Mark W. Kroll

Present Understanding of Shock Polarity for Internal Defibrillation: The Obvious and Non-Obvious Clinical Implications

Background: Uncertainty about the best electrode configuration has combined with the programming flexibility in modern implantable cardioverter‐defibrillators (ICDs) to result in routine polarity reversal during an implant to deal with a high defibrillation threshold (DFT). We feel that this practice is not always supported by the clinical data and the present scientific understanding of defibrillation.

“Tuned” Defibrillation Waveforms Outperform 50/50% Tilt Defibrillation Waveforms: A Randomized Multi-Center Study

Introduction: A superior performance of a tuned waveform based on duration using an assumed cardiac membrane time constant of 3.5 ms and of a 50/50% tilt waveform over a standard 65/65% tilt waveform has been documented before. However, there has been no direct comparison of the tuned versus the 50/50% tilt waveforms.

Does an SVC electrode further reduce DFT in a hot-can ICD system?

Pectorally implanted ICDs that defibrillate with the RV electrode and the ICD housing have gained clinical acceptance. However, it is still debatable whether adding an SVC electrode connected to the housing will further reduce the threshold of defibrillation (DFT). This study utilized eight pigs. DFTs were measured with a 50 V step‐down protocol starting at 650 V (20 J). Shock strength for 50% success (E50) was estimated with the average of three reversals. In addition to a dummy device, Lead I (Pacesetter Models 1558 and 1538) or Lead II (Endotak 72) were used. Leads I are active fixation, true bipolar sensing with 5‐cm shocking coils. Lead II has an integrated bipolar sensing with a 4.7‐cm RV and 6.9‐cm SVC shocking coils. A 95 μF defibrillation system was used to deliver a 44% tilt tuned biphasic 1.6/2.5 ms waveform, and to measure lead impedance. The RV electrode was the anode during phase I. With Lead I RV → CAN the DFT was 531 ± 75 V (13.6 ± 3.8 J) and the E50 was 496 ± 89 (12 ± 4.3 J). These were not significantly (NS) different than the DFT for RV → CAN and SVC which was 518 ± 84 V (13 ± 4.2 J) or the E50 which was 476 ± 84 V (11 ± 3.9 J). Similar results were obtained with Lead II. Despite a decrease in lead impedance there was no apparent benefit from the addition of the SVC electrode. Lead I provided equivalent DFT performance to Lead II.

Theoretical possibility of ventricular fibrillation during use of TASER neuromuscular incapacitation devices

Introduction: TASER devices deliver electrical pulses that temporarily incapacitate suspects. This study analyzes the theoretical possibility of ventricular fibrillation (VF) induction by TASER currents.

Plateau waveform shape allows a much higher patient shock energy tolerance in AF patients.

Objectives: To evaluate the possible pain reduction of the plateau waveform in atrial fibrillation (AF) patients.

Medical safety of TASER conducted energy weapon in a hybrid 3-point deployment mode

Introduction: TASER conducted energy weapons (CEW) deliver electrical pulses that can temporarily incapacitate subjects. The goal of this paper is to analyze the distribution of TASER CEW currents in the heart and surrounding organs and to understand theoretical chances of triggering cardiac arrhythmias, of capturing the vagus and phrenic nerves and producing electroporation of skeletal muscle structures. The CEW operates in either probe mode or drive-stun (direct contact) mode. There is also a hybrid mode in which current is passed from a single probe to either or both of 2 drive-stun electrodes on the weapon, presumed to be in direct contact with the skin. Methods and Results: The models analyzed herein describe strength-duration thresholds for myocyte excitation and ventricular fibrillation (VF) induction. Finite element modeling (FEM) was used to approximate current density in the heart for worst-case TASER electrode placement. The FEMs theoretically estimated that maximum TASER CEW current densities in the heart and in neighboring organs are at safe levels. A 3-point deployment mode was compared to probe-mode deployment. The margins of safety for the 3-point deployment were estimated to be as high as or higher than for the probe-mode deployment. Conclusion: Numerical modeling estimated that TASER CEWs were expected to be safe when deployed in 3-point mode. In drive-stun, probe-mode or 3-point deployments, the CEWs had high theoretically approximated safety margins for cardiac capture, VF, phrenic or vagus nerve capture and skeletal muscle damage by electroporation.

Energy steering of biphasic waveforms using a transvenous three electrode system.

The optimal electrode configuration for endocardial defibrillation is still a matter of debate. Current data suggests that a two pathway configuration using the right ventricle (RV) as cathode and a common anode constituted by a superior vena cava (SVC) and a pectoral can (C) is the most effective combination. This may be related to the more uniform voltage gradient created by shocks delivered using this configuration. We hypothesized that more effective waveforms could be obtained by varying the distribution of the shock current between the two pathways of a three electrode endocardial defibrillation system. In 12 pigs, we compared the characteristics and the defibrillation efficacy of six biphasic waveforms discharged using either a two (RV → C) or a three (RV → SVC + C) electrode combination with the following configurations: Configuration 1 (W1): the RV apical coil was used as a cathode and the subcutaneous C as anode (RV → C). Configuration 2 (W2): The RV was used as cathode and the combination of the atriocaval coil (SVC) and the subcutaneous C as anode (RV → SVC + C). Configuration 3 (W3): The RV → C was used for the first 25% off + and RV → SVC + C for the remainder of the discharge including f 2. Configuration 4 (W4): The RV → C was used for the first 50% off + and RV → SVC + C for the remainder of the discharge including f 2. Configuration 5 (W5): The R V → C was used for the first 75% off + and RV → SVC + C for the remainder of the discharge including f 2. Configuration 6 (W6): The RV → C was used for f + and RV → SVC + C for f2. As an increasing fraction of the waveform was discharged using the RV → SVC + C pathways, the impedance and the pulse width decreased while the tilt, the peak, and the average current significantly increased. The waveforms delivered using the RV → SVC + C configuration for 100% or 75% of their duration had significantly lower stored energy DFT than the other waveform. Current distribution between three endocardial electrodes can be altered during the shock and generates waveforms with different characteristics. Shocks with 75% or more of the current flowing to the RV → SVC + C required the lowest stored energy to defibrillate. This method of energy steering could be used to optimize current delivery in a three electrodes system.

Multi-organ effects of Conducted Electrical Weapons (CEW) — A review

Since the introduction of the Conducted Electrical Weapons (CEW) several studies have been conducted and multiple reports have been published on safety of these devices from a medical point of view. Use of these devices in different situations and reported deaths attracts media attention and causes general anxiety around these devices. These devices have several limitations- such as rate of fire or maximum effective range in comparison to fire arms. Here we wish to review medical publications regarding the safety of these devices based on different systems.