EP Lab Digest - May 2008 - (Page 55)

MAY 2008 EP CASE STUDY 55 The manufacturers of all these systems we use need to study this further to analyze what role, if any, their particular product plays in this, and to help identify the cause. (for less than 1 minute), after which a fourth shock at 200 joules was able to successfully defibrillate patient. Rhythm strips printed by the device showed the following information: • Shock #1: 200-J selected, 204.6J delivered; impedance 76.2 ohms; 25.6 Amps • Shock #2: 200-J selected, 203.9J delivered; impedance 74.7 ohms; 26.6 Amps • Shock #3: 200-J selected, 204.0J delivered; impedance 74.7 ohms; 26.7 Amps • Shock #4: 200-J selected, 203.4J delivered; impedance 69.9 ohms; 28.3 Amps and further bench testing, which was indeterminate. At that point they decided that an additional evaluation of the EP lab environment was necessary, and an engineer returned once again in January of 2008 to perform additional tests on the equipment. Their findings, although still inconclusive, indicated that “defibrillation current was likely being shunted away from the patient due to other connections that were incompatible with defibrillation energy.” Discussion Shunting of defibrillation energy is not a phenomenon that is unique to biphasic waveform defibrillators.In this setting,shunting refers to the diversion of energy through non-myocardium on its path from one defibrillator pad to the other. Although it may seem counterintuitive, the lower the chest wall impedance, the less current travels through the ventricles. Instead, the flow of energy diffuses through the entire area of thorax between the pads, which requires a greater peak current to be delivered (Figure 1). Conversely, the more resistance that is offered by these non-cardiac structures, the more current is preferentially directed through the heart, which literally becomes a See DEFIBRILLATION ENERGY page 57 Follow-up Testing Following each multiple shock episode, the defibrillator was inspected by the hospital’s Biomedical Engineering Department and found to be functioning properly. Unit settings and calibrations were verified using test shocks and measuring equipment in parallel to the defibrillator, but no evidence of device failure could be found. Pads used in these cases were the defibrillator manufacturer’s brand and the recommended model. They were retained and checked, but appeared to be free of defect to our biomed staff and the manufacturer. The electronically recorded event logs in the defibrillator units were downloaded and shipped to the manufacturer for review by their clinical, algorithm, and engineering staff. The manufacturer arranged to send engineers out to our facility in an attempt to determine the cause of the multiple shock episodes we experienced. In September of 2007, engineers from the defibrillator manufacturer visited our EP lab to observe the use of the model and identify all of the equipment being used within the lab in conjunction with the defibrillators. Review of the event logs and the results of the testing that was done showed that the defibrillators were working as designed/intended and performing to specifications. Following this visit, they requested a set of each cable we connected to the patient during these EP studies for impedance measurements http://www.atricure.com/ORLab

Table of Contents Feed for the Digital Edition of EP Lab Digest - May 2008

EP Lab Digest - May 2008 Is There an Under-Referral of Women for Atrial Fibrillation Ablation? A Hybrid Approach to the Cure of Atrial Fibrillation Contents Letter from the Editor Spotlight Interview: University of Michigan Health System 10-Minute Interview: Amit J. Shanker, MD Modular EP Units: Are They Possible? One Hospital’s Experience All About My Job: Technician Supervisor (New Column!) Alcohol Septal Ablation in the Cath Lab: What is it All About? About the Canadian Heart Rhythm Society: Interview with Martin J. Gardner, MD, FRCP(C), FACC Email Discussion Group: May 2008 Second Annual Salary Survey My First Year in Electrophysiology: What Have I Got Myself Into? Highlight on Technology: Video-Audio Integration for the EP Lab On the Horizon: A New Remote Catheter Manipulation System Striving for Excellence in the Care of Cardiac Patients Five Reasons to Participate with a Professional Organization Suspected Shunting of Defibrillation Energy in the EP Lab Can Digital Music Players Cause Interference with Implantable Devices? ECG 101: Ambulatory ECG Monitoring Events Calendar Industry News and Products Classifieds Advertisers Index

EP Lab Digest - May 2008

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