Ann Thorac Surg 1999;68:2263-2266
© 1999 The Society of Thoracic Surgeons
Original Articles
Value of saphenous vein graft markers during subsequent diagnostic cardiac catheterization
Linda R. Peterson, MDa,
Clark R. McKenzie, MDa,
Philip A. Ludbrook, MDa,
Thoralf M. Sundt, III, MDb,
John O. Eichling, MDc,
Ginger Schardan-Watson, RNd,
Alan J. Tiefenbrunn, MDa
a Division of Cardiovascular Medicine, Washington University School of Medicine, St. Louis, Missouri, USA
b Department of Cardiothoracic Surgery, Washington University School of Medicine, St. Louis, Missouri, USA
c Division of Radiation Safety, Department of Radiology, Washington University School of Medicine, St. Louis, Missouri, USA
d Department of Cares, Children’s Hospital, St. Louis, Missouri, USA
Address reprint requests to Dr Peterson, Division of Cardiovascular Medicine, Washington University School of Medicine, Campus Box 8086, 660 South Euclid Ave, St. Louis, MO 63110
e-mail: lpeterso{at}imgate.wustl.edu
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Abstract
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Background. Although saphenous vein graft (SVG) markers have been available for many years, they have not been widely used in coronary artery bypass graft (CABG) surgery. This is likely due to the paucity of data regarding the utility of these markers in postsurgery cardiac catheterization.
Methods. We performed a prospective study of all post-CABG patients undergoing cardiac catheterization at Barnes-Jewish Hospital over a 6-month period to test our hypothesis that SVG markers would have a beneficial effect on these procedures. Differences in total procedure (arterial) time, time to image only the SVGs, fluoroscopy time, amount of contrast used, number of aortotomies, and number of views required were compared in patients with and without markers.
Results. Post-CABG patients undergoing catheterization who had markers (n = 76) required significantly less total procedure time (p = 0.007), fluoroscopy time (p = 0.02), and contrast use (p = 0.008). Even after adjusting for the numbers of SVG ostia and numbers of cine views, patients with markers still required less catheterization and fluoroscopy time (p < 0.01, p < 0.02) and time to image only the SVGs (p < 0.05) than those without markers (n = 106).
Conclusions. SVG markers improve the efficiency of post-CABG catheterizations; they decrease the exposure of patients and cardiologists to ionizing radiation, and they decrease the exposure of patients to potentially toxic contrast agents. SVG markers are beneficial to the vast majority of post-CABG patients.
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Introduction
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Coronary artery disease (CAD) is the leading cause of death in the adult population of the United States [1], and it accounts for significant morbidity and national expenditure. Coronary artery bypass grafting (CABG) has been shown to be an effective therapy for relieving angina in patients with symptomatic obstructive CAD [2–5]. In addition, in patients with depressed left ventricular function or disease involving the left main trunk, CABG reduces mortality [4]. Use of segments of autologous vein to bypass proximal coronary lesions was first accomplished by Favaloro, in 1967 at the Cleveland Clinic [6], and quickly became the most common means of surgical treatment for CAD. In the 1970s, the use of markers on the proximal aorta was introduced to note where the aorto-vein graft coronary anastomoses were located. However, the use of these markers has not been widely endorsed by the surgical community and there is significant institutional variation with regard to this practice.
As the number of CABG procedures performed annually continues to grow (from 1983 to 1993 it is estimated that the number of CABGs performed in the United States increased from 162,000 to 241,000 per year) [7] and as the population with saphenous vein grafts (SVG) ages, a growing number of patients requires cardiac catheterization after CABG. Atherosclerosis and clinically significant degeneration occurs in approximately 50% of SVGs at 5 years [8], making periodic examination of the grafts imperative. However, few studies have addressed the impact of SVG markers on the morbidity and the efficiency of angiography after CABG.
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Material and methods
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Consecutive patients who had undergone CABG and were referred for coronary angiography in the cardiac catheterization laboratory of Barnes-Jewish Hospital were recruited from October 1996 through March 1997. Approval for the study was obtained from the Institutional Review Board of Washington University School of Medicine. All catheterization data were collected prospectively. The total procedure time (arterial time), fluoroscopy time, amount of contrast used, and the number of views and ostia of the SVGs were recorded on a standardized data form. A timer recording the time necessary for cannulation and imaging of only the SVGs was started after the native coronary arteries had been imaged and the timer was stopped when all images of only the SVGs were obtained. Markers were prospectively considered to be present if the attending cardiologist thought that preangiography fluoroscopy demonstrated circumferential circular wires, small circular markers placed near the SVG ostium, or that surgical stainless steel clips or staples clearly indicated SVG ostia. If there were many surgical staples seen on fluoroscopy, as is often the case in patients who have had a left internal mammary artery graft (LIMA) placed, and if no clips or staples were obviously and distinctly placed on the aorta, away from the LIMA, then the patient was classified as having no markers. If, on the other hand, a surgical clip or staple was thought to be an obvious SVG aortotomy marker on preangiography fluoroscopy, then the patient was classified as having SVG markers. Although some surgeons document in their operative notes that they placed SVG markers, in our experience this documentation is rare, and thus routine corroboration between the operative note’s record of SVG marker presence and preangiography fluoroscopy was not done. Patients were excluded if they had undergone more than one CABG procedure with a mixture of marked and unmarked grafts, if only in situ internal mammary arteries were used, or if a nonfemoral artery approach was used. Statistical analysis was performed by use of the SAS system, with findings reported as the mean ± SD (Table 1). In addition, to show that the means were not extremely skewed by the data from a few patients (although the data did not exactly fit a bell-shaped curve), we also determined the medians, ranges, and 75th percentiles for all endpoints (Table 2). Also, since the number of SVG aortotomy ostia and number of views filmed at catheterization could influence all of the endpoints listed above, particularly the SVG time, we determined the SVG time per ostium and the SVG time per view in each patient and compared the results from patients without markers to the results in patients with markers. Unpaired t tests were used to compare data obtained from patients with and without vein graft markers. The relationship between SVG time (the dependent variable) and both of the (independent) variables: (1) number of views, (2) number of ostia, and presence or absence of SVG markers were determined using linear regression analyses. p values less than 0.05 were considered indicative of a statistically significant difference.
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Results
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A total of 182 patients was considered for enrollment in the study. Findings in patients with prior CABG and fluoroscopically demonstrated SVG markers (n = 76) were compared with those in similar patients with no SVG markers (n = 106). Means and standard deviations for the time variables, contrast amount, number of aortotomies for the SVGs, and number of views required in both groups of patients are listed in Table 1. Patients with SVG markers required less total procedure time (p = 0.007), less fluoroscopy time (p = 0.02), and less time to image the SVG (although the difference in time for imaging only the SVGs was not statistically significant) than patients without SVG markers. Mean contrast volume needed was also significantly less in the patients with markers than in those without (p = 0.008). There were significantly more SVG ostia per patient in those with markers (p = 0.0005), but the number of cine views was not quite statistically different in the two groups of patients (p < 0.06). Since a greater number of SVG ostia and of views obtained during the catheterization could increase all of the time endpoints, we analyzed the SVG time per ostium and the SVT time per view, and they were both less in the patients with markers than in those without markers (p = 0.04 and p = 0.07, respectively). We also analyzed the data using linear regression analyses to account for both the number of ostia and the number of views. After this statistical adjustment, patients with markers required less adjusted total case time (p < 0.01), fluoroscopy time (p < 0.02), and time to image only the SVGs (p < 0.05) compared with their counterparts without SVG markers.
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Comment
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This study’s results demonstrate the importance of SVG markers in improving the efficiency and potentially lowering the morbidity of cardiac catheterization in patients who have undergone a CABG. SVG markers assist the angiographer by pinpointing the ostium of the aortovein graft anastomosis, and by demonstrating the number of vein graft ostia that must be cannulated at catheterization. This information is essential for the performance of a complete and thorough angiographic examination, especially in patients who need an urgent or emergency catheterization and for whom the CABG operation note is not immediately available. Indeed, the shorter catheterization procedure times in patients with SVG markers would reduce time to reperfusion in those who require emergency angioplasty for myocardial infarction, a reduction that has been shown to have a positive impact on recovery of left ventricular function and mortality [9]. Indeed, the most important clinical effect of SVG markers is that they help insure that a post-CABG catheterization is complete, and that no SVGs are missed. However, this study was not designed to evaluate how many angiograms were incomplete because of the lack of SVG markers (which would only be apparent if a clinical event occurred during long-term follow-up). It is important to note, though, that during the period of this study there was one patient, who did not have SVG markers and whose CABG report was misleading, who had an incomplete angiogram and subsequently an incomplete redo CABG.
Patients with SVG markers required less contrast, which has benefits in reducing the incidence of decrements in glomerular filtration rate and the overt nephropathy that can be associated with cardiac catheterization. Although the unadjusted time to image the SVGs alone was not statistically significantly less in the patients with markers, these patients had more grafts and more views were taken. Thus, SVG time per ostia and SVG time per view, and the adjusted SVG time (that account for both the number of ostia and the number of views) were important to evaluate. The adjusted time necessary to visualize the grafts during catheterization were significantly reduced; thus, the amount of time spent probing the aorta to find the SVGs is reduced, which may decrease the risk of atheroemboli [10]. Indeed, atherosclerosis and plaque formation in the aortic arch has been shown to be an important risk factor for stroke [11–13] and other systemic embolization [14].
Another benefit of SVG marker placement is that both patients and the physicians performing the cardiac catheterization procedures are exposed to less ionizing radiation. In our study, the mean excess additional fluoroscopy time in a patient without vein graft markers was 199 seconds or 3.3 minutes, which corresponds to an "effective dose equivalent" of 70 mrems, approximately the same amount of radiation that would be incurred from nine posteroanterior (PA) and lateral chest x-ray examinations. The additional fluoroscopy time and radiation exposure in the patient without graft markers who underwent the longest procedure (compared with those in the patient in the group with markers undergoing the longest procedure) was 1,200 seconds (20 minutes) or 400 mrems (effective dose equivalent), or approximately what would be incurred from 50 PA and lateral chest x-ray examinations.
Our findings support those of Eisenhauer and colleagues [15] who also noted reductions in fluoroscopy time, necessary contrast volume, and number of catheters needed per procedure. However, there are important differences between the two studies. Eisenhauer and associates conducted a retrospective review of a catheterization database [15]; our study was prospective in design and documented the actual time needed to find and study each individual vein graft’s ostium. Also, since our study was prospective, we were better able to determine whether patients who had surgical clips placed near the ostia of SVGs had markers or not, depending on whether or not the attending physician prospectively thought the clips were indeed marking the ostia (see Material and Methods). In spite of these differences, the conclusions of the two studies are remarkably concordant: SVG markers decrease time of catheterization, fluoroscopy time, and contrast use. However, there is no clear consensus among cardiothoracic surgeons that placing SVG markers is necessary. Although reducing surgical complexity has been offered as a reason to forgo marker placement, there is no convincing data in the literature to support this, and as Eisenhauer and colleagues [15] noted, time on cardiopulmonary bypass is not necessarily prolonged since most markers can be placed after the patient has been weaned from bypass. In addition, although large SVG markers that encircle graft ostia could migrate from the aorta onto the graft itself and cause graft failure, the use of small round, washer-like markers placed next to the ostium of the SVG (as opposed to wires encircling the graft ostium) would be very unlikely to cause graft stenosis, even if the marker were to migrate. Also, because the washer-like markers placed next to the graft are so small, they are unlikely to take up a significant amount of space on the surface of the aorta, and thus should not impede redo CABG. There are, of course, rare patients in whom placing SVG markers may not be desirable, such as those patients with connective tissue diseases (eg, pseudoxanthoma elasticum) in whom the aorta may not tolerate the small amount of additional sewing that placement of the marker requires [16]. However, most patients undergoing CABG tolerate placement of SVG markers very well.
Limitations of this study
This study was not designed or powered to be able to evaluate the effect of SVG markers on patient morbidity or mortality. Such a study would require long-term follow-up of many more patients. In addition, this study was not designed to evaluate the difficult-to-study question of how many angiograms were incomplete.
In sum, the advantages of the use of SVG markers with respect to improving the efficiency of post-CABG cardiac catheterization, decreasing its morbidity, decreasing the amount of ionizing radiation exposure for the patient and the cardiologist, and improving diagnostic accuracy in the vast majority of patients appear to outweigh any risk or inconvenience of placing these markers at the time of bypass surgery.
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Acknowledgments
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The authors express their appreciation for the contributions of all of the attending cardiologists, and to Frank R. Reed and the staff of the Barnes Hospital Catheterization Laboratory. We also recognize the statistical assistance of Kenneth B. Schechtman, PhD, the editorial assistance of Beth E. Engeszer and Benico Barzilai, MD, and the secretarial assistance of Ava L. Ysaguirre.
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Accepted for publication June 3, 1999.
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Abstract
Introduction
