Implantable Cardiac Devices

Each year, surgeons implant on the order of a million cardiac devices worldwide. Some implants, like pacemakers, boost slow heart rates to give patients more energy. Others, like implantable cardioverter defibrillators (ICDs), shock fast or irregular heartbeats into stable rhythms to avoid heart attacks. Many devices combine both features. Some can even resynchronize failing hearts.

A typical surgery involves placing a power/controller device just under the breast. Electrical wires run from it through a vein and into the interior of the heart. The device monitors heartbeats, delivering electrical pulses to keep the proper speed and rhythm.

The procedure usually takes one or two hours under local anesthesia, as close to routine as serious surgery ever gets. Aside from avoiding heavy lifting and extreme arm motions for a few weeks, patients can return immediately to their normal lives. They play tennis, golf, or even basketball. Some run marathons.

Cardiac devices are so successful, it is easy to forget the incredible biomedical engineering behind them. The first pacemakers from the 1960s and 1970s were large and power-hungry. They ran at only one speed, limiting patients' activities. Any adjustments (or simply inserting new batteries) required a second operation.

Just keeping the devices running was a challenge. Engineers had to keep salty body fluids from corroding equipment and antibodies from attacking wiring. They did it with hermetically sealed titanium cases and ceramic or glass interfaces that protect wire connections. 

They also added functionality. They developed longer-lasting batteries and units they could program without removal. Using motion detectors (and now gyroscopes), they developed circuitry that adjusted heart rates based on whether someone was sitting, walking, or playing active sports. 

The most recent advances include "leadless" devices that integrate controllers, batteries, and electrodes into a single nodule small enough to implant into the wall of the heart. 

While cardiac device surgery has become unremarkable, clearly there is nothing routine about the technology involved.