According to statistics released by Medtronic, the Sprint Fidelis leads are more than twice as likely to fracture as another type of lead wire manufactured by the company. Fractured lead wires can cause a defibrillator to fail to deliver a life-saving jolt of electricity in the event of a heart attack, or can cause the device to deliver repeated, unnecessary shocks to a patient’s heart. According to the FDA, there have been at least 1,600 reports of injury or malfunction with the Sprint Fidelis leads so far.

Despite the high number of injury reports, Medtronic waited until months after it knew of the potential dangers of its lead wires before issuing the Sprint Fidelis recall. Dr. Sidney Wolfe of the consumer group Public Citizen compares Medtronic’s slow response to that of another heart device company faced with heart device problems in 2005. Critics have accused Guidant Corp. of failing to acknowledge defects in the company’s pacemakers and defibrillators after medical experts tried to warn them.

Dr. Robert Hauser—who published a study on the potential health risks of the Sprint Fidelis leads six months before the recall—also criticizes the FDA for failing to quickly demand a Sprint Fidelis recall. He says that the agency failed to force Medtronic to issue the Sprint Fidelis recall after learning of problems with the lead wires.