What's Under Cheney's Skin...

Dick Cheney called it a "pacemaker plus," but the pager-size device that was tucked under the Vice President's skin and wired to his heart Saturday morning might just as accurately be described as a "defibrillator plus"--a portable E.R. that can, if necessary, jump-start the heart like the big electrical paddles that appear with such regularity on TV hospital dramas.

The model the V.P. received--a Medtronic Gem III DR--is a miracle of medical miniaturization, a fully automated, battery-powered, custom-programmed combination pacemaker and defibrillator that can monitor the complex rhythms of the heart and correct any abnormalities it discovers with carefully measured pulses of electricity.

If Cheney's heart rate slows to fewer than 40 or 50 beats per minute, for example, the Gem III DR's pacemaker function will speed it up with a series of short bursts of about 5 volts each. If his heart starts pumping too fast, the defibrillator portion will release longer bursts in quick succession to slow it down. And if it starts beating dangerously fast--more than 200 beats per minute--Gem III DR will restart it with a jolt measuring a few hundred volts (enough to feel like a swift kick in the chest).

Cheney's battery should last from five to eight years, depending on use. If it runs out, doctors can replace it with minor surgery.

With the device in place, the Vice President's prognosis is good. Patients with an irregular heartbeat who get these mechanical aids cut in half their chance of dying from a cardiac event.