“I’m Clear, You’re Clear, Everybody’s Clear”
A Tradition No Longer Necessary for Defibrillation?
In emergency defibrillation of ventricular arrhythmias or elective cardioversion of atrial arrhythmias, a potent electric shock is passed through the torso of the patient to briefly terminate all electrical activity and allow an organized, perfusing rhythm to emerge. The electric shock is administered via electrodes placed on the patient’s chest, usually in anterior-apical or anterior-posterior positions. For many years, hand-held paddle electrodes were pressed by a rescuer against the patient’s chest; more recently, pregelled self-adhesive electrode pads with nonconductive backing have achieved widespread use.
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Possible danger to a rescuer compressing the chest or simply touching a patient who is receiving a defibrillating shock has long been recognized; stray electric current passing through a rescuer could possibly induce a lethal arrhythmia. Such danger would be heightened if the rescuer were simultaneously in contact with highly conductive material (ie, body fluids or leaking or disrupted intravenous fluid cannulas). To avoid this hazard, generations of rescuers, from lay persons to cardiologists, have been instructed to “clear” the patient before shock delivery.1,2 Physical separation of the rescuer from the patient ensures that no electric current will inadvertently enter the rescuer’s body and thereby ensures safety. But in clearing the patient, chest compressions are necessarily interrupted. Such interruptions are undesirable; they degrade the quality of cardiopulmonary resuscitation and are contrary to the 2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care, which call for minimizing interruptions to chest compression.1
In this issue of Circulation, Lloyd et al3 report a clinical experiment of direct relevance to this dilemma. The subjects were patients undergoing elective cardioversion for atrial arrhythmias or electrophysiological study likely to require external defibrillation or cardioversion. The physician coinvestigators simulated chest compressions by placing their hands on the patient’s chest; polyethylene medical gloves were worn. Twenty pounds of downward force were applied. An electric connection between the “rescuer” and the patient was established allowing a return pathway for leakage current across a rescuer; the patient being shocked was thereby the voltage source and the rescuer the load. The leakage current and voltage across the rescuer were measured during biphasic waveform shock delivery at energies of 100 to 360 J.
None of the physician rescuers sensed any shock. The mean leakage current measured was low, 283±140 μA (range 19 to 907 μA). The authors point out that this mean current is below the average amount of current exposure from a home body-fat monitoring scale (500 μA) or that used in cardiac impedance plethysmography. It is also below several safety standards for leakage current from medical equipment. Voltage differences between the investigator’s wrist and thigh were also low.
This experiment is in the great medical tradition of self-experimentation where physician investigators assume an unknown risk to themselves. Were courses in the History of Medicine required (rather than elective) in all medical schools, every cardiologist would be familiar with the epochal experiments of Werner Forssmann, the first physician to catheterize a human heart: his own. In 1929, in Germany, Forssmann was determined to demonstrate that a catheter could be safely introduced into the human heart, as had already been done in horses. Defying direct instructions from his superior, Forssmann secretly inserted a ureteral catheter into his arm, advanced the catheter, and assisted by a nurse, walked down a flight of stairs to the x-ray department. The chest x-ray clearly showed the catheter in the right atrium; the image has been reproduced in many cardiology texts. Forssmann survived, and his brave experiment laid the foundation on which Andre Cournand and Dickinson Richards developed the technique of clinical cardiac catheterization at Bellevue Hospital in New York in the 1940s. The 3 physicians ultimately shared the Nobel Prize for their work. This entire story is eloquently recounted in Lawrence K. Altman’s Who Goes First? The Story of Self- Experimentation in Medicine4 which should be required reading for every physician-investigator. Mindful of the risks of experimentation to both investigator and subject, Rosalyn Yalow, another Nobel Prize awardee, said, “In our laboratory, we always used ourselves because we are the only ones who can give truly informed consent.”5
So, should we no longer clear the patient who is about to be defibrillated? Should chest compressions be continued through defibrillation?
Some caveats apply. The investigators in the study of Lloyd et al3 wore gloves, which would provide insulation against electrical current flowing through the rescuers; in the real world, gloves are not always available or worn. The shocks were delivered through self-adhesive pregelled pad electrodes; although these are preferred (and are universally available on automated external defibrillators), hand-held paddle electrodes have not disappeared from manual defibrillators and are still used. The authors point out the hazards of using such electrodes: arcing due to inconsistencies in electrode location and contact and variability in the distribution of electrode gels or pastes applied to the metallic discs of the paddles, leading to stray electric currents. Patients should still be cleared when hand-held paddle electrodes are used.
Defibrillating shocks typically cause a powerful tetanic contraction of skeletal muscles. If a rescuer is forcibly compressing the chest at the moment of shock delivery, could the combined force of the downward compression from the rescuer plus the upward heave of the patient (typically resulting from the shock-induced tetanic contraction) result in severe trauma to the victim (rib fractures, flail chest), the rescuer (wrist or arm fractures), or both?
The study by Lloyd et al3 should lead the American Heart Association to consider a modification of the 2005 Guidelines: Chest compressions may be safely continued through defibrillation provided that self-adhesive pad electrodes are used and gloves are worn. Clinical experience will tell if injuries to patients or rescuers result when chest compression and defibrillation occur simultaneously; perhaps a registry of such injuries may be appropriate. The happy result of such a Guidelines change would be to advance the cause of achieving “effective” chest compressions during CPR: push hard, push fast, minimize interruptions.1
The opinions expressed in this article are not necessarily those of the editors or of the American Heart Association.
2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Part 5: Electrical therapies. Circulation. 2005;112 (Suppl) IV-35–IV-46.
American Heart Association. BLS for Healthcare Providers. Dallas, Tex. American Heart Association; 2006:32.
Lloyd MS, Heeke B, Walter PF, Langberg JJ. Hands-on defibrillation; An analysis of electrical current flow through rescuers in direct contact with patients during biphasic external defibrillation. Circulation. 2008; 117: 2510–2514.
Altman LK. Who Goes First? The Story of Self-Experimentation in Medicine. Berkeley, Calif. University of California Press; 1998: 38–52.
Altman LK. Who Goes First? The Story of Self-Experimentation in Medicine. Berkeley, Calif. University of California Press; 1998: 314.