Shedding new light on coronary bypass surgery
For the first time in the United States, doctors use laser-based imaging system during open-heart surgery
In a coronary bypass, surgeons often graft a leg vein from a coronary artery to the aorta so that blood flow can circumvent the blocked or narrowed vessel.
A new imaging system that lets doctors see the blood pathways they have created while the patient's chest is still open during coronary bypass surgery was used for the first time in the United States in several operations at the medical center over the last three weeks.
Up until this technology became available, doctors usually were not able to confirm whether a coronary bypass surgery had been successful while the patient was still on the operating table. In most cases, only after the chest had been closed could doctors get an image of the heart and see whether blood was flowing through the newly created vessels.
This new technique has "turned on the lights in the surgical suites," said Peter Fitzgerald, MD, PhD, associate professor of cardiovascular medicine. Fitzgerald and his colleagues Scott Mitchell, MD, professor of cardiothoracic surgery, and assistant professor Marc Pelletier, MD, used the new technology in surgery for the first time in the United States on March 16. Since then, they have used the system successfully in three more surgeries.
The technology, called the SPY Intra-operative Imaging System, was approved in January by the U.S. Food and Drug Administration for use in coronary artery bypass surgery, the most common open-heart surgery in the country with more than 300,000 patients undergoing the procedure every year.
The system, made by Novadaq Technologies, has been used successfully for several years in Asia, Europe and Canada, where Pelletier had used it on a number of occasions as a cardiac surgeon at the University of Toronto.
Fitzgerald was instrumental in bringing the system to the United States. Both he and Robert Robbins, MD, chair of cardiothoracic surgery, are on Novadaq's scientific board.
Coronary artery bypass is done when blood flow to the heart is impaired because of blocked vessels that can't be unclogged through drugs, mechanical scraping or the use of a stent to hold an obstructed artery open. The procedure involves grafting vessels from other parts of the body to create alternative conduits of blood flow to the heart. Traditionally the grafts are created from leg veins, but surgeons now frequently use arteries from the forearm and thorax.
"When the patient is open in the operating room and the surgeons have spent all this time and technical skill to restore blood flow for the patient, they look at the heart as it starts beating and see if all of the grafts look fine," explained Fitzgerald. "But this is without any objective criteria."
Around 5 to 8 percent of the time, he said, a graft that initially looked fine doesn't work well. This can lead to unsatisfactory results and sometimes may require another procedure such as coronary stenting or repeat coronary bypass surgery. What surgeons have needed is the ability to see whether blood was flowing so that any needed corrections could be made on the spot. Until now, there have been few good options.
The SPY system uses a fluorescent green dye that attaches to proteins in the blood and emits light when stimulated by a very low-energy laser. The technique does not heat up heart tissue and does not pose any risk to the staff in the operating room. The injected dye lights up blood flowing through the veins and arteries in real time, an action that can be projected on a screen and saved.
This new technology provides in several minutes the same information gleaned from the current gold standard for visualizing coronary artery blockages: the angiogram. An angiogram uses X-rays and a contrast dye that is injected into the heart via a thin, flexible tube inserted in the arm or leg. The procedure is almost always performed after surgery, sometimes hours later or even the next day. Fitzgerald said it's possible to do an angiogram during surgery, but it's time-consuming, cumbersome and exposes everyone in the operating room to X-rays.
"It would be ideal if the surgeons could see what they are doing so they don't close the chest being one conduit short," said Fitzgerald. "Now for the first time the surgeons can take a picture with a direct way to assess how efficient their procedure has been."
As a cardiac surgeon, Pelletier said he appreciated having the capability to see any imperfections in the grafts during surgery and make the necessary corrections.
"Spending a few extra minutes during a four-hour operation can have benefits to the patient that will last for years," Pelletier said.
With the new capability at Stanford, a team of cardiologists and heart surgeons is spearheading a large nationwide clinical trial to systematically assess the effectiveness of SPY as well as compare it with the other ways of assessing blood flow during surgery. The research team will also track and report on how often grafts are not optimal on the first try.
Beyond the FDA-approved use in visualizing cardiac bypass graft function, Fitzgerald is hopeful that the technology will inspire other advances.
"Every time you have a new diagnostic tool, it stimulates new technology for therapy," Fitzgerald said, pointing to colonoscopy as an example. "It wasn't until we had a video camera illuminating the inside of the gut that we learned how to take out polyps and learned to stage colorectal cancer," he explained. "We finally turned on the light inside. This is the same thing."