Question 34 - Reading Comprehension Practice Test for the HESI Exam

A research team from the University of Bonn has succeeded for the first time in using light stimuli to stop life-threatening cardiac arrhythmia in mouse hearts. Furthermore, as shown in computer simulations at Johns Hopkins University, this technique could also be used successfully for human hearts. The study opens up a whole new approach to the development of implantable optical defibrillators, in which the strong electrical impulses of conventional defibrillators are replaced by gentler, pain-free light impulses. The Journal of Clinical Investigation has now published the results. Ventricular fibrillation! When the heart muscle races and no longer contracts in an orderly fashion, sudden death often follows due to the lack of blood circulation. In such an emergency, a defibrillator helps to restore normal heart activity by means of intense electrical shocks. In patients with a known risk for these arrhythmia, the prophylactic implantation of a defibrillator is the treatment of choice. If ventricular fibrillation is detected, a pulse of electricity is automatically generated, which normalizes the excitation of the heart muscle and saves the person’s life.

“When an implanted defibrillator is triggered, which unfortunately can also happen because of false detection of arrhythmia, it is always a very traumatic event for the patient”, says the head of the study, Junior-Professor Philipp Sasse of the Institute of Physiology I at the University of Bonn. “The strong electrical shock is very painful and can even damage the heart further”. Therefore, Professor Sasse’s team investigated the principles for a pain-free, gentler alternative. As the scientists have now shown, ventricular fibrillation can be stopped by optical defibrillation.

Optical defibrillation requires gene transfer

The team used the new method of “optogenetic” stimulation of mouse hearts, which had genes inserted for so-called channelrhodopsins. These channels are derived from a green algae and change the ion permeability of heart cell membranes when illuminated. When the researchers triggered ventricular fibrillation in the mouse heart, a light pulse of one second applied to the heart was enough to restore normal rhythm. “This is a very important result”, emphasizes lead author Dr. med. Tobias Brügmann of Professor Sasse’s team. “It shows for the first time experimentally in the heart that optogenetic stimulation can be used for defibrillation of cardiac arrhythmia”. It also worked in normal mice that received the channelrhodopsin through injection of a biotechnologically-produced virus. This shows a possible clinical application, because similar viruses have already been used for gene therapy in human patients.”