The Food and Drug Administration said Tuesday a recall of more than 110,000 Boston Scientific imaging catheters used with intravascular ultrasound systems was deemed Class 1, its most serious.

The recall, announced last month, applies to the iCross 40 Mhz Coronary Imaging Catheter, sold in the United States and its territories, and the Atlantis SR Pro2 version, distributed internationally, the FDA said. The devices are used to check for pathologies inside the coronary arteries for patients who are candidates for angioplasties.

The FDA said the catheter tip can snap inside the patient, causing tissue and blood vessel injury, or even a heart attack.

The Natick, Mass.-based device company first announced a voluntary recall of the products in a May 27 letter to customers. At the time, the recall was said to affect 29,664 units.

In its notice, Boston Scientific said it had confirmed eight cases of catheter tip detachments in the United States and Puerto Rico due to "embrittlement" between April 1, 2010 and May 10, 2011. Based on market data, this translates to a break rate of 0.027 percent, the company said.

"To date, the majority of confirmed brittle tip detachments have been successfully retrieved (typically snared percutaneously)," the company said in a statement. "Because the potential for tip detachment is undetectable prior to use, modifications to the IVUS procedure will have little impact on the likelihood of occurrence of these events."

Boston Scientific said it would replace affected catheters free of charge.

Class 1 recalls mean there's a reasonable probability that use of the product could result in serious injury or death, the FDA said. Adverse events should be reported to the FDA's Medwatch Program by phone at 1-800-FDA-1088 or on its website, www.fda.gov/medwatch.