Kings of CABG: Surgeons Adapt Methods for Patients

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Coronary artery bypass graft (CABG) surgery has undergone many changes, and continues to evolve. Some of the debates currently being played out within clinical practice include radial artery vs. saphenous vein grafts, open vs. endoscopic vein harvesting, CABG on- vs. off-pump and how best to reduce CABG-related stroke.

Radial artery vs. saphenous grafts

The Society of Thoracic Surgeons database indicates that more than 10,000 patients in the U.S. received radial artery grafts in 2008, about 6 percent of total CABG patients. However, the efficacy of radial artery grafts is unclear, based on the current literature.

In a recent study of 733 VA patients from February 2003 to February 2009, Steven Goldman, MD, of the Southern Arizona VA Health Care System and the University of Arizona Sarver Heart Center in Tucson, and colleagues found that the use of a radial artery graft compared with a saphenous vein graft did not result in improved angiographic patency at one year—89 percent for each (JAMA 2011;305(2):167-174).

Goldman says that prior to the study, he and his colleagues hypothesized that the radial artery would have a superior patency because surgeons have likened arterial grafts to the internal mammary artery, which has a better graft patency than veins. While he and his colleagues were surprised by the findings, Goldman says that there has not been much clinical data to support the assumption that radial arterial grafts are superior.

Prior to the study, some surgeons had already begun to reduce utilization of radial artery grafting due to sub-optimal in-practice outcomes. "The JAMA study validates my experience after 25 years in clinical practice, during which time radial artery grafting has experienced two periods of gaining and losing popularity," explains Daniel M. Goldfaden, MD, a cardiothoracic surgeon at HCA's Redmond Regional Medical Center in Rome, Ga. "In both instances, the conduit lost favnor because of high early failure rates."

Since  the most recent resurgence of radial artery use, which began about eight to 10 years ago because of new drug protocols to control spasm, Goldfaden and colleagues have essentially discontinued the use of radial grafting, reserving those arteries for patients who do not have another conduit or, occasionally, in "younger patients with a major graft in an artery that we cannot bypass with an internal mammary," he says.

Joseph F. Sabik III, MD, chairman of thoracic and cardiovascular surgery at Cleveland Clinic, agrees that radial artery grafts can be effective in the right patient. "The patency with radial artery grafts is best when used to bypass an artery that is totally blocked or has severe stenosis, as the guidelines suggest, while it's not as effective to bypass an artery with moderate stenosis," he says.  

"There also is significantly more morbidity in harvesting radial grafts," states Michael J. Mack, MD, medical director of cardiovascular surgery for the Baylor Healthcare System in Plano, Texas. "Due to the lack of proven benefits, we use far fewer radial artery grafts than we did even three to four years ago."

An economic analysis by Goldman et al found no significant difference between the two conduits in the cost of surgery, the cost to the patient or the cost to the U.S. healthcare system at one year. "The radial artery graft cohort hospitalization costs were slightly higher than the saphenous vein graft cohort because surgical preparatory costs for the radial artery conduit were more expensive, even though saphenous vein graft recipients were released from the ICU earlier," Goldman says.

However, because long-term patency remains an important clinical question, the VA has funded Goldman and his colleagues to collect angiographic data for five years of follow-up on these patients to define chronic graft patency. The cost considerations also will be assessed.

Open vs. endovascular vein harvesting

While saphenous vein grafting is still the most common conduit, it has traditionally necessitated open harvesting, requiring linear incisions along the course of the vein, which has led to various complications. Endoscopic vein harvesting (EVH), a procedure developed to eliminate the need for the long incisions associated with open harvesting, has been shown to reduce the risk of wound infection and other complications, lessen postoperative pain, shorten the patient's length of stay in the hospital and lead to greater patient satisfaction. However, less is known about long-term graft patency and clinical outcomes.

The surgeons at Redmond have been using EVH for about eight to 10 years. "After a short period of training, our physician assistants [PAs] can endoscopically harvest the vein at least as fast as with an open technique. Simultaneously, the surgeons can perform internal mammary harvest, and the dual workload saves time," Goldfaden explains. "We have noticed no change in our closure rates."

Also, he observes that the "patients are much more comfortable, as they heal faster and have less swelling. Previously, leg incisions were often challenging, especially in patients with chronic leg edema or diabetes."

In fact, an analysis of 8,542 patients (see chart page 7) found that the use of EVH during CABG was not associated with harm or decreased survival compared with open vein harvesting (Circulation 2011;123:147-153). In an accompanying editorial, Aranki and Shopnick suggest that open vein harvesting will become "obsolete" in a few years, because, among other reasons, five of nine PAs at Brigham and Women's Hospital in Boston have never even performed open vein harvesting (Circulation 2011;123:127-128).

However, some data point to negative outcomes with EVH. In fact, Lopes et al found that EVH is independently associated with vein graft failure and adverse clinical outcomes (N Engl J Med 2009;-361:235-244), but the authors stressed the need for further investigation, including a randomized, controlled trial to validate their findings. Despite these NEJM results, Mack, who was part of that retrospective review, says, "Endoscopic vein harvesting is so patient-friendly, and because it has dramatically reduced the morbidity associated with vein harvesting, it is a genie that is never going back in the bottle."

Sabik adds that whether the procedure is performed via open vein harvesting or endoscopically, the key is to take the vein atraumatically, which requires a skilled operator. "Due to the improved patient comfort and reduction in leg complications—which in previous years were pervasive and common—open vein harvesting may become obsolete some day. However, the proper operator training with EVH needs to occur," he says.

With increasing utilization of EVH, Mack says surgery departments need to focus on improving techniques, because some factors could contribute to less effective outcomes, such as the way the vein is handled or harvested. "Due to the trauma associated with EVH, the vein graft patency rate may be less favorable, but using a best practices technique could reduce that trauma and improve graft patency," he says.

Aranki and Shopnick also wrote that EVH is "considerably more expensive than open vein harvesting by many hundreds of dollars. … However, the reduction in pain, leg wound infections and hospital stay may put both techniques at financial parity."

While the disposable equipment used with EVH is more expensive, Mack says the inpatient length of stay is not necessarily altered with either operative technique. However, the economic justification could be seen in outpatient resources, including a reduction in outpatient visits and wound care in physician offices, which means EVH could save money to the overall healthcare system.

CABG-related stroke prevention

While the number of patients undergoing first-time isolated CABG surgery decreased, the percentage of those who underwent endoscopic vein harvesting actually increased in this study of a New England population. Source: Dacey, L. J. et al. Circulation 2011;123:147-153.
Early postoperative stroke is a serious adverse event after CABG for the approximately 250,000 people who undergo CABG in the U.S. annually. Despite its debilitating neurological effects, the low frequency of the index event limits the ability of most investigations to power for the effect.

While the current stroke risk associated with CABG in the U.S. is approximately 1 percent, Mack says zero is "a very achievable goal."

In the SYNTAX trial, which compared CABG with PCI in patients with complex disease, the major difference between the two approaches was in their complication rates, Sabik says. "The early results of SYNTAX showed that the surgical patients were trading the stroke risk for the risk of re-intervention with PCI." Sabik and his colleagues wondered if their data replicated the findings in SYNTAX.

In a study of 45,433 patients who underwent CABG from 1982 to 2009 at Cleveland Clinic, Tarakji et al found that the occurrence of stroke after CABG had declined, despite an increase in risk profiles because of the older age of patients (JAMA 2011;305(4):381-390). "We were seeking to understand which patients experienced intra-operative and postoperative stroke following CABG, why they occurred and if the different operative procedures influenced that risk," explains Sabik, who was a co-investigator on the study.

They found that 1.6 percent of patients experienced a stroke. Occurrence of stroke peaked in 1988 at 2.6 percent. Since that time, the stroke rate has slowly declined by 4.69 percent annually, despite an increasing patient risk profile, such as a higher prevalence of preoperative stroke, hypertension and diabetes.

To help reduce stroke, Mack recommends several precautions such as pre-operative screening of high-risk patients (those with known peripheral vascular disease, previous stroke or previous carotid surgery) and an epiaortic ultrasonogram to screen for aortic disease in cases where a graft will be placed on the aorta. If disease is found in the ascending aorta, the patient should be treated off-pump and without aortic manipulation, such as cannula placement for cardiopulmonary bypass or graft placement. If there is a non-diseased area on the ascending aorta, a clampless device could be placed on the vessel. Finally, postoperative atrial fibrillation is difficult to manage and the role of anticoagulation is unclear, but those patients "should probably be anticoagulated to decrease stroke risk," Mack says.

"Many techniques can be adopted to reduce stroke, but they are not being practiced in a uniform and universal fashion," Mack says.

With intra-operative stroke, different surgical techniques are associated with different risks. Tarakji et al in the aforementioned JAMA study found that unadjusted rates of stroke were highest among patients who had on-pump CABG with hypothermic circulatory arrest (5.3 percent), and lowest among those who had off-pump CABG (0.14 percent) and on-pump beating-heart CABG (0 percent). The risk of intra-operative stroke was intermediate for those undergoing on-pump arrested-heart CABG (0.50 percent).

"There are certain risk factors associated with stroke; however, by choosing the proper operative technique, we can lower stroke risk overall and lower the risk of intra-operative stroke to similar rates of PCI," says Sabik. For instance, an elderly patient with extensive atherosclerosis or previous stroke would benefit from an off-pump procedure, he suggests. Conversely, for a younger patient without many risk factors, who is undergoing a complex arterial revascularization, the operator could utilize on-pump without increasing the stroke risk.

"We no longer have one method of undertaking CABG, but we have several ways, which need to be selected according to what is best for the specific patient profile," Sabik notes. "If we individualize treatment, stroke doesn't have to be a trade-off between CABG and PCI, as the risk of stroke can be similar."

On-pump vs. off-pump CABG

In different eras, the popularity of performing CABG either on- or off-pump has risen and declined. For more than 40 years, the use of cardiopulmonary bypass pumps defined CABG procedures with good outcomes and relative ease of use (Ann of Thorac Surg 1992;54:1085-92). However, the oft-cited Khan et al study found that the graft patency rate was lower at three months in the off-pump group than in the on-pump group (N Eng J Med 2004;350:21-28).

Yet, many surgeons have uniformly ceased to utilize the off-pump technique. "At our practice, we don't perform very much off-pump CABG anymore, while approximately five to seven years ago we were using off-pump in as many as 25 to 30 percent of our cases," Goldfaden says. "We found that our complication rate did not improve with off-pump and it was technically more challenging. However, in selected populations, such as stable patients with anterior circulation and larger vessels, off-pump is still a good technique."   

A recent randomized trial points in the same direction, as Shroyer et al found that patients in the off-pump arm had worse composite outcomes and poorer graft patency than patients in the on-pump group (N Engl J Med 2009;361:1827-1837).

Yet, off-pump CABG still has its advocates. "Despite my enthusiasm and that of others, the adoption rate of off-pump CABG has remained fairly static at about 20 percent," says Mack, who attributes this to its user-unfriendliness. Also, the lack of standardization or clearly defined guidelines allows practitioners to cite evidence that supports their biases. However, Mack contends that every surgeon needs to become comfortable with the off-pump technique, so it can be utilized in the highest risk patients.

Mack defines these highest risk patients who should always receive off-pump as elderly (75 years or older) who are at risk for stroke, those with poor left ventricular function, re-operative patients and those with renal insufficiency.

Again, Sabik recommends the need to tailor the operative technique to the individual patient. "We need to assess the patient, and decide which cases could be best treated off-pump and which cases could be best treated on-pump. The key is to be facile with both," he says. "These techniques make up our armamentarium of tools."