Heart device maker Medtronic PLC is warning doctors worldwide to use extra care when inserting a popular new kind of heart valve in some patients, following reports of 19 deaths from severe blood vessel trauma.

In a letter publicized late Tuesday, the Minnesota-run company informed doctors that it is voluntarily updating its instructions for using the minimally invasive EnVeo R delivery system, which doctors use to implant the Evolut R aortic valve in the heart. The device is used to treat a narrowing of the valve called aortic stenosis, which can lead to heart failure, irregular heart beats and fainting.

An internal analysis of global Medtronic data recently turned up 39 cases in which patients sustained damage to their arteries while doctors used the EnVeo R system. Although the number of incidents was considered low in the context of tens of thousands of valve replacements, the complication is often lethal — 19 of those patients died.

"When they looked at patients with vascular trauma, they noticed that there is a high mortality rate," said Dr. Gregory Helmer, cardiologist and director of the University of Minnesota transcatheter aortic valve replacement (TAVR) program. "They're bringing this to light basically to just make everyone aware and improve the overall safety of the TAVR procedure."

The new instructions caution doctors not to "force" the delivery system if they encounter resistance in the blood vessels, and to pay close attention to patients who may have complex or weakened arteries — steps to minimize the risk that the device will puncture or damage a blood vessel during the procedure.

Transcatheter valves are high-growth devices for Medtronic and the handful of companies that sell them worldwide because they avoid open-heart surgery. The valves are implanted with a long tube called a delivery catheter that is so thin it can be advanced to the heart through the body's natural blood vessels.

With an average sticker price of around $30,000, the new valves are more expensive but require less recovery time than traditional surgery. In the U.S. they're only approved for patients at high risk of complications from traditional surgery, which means the patient population tends to be older and more frail.

Earlier this month, Medtronic alerted doctors that some patients may have an increased risk of damage to the blood vessels. The letter was mentioned in an alert publicized by the U.S. Food and Drug Administration on Tuesday.

The alert pertained to about 7,300 EnVeo R delivery systems in the U.S. and more than 24,000 worldwide.

Technically, the FDA classified Medtronic's letter as a medium-severity recall, but no product is actually being sent back to the company because the device isn't considered defective. Medtronic transcatheter valves that have already been successfully implanted are not affected by the recall.

The risks from using transcatheter valves in complex patient anatomies came to light after Medtronic employees recreated three-dimensional models of tortuous blood-vessel networks.

"Through this research it was noted that complex anatomical configurations increase the risk of vascular trauma," spokesman Joey Lomicky said via e-mail. "The 3-D modeling will also help for future iterations of the device as we better understand these complex patient anatomies."

The new instructions say patients who have at least two of the five complex anatomical features they identified are at increased risk of vascular trauma, including tight bends or significant calcification in the aortic arch at the top of the heart.

Doctors using the EnVeo R in a procedure are urged to carefully study live-motion X-rays and retract the delivery system if the tip of the device bends unexpectedly. "If significant resistance is encountered during an advancement of the delivery system, do not force passage," the recommendations say.

"It's pretty common sense, but I think they're just trying to increase awareness of proper technique," Helmer said. "Sometimes people, if they meet resistance, they just push harder. And really what you need to do is back off," and consider how best to proceed.

Medtronic said in its statement that the updated instructions will be implemented in future physician-training programs, and doctors who already had the training would be informed about the updates.

"While reports of vascular trauma during transcatheter aortic valve replacement procedures are infrequent (0.136 percent based on units distributed as of May 2016), events have been severe in certain cases," Lomicky's e-mail noted.

The company letter to doctors said that the 0.136 percent rate was lower than rates for vascular traumas like aortic disruption, which has been documented in 0.4 percent of cases in the Transcatheter Valve Therapy registry run by independent medical societies.

Several studies have found that transcatheter valves in general are as safe, or safer, than traditional valve surgery in the patient populations in which they're used.

Joe Carlson • 612-673-4779