Cardiac surgery is changing. There’s no denying it. More and more, minimally invasive and beating heart surgical procedures are being eyed to replace traditional, open-chest, stopped-heart procedures. Early results indicate the new techniques are reducing patient recovery times and, so far, outcomes look positive. And medical imaging technologies are helping drive that change.
You don’t have to be a brain surgeon – or a heart surgeon – to know that minimally invasive surgery means greater reliance on imaging techniques. But imaging the heart presents unique challenges that imaging other organs does not since the heart is constantly in motion. While taking images prior to surgery has served well to provide a good set of reference points, imaging the heart accurately during surgery requires real-time images so the surgeon can track the placement of instruments and therapeutic devices in relation to the beating heart. And imaging immediately following the procedure can provide a valuable confirmation that the surgery was performed correctly.
Less vision, more imaging
In the past, heart surgery meant a cracked sternum and a fully opened chest. But minimally invasive techniques, such as a mini thoracotomy, have gained widespread acceptance in recent years. Today, cardiac surgeons are taking it even one step further.
The latest minimally invasive techniques being investigated are “port access” coronary artery bypass surgery and minimally invasive direct coronary artery bypass (MIDCAB). Both techniques are accomplished endoscopically via small incisions in the chest.????
Equipment manufacturers are doing their part to introduce innovative surgical products to assist with minimally invasive surgery and improve endoscopic imaging techniques. Computer Motion Inc. (Fort Lauderdale, Fla.) develops products to facilitate robotically assisted minimally invasive cardiac surgery. In November, the company announced the world’s first beating heart, port-access cardiac hybrid revascularization procedure was performed at London Health Sciences Centre (London, Ontario, Canada) using its ZEUS Robotic Surgical System. The ZEUS system uses three voice-controlled robotic arms, including one to position the endoscope and two to manipulate surgical instruments. The imaging advantage is that the endoscope is held perfectly still and controlled by the surgeon’s voice, eliminating the need for human hands on the scope. Other companies making minimally invasive cardiac surgery devices include Heartport Inc. (Redwood City, Calif.) and CardioThoracic Systems Inc. (Cupertino, Calif.).
Echoing praises
But medical imaging’s role goes well beyond the use of endoscopes. In the mid-1980s, researchers began looking at transesophageal echocardiography (TEE) as a method of imaging the heart during surgery. Because a TEE probe is placed several inches down the esophagus, which sits only a half inch behind the heart, it provides optimal placement for cardiac imaging, says Scott T. Reeves, M.D., associate professor of anesthesiology and perioperative medicine at Medical University of South Carolina Children’s Hospital (Charleston, S.C.).
Reeves explains that the early TEE devices in the mid-1980s were endoscopes with a Doppler probe at the end. By 1998, TEE was widely accepted to the point where there was a board examination in TEE instituted by the National Board of Echocardiography, a part of the Board of National Medical Examiners. TEE is now used regularly during minimally invasive bypass procedures to watch the heart as the surgeons occlude vessels. This alerts the surgeon if the patient is having trouble much earlier than blood pressure or EKG changes did.
Steven Konstadt, M.D., a professor of anesthesiology and co-director of the division of cardiothoracic anesthesia at Mount Sinai School of Medicine (New York) is another proponent of using TEE during cardiac surgery, including minimally invasive surgeries. Konstadt says TEE is used to localize where some of the catheters are placed in port-access surgery.
“It helps define when they’ve put the cannula in the right place,” he says. “And in the aorta [to occlude the aorta with the catheter up the femoral artery], echo helps define when you’ve done it.” Konstadt also says TEE has improved the surgeon’s ability to do mitral valve repairs instead of replacements or to help determine when to forego a replacement.
Reeves concurs with that assessment, saying, “[With TEE], as soon as we come off bypass we can see if the repair was accurate or not. If it’s not, then we can go back and repair it again or replace it. Before, we didn’t have the ability to do that.”
TEE also is useful in examining the ascending and descending aorta prior to and during surgery to better assess stroke risk after surgery. Konstadt says patients coming from cardiopulmonary bypass have a higher incidence of stroke than patients having non-cardiac surgery.
“The reason for that is that the surgeons have to manipulate the ascending aorta,” says Konstadt. “They sew the coronary grafts onto it, but they also put clamps and cannulas on it. If there happens to be plaque in that area, the thinking is that the plaque is broken off and goes up the blood stream to the brain and causes the stroke.”
Konstadt feels TEE can be used to look at the aorta before the surgeon manipulates it and see whether or not there are plaques present. The surgeon can then decide where to safely place a clamp and hopefully avoid causing a stroke.
In addition to the clinical benefits, TEE may provide cost advantages as well [see “Cost Effectiveness is Simply a Byproduct”]. Bringing a patient back for surgical repairs costs the patient and hospital time and money. Using TEE prior to the surgery can detect any missed problems. Reeves estimates that in 15 to 25 percent of patients he sees, TEE detects a new problem that the surgeon did not know of going into the operating room. That means the problem can be fixed during surgery and won’t appear in post-surgery evaluations and require call-backs.
TEE: Cost Effectiveness is Simply a ByproductProfessor Norman Silverman, M.D., a professor of pediatric radiology and cardiology at University of California San Francisco School of Medicine, doesn’t like the term “cost-effective” when discussing heart surgery. He feels the advantages of transesophageal echocardiography (TEE) are in fact cost effective, but says that is simply a favorable byproduct of the improved clinical results achieved with TEE. “[Bringing imaging specialists to the OR] means another pair of hands and another brain in there,” says Silverman. “And not for the surgeons benefit. I’m another agent for the patient. I’m not the surgeon’s lackey. I’m not there to tell him he’s done a great job when he’s not done a great job. Whether or not it’s cost effective, I don’t even want to get into that.” But Sliverman goes on to point out that if administrators require a cost justification, a single lawsuit for something that’s left wrong in a patient during surgery will mean much more money than using TEE on a regular basis. And TEE provides that extra security while the patient is still on the table, making it cost-effective regardless. “One thing that used to terrify me was coming to receive a patient from the operating room on a bed with 100 drips going and tubes all over the place,” recalls Silverman. “They would roll the patient in and put him on the bed and I’d be making an assessment on that patient for the first time.” The use of TEE in the operating room during surgery has changed all of that for Silverman. Now he’s in the operating room with the patients and says he’s able to monitor and appreciate this patient’s condition because he saw that patient before and during the operation and he’s there after the operation when the patient is nursed off of bypass. |
Using TEE directly following surgery to ensure the surgery was successful also can minimize the expense and trauma of surgical call-backs. Reeves says savings to the hospital could amount to as much as $2,000 per procedure.
Laser sighting
One new cardiac surgical technique gaining acceptance is angiogenesis, sometimes called transmyocardical revascularization (TMR). TMR is performed on patients that need to get more blood to the heart because certain vessels have been damaged. This condition is often the cause of angina pain. To alleviate this, a laser is used to burn holes in the heart wall, allowing more blood to flow into the heart chamber and hopefully allow the patient to grow new vessels.
The key to success in TMR is knowing how far the laser has burned through the wall of the heart and how many punctures to make in a given area. That’s where imaging comes in. ???
“When the surgeon performs TMR as an open procedure, he puts a laser on the outside of the heart and wants to burn through the heart with the minimum amount of energy, but wants to make sure he’s gone through the endocardium,” Konstadt says. “Echocardiography can define when he’s gone through the endocardium,”
Biosense Webster Inc. (Diamond Bar, Calif.) is working on another method of using images to assist in TMR. The NOGA Cardiac Navigation System from Biosense is an intrabody navigation and localization technology with image and data processing capabilities. The NOGA system works by placing a miniature location sensor and electrodes into the left ventricle of the heart to acquire and record intracardiac electrical activation and endocardial motion in real-time.
Using the percutaneous technique, the NOGA system provides a real-time image of the catheter tip inside the left ventricle through a low intensity magnetic field that provides information to a proprietary global positioning computer. The acquired data is reconstructed into the 3D “map” of the myocardial status.
The NOGA system lets the cardiologist make sure that the density of drilling in TMR is consistent and the holes drilled in the heart muscle are not too close or far apart from each other.
According to Harold Wodlinger, new business consultant with Cedara Software (Mississauga, Ontario, Canada) who specializes in cardiology, the NOGA system also helps identify the tissue that needs to be addressed in TMR by measuring the wall motion and electrical activation at each site. If the muscle is electrically conducting and still moving, then its still alive and that is where the surgeon can place holes effectively. The ventricular electrical and mechanical information (color scales) from the map are used to understand the viability of the ventricular wall.
The NOGA system has been cleared for diagnostic use in the U.S. since 1997 and is now in clinical trials for use with percutaneous transluminal myocardial revascularization (PTMR). PTMR is the angiogenesis method wherein a catheter-based laser is fed up the femoral artery, into the ventricle of the heart and is used to create the holes in the heart from the inside out. NOGA is being studied as an adjunct to fluoroscopy to monitor the position and status of the laser catheter in PTMR.
“C”ing is believing
Confirming the results of a minimally invasive procedure typically requires a trip to the cardiac cath lab to be imaged – often in another part of the hospital. But Robert Lazzara, M.D., has taken steps to streamline that process.
As director of minimally invasive surgery at Providence Seattle Medical Center (Seattle) and director of clinical sciences at the Hope Heart Institute (Seattle), Lazzara started bringing a portable C-arm into the operating room to confirm the results of his surgeries while the patient was still on the operating table. In doing that, Lazzara has created what he calls a “common room” in which diverse cardiac and vascular procedures can be performed at once.
TEE TransducersThe following manufacturers offer transesophageal echocardiography (TEE) transducers:
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“The purpose of the common room is to be able to treat atherosclerotic problems in the heart and circulatory tree by any number of techniques,” Lazzara says. “We can do that with open surgical techniques, minimally invasive techniques or by endovascular techniques. We’re also able to perform hybrid procedures. For example, I may do a bypass procedure and combine it with a stent in the coronary circulation.”
Lazzara has been working with a 9600 C-arm from GE OEC Medical Systems Inc. (Salt Lake City, Utah). Steve Gibson, product manager for GE OEC, says the company sees intraoperative angiography as a target for future growth in mobile C-arms and is developing products with that in mind. Gibson sees coronary angiography moving to the emergency room and the intensive care unit as well as in the operating room.
“We’re trying to mimic the technologies and capabilities in the cath lab in a C-arm,” Gibson says. “If you’ve ever been in a hospital when they’ve rushed a patient from surgery or ICU into the cath lab – it’s not a pretty picture. They’re carrying the whole bed, and liquids and fluids and IVs and monitors. It’s much more convenient to come to the patient for imaging.”
Lazzara says that as surgeons move toward robotically-assisted and minimally invasive cardiac procedures, there will be a greater combining and overlapping of procedures.
“Are we using these machines specifically for minimally invasive techniques at this time? The answer is no,” Lazzara says. “We’re using them to confirm that the surgical techniques are working well or we’re using them in conjunction with a minimally invasive cardiac technique combined with an endovascular technique. I think imaging capabilities will play a much more important role as all of these subspecialties come together to define protocols and the proper way to treat these patients.”
The use of such hybrid procedures, however, will require that various hospital departments work in cooperation. Lazzara says there is still some reluctance by surgeons to let other specialists in on their turf. He sees two factions – older surgeons who have no interest in changing their practice scope and the new generation of surgeons just coming up that realize that change is inevitable. According to Lazzara, this latter group is typically in their 30s and 40s and want to know what role they can play in that change and how can they can help direct it.
When it comes to the acceptance of imaging’s use in surgery, Nicole Filiatrault, communications manager for the Surgical Navigation Network (SNN of Mississauga, Ontario, Canada) feels that cardiologists could take a lead from neurosurgeons. The SNN is a consortium of independent companies formed to develop image-guided surgery technology products for a variety of image guidance areas. According to Filiatrault, the neurosurgeons have openly adopted image guidance as the future of their craft.
“[With neurosurgeons], initially we got a response that said ‘we’ve been doing this for years without this tool and we’re doing just fine.'” Filiatrault says. “However, they did find fairly quickly in neuro that [using imaging] allowed them to make smaller craniotomies, it reduced time in surgeries and it would reduce the recovery time of the patients. Now, image-guided surgery is becoming a standard of care in neurosurgery. We’re into community hospitals with it.”
Images on the horizon
So what does the future hold for imaging’s role in the cardiac OR? Most experts agree that as cardiac surgery moves to a minimally invasive approach, imaging technologies and techniques become more important to the surgeon and will foster the development of new surgical procedures.
For example, the use of ultrasound contrast agents with TEE is another new area of interest being explored that may open a variety of new doors in cardiac procedures. While it is in the early stages, Children’s Hospital’s Reeves says he thinks contrast enhancement may improve TEE imaging as it has in other applications.
“Right now, I think the main indication for [contrast enhancement] is looking at wall motion abnormalities in patients that are difficult to evaluate,” says Reeves. “I think within a few years, the applications will include a lot more corrective procedures like looking for hard-to-diagnose lesions.”
Cedara’s Wodlinger expects the use of MRI for cardiac angiography to grow dramatically in the future to assist in planning the cardiac procedures. MRI can ensure that when the case gets into the traditional cath lab, it can be scheduled properly. Wodlinger also feels that it will ease workflow problems within the cath lab dramatically and save money.
“It’s about one-third the cost to do an MRI angiogram than a traditional angiogram,” he says. “From our perspective, what this means is you have at least three sources of data for the same procedure – fluoroscopy, intravascular ultrasound and MRI data.” Cedara is working on software that will combine the images on a single workstation. Using those combined images during surgery is expected to advance minimally invasive surgeries while streamlining existing procedures.
