Medtronic Inc.’s SynchroMed infusion pumps were found to have four flaws that have led to 14 patient deaths, spurring U.S. regulators to issue their most serious recall on the implantable device used to deliver pain and other medications.

Medtronic, the world’s largest heart device maker, notified customers in early June about the flaws that may interfere with the safe and reliable delivery of medications using the SynchroMed Implantable Infusion System, the Minneapolis-based company said in a statement. Each flaw specified in the notifications was deemed a Class 1 recall by the U.S. Food and Drug Administration, denoting potential life-threatening issues.

Fourteen patients have died since 1996 while using the SynchroMed System, Donna Marquard, a Medtronic spokeswoman, said. The most common complication was the inadvertent injection of a drug into the patient’s subcutaneous tissue, rather than into the pump, which led to 11 deaths. Two patients died from a blockage and another from an electrical short.

Harm may also have stemmed from use of the priming bolus, a function that allows drugs to move quickly from the pump to the tip of the catheter to deliver medication while the patient is under medical supervision, Medtronic said in its statement. The company said it found that any time the feature is used, the drug mixes with sterile water or cerebrospinal fluid, which may led to dilution of the drug or an extra delivery of medication.

While the flaw can lead to an overdose or not enough of a drug being delivered, the company hasn’t linked it to specific complications in individual patients, given other factors such as drug dosage, patient medical history and the use of other medications at the same time, Marquard said in an e-mail.

Medtronic recalled two types of the pumps in December after reports they may fail to properly delivery medicines, potentially leading to a return of symptoms and potentially death. The concern identified then was a risk of stalling and not properly delivering medicines, particularly when they were used with unapproved drugs. Visit Bloomberg for the story.