The pacemaker may seem like a miracle of modern medicine, but it actually has a lot of drawbacks. Most patients who have had the device implanted say they would go back to the days they before they needed it in, well, a heartbeat.
But a new discovery is poised to make the pacemaker obsolete. Using genes harvested from algae, researchers in Israel have managed to pace the heart of a rat without the need for electricity or implantation. All they used was a pulse of blue light.
Since their invention in the 1950s, pacemakers have had a few updates: they got batteries, they became implantable, they became a bit sleeker and were decked out with microprocessors—but their fundamental problems have never changed. They are regularly associated with infections and need to be removed every few years to have their battery replaced. That means regular, repeated surgery.
Most importantly, the pacemaker is not nearly as effective in moving electricity around the heart muscles. There’s a highway of electrical conduction that passes through a normal, healthy heart. When an electrical signal travels down this highway it shoots straight into the ventricles and every portion of the heart beats in synchronicity. But a pacemaker can only connect via electrodes to one or two spots. That means when they trigger electricity it can’t use the highway—it has to move much more slowly down the backroads. All the parts of the heart don’t beat at the same time. It’s a degraded form of heartbeat. It works, but not as well.
These drawbacks are why Lior Gepstein, a cardiologist and physiologist at the Technion Institute of Technology in Israel, has turned to optogenetics (a field of science that uses light to control cells) for alternatives. Specifically, Gepstein and his colleagues turned to green algae that is sensitive to blue light. At the genetic level, these algae have proteins that help them determine how close they are to a light source so they can move closer to it if they need more energy or further away if they need less.
Gepstein wondered if the DNA that creates these light-responsive proteins could be produced by cardiac muscle cells, giving them the ability to beat when they are exposed to light. It’s not a ridiculous idea. Neuroscientists have been using these genes in the brain for a few years now. Optogenetics was developed specifically for controlling the triggering of neurons without the need for physical interaction with the brain. Rather than opening up a mouse’s head and tapping on different areas of its brain to see what effect it has, scientists use the algal DNA for a much more targeted way to see which neurons trigger different actions. The creation of the field completely transformed how scientists study the brain. But it had never been used in the heart.
So Gepstein and his colleagues used denatured viruses (a traditional tool in gene therapy) to deliver the algal DNA that codes for CHP2 into the heart of a rat. A few weeks later the rat’s heart cells began producing the light sensitive protein. Then the researchers shined a blue light on its heart—and the heart responded by beating.
“We opened the chest. The blue light was directly pointing to the heart so we had nothing between the optical fiber and the heart. Every flash of blue light generated electrical activity in the pacemaker cells but then propagated and caused the entire heart to contract,” Gepstein says.
It was a non-electrical pulse of the heart that had never been achieved in a clinical setting before. Later, when reporting on his findings to a conference of his peers, Gepstein says, the reaction from the audience was that “people were amazed with their mouths open.”
Since that initial test the researchers have been able to inject the DNA into up to four different areas of the heart and watch them react to the light simultaneously. They’ve also discovered other proteins that are capable of suppressing electrical activity, which could be useful for patients who need pacemakers to give them electrical shocks (like a defibrillator) when their heart rate becomes irregular and needs a reset.
Though the research is promising, there is still much work to be done. Blue light isn’t good at penetrating tissue, so the light pacing only works with direct exposure. And, of course, it’s only been shown to work in rats. That said, other researchers are already modifying the proteins to respond to near red or infrared, which could solve the problem of tissue penetration entirely. Ultimately, as this new type of pacemaker begins to make its way into reality, Gepstein and his colleagues have opened a whole new world of optogenetics and shown it’s no longer just for the brain.