Morphology and histology of human and canine internal thoracic arteries.

BACKGROUND: We evaluated human and canine internal thoracic arteries (ITAs) to determine whether the latter is valid for studies relevant to clinical use. METHODS: We studied 19 human ITAs obtained from 1 female and 14 male victims of recent fatal accidents who had no evidence of cardiovascular disease (mean age = 39+/-19 years; range = 15 to 79 years), and ITAs of 21 randomly-selected mongrel dogs of both sexes, weighing 18-40 kg (average = 24.3+/-5.7 kg). Specimens were fixed in formalin at a controlled pressure of 120 mm Hg, before extensive assessment that included intimal thickening, condition of the internal elastic lamina, and number of medial elastic lamellae and vasa vasorum. RESULTS: The canine morphology and histology were similar to the human ITAs, but there was no intimal hyperplasia, and the media and adventitia were thinner (ITAs of humans older than 40 years had significant increases in medial thickness, as well as in overall length). Morphologically and histologically, the left and right canine ITAs were almost completely the same. CONCLUSIONS: Canine ITAs are valid for bilateral comparative studies and are a useful tissue source and model for clinically-relevant experimental studies.     

Arteriosclerosis of the gastroepiploic and internal thoracic arteries

Arteriosclerosis of the right gastroepiploic artery (GEA) and the internal thoracic artery (ITA) were compared by pathological observation. Specimens were obtained from 35 patients who underwent coronary artery bypass grafting with simultaneous use of these two kinds of arterial grafts. Degree of arteriosclerosis was classified in five categories: 0, normal; 1, luminal narrowing less than 25%; 2, luminal narrowing between 25% and 50%; 3, luminal narrowing greater than 50%; and 4, overt atherosclerosis with ulceration or calcification. The number of arteries with degree 0, 1, 2, 3, and 4 was 16 (46%), 15 (43%), 3 (9%), 0, and 1 (3%) in GEA and 27 (77%), 8 (23%), 0, 0, and 0 in ITA, respectively. Incidence of degree 0 was higher in ITA, but differences were not significant. The mean wall thickness was 0.30 +/- 0.13 mm in GEA and 0.21 +/- 0.07 mm in ITA (p less than 0.05). In 23 patients who underwent postoperative angiography, all 46 arterial grafts were patent without focal stenosis. We conclude that GEA has slightly more intimal thickening than ITA, but significant luminal narrowing caused by arteriosclerosis is rare. Gastroepiploic artery can be expected to be a suitable conduit for coronary artery bypass grafting.     

Differential effect of cerivastatin and L-arginine on the vascular function of human radial and left internal thoracic arteries

BACKGROUND: There are a number of strategies to restore/preserve endothelial function. We have compared the effects of Cerivastatin (CS) to those of L-arginine (L-ARG) supplementation on the endothelial function of human arterial grafts. METHODS: During coronary artery bypass grafting, specimens of radial artery (RA) and left internal thoracic artery (LITA) were obtained. Specimens were divided into vascular rings, which were incubated with either 10(-6) mol/L CS, 10(-3) mol/L L-ARG, or vehicle (control) for 2 or 24 hours. Endothelial function was examined with acethylcholine (10(-9) to 10(-5) mol/L) following contraction by 3 x 10(-8) mol/L endothelin-1. RESULTS: Although no significant differences were observed in the RA at 2 hours, after 24 hours incubation, endothelium-dependent vasodilatation was significantly higher in CS group (68.4 +/- 5.0%; n = 6) compared to L-ARG group (49.9 +/- 5.4%; n = 7, p < 0.05) and control group (33.8 +/- 2.9%; n = 13, p < 0.0001). In addition, there was a significant increase in L-ARG group compared to control (p < 0.01). After 2 hours incubation of the LITA, CS failed to enhance endothelium-dependent vasodilatation compared to control (44.1 +/- 4.9%; n = 9, vs. 40.0 +/- 5.2%; n = 16, respectively, NS), while L-ARG increased it (64.7 +/- 4.9%; n = 7, p < 0.05 vs. CS and p < 0.01 vs. control). However, this increase disappeared at 24 hours although there was a higher trend of endothelium-dependent vasodilatation in CS group (30.3 +/- 3.7%; n = 8 in L-ARG, 56.5 +/- 8.8%; n = 9 in CS and 41.0 +/- 5.5%; n = 18 in control). CONCLUSIONS: CS preserved endothelium-dependent vasodilatation of RA greater than L-ARG. These findings suggest that the use of statins may be an effective therapeutic strategy to preserve endothelial function in the RA grafts, and could have important implications in the clinical practice.     

Contractile effects of arginine analogues on human internal thoracic and radial arteries

OBJECTIVES: Plasma levels of endogenous guanidino-substituted analogues of L -arginine are increased in various pathologic conditions. In the present study we determined the effects of some of these compounds on basal and stimulated release of nitric oxide in human internal thoracic and radial arteries. METHODS: Rings of human internal thoracic and radial arteries were obtained from 16 multiorgan donors. The rings were suspended in organ baths for isometric recording of tension. RESULTS: N(G)-monomethyl L -arginine (10(-6) to 10(-3) mol/L) and N(G),N(G)-dimethyl L -arginine (10(-6) to 10(-3) mol/L) caused concentration- and endothelium-dependent contractions. Maximal force of contractions for N(G)-monomethyl L -arginine and N(G),N(G)-dimethyl L -arginine in the internal thoracic artery were 18.0% +/- 4.3% and 17.8% +/- 3.8%, respectively, of the contraction to 100 mmol/L KCl, and those found in the radial artery were 9.6% +/- 2.5% and 9.1% +/- 2.4%, respectively. Aminoguanidine (10(-5) to 3 x 10(-3) mol/L) and methylguanidine (10(-5) to 3 x 10(-3) mol/L) produced endothelium-independent contractions. L -Arginine (10(-3) mol/L) prevented the contractions by N(G)-monomethyl L -arginine and N(G),N(G)-dimethyl L -arginine but did not change contractions induced by aminoguanidine and methylguanidine. N(G)-monomethyl L -arginine and N(G),N(G)-dimethyl L -arginine inhibited, in a concentration-dependent manner, the endothelium-dependent relaxation to acetylcholine in the internal thoracic artery and had little attenuating effect in the radial artery; aminoguanidine and methylguanidine were without effect. CONCLUSIONS: The results suggest that the contractions induced by N(G)-monomethyl L -arginine and N(G),N(G)-dimethyl L -arginine are due to inhibition of both basal and stimulated nitric oxide production, whereas aminoguanidine and methylguanidine do not affect the synthesis of nitric oxide. An increase in the plasma concentration of N(G)-monomethyl L -arginine and N(G),N(G)-dimethyl L -arginine is likely to represent a risk factor for abnormal vasomotor tone in conduit arteries used as coronary grafts.     

Composite arterial grafting with double skeletonized internal thoracic arteries.

OBJECTIVES: Composite arterial grafting is a surgical technique for arterial myocardial revascularization, in which free arterial conduits are proximally anastomosed end-to-side to an intact internal thoracic artery (ITA). This report describes technical aspects and results of composite grafting using bilateral skeletonized ITAs. METHODS: From April 1996 to February 1999, 1057 patients underwent coronary artery bypass grafting (CABG) using bilateral skeletonized internal thoracic arteries. In 600 of them (57%), composite arterial grafting was performed. There were 452 men and 148 women. The mean age was 69 +/- 7 years. Two-hundred and six patients (34%) were diabetics, 84 (14%) had severe left ventricular dysfunction (ejection fraction of < 35%), and 26 (4.3%) underwent emergency operations. In 574 patients, the right ITA was used as a free graft connected to the in-situ left ITA. In 26, the free left ITA was attached to the in-situ right ITA, and in 38, mini-composite grafts (free distal left ITA on the left ITA, or free distal right ITA on the right ITA) were constructed. The average number of grafts was 3.0/patient (range, 2--6). RESULTS: The operative mortality was 2.8% (n = 17), and there were ten (1.7%), deep sternal wound infections. The mean follow-up was 25 months (range, 14--36 months). The 3-year survival was 92.5%. Ninety-seven percent of the surviving patients were angina-free. CONCLUSIONS: We currently perform this surgery routinely in most patients referred for CABG, and regard bilateral skeletonized internal thoracic arteries as the most appropriate arterial conduits for the composite technique.     

Myocardial revascularization with modified T-graft using bilateral internal thoracic arteries.

OBJECTIVE: By using a T-graft configuration, the myocardium may be completely revascularized with bilateral internal thoracic arteries. This study aimed to evaluate the perioperative morbidity and mortality in a single surgeon's early experience with a modified T-graft using bilateral internal thoracic arteries. METHODS: Between October 1994 to April 1997, 200 consecutive patients mostly selected per protocol, received a T-graft with bilateral internal thoracic arteries for stable angina pectoris (n = 157) or unstable angina pectoris (n = 43). The mean age of patients was 56 years (range of 36 to 78 years). There were 171 males and 29 females. Forty-three patients had diabetes. Concomitant procedures were performed in 8 patients. RESULTS: In 190 patients (95%), total arterial revascularization of the myocardium was achieved solely by the use of bilateral internal thoracic arteries in a T-graft configuration and the number of anastomoses per patient averaged 4.2. Ten patients (5%) received supplemental saphenous veins in addition to T-grafts for low cardiac output (n = 3), intraoperative regional ischaemia (n = 2), postoperative myocardial ischaemia (n = 2) and inadequate conduits (n = 3). The 30-day mortality was 0.5%. Perioperative myocardial infarct occurred in 2 patients (1.0%). Reasons encountered for early re-operation included bleeding (n = 7), sternal dehiscence (n = 5), suppurative sternitis (n = 3) and myocardial ischaemia (n = 2). Twelve patients received inotropes and intraaortic balloon counterpulsation was employed in 3 patients. CONCLUSION: When bilateral internal thoracic arteries were used in a T-graft configuration, total arterial revascularization of the myocardium was achieved with an acceptably low morbidity and mortality.     

The impact of chronic renal failure on atherosclerosis of the internal thoracic arteries

BACKGROUND: Little is known about the impact of renal failure on atherosclerotic changes in the internal thoracic artery (ITA). METHODS: A total of 20 consecutive patients on chronic dialysis who underwent coronary artery bypass grafting (CABG) during April 1998 through September 1999 were investigated. The 20 control patients were selected from the same interval to rigorously match risk factors. Atherosclerosis of the ITA collected from each patient was analyzed using the subjective evaluation proposed by Kay and colleagues. RESULTS: There were no cases of greater than 25% atherosclerotic luminal narrowing among a total of 35 ITA specimens from dialysis patients. The degree of atherosclerosis was not significantly different from that of the specimens from matched patients (p = 0.18). No calcification was found in ITA grafts either microscopically or macroscopically. The number of elastic lamellae, an index of the elasticity of the ITA graft, was not significantly different from those obtained from the matched patients. Analysis of preoperative coronary angiography revealed that coronary calcification was significantly more frequent in dialysis patients (15 patients, 75%) than in matched patients (p < 0.05). By analysis of postoperative angiography in dialysis patients, no evidence of atherosclerotic changes was found in 28 opacified ITAs. In addition, despite the presence of calcification in the native coronary, no calcification was evident along the entire length of the ITAs. CONCLUSIONS: This study revealed the minimal impact of chronic renal failure on atherosclerotic changes in the ITA. The results of this study support the continued use of ITA grafting in dialysis patients.     

Effects of cerivastatin on vascular function of human radial and left internal thoracic arteries

Background. Statins may enhance vascular function independently of effects on cholesterol. This study investigated the ability of statins to modulate the vascular recovery of arteries used as coronary bypass grafts.

Methods. Specimens of radial artery and left internal thoracic artery were obtained during coronary artery bypass grafting. The specimens were divided into vascular rings, which were incubated in the absence or presence of cerivastatin (10⁻⁶ mol/L) for either 2 or 24 hours. Using an organ bath technique, endothelial function was examined using acetylcholine (10⁻⁹ to 10⁻⁵ mol/L) after contraction by 3×10⁻⁸ mol/L of endothelin-1.

Results. Time-related endothelial dysfunction was shown in the control group of radial artery but not in the cerivastatin group: maximal endothelium-dependent vasodilation in the control and cerivastatin groups were 56.8% ± 10.2% and 65.9% ± 10.1% at 2 hours and 39.4% ± 4.7% and 68.4% ± 5.0% (p < 0.01, vs control) at 24 hours, respectively. On the other hand, in the left internal thoracic artery, those in the control and cerivastatin groups were 38.3% ± 8.2% and 45.0% ± 5.5% at 2 hours and 38.1% ± 8.2% and 56.5% ± 8.8% at 24 hours, respectively (NS).

Conclusions. In radial artery, cerivastatin significantly preserved endothelium-dependent vasodilation, which diminished with time in the control group. This could have very important implications in the clinical practice of coronary artery bypass grafting.     

Histamine H1 and H2 receptor-mediated vasoreactivity of human internal thoracic and radial arteries

BACKGROUND: Although internal thoracic arteries (ITAs) and radial arteries (RAs) have been shown to have similar patency, RAs tend to be more vasospastic postoperatively compared with ITAs. Therefore, the purpose of this study was to examine the effect of histamine subclass 1 (H1) receptors and histamine subclass 2 (H2) receptors on vasoreactivity in human ITAs and RAs. METHODS: Vessels were obtained from coronary artery bypass grafting patients. Human arterial rings (2 mm) were mounted in tissue baths, and baseline contractility was determined. Histamine concentration response curves (10(-9)-10(-3) mol/L) were performed in the absence or presence of diphenhydramine (H1 antagonist, 10(-4) mol/L) or famotidine (H2 antagonist, 10(-4) mol/L). Comparison of curves was performed by 2-way analysis of variance with repeated measures and a Bonferroni post-t test. RESULTS: Maximal contraction to histamine was significantly greater in RA (8.3 +/- 0.8 g, n = 6) than in ITA (2.9 +/- 0.3, n = 6), (P < .05). However, there was no difference in sensitivity. Histamine-mediated responses of both RA and ITA were blocked by pre-exposure to H1 antagonist, whereas an H2 antagonist only partially inhibited RA responses while blocking most of the ITA response to histamine. CONCLUSION: These studies suggest that H1 receptors alone cause contraction in RA but not in ITA, which may have potential linkage to patency and vasospasm. Further studies are necessary to identify the exact role of H2 receptors in ITA.