Ann Thorac Surg 1998;65:731-734
© 1998 The Society of Thoracic Surgeons
Original Articles: Cardiovascular
Angiographic Follow-up of Internal Thoracic Artery for Free Bypass Grafting
Tomoyuki Masuda, MD,
Yasuo Matsuda, MD,
Yoshinori Tanimoto, MD,
Kensuke Sakata, MD,
Kenji Hayashi, MD,
Yurio Kobayashi, MD
Cardiovascular Center, Saiseikai Shimonoseki Hospital, Shimonoseki, Japan
Accepted for publication September 17, 1997.
Dr Masuda, Saiseikai Shimonoseki Hospital, Kifune 3-4-1, Shimonoseki, Yamaguchi 751, Japan.
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Abstract
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Background. The use of free internal thoracic artery (ITA) grafts in patients with smaller body surface areas has been questioned because of technical difficulties and inadequate graft flow.
Methods. To evaluate postoperative changes in the diameter of free ITA grafts, we performed coronary angiography immediately after coronary artery bypass grafting and then again at a mean of 42 ± 6 months later. In 20 consecutively treated patients, 21 free ITAs were used as bypass conduits. Two ITA grafts that were patent at the time of the first angiography had closed at the second angiography. Postoperative changes in ITA graft diameter were measured in the 19 patent ITA grafts.
Results. At the first angiography, the mean diameters of the proximal, middle, and distal ITA grafts were 2.28 ± 0.45 mm, 2.34 ± 0.39 mm, and 2.12 ± 0.38 mm, respectively. At the second angiography, the mean diameters of the proximal, middle, and distal ITA grafts were 2.85 ± 0.50 mm, 2.89 ± 0.53 mm, and 2.72 ± 0.53 mm, respectively. All segments of the ITA grafts had dilated significantly between the first and second angiographic evaluations (p < 0.01). The percentage change in graft diameter was greater when the initial ITA diameter was less than 2.3 mm (32.0% ± 28.0%) than when it was 2.3 mm or more (18.8% ± 11.3%) (p < 0.05).
Conclusions. The postoperative increase in free ITA graft diameter depends on coronary blood flow requirements.
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Introduction
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Although an internal thoracic artery (ITA) graft has a higher late patency rate than a saphenous vein graft [1][2][3], there are limitations to the use of in situ ITA grafts [4][5][6][7][8]. An in situ ITA graft is not able to reach a distal coronary artery when the in situ thoracic pedicle is too short. An in situ right ITA graft should not be used to revascularize the anterior descending, diagonal, or upper circumflex branches because the risk of dividing or injuring the underlying artery is great during reentry for reoperation. On the other hand, grafting of the free right ITA to the anterior descending or circumflex vessel avoids potential injury during reentry; the free graft will reach any coronary branch. However, the use of an in situ ITA graft in a patient with a smaller body surface area has been questioned [9]. The purpose of the present study was to evaluate changes in the diameter of small ITA grafts over time.
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Material and Methods
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Preoperative Clinical Characteristics
From September 1989 through May 1992, 43 patients received free ITA grafts at our institution. Of these 43 patients, the initial consecutively seen 23 patients were scheduled to undergo a second postoperative coronary angiography. Two patients did not consent to the second angiography and 1 patient could not be contacted at the scheduled time of the second angiography. Therefore, the study population consisted of 20 patients (17 men and 3 women).
The first postoperative coronary angiography was performed within 1 month after operation. The mean interval between the first and second postoperative angiographic evaluations was 42 ± 6 months. At the time of operation, the mean patient age was 54 ± 7 years (range, 42 to 68 years). The mean body surface area was 1.68 ± 0.14 m2 (1.72 ± 0.10 m2 in the men and 1.48 ± 0.11 m2 in the women), the mean height was 156 ± 26 cm, and the mean weight was 64 ± 8 kg.
During the angiographic follow-up examination, hypertension of greater than 160/95 mm Hg or under-treatment of hypertension was documented in 8 patients (40%). Two patients (10%) had diabetes. A serum cholesterol level of more than 240 mg/dL was found in 6 (30%) patients. A smoking history of more than 1 pack per day was elicited from 2 patients (10%). Six patients (30%) had a family history of coronary artery disease. The New York Heart Association functional class was used to describe preoperative angina in most of the patients. One patient (5%) was in class I, 14 (70%) were in class II, 4 (20%) were in class III, and 1 (5%) was in class IV.
The extent of coronary atherosclerosis was classified at angiography and was based on an estimated luminal narrowing of 70% or more. This degree of narrowing was present in 2 vessels in 8 patients (40%) and in three vessels in 11 patients (55%). Narrowing of the left main luminal diameter by 50% or more was found in 1 patient (5%). Preoperative left ventricular function was normal in 5 patients (25%), mildly impaired (impairment confined to one of five myocardial segments) in 4 patients (20%), moderately impaired (impairment in two or three segments) in 9 patients (45%), and severely impaired (global impairment) in 2 patients (10%).
Surgical Procedure
A median sternotomy incision was used in all patients. A Favaloro retractor was used to facilitate exposure of the ITA. The ITA was mobilized from the chest wall with the aid of electrocautery within its pedicle of concomitant veins, surrounding fat, and fascia. Larger side branches were controlled with hemostatic clips. After the administration of heparin, the pedicle was transected and covered with a papaverine-soaked sponge until used.
Cardiopulmonary bypass and cold potassium crystalloid cardioplegia were used in all patients. During cardiac arrest, all distal coronary anastomoses were constructed with interrupted siliconized 7-0 silk sutures, and all proximal anastomoses were constructed into the aorta with interrupted 7-0 polypropylene sutures after an aortotomy had been made. The aortotomy consisted of a 7-mm slitlike incision in the aorta; it was not circular or punched out. An incisional aortotomy was considered more feasible for the small ITA.
Clinical and Angiographic Follow-up
Cardiac medications were prescribed to create similar conditions at the time of the sequential angiographic evaluations. Calcium-channel blockers were being taken by 12 patients (60%) and nitrates by 20 patients (100%) at the first postoperative angiography. Calcium-channel blockers were being taken by 10 patients (50%) and nitrates by 18 patients (90%) at the second postoperative angiography. Aspirin was being taken by 20 patients (100%) at the first angiography and by 18 patients (90%) at the second angiography. None of the patients required the medications for control of angina.
Coronary artery diameters were measured in the 30-degree right anterior oblique projection in end-diastole using Vernier calipers [10][11]. The catheter was measured at its tip, which was positioned within the corresponding coronary artery ostium. Actual coronary artery diameters were calculated by reference to the catheter tip.
The free ITA grafts were measured in their proximal, middle, and distal thirds. The left main trunk was measured distally before the bifurcation of the left anterior descending coronary artery and the circumflex coronary artery. The proximal, middle, and distal segments of the left anterior descending coronary artery, the circumflex coronary artery, and the right coronary artery then were measured. The coronary artery distal to the graft was not measured, considering the influence of the graft flow. The percentage change in the luminal diameter of the ITA was calculated as follows: 
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Statistical Analysis
All values are expressed as means plus or minus the standard deviation. A paired t test was used to evaluate changes in the luminal diameter between the first and second angiographic evaluations. An unpaired t test was used to evaluate differences in ITA luminal diameter between groups with larger and smaller initial ITA diameters, and between groups with progressed and nonprogressed proximal lesions. A p value of less than 0.05 was considered statistically significant.
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Results
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We performed 21 free ITA grafts, 13 in situ ITA grafts, and 14 saphenous vein grafts. The locations of the free ITA grafts are shown in Table 1. The mean number of grafts per patient was 2.4. No operative deaths occurred. One patient required reoperation for persistent bleeding. One patient had a transient elevation of the left diaphragm. No patient had a perioperative myocardial infarction or stroke.
At the first postoperative angiography, 21 free ITA grafts and 13 in situ ITA grafts were patent and 2 saphenous vein grafts were closed. At the second postoperative angiography, all 13 in situ ITA grafts, 19 of 21 free ITA grafts, and 10 of 12 saphenous vein grafts were patent. The sites of direct aortic anastomosis were widely patent in 19 free ITA grafts. In 2 patients who had occlusion of their free ITA grafts at the second angiography, the diameters of the proximal, middle, and distal grafts at the first angiography were 2.48, 2.24, and 2.17 mm, respectively, in 1 patient and 2.58, 2.58, and 2.06 mm, respectively, in the other. In 1 of these patients, the native coronary artery distal to the bypass anastomosis showed the progression of atherosclerosis. All 20 patients were free of angina at the first angiography. At the second angiography, 1 patient had angina and 1 patient had symptoms of congestive heart failure. The remaining 18 patients had returned to work and full activity.
The sizes of the ITA grafts at the first and second postoperative angiographic evaluations are shown in Table 2. The diameters of the proximal, middle, and distal ITA grafts increased significantly between the first and second evaluations. The native coronary arteries were measured in 9 right coronary arteries, 10 left anterior descending coronary arteries, and 9 left circumflex coronary arteries that were not grafted. The mean diameter was 2.58 ± 0.69 mm at the first angiography and 2.57 ± 0.90 mm at the second angiography. The diameters of the native coronary arteries did not change significantly between the two angiographic evaluations.
Fig 1 shows the relation between ITA graft diameter at the first angiography compared with the second angiography. An increase in ITA diameter at the second angiographic evaluation was observed more frequently in grafts that had a smaller diameter at the first evaluation. Internal thoracic artery segments were divided into two groups according to the mean graft diameter at the first angiographic evaluation. The percentage increase in luminal diameter was significantly greater when the initial diameter was 2.3 mm or less (32.0% ± 28.0%) than when it was more than 2.3 mm (18.8% ± 11.3%) (p < 0.05) (Fig 2). The severity of the stenosis proximal to the ITA graft had progressed in 14 lesions and had not progressed in 5 lesions. The mean percent increase in ITA graft diameter was 30.6% in patients in whom the proximal lesion had progressed and 10.3% in those in whom it had not (p < 0.01). Representative frames from the sequential angiographic evaluations in an individual patient are shown in Fig 3.
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Free internal thoracic artery (ITA) graft diameters at the first and second angiographic evaluations. An increase in free ITA graft diameter at the second angiography was observed more frequently in grafts that had smaller diameters at the first angiography.
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The percentage increase in luminal diameter was significantly greater when the initial diameter was 2.3 mm or less than when it was more than 2.3 mm. (ITA = internal thoracic artery.)
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Serial angiographic frames from a representative case. The arrows indicate a right free internal thoracic artery graft to the circumflex artery. An increase in the diameter of the graft was observed between the first (A) and second (B) angiographic evaluations.
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Comment
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Operative Technique
The technical difficulties associated with free ITA graft proximal anastomosis have been reported, especially when aortic atherosclerosis is present or the ITA is small [6][12][13]. In the present study, the mean body surface area was 1.72 m2 in the men and 1.48 m2 in the women. These areas are smaller than those seen in western countries [9]. The size of the free ITA grafts also is considered to be smaller [9][14]. Aortotomy was accomplished with a slitlike incision instead of the large, punched-out hole that seems to be more suitable for anastomosis of a small ITA to the ascending thoracic aorta. Stenosis or occlusion at the site of the anastomosis of the free ITA to the aorta was not observed at the first postoperative angiographic evaluation. Two free ITA grafts were occluded at the second postoperative angiographic evaluation, although the size of the ITA grafts was not significantly small. The present results suggest that it is technically feasible to anastomose a small ITA to the aorta.
Changes in Internal Thoracic Artery Graft Diameter
Previous studies have reported the enlargement of in situ ITA grafts at late postoperative angiographic evaluations [15][16]. In this study we measured the diameters of free ITA grafts in sequential angiographic evaluations. In situ ITA grafts and free ITA grafts are not significantly different in regard to their patency, vascular wall cellular structure, or perfusion of the vasa vasorum [17]. In the present study, the free ITA grafts dilated between the first and second angiographic evaluations. The diameters of nongrafted native coronary arteries were measured as a reference for comparison with the changes in ITA graft diameters. The diameters of the native coronary arteries were unchanged between the first and second angiographic evaluations. Enlargement of free ITA grafts measured under the same conditions could be documented by comparison with unchanged native coronary arteries. Further, prominent enlargement of free ITA grafts was observed more frequently in those grafts that initially were smaller (Fig 2).
The diameters of free ITA grafts had increased more in patients in whom the proximal artery lesion had progressed than in those in whom it had not. It has been reported that postoperative enlargement of in situ ITA grafts depends on coronary blood flow requirements [18][19]. When stenosis of the grafted artery is severe and flow through the ITA graft is sufficient, the diameter of the ITA graft increases postoperatively. The flow through in situ ITA grafts increases when the competitive antegrade flow through proximal coronary lesions decreases [16]. The physiologic adaptation of the ITA may be one of the reasons for the excellent long-term patency of this conduit [19].
Study Limitations
The number of patients included in this study was limited. Further investigation should confirm the excellent long-term adaptability of the free ITA graft.
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Acknowledgments
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We thank John R. Kramer, MD, Cleveland Clinic Foundation, for assistance in reviewing the manuscript.
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References
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Abstract
Introduction
