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Pacemaker surgery typically requires a doctor to make an incision above a patient’s heart, dig a cavity into which he can implant the heartbeat-regulating device, and then connect the pulse generator to wires delivered through a vein near the collarbone. Such surgery could soon be completely unnecessary. Instead, doctors could employ miniaturized wireless pacemakers that can be delivered into the heart through a major vein in the thigh.

On Monday, doctors in Austria implanted one such device into a patient—the first participant in a human trial of what device-manufacturer Medtronic says is the smallest pacemaker in the world. The device is 24 millimeters long and 0.75 cubic centimeters in volume—a tenth the size of a conventional pacemaker. Earlier this year, another device manufacturer, St. Jude Medical, bought a startup called Nanostim that makes another tiny pacemaker, and St. Jude is offering it to patients in Europe. This device is 41 millimeters long and one cubic centimeter in volume.

Doctors can implant such pacemakers into the heart through blood vessels, via an incision in the thigh. They use steerable, flexible tubes called catheters to push the pacemakers through a large vein.

The two new devices are the latest effort to make heart surgery less traumatic. Doctors began to widely use less invasive heart treatments in the late 1990s, when artery-unclogging balloons delivered by catheters started to replace bypass surgeries. Other cardiac technologies like stents, which prop open weak or narrow arteries, can also be delivered through blood vessels. More recently, researchers have developed artificial valves for patients whose natural valves have become damaged; these devices can also be delivered by catheters snaking through large blood vessels.

Brian Lindman, a cardiovascular specialist at Washington University School of Medicine, and colleagues have found that less invasive catheter-based procedures for valve repair can be safer for high-risk elderly patients and can enable doctors to treat patients who are too frail to undergo surgery. More recently, Lindman published a study suggesting that the transcatheter method may improve the odds of survival for diabetic patients as well. However, for some cardiac treatments such as valve repair, a more invasive surgery enables longer-lasting repairs, and so may be the better option for patients strong enough for surgery. “Surgery or transcatheter is not always better,” says Lindman. “It depends on the cardiac problem and on the nuances of each procedure.”

Both tiny pacemakers are now being tested in human trials, and St. Jude’s has been approved for use in patients in Europe. The device manufacturers say the batteries in the tiny pacemakers will last up to eight or 10 years when running at full-stimulating capacity. The new pacemakers are also “leadless”—that is, they don’t require long electrodes winding their way into heart. Instead, these devices sit inside the heart. Small prongs on Medtronic’s device fasten it to heart tissue, and an electrode that touches the heart delivers electric pulses. This new design reduces the amount of power required by the device and eliminates a major source of device failure (see “A Pacemaker the Size of a Tic Tac”).

Medtronic has also developed a miniaturized cardiac monitor for patients with arrhythmias or undiagnosed heart problems. Cardiac monitors continuously track heart activity; patients undergoing testing may have to wear a portable device around their neck, which hooks up to wires from several electrodes stuck to the chest, perhaps for days at a time. Doctors can implant Medtronic’s new monitor using a syringe-like system that inserts the device into a small incision above the heart that is just eight millimeters deep. The monitor can then wirelessly transmit heartbeat data to a bedside monitor or potentially even to a smart phone, says Mark Phelps, an engineer leading Medtronic’s miniaturization efforts

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Credit: Photograph courtesy of Medtronic

Tagged: Biomedicine, pacemakers

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