Serial lead impedance measurements confirm fixation of helical screw electrodes during pacemaker implantation

Impedance in the Diagnosis of Lead Malfunction

Impedance is the ratio of voltage to current in an electrical circuit. Cardiovascular implantable electronic devices measure impedance to assess the structural integrity electrical performance of leads, typically using subthreshold pulses. We review determinants of impedance, how it is measured, variation in clinically measured pacing and high-voltage impedance and impedance trends as a diagnostic for lead failure and lead-device connection problems. We consider the differential diagnosis of abnormal impedance and the approach to the challenging problem of a single, abnormal impedance measurement. Present impedance provides a specific but insensitive diagnostic. For pacing circuits, we review the complementary roles of impedance and more sensitive oversensing diagnostics. Shock circuits lack a sensitive diagnostic. This deficiency is particularly important for insulation breaches, which may go undetected and present with short circuits during therapeutic shocks. We consider new methods for measuring impedance that may increase sensitivity for insulation breaches.

[Foreseeable variation in parameters measured at implant and follow-up of permanent pacemaker active fixation electrodes]

OBJECTIVES

To analyze the variations in the parameters relative to active fixation electrodes at the time of implantation and over subsequent follow-up during 6 months of the acute phase of implantation.

DESIGN

A descriptive, analytical, prospective, observational cohort study was made of consecutive cases over a period of 8 months (April-December 2010).

SETTING

Pacing unit of an Intensive Care Unit.

PATIENTS OR PARTICIPANTS

Patients undergoing permanent pacemaker implantation with active fixation electrodes, implanted in both atrium and ventricle, Interventions: Measurement of variables described with a threshold analyzer during electrode fixation and at different times during the study, Main compared variables: threshold, impedance and intrinsic activity (both atrial and ventricular) before and after fixation, at 48 hours, at one month and 6 months, Comparisons were made using the Student t-test for paired data, assuming significance for p<0,05, and ANOVA to analyze the successive changes over ambulatory follow-up.

RESULTS

We analyzed 40 patients, with 19 atrial and 40 ventricular electrodes, In fixation, the electrodes showed significant variation in the impedance values of the atrial lead (1,188,53 ± 397,26 vs 610,69 ± 326,30 ohms, p<0,0001) and ventricular lead (1,512,93 ± 718,07 vs 768,80 ± 224,90 ohms, p>0,0001), In the first 48 hours it was coupled with a decrease in ventricular (0,86 ± 0,35 vs 0,48 ± 0,23 volts, p = 0,0001) and atrial pacing threshold (1,10 ± 0,39 vs 0,43 ± 0,23 volts, p = 0,0003), and p-wave sensing (3,61 ± 2,25 vs 2,32 ± 1,09 mV, p = 0,0463), Over follow-up we found the parameters to be stable, with no significant changes.

CONCLUSIONS

After active lead fixation, a fall in impedance of the antrial and ventricular is expected, Over the next 48 hours improvement in atrial and ventricular threshold may occur, in contrast to the sensitivity of the intrinsic activity, which reached significance at the P wave measured after 48 hours, These values stabilize over patient follow-up and do not differ significantly in the studied acute patient course.

Variation in Pacing Impedance: Impact of Implant Site and Measurement Method

BACKGROUND

Variations in pacing impedance may be observed during implantation of various active fixation pacing leads. However, these variations can be influenced by the nature of the fixation, the implant site, or the measurement method. Here we describe implant dynamics for a 4.1F, catheter-delivered pacemaker lead.

METHODS

Endocardial active fixation leads were implanted under direct intracardiac visualization in two right atrial sites and three right ventricular sites in isolated swine (n = 6) and human (n = 4) hearts. Impedance measurements were recorded at each site employing three different measurement techniques-Pacing System Analyzer (PSA) 5311, PSA 2090, and the Impedance Tone Box (Medtronic, Inc., Minneapolis, MN, USA)-with four different degrees of lead fixation: helix touching, one turn fixed (1 TF), two turns fixed (2 TF), and overtorqued.

RESULTS

Pacing impedances increased from touching to 1 TF to 2 TF at all implant sites in both swine and human hearts. Overtorquing applied to leads was associated with visible distortion at the endocardial tissue-lead interface in at least 60% of swine (18 of 30 implants) and human hearts (nine of 14 implants). Impedance values in the right atrial high septum were significantly larger than in any other implant site (P < 0.05). The three measurement methods did not yield significantly different impedance measurements.

CONCLUSIONS

Variations in measured impedances were associated with the nature of implant fixation at all sites in both swine and human hearts.