Light relief for heart attacks
Image: Mapping and manipulating the heart with laser light [Crocini et al]
In a breakthrough for arrhythmia victims, Italy-based researchers have developed a novel method to restore regular heart rhythm with light, rather than electrical shocks.
By combining wide-field fluorescence macroscopy with laser scanning, Dr Leonardo Sacconi from the European Laboratory of Non-Linear Spectroscopy, and colleagues, map and control the activity of whole mouse hearts with sub-millisecond temporal resolution.
"We've fully exploited the advantages of light to defibrillate arrhythmic events in mouse hearts," highlights Sacconi. "This is the first method to demonstrate that optogenetics in the heart can be used to investigate [arrhythmias]."
"Importantly, defibrillation energies can be reduced by applying discrete [light] stimulation patterns," he adds.
As part of their investigations, the researchers used hearts from mouse models modified to express light-sensitive protein, Channelrhodopsin 2 (ChR2). The hearts were also loaded with red-shifted voltage sensitive dye.
The researchers built a wide-field macroscope, operating at 2000 frames a second, to map electrical activity in the hearts.
The instrument included a red LED to excite the voltage sensitive dye in the hearts and a continuous-wave blue laser to activate the ChR2 and manipulate cardiac electrical activity.
Crucially, the researchers developed an ultrafast laser-scanning system to characterise arrhythmias and draw ChR2 stimulation patterns across entire organs according to the heart rhythms.
In this way, they used the macroscope and laser scanning system to monitor the response of a heart to ChR2 patterns with, say, different illumination intensities and pulse durations. And on inducing fast heart-rates used the set-up to apply customised ChR2 stimulation patterns and interrupt arrhythmias.
Optical manipulation of hearts; four patterns of stimulation. Fluorescence images of a ChR2-expressing heart stained with voltage sensitive dye followed by frames of optical mapping recorded from the same heart (red: electrical activation, blue: baseline) Far right: colour-scaled isochronal map of action potential. [Crocini et al; Nature Scientific Reports]
"To date, electrical re-setting of the heart has been the rule to successfully treat ventricular tachycardias.," says Sacconi. "[But] we have found and optimised [ChR2 stimulation] patterns capable of interrupting arrhythmias with 25-fold less irradiation energy than a whole heart intervention."
The researchers believe the proposed set-up can also be applied in larger hearts, although more sophisticated stimulation patterns may be required to tackle more complex arrhythmias, such as ventricular fibrillation.
Research is published in Nature Scientific Reports.