EP Lab Digest - May 2008 - (Page 54)

54 EP CASE STUDY MAY 2008 Suspected Shunting of Defibrillation Energy in the EP Lab: A Case Study of Multiple-shock Incidents Using Biphasic External Defibrillators Following Induced Ventricular Fibrillation Michael L. Arnold, RN Tucson, Arizona A 15A B 7.5A 95% 90% 0.75A transcardiac current 0.75A transcardiac current Figure 1. Diagram demonstrating the effect of shunting in the face of low transthoracic resistance resulting in high transthoracic current and greater energy diversion (Panel A). Panel B shows high transthoracic resistance. Note that a 50% decrease in transthoracic current (in Amps) is possible through a 5% reduction in shunting (values in red box). (Reprinted with permission from EP Lab Digest 2002;3:1–7) Patient #1: The first patient was a 43-year-old male, of medium to large build (weight: 94.9 kg, height: 182 cm, BMI: 27.6) with a medical history of previous myocardial infarction with no evidence of acute ischemia or history of anti-arrhythmic drug therapy. Ventricular fibrillation was induced during an electrophysiology study to evaluate a syncopal episode. The patient required three high-energy shocks at the manufacturer’s recommended dose of 150 joules in immediate succession with defibrillator pads in anterior-posterior configuration in proper position as designated on the packaging for the pads. The third delivered shock, at 150 joules, successfully defibrillated the patient. Rhythm strips printed by the device showed the following information: • Shock #1: 150-J selected, 155-J delivered; impedance 100.6 ohms; 17.1 Amps • Shock #2: 150-J selected, 155-J delivered; impedance 98.5 ohms; 17.8 Amps • Shock #3: 150-J selected, 155-J delivered;impedance 100.1 ohms;17.7 Amps Patient #2: The second patient was a 66-year-old male of large build (weight: 100 kg, height: 183 cm, BMI: 29.9) with a medical history of coronary artery disease free of acute ischemia and no history taking antiarrhythmic drugs.Ventricular fibrillation was also induced during stimulation in an electrophysiology study. This patient was given three high-energy shocks (200-J) in immediate succession. Chest compressions were performed briefly by an EP staff member efibrillation using biphasic energy delivery is quickly becoming the standard in the acute care setting. The major defibrillator manufacturers are racing to convert their product lines, and the models generating monophasic waveforms are becoming extinct. This shift has been based, in large part, upon a study published in Circulation in 2000 by Schneider et al; their research showed that within the first shock series, 98% of ventricular fibrillation (VF) patients were defibrillated with 150-J biphasic shocks, compared with 69% of patients defibrillated with 200- to 360-J monophasic shocks.1 The results of this and other studies prompted the American Heart Association to adopt the use of biphasic waveform defibrillation as a Class IIa intervention2 and make it part of the most current Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiac Care. D In keeping with the AHA recommendations, our electrophysiology lab, which performs over 1,000 studies and device implants each year, upgraded to biphasic defibrillators in August of 2007 as part of a hospital-wide changeover. Like most EP labs, a portion of our procedure volume includes studies to evaluate patients for VT/VF as an indication for ICD implantation. External defibrillation is used as second-line therapy for patients in whom VT or VF is induced during EP studies or during defibrillation threshold testing post ICD implant. Our previous protocol was to deliver 360-J of monophasic energy in situations during EP studies when the patient could not be paced out of VT, VF was induced, or when defibrillation by an ICD was unsuccessful on its second attempt.The 360-J monophasic dose was known to have a negligible failure rate for first-shock defibrillation success in the controlled setting of our EP lab. As stated earlier, biphasic defibrillators demonstrated a 98% success rate, with 96% success on the first shock in the out-of-hospital setting of VF, despite the average time down prior to first attempted defibrillation being 8.9 ± 3.0 minutes.1 Because of these results and our previously high success rate with the monophasic defibrillators, the EP staff and physicians were alarmed when the first patient we were forced to externally defibrillate with the new units required three 150-J shocks in immediate succession. The physician on the case called the manufacturer directly to discuss pad placement (which was anterior-posterior) and energy selection, and confirmed they were in accordance with their recommendations. The service representative suggested alternate site pad placement (anterior-apical) and assured the physician that there was no proven increase in efficacy with 200-J shocks,but again offered this as an alternative. When the same physician had a patient that required four shocks at 200-J eight days later, in a different electrophysiology suite using a different unit of the same model biphasic defibrillator, the products were pulled from the department and the manufacturer was contacted for further investigation. Figure 2. “Type CF [cardiac floating] Defibrillation Proof” symbol, which must be indicated on each point of connection to the patient based on newer safety guidelines. Editor’s Note:This article underwent peer review by one or more members of EP Lab Digest’s editorial board. Figure 3. Cooke’s diagram, showing “Waveform adjustment for various levels of transthoracic impedance. Increased transthoracic impedance is addressed by waveform customization rather than escalating energy. Note that low impedance requires higher peak current to address greater shunting in that circumstance.”3 (Reprinted with permission from EP Lab Digest 2002;3:1–7)

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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