In an article published this week in Chaosby AIP Publishing Researchers at Sergio Arboleda University in Bogota, Colombia, and the Georgia Institute of Technology in Atlanta used an electrophysiological computer model of the heart’s electrical circuits to examine the effect of the applied voltage field in several fibrillation-defibrillation scenarios. They found that much less energy was required than is currently used in state-of-the-art defibrillation techniques.

The results were not at all what we expected. We learned that the mechanism of very low energy defibrillation is not related to the timing of the excitation waves as we thought, but rather to the ability of the waves to propagate through regions of tissue that do not have not had time to fully recover. previous excitement. Our objective was to find the optimal temporal variation of the applied electric field over an extended time interval. As the duration of the time interval was not known a priori, it was incremented until a defibrillation protocol was found. »

Roman Grigoriev, author

The authors applied an adjoint optimization method, which aims to achieve a desired outcome, defibrillation in this case, by solving the electrophysiological model for a given voltage input and working backward in time to determine the profile correction voltage that will successfully defibrillate an irregular heart. activity while minimizing energy.

Energy reduction in defibrillation devices is an active area of ​​research. Although defibrillators are often successful in stopping dangerous arrhythmias in patients, they are painful and damage heart tissue.

“Existing low-energy defibrillation protocols produce only a moderate reduction in tissue damage and pain,” Grigoriev said. “Our study shows that these can be completely eliminated. Conventional protocols require significant power for implantable cardioverter-defibrillators (ICDs), and replacement surgical procedures carry significant health risks.”

At a normal rate, electrochemical waves triggered by pacemaker cells at the top of the atria travel through the heart, causing synchronized contractions. During arrhythmias, such as fibrillation, the excitation waves begin to spin rapidly instead of propagating through and leaving the tissues, as in the case of a normal rhythm.

“Under certain conditions, an excitation wave may or may not propagate through tissue. This is called the ‘vulnerable window,'” Grigoriev said. “The outcome depends on very small changes in the timing of the excitation wave or very small external disturbances.

“The very low energy defibrillation mechanism that we discovered exploits this sensitivity. The variation of the electric field profile over a relatively long time interval makes it possible to block the propagation of rotating excitation waves through the “sensitive” regions of the tissues, thereby ending irregular electrical activity in the heart.