Ann Thorac Surg 2002;73:1856-1859
© 2002 The Society of Thoracic Surgeons
Original article: cardiovascular
Right internal mammary artery and radial artery composite in situ pedicle graft in coronary artery bypass grafting
Lokeswara Rao Sajja, MCha,
Gopichand Mannam, FRCS(CT)*b
a Division of Cardiothoracic Surgery, Medwin Hospitals, Hyderabad, India
b Division of Cardiothoracic Surgery, CARE Hospital, The Institute of Medical Sciences, Hyderabad, India
Accepted for publication March 1, 2002.
* Address reprint requests to Dr Mannam, CARE Hospital, The Institute of Medical Sciences, Road No. 1, Banjara Hills, Hyderabad 500034, A. P. India
e-mail: gmannam{at}yahoo.com
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Abstract
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Background. The use of two internal mammary artery grafts in coronary artery bypass grafting has been associated with decreased risks of death, reoperation, and angioplasty. However, bilateral internal mammary artery takedown is associated with higher incidence of sternal wound infection, particularly in people with diabetes and in elderly and obese patients. This study was conducted to explore the feasibility of using right internal mammary artery (RIMA) and radial artery (RA) as a composite graft while preserving the distal two thirds of the RIMA to leave the sternal blood supply intact.
Methods. Eighteen patients underwent coronary artery bypass grafting using proximal RIMA and RA composite graft as one of the bypass conduits. The distal two thirds of the RIMA was left intact to preserve sternal blood supply. The graft-free flows of the RIMA and RA composite graft and of the left internal mammary artery graft and the length of the composite graft had been measured. The graft patency and the flow in the distal part of the unharvested RIMA was evaluated postoperatively 2 weeks after the procedure. In 6 of these patients the graft patency was evaluated by selective angiography.
Results. There was no hospital mortality or incidence of perioperative myocardial infarction. None of the patients needed intraaortic balloon pump support postoperatively. There was no sternal wound infection. The vessels grafted were distal right coronary artery (n = 7), posterior descending artery (n = 8), obtuse marginal branches (n = 3), and posterolateral ventricular branch (n = 1); 1 patient received the composite graft as a sequential graft to the posterior descending artery and posterolateral left ventricular branches. The mean graft-free flow of the RIMA and RA composite graft was 98.06 ± 16.93 mL/min compared to left internal mammary artery flows of 55.80 ± 8.99 mL/min. All 16 patients who had a good echo window showed patent grafts when evaluated by two-dimensional echocardiography and color Doppler echocardiography. All of the 6 patients in whom the angiogram was repeated postoperatively showed patent RIMA and RA grafts.
Conclusions. Myocardial revascularization using proximal RIMA and RA in situ pedicle graft was safe in patients with diabetes and in obese and chronic obstructive pulmonary disease patients. This graft was useful to revascularize posterior descending artery, posterolateral ventricular branches of right coronary artery, and obtuse marginal branches where a left internal mammary artery and RA composite graft cannot be used because of technical reasons. Its usage was not associated with sternal wound infection.
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Introduction
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Arteriosclerosis of the saphenous vein graft continues to be the major cause of late failure of coronary artery bypass grafting [1]. The left internal mammary artery (LIMA) is an ideal bypass conduit because it remains free of arteriosclerosis even at late follow-up [2, 3]. In situ internal mammary artery (IMA) pedicle grafts are particularly indicated in young patients with long expected survival. Although the use of LIMA alone is not associated with increased incidence of sternal wound infection in patients with diabetes [4], the takedown of bilateral IMAs is associated with increased incidence (2.45% to 6.9%) of sternal wound infection in patients with diabetes and in obese and elderly patients [5, 6]. The use of bilateral IMA grafting doubles the odds ratio of risk compared with the use of a single mammary graft, and the combination of diabetes and double IMA grafts increase the odds ratio 13.9-fold [7]. The in situ right internal mammary artery (RIMA) is shorter and usually does not reach the target arteries such as the posterior descending artery, the posterolateral left ventricular branches, and the obtuse marginal branches. The free RIMA grafts to the right coronary artery have the limitation of lower long-term patency rates, about 75% when evaluated at a mean period of 94 months [8]. Using the radial artery (RA) graft with RIMA as the source of arterial inflow and at the same time preserving the blood supply to the body of the sternum on the right side may reduce the incidence of postoperative sternal wound infection. This composite pedicle graft was based on the proximal RIMA because it is reported that "inverted" pedicled grafts based on the superior epigastric and musculophrenic branches are not recommended because of a predictably low flow through an inferiorly based pedicle [9]. In addition, composite arterial conduits (branched, lengthened, or both) constructed using one or both IMAs and RA make them suitable for revascularizing all myocardial territories [10].
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Patients and methods
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Between July 2000 and October 2001, 18 patients underwent coronary artery bypass grafting using a RIMA and RA composite in situ graft, which was made by the anastomosis of the proximal inch of RIMA to the free RA graft. There were 16 men and 2 women, with mean age of 59.47 ± 10.29 years (range 45 to 76 years). Eleven patients had type II diabetes and were on insulin, 8 had chronic obstructive pulmonary disease, 6 were obese with a mean body mass index of 32.6 (range 31.14 to 34.97), and 3 patients had atherosclerotic ascending aorta. All the patients had New York Heart Association class III or class IV angina. Six patients had suffered acute myocardial infarction before surgery. The anastomosis of RIMA and RA was constructed in end to end fashion, and the middle and distal thirds of the RIMA were left undisturbed. This is a new technique of RIMA usage that preserves the blood supply to the body of the sternum on the right side. This study has been approved by the institutional ethics committees, and informed consent has been obtained from all these patients to perform the operation using this technique and to perform postoperative surveillance of the graft patency. Six of the patients gave consent to undergo postoperative angiographic evaluation.
The patients had either double-vessel disease (n = 5) or triple-vessel disease (n = 13) and had significant stenosis in the diseased vessels. The free flows of LIMA grafts and of the RIMA and RA composite grafts were measured. The length of RIMA and RA composite grafts had also been recorded. Postoperatively, the graft patency was assessed using a noninvasive method with high-frequency transthoracic echocardiography as described by De Simone and colleagues [11]. The graft patency was confirmed in 6 of these patients by selective angiography. The color Doppler echocardiography evaluation of the graft correlated well with angiography.
Technique of anesthesia
The patients were premedicated with diazepam (0.1 mg/kg) orally the night before the procedure. Intraoperatively, electrocardiogram, RA and femoral artery pressures, pulmonary artery pressures, nasopharyngeal temperature, and urinary output were monitored. The induction of anesthesia was achieved with fentanyl citrate (10 to 12 µg/kg), midazolam (0.1 mg/kg), and vecuronium bromide (0.1 mg/kg). The anesthesia was maintained with supplemental doses of fentanyl, propofol, and low-concentration doses of isoflurane as necessary. All these patients were started on intravenous infusion of diltiazem (4 mg/h) and nitroglycerine infusion before the harvest of RA was begun.
Arterial conduit harvest technique
The RA was harvested using extrafascial technique as described previously [12]. After standard median sternotomy, the LIMA was harvested as a pedicle graft using ectrocautery and standard technique. The proximal third of the RIMA was harvested as a pedicle graft up to the junction of manubrium of sternum and body of sternum. The lower two thirds of the RIMA was left intact to continue the blood supply to the sternum.
After systemic heparinization (2 to 4 mg/kg), the RIMA was divided after it was clipped distally at the level of junction of manubrium of sternum and body of the sternum. The proximal end of the free radial graft was anastomosed to the distal end of the proximal RIMA in end to end fashion using either 7-0 or 8-0 polypropylene continuous suture tied at the heel and the toe before the institution of cardiopulmonary bypass. The LIMA was divided distally just proximal to its bifurcation into musculophrenic and superior epigastric arteries. The free flows of the blood from the distal end of both of the divided conduits were measured simultaneously for a period of 1 minute, and then the distal ends were clipped. Both the conduits were covered with a gauze soaked in papaverine solution (4 mg/mL) to minimize vasospasm.
Surgical technique
All patients underwent operation through a standard median sternotomy incision. In 14 of these patients, myocardial revascularization was performed on cardiopulmonary bypass, which was instituted in standard fashion, and myocardial protection was achieved using the intermittent ischemic fibrillatory arrest technique. In the remaining 4 patients revascularization was carried out on a beating heart. A tissue stabilizer (Octopus II or 3, Medtronic Inc, Minneapolis, MN) and intracoronary shunts (Medtronic Inc, Grand Rapids, MI) were used during the construction of the distal anastomoses. Intravenous infusion of nitroglycerine (2 to 5 µg · kg-1 · min-1) and diltiazem (2 to 4 mg/h) were continued to minimize the graft spasm until the first or second postoperative day, after which patients were given oral diltiazem.
Postoperative evaluation of graft patency
The anatomic and functional evaluation of graft patency was done by color Doppler echocardiography and transthoracic echocardiography using a linear vascular 10-MHz probe with superficial package of Vivid Five (GE Medical Systems, Milwaukee, WI) in 16 of these patients, all of whom had good echo window at 2 weeks after the operation. The probe was positioned in the right first and second intercostal spaces. The RIMA and RA graft diameter, peak systolic velocity, and peak diastolic velocity were measured in these patients. In 6 of these patients the graft patency was confirmed by selective angiography between 3 months and 1 year postoperatively.
Statistical analysis
A t test was employed to assess the statistical significance of differences in mean values, and the data were considered significant if the p value was less than 0.05.
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Results
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All 18 patients received RIMA and RA in situ graft. The intraoperative free flows of RIMA and RA grafts ranged from 72 to 135 mL/min (mean 98.06 ± 16.93 mL/min), and LIMA free flows ranged from 45 to 75 mL/min (mean 55.80 ± 8.99 mL/min); these data are shown in Figure 1.
The increase of 42.56 mL/min (77%) in the mean blood flow (95% confidence interval 31.1 to 53.3 mL/min) was highly significant statistically (t14df = 6.99, p < 0.001). The mean diameter of proximal RIMA was 2.81 ± 0.30 mm (range 2.5 to 3.0 mm) and of the distal LIMA was 1.89 ± 0.21 mm (range 1.5 to 2.0 mm).
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Fig 1. Comparison of free blood flows between left internal mammary artery (LIMA) and right internal mammary artery (RIMA) and radial artery (RA) composite graft. The mean blood flow was 55.80 mL/min (± 8.99 mL/min) for LIMA and 98.06 mL/min (± 16.93 mL/min) for RIMA + RA. The increase of 42.56 mL/min (77%) in the mean blood flow (95% confidence interval 31.1 to 55.3 mL/min) was highly significant statistically (t14df = 6.99, p < 0.001).
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The target arteries grafted were distal right coronary artery (n = 7), posterior descending artery (n = 8), obtuse marginal branches (n = 3), and posterolateral left ventricular branch (n = 1); 1 patient received the composite graft as a sequential graft to both the posterior descending artery and posterolateral left ventricular branches. There was no hospital mortality. All the patients had uneventful recovery. There was no incidence of perioperative myocardial infarction (based on electrocardiogram or enzymatic evidence). There was no incidence of perioperative stroke, lung problems, or sternal wound infection. The postoperative evaluation of graft patency was carried out by color Doppler echocardiography and transthoracic echocardiography, which demonstrated a mean peak systolic velocity of 23.85 ± 2.54 cm/s and a mean peak diastolic velocity of 39.54 ± 3.86 cm/s at rest; these measurements were suggestive of patent grafts. In 16 patients a good signal of the diastolic flow of the RIMA and RA graft could be obtained by color Doppler echocardiography. In the 6 patients who consented to postoperative angiographic evaluation, graft patency was confirmed by selective angiography of the RIMA (Figs 2, 3).
All the patients were free of angina during the follow-up period, which ranged from 1 to 16 months (mean 12.8 months). In all patients a pulsatile flow in the distal RIMA could be demonstrated using color Doppler echocardiography.
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Fig 2. Postoperative selective angiogram of right internal mammary artery (RIMA) and radial artery (RA) graft (proximal part). Arrowhead points to the anastomotic site of RIMA with RA.
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Fig 3. Postoperative angiogram of right internal mammary artery and radial artery (RA) graft (distal part). Arrowhead points to the anastomotic site of RA with posterior descending artery.
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Comment
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Bilateral IMA grafting does not increase surgical mortality [13] and has proved to be more beneficial in terms of long-term survival than LIMA alone [14]. However, bilateral mammary artery harvest has been reported to be associated with a higher incidence of deep sternal wound infection in patients with diabetes and in obese and elderly patients [5, 6]. Furthermore, in situ RIMA graft has the limitation of length, and free RIMA graft has the problem of lower long-term patency [8]. Although the early and midterm patency rates for free RA grafts have been reported to be good [15–17], early graft occlusion in 10% of RA grafts [18] can be attributed to the technical difficulties encountered during the proximal anastomosis of the RA to the ascending aorta. This is probably caused by the disparity of the luminal size and wall thickness between the aorta and the RA. The composite arterial conduits have been used for surgical revascularization for coronary artery disease with improved midterm angiographic patency rates [19]. It has also been reported that composite grafts of LIMA and RA have higher free flows compared to LIMA flow alone [20]. The technique described in this article has the advantage of ease of anastomosis because of the similarity of the wall thickness and the luminal size of proximal RIMA and RA. This technique also adds to the length of the conduit, and this graft has the advantage of being usable as an in situ graft for revascularizing the branches of the right coronary artery, ie, the posterior descending artery and posterolateral left ventricular branches, which is not possible using an in situ RIMA graft. This technique has the additional benefit of having an alternate source of arterial inflow for the RA, unlike when it is used with LIMA as a T or Y graft. We have used this composite graft passing through the transverse sinus to revascularize the stenosed obtuse marginal branches in which the LIMA graft was used as a sequential graft to bypass the left anterior descending coronary artery and the high diagonal branch or ramus intermedius. Using this technique, we can preserve the vascularity of the sternum by leaving the middle and distal thirds of the RIMA, which theoretically minimizes the incidence of wound infection in patients with diabetes, patients with chronic obstructive pulmonary disease, and obese patients. However, the objectivity of this assumption must be evaluated with isotope or other studies.
Limitations of the study
This study involves too small a number of patients and too short a follow-up period to draw any firm conclusions. Further randomized studies are required to validate the theoretical advantage of the procedure, and objective studies are necessary to document the preservation of the sternal blood supply with this technique. Although the Doppler echocardiography study is an accepted method of assessing IMA graft patency, serial angiographic studies should be carried out to validate this technique.
Our data suggest that the use of RIMA and RA in situ graft has the advantage over other techniques of revascularizing the branches of the right coronary artery (posterior descending artery, posterolateral left ventricular branches) and the branches of the left circumflex artery, where a LIMA and RA Y graft is technically difficult. This technique is also useful in revascularizing the right coronary artery territory in patients with atherosclerotic or calcified ascending aorta on a beating heart. The higher early graft patency rates and minimal sternal wound infection make this composite graft an ideal conduit when bilateral mammary artery usage is risky in patients with diabetes, obese patients, and patients with chronic obstructive pulmonary disease.
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Acknowledgments
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We thank Dr A. V. Anjaneyulu, DM, for doing the echocardiographic evaluation of the patients. We appreciate the assistance of Mr Guru Prasad Sistla, MS, for statistical analysis and Mr Pavan K. Munagala for preparing the manuscript.
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Abstract
Introduction
