Injectable electrodes may be able to prevent fatal heart arrhythmia

Heart attacks and strokes caused by electrical misfiring in the heart are among the world’s leading causes of death. Researchers have now developed a “liquid wire” that, when injected into pig hearts, can guide the organs back to normal rhythm.

The findings, which were presented here this week at an American Chemical Society meeting, are “impressive and really cool,” according to Thomas Mansell, a biomolecular engineer at Iowa State University who was not involved in the research. “It’s an exciting study,” Usha Tedrow, a cardiac electrophysiologist at Harvard Medical School who was not involved in the research, agrees. She claims that if the findings are applied to people, it could save thousands of lives each year.

The heart’s rhythm is maintained by “pacemaker” cells. They are located at the top of the organ and produce a mild electrical pulse that travels down through the cardiac muscle, causing the four chambers of the heart to pulse in the familiar two-part “lub-dub” beat. Scar tissue in cardiac muscle can prevent necessary electrical signals from propagating efficiently after a heart attack or other injury. Arrhythmias, which cause the heart to flutter quickly or beat too slowly, are frequently the result, and can lead to a stroke or heart attack.

Medications and ablation therapy, in which some of the pacemaker cells are frozen or fried, can help.

Other patients require the implantation of a defibrillator. If an arrhythmia is detected, the device sends a powerful electrical pulse to the top of the heart to shock the muscle back into normal rhythm. It can be excruciating. “Patients never know when they’re going to be shocked,” says Elizabeth Cosgriff-Hernandez, a biomaterials engineer at the University of Texas at Austin. Many people develop chronic anxiety and depression.

Cardiologists would love to use an electrode that delivers a milder and potentially less painful pulse to the heart’s lower chambers as well as the upper chambers.

Other patients require the implantation of a defibrillator. If an arrhythmia is detected, the device sends a powerful electrical pulse to the top of the heart to shock the muscle back into normal rhythm. It can be excruciating. “Patients never know when they’re going to be shocked,” says Elizabeth Cosgriff-Hernandez, a biomaterials engineer at the University of Texas at Austin. Many people develop chronic anxiety and depression.

Cardiologists would love to use an electrode that delivers a milder and potentially less painful pulse to the heart’s lower chambers as well as the upper chambers.

A thin metal electrode can be threaded through a coronary vein on the outside of the heart to reach the middle regions of the heart, where it can stimulate the lower chambers. However, many patients’ coronary veins are too narrow or have partial occlusions, making this impossible.

In order to circumvent this issue, Cosgriff-Hernandez and her colleagues set out to develop a liquid-like gel that could be injected down the length of a coronary vein. The gel would then harden quickly, transforming into a conductive, flexible plastic. A thin metal electrode can be threaded through a coronary vein on the outside of the heart to reach the middle regions of the heart, where it can stimulate the lower chambers. However, many patients’ coronary veins are too narrow or have partial occlusions, making this impossible.

In order to circumvent this issue, Cosgriff-Hernandez and her colleagues set out to develop a liquid-like gel that could be injected down the length of a coronary vein. The gel would then harden quickly, transforming into a conductive, flexible plastic.

To accomplish this, the team created a gel out of two components: The first, known as poly(ether urethane diacrylamide) or PEUDAm, eventually forms the plastic; the second, N-acryloyl glycinamide, connects the PEUDAm molecules. Both molecules are liquids when they are separated.

The researchers then fed both through an ultrathin divided catheter that separates the liquids and inserted the catheter into a coronary vein near the top of live pig hearts. The liquids were pushed down the vein and its tributaries, and the catheter was removed. When the two liquids came into contact inside the vein, the compounds reacted quickly and hardened into a flexible wire.

“It worked the first time I tried it.” “It was really exciting,” Cosgriff-Hernandez told the meeting’s attendees. A battery of tests revealed that the wires were stable, conductive, and nontoxic.

In another set of tests, the scientists scarred some of the pigs’ heart tissue to mimic humans with heart muscle damage. They then injected the liquid wire and connected it to a traditional battery-powered heart pacemaker after it hardened. The pacemaker induced a heart rhythm that was close to normal. Today’s high-intensity shocks can’t compete, according to team member Mehdi Razavi, a cardiologist at the Texas Heart Institute.

According to Cosgriff-Hernandez, getting these potentially lifesaving flexible wires into human hearts is still a long way off. She emphasises that the team must first test the injectable wires in animal models of heart disease. Tedrow adds that the material must also demonstrate stability and safety in long-term animal studies before human trials can begin. However, if that is also successful, it could be a huge win for biomaterials researchers and patients, she says.

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