University of Minnesota
Institute of Technology
myU OneStop

Electrical and Computer Engineering

The Physics of Traumatic and Therapeutic Electrical Shocks

Presenter:  Dr. Mark Kroll
                     Mark Kroll and Associates
                     Corp Director of Haemonetics and Taser International

The ancient Romans and Andeans considered a lightning death to be divine punishment and denied burial rites to victims.
The first recorded artificial electrocution occurred in 1879 and led to a flurry of research culminating in the State of New
York adopting electrocution for capital punishment in 1890.

We now recognize three direct mechanisms by which an electrical shock can cause a cardiac arrest. Non-fatal injuries
are primarily due to Joule heating and electroporation, which is the high-field breakdown of the excellent insulation
around all active cells in the body. Therapeutic shock applications are best understood with a simple model of active
cells. The capacitive cell membrane provides (in conjunction with intercellular resistance) a low-pass filter to electrical
stimulation. The time constant ranges from a low of 100 μs in skeletal muscle nerves to the extreme of 400 ms in the
uterine muscle. Due to the curved fields the time constant varies with the distance from an electrode to the tissue. For
example, the tau of the all-important heart cells varies from 100 μs (pacemaker lead tip in the heart) to 3 ms (chest
patches). After the low-pass filter, the cells are essentially monostable multivibrators with various ON (activation) times.
Some organs — e.g. the heart — have a single contraction per activation with constant contraction strength. The skeletal
muscles are essentially frequency modulated and their contraction strength is basically proportional to the stimulation
frequency (0-70 Hz). We will discuss the applications of this simple model for optimizing the defibrillator and the
TASER conducted electrical weapon.

Dr. Mark Kroll (BS ’75, MS ‘83, Ph.D. ‘ 87 at University of Minnesota and MBA ‘90 University of St. Thomas)
contributed to the invention of the implantable cardioverter defibrillator(IDC). Today, every ICD sold in the world
has at least one licensed Kroll patent. More than one million human beings have his patents in their bodies.
In addition, Kroll contributed to the development of the external defibrillator with electrical CPR assist.

Kroll holds more than 350 patents and is the most prolific inventors of medical devices in the world. His
research specialty is the effects of electricity on the human body and he is the discoverer of the “burping”
effect explaining biphasic defibrillation waveforms. Kroll has lectured in more than 30 countries on topics
including defibrillation, the invention process, electrical safety, and medical device startups.

He is co-editor of four books and has written more than 200 papers, book chapters, and abstracts.
Among Kroll’s honors and awards are the University of Minnesota Outstanding Achievement Award,
The Engineering in Medicine and Biology Society 2010 Career Achievement Award, Fellow of IEEE,
Fellow of the American College of Cardiology, and Fellow of Heart Rhythm Society. Kroll serves as an
Adjunct Professor of Biomedical Engineering, University of Minnesota and California Polytechnic
University, San Luis Obispo. He is a Distinguished Guest Faculty for UCLA’s Creativity and Innovation