Real-time monitoring of an implantable cardiac device during taser device discharge

Introduction

Key Teaching Points.

• •Electronic control devices (ECD) deliver electrical impulses to the body that can be detected by modern implantable cardiac devices.
• •Health care professionals and law enforcement professionals should be aware of potential interaction between these two increasingly prevalent electronic systems.

Taser™ (Axon Enterprise, Inc, Seattle, WA) and other electronic control devices (ECD) are near-ubiquitous law enforcement tools that use darts fired from a handgun-shaped device to deliver an electrical shock to a human with the intention of nonlethal muscular tetany and incapacitation. A commonly used device discharges 2,000 volts in short pulses of around 0.110 ms at a frequency of 19–22 Hz, delivering a current of approximately 2.1 mA.^1,2 To our knowledge, the real-time effects of ECD exposure on an implantable cardiac device (CIED) have not been described. Herein, we present our findings of simultaneous interrogation of a cardiac resynchronization therapy pacemaker while being intentionally subjected to ECD discharge under the supervision of a physician as part of required training for law enforcement.

Case report

A 24-year-old male subject with a history of tetralogy of Fallot, status post transannular patch repair and pulmonic valve repair, complicated by complete heart block, had a normally functioning Percepta Quad™ cardiac resynchronization therapy pacemaker (Medtronic, Minneapolis, MN) implanted in 2019. He decided to train to become a law enforcement officer in the state of Georgia, which requires recruits to be shot with an ECD in a controlled environment in order to carry the device in the field. After lengthy discussions with his congenital cardiac team and his training agency, arrangements were made for his treating electrophysiologist and clinical team to be present with real-time interrogation of his device at the time of this exposure to monitor his heart rhythm and address any potential issues the impulse may have had on the CIED.

At baseline, his underlying rhythm was sinus with complete AV block and a junctional escape at 40 beats/min. Impedance values, sensing (4.4 mV p waves, 20 mV r waves), and capture thresholds were normal and stable just prior to ECD delivery. Since the patient had a reliable junctional escape, the device was programmed DDDR 60–180 with bipolar sensing to examine for evidence of electromagnetic interference (EMI) on all channels (0.45 mV atrial, 2.8 mV ventricular). This programming was similar to his chronic settings. Recruits are asked to lie prone on a mat and are assisted by 2 officers for ECD delivery. They are required to state their name and unit number to acknowledge agreement to receive ECD delivery, which was done at 9:37 AM by our patient. Electrograms shown in Figure 1 reveal expectant sinus tachycardia at this time. The electrode barbs were deployed to the patient’s posterior thigh and mid paraspinal region and ECD shock was delivered. At the onset of delivery, atrial oversensing of the EMI was instantly detected by the device (red arrow), triggering mode switch behavior. Ventricular sensed events were noted that appeared to be true ventricular events rather than oversensing (black arrow). Discrete spikes were seen on the right ventricular bipolar pacing channel (top), atrial bipolar pacing channel (middle), and left ventricular / can channel (bottom). These occur at a frequency of about 20 Hz (inset), which is similar to manufacturer’s specifications. After several seconds of delivery, normal pacing function (mode switched followed by DDDR) and stable electrical parameters were observed.

Figure 1.

Top panel shows device settings and measured sensitivity prior to the exposure. Main panel shows sinus tachycardia with biventricular pace tracking followed by the electromagnetic interference (EMI), recognized as atrial tachyarrhythmia triggering mode switch at the onset of taser shock (red arrow). This occurred simultaneously with taser discharge. Two ventricular sensed events were also noted (black arrows), which were characteristic of true ventricular events and distinct from the EMI signal. EMI from the taser (blue inset) had a frequency of spikes that was in the range of reported duty cycles of this device.

Discussion

We describe the first report, to our knowledge, of a monitored interrogation of a CIED during ECD delivery. The case reveals 2 key findings. First, we show that the ECD impulses are readily detected by sensing channels at nominal settings and would be potentially dangerous to those receiving ECD shocks in the field owing to the potential of asystole in pacemaker-dependent patients or inappropriate implantable cardioverter-defibrillator (ICD) shocks in those with ICDs. While the amplitude of the EMI in this example did not register on the ventricular sense amplifier, different sensing configurations and autogain features in defibrillator sensing circuits would increase the risk of inappropriate sensing. Subcutaneous ICDs would be expected to exhibit particular vulnerability to oversensing from this form of electromagnetic interference given the larger sensing fields compared to an intracardiac bipolar configuration. Our patient’s example highlights the importance of short (3–5 seconds) and isolated ECD shock duration on the part of law enforcement to mitigate this risk to the population at large. Generally, the programming of ECD devices is such that a single trigger pull yields a programmed short burst, but holding of the trigger can yield prolonged discharges.¹ We feel that the findings of this case are generalizable across all well-known models of ECD that use fired darts and deliver high-voltage impulses. An example of the output from 1 ECD device is as follows: pulse charge 63 microcoulombs, pulse rate 22 Hz, pulse duration 45 microseconds, current delivered per pulse 0.0015 A, energy per pulse 0.104 J, peak voltage range 1500–2600 V (Physical Assessment of TASER 7, Defense Science and Technology Laboratory – Counter Terrorism and Security, March 2020). Finally, sensed ventricular events were observed during the ECD shock that were not present before or after the delivery. These events seem to be true ventricular events rather than EMI from the characteristics of the device.

There are a number of reports of subjects suffering cardiac arrest shortly after receiving or during shocks, with a suggestion that the location of the darts on the chest, and therefore the current path of the applied impulse, has an impact on the risk of dangerous arrhythmias.^1,3 Additionally, animal studies have shown myocardial capture from energies and duty cycles similar to those in use.⁴ In this case, the ECD probes were deployed in the patient’s posterior thigh and mid paraspinal region, an area with a lower risk of electrical capture compared to thoracic discharges, given the fact that his heart was not directly within the electrical vector of the discharge.^1,5 Electrocardiographic effects before, during, and after ECD shock have also been reported.⁶ These ventricular events could represent ectopy due to the physiologic stress of the shock, but were within seconds of delivery and were not observed during his sinus tachycardia leading up to exposure. It is entirely plausible, therefore, that these events represent myocardial capture by the ECD discharge. It is not surprising that device function was unaltered in any permanent way from the ECD, given the total energy is far less than a cardioversion, which is accepted as safe in those with CIEDs.

Conclusion

In this first report of real-time monitoring during ECD/taser exposure, we directly demonstrate prominent EMI from ECD devices, which highlights the need for caution for use of these devices on those with CIEDs.