Debbie Burke, a 61-year-old mother of five, went to a Baltimore hospital last month where a surgeon put an advanced implantable heart defibrillator made by St. Jude Medical inside her chest.

Fifteen days later, St. Jude and the U.S. Food and Drug Administration recalled the device because the battery may die with almost no warning. Burke soon discovered that although Little Canada-based St. Jude had fixed the problem in 2015 that led to the recall, the company kept selling its stock of older units, including the device she got.

“That bothers me, it does bother me a lot. And I think it would bother anybody,” Burke said by phone from her Baltimore home. “They say there’s just a small chance [of the battery failing]. … That’s not very comforting when you are saying that to somebody whose doctors are saying, ‘You need this. This could save your life.’ ”

There have been two confirmed cases of patients dying after the battery problem caused their St. Jude devices not to administer lifesaving shocks, one in 2014 and another earlier this year. The FDA says the incidence rate of the battery problem is not known, though St. Jude says the rate is very low.

In interviews this week, executives at St. Jude said they moved as quickly as possible with the information they had about the battery problem. They have studied the issue closely since it first was revealed in a journal article in December 2014, and they promptly informed doctors around the world once the official decision to recall the devices was made.

But St. Jude acknowledges that it continued to ship its stock of old devices for 17 months after making a design improvement that reduced the potential for the device to lose power unexpectedly.

It’s not clear when St. Jude started selling devices with the new batteries, or if there was a period when both versions were being sold without any disclosure of the difference. The affected devices include various models of Fortify, Unify, and Assura.

Company executives said that when they changed the battery design on May 23, 2015, in response to the issue identified in 2014, they had no way to know that the problem eventually would be widespread enough to spark a recall affecting 350,000 devices implanted in patients throughout the world, Chief Medical Officer Dr. Mark Carlson said.

Risk seemed small in 2015

In May 2015, the battery problem seemed to pose a very small risk to patients, and adjusting the design to address the issue was considered part of St. Jude’s “continuous improvement” process, Carlson said.

“We have a device that at that time is performing well, and we are making it even better,” Carlson said Thursday, describing the decision in May 2015 not to tell the public about the design change. “If we had known, or the [St. Jude] Medical Advisory Board had known in 2015 what we know in 2016, I’m sure that their advice and our actions would have been very different.”

The design change was approved by regulators, including the FDA. Agency spokeswoman Angela Stark said via e-mail that the agency didn’t initially require St. Jude to recall the old devices after the design change because the data then showed that the rate of problems stemming from the old design was low and consistent with rates of problems seen in other models on the market. Information uncovered since then showed the risk was greater than initially thought, she said.

“St. Jude is no longer selling the affected devices, and has instructed health care providers not to implant any unused affected devices and to send them back” to the manufacturer, Stark wrote. Neither St. Jude nor the FDA yet knows how many unused devices will be returned.

Defibrillators lead revenue

Defibrillators, St. Jude’s biggest product line, accounted for nearly $1.6 billion in sales last year, about 29 percent of the company’s total. St. Jude shareholders last week approved a $25 billion sale of the company to Illinois-based Abbott Laboratories. News of the massive recall has not caused Abbott to change its public stance on the deal, which is expected to close by the end of the year.

Doctors say the timing of the recall is of concern, partly because they learned about the issue with the older batteries at almost the same time that the public did.

That meant physicians kept implanting patients with devices that had the older batteries, even in people whose daily health depends on their defibrillators working as pacemakers to improve the heart’s output of oxygenated blood.

“I’m very angry because those patients put their lives in my hands,” said Dr. Kevin Campbell, a North Carolina cardiac electrophysiologist who said he unknowingly implanted the older devices in patients after St. Jude came up with a better design. “If it’s a big-enough deal to change the manufacturing process, then pull it off the shelf.”

Campbell said the Heart Rhythm Society is developing medical guidelines for how to treat defibrillator patients whose devices have the old batteries.

Dr. George Crossley III, a cardiologist in Nashville, Tenn., said his patients who are diagnosed as pacemaker-dependent will be offered the chance to have their devices replaced “prophylactically,” meaning patients would be able to have it surgically removed even without signs that the machine is on the verge of failure.

The FDA and St. Jude have recommended St. Jude defibrillator patients with the older batteries go on home monitoring, which can read the device’s battery level whenever the patient is in range of a monitoring device. All patients with St. Jude devices affected by the recall should seek care immediately if they feel the vibratory alarm go off in their chest, because the battery may short out and completely deplete in less than 24 hours.

“Our experience at Vanderbilt is that the devices go down very quickly, if they go down,” Crossley said, referring to patients at Vanderbilt University Medical Center in Nashville.

Source of the problem

The problem is lithium.

An implantable cardioverter defibrillator (ICD) uses a small, lithium battery to monitor the heart and deliver shocks if the patient goes into sudden cardiac arrest. An advanced ICD called a cardiac resynchronization therapy defibrillator (CRT-D) can also act as a pacemaker.

All defibrillators with lithium-chemistry batteries are vulnerable to the formation of globs of lithium outside the power cell. What St. Jude’s engineers discovered was that if the electrically conductive glob of lithium happened to form on their batteries in a place that bridges its two main components, the anode and cathode, that can create a short circuit that rapidly depletes the battery. Sometimes the lithium cluster vanishes again after the short circuit, making it much harder to pinpoint the problem.

Cottage Grove resident Christine Norton, who had a St. Jude defibrillator with an old battery implanted six months after St. Jude fixed the design, said her primary concern is not to point fingers, but to understand what happened.

But she said she’s not considered pacemaker-dependent, and she lives close enough to major medical centers that she could get medical help if she needed it quickly. “I’d just like people to learn from this,” she said.