Millions of pacemakers have been successfully implanted in the past half century to regulate erratic heartbeats, but the electrical leads, which connect the device to the heart, complicate the surgery and increase infection risks. The heart's continuous and vigorous beating also creates strain on the leads and can damage them over time.

Now researchers seek to go wireless. In a new pacemaker called the Wireless Cardiac Stimulation (WiCS) system, a wireless electrode replaces one or more leads. California start-up EBR Systems, working with English technology-development firm Cambridge Consultants, recently announced their system was successfully implanted in 100 patients needing cardiac resynchronization therapy (CRT) during a series of human clinical trials in Europe. (Wireless signaling is not entirely new to pacemakers—doctors have for the past few years been able to communicate with them via the Internet or even smart phones.)

CRT patients suffer from a type of chronic heart failure requiring both the left and right ventricles to be paced. Normally, such devices require the implantation of three leads, the trickiest of which is threaded through a complex route running from the right atrium, into the coronary sinus on the outside surface of the heart, and then to the left ventricle. In the new device, a small electrode inserted in the left side of the heart replaces one or more of the leads.

In the system, a conventional pacemaker, implanted just below the collarbone in the left side of the chest, sends out a signal through a lead running into the heart's right side. The WiCS unit, implanted near the heart, wirelessly senses the pacemaker's pulse via this lead; it then sends an ultrasonic signal to the wireless electrode on the left side, which converts the sonic energy into electrical energy to pace the left ventricle synchronously with the right.

Advances in low-power microelectronics and improved digital signal processing at high speed and low power enabled the system, says Andrew Diston, Cambridge's director of global medical technology. The ultimate goal is to eliminate all wire leads, making the pacemaker easier to implant. Another goal is to integrate the functions of the conventional pacemaker and the WiCS into a single device.

Wireless technology is notoriously tough on battery life. Diston says that most of the pacemaker's battery—generally lasting seven or eight years before needing to be replaced—is still dedicated to monitoring the heart and deciding when to pace. The WiCS system has its own battery, and no modification to existing pacemakers is required, he added.

Diston is hesitant to set a time frame for the system's availability to the general public. WiCS continues to be tested in human clinical trials in Europe and will first be available there. Before it is made available in the U.S., it will need successful clinical trials here and approval from the U.S. Food and Drug Administration.

WiCS is potentially a disruptive technology, says Bruce Wilkoff, director of cardiac pacing and tachyarrhythmia devices at the Cleveland Clinic, who was not involved with the research. It is still immature, he adds, because it requires other components to coordinate the stimulation.

Given that wireless technology is typically not as reliable as its wired counterpart, the largest concern involves the signal—whether the ultrasound will penetrate the heart muscle consistently and efficiently transfer energy to the wireless lead, Wilkoff says. Still, he adds, "I don't think that there is any concern about safety."

Pacemakers in general require patients to take certain safety precautions, such as not placing cell phones directly against the chest and avoiding strong electric or magnetic fields. Whereas some newer pacemakers are not affected by magnetic resonance imaging (MRI) scans, patients should consult their physicians before undergoing such tests. The addition of wireless to a pacemaker does not change the need to take these precautions.

Some experiments to "hack" into pacemakers capable of communicating wirelessly with computers and smart phones have been demonstrated by security researchers, but there have been no reported incidents of wireless pacemaker data being tampered with to the detriment of a patient. Still, researchers from the Massachusetts Institute of Technology and the University of Massachusetts Amherst say they are developing a jamming device that could be used to shield pacemakers from cyber attackers.

EBR and Cambridge are not only ones working on wireless pacemakers. Minneapolis-based Medtronic, Inc., last year introduced plans for a small, self-contained and fully leadless pacemaker the company hopes to market within three or four years. The Medtronic titanium-encased device will have a circuit board, an oscillator to generate current, a capacitor to store and rapidly dispense charge, memory to store data, and a telemetry system to wirelessly transfer that data to a computer or smart phone.

Unlike WiCS, however, Medtronic's bullet-shaped pacemaker, about the size of an antibiotic pill, would be delivered directly into a patient's right ventricle through a catheter, without surgery. Unfortunately, as currently designed, the Medtronic device could not be repositioned or retrieved from the heart after its seven-year battery failed. It would remain in the heart to be replaced by a new miniature pacemaker.