Low-Energy Defibrillation Devices

 


New research about defibrillation devices was released this month in a journal called Chaos. The team consisted of scientists from Sergio Arboleda University in Bogata and The Georgia Institute of Technology in Atlanta.  

The group used an electrophysiological computer model of the human heart. The heart's electrical circuits were examined to understand the effect of the applied voltage field. The scientists determined that far less energy is needed than is currently used in contemporary fibrillation-defibrillation practices.

The paper was written by Roman Grigoriev. He explains, "The results were not at all what we expected. We learned the mechanism for ultra-low-energy defibrillation is not related to whether the waves manage to propagate across regions of the tissue which have not had the time to fully recover from a previous excitation. Our focus was on finding the optimal variation in time of the applied electric field over an extended time interval. Since the length of time intervals is not known a propri, it was incremented until a defibrillating protocol was found."

Reducing energy in defibrillation devices is a growing area of research. Current defibrillators are successful by stopping arrhythmias, they are painful and can cause damage.

Grigoriev said, "Existing low energy defibrillation protocols yield only a moderate reduction in tissue damage and pain. Our study shows these can be completely eliminated. Conventional protocols require substantial power for implantable defibrillators- cardioverters (ICDs) and replacement surgeries carry substantial health risks." 

When the heart has a normal rhythm, electro chemical waves cause synchronized contractions. These are triggered by pacemaker cells at the top of the atria. When the heart is experiencing arrhythmias, the excitation waves rotate instead of propagate through. It leaves, then the tissue and the heart have a regular rhythm again.

Grigoriev summarizes, "Under some conditions, an excitation wave may or may not be able to propagate through the tissue. This is called the 'vulnerable window'. The outcome depends on very small changes in the timing of the excitation wave or very small external perturbations. The mechanism of the ultra low energy defibrillation we uncovered exploits this sensitivity. Varying the electrical field profile over a relatively longtime interval allows blocking the propagation of the rotating excitation waves through the 'sensitive' regions of tissue, successfully terminating the irregular electric activity in the heart."

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