High pacing impedances: are you overtorquing your leads?
BACKGROUND
Variations in measured pacing impedances that occur at the time of lead implantation remain largely unexplained and may be due to the morphology of the tissue-lead interface.


METHODS
An endocardial pacing lead was implanted under direct endoscopic visualization and parameters were measured for defined stages of implantation into multiple sites within the right atrium of in vitro swine hearts (n = 6, 38 implants), in vivo swine hearts (n = 2, 10 implants), and an in vitro human heart (n = 1, 15 implants).


RESULTS
Steady increases in impedance values up to 2 turns fully fixed (2TF) were associated with minimal tissue distortion in all implants. Overtorquing of the in vitro swine implants resulted in severe distortion at the tissue-lead interface demonstrating either tissue wrapping (24 implants) or tissue coring (14 implants). Impedance and threshold values remained elevated (953 +/- 282 Omega, 7.86 +/- 3.0 V; both P < 0.05 vs 2TF) during tissue distortion/wrapping, while tissue-cored implants were associated with significant decreases (552 +/- 187 Omega, 6.2 +/- 2.2 V; both P < 0.05 vs 2TF). P-wave amplitudes demonstrated no significant changes or correlation to tissue distortion. Importantly, both swine in vivo and human in vitro data demonstrated similar trends compared with the swine in vitro data.


CONCLUSIONS
In this study, one is able to directly observe and correlate the degree of distortion at the tissue-lead interface with measured electrical parameters. Instantaneous impedance values obtained during fixation serve as a superior indicator of an acceptable lead implantation, and should therefore be carefully monitored during implantation.
Laske
Timothy G
TG
Medtronic, Inc., Minneapolis, MN, USA.
Vieau
Sarah A
SA
Skadsberg
Nicholas D
ND
Iaizzo
Paul A
PA
D000818:Animals; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D017097:Electric Impedance; D004567:Electrodes, Implanted; D004724:Endoscopy; D004867:Equipment Design; D006801:Humans; D066298:In Vitro Techniques; D010138:Pacemaker, Artificial / Q000592:standards*; D013552:Swine; D019415:Torque