An Ultrasonic Implant for Fighting Heart Failure
Every year in the United States, about 150,000 patients with heart failure undergo surgery to have cardiac resynchronization therapy (CRT) devices implanted. These send regular jolts of electricity through their hearts to keep the chambers pumping in unison. However, about 50,000 of those people will receive no benefit from this invasive and expensive procedure—and find that they have few options left to keep them alive.
Now, a new device offers hope to these “non-responders.” A tiny wireless implant controlled by ultrasonic pulses uses a novel approach to heartbeat maintenance, and is now on the market in Europe. In the United States, cardiologists are now working with the Food and Drug Administration on a clinical trial that will likely begin in 2017.
The WiSE (Wireless Stimulation of the Endocardium) technology from EBR Systems was put through its paces in a recently completed European study, which enrolled heart failure patients who hadn’t improved after receiving a traditional CRT device or who weren’t considered eligible for one. The study found that 85 percent of subjects improved in the six months after receiving a WiSE implant.
“I’m pretty excited about this therapy,” says Jagmeet Singh, a cardiologist at Massachusetts General Hospital and the principle investigator for the proposed FDA trial. The other options for non-responders, Singh notes, are ventricular assist devices, which require both an implant and bulky external gear, or trying for a heart transplant. “Those are aggressive and costly interventions that impact lifestyle in a huge way,” Singh says. “This strategy gives us another option.”
Today’s CRT implants use three electrodes attached by wires, called leads, to keep the heart’s chambers pumping together. Two leads go into the right atrium and right ventricle, which send blood to the lungs to pick up oxygen. The third lead must stimulate the left ventricle, which sends oxygenated blood out to the body. But placing a foreign object inside that chamber is risky; any blood clot that forms around it can break off, be carried away by the bloodstream, and potentially clog a blood vessel. That’s why cardiologists place the third electrode on the outside of the left ventricle for typical CRT devices.
Singh says that placing that third lead is tough, because the surgeon must snake it through a narrow vein that wraps around the outside of the heart. “Getting it to the right place is really challenging,” he says. “Where you put the lead along the surface of the heart is limited by the anatomy of that branching vein.” Precise placement is important, because patients who have suffered heart attacks have patches of inert scar tissue on their hearts, and stimulating the heart at those spots won’t do any good.
The WiSE technology incorporates several clever innovations. Its tiny electrode, about the size of a grain of rice, hooks into the inner wall of the left ventricle, explains EBR Systems CEO Allan Will. It’s covered by a “little polyester scaffold,” he says, and heart cells quickly grow over to encapsulate it.
It can be small enough for this strategy to work because the electrode doesn’t contain a battery or microprocessor on anything else fancy. Inside the electrode are 47 piezoelectric elements that simply generate an electric charge when subjected to mechanical stress. And that stress is supplied by focused ultrasonic waves that hit the electrode in the desired rhythm for the heartbeat.
The WiSE system consists of the electrode inside the left ventricle and an ultrasonic transmitter that’s implanted between the ribs.
Since the WiSE system is being used as a technology of last resort, the patients who receive it already have another implant: either a conventional CRT device, which hasn’t helped them, or a standard pacemaker, which keeps the basic beat, but isn’t up to the task of synchronizing the heart chambers. That means the WiSE transmitter can pick up the rhythm of the heartbeat that’s being sent to the right chambers, and coordinate the ultrasonic pulses it sends to the left ventricle. “This is done with every beat of the heart,” says Will. “We get the signal and stimulate the heart within 5 milliseconds, it’s nearly instantaneous.”
Singh, the cardiologist, says the WiSE system can more closely mimic the “natural activation of the heart,” because its electrode is nestled inside the organ. In a natural heartbeat, a wave of electricity starts inside the heart and spreads outward through the cardiac cells, causing them to contract. “With conventional CRT the electrode is on the outside of the heart, so the signal goes from the outside in. But that’s against mother nature,” Singh says.
By Eliza Strickland | Spectrum IEEE