This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Swerdlow, C. D. Articles by Laks, M. Search for Related Content PubMed PubMed Citation Articles by Swerdlow, C. D. Articles by Laks, M. Related Collections Arrhythmias, clinical electrophysiology, drugs CPR and emergency cardiac care

(Circulation. 1999;99:2559-2564.)
© 1999 American Heart Association, Inc.

Clinical Investigation and Reports

Cardiovascular Collapse Caused by Electrocardiographically Silent 60-Hz Intracardiac Leakage Current

Implications for Electrical Safety

Charles D. Swerdlow, MD; Walter H. Olson, PhD; Mark E. O'Connor, BS; Donna M. Gallik, MD; Robert A. Malkin, PhD; Michael Laks, MD

From the Division of Cardiology, Cedars-Sinai Medical Center, Los Angeles, Calif (C.D.S., D.M.G.); Medtronic Inc, Minneapolis, Minn (W.H.O., M.E.O.); the Joint Department of Biomedical Engineering at The University of Memphis and the University of Tennessee-Memphis, Memphis, Tenn (R.A.M.); and the Division of Cardiology, Harbor-UCLA Medical Center, Torrance, Calif (M.L.).

Correspondence to Charles D. Swerdlow, MD, 8635 W Third St, Suite 1190 W, Los Angeles, CA 90048. E-mail swerdlow{at}ucla.edu

Background—The national standard for safe 60-Hz intracardiac leakage current under a single-fault condition is 50 µA. This standard is intended to protect patients from alternating current (AC) at levels below the threshold for sensation, but the minimum unsafe level for AC in closed-chest humans is not known. To determine this value, we studied 40 patients at testing of implantable cardioverter-defibrillators using a programmable source of 60-Hz AC.

Methods and Results—We applied AC for 5-second test periods in increasing strengths until ventricular fibrillation (VF) was induced or 1 mA was reached. Two current paths were tested: bipolar, between tip and ring electrodes of a right ventricular pacing catheter, and unipolar, from tip to a remote electrode. We observed a characteristic sequence of 3 responses as AC was increased: (1) intermittent ventricular capture with QRS morphology identical to pacing through the electrodes (minimum value, 20 µA); (2) continuous capture at cycle length 282±88 ms (minimum value, 32 µA); and (3) VF persisting after AC termination (minimum value, 49 µA). Continuous capture caused loss of pulsatile arterial pressure and cardiovascular collapse (mean arterial pressure, 32±8 mm Hg) for the duration of AC with no ECG evidence of AC stimulation. Thus, the clinical picture was that of hypotensive ventricular tachycardia (VT). The continuous-capture threshold was 50 µA in 9 patients (22%) for bipolar AC and in 5 (12%) for unipolar AC. All patients showed continuous capture over a wide range for both bipolar AC (68±18 to 216±238 µA) and unipolar AC (84±27 to 278±226 µA).

Conclusions—Leakage current causes cardiovascular collapse at levels below the VF threshold. Stimulation by silent AC that is neither felt nor visible on the ECG presents as hypotensive VT. In patients with intracardiac electrodes, leakage current less than or equal to the present standard of 50 µA may cause VT or VF. The safety standard for leakage current lasting 5 seconds should be 20 µA. This standard should be based on the continuous-capture threshold.

Key Words: electrical stimulation • fibrillation • tachyarrhythmias

This article has been cited by other articles:

				M. S. Lloyd, B. Heeke, P. F. Walter, and J. J. Langberg Hands-On Defibrillation: An Analysis of Electrical Current Flow Through Rescuers in Direct Contact With Patients During Biphasic External Defibrillation Circulation, May 13, 2008; 117(19): 2510 - 2514. [Abstract] [Full Text] [PDF]

				A. H. Kadish, A. E. Buxton, H. L. Kennedy, B. P. Knight, J. W. Mason, C. D. Schuger, C. M. Tracy, W. L. Winters Jr, A. W. Boone, M. Elnicki, et al. ACC/AHA Clinical Competence Statement on Electrocardiography and Ambulatory Electrocardiography: A Report of the ACC/AHA/ACP-ASIM Task Force on Clinical Competence (ACC/AHA Committee to Develop a Clinical Competence Statement on Electrocardiography and Ambulatory Electrocardiography) Endorsed by the International Society for Holter and Noninvasive Electrocardiology Circulation, December 18, 2001; 104(25): 3169 - 3178. [Full Text] [PDF]

				A. H. Kadish, A. E. Buxton, H. L. Kennedy, B. P. Knight, J. W. Mason, C. D. Schuger, C. M. Tracy, W. L. Winters Jr, A. W. Boone, M. Elnicki, et al. ACC/AHA clinical competence statement on electrocardiography and ambulatory electrocardiography: A report of the ACC/AHA/ACP-ASIM Task Force on Clinical Competence (ACC/AHA Committee to Develop a Clinical Competence Statement on Electrocardiography and Ambulatory Electrocardiography) Endorsed by the International Society for Holter and Noninvasive Electrocardiology J. Am. Coll. Cardiol., December 1, 2001; 38(7): 2091 - 2100. [Full Text] [PDF]

				M. M. Laks, R. Arzbaecher, D. Geselowitz, J. J. Bailey, and A. Berson Revisiting the Question : Will Relaxing Safe Current Limits for Electromedical Equipment Increase Hazards to Patients? Circulation, August 22, 2000; 102(8): 823 - 825. [Full Text] [PDF]