BY ROBERT F. SERVICE
Liquid wires could restore a healthy beat to damaged hearts. MEHDI RAZAVI/TEXAS HEART INSTITUTESAN DIEGO—Heart attacks and strokes triggered by electrical misfiring in the heart are among the biggest killers on the planet. Now, researchers have created a “liquid wire” that, when injected into pig hearts, can guide the organs to a normal rhythm.
SAN DIEGO—Heart attacks and strokes triggered by electrical misfiring in the heart are among the biggest killers on the planet. Now, researchers have created a “liquid wire” that, when injected into pig hearts, can guide the organs to a normal rhythm.
The results, presented here this week at a meeting of the American Chemical Society, are “impressive and really cool,” says Thomas Mansell, a biomolecular engineer at Iowa State University who was not involved with the work. “It’s an exciting study,” agrees Usha Tedrow, a cardiac electrophysiologist at Harvard Medical School, also not involved in the work. If the findings translate to people, she says, it could save thousands of lives each year.
“Pacemaker” cells keep the heart in rhythm. Located at the top of the organ, they produce a mild electrical pulse that travels down through the cardiac muscle, causing the heart’s four chambers to pulse in the familiar two-part “lub-dub” beat. After a heart attack or other injury, scar tissue in cardiac muscle can prevent the needed electrical signals from propagating efficiently. The result is often arrhythmias that can either cause the heart to flutter quickly or beat too slowly, conditions that can lead to a stroke or heart attack.
Medications and a procedure known as ablation therapy—in which some of the pacemaker cells are frozen or fried—can help. Other patients must have a defibrillator implanted. If the device detects arrhythmia, it sends a powerful electrical pulse to the top of the heart to shock the muscle back into normal rhythm. It can be painful. “Patients never know when they’ll be shocked,” says Elizabeth Cosgriff-Hernandez, a biomaterials engineer at the University of Texas, Austin. Many wind up with chronic anxiety and depression.
Cardiologists would love to use an electrode that delivers a milder and potentially less painful pulse, not only to the top of the heart, but also to the lower chambers. One option is to thread a thin metal electrode through a coronary vein on the outside of the heart to reach the middle regions of the heart, where it can stimulate the heart’s lower chambers. But the coronary veins of many patients are too narrow or have partial occlusions, making that impossible.
In hopes of getting around this problem, Cosgriff-Hernandez and her colleagues set out to create a liquid like gel they could inject throughout the length of a coronary vein. The gel would then rapidly harden into a conductive, flexible plastic. (Blood returning through the heart would then flow through other veins.)
To pull this off, the team created a gel from two components: One, called poly(ether urethane diacrylamide) or PEUDAm, eventually forms the plastic; the other, N-acryloyl glycinamide, links the PEUDAm molecules together. When separate, both molecules are liquids.
The researchers then fed both through an ultrathin divided catheter that keeps the liquids separate and inserted the catheter into a coronary vein at the top of the hearts of live pigs. The team pushed the liquids down the vein and its tributaries and removed the catheter. Once the two liquids met inside the vein, the compounds reacted within minutes and hardened into a flexible wire.
“It worked the first time. It was really exciting,” Cosgriff-Hernandez told attendees at the meeting. A bevy of tests showed the wires to be stable, conductive, and nontoxic.
In another round of tests, the scientists scarred some of the heart tissue of the pigs to resemble humans with heart muscle damage. They then injected the liquid wire and, after it hardened, connected it to a traditional battery-powered heart pacemaker. The pacemaker triggered a near-normal heart rhythm. The high-intensity shocks patients receive today can’t match that performance, says team member Mehdi Razavi, a cardiologist at the Texas Heart Institute.
Getting these potentially lifesaving flexible wires into human hearts remains a way off, Cosgriff-Hernandez says. She notes that before that happens, the team needs to test the injectable wires in animal models of heart disease. Tedrow adds that the material will also need to prove stable and safe in long-term studies in animals before human trials can be attempted. But if that proves equally successful, it could be a major win for biomaterials researchers, and patients, she says.
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