More energy better when multiple shocks required to restart the heart

March 27, 2007

Results published in the March 27 issue of Circulation suggest that more energy is better when multiple shocks are required to restart the heart. The study is the first randomized trial ever to compare fixed and escalating energy levels in defibrillators used for treating cardiac arrest outside the hospital.

“We found that in people who received the escalating shock pattern, 36.6 per cent of shocks resulted in a normal heart rhythm compared to 24.7 per cent of shocks in those who received the fixed shock pattern,” said lead author Dr. Ian Stiell, a Senior Scientist at the Ottawa Hospital Research Institute, Professor and Chair of Emergency Medicine at the University of Ottawa, and Emergency Department Physician at The Ottawa Hospital. “We hope to repeat this research in a larger group of patients to determine if the escalating energy pattern also impacts survival and other outcomes,” he added.

The study included 221 patients in cities across Canada treated by paramedics or other first responders for cardiac arrest due to ventricular fibrillation, a condition in which the heart “quivers” rather than pumping blood to the brain and body. The study compared two common shock energy regimens used in automated external defibrillators. Patients received either 150 joules for all shocks or 200 joules for the first shock, 300 joules for the second, and 360 joules for remaining shocks as required. First responders were not aware of the energy levels delivered to individual patients. The study was funded by Physio-Control, based in Redmond, Wash., a wholly owned subsidiary of Medtronic, Inc.

Approximately 40,000 Canadians and 335,000 Americans experience sudden cardiac arrest each year. The vast majority of these cases occur outside the hospital, and although survival is less than five per cent, this can be greatly increased by early CPR and defibrillation.

“This study demonstrates the enduring commitment held by Physio-Control to partner with leaders in the field to further scientific understanding of defibrillation and resuscitation,” said Paula Lank, vice president of regulatory and clinical affairs for Physio-Control. “With a scientifically rigorous design, this study has demonstrated that the full energy biphasic capability built into all our defibrillators is beneficial to patients.”

About the Ottawa Hospital Research Institute
The Ottawa Hospital Research Institute (OHRI) is the research arm of The Ottawa Hospital and an affiliated institute of the University of Ottawa. The OHRI includes more than 1,200 scientists, clinicians, graduate students, postdoctoral fellows, and staff conducting research to improve the understanding, prevention, diagnosis, and treatment of human disease. For more information visit

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