Could Future Defibrillators Use Light?

American and German researchers used light instead of electricity to restore normal rhythm to the hearts of mice, as well as in a computational model of a human heart..

Nancy Crotti

Scientists have shown that beams of light could replace electric shocks in patients with cardiac arrhythmia, indicating the possibility of a new type of implantable defibrillator.

The researchers from Germany's University of Bonn and Johns Hopkins University used high-tech human heart models and mouse experiments in their studies, whose findings were published online in The Journal of Clinical Investigation.

Current devices deliver pulses of electricity that are extremely painful and can damage heart tissue. Light-based treatment, the Johns Hopkins and Bonn researchers say, should provide a safer and gentler remedy for patients at high risk of arrhythmia, an irregular heartbeat that can cause sudden cardiac death within minutes.

The researchers based their work on advances in the field of optogenetics, in which light-sensitive proteins are embedded in living tissue, enabling the use of light sources to modify electrical activity in cells.

"We are working towards optical defibrillation of the heart, where light will be given to a patient who is experiencing cardiac arrest, and we will be able to restore the normal functioning of the heart in a gentle and painless manner," said Natalia Trayanova, a biomedical engineering professor who supervised the research at Johns Hopkins.

The researchers at Johns Hopkins performed an analogous experiment within a detailed computer model of a human heart, derived from MRI scans of a patient who had experienced a heart attack and was now at risk for arrhythmia. They found that the blue light that worked on mice could not penetrate human heart tissue, and substituted red light, which has a longer wavelength.The Bonn team conducted tests on beating mouse hearts whose cells had been genetically engineered to express proteins that react to light and alter electrical activity within the organ. They triggered ventricular fibrillation in the mouse heart, and found that a light pulse of one second applied to the heart was sufficient to restore normal rhythm.

"The simulations revealed the precise ways in which light alters the collective electrical behavior of the cells in the heart to achieve the desired arrhythmia termination," Trayanova said in a statement from Johns Hopkins.

Development of light-based implantable defibrillators could be five to 10 years away. Meanwhile, development of more traditional atrial fibrillation devices continues apace. Medtronic and St. Jude Medical have both introduced implantable cardiac pacemakers that forego the need to run leads to the heart, avoiding problems such as infection. The devices both have long battery life--12 years for the Medtronic's Micra and 13 years for St. Jude's Nanostim.

FDA approved the Micra in April for patients with atrial fibrillation or other dangerous arrhythmias such as bradycardia-tachycardia syndrome. The Micra is less than one-tenth the size of traditional pacemakers, and a bit smaller than St. Jude's Nanostim leadless pacemaker that has been approved in the European Union since late 2013.

Boston Scientific has also had a great deal of success with its FDA-approved S-ICD technology, which places a pulse generator and electrode just under the skin, leaving the heart and blood vessels untouched and reducing complications associated with conventional ICDs.

Nancy Crotti is a contributor to Qmed.

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[Graphic by Patrick M. Boyle/Johns Hopkins University]