By Marti Webb Slay
Significant medical developments are the result of creative thinking, attention to scientific data and good teamwork. Sometimes, they are also the result of a dose of good luck.
For David Sibley, MD, chief of the Division of Cardiology and director of the Cardiac Catheterization Lab Interventional Cardiology at Princeton Baptist Medical Center, a chance encounter in 1984 gave him insight into a new and more effective way to determine if coronary artery disease was slowing delivery of oxygen to a patient’s heart.
Performed during a heart catheterization, instantaneous wave-free ratio, or iFR, is a way to assess stenosis and the degree to which it limits blood flow to the heart. It helps cardiologists determine when surgical or percutaneous intervention is necessary.
But the road to today’s standard procedure has its roots in 1984, when Sibley ran late and missed a bus to the American Heart Association meeting.
“I was a first-year fellow at UAB’s cardiovascular department when this odyssey started for me,” he said. He was learning how to do coronary angiograms to determine if someone had significant coronary disease and needed surgical intervention or percutaneous coronary intervention (PCI). Balloon angioplasty was very new, and stents were not yet being used. He was one of the first interventional fellows in cardiology at UAB.
That American Heart Association meeting in Miami was his first big cardiac meeting. He ran late his first day, missed the bus, and when he arrived by taxi, he was unsure where to go. After taking a wrong turn, he ended up in the poster section, where he met Dr. Mal Marcus from the University of Iowa.
Instead of angiograms, Marcus was investigating a whole new method to measure coronary disease. “He was measuring coronary blood flow in the coronary arteries with a Doppler device attached to the outside of the vessel while the CV surgeons were performing open heart surgery,” Sibley said. “He was measuring actual blood flow and comparing the results to angiograms and showing how the two correlated. The angiogram showed anatomy and the Doppler crystal showed physiology. Physiology was the more accurate predictor of measuring the importance of the patient’s coronary artery disease.
“His findings fascinated me. I had just spent months learning about coronary angiograms, and here was an expert telling me it wasn’t the best way to determine how we should treat a patient.”
As Sibley mused over this new insight, he asked himself how to apply this information in a way that would help diagnose how a patient should be treated, whether by intervention or medical therapy. He came up with the idea of putting a Doppler-tipped 1mm catheter over the guidewire to measure coronary blood flow during a heart cath. “Can the patient increase blood flow in the coronaries to meet the demands of the heart? That was the major issue. It was assumed if there were a 50 percent blockage, that reduced coronary blood flow. But that was a leap,” he said.
Sibley discussed his idea with Huntley Millar, who was well known for developing high fidelity catheters, and Millar designed the requested catheter within a few months. In the meantime, Sibley found an advisor at UAB for the project and received $25,000 funding, a lab and a technician for the research.
The testing had to begin with animals. “We were talking about taking an instrument and putting it inside a coronary artery on the surface of the heart and then hooking the other end of it to the AC adaptor in the wall,” Sibley said. “I don’t think that had ever been done.”
The animal research was successful, and the next step was to perform the test on a patient. “We did it on our first patient in UAB’s Quarterback Tower, and for the first time that I know of, we had online in the cath lab, blood pressure, EKG and coronary blood flow on the ocilloscope in front of us on a live patient. I’ll never forget it. There were a lot of people watching us. You could also hear it on the audio, how the flow would increase as we stimulated coronary flow in the coronary arteries,” he said.
When Sibley had data on 10 patients, he was able to present at the American Heart Association meeting in 1985, as a second-year fellow, and in December 1986, he was published in the Journal of the American College of Cardiology. He also travelled extensively around the world to lecture on the procedure.
Today’s iFR measurement, which is a standard of care in cardiology, is a direct follow-up to Sibley’s efforts as a UAB fellow.
“I can’t take all the credit for this,” Sibley said. “Dr. Robert Wilson at the University of Iowa was working on it too, with Mal Marcus, but the side-mounted blunt probe they were using made it difficult to obtain consistent results.” Sibley’s idea to put the Doppler technology on the end of the catheter and over a guidewire moved the technology forward.
Despite his success in research and the development of this technology, Sibley’s interest was in working in private practice, and when he was invited to develop the interventional cardiology department at Princeton, he decided to make the move. The department had completed only three angioplasties before his arrival, and he performed 250 in his first year.
“It was a very exciting time for me, and also a lot of work,” Sibley said. “I can’t say enough about Drs. Harriet Dustin and Suzanne Oparil at UAB for giving me, a first year fellow, $25,000 in funding, a lab and a tech. It was a stretch.”
And one that paid off for the field of interventional cardiology.
