Changes in pacing lead impedance over time predict lead failure

Evidence to support magnetic resonance conditional labelling of all pacemaker and defibrillator leads in patients with cardiac implantable electronic devices

AIMS

Many cardiac pacemakers and defibrillators are not approved by regulators for magnetic resonance imaging (MRI). Even following generator exchange to an approved magnetic resonance (MR)-conditional model, many systems remain classified 'non-MR conditional' due to the leads. This classification makes patient access to MRI challenging, but there is no evidence of increased clinical risk. We compared the effect of MRI on non-MR conditional and MR-conditional pacemaker and defibrillator leads.

METHODS AND RESULTS

Patients undergoing clinical 1.5T MRI with pacemakers and defibrillators in three centres over 5 years were included. Magnetic resonance imaging protocols were similar for MR-conditional and non-MR conditional systems. Devices were interrogated pre- and immediately post-scan, and at follow-up, and adverse clinical events recorded. Lead parameter changes peri-scan were stratified by MR-conditional labelling. A total of 1148 MRI examinations were performed in 970 patients (54% non-MR conditional systems, 39% defibrillators, 15% pacing-dependent) with 2268 leads. There were no lead-related adverse clinical events, and no clinically significant immediate or late lead parameter changes following MRI in either MR-conditional or non-MR conditional leads. Small reductions in atrial and right ventricular sensed amplitudes and impedances were similar between groups, with no difference in the proportion of leads with parameter changes greater than pre-defined thresholds (7.1%, 95% confidence interval: 6.1-8.3).

CONCLUSIONS

There was no increased risk of MRI in patients with non-MR conditional pacemaker or defibrillator leads when following recommended protocols. Standardizing MR conditions for all leads would significantly improve access to MRI by enabling patients to be scanned in non-specialist centres, with no discernible incremental risk.

Impact of magnetic resonance imaging on functional integrity of non-conditional cardiovascular implantable electronic devices

BACKGROUND

Cardiovascular implantable electronic devices (CIEDs) have historically restricted the use of magnetic resonance imaging (MRI) due to the potential clinical and configurational risks associated with electromagnetic interference. In this study, the authors investigated the impact of MRI on the functional integrity of non-conditional CIEDs and their clinical correlates.

METHODS

In this prospective, observational single-center study, we enrolled patients undergoing MRI over a 5-year period. Prior to assessing the impact of MRI on CIEDs, we performed interrogations in sequential duplication to assess the intrinsic variability of devices. Subsequently, we performed interrogations immediately after MRI, and monitored changes in device parameters and clinical events.

RESULTS

We completed 492 MRI studies, 58% in patients with permanent pacemakers (PPMs) and 42% with implantable cardioverter defibrillators (ICDs). Subsequent MRI exposures occurred in 15% encounters. Accounting for intrinsic variability in CIED leads, there were no significant changes in RA, RV, or LV parameters after MRI, regardless of the region imaged (thoracic vs. non-thoracic), type of CIED (PPMs vs. ICDs) and among those with serial MRIs. When ranked for % change pre- to post-MRI, the majority of RA, RV, and LV metrics for thresholds, sensing, and impedance conformed to ≤20% change from baseline. No significant clinical adverse cardiac events or effect on device microcircuitry occurred during the study.

CONCLUSION

Incorporating a novel reproducibility tactic, there were neither clinically meaningful device parameter changes nor adverse clinical events during or following MRIs, suggesting the effects of MRI on non-conditional CIED integrity are far less than previously perceived.

Safety of Magnetic Resonance Imaging in Patients with Cardiac Devices

BACKGROUND

Patients who have pacemakers or defibrillators are often denied the opportunity to undergo magnetic resonance imaging (MRI) because of safety concerns, unless the devices meet certain criteria specified by the Food and Drug Administration (termed "MRI-conditional" devices).

METHODS

We performed a prospective, nonrandomized study to assess the safety of MRI at a magnetic field strength of 1.5 Tesla in 1509 patients who had a pacemaker (58%) or an implantable cardioverter-defibrillator (42%) that was not considered to be MRI-conditional (termed a "legacy" device). Overall, the patients underwent 2103 thoracic and nonthoracic MRI examinations that were deemed to be clinically necessary. The pacing mode was changed to asynchronous mode for pacing-dependent patients and to demand mode for other patients. Tachyarrhythmia functions were disabled. Outcome assessments included adverse events and changes in the variables that indicate lead and generator function and interaction with surrounding tissue (device parameters).

RESULTS

No long-term clinically significant adverse events were reported. In nine MRI examinations (0.4%; 95% confidence interval, 0.2 to 0.7), the patient's device reset to a backup mode. The reset was transient in eight of the nine examinations. In one case, a pacemaker with less than 1 month left of battery life reset to ventricular inhibited pacing and could not be reprogrammed; the device was subsequently replaced. The most common notable change in device parameters (>50% change from baseline) immediately after MRI was a decrease in P-wave amplitude, which occurred in 1% of the patients. At long-term follow-up (results of which were available for 63% of the patients), the most common notable changes from baseline were decreases in P-wave amplitude (in 4% of the patients), increases in atrial capture threshold (4%), increases in right ventricular capture threshold (4%), and increases in left ventricular capture threshold (3%). The observed changes in lead parameters were not clinically significant and did not require device revision or reprogramming.

CONCLUSIONS

We evaluated the safety of MRI, performed with the use of a prespecified safety protocol, in 1509 patients who had a legacy pacemaker or a legacy implantable cardioverter-defibrillator system. No long-term clinically significant adverse events were reported. (Funded by Johns Hopkins University and the National Institutes of Health; ClinicalTrials.gov number, NCT01130896 .).

Assessing the Risks Associated with MRI in Patients with a Pacemaker or Defibrillator

BACKGROUND

The presence of a cardiovascular implantable electronic device has long been a contraindication for the performance of magnetic resonance imaging (MRI). We established a prospective registry to determine the risks associated with MRI at a magnetic field strength of 1.5 tesla for patients who had a pacemaker or implantable cardioverter-defibrillator (ICD) that was "non-MRI-conditional" (i.e., not approved by the Food and Drug Administration for MRI scanning).

METHODS

Patients in the registry were referred for clinically indicated nonthoracic MRI at a field strength of 1.5 tesla. Devices were interrogated before and after MRI with the use of a standardized protocol and were appropriately reprogrammed before the scanning. The primary end points were death, generator or lead failure, induced arrhythmia, loss of capture, or electrical reset during the scanning. The secondary end points were changes in device settings.

RESULTS

MRI was performed in 1000 cases in which patients had a pacemaker and in 500 cases in which patients had an ICD. No deaths, lead failures, losses of capture, or ventricular arrhythmias occurred during MRI. One ICD generator could not be interrogated after MRI and required immediate replacement; the device had not been appropriately programmed per protocol before the MRI. We observed six cases of self-terminating atrial fibrillation or flutter and six cases of partial electrical reset. Changes in lead impedance, pacing threshold, battery voltage, and P-wave and R-wave amplitude exceeded prespecified thresholds in a small number of cases. Repeat MRI was not associated with an increase in adverse events.

CONCLUSIONS

In this study, device or lead failure did not occur in any patient with a non-MRI-conditional pacemaker or ICD who underwent clinically indicated nonthoracic MRI at 1.5 tesla, was appropriately screened, and had the device reprogrammed in accordance with the prespecified protocol. (Funded by St. Jude Medical and others; MagnaSafe ClinicalTrials.gov number, NCT00907361 .).

[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.

Effect of insulation material in aging pacing leads: comparison of impedance and other electricals: time-dependent pacemaker insulation changes

BACKGROUND

There has been concern over declining bipolar (BP) impedance (Z) in aging polyurethane (PU) cardiac pacing leads. Subsequently, a prospective study was conducted comparing BP Z, threshold (Th), and R-wave sensing amplitude of 55D PU-insulated (Model 4024, Medtronic, Inc., Minneapolis, MN, USA) and silicone-insulated (Model 5024) leads.

METHODS

This study was initiated by The Iowa Heart Center. Patients with Model 4024 (N = 162) or 5024 (N = 120) pacing leads with at least 6 years implant time were enrolled and followed for an additional 5 years.

RESULTS

There was a significant drop in the mean BP Z for the Model 4024 population, between enrollment (6 years) and the final endpoint (11 years), which was in contrast to the Model 5024 which did not see a significant drop in its mean BP Z for this same period. The trend difference seen in the means between the two models was statistically significant (P < 0.0001). In addition, a statistically significant relationship was found between dropping BP Z and rising Th (P < 0.0001). The analysis showed that if BP Z dropped below 200 ohms, the probability of having a >3X increase over baseline, in Th at 2.5 V, increases from approximately 3-7% to as high as 30%.

CONCLUSIONS

A significant drop in BP Z observed in the PU-insulated Model 4024 lead was not present in the silicone-insulated Model 5024 lead. The statistically significant relationship between dropping BP Z and rising Th helps to understand how to better manage patients with aging leads.

A prospective evaluation of a protocol for magnetic resonance imaging of patients with implanted cardiac devices

BACKGROUND

Magnetic resonance imaging (MRI) is avoided in most patients with implanted cardiac devices because of safety concerns.

OBJECTIVE

To define the safety of a protocol for MRI at the commonly used magnetic strength of 1.5 T in patients with implanted cardiac devices.

DESIGN

Prospective nonrandomized trial. (ClinicalTrials.gov registration number: NCT01130896) SETTING: One center in the United States (94% of examinations) and one in Israel.

PATIENTS

438 patients with devices (54% with pacemakers and 46% with defibrillators) who underwent 555 MRI studies.

INTERVENTION

Pacing mode was changed to asynchronous for pacemaker-dependent patients and to demand for others. Tachyarrhythmia functions were disabled. Blood pressure, electrocardiography, oximetry, and symptoms were monitored by a nurse with experience in cardiac life support and device programming who had immediate backup from an electrophysiologist.

MEASUREMENTS

Activation or inhibition of pacing, symptoms, and device variables.

RESULTS

In 3 patients (0.7% [95% CI, 0% to 1.5%]), the device reverted to a transient back-up programming mode without long-term effects. Right ventricular (RV) sensing (median change, 0 mV [interquartile range {IQR}, -0.7 to 0 V]) and atrial and right and left ventricular lead impedances (median change, -2 Ω [IQR, -13 to 0 Ω], -4 Ω [IQR, -16 to 0 Ω], and -11 Ω [IQR, -40 to 0 Ω], respectively) were reduced immediately after MRI. At long-term follow-up (61% of patients), decreased RV sensing (median, 0 mV, [IQR, -1.1 to 0.3 mV]), decreased RV lead impedance (median, -3 Ω, [IQR, -29 to 15 Ω]), increased RV capture threshold (median, 0 V, IQR, [0 to 0.2 Ω]), and decreased battery voltage (median, -0.01 V, IQR, -0.04 to 0 V) were noted. The observed changes did not require device revision or reprogramming.

LIMITATIONS

Not all available cardiac devices have been tested. Long-term in-person or telephone follow-up was unavailable in 43 patients (10%), and some data were missing. Those with missing long-term capture threshold data had higher baseline right atrial and right ventricular capture thresholds and were more likely to have undergone thoracic imaging. Defibrillation threshold testing and random assignment to a control group were not performed.

CONCLUSION

With appropriate precautions, MRI can be done safely in patients with selected cardiac devices. Because changes in device variables and programming may occur, electrophysiologic monitoring during MRI is essential.

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.

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.