The problem: Wires in St. Jude Medical's QuickSite and QuickFlex pacemaker leads have been found to break through their outer silicone insulation.
How it works: A lead is a wire that runs from a pacemaker to the heart. This type of lead is called a left ventricular lead, and it helps synchronize both sides of the heart to beat more efficiently.
When introduced: QuickSite, 2004; QuickFlex, 2007.
Number sold: 171,000 worldwide; 59,000 in the United States.
What's being done: St. Jude now sells improved leads. The company sent a letter to doctors Wednesday advising them about the problem with older leads.