Switchable Faraday shielding with application to reducing the pain of internal cardiac defibrillation while permitting external defibrillation.

Switchable Faraday shielding is desirable in situations where electric field shielding is required at certain times and undesirable at other times. In this study, electrostatic finite element modeling was used to assess the effect of different shield geometries on the leakage of an internally applied field and penetration of an externally applied field. "Switching OFF" the shield by electrically disconnecting shield faces from each other was shown to significantly increase external field penetration. Applying this model to defibrillation, we looked at the effect of spacing and size of shield panels to maximize the ability to deliver an external defibrillation shock to the heart when shield panels are disconnected while providing acceptably low leakage of internal defibrillation shocks to avoid painful skeletal muscle capture when shield panels are connected. This analysis may be useful for designing internal defibrillator electrodes that preserve the efficacy of internal and external defibrillation while avoiding the significant morbidity associated with painful defibrillator shocks. Similar analysis could also guide optimizing the switchable Faraday shielding concept for other applications.

Novel electrode design for potentially painless internal defibrillation also allows for successful external defibrillation.

BACKGROUND: Implantable cardioverter defibrillators (ICDs) save lives, but the defibrillation shocks delivered by these devices produce substantial pain, presumably due to skeletal muscle activation. In this study, we tested an electrode system composed of epicardial panels designed to shield skeletal muscles from internal defibrillation, but allow penetration of an external electric field to enable external defibrillation when required. METHODS AND RESULTS: Eleven adult mongrel dogs were studied under general anesthesia. Internal defibrillation threshold (DFT) and shock-induced skeletal muscle force at various biphasic shock strengths were compared between two electrode configurations: (1) a transvenous coil placed in the right ventricle (RV) as cathode and a dummy can placed subcutaneously in the left infraclavicular fossa as anode (control configuration) and (2) RV coil as cathode and the multielectrode epicardial sock with the panels connected together as anode (sock-connected). External DFT was also tested with these electrode configurations, as well as with the epicardial sock present, but with panels disconnected from each other (sock-disconnected). Internal DFT was higher with sock-connected than control (24 +/- 7 J vs. 16 +/- 6 J, P < 0.02), but muscle contraction force at DFT was greatly reduced (1.3 +/- 1.3 kg vs. 10.6 +/- 2.2 kg, P < 0.0001). External defibrillation was never successful, even at 360 J, with sock-connected, while always possible with sock-disconnected. CONCLUSION: Internal defibrillation with greatly reduced skeletal muscle stimulation can be achieved using a novel electrode system that also preserves the ability to externally defibrillate when required. This system may provide a means for painless ICD therapy.

Internal defibrillation with minimal skeletal muscle activation: a new paradigm toward painless defibrillation.

BACKGROUND: Shock-induced pain produces substantial morbidity in recipients of implantable cardioverter-defibrillators (ICDs). This pain likely derives from activation of skeletal muscle and associated nerves in the chest and abdomen. In an effort to develop a painless defibrillation system, we designed an electrode arrangement that incorporates a conductive sock placed around the heart to confine the electric shock field to cardiac tissue. OBJECTIVES: The purpose of this study was to test whether cardiac defibrillation could be achieved without skeletal muscle activation using a novel electrode system. METHODS: Eight adult mongrel dogs were studied. Force of skeletal muscle contraction was measured by strain gauges attached to the forelimbs during delivery of internal shocks ranging in energy from 0.1 to 31 J. Biphasic shocks were delivered (1) between a right ventricular coil and a subcutaneous dummy can (standard configuration), and (2) between a left ventricular coil and an epicardial electrode sock. Internal and external defibrillation thresholds (DFTs) were determined for each electrode configuration. RESULTS: Shock-induced muscle contraction force was significantly lower using the sock electrode than with standard ICD electrodes at every shock energy level tested (P < .0001). Internal DFT was similar between electrode configurations (sock electrode: 8.6 +/- 4.2 J; standard: 11.0 +/- 6.3 J, P = .4), but muscle contraction force at DFT was greatly reduced with the new electrode system (1.8 +/- 2.0 kg vs 10.6 +/- 2.1 kg, P < .0001). The sock electrode rendered external defibrillation impossible, however, even at 360 J. CONCLUSION: Skeletal muscle activation induced by ICD shocks can be greatly reduced using an electrode system that confines the electric shock field to the heart. Refinement of this strategy may allow for delivery of painless shocks by ICDs. Further development is needed to overcome implant complexity and the higher external DFT with this type of electrode system.

Direct visualization of coronary sinus ostium and branches with a flexible steerable fiberoptic infrared endoscope.

BACKGROUND: Placement of electrophysiology catheters and pacing leads in the coronary sinus is challenging in some patients, particularly those with dilated cardiomyopathy. We hypothesized that cannulation of the coronary sinus and its branches can be facilitated by direct visualization. This study reports our experience with navigation into and within the coronary sinus in a closed-chest animal preparation, using a flexible steerable fiberoptic infrared endoscope that allows visualization through flowing blood. OBJECTIVES: The purpose of this study was to assess the feasibility of direct visualization of endocardial structures through infrared endoscopy. METHODS: Internal jugular venous access was obtained in 10 healthy mongrel dogs (weight 35-45 kg). The infrared endoscope (2900 fiber imaging bundle, wavelength 1,620 nm, frame rate 10-30/s, 320 x 256 pixels) was advanced to the coronary sinus ostium and branches by direct visualization of anatomic landmarks, such as the tricuspid valve and inferior vena cava. Localization was confirmed by fluoroscopy, contrast injection, and pathologic examination. RESULTS: Structures such as the tricuspid valve and inferior vena cava were visualized at distances of 1 to 2 cm, allowing successful coronary sinus identification and engagement in all 10 dogs. Coronary sinus branch images closely resembled pathologic findings. CONCLUSION: Direct visualization of the coronary sinus ostium and branches is possible through infrared endoscopy. This technique likely will facilitate coronary sinus engagement and navigation for pacing lead and catheter placement.