From the Mercury Capillary Electrometer to the Wireless, Battery-Less Pacemaker: State-of-the-Art Innovations in the Treatment of Arrhythmia

In this article, we provide a brief review of the historical progression of cardiac electrophysiology as well as highlight recent developments in our research lab to advance the treatment of arrhythmia.

Background of Cardiac EP

Electrocardiogram
In 1887, Augustus Waller recorded the first human electrocardiogram (ECG) with a mercury capillary electrometer, which consisted of a single fine-draw glass tube that was filled with mercury and immersed in sulfuric acid.¹ This instrument was capable of recording the body’s surface voltage changes on photographic paper, which was detected by moving the mercury in response to potential electrical changes.² 

New Developments in EP

Myocardial ischemia reduces myocardial conduction velocity, which causes conduction block and ventricular tachycardia. Our team previously showed that carbon nanotube fibers (CNTFs), developed at Professor Matteo Pasquali’s lab at Rice University, have the unique properties of electrical conductivity along with flexibility and fatigue resistance. When sewn across epicardial scar in a surgical sheep model, CNTFs restore physiologic transmyocardial conduction velocity through myocardial scar (Figure 1). In recent experiments performed at the Texas Heart Institute and at the University of Sassari, Mark McCauley (currently at the University of Illinois at Chicago) and our colleague Professor Lucia Gemma Delogu studied the toxicity profile of CNTF in living systems. To determine the biocompatibility and non-toxicity of CNTF in organic systems, CNTF interaction with human whole blood was evaluated (ex vivo) — including in mice — for up to three months. These ex vivo and in vivo studies showed that CNTF did not cause significant inflammatory tissue response, foreign body reaction, or excessive growth of fibrous tissue. Thus, CNTF was demonstrated to be a unique conductive and biocompatible material to restore electrical conduction in diseased myocardium; it may provide a long-term treatment solution for diseased and electrically excitable tissues. In 2015, Drs. Pasquali and Medhi Razavi were recognized for their work with a Collaborative Sciences Award from the American Heart Association (AHA).

In our study, we explored the use of an original device to deform the esophagus and continually monitor luminal temperature to prevent atrio-esophageal fistula complications. A modified nasogastric tube (18 Fr) (Figure 2) was placed in the esophagus of porcine and ovine cadavers to deform the esophagus and monitor the internal temperature of the esophagus. The extent of deformation of the esophagus was calculated in situ and in excised specimens. The native size of the esophagus was found to be 18.5 ± 4.1 mm. Placement of the device and applying suction through the openings on the tube reduced the width to 13.1 ± 2.3 mm. Deformation of the esophagus was easily achieved by use of the modified nasogastric tube. This finding has paved the way to the possibility of further developing simple devices to protect the esophagus during RF ablation.

Novel wireless pacing devices have allowed physicians to reduce the complications associated with traditional pacemaker leads¹⁶; however, wireless pacing mechanisms are still dependent on an incorporated battery, which increases the overall bulk and size of the device. This size restriction may lead to limited placement location and increased risk of dislodgement and embolism.¹⁶ We are working with several professors — primarily Dr. Aydin Babakhani (who developed the technology) and Dr. Behnaam Aazhang from Rice University Electrical and Computer Engineering, as well as Dr. Farshad Raissi at UCSD — to develop a wireless, battery-less pacemaker system that harvests energy from RF radiation transmitted by an external battery pack.¹⁷ Recently, we tested the feasibility of a wirelessly powered microchip that can be implanted directly into the heart to capture ventricular myocardium. A microchip (4 x 1 mm), which was placed on a 16 x 3.8 mm printed circuit board, was utilized to provide pacing to an ovine model (Figure 3). The microchip had an on-chip receiving antenna to receive incoming radiofrequency (GHz), and converted the electromagnetic signal from AC to DC power. The generated power was then stored briefly in a capacitor and outputted using a digital switch. The standard pacing leads were sutured to the epicardial surface to pace the heart. A decapolar catheter was sutured on the ventricle to characterize the electrophysiology of the heart, and the LABSYSTEM PRO EP Recording System (Boston Scientific) was used to collect data from this catheter. The result of this study showed that with an output of 1.3V and pulse-width of 2 ms, this innovative new pacemaker — without the need for an on-board battery — was capable of epicardial capture at various cycle lengths in an ovine model. These findings support the possibility of developing a pacemaker with improved overall function that poses far less complications. 

References

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12. Chavez P, Messerli FH, Casso Dominguez A, et al. Atrioesophageal fistula following ablation procedures for atrial fibrillation: systematic review of case reports. Open Heart. 2015;2:1-9.
13. Gilcrease GW, Stein JB. A delayed case of fatal atrioesophageal fistula following radiofrequency ablation for atrial fibrillation. J Cardiovasc Electrophysiol. 2010;21:708-711. 
14. Mateos JC, Mateos E, Peña TG, et al. Simplified method for esophagus protection during radiofrequency catheter ablation of atrial fibrillation--prospective study of 704 cases. Rev Bras Cir Cardiovasc. 2015;30(2):139-147. 
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16. Bernard ML. Pacing Without Wires: Leadless Cardiac Pacing. Ochsner J. 2016;16(3):238-242. 
17. Texas team debuts battery-less pacemaker. Rice University News & Media. Published June 5, 2017. Available online at https://news.rice.edu/2017/06/05/texas-team-debuts-battery-less-pacemaker/. Accessed July 12, 2017.