stimulation and/or battery depletion. Surface damage appears to be due to an environmental stress cracking (ESC) mechanism. ESC requires both a surface active agent from the hostile biological environment, and stress in excess of a threshold value. The minor surface damage or “frosting” of the eleven explanted leads was typically 10 to 15 microns deep on leads implanted about one year, although one device (15 months) had 30 micron cracks. No lead failures in this series were attributed to this shallow cracking mechanism. The severe cracking of the six Medtronic leads leading to insulation failure was thought to be due to the unusually high tensile stresses imposed by manufacturing processes and ligatures. The incidence of failure was 7% (5/74) for the Medtronic 6991 U and 0.2% (1/454) for the Medtronic 6971, Medtronic lead manufacturing processes have been modified to reduce the high residual tensile stresses and a fixation sleeve has been added to reduce ligature stress.

The biostability of cardiac lead insulation materials as assessed from long‐term human implants

“…15 Previous literature concerning the clinical biostability of cardiac lead insulation materials indicate that silicone is exceptionally biostable, 1,[20][21][22][23] while PEUs, such as Pellet-haneV R 80A and 55D often exhibit surface cracking. 7,20,24 However, most reports on the clinical biostability of insulation materials had significant limitations because they were either based on monitoring of electrical malfunctions of leads, in which case no visual, chemical, or mechanical data is available for the insulation material, [24][25][26][27] case studies based on very small sample sizes of explanted leads, 27 or employed a limited number of material characterization methods. 7,20,24 This study addresses the limitations inherent in in vitro, animal, and past clinical-based studies by evaluating the clinical biostability of three of the most common cardiac lead insulation materials.…”

Implantable Transvenous Pacing Leads:

“…They exhibit high tensile and tear strengths, flexibility, and a low coefficient of friction when wetted with blood. Pellethane 2363 (Upjohn Co., CPR Division, Torrance, CA, USA) rapidly became popular, but by 1981, a number of disturbing reports described in‐vivo degradation of implanted polyurethane with surface cracking and subsequent insulation failure 17–19 . Continuing research revealed that some polyurethane insulation failures were, at least in part, related to specific manufacturing processes and surface trauma during and following implantation.…”

Poly(ether) Urethane Reactivity with Metal-Ion in Calcification and Environmental Stress Cracking

“…Others have found that, as with pacemaker leads, cracking of PEU diaphragms of blood pumps is at right angles to the crease of the diaphragm [18]. In 452 the case of the pacemaker lead insulation, cracks are found circumferentially, at right angles to the induced strain [14]. This and other observations have led to the hypothesis that ESC may and CA does result from initial calcium ion complexation which generates regions of high stress.…”

“…Upon removal, and after drying, most leads present a &dquo;frosted&dquo; appearance [14]. The depth of penetration of the crazes or surface cracks in portions of leads which average 125 microns in thickness, ranges from 2.5 to 30 microns in specific leads.…”