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Improvement of Myocardial Stress Perfusion After Off-Pump Revascularization Using Bilateral Internal Thoracic In Situ Grafts Versus Y-Composite Grafts
Chang Hyun Kang, MD, Ki-Bong Kim, MD, Chun Soo Park, MD, Jin Chul Paeng, MD, and Dong Soo Lee, MD Departments of Thoracic and Cardiovascular Surgery, and Nuclear Medicine, Seoul National University Hospital, Seoul, Korea
Background. There is a concern that revascularization using bilateral internal thoracic arteries (ITA) as a composite graft may not supply sufficient blood flow to a wider area of myocardium when compared with grafting using bilateral in situ ITAs. Methods. One-hundred three patients who underwent off-pump coronary artery bypass using bilateral ITAs for revascularization of the left coronary system were studied prospectively. Bilateral ITAs were used as in situ grafts in 49 patients (group 1) and as a Y-composite graft in 54 patients (group 2). Resting and stress myocardial single-photon emission computed tomography (SPECT) was performed preoperatively and 3 months postoperatively. Myocardial perfusion was automatically quantified and expressed as a percentage of the maximal uptake. The left coronary territory was divided into 16 segments. A total of 379 segments (154 segments in group 1; 225 segments in group 2) that indicated decreased stress perfusion preoperatively were included in this study. Results. Resting myocardial perfusion revealed no significant differences with regard to both the preoperative (77.5 ⴞ 9.3% vs 78.8 ⴞ 8.8%) and postoperative SPECT
(78.3 ⴞ 10.0% vs 77.2 ⴞ 10.5%) between groups 1 and 2 (p ⴝ not significant [NS]). However, stress myocardial perfusion was significantly lower in group 1 preoperatively (62.5 ⴞ 10.8% vs 65.4 ⴞ 10.1%, p < 0.01). Although it improved postoperatively, there were no differences regarding postoperative stress myocardial perfusion between the two groups (75.5 ⴞ 11.3% vs 75.0 ⴞ 11.7%; p ⴝ NS). The degree of improvement regarding stress myocardial perfusion (difference between the preoperative and postoperative values) was higher in group 1 than in group 2 (13.0 ⴞ 9.4% vs 9.6 ⴞ 10.0%, p < 0.005). Conclusions. Myocardial SPECT demonstrated that revascularization using bilateral in situ ITAs exhibited a greater level of improvement with regard to stress perfusion postoperatively compared with Y-composite grafts. However, because there was no considerable difference with regard to postoperative stress perfusion between the two groups, revascularization using a Y-composite graft might also be sufficient for revascularization of the left coronary territory.
T
The aims of this study included (1) to compare myocardial perfusion between bilateral in situ ITAs and Y-composite ITAs and (2) to elucidate any difference with regard to myocardial stress perfusion between the bilateral in situ ITAs and Y-composite ITAs, based on resting and stress myocardial quantitative gated single-photon emission computed tomography (SPECT) performed preoperatively and 3 months after off-pump CABG (OPCAB).
he use of the left internal thoracic artery (ITA) with supplemental saphenous vein grafts has been the standard technique for coronary artery bypass grafting (CABG) in patients who exhibit multivessel disease. Recently, advantages such as enhanced long-term survival rates and greater freedom from reinterventions with the use of two ITAs instead of one have been demonstrated [1, 2]. Bilateral ITAs are used as bilateral in situ grafts or as a composite graft. Although a composite graft has indicated an increased coronary flow reserve through the graft [3, 4], there is a concern that because the composite arterial graft exhibits a single blood source, it may not supply sufficient blood flow to a wider area of myocardium [5, 6]. Accepted for publication June 11, 2004. Address reprint requests to Dr Kim, Department of Thoracic and Cardiovascular Surgery, Seoul National University Hospital, 28 Yeun-Kun Dong, Chong-Ro Ku, Seoul 110 –744, Korea; e-mail: [email protected].
© 2005 by The Society of Thoracic Surgeons Published by Elsevier Inc
(Ann Thorac Surg 2005;79:93– 8) © 2005 by The Society of Thoracic Surgeons
Material and Methods A total of 103 consecutive patients who underwent OPCAB for multivessel coronary artery disease between January 2000 and December 2002, were studied in a prospective nonrandomized manner. A computer-based patient database system was used for this prospective 0003-4975/05/$30.00 doi:10.1016/j.athoracsur.2004.06.056
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study. Myocardial SPECT was performed as a part of the routine clinical follow-up. Patient inclusion criteria included (1) patients who underwent myocardial revascularization under OPCAB, (2) patients who received skeletonized bilateral ITAs as either in situ grafts or a Y-composite graft for complete revascularization of the left coronary territory, (3) patients whose graft patency was confirmed by postoperative coronary angiography performed before discharge, and (4) patients in whom both the resting and stress myocardial SPECT were performed preoperatively and 3 months postoperatively. The patients who received other arterial grafts or free grafts anastomosed on the ascending aorta to revascularize the left coronary territory, or patients who did not receive the stress myocardial SPECT preoperatively because of intractable resting angina or an urgent or emergent situation were excluded from this study. Bilateral ITAs were used as in situ grafts in 49 patients (group 1) and as Y-composite grafts in 54 patients (group 2). All patients halted aspirin therapy the day before surgery and resumed it (300 mg/d) one day postoperatively. Postoperative (1.4 ⫾ 1.1 day) coronary angiography was performed in all of the patients and all of the grafts were confirmed as patent. There were no differences between the two groups in terms of sex, age, preoperative risk factors, ratio of unstable to stable angina, left ventricular ejection fraction measured by transthoracic echocardiography, and angiographic diagnosis (Table 1).
Surgical Methods and Revascularization Strategies OPCAB using skeletonized bilateral ITAs was performed as previously described [7]. The patients were heparinized with an initial dose of 1.5 mg/kg of heparin and periodically received supplemental doses to maintain an activated clotting time of ⬎300 seconds during OPCAB. Bilateral ITAs were preferred for use as in situ grafts for revascularization of the left coronary territory based on the assumption that two blood sources would be more favorable than a single blood source to improve longterm outcome. The right ITA was commonly used to revascularize the LAD by crossing the midline, or occasionally to revascularize the ramus or high obtuse marginal branch through the transverse sinus as an in situ graft. If the right ITA was too short to reach the left coronary territory or if the left coronary territory could not be completely revascularized with the bilateral in situ ITA grafts, a Y-composite graft was constructed before starting the distal anastomoses. In most instances of Y-composite graft construction, the right ITA was divided at its proximal section and was anastomosed to the side of the left ITA in a Y fashion using an 8-0 polypropylene continuous suture. Most of these end-to-side Y anastomoses were performed at the level of the pulmonary artery, and occasionally the right ITA was anastomosed to the distal left ITA unless it reached an optimal vessel such as the distal left circumflex territory. A sequential anastomosing technique was used for additional revascularization in both groups. The right coronary artery
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territory was revascularized using right gastroepiploic artery, radial artery, or saphenous vein grafts. Indication for bypass grafting occurred when the degree of native coronary stenosis was greater than 75%. Protamine was not given at the end of the procedure. The operations were all performed by a single surgeon (K-B.K.).
Myocardial SPECT Test Thallium-201 rest/dipyridamole stress technetium-99m methoxyisobutylisonitrile (MIBI) gated SPECT was performed before OPCAB. Thallium-201 (111 MBq) was injected at rest and SPECT was performed; dipyridamole (0.56 mg/kg) was then injected for more than 4 minutes to induce stress for assessment of the coronary perfusion reserve, and technetium-99m (925 MBq) was injected 3 minutes after stress. Gated technetium-99m-MIBI SPECT was performed 90 minutes after stress using a dual-head camera equipped with a low-energy high-resolution collimator (Vertex EPIC; ADAC Laboratories, Malpitas, CA). Thallium -201 rest/dipyridamole stress technetium-99mMIBI gated SPECT was repeated 3 months (102 ⫾ 20 days) after OPCAB as a follow-up examination, using the same protocol as was used for the preoperative study. A 20-segment model was adopted for regional analysis (Fig 1). Each segment was subtended to two coronary arterial territories (right and left coronary territories), and all of the 16 segments representing the left coronary territory (left anterior descending artery and left circumflex artery territories) were analyzed as a whole. The segments representing the right coronary artery territory were excluded.
Normal Korean Value of Myocardial SPECT Test (Control Group) To evaluate normal regional variation of perfusion and attenuation characteristics, myocardial SPECT tests were performed in an additional 55 Korean patients (28 males, 27 females; mean age of 49 ⫾ 9 years). They exhibited a low preexamination likelihood (⬍ 5%) of coronary artery disease [8], and were regarded by nuclear medicine physicians as normal dependent upon visual analysis of the SPECT images. In this control group, segmental perfusion was quantified with the same protocol as the patient groups (Fig 2).
Quantification of Myocardial Regional Perfusion After a review assessed by two experts with regard to overall image quality, the reconstructed images were analyzed with an automatic quantifying software package (AutoQUANT; ADAC Laboratories, Malpitas, CA) without manual intervention. Resting and stress segmental myocardial perfusion was quantified by measuring radioactivity and expressed as the percentage of the maximal radioactivity uptake. We studied the reversible ischemic myocardial area of the left coronary territory in the analysis. Normal preoperative perfusion segments, defined as those ⫺1 standard deviation (SD) over the control group preoperative stress SPECT test, were excluded. Resting perfusion defect segments, suggesting myocardial damage, were defined
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Table 1. Preoperative Characteristics and Risk Factors of Study Patients
Sex (Male : Female) Age (year) LVEF (%) Unstable : Stable Risk factors, n (%) Smoking Hypertension Diabetes mellitus Hyperlipidemia CRF PMH of stroke Angiographic diagnosis, n (%) Three-vessel disease Two-vessel disease LMD with or without peripheral disease CRF ⫽ chronic renal failure;
LMD ⫽ left main disease;
Group 1 (n ⫽ 49)
Group 2 (n ⫽ 54)
p Value
41:8 60.3 ⫾ 9.35 55.7 ⫾ 10.1 39:10
41:13 62.6 ⫾ 6.89 58.7 ⫾ 10.0 44:10
0.330 0.148 0.134 0.809
20 (40.8%) 30 (61.2%) 20 (40.8%) 9 (18.4%) 1 (2%) 10 (20.4%)
25 (46.3%) 33 (61.1%) 22 (40.7%) 17 (31.5%) 2 (3.7%) 6 (11.1%)
0.575 0.991 0.994 0.126 1.000 0.193
36 (73.5%) 9 (18.4%) 17 (34.7%)
42 (77.8%) 7 (13.0%) 15 (27.8%)
0.611 0.450 0.449
LVEF ⫽ left ventricle ejection fraction;
as those ⫺1 SD below the control group preoperative rest SPECT test, and were also excluded from the analysis. To evaluate the postoperative improvement of myocardial stress perfusion, the difference with regard to stress perfusion between preoperative and postoperative SPECT was compared between groups 1 and 2. A total of 379 reversible ischemic segments (154 segments in group 1; 225 segments in group 2) of the left coronary territories were included in the analysis.
PMH ⫽ past medical history.
reoperation for bleeding (2.0% vs 7.4%) between groups 1 and 2 (p ⫽ NS). We did not experience any low cardiac output syndrome, mediastinitis, or stroke in either group (Table 3).
Statistical Analysis Statistical analysis was performed using SPSS 11.0 software (SPSS Inc., Chicago, IL). The significance regarding differences between the two groups was assessed by the paired Student’s t test for the continuous variable. The discrete variables were analyzed using 2 and Fisher’s exact tests. All results were expressed as mean ⫾ SD and a value of p less than 0.05 was considered to be statistically significant.
Results Clinical Results The average number of distal anastomoses per bilateral ITA was smaller in group 1 than in group 2 (2.4 ⫾ 0.5 vs 2.7 ⫾ 0.7; p ⬍ 0.01), although there was no significant difference regarding the average number of distal anastomoses per patient between the two groups (3.1 ⫾ 0.7 in group 1 vs 3.3 ⫾ 0.9 in group 2;p ⫽ not significant [NS]). A smaller number of patients in group 1 required sequential anastomoses than in group 2 (28.6% vs 57.4%; p ⬍ 0.01), and a smaller number of sequential anastomoses using ITAs were performed in group 1 than in group 2 (12.0% vs 27.0%; p ⬍ 0.01) (Table 2). There were no significant differences regarding the incidence of postoperative morbidities such as atrial fibrillation (22.4% vs 18.5%), perioperative myocardial infarction (4.1% vs 1.9%), acute renal failure (2.0% vs 0%), and
Fig 1. Twenty-segment model for quantification of myocardial regional perfusion. (LAD ⫽ left anterior descending coronary artery; LCX ⫽ left circumflex coronary artery; RCA ⫽ right coronary artery.)
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Fig 2. Normal Korean values of myocardial single-photon emission computerized tomography. (A) Male; (B) female.
Myocardial SPECT Test In the restsing SPECT, the mean values of preoperative segmental perfusion were 77.5% ⫾ 93% in group 1 and 78.8 ⫾ 8.8% in group 2. The mean values of postoperative segmental perfusion were 78.3 ⫾ 10.0% in group 1 and 77.2 ⫾ 10.5% in group 2, respectively (p ⫽ NS). In the stress SPECT, the mean values of preoperative segmental perfusion were significantly lower in group 1 than in group 2 (62.5 ⫾ 10.8% vs 65.4 ⫾ 10.1%; p ⬍ 0.01) although there was no difference with regard to the postoperative segmental perfusion between groups 1 and 2 (75.5 ⫾ 11.3% vs 75.0 ⫾ 11.7%;p ⫽ NS). The difference
between the preoperative and postoperative SPECT with regard to stress perfusion was higher in group 1 than in group 2 (13.0 ⫾ 9.4 vs 9.6 ⫾ 10.0; p ⬍ 0.01) (Table 4).
Comment This study demonstrated two main findings. First, both the bilateral in situ ITAs and Y-composite grafts improved the stress myocardial perfusion after OPCAB, and there were no considerable differences regarding the postoperative myocardial stress perfusion between the two groups. Second, revascularization using bilateral in
Table 2. Comparison of Distal Anastomoses
Distal anastomoses/patient Distal anastomoses/bilateral ITAs Patients with sequential anastomosis Sequential anastomoses/ITA anastomoses ITA ⫽ internal thoracic artery.
Group 1
Group 2
p Value
3.1 ⫾ 0.7 2.4 ⫾ 0.5 14 out of 49 (28.6%) 14 out of 117 (12.0%)
3.3 ⫾ 0.9 2.7 ⫾ 0.7 31 out of 54 (57.4 %) 40 out of 148 (27.0%)
0.104 0.005 0.003 0.001
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Table 3. Postoperative Morbidities
Atrial fibrillation PMI ARF Reoperation for bleeding LCOS Mediastinitis Stroke
Group 1
Group 2
p Value
11 (22.4%) 2 (4.1%) 1 (2.0%) 1 (2.0%) 0 0 0
10 (18.5%) 1 (1.9%) 0 4 (7.4%) 0 0 0
0.621 0.603 0.224 0.366 ... ... ...
ARF ⫽ acute renal failure; LCOS ⫽ low cardiac output syndrome; PMI ⫽ perioperative myocardial infarction.
situ ITAs exhibited a greater degree of improvement regarding myocardial stress perfusion to supply the left coronary territory, compared with the improvement observed using the Y-composite graft. Enhanced long-term survival rates have been indicated when bilateral ITAs are used rather than a single ITA in patients exhibiting multivessel disease [1, 2]. The skeletonized technique for harvesting the ITA allowed additional length and easier use of ITAs with favorable results [7, 9, 10]. Those results have provided the foundation for using bilateral ITAs to achieve complete myocardial revascularization. The use of bilateral ITAs as in situ grafts exhibits the assumptive advantage that multiple blood sources may be more favorable than a single blood source for improving long-term outcome. The prerequisite for using bilateral in situ ITAs for complete arterial revascularization is sufficient length for an in situ right ITA to reach the desired anastomotic site on the left coronary territory. Despite the extra length obtained by skeletonization, the length of the right ITA is the main limitation for bilateral in situ ITA grafting. Construction of a composite graft such as a Y or T graft increases the length of the ITA, and allows the extensive use of bilateral ITA grafts to revascularize the left coronary system as well as the right coronary system [11]. Although construction of a composite graft has revealed increased coronary flow reserve and favorable outcome [3, 4, 11–13], there is a concern that because the composite arterial graft only harbors a single blood source, it may not supply sufficient blood flow to a wider area of myocardium [5, 6]. Lev-Ran and associates [6] revealed a decreased angina recurrence and an increased midterm survival rate regarding patients with in situ grafts, although early results of the patients with composite grafts were comparable with those of in situ grafts. In their study, postoperative coronary angiography was performed in 5.9% of their patients and the patency of the composite grafts was much lower than in situ grafts. They suggested technical errors related to the complexity of composite grafting to be the cause of the differences regarding late follow-up results. We confirmed the patency of all grafts using postoperative coronary angiography. Although we did not demonstrate the midterm results, there were no considerable differences regarding the incidence of early postoperative morbidities such as atrial fibrillation, peri-
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operative myocardial infarction, acute renal failure, or bleeding reoperation between the two groups. Sakaguchi and associates [5] demonstrated a substantially higher coronary flow reserve in the in situ group than in the composite group using analysis of positron emission tomography (PET) images performed 2 weeks after CABG. They suggested that the composite graft was unable to fully respond to the flow demand of the whole left coronary system. As the authors indicated, their study was performed early after surgery, when the use of cardiopulmonary bypass may affect the regional myocardial blood flow. The present study consisted of patients who underwent OPCAB. We performed myocardial SPECT 3 months after OPCAB, when ischemic myocardial dysfunction would be expected to have recovered from ischemia after revascularization [14]. Our study indicated a significantly higher degree of difference between the preoperative and postoperative stress SPECT in group 1 than in group 2. A higher degree of difference between the preoperative and postoperative stress SPECT suggests that bilateral in situ ITAs experienced a greater improvement with regard to myocardial stress perfusion after surgery, which supplied the entire left coronary territory, compared with the Y-composite graft. Although the degree of difference between the preoperative and postoperative stress SPECT was higher in group 1, there was no marked difference with regard to stress perfusion between the two groups after OPCAB. These results suggest that both the bilateral in situ ITAs and composite grafts are able to fully respond to the flow demand of the left coronary territory, even though bilateral in situ ITAs indicate a higher degree of improvement regarding myocardial stress perfusion after surgery. We preferred bilateral in situ ITAs for complete revascularization of the left coronary territory. If the right ITA was too short to reach the left coronary territory or if the left coronary territory could not be completely revascularized with bilateral in situ ITA grafts, a Y-composite graft was then constructed. Although the segmental perfusion in the preoperative stress SPECT was significantly lower in group 1, the number of distal anastomoses per bilateral ITAs and the number of sequential anastomoses were higher in group 2. Group 1 may have exhibited more proximal coronary artery disease that required a smaller number of distal anastomoses, and group 2 may have exhibited more peripheral and multiTable 4. Comparison of Segmental Perfusion Values Between the Two Groups
Rest (% uptake) Preoperative Postoperative Stress (% uptake) Preoperative Postoperative Difference in stress perfusion
Group 1
Group 2
p Value
77.5 ⫾ 9.3 78.3 ⫾ 10.0
78.8 ⫾ 8.8 77.2 ⫾ 10.5
0.176 0.284
62.5 ⫾ 10.8 75.5 ⫾ 11.3 13.0 ⫾ 9.4
65.4 ⫾ 10.1 75.0 ⫾ 11.7 9.6 ⫾ 10.0
0.008 0.705 0.001
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ple coronary arterial disease that required a larger number of distal grafts. Proximal coronary artery disease may decrease stress perfusion in a wider coronary territory than peripheral coronary arterial disease, and may have caused the lower preoperative stress perfusion level in group 1. As to the effect of sequential grafting on coronary perfusion, the authors do not believe that multiple sequential anastomoses caused flow steal and decreased coronary perfusion. This was demonstrated based on the evaluation that more frequent sequential grafting in group 2 did not decrease the postoperative myocardial stress SPECT when compared with group 1 who exhibited a smaller number of sequential grafts. On the contrary, we believe that incomplete revascularization may result in a residual ischemic area and consequently a decreased coronary perfusion.
Limitations There are limitations to the present study that must be recognized. First, the present study was not performed in a randomized manner, because randomized controlled trials with regard to this type of study are often unrealistic and impractical. Although the study involved a relatively small number of patients and was not randomized, the trial was performed prospectively using a computer-based database system. Second, there is a base line difference between the two groups. In the stress SPECT, the mean values of preoperative segmental myocardial perfusion were significantly lower in group 1 than in group 2. To overcome this base line difference, we calculated the difference of stress perfusion between the preoperative and postoperative SPECT and compared the two groups. Third, using coronary angiography to confirm the graft patency was performed in the early postoperative period and the myocardial SPECT was performed 3 months after OPCAB. Some grafts may have occluded during the 3 postoperative months, which would affect the results of postoperative myocardial SPECT. Myocardial SPECT demonstrated that revascularization using bilateral in situ ITAs exhibited a higher degree of improvement regarding myocardial stress perfusion supplying the left coronary territory, compared with that using a Y-composite graft. However, because there was no considerable difference with regard to postoperative stress perfusion between the two groups, revasculariza-
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tion using a Y-composite graft might also be sufficient for revascularization of the left coronary territory.
References 1. Buxton BF, Komeda M, Fuller JA, Gordon I. Bilateral internal thoracic artery grafting may improve outcome of coronary artery surgery: risk-adjusted survival. Circulation 1998;98: II1– 6. 2. Lytle BW, Blackstone EH, Loop FD, et al. Two internal thoracic artery grafts are better than one. J Thorac Cardiovasc Surg 1999;117:855–72. 3. Royse AG, Royse CF, Groves KL, Bus B, Yu G. Blood flow in composite arterial grafts and effect of native coronary flows. Ann Thorac Surg 1999;68:1619 –22. 4. Wendler O, Hennen B, Markwirth T, et al. T grafts with the right internal thoracic artery to left internal thoracic artery versus the left internal thoracic artery and radial artery: flow dynamics in the internal thoracic artery main stem. J Thorac Cardiovasc Surg 1999;118:841– 8. 5. Sakaguchi G, Tadamura E, Ohnaka M, Tambara K, Nishimura K, Komeda M. Composite arterial Y graft has less coronary flow reserve than independent grafts. Ann Thorac Surg 2002;74:493– 6. 6. Lev-Ran O, Paz Y, Pevni D, et al. Bilateral internal thoracic artery grafting: Midterm results of composite versus in situ crossover graft. Ann Thorac Surg 2002;74:704 –11. 7. Kim K-B, Cho KR, Chang W-I, Lim C, Ham BM, Kim YL. Bilateral skeletonized internal thoracic artery graftings in off-pump coronary artery bypass: early result of Y versus in situ grafts. Ann Thorac Surg 2002;74:S1371– 6. 8. Pryor DB, Shaw L, Harrell FE Jr, et al. Estimating the likelihood of severe coronary artery disease. Am J Med 1991;90:553– 62. 9. Gurevitch J, Paz Y, Shapira I, et al. Routine use of bilateral skeletonized internal mammary arteries for myocardial revascularization. Ann Thorac Surg 1999;68:406 –11. 10. Kramer A, Mastsa M, Paz Y, et al. Bilateral skeletonized internal thoracic artery grafting in 303 patients seventy years and older. J Thorac Cardiovasc Surg 2000;120:290 –7. 11. Calafiore AM, Contini M, Vitolla G, et al. Bilateral internal thoracic artery grafting: Long-term clinical and angiographic results of in situ versus Y grafts. J Thorac Cardiovasc Surg 2000;120:990 – 8. 12. El Nakadi B, Choghari C, Joris M. Complete myocardial revascularization with bilateral internal thoracic artery T graft. Ann Thorac Surg 2000;69:498 –500. 13. Tector AJ, McDonald ML, Kress DC, Downey FX, Schmahl TM. Purely internal thoracic artery grafts: Outcomes. Ann Thorac Surg 2001;72:450 –5. 14. Vanoverschelde JLJ, Depré C, Gerber BL, et al. Time course of functional recovery after coronary artery bypass graft surgery in patients with chronic left ventricular ischemic dysfunction. Am J Cardiol 2000;85:1432–9.
Background. There is a concern that revascularization using bilateral internal thoracic arteries (ITA) as a composite graft may not supply sufficient blood flow to a wider area of myocardium when compared with grafting using bilateral in situ ITAs. Methods. One-hundred three patients who underwent off-pump coronary artery bypass using bilateral ITAs for revascularization of the left coronary system were studied prospectively. Bilateral ITAs were used as in situ grafts in 49 patients (group 1) and as a Y-composite graft in 54 patients (group 2). Resting and stress myocardial single-photon emission computed tomography (SPECT) was performed preoperatively and 3 months postoperatively. Myocardial perfusion was automatically quantified and expressed as a percentage of the maximal uptake. The left coronary territory was divided into 16 segments. A total of 379 segments (154 segments in group 1; 225 segments in group 2) that indicated decreased stress perfusion preoperatively were included in this study. Results. Resting myocardial perfusion revealed no significant differences with regard to both the preoperative (77.5 ⴞ 9.3% vs 78.8 ⴞ 8.8%) and postoperative SPECT
(78.3 ⴞ 10.0% vs 77.2 ⴞ 10.5%) between groups 1 and 2 (p ⴝ not significant [NS]). However, stress myocardial perfusion was significantly lower in group 1 preoperatively (62.5 ⴞ 10.8% vs 65.4 ⴞ 10.1%, p < 0.01). Although it improved postoperatively, there were no differences regarding postoperative stress myocardial perfusion between the two groups (75.5 ⴞ 11.3% vs 75.0 ⴞ 11.7%; p ⴝ NS). The degree of improvement regarding stress myocardial perfusion (difference between the preoperative and postoperative values) was higher in group 1 than in group 2 (13.0 ⴞ 9.4% vs 9.6 ⴞ 10.0%, p < 0.005). Conclusions. Myocardial SPECT demonstrated that revascularization using bilateral in situ ITAs exhibited a greater level of improvement with regard to stress perfusion postoperatively compared with Y-composite grafts. However, because there was no considerable difference with regard to postoperative stress perfusion between the two groups, revascularization using a Y-composite graft might also be sufficient for revascularization of the left coronary territory.
T
The aims of this study included (1) to compare myocardial perfusion between bilateral in situ ITAs and Y-composite ITAs and (2) to elucidate any difference with regard to myocardial stress perfusion between the bilateral in situ ITAs and Y-composite ITAs, based on resting and stress myocardial quantitative gated single-photon emission computed tomography (SPECT) performed preoperatively and 3 months after off-pump CABG (OPCAB).
he use of the left internal thoracic artery (ITA) with supplemental saphenous vein grafts has been the standard technique for coronary artery bypass grafting (CABG) in patients who exhibit multivessel disease. Recently, advantages such as enhanced long-term survival rates and greater freedom from reinterventions with the use of two ITAs instead of one have been demonstrated [1, 2]. Bilateral ITAs are used as bilateral in situ grafts or as a composite graft. Although a composite graft has indicated an increased coronary flow reserve through the graft [3, 4], there is a concern that because the composite arterial graft exhibits a single blood source, it may not supply sufficient blood flow to a wider area of myocardium [5, 6]. Accepted for publication June 11, 2004. Address reprint requests to Dr Kim, Department of Thoracic and Cardiovascular Surgery, Seoul National University Hospital, 28 Yeun-Kun Dong, Chong-Ro Ku, Seoul 110 –744, Korea; e-mail: [email protected].
© 2005 by The Society of Thoracic Surgeons Published by Elsevier Inc
(Ann Thorac Surg 2005;79:93– 8) © 2005 by The Society of Thoracic Surgeons
Material and Methods A total of 103 consecutive patients who underwent OPCAB for multivessel coronary artery disease between January 2000 and December 2002, were studied in a prospective nonrandomized manner. A computer-based patient database system was used for this prospective 0003-4975/05/$30.00 doi:10.1016/j.athoracsur.2004.06.056
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study. Myocardial SPECT was performed as a part of the routine clinical follow-up. Patient inclusion criteria included (1) patients who underwent myocardial revascularization under OPCAB, (2) patients who received skeletonized bilateral ITAs as either in situ grafts or a Y-composite graft for complete revascularization of the left coronary territory, (3) patients whose graft patency was confirmed by postoperative coronary angiography performed before discharge, and (4) patients in whom both the resting and stress myocardial SPECT were performed preoperatively and 3 months postoperatively. The patients who received other arterial grafts or free grafts anastomosed on the ascending aorta to revascularize the left coronary territory, or patients who did not receive the stress myocardial SPECT preoperatively because of intractable resting angina or an urgent or emergent situation were excluded from this study. Bilateral ITAs were used as in situ grafts in 49 patients (group 1) and as Y-composite grafts in 54 patients (group 2). All patients halted aspirin therapy the day before surgery and resumed it (300 mg/d) one day postoperatively. Postoperative (1.4 ⫾ 1.1 day) coronary angiography was performed in all of the patients and all of the grafts were confirmed as patent. There were no differences between the two groups in terms of sex, age, preoperative risk factors, ratio of unstable to stable angina, left ventricular ejection fraction measured by transthoracic echocardiography, and angiographic diagnosis (Table 1).
Surgical Methods and Revascularization Strategies OPCAB using skeletonized bilateral ITAs was performed as previously described [7]. The patients were heparinized with an initial dose of 1.5 mg/kg of heparin and periodically received supplemental doses to maintain an activated clotting time of ⬎300 seconds during OPCAB. Bilateral ITAs were preferred for use as in situ grafts for revascularization of the left coronary territory based on the assumption that two blood sources would be more favorable than a single blood source to improve longterm outcome. The right ITA was commonly used to revascularize the LAD by crossing the midline, or occasionally to revascularize the ramus or high obtuse marginal branch through the transverse sinus as an in situ graft. If the right ITA was too short to reach the left coronary territory or if the left coronary territory could not be completely revascularized with the bilateral in situ ITA grafts, a Y-composite graft was constructed before starting the distal anastomoses. In most instances of Y-composite graft construction, the right ITA was divided at its proximal section and was anastomosed to the side of the left ITA in a Y fashion using an 8-0 polypropylene continuous suture. Most of these end-to-side Y anastomoses were performed at the level of the pulmonary artery, and occasionally the right ITA was anastomosed to the distal left ITA unless it reached an optimal vessel such as the distal left circumflex territory. A sequential anastomosing technique was used for additional revascularization in both groups. The right coronary artery
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territory was revascularized using right gastroepiploic artery, radial artery, or saphenous vein grafts. Indication for bypass grafting occurred when the degree of native coronary stenosis was greater than 75%. Protamine was not given at the end of the procedure. The operations were all performed by a single surgeon (K-B.K.).
Myocardial SPECT Test Thallium-201 rest/dipyridamole stress technetium-99m methoxyisobutylisonitrile (MIBI) gated SPECT was performed before OPCAB. Thallium-201 (111 MBq) was injected at rest and SPECT was performed; dipyridamole (0.56 mg/kg) was then injected for more than 4 minutes to induce stress for assessment of the coronary perfusion reserve, and technetium-99m (925 MBq) was injected 3 minutes after stress. Gated technetium-99m-MIBI SPECT was performed 90 minutes after stress using a dual-head camera equipped with a low-energy high-resolution collimator (Vertex EPIC; ADAC Laboratories, Malpitas, CA). Thallium -201 rest/dipyridamole stress technetium-99mMIBI gated SPECT was repeated 3 months (102 ⫾ 20 days) after OPCAB as a follow-up examination, using the same protocol as was used for the preoperative study. A 20-segment model was adopted for regional analysis (Fig 1). Each segment was subtended to two coronary arterial territories (right and left coronary territories), and all of the 16 segments representing the left coronary territory (left anterior descending artery and left circumflex artery territories) were analyzed as a whole. The segments representing the right coronary artery territory were excluded.
Normal Korean Value of Myocardial SPECT Test (Control Group) To evaluate normal regional variation of perfusion and attenuation characteristics, myocardial SPECT tests were performed in an additional 55 Korean patients (28 males, 27 females; mean age of 49 ⫾ 9 years). They exhibited a low preexamination likelihood (⬍ 5%) of coronary artery disease [8], and were regarded by nuclear medicine physicians as normal dependent upon visual analysis of the SPECT images. In this control group, segmental perfusion was quantified with the same protocol as the patient groups (Fig 2).
Quantification of Myocardial Regional Perfusion After a review assessed by two experts with regard to overall image quality, the reconstructed images were analyzed with an automatic quantifying software package (AutoQUANT; ADAC Laboratories, Malpitas, CA) without manual intervention. Resting and stress segmental myocardial perfusion was quantified by measuring radioactivity and expressed as the percentage of the maximal radioactivity uptake. We studied the reversible ischemic myocardial area of the left coronary territory in the analysis. Normal preoperative perfusion segments, defined as those ⫺1 standard deviation (SD) over the control group preoperative stress SPECT test, were excluded. Resting perfusion defect segments, suggesting myocardial damage, were defined
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Table 1. Preoperative Characteristics and Risk Factors of Study Patients
Sex (Male : Female) Age (year) LVEF (%) Unstable : Stable Risk factors, n (%) Smoking Hypertension Diabetes mellitus Hyperlipidemia CRF PMH of stroke Angiographic diagnosis, n (%) Three-vessel disease Two-vessel disease LMD with or without peripheral disease CRF ⫽ chronic renal failure;
LMD ⫽ left main disease;
Group 1 (n ⫽ 49)
Group 2 (n ⫽ 54)
p Value
41:8 60.3 ⫾ 9.35 55.7 ⫾ 10.1 39:10
41:13 62.6 ⫾ 6.89 58.7 ⫾ 10.0 44:10
0.330 0.148 0.134 0.809
20 (40.8%) 30 (61.2%) 20 (40.8%) 9 (18.4%) 1 (2%) 10 (20.4%)
25 (46.3%) 33 (61.1%) 22 (40.7%) 17 (31.5%) 2 (3.7%) 6 (11.1%)
0.575 0.991 0.994 0.126 1.000 0.193
36 (73.5%) 9 (18.4%) 17 (34.7%)
42 (77.8%) 7 (13.0%) 15 (27.8%)
0.611 0.450 0.449
LVEF ⫽ left ventricle ejection fraction;
as those ⫺1 SD below the control group preoperative rest SPECT test, and were also excluded from the analysis. To evaluate the postoperative improvement of myocardial stress perfusion, the difference with regard to stress perfusion between preoperative and postoperative SPECT was compared between groups 1 and 2. A total of 379 reversible ischemic segments (154 segments in group 1; 225 segments in group 2) of the left coronary territories were included in the analysis.
PMH ⫽ past medical history.
reoperation for bleeding (2.0% vs 7.4%) between groups 1 and 2 (p ⫽ NS). We did not experience any low cardiac output syndrome, mediastinitis, or stroke in either group (Table 3).
Statistical Analysis Statistical analysis was performed using SPSS 11.0 software (SPSS Inc., Chicago, IL). The significance regarding differences between the two groups was assessed by the paired Student’s t test for the continuous variable. The discrete variables were analyzed using 2 and Fisher’s exact tests. All results were expressed as mean ⫾ SD and a value of p less than 0.05 was considered to be statistically significant.
Results Clinical Results The average number of distal anastomoses per bilateral ITA was smaller in group 1 than in group 2 (2.4 ⫾ 0.5 vs 2.7 ⫾ 0.7; p ⬍ 0.01), although there was no significant difference regarding the average number of distal anastomoses per patient between the two groups (3.1 ⫾ 0.7 in group 1 vs 3.3 ⫾ 0.9 in group 2;p ⫽ not significant [NS]). A smaller number of patients in group 1 required sequential anastomoses than in group 2 (28.6% vs 57.4%; p ⬍ 0.01), and a smaller number of sequential anastomoses using ITAs were performed in group 1 than in group 2 (12.0% vs 27.0%; p ⬍ 0.01) (Table 2). There were no significant differences regarding the incidence of postoperative morbidities such as atrial fibrillation (22.4% vs 18.5%), perioperative myocardial infarction (4.1% vs 1.9%), acute renal failure (2.0% vs 0%), and
Fig 1. Twenty-segment model for quantification of myocardial regional perfusion. (LAD ⫽ left anterior descending coronary artery; LCX ⫽ left circumflex coronary artery; RCA ⫽ right coronary artery.)
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Fig 2. Normal Korean values of myocardial single-photon emission computerized tomography. (A) Male; (B) female.
Myocardial SPECT Test In the restsing SPECT, the mean values of preoperative segmental perfusion were 77.5% ⫾ 93% in group 1 and 78.8 ⫾ 8.8% in group 2. The mean values of postoperative segmental perfusion were 78.3 ⫾ 10.0% in group 1 and 77.2 ⫾ 10.5% in group 2, respectively (p ⫽ NS). In the stress SPECT, the mean values of preoperative segmental perfusion were significantly lower in group 1 than in group 2 (62.5 ⫾ 10.8% vs 65.4 ⫾ 10.1%; p ⬍ 0.01) although there was no difference with regard to the postoperative segmental perfusion between groups 1 and 2 (75.5 ⫾ 11.3% vs 75.0 ⫾ 11.7%;p ⫽ NS). The difference
between the preoperative and postoperative SPECT with regard to stress perfusion was higher in group 1 than in group 2 (13.0 ⫾ 9.4 vs 9.6 ⫾ 10.0; p ⬍ 0.01) (Table 4).
Comment This study demonstrated two main findings. First, both the bilateral in situ ITAs and Y-composite grafts improved the stress myocardial perfusion after OPCAB, and there were no considerable differences regarding the postoperative myocardial stress perfusion between the two groups. Second, revascularization using bilateral in
Table 2. Comparison of Distal Anastomoses
Distal anastomoses/patient Distal anastomoses/bilateral ITAs Patients with sequential anastomosis Sequential anastomoses/ITA anastomoses ITA ⫽ internal thoracic artery.
Group 1
Group 2
p Value
3.1 ⫾ 0.7 2.4 ⫾ 0.5 14 out of 49 (28.6%) 14 out of 117 (12.0%)
3.3 ⫾ 0.9 2.7 ⫾ 0.7 31 out of 54 (57.4 %) 40 out of 148 (27.0%)
0.104 0.005 0.003 0.001
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Table 3. Postoperative Morbidities
Atrial fibrillation PMI ARF Reoperation for bleeding LCOS Mediastinitis Stroke
Group 1
Group 2
p Value
11 (22.4%) 2 (4.1%) 1 (2.0%) 1 (2.0%) 0 0 0
10 (18.5%) 1 (1.9%) 0 4 (7.4%) 0 0 0
0.621 0.603 0.224 0.366 ... ... ...
ARF ⫽ acute renal failure; LCOS ⫽ low cardiac output syndrome; PMI ⫽ perioperative myocardial infarction.
situ ITAs exhibited a greater degree of improvement regarding myocardial stress perfusion to supply the left coronary territory, compared with the improvement observed using the Y-composite graft. Enhanced long-term survival rates have been indicated when bilateral ITAs are used rather than a single ITA in patients exhibiting multivessel disease [1, 2]. The skeletonized technique for harvesting the ITA allowed additional length and easier use of ITAs with favorable results [7, 9, 10]. Those results have provided the foundation for using bilateral ITAs to achieve complete myocardial revascularization. The use of bilateral ITAs as in situ grafts exhibits the assumptive advantage that multiple blood sources may be more favorable than a single blood source for improving long-term outcome. The prerequisite for using bilateral in situ ITAs for complete arterial revascularization is sufficient length for an in situ right ITA to reach the desired anastomotic site on the left coronary territory. Despite the extra length obtained by skeletonization, the length of the right ITA is the main limitation for bilateral in situ ITA grafting. Construction of a composite graft such as a Y or T graft increases the length of the ITA, and allows the extensive use of bilateral ITA grafts to revascularize the left coronary system as well as the right coronary system [11]. Although construction of a composite graft has revealed increased coronary flow reserve and favorable outcome [3, 4, 11–13], there is a concern that because the composite arterial graft only harbors a single blood source, it may not supply sufficient blood flow to a wider area of myocardium [5, 6]. Lev-Ran and associates [6] revealed a decreased angina recurrence and an increased midterm survival rate regarding patients with in situ grafts, although early results of the patients with composite grafts were comparable with those of in situ grafts. In their study, postoperative coronary angiography was performed in 5.9% of their patients and the patency of the composite grafts was much lower than in situ grafts. They suggested technical errors related to the complexity of composite grafting to be the cause of the differences regarding late follow-up results. We confirmed the patency of all grafts using postoperative coronary angiography. Although we did not demonstrate the midterm results, there were no considerable differences regarding the incidence of early postoperative morbidities such as atrial fibrillation, peri-
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operative myocardial infarction, acute renal failure, or bleeding reoperation between the two groups. Sakaguchi and associates [5] demonstrated a substantially higher coronary flow reserve in the in situ group than in the composite group using analysis of positron emission tomography (PET) images performed 2 weeks after CABG. They suggested that the composite graft was unable to fully respond to the flow demand of the whole left coronary system. As the authors indicated, their study was performed early after surgery, when the use of cardiopulmonary bypass may affect the regional myocardial blood flow. The present study consisted of patients who underwent OPCAB. We performed myocardial SPECT 3 months after OPCAB, when ischemic myocardial dysfunction would be expected to have recovered from ischemia after revascularization [14]. Our study indicated a significantly higher degree of difference between the preoperative and postoperative stress SPECT in group 1 than in group 2. A higher degree of difference between the preoperative and postoperative stress SPECT suggests that bilateral in situ ITAs experienced a greater improvement with regard to myocardial stress perfusion after surgery, which supplied the entire left coronary territory, compared with the Y-composite graft. Although the degree of difference between the preoperative and postoperative stress SPECT was higher in group 1, there was no marked difference with regard to stress perfusion between the two groups after OPCAB. These results suggest that both the bilateral in situ ITAs and composite grafts are able to fully respond to the flow demand of the left coronary territory, even though bilateral in situ ITAs indicate a higher degree of improvement regarding myocardial stress perfusion after surgery. We preferred bilateral in situ ITAs for complete revascularization of the left coronary territory. If the right ITA was too short to reach the left coronary territory or if the left coronary territory could not be completely revascularized with bilateral in situ ITA grafts, a Y-composite graft was then constructed. Although the segmental perfusion in the preoperative stress SPECT was significantly lower in group 1, the number of distal anastomoses per bilateral ITAs and the number of sequential anastomoses were higher in group 2. Group 1 may have exhibited more proximal coronary artery disease that required a smaller number of distal anastomoses, and group 2 may have exhibited more peripheral and multiTable 4. Comparison of Segmental Perfusion Values Between the Two Groups
Rest (% uptake) Preoperative Postoperative Stress (% uptake) Preoperative Postoperative Difference in stress perfusion
Group 1
Group 2
p Value
77.5 ⫾ 9.3 78.3 ⫾ 10.0
78.8 ⫾ 8.8 77.2 ⫾ 10.5
0.176 0.284
62.5 ⫾ 10.8 75.5 ⫾ 11.3 13.0 ⫾ 9.4
65.4 ⫾ 10.1 75.0 ⫾ 11.7 9.6 ⫾ 10.0
0.008 0.705 0.001
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ple coronary arterial disease that required a larger number of distal grafts. Proximal coronary artery disease may decrease stress perfusion in a wider coronary territory than peripheral coronary arterial disease, and may have caused the lower preoperative stress perfusion level in group 1. As to the effect of sequential grafting on coronary perfusion, the authors do not believe that multiple sequential anastomoses caused flow steal and decreased coronary perfusion. This was demonstrated based on the evaluation that more frequent sequential grafting in group 2 did not decrease the postoperative myocardial stress SPECT when compared with group 1 who exhibited a smaller number of sequential grafts. On the contrary, we believe that incomplete revascularization may result in a residual ischemic area and consequently a decreased coronary perfusion.
Limitations There are limitations to the present study that must be recognized. First, the present study was not performed in a randomized manner, because randomized controlled trials with regard to this type of study are often unrealistic and impractical. Although the study involved a relatively small number of patients and was not randomized, the trial was performed prospectively using a computer-based database system. Second, there is a base line difference between the two groups. In the stress SPECT, the mean values of preoperative segmental myocardial perfusion were significantly lower in group 1 than in group 2. To overcome this base line difference, we calculated the difference of stress perfusion between the preoperative and postoperative SPECT and compared the two groups. Third, using coronary angiography to confirm the graft patency was performed in the early postoperative period and the myocardial SPECT was performed 3 months after OPCAB. Some grafts may have occluded during the 3 postoperative months, which would affect the results of postoperative myocardial SPECT. Myocardial SPECT demonstrated that revascularization using bilateral in situ ITAs exhibited a higher degree of improvement regarding myocardial stress perfusion supplying the left coronary territory, compared with that using a Y-composite graft. However, because there was no considerable difference with regard to postoperative stress perfusion between the two groups, revasculariza-
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tion using a Y-composite graft might also be sufficient for revascularization of the left coronary territory.
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