Ventricular Fibrillation Threshold vs Alternating Current Shock Duration Mark W. Kroll, PhD, FIEEE; Dorin Panescu, PhD, FIEEE ; Peter E. Perkins, MSEE, LFIEEE, Reinhard Hirtler, Dipl Ing; Michael Koch, MS; Christopher J. Andrews, PhD, MD * Abstract: Introduction: International basic safety limits for utility-frequency electrical currents have long been set by the International Electrotechnical Commission 60479-1 stand- ard. These were inspired by a linear-section plot proposed by Biegelmeier in 1980 with current given as a function of the shock duration. This famous plot has contributed to safe elec- trical circuit design internationally and has properly earned significant amount of respect over its 35 years of life. How- ever, some possible areas for improvement have been sug- gested. Methods: We searched for all animal studies of ventricular fibrillation threshold versus duration that used a forelimb to hindlimb connection that had at least 3 durations tested. We found 6 such studies and they were then used to calculate a new C3 curve after normalizing the data. Results: A rational function model fit the animal data with r 2 = .96. Such a correlation calculation tends to underweight the smaller values, so we also correlated the log threshold values and this had a correlation of r 2 =.94. Conclusion: Existing ventricular fibrillation threshold cur- rent versus duration data can be fitted with a simple rational function. This can provide a useful update to IEC 60479-1. I. INTRODUCTION International basic safety limits for utility-frequency electrical currents have long been set by IEC (Interna- tional Electrotechnical Commission). These limits were inspired by a linear-section plot proposed by Biegel- meier in 1980 with current given as a function of the shock duration as seen in Figure 1.[1] The linear-section “b” curve lower line for a “non- fibrillating” current had 500 mArms for a short shock (de- fined as 10 ms for this paper) and 50 mArms for a long shock (defined as 10 seconds for this paper). Biegel- meier’s upper “a” line was for a 50% risk of VF (ventric- ular fibrillation) had 1800 mArms for a short shock and 100 mArms for a long shock. In addition, an intermediate line (C2) was added to give an intermediate 5% risk of VF. The IEC 60479-1 * M. W. Kroll is an Adjunct Professor of Biomedical Engineering at the University of Minnesota, Minneapolis, MN (email: mark@kroll.name). D. Panescu is Chief Technical Officer, Vice President R&D, HeartBeam, Inc. (email: panescu_d@yahoo.com). P. Perkins is an independent consultant (email: peperkinspe@cs.com). R. Hirtler formerly with the Electrical Safety Foundation, Vienna and now independent consultant (email: reinhard.hirtler@chello.at. M. Koch is with Eaton Industries, Vienna (email: Mi- chael.Koch5@gmx.at). C.J. Andrews is an independent consultant (email: chris.a@pobox.com). That curve was then rounded and rotated to give the pre- sent version as seen in IEC 60479-1 (Their fig. 20) and our Figure 2.[2] Figure 1. Original Biegelmeier current vs. duration curve. International basic safety limits for utility-frequency electrical currents are based on the line for a “generally considered safe” current (now called the “C1” line) had 500 mArms for a short shock and a current level appearing to be 35-40 mArms for a long shock. We say “appearing to be” as the standard never gave a table for these values but rather presented curves which were open to interpre- tation and copying errors. The upper line for a 50% risk of VF (ventricular fibrillation) (now called the “C3” line) had a current level appearing to be 1500-1600 mArms for a short shock and 80 mArms for a long shock. IEC 60479-1 also has non-cardiac lines “a” (startle- reaction) and “b” (let-go immobilization) which are not relevant to this paper. Nor are they related to Biegel- meier’s “a” and “b” curves. Note that the C1 long- shock (10 s) current was reduced from 50 mA (Biegel- meier’s proposal) to below 40 mA and has served as a 2021 43rd Annual International Conference of the IEEE Engineering in Medicine & Biology Society (EMBC) Oct 31 - Nov 4, 2021. Virtual Conference 978-1-7281-1178-0/21/$31.00 ©2021 IEEE 1257