A pacemaker that regulates the heart by wirelessly zapping it with pulses of ultrasound from outside the organ is currently undergoing human trials in Europe.

Conventional pacemakers stimulate the heart tissue via electrical leads that are fed into the heart through a vein. But leads can fail, requiring additional surgery to remove and replace them. The conventional approach also restricts where the therapeutic shock can be delivered.

The new device uses focused acoustic waves that are picked up by a small receiver implanted permanently inside the heart, converting the energy into electricity. Unlike radio waves, ultrasound can pass through tissue at high-enough energy levels without causing any heating.

“This represents a significant breakthrough, eliminating the lead in the heart,” says Paul Skjefte, marketing strategist for EBR Systems, the company that created the pacemaker. The startup, based in Sunnyvale, California, was spun out of research by founder Debra Echt, a former professor of medicine and a cardiologist at Vanderbilt University.

The new device, called the wireless cardiac stimulation (WiCS) system, works like an RFID tag in that the receiver has no power supply of its own, and instead gets all its power and signal wirelessly, but with ultrasound instead of radio waves, says Andy Diston, head of global medical technology practice at U.K.-based Cambridge Consultants, which has partnered with EBR Systems to help commercialize the technology. “The receiver is tiny, about 10 millimeters long and one millimeter in diameter. It’s like a grain of rice and entirely passive. It gets its energy from the transmitter,” he says.

The ultrasonic signal comes from a pacemaker-like box implanted in the chest above the ribs. The box contains an array of ultrasonic transducers that steer and focus the beam toward the receiver. The receiver picks up the signal and converts it into an electrical signal that regulates the heart.

WiCS is initially being tested with conventional pacemakers—with both devices implanted—as a way to provide a form of treatment for chronic heart failure called cardiac resynchronization therapy (CRT), where chambers on both sides of the heart need to be paced. Because it is not safe to place a lead permanently in the femoral aorta—the only main entry point to the left ventricle—surgeons normally have to painstakingly thread one through blood vessels running on the outside of the heart in order to reach the left side.

The WiCS system avoids this by embedding the ultrasonic receiver in the left ventricle. This is the first time that physicians can choose where in the heart this CRT therapy can be delivered, which means it can be optimized, says Skjefte.

Lead placement is an issue with CRT, says Andrew Grace, a consultant cardiologist at Papworth Hospital in Cambridge, U.K. “If one could place the pulse where you wanted in the heart, that would be good. If it is made to reliably work, then this will be an advance,” he says.

This is not the first leadless cardiac device. Grace was one of the first cardiologists to try out a device called the subcutaneous implantable cardioverter-defibrillator (S-ICD), made by Cameron Health of San Clemente, California. The S-ICD became available in 2009. But although it doesn’t require the placement of leads inside the heart (instead it uses an external one to deliver shocks), it can only deliver the type of powerful shocks that are used for defibrillation, so it’s not capable of pacing. “But other companies like Medtronic are also developing systems that have no leads,” says Grace.

EBR Systems has not said how many patients have so far been implanted with the device, or when it will be approved for clinical use. “Our initial clinical sites are in the Netherlands, Germany, and Switzerland. We have successfully treated heart-failure patients who were previously left with few options,” he says.