Rebecca Frost got her first defibrillator in 2002, after she collapsed from cardiac arrest in the parking lot of a Walmart near Asheville, N.C.
The battery-powered device, implanted in her chest, monitored the rhythm of her heart. Over the next year, it saved her life several times by sending electrical shocks through wires to her heart when it began beating dangerously fast.
More than a hundred thousand patients each year get implantable defibrillators to monitor their hearts. But the traditional models, which have wires threaded into the heart, can also cause problems.
The batteries have to be replaced periodically, and when Frost had that done, she developed...