Volcano (NSDQ:VOLC) this month agreed to stipulate that St. Jude Medical (NYSE:STJ) isn’t infringing a pair of its fractional flow reserve patents, but vowed to appeal a federal judge’s interpretation of the patents’ claims.

Volcano sued St. Jude in a Delaware federal court in April 2013, alleging infringement of a pair of patents covering its PrimeWire FFR device by St. Jude’s competing PressureWire Certus and Aeris devices. The FFR devices are designed to measure arterial blood pressure.

Last January Judge Richard Andrews of the U.S. District Court for Delaware construed the term "flexible element" in both of the Volcano patents in favor of St. Jude, according to court documents. Volcano had argued that the term should encompass coils, hypotubes and balloons, but Andrews agreed with St. Jude’s assertion that the "flexible element" term means a coil, according to the documents.

That ruling prompted Volcano and St. Jude Medical to sign a stipulation that St. Jude doesn’t infringe the patents, according to the documents and regulatory filings with the SEC.

"Volcano intends to appeal the claim construction ruling," the San Diego-based company said in a filing.

The technology covered by the patents was invented by researchers at Volcano’s corporate predecessor, Cardiometrics, according to the documents. Volcano alleged that Douglas Corl, Robert Obara and John Ortiz "were the first to invent a pressure sensing guide wire that uses a solid state pressure sensor." The 2 patents, both covering technology for an "Ultra Miniature Pressure Sensor," issued March 5, 2013, to Volcano, court records show.