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Fate of internal mammary artery grafted on to totally occluded coronary arteries
International Journal of Cardiology 93 (2004) 305 – 306 www.elsevier.com/locate/ijcard
Letter to the Editor
Fate of internal mammary artery grafted on to totally occluded coronary arteries Mehmet Birhan Yilmaz*, Yesim Akin, Senay Funda Biyikoglu, Hakan Altay, Umit Guray, Erdal Duru, Sule Korkmaz Yuksek Ihtisas Hospital, Cardiology Clinic, Sihhiye, Ankara, Turkey Received 2 November 2002; accepted 8 January 2003
1. Introduction The internal mammary artery (IMA) has been shown to be the optimal conduit for patients undergoing coronary artery bypass surgery on the basis of superior patency rates and clinical performance [1]. Use of the IMA as a coronary artery bypass graft has been shown to be associated with improved survival [2]. It is well established that arterial grafts adapt to local blood flow demand [3]. It has also been shown that the IMA responds to changes in flow demand due to progression of stenosis in the recipient coronary artery [4]. Although, there has been growing interest in graft failure due to competitive flow, which is thought to be due to coronary artery with less than critical stenosis which presents less resistance than the IMA graft, so that distal perfusion preferentially favored the competitive, residual native flow, causing the IMA graft to wither or string [5], little is known about IMA, grafted to totally occluded coronary arteries particularly if there is less demand due to collateral development or myocardial necrosis following infarction.
2. Materials and methods From January 1999 to September 2002, we retrospectively evaluated the records of cine angiograms at our institution and among all we could reach the file information of 11 patients (group 1) with occluded left IMA, which had been grafted to the totally occluded left anterior descending artery (LAD) previously. All data were gathered from files, particularly of echocardiographic evaluation performed at
our institution before coronary artery bypass surgery. Patients lacking data were not included in our study. For comparison, age and sex-matched 15 patients (group 2) with patent left IMA grafted to totally occluded LAD artery and without lacking searched data were evaluated separately. All patients underwent coronary angiography by the Seldinger technique. Selective coronary angiograms and left IMA angiography were performed with appropriate catheter. When the left IMA was not visualised, nitroglycerine was administered and contrast injection was repeated. Patients with anastomotic occlusion of IMA were not included in our study, considering the fact that technical factors could influence the fate. In past echocardiographic records of both groups of patients, segmental wall motion score indices, which had been evaluated as normal motion: 1, hypokinesis: 2, akinesis: 3, dyskinesis: 4 over 16 segments, were identified and wall motion score index (WMSI) was derived from sum of grading of these segments. 2.1. Statistical analysis Summary statistics of patient groups were presented as frequencies and percentages for categorical variables and mean F standard deviation for parametric variables. Univariate associations for nominal variables were compared using the chi-square test. The two-tailed Student t-test was used for continuous variables. Data were analysed using SPSS 10.0 version and a P value < 0.05 was considered statistically significant.
3. Results * Corresponding author. SSK Bloklari 70/7, 06170 Yenimahalle, Ankara, Turkey. Tel.: +90-0312-346-9401. E-mail address: [email protected] (M.B. Yilmaz). 0167-5273/$ - see front matter D 2003 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/S0167-5273(03)00160-8
Mean time period from bypass grafting to repeat coronary angiography were similar in both groups (group 1: 4.4 F 2.2 vs. group 2: 4.6 F 2.2 years, P = 0.8). All coronary
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angiograms in both groups were performed for new or worsening symptoms. In terms of age, total cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, triglyceride, glucose level, no significant difference was noted between two groups (Table 1). Besides, distribution of conventional risk factors; hypertension, diabetes mellitus, smoking habitus and sex was not significantly different between groups (Table 2). WMSI, before bypass surgery, in group 1 was significantly worse than that in group 2 (28 F 2 vs. 20 F 2, respectively, P < 0.001).
Table 2 Distribution of conventional risk factors Group
N (%)
P
Hypertension
Group 1 Group 2
5 (55) 4 (28)
NS
Diabetes mellitus
Group 1 Group 2
1 (11) 3 (21)
NS
Smoking
Group 1 Group 2
3 (33) 3 (21)
NS
Sex (male/female)
Group 1 Group 2
6/3 12/3
NS
NS: Nonsignificant.
4. Discussion The IMA is the graft of choice for coronary artery bypass because it is generally free of atherosclerosis having high patency rate as graft. It is known that inappropriate anastomosis and technical insufficiency during dissection of the graft conduit can result in narrowing and obstruction of the arterial graft [5]. Besides, damage during harvesting and mobilisation, spasm, inflammation as part of a post-pericardiotomy syndrome, or a steal phenomenon arising from a large undivided proximal branch of the IMA may lead to occlusion of graft [5,6]. The IMA is mobilised as a lymphovascular pedicle, thus preserving the vasa vasorum and vascular smooth muscle, which remains functional. This permits the graft to retain a flexible caliber and blood flow that is dictated by myocardial demands. Seki et al. [7] showed that internal thoracic artery grafts have flow adaptability responding to the flow demand of the recipient coronary artery.
However it is not well established that IMA, as a graft, retains patency when the metabolic need of revascularised myocardium is less than thought due to collaterals or more speculatively absent due to necrosis. In our study, we found that the WMSI, which provides clues about the amount of injured or infarcted myocardium, in patients with occluded left IMA, was worse than those with patent IMA. Abnormal WMSI provides echocardiographic correlate of injured or infarcted myocardium which is well known to require less metabolically and, hence, less blood flow demand either from recipient or graft. In conclusion, we think that grafting of IMA to totally occluded artery, in our study LAD, without well documented metabolic need through tissue imaging modalities might lead to failure of IMA graft, which is known to respond metabolic demand of recipient myocardium. Major limitation of our observational study might be lack of more precise methods to define tissue requirements before surgery.
Table 1 Distribution of parametric variables
Age (years)
Group
Mean F standard deviation
P
Group 1 Group 2 Group 1
59.6 F 10 62 F 9.3 187 F 44
NS
Group 2 Group 1
202 F 40 35 F 5
NS
Group 2 Group 1
37 F 7 123 F 30
NS
Group 2 Group 1
132 F 35 149 F 80
NS
Group 2 Group 1
163 F 80 118 F 17
NS
Group 2 Group 1
116 F 52 28 F 2
< 0.001
Group 2
20 F 2
NS
Total cholesterol
HDL cholesterol
LDL cholesterol
Triglyceride
Glucose
WMSI NS: Nonsignificant, WMSI: wall motion score index.
References [1] Barner HB, Standeven JW, Reese J. Twelve-year experience with internal mammary artery for coronary artery bypass. J Thorac Cardiovasc Surg 1985;90:668 – 75. [2] Loop FD, Lytle BW, Cosgrove DM, et al. Influence of the internal mammary artery graft on 10-year survival and other cardiac events. New Engl J Med 1986;314:1. [3] Singh RN, Beg BA, Kay EB. Physiologic adaptability: the secret of success of the internal mammary artery grafts. Ann Thorac Surg 1986;41:247 – 50. [4] Dincer B, Barner HB. The occluded internal mammary artery graft: restoration of patency after apparent occlusion associated with progression of coronary disease. J Thorac Cardiovasc Surg 1983;85:318 – 20. [5] Mills NL, Ochsner JL. Technique of internal mammary-to-coronary artery bypass. Ann Thorac Surg 1974;17:237 – 46. [6] Singh RN, Sosa JA. Internal mammary artery – coronary artery anastomosis. Influence of the side branches on surgical result. J Thorac Cardiovasc Surg 1981;82:909 – 14. [7] Seki T, Kitamura S, Kawachi K, et al. A quantitative study of postoperative luminal narrowing of the internal thoracic artery graft in coronary artery bypass surgery. J Thorac Cardiovasc Surg 1992;104: 1532 – 8.
Letter to the Editor
Fate of internal mammary artery grafted on to totally occluded coronary arteries Mehmet Birhan Yilmaz*, Yesim Akin, Senay Funda Biyikoglu, Hakan Altay, Umit Guray, Erdal Duru, Sule Korkmaz Yuksek Ihtisas Hospital, Cardiology Clinic, Sihhiye, Ankara, Turkey Received 2 November 2002; accepted 8 January 2003
1. Introduction The internal mammary artery (IMA) has been shown to be the optimal conduit for patients undergoing coronary artery bypass surgery on the basis of superior patency rates and clinical performance [1]. Use of the IMA as a coronary artery bypass graft has been shown to be associated with improved survival [2]. It is well established that arterial grafts adapt to local blood flow demand [3]. It has also been shown that the IMA responds to changes in flow demand due to progression of stenosis in the recipient coronary artery [4]. Although, there has been growing interest in graft failure due to competitive flow, which is thought to be due to coronary artery with less than critical stenosis which presents less resistance than the IMA graft, so that distal perfusion preferentially favored the competitive, residual native flow, causing the IMA graft to wither or string [5], little is known about IMA, grafted to totally occluded coronary arteries particularly if there is less demand due to collateral development or myocardial necrosis following infarction.
2. Materials and methods From January 1999 to September 2002, we retrospectively evaluated the records of cine angiograms at our institution and among all we could reach the file information of 11 patients (group 1) with occluded left IMA, which had been grafted to the totally occluded left anterior descending artery (LAD) previously. All data were gathered from files, particularly of echocardiographic evaluation performed at
our institution before coronary artery bypass surgery. Patients lacking data were not included in our study. For comparison, age and sex-matched 15 patients (group 2) with patent left IMA grafted to totally occluded LAD artery and without lacking searched data were evaluated separately. All patients underwent coronary angiography by the Seldinger technique. Selective coronary angiograms and left IMA angiography were performed with appropriate catheter. When the left IMA was not visualised, nitroglycerine was administered and contrast injection was repeated. Patients with anastomotic occlusion of IMA were not included in our study, considering the fact that technical factors could influence the fate. In past echocardiographic records of both groups of patients, segmental wall motion score indices, which had been evaluated as normal motion: 1, hypokinesis: 2, akinesis: 3, dyskinesis: 4 over 16 segments, were identified and wall motion score index (WMSI) was derived from sum of grading of these segments. 2.1. Statistical analysis Summary statistics of patient groups were presented as frequencies and percentages for categorical variables and mean F standard deviation for parametric variables. Univariate associations for nominal variables were compared using the chi-square test. The two-tailed Student t-test was used for continuous variables. Data were analysed using SPSS 10.0 version and a P value < 0.05 was considered statistically significant.
3. Results * Corresponding author. SSK Bloklari 70/7, 06170 Yenimahalle, Ankara, Turkey. Tel.: +90-0312-346-9401. E-mail address: [email protected] (M.B. Yilmaz). 0167-5273/$ - see front matter D 2003 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/S0167-5273(03)00160-8
Mean time period from bypass grafting to repeat coronary angiography were similar in both groups (group 1: 4.4 F 2.2 vs. group 2: 4.6 F 2.2 years, P = 0.8). All coronary
306
M.B. Yilmaz et al. / International Journal of Cardiology 93 (2004) 305–306
angiograms in both groups were performed for new or worsening symptoms. In terms of age, total cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, triglyceride, glucose level, no significant difference was noted between two groups (Table 1). Besides, distribution of conventional risk factors; hypertension, diabetes mellitus, smoking habitus and sex was not significantly different between groups (Table 2). WMSI, before bypass surgery, in group 1 was significantly worse than that in group 2 (28 F 2 vs. 20 F 2, respectively, P < 0.001).
Table 2 Distribution of conventional risk factors Group
N (%)
P
Hypertension
Group 1 Group 2
5 (55) 4 (28)
NS
Diabetes mellitus
Group 1 Group 2
1 (11) 3 (21)
NS
Smoking
Group 1 Group 2
3 (33) 3 (21)
NS
Sex (male/female)
Group 1 Group 2
6/3 12/3
NS
NS: Nonsignificant.
4. Discussion The IMA is the graft of choice for coronary artery bypass because it is generally free of atherosclerosis having high patency rate as graft. It is known that inappropriate anastomosis and technical insufficiency during dissection of the graft conduit can result in narrowing and obstruction of the arterial graft [5]. Besides, damage during harvesting and mobilisation, spasm, inflammation as part of a post-pericardiotomy syndrome, or a steal phenomenon arising from a large undivided proximal branch of the IMA may lead to occlusion of graft [5,6]. The IMA is mobilised as a lymphovascular pedicle, thus preserving the vasa vasorum and vascular smooth muscle, which remains functional. This permits the graft to retain a flexible caliber and blood flow that is dictated by myocardial demands. Seki et al. [7] showed that internal thoracic artery grafts have flow adaptability responding to the flow demand of the recipient coronary artery.
However it is not well established that IMA, as a graft, retains patency when the metabolic need of revascularised myocardium is less than thought due to collaterals or more speculatively absent due to necrosis. In our study, we found that the WMSI, which provides clues about the amount of injured or infarcted myocardium, in patients with occluded left IMA, was worse than those with patent IMA. Abnormal WMSI provides echocardiographic correlate of injured or infarcted myocardium which is well known to require less metabolically and, hence, less blood flow demand either from recipient or graft. In conclusion, we think that grafting of IMA to totally occluded artery, in our study LAD, without well documented metabolic need through tissue imaging modalities might lead to failure of IMA graft, which is known to respond metabolic demand of recipient myocardium. Major limitation of our observational study might be lack of more precise methods to define tissue requirements before surgery.
Table 1 Distribution of parametric variables
Age (years)
Group
Mean F standard deviation
P
Group 1 Group 2 Group 1
59.6 F 10 62 F 9.3 187 F 44
NS
Group 2 Group 1
202 F 40 35 F 5
NS
Group 2 Group 1
37 F 7 123 F 30
NS
Group 2 Group 1
132 F 35 149 F 80
NS
Group 2 Group 1
163 F 80 118 F 17
NS
Group 2 Group 1
116 F 52 28 F 2
< 0.001
Group 2
20 F 2
NS
Total cholesterol
HDL cholesterol
LDL cholesterol
Triglyceride
Glucose
WMSI NS: Nonsignificant, WMSI: wall motion score index.
References [1] Barner HB, Standeven JW, Reese J. Twelve-year experience with internal mammary artery for coronary artery bypass. J Thorac Cardiovasc Surg 1985;90:668 – 75. [2] Loop FD, Lytle BW, Cosgrove DM, et al. Influence of the internal mammary artery graft on 10-year survival and other cardiac events. New Engl J Med 1986;314:1. [3] Singh RN, Beg BA, Kay EB. Physiologic adaptability: the secret of success of the internal mammary artery grafts. Ann Thorac Surg 1986;41:247 – 50. [4] Dincer B, Barner HB. The occluded internal mammary artery graft: restoration of patency after apparent occlusion associated with progression of coronary disease. J Thorac Cardiovasc Surg 1983;85:318 – 20. [5] Mills NL, Ochsner JL. Technique of internal mammary-to-coronary artery bypass. Ann Thorac Surg 1974;17:237 – 46. [6] Singh RN, Sosa JA. Internal mammary artery – coronary artery anastomosis. Influence of the side branches on surgical result. J Thorac Cardiovasc Surg 1981;82:909 – 14. [7] Seki T, Kitamura S, Kawachi K, et al. A quantitative study of postoperative luminal narrowing of the internal thoracic artery graft in coronary artery bypass surgery. J Thorac Cardiovasc Surg 1992;104: 1532 – 8.