World’s tiniest pacemaker could save babies born with heart defects

By Stephen Beech

The world’s tiniest pacemaker - smaller than a grain of rice - could help save babies born with heart defects, say scientists.

The miniature device can be inserted with a syringe and then dissolves after it’s no longer needed.

American engineers created the pacemaker so tiny that it can fit inside the tip of a syringe — and be non-invasively injected into the body.

Although it can work with hearts of all sizes, researchers say it is particularly well-suited to the tiny, fragile hearts of newborn babies with congenital heart defects.

It measures just 1.8 millimeters in width, 3.5 millimeters in length and one millimeter in thickness, but still delivers as much stimulation as a full-sized pacemaker.

The tiny pacemaker is paired with a small, soft, flexible, wireless, wearable device that mounts onto a patient’s chest to control pacing.

When the wearable device detects an irregular heartbeat, it automatically shines a light pulse to activate the pacemaker.

The short pulses - which penetrate through the patient’s skin, breastbone and muscles - control the pacing.

Designed for patients who only need temporary pacing, the pacemaker simply dissolves after it’s no longer needed.

The team of engineers from Northwestern University explained that the pacemaker’s components are biocompatible, so they naturally dissolve into the body’s biofluids, bypassing the need for surgical extraction.

A study, published in the journal Nature, shows the device’s efficiency across several large and small animal models as well as human hearts from deceased organ donors.

Northwestern bioelectronics pioneer Professor John Rogers, who led the development project, said: “We have developed what is, to our knowledge, the world’s smallest pacemaker.

“There’s a crucial need for temporary pacemakers in the context of pediatric heart surgeries, and that’s a use case where size miniaturization is incredibly important.

"In terms of the device load on the body — the smaller, the better.”

Northwestern experimental cardiologist Professor Igor Efimov, who co-led the study, said: “Our major motivation was children.

“About 1% of children are born with congenital heart defects - regardless of whether they live in a low-resource or high-resource country.

"The good news is that these children only need temporary pacing after a surgery.

"In about seven days or so, most patients’ hearts will self-repair.

"But those seven days are absolutely critical.

"Now, we can place this tiny pacemaker on a child’s heart and stimulate it with a soft, gentle, wearable device.

"And no additional surgery is necessary to remove it.”

The project builds on a previous collaboration between Rogers and Efimov, in which they developed the first dissolvable device for temporary pacing.

Many patients require temporary pacemakers after heart surgery - either while waiting for a permanent pacemaker or to help restore normal heart rate during their recovery.

For the current standard of care, surgeons sew the electrodes onto the heart muscle during surgery.

Wires from the electrodes exit the front of a patient’s chest, where they connect to an external pacing box that delivers a current to control the heart’s rhythm.

When the temporary pacemaker is no longer needed, surgeons remove the pacemaker electrodes.

But potential complications include infection, dislodgement, torn or damaged tissues, bleeding and blood clots.

Efimov said: “Wires literally protrude from the body, attached to a pacemaker outside the body.

“When the pacemaker is no longer needed, a physician pulls it out.

"The wires can become enveloped in scar tissue. So, when the wires are pulled out, they can potentially damage the heart muscle.

"That’s actually how Neil Armstrong died. He had a temporary pacemaker after a bypass surgery.

"When the wires were removed, he experienced internal bleeding.”

Rogers said: “Our original pacemaker worked well.

“But the size of its receiver antenna limited our ability to miniaturize it.

"Instead of using the radio frequency scheme for wireless control, we developed a light-based scheme for turning the pacemaker on and delivering stimulation pulses to the surface of the heart.

"This is one feature that allowed us to dramatically reduce the size.”

The research team also reimagined its power source.

Instead of using near-field communication to supply power, the new pacemaker operates through the action of a galvanic cell, a simple battery that transforms chemical energy into electrical energy.

Rogers said: “When the pacemaker is implanted into the body, the surrounding biofluids act as the conducting electrolyte that electrically joins those two metal pads to form the battery.

“A very tiny light-activated switch on the opposite side from the battery allows us to turn the device from its ‘off’ state to an ‘on’ state upon delivery of light that passes through the patient’s body from the skin-mounted patch.”

If the patient’s heart rate drops below a certain rate, the wearable device detects the event and automatically activates a light-emitting diode.

The light then flashes on and off at a rate that corresponds to the normal heart rate.

Efimov said: “Infrared light penetrates very well through the body.

“If you put a flashlight against your palm, you will see the light glow through the other side of your hand."

Rogers said: “The heart requires a tiny amount of electrical stimulation.

“By minimizing the size, we dramatically simplify the implantation procedures, we reduce trauma and risk to the patient, and, with the dissolvable nature of the device, we eliminate any need for secondary surgical extraction procedures.”

Efimov said: “We could incorporate our pacemakers into other medical devices like heart valve replacements, which can cause heart block.”

The Northwestern team says the technology’s versatility opens other possibilities for use in bioelectronic medicines, including helping nerves and bones heal, treating wounds and blocking pain.

Rogers added: "Because it’s so small, this pacemaker can be integrated with almost any kind of implantable device."