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Suppression of Cautery-Induced Electromagnetic Interference of Cardiac Implantable Electrical Devices by Closely Spaced Bipolar Sensing

Suresh, Mithun, BSEE*; Benditt, David G., MD*,‡; Gold, Barbara, MD; Joshi, Girish P., MB BS, MD, FFARCSI§; Lurie, Keith G., MD*,‡

doi: 10.1213/ANE.0b013e3182172a18
Technology, Computing, and Simulation: Brief Report
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BACKGROUND: Electromagnetic interference (EMI) induced by electrocautery during surgery in patients with cardiac pacemakers or implanted cardioverter-defibrillators (ICDs) may inhibit pacing and cause inappropriate tachyarrhythmia oversensing. In particular, susceptibility to EMI may be enhanced in ICDs by frequently used wide interelectrode sensing (i.e., integrated bipolar sensing). Consequently, ICD function is usually disabled preoperatively and restored later by noninvasive programming. Because sensing by closely spaced electrodes (i.e., true bipolar) may be less susceptible to EMI, preoperative programming to a true bipolar mode may minimize the need for perioperative programming while preserving device function.

METHODS: Our study population consisted of 23 consecutive patients either receiving a new ICD or undergoing ICD pulse generator change. In each patient, electrocautery-induced EMI was initiated with the ICD in the closely spaced sensing configuration and again during widely spaced sensing.

RESULTS: In comparing the 2 sensing modes, right ventricular electrogram amplitude was significantly greater and EMI noise amplitude tended to be greater with widely spaced bipolar sensing. Furthermore, widely spaced bipolar sensing was associated with ICD pacing inhibition in 22 of 23 patients and incorrect “ventricular fibrillation” detection in 17 of 23 patients. Conversely, closely spaced bipolar sensing was not accompanied by either pacing inhibition or incorrect ventricular fibrillation sensing.

CONCLUSION: Closely spaced bipolar sensing (i.e., true bipolar) appropriately rejects electrocautery-induced EMI. Programming implanted devices to closely spaced bipolar sensing may minimize the need for perioperative reprogramming while preserving intraoperative device operation.

Published ahead of print May 4, 2011

From the Departments of *Medicine and Anesthesiology, University of Minnesota Medical School, Minneapolis; the Central Minnesota Heart Center, St. Cloud, Minnesota; and §Department of Anesthesiology and Pain Management, University of Texas Southwestern Medical Center, Dallas, Texas.

Conflict of Interest: See Disclosures at the end of the article.

Reprints will not be available from the authors.

Address correspondence to David G. Benditt, MD, Mail Code 508, 420 Delaware St. SE, Minneapolis, MN 55455. Address e-mail to bendi001@umn.edu.

Accepted February 15, 2011

Published ahead of print May 4, 2011

Electrocautery-induced electromagnetic interference (EMI) may adversely affect the operation of implanted cardiac pacemakers or implanted cardioverter-defibrillators (ICDs) during surgery.1 In the case of an ICD, cautery-induced EMI might be misinterpreted by the device sensing circuit as ventricular fibrillation (VF), resulting in an inappropriate shock. In the case of a pacemaker, the outcome may be inhibition of essential pacing. Consequently, these implanted devices are often programmed preoperatively to a nonsensing mode. Subsequently, reprogramming to baseline state must be undertaken postoperatively.1,2 Thus, at least 2 programming interventions are needed.

We hypothesized that programming ICDs to a true bipolar sensing mode (i.e., closely spaced sensing electrodes), as opposed to the often-used integrated bipolar mode (i.e., widely spaced bipolar sensing electrodes), may provide sufficient EMI signal attenuation to avert adverse effects of electrocautery-induced EMI during surgical procedures while preserving intraoperative ICD function. To this end, we examined whether a closely spaced bipolar electrode configuration minimized device sensing of electrocautery-induced EMI signals, even when the EMI was initiated in the immediate vicinity of the implantation site.

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METHODS

The Central Minnesota Heart Center IRB approved the study protocol and all patients gave written informed consent. The study population consisted of consecutive patients, each of whom was either receiving an initial ICD implant or was undergoing ICD generator replacement; electrocautery was used in the customary manner for these procedures. Implanted devices were programmed to the closely spaced (“true”) bipolar or the widely spaced (“integrated”) bipolar modes in random order.

The ring and tip electrodes of the ICD lead comprise the true closely spaced bipolar electrode configuration (Fig. 1). The integrated widely spaced bipolar electrode configuration uses the distal defibrillation coil and the tip electrode (Fig. 1). The important difference between these 2 configurations is the distance between their sensing electrodes (integrated bipolar pair approximately 4 cm; true bipolar 1–1.5 cm depending on lead model). The larger the interelectrode distance, the more of the electrocautery-induced electrical field is encompassed by the sensing electrodes (Fig. 2). Both electrode configurations were tested in each patient.

Figure 1

Figure 1

Figure 2

Figure 2

During testing, unipolar electrocautery (Force FX™; Valleylab, Boulder, CO) was performed for 1 to 4 seconds; the duration of each electrocautery application was determined by the needs of the operator at the time. However, cautery duration was approximately the same for both sensing modes. The grounding pad was placed on the leg, hip, or abdomen, depending on where it would adhere best with the least patient discomfort. The electrocautery signal was sinusoidal (390 kHz) at 45 W for one patient and 30 W for all others3; electrocautery power was determined by the operator based on factors such as patient size.

Signals recorded during electrocautery were lead II electrocardiogram, ICD marker channel, and right ventricle electrogram (R wave). Lead II electrocardiogram tracing was used to determine peak amplitude of the EMI noise signal during electrocautery application. The variables recorded during electrocautery application included amplitude (mV) of the right ventricular electrogram, sensing lead impedance, postelectrocautery pacing threshold, and assessment of the average value of the detected EMI signal amplitude. All reported values were based on an average of 5 to 8 sequential measurements obtained using a Medtronic, Inc. (Minneapolis, MN) model 2090 programmer (amplitude resolution is approximately 0.1 mV). The programmed ICD pulse generator sensitivity was 0.3 mV. Additionally, during electrocautery application, the presence or absence of pacing inhibition and incorrect VF detection (i.e., EMI misinterpreted as VF and labeled as such on the ICD marker channel) were documented by the electrophysiologist/cardiologist present throughout the procedure.

Paired t tests were used to assess the statistical significance of differences in R-wave amplitude, EMI noise amplitude, lead impedance, and pacing threshold between the true and integrated bipolar configurations. Data are presented as mean ± SD. A P value of <0.05 was considered statistically significant.

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RESULTS

Twenty-three patients (19 men, 4 women; mean age 68 ± 14 years) were included: 13 undergoing new ICD implants and 10 requiring ICD generator replacements. All patients had ICDs manufactured by Medtronic, Inc.; however, ICD leads were from several manufacturers (Sprint Quattro Secure®, Medtronic, Inc. [15 patients]; Endotak Endurance®, Boston Scientific, Inc., Natick, MA [1 patient]; and Riata®, St. Jude Medical, Inc., St. Paul, MN [7 patients]).

With regard to EMI amplitude, there was no statistically significant difference between the 2 electrode configurations (Table 1). Nevertheless, pacing inhibition occurred during electrocautery in 22 of 23 individuals when the ICD was in the widely spaced (integrated) bipolar mode (Fig. 3). No pacing inhibition occurred when in the true bipolar mode. EMI from electrocautery was misinterpreted as VF by the ICD detection algorithm in 17 of 23 patients when the ICD was in the integrated bipolar mode (Fig. 4) and in 0 of 23 patients when in the true bipolar mode.

Table 1

Table 1

Figure 3

Figure 3

Figure 4

Figure 4

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DISCUSSION

The principal observation in this study was that when programmed to a closely spaced bipolar sensing configuration (i.e., interelectrode distance of 1–1.5 cm), ICDs were less susceptible to the adverse impact of EMI induced by unipolar electrocautery applied close to the ICD pulse generator compared with the effect of the same cautery applied when the ICD was programmed to the often-used integrated bipolar mode (i.e., wider interelectrode distance). Closely spaced bipolar sensing eliminated EMI-induced pacing inhibition and VF “oversensing” encountered with the integrated bipolar sensing configuration.

The farther apart sensing electrodes are set, the greater the susceptibility to EMI.4 Widely spaced electrodes typically cross a larger portion of the EMI voltage gradient (Fig. 2), and as a result the sensing “horizon” will be larger than is the case for more closely spaced electrode pairs.5 Consequently, in the operating room, electrocautery-induced EMI is more readily detected by the widely spaced bipolar configuration6; conversely, a closely spaced bipolar configuration is less likely to experience pacing inhibition and inappropriate sensing in the presence of electrocautery.

Typically, patients with implanted pacemakers or ICDs who are to undergo a planned operative procedure have their implanted device programmed to disable sensing in the immediate preoperative period (i.e., usually only a few hours before the procedure); this is done to permit electrocautery to be used safely (e.g., disabling sensing reduces the chance of a cautery signal triggering pacemaker inhibition or an inappropriate ICD shock).1,7,8 In this regard, although reprogramming is relatively straightforward technically, it requires that either a manufacturer's representative or a specially trained clinician/nurse be present with the appropriate (manufacturer-dependent) programmer. In the absence of appropriate expertise and/or equipment, a planned procedure may need to be delayed or canceled. Similarly, the implanted device must be programmed back to its original settings postoperatively. The need for perioperative device programming can be inconvenient, delay treatment, and increase costs. The latter is particularly likely in cases in which on-site personnel and/or programmers are not readily available (i.e., rural hospitals, emergency situations, after hours, etc.).

The observations reported herein suggest that the programming of ICDs to a closely spaced bipolar configuration well in advance (days to weeks) of a planned procedure may be useful; this step can be accomplished during regular business hours in device follow-up clinics skilled in this activity. In the case of ICDs, the sensing capability remains active (albeit somewhat less sensitive to detection of low-amplitude signals) in the closely spaced bipolar mode and thus the patient remains protected. The planned procedure can take place without need for further intervention. Postoperatively, if the attending cardiologist prefers the additional detection sensitivity offered by widely spaced sensing electrodes, the device can be programmed back to original settings in the device clinic at some convenient time.

In the future, it may be possible to effect programming steps remotely. Because most current generation pacemakers and defibrillators are already capable of communicating via telephone or Internet, a physician prescription could be used to effect a temporary programming change that would cover the planned operative date.1 Remote programming may also be helpful in emergent scenarios. A less-complex solution would be a single elective preoperative programming during a routine clinic visit with a built-in calendar-based initiation and “time out” such that the device returns to preoperative settings automatically after the procedure. The latter, of course, would not be helpful in emergencies. Finally, in the case of the ICD, a purpose-built universal simple programmer capable of assuring that the device is temporarily programmed to a true bipolar mode may be effective.

There are important limitations to this study. First, we examined a relatively small patient population with only 1 manufacturer's devices. It is possible that with other ICD models, results could differ. Furthermore, not all manufacturers offer the capability of reprogramming from widely spaced (integrated) sensing to the closely spaced bipolar modes. Second, the proposed approach does not entirely obviate device reprogramming preoperatively, but removes it from the busy operating room environment. A clinical study is needed to assess the actual utility of such a proposal, and safety during preoperative and postoperative periods of using the true bipolar sensing mode because narrower electrode spacing does diminish the sensing “horizon.” Finally, the reprogramming approach proposed herein is not immediately applicable in emergent situations. However, remote programming capability, as discussed above, may overcome this limitation because all manufacturers and many large device follow-up clinics already offer around-the-clock consultative assistance and remote follow-up service.

In conclusion, a closely spaced (“true”) bipolar sensing configuration seems to reduce the risk of implanted device malfunction caused by electrocautery-induced EMI. In the case of ICDs, reprogramming to closely spaced bipolar sensing from the frequently used integrated bipolar configuration offers several advantages: (a) programming can be undertaken in advance of the procedure and thereby eliminate the need to have programmers and/or specialized personnel present in the operating room area, (b) antitachyarrhythmia therapy and crucial pacing functions remain operative, and (c) postoperative reprogramming to baseline settings is removed from the busy operating room environment and can be delayed until a more convenient time.

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DISCLOSURES

Name: Mithun Suresh, BSEE.

Conflicts of Interest: This author has no conflicts of interest to declare.

Name: David G. Benditt, MD.

Conflicts of Interest: Dr. Benditt is a consultant for and holds equity in Medtronic, Inc., St. Jude Medical, Inc.

Name: Barbara Gold, MD.

Conflicts of Interest: This author has no conflicts of interest to declare.

Name: Girish P. Joshi, MB BS, MD, FFARCSI.

Conflicts of Interest: This author has no conflicts of interest to declare.

Name: Keith G. Lurie, MD.

Conflicts of Interest: This author has no conflicts of interest to declare.

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ACKNOWLEDGMENTS

The authors thank the nurses and technicians of the Electrophysiology Laboratories at Central Minnesota Heart Center for invaluable assistance with this project.

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REFERENCES

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3. Valleylab. Force FX™ Electrosurgical Generator Technical Specifications. Available at: http://www.valleylab.com/product/es/generators/pdf/Lforcefx.pdf. Accessed February 22, 2011
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