Greater contractility of internal mammary artery bifurcation: possible cause of low patency rates

Longitudinal histomechanical heterogeneity of the internal thoracic artery

The internal thoracic artery (ITA) is the principal choice for coronary artery bypass grafting (CABG) due to its mechanical compatibility, histological composition, anti-thrombogenic lumen, and single anastomotic junction. Originating at the subclavian artery, traversing the thoracic cavity, and terminating at the superior epigastric and musculophrenic bifurcation, bilateral ITAs follow a protracted circuitous pathway. The physiological hemodynamics, anatomical configuration, and perivascular changes that occur throughout this length influence the tissue's microstructure and gross mechanical properties. Since histomechanics play a major role in premature graft failure we used inflation-extension testing to quantify the regional material and biaxial mechanical properties at four distinct locations along the left (L) and right (R) ITA and fit the results to a structurally-motivated constitutive model. Our comparative analysis of 44 vessel segments revealed a significant increase in the amount of collagen but not smooth muscle and a significant decrease in elastin and elastic lamellae present with distance from the heart. A subsequent decrease in the total deformation energy and isotropic contribution to the strain energy was present in the LITA but not RITA. Circumferential stress and compliance generally decreased along the length of the LITA while axial stress increased in the RITA. When comparing RITAs to LITAs, some morphological and histological differences were found in proximal sections while distal sections revealed differences predominantly in compliance and axial stress. Overall, this information can be used to better guide graft selection, graft preparation, and xenograft-based tissue-engineering strategies for CABG.

Branched internal mammary conduit permits non-sequenced total arterial revascularization

Recent trends in cardiac surgery have encouraged total arterial coronary revascularization, citing advantages in long-term patency and overall mortality. Often relying on sequenced, composite, and free-graft strategies, total arterial coronary revascularization is limited by conduit availability and surgical complexity. We present the use of bilateral internal mammary artery grafts to achieve nonsequential 3-vessel total arterial coronary revascularization using the preserved distal bifurcation of the right internal mammary artery. Utilization of distal internal mammary artery branches should be considered a viable strategy in select patients and can broaden the opportunities for total arterial coronary revascularization in patients with multivessel coronary disease.

Segmental Difference in Vasoreactivity of the Human Right Gastroepiploic Artery

BACKGROUND

The gastroepiploic artery (GEA) plays an important role in the era of multiple arterial revascularization, but spasm is a major matter of concern. The internal thoracic artery has been shown to have a strong tendency to spasm in its distal bifurcating part, whereas the segmental difference in vasoreactivity of the GEA has never been performed.Methods and Results:The full length of the GEA obtained from 21 patients undergoing a total gastrectomy was divided into 3 sections: proximal (5 cm from the origin), middle, and distal (5 cm from the end). Concentration-response curves for vasoconstrictors (phenylephrine, prostaglandin F2α, and endothelin-1) and vasodilators (carperitide, nitroglycerin, and nifedipine) were then established using organ baths. All the vasoconstrictors and vasodilators produced concentration-dependent responses in each section. As the concentration of the vasoconstrictors increased, segments at the distal section showed a significantly greater contraction than those at the middle and proximal sections regardless of the type of vasoconstrictor. The effective concentration of drugs that caused 50% of the maximal response for endothelin-1 was significantly greater in the distal section than that in the proximal sections. No significant difference was found in vasodilators-induced relaxation.

CONCLUSIONS

The contractility increases toward to the end of the GEA. Clinically, the distal portion of the GEA should be trimmed off and not be used as an anastomotic site wherever possible.

Retroaortic right internal thoracic artery grafting of circumflex artery targets

BACKGROUND

Retroaortic right internal thoracic artery grafting has failed to gain popularity. We aimed to delineate patient correlates of eligibility, distribution of targets, and effects of target remoteness on outcome and risk of retroaortic bleeding.

METHODS

Data of 861 patients undergoing skeletonized bilateral internal thoracic artery grafting (2007-2012) were analyzed according to retroaortic (n = 300) or T-graft configuration. Retroaortic graft subgroups were categorized according to proximal (first obtuse marginal, ramus) or distal (2nd, 3rd, or sequential 1st-2nd obtuse marginal) circumflex artery targets.

RESULTS

LOESS curve analyses revealed that taller patients had a higher likelihood of retroaortic grafting. The distribution of 337 retroaortic graft targets (300 patients) was first obtuse marginal in 74.5%, 2nd marginal in 12.4%, ramus in 11.2%, 3rd marginal in 1.9% and sequential 1st-2nd marginal in 12.3%. The success rate in reaching proximal and distal circumflex artery targets was 97% and 30%, respectively, 5-year survival (92.2%) and freedom from major adverse cardiac and cerebrovascular events (85.8%) were comparable between proximal and distal retroaortic graft subgroups. Distal circumflex artery targets had no effect on the occurrence of major adverse cardiac and cerebrovascular events. The incidence of retroaortic bleeding from skeletonized retroaortic grafts was 0.6%.

CONCLUSIONS

Taller patients have a greater likelihood of qualifying for retroaortic grafting. This technique is highly reproducible for proximal but not distal circumflex artery targets. Distal circumflex artery targets are not independent correlates of early or late adverse outcomes. The risk of retroaortic bleeding is low despite retroaortic right internal thoracic artery skeletonization.

Concomitant grafting of both postbifurcation internal thoracic artery branches

OBJECTIVE

We aimed to assess the clinical outcome and graft patency after concomitant grafting of both postbifurcation internal thoracic artery (ITA) branches.

METHODS

Between 2007 and 2013, 17 patients (14 men; mean [SD] age, 60 [9.3] years) underwent skeletonized bifurcated ITA grafting. Respective targets were restricted to non-left anterior descending (LAD) area. In all patients, a complementary standard ITA was used to graft the LAD artery. Graft patency was assessed by standard coronary angiography or serial multidetector computed tomography.

RESULTS

Of the bifurcated conduits, 94% were right ITA. Respective right ITA target sets were first and second obtuse marginal arteries (M1-M2) (n = 12), ramus-M1 (n = 2), and distal right coronary artery-posterior descending artery (n = 2). Right ITAs were mobilized retroaortic (via the transverse sinus) in 14 patients (82%) (to circumflex artery targets). Circumflex artery targets comprised 88.2% of all anastomoses (30/34). There were no early mortalities, myocardial infarctions, or hypoperfusion syndromes. During median follow-up of 44 months (range, 3-63), there was no late mortality. Overall reintervention rate was 11.7%, and bifurcated ITA-related reintervention rate was 5.8%. At 5 years, freedom from major adverse cardiac or cerebrovascular event related to bifurcated ITA respective territory was 87% (Kaplan-Meier). Coronary imaging was achieved in 76% of the patients (elective multidetector computed tomography, n = 9; symptoms-directed coronary catheterization, n = 4). Bifurcation branch patency rate was 88.4% (23/26) at a median of 3.5 years.

CONCLUSIONS

Grafting both postbifurcation ITA branches is technically feasible and may be selectively considered. Current observations are valid for skeletonized conduits and limited to non-LAD targets. These preliminary findings should be corroborated by larger data sets.

A simple modification for a longer and larger internal thoracic artery as a composite Y-graft

OBJECTIVES

Coronary artery bypass grafting (CABG) using bilateral internal thoracic artery (BITA) has been proven to improve survival. Many surgeons use the composite Y-graft which is made of left ITA (LITA) and right ITA (RITA) grafts. The LITA is typically anastomosed to left anterior descending artery (LAD). However, we have used RITA for LAD instead of LITA and reviewed the patency of ITA grafts and their clinical outcomes.

METHODS

We analyzed 48 patients who underwent CABG using a BITA composite Y-graft from 2002 to 2012. In 30, LITA was anastomosed to LAD (Group L). The other 18 had RITA to LAD anastomosis (Group R).

RESULTS

The mean age of Group R was higher than that of Group L (p = 0.009). Postoperative angiography was performed in 35 patients (73%). Two patients in Group L and none of the patients in Group R had an ITA graft failure. The incidence of ITA graft failure and new adverse cardiovascular events were not different between the two groups.

CONCLUSION

The clinical outcome of RITA to LAD anastomosis is comparable with anastomosis of LITA to LAD in CABG using BITA composite Y-grafts. This technique may be useful when longer and larger ITA grafts are needed.

Early and late outcome of skeletonised bilateral internal mammary arteries anastomosed to the left coronary system

OBJECTIVES

To investigate in a retrospective study the technical aspects of using the in situ bilateral internal mammary arteries (IMAs), with the right IMA (RIMA) used for revascularisation of the circumflex system, and to evaluate early and late outcome.

MATERIALS AND METHODS

Between January 1997 and July 2003, 552 consecutive patients underwent grafting of the circumflex artery system with an in situ skeletonised RIMA routed through the transverse sinus (eventually retrocaval). Mean (SD) age was 63.8 (11) years. 331 (60%) patients underwent total arterial myocardial revascularisation. Mean follow up was 26 (9) months.

RESULTS

The success rate of skeletonised RIMA grafting to the circumflex branch was 100%. There were 19 (3.4%) in-hospital deaths. Perioperative myocardial infarction occurred in 12 (2.2%) patients. In 155 patients undergoing postoperative angiography, two had an occluded RIMA and a string-like phenomenon was seen in three RIMA and one left IMA (LIMA). Three RIMA and three LIMA had stenotic lesions. The patency rates of RIMA and LIMA were 94% and 97.4%, respectively. Strong predictors of non-functional IMA grafts were a recipient coronary artery diameter of < 1.5 mm (p = 0.022), < 60% stenosis of the recipient coronary artery (p = 0.015), diffuse stenotic lesions of the recipient coronary artery (p = 0.018), and a small IMA calibre (p = 0.0001). Cumulative actuarial survival at three years was 96.4% and event-free cumulative survival was 93.8%.

CONCLUSIONS

Use of the bilateral IMAs offers the possibility of constructing various configurations, making total arterial myocardial revascularisation possible with a minimum number of arterial conduits. Use of the skeletonised RIMA through the transverse sinus and eventually retrocavally can reach most branches of the circumflex system and is associated with an excellent patency rate. Patients who received bilateral IMA grafts for left coronary system revascularisation had improved early and late outcomes and decreased risk of death, reoperation, and angioplasty.

In situ retrocaval skeletonized right internal thoracic artery anastomosed to the circumflex system via transverse sinus: Technical aspects and postoperative outcome

BACKGROUND

The aim of this study was to investigate whether, by using the in situ right internal thoracic artery via the transverse sinus (eventually retrocaval), both the proximal and distal major branches of the circumflex system could be grafted and to evaluate the early and late outcome in these patients.

METHODS

Between January 1997 and March 2002, 452 consecutive patients underwent grafting of the circumflex system with the in situ skeletonized right internal thoracic artery routed via the transverse sinus. The mean age was 62.4 +/- 10.3 years. A mean of 2.2 +/- 0.3 arterial grafts per patient were used, and 271 (60%) patients underwent total arterial myocardial revascularization. At 3 months after surgery, 86 patients (right Y or T graft) underwent echo color Doppler imaging before and after an adenosine provocative test. The mean follow-up was 27 +/- 8 months.

RESULTS

The success rate of skeletonized right internal thoracic artery grafting to the circumflex system branch was 100%. There were 15 (3.4%) hospital deaths. In 116 patients who underwent postoperative angiography, the total patency rates of the right and left internal thoracic arteries were 94% and 96.6%, respectively. Strong predictors for nonfunctional internal thoracic artery grafts were a small internal thoracic artery caliber (P <.001), recipient coronary artery diameter less than 1.5 mm (P =.012), stenotic lesions of less than 60% (P =.016), and diffuse stenotic lesions (P =.015) of the recipient coronary artery. In 86 patients who underwent postoperative echo color Doppler imaging, the flow reserves at the main stem of the left and right internal thoracic arteries were 2.24 +/- 0.5 and 2.48 +/- 0.6, respectively. Cumulative actuarial survival at 3 years was 96.3%, and event-free cumulative survival was 93%. The Cox model revealed a left ventricular ejection fraction of less than 35% (P =.016), age greater than 70 years (P =.025), New York Heart Association grade greater than III (P =.0019), nontotal arterial myocardial revascularization (P =.002), and the preoperative presence of more than 1 ischemic area (P <.001) as strong predictors for poor overall cumulative event-free survival.

CONCLUSIONS

The skeletonized right internal thoracic artery, placed via the transverse sinus and eventually retrocaval, can reach most branches of the circumflex system and is associated with an excellent patency rate. The predictors for poor overall event-free survival seem to be similar to those of the general population undergoing conventional coronary artery bypass grafting. Use of bilateral internal thoracic arteries and in situ right internal thoracic artery grafting via the transverse sinus offers the possibility of various configuration constructions, making possible total arterial myocardial revascularization with a minimum number of arterial conduits.

Comparison of vasoactive response of left and right internal thoracic arteries to isosorbide-dinitrate and nitroglycerin: an in vitro study

OBJECTIVE

The internal thoracic artery (ITA) is the most important graft in coronary artery bypass grafting. Its distal region is, however, prone to vasospasm. We studied the effects of nitroglycerin (NTG) and isosorbide-dinitrate (DSDN) on distal segments of left versus right ITA.

METHODS

Rings of distal segments (6 to 9 mm proximal to bifurcation) of the human left and right ITA were studied. After baseline contraction of the rings, achieved using 60 mmol/L of KCl, they were exposed to increasing doses of ISDN and NTG (10 to 100 microg/ml), and dose-response curves were recorded.

RESULTS

The contractile response of left ITA rings to KCl were significantly lower than those of right ITA rings (1.87 +/- 0.25 g versus 3.5 +/- 0.61 g, p < 0.005). Both nitrates inhibited the contractile response in a concentration-dependent manner, with relaxing effects of ISDN higher than those of NTG (p < 0.01) in both left and right ITA rings.

CONCLUSIONS

The distal segment of the left ITA is less prone to vasospasm than that of the right. ISDN has a considerably higher relaxant effect on this segment than NTG. We therefore recommend favoring high doses of ISDN over NTG as an antispastic measure.

Technical aspects and outcome of in situ right internal thoracic artery grafting to the major branches of the circumflex artery via the transverse sinus

BACKGROUND

Little is known about the anatomic limitations of in situ right internal thoracic artery (RITA) grafting to the circumflex artery.

METHODS

To evaluate the technical aspects and outcome of revascularization of the proximal and distal major branches of the circumflex artery (obtuse marginal [OM] branch and posterolateral [PL] branch), a total of 145 patients who possessed a graftable branch of the circumflex artery were enrolled into the prospective project. There were 73 patients who had the PL branch as a primary target and 72 patients with OM branches, which were allocated by a blinded observer who reviewed the preoperative angiography.

RESULTS

Changes of primary target vessels were required in 9 patients (6.2%), yielding an overall success rate of RITA grafting of 93.8%. The success rates of RITA grafting to the OM branch and the PL branch were 95.8% (69/72; CI 88.3% to 99.1%) and 91.7% (67/73; CI 83.0% to 96.9%), respectively. The univariate analysis identified grafting under hypothermic ventricular fibrillation as predictors of inability to use in situ RITA grafting for revascularization of the circumflex artery. RITA grafting to the PL branch is not identified as a predictor. Postoperative angiography in 136 patients revealed only one occlusion (0.75%) of the RITA graft anastomosed to the marginal artery. There were no significant differences in patency rates between left and right ITA grafts.

CONCLUSIONS

This prospective study showed that in situ RITA was, in most cases, able to reach most branches of the major circumflex artery and demonstrated an excellent patency rate.

Vasoactive response of different parts of human internal thoracic artery to isosorbide-dinitrate and nitroglycerin: an in-vitro study

OBJECTIVE

The left internal thoracic artery (LITA) is the most important graft for coronary artery bypass grafting (CABG). Its distal region is, however, prone to vasospasm. The effect of nitroglycerin (NTG) and isosorbide-dinitrate (ISDN) on different segments of this region was studied.

METHODS

Rings of three segments of the LITA were studied: 6-9 mm proximal to the bifurcation (part A); 1-3 mm proximal to the bifurcation (part B); and 3-6 mm distal to the bifurcation (part C). After baseline, maximal contraction of the rings was achieved using 60 mmol/l of KCl, they were exposed to increasing doses of ISDN and NTG (10-100 microg/ml), and dose-response curves were recorded.

RESULTS

The contractile response of part A to KCl was significantly lower than that of parts B and C (1.87+/-0.25 versus 4.05+/-0.39 and 7.64+/-0.54 g, respectively; P<0.001). Both nitrates inhibited the contractile response in a concentration-dependent manner. The relaxing effects of both nitrates on part A was most pronounced (P<0.01), with the effect of ISDN being higher than that of NTG (P<0.01).

CONCLUSIONS

The region 6-9 mm proximal to the LITA bifurcation is less prone to vasospasm, and has greater relaxation responses to ISDN and NTG than the more vasospastic distal parts of the LITA. We recommend avoiding the use of the very distal part of this artery during CABG, and to use high doses of ISDN rather than NTG as an anti-spastic measure.

Pharmacology of coronary artery bypass grafts

Spasm of arterial and venous graft conduits can occur both during harvesting and after the graft is connected. Attempts to overcome spasm during harvesting by probing or hydraulic distension can cause structural damage to the graft, which may impair short- and long-term patency. After a coronary artery bypass graft is connected, spasm can cause major problems with myocardial perfusion. To select the best pharmacologic agent to prevent or reverse vasoconstriction in a graft requires an understanding of the reactivity of that particular type of graft to vasoconstrictor and vasodilator agents. The pharmacologic reactivity of venous and arterial graft conduits has been documented through extensive studies of isolated vessels in the organ bath and of in situ grafts in the body. In this review we summarize the current state of knowledge of the reactivity of arterial and venous grafts to vasoconstrictor and vasodilator agents and describe the practical application of this knowledge in the operating room and in the postoperative period.

Long-term patency rate of right internal thoracic artery bypass via the transverse sinus

BACKGROUND

Although concern regarding patency and possible compromise of graft blood flow by routing the right internal thoracic artery (RITA) through the transverse sinus has been raised, little is known about long-term patency.

METHODS AND RESULTS

To evaluate long-term patency of in situ RITA bypass via the transverse sinus, our first 115 patients (94 men, 21 women; mean age, 62.5 years; range, 13 to 77 years) who were alive in 1998 were enrolled for angiographic study. Only good-caliber grafts with no occlusion, string sign, or significant stenosis were considered patent. Early postoperative angiography had been performed 2 to 3 weeks after surgery in 114 patients. The early patency rates were 97.1% for RITA and 95.4% for left internal thoracic artery (LITA) grafts. Of 109 long-term survivors, 73 (67.0%) consented to have late angiographic restudy at a mean of 59 months (range, 9 to 93 months); 89.9% of RITA and 92.3% of LITA grafts were patent. Cumulative patency rates (actuarial curves) at 6 years were 89.3% (95% CI, 85% to 94%) for RITA and 94.5% (95% CI, 92% to 97%) for LITA, the differences not reaching statistical significance (multivariate Cox analysis).

CONCLUSIONS

Our study demonstrated good long-term patency of in situ RITA bypass grafting via the transverse sinus for revascularization of the circumflex and diagonal arteries and supports its continued use.

Endothelin-1 and neutrophil activation during heparin-coated cardiopulmonary bypass

BACKGROUND

Heparin-coated circuits attenuate the systemic inflammatory response to cardiopulmonary bypass. The present study compares two different heparin coatings in terms of the release of endothelin-1 and neutrophil glycoproteins.

METHODS

Forty low-risk patients undergoing coronary artery bypass grafting were investigated, having cardiopulmonary bypass with a Duraflo II heparin-coated circuit (n = 10), an identical but uncoated circuit (n = 10), a Carmeda BioActive Surface heparin-coated circuit (n = 10), or an identical but uncoated circuit (n = 10). A standard systemic heparin dosage was used in all patients. Endothelin-1 and the neutrophil glycoproteins lactoferrin and myeloperoxidase were quantified throughout the operation and 3 hours postoperatively.

RESULTS

Enhanced plasma levels of endothelin-1, lactoferrin, and myeloperoxidase were observed during and after uncoated cardiopulmonary bypass, but this was not associated with clinical side effects. Compared with the respective uncoated controls, Duraflo II attenuated only the lactoferrin levels, whereas Carmeda BioActive Surface was associated with lower levels of both endothelin-1, lactoferrin, and myeloperoxidase. Of the two heparin coatings, Carmeda BioActive Surface proved more effective than Duraflo II in attenuating the levels of these substances.

CONCLUSIONS

The plasma levels of endothelin-1, lactoferrin, and myeloperoxidase increase during cardiopulmonary bypass in coronary artery bypass grafting, but this has no clinical side effects in low-risk patients. The increase is attenuated using heparin-coated extracorporeal circuits, and then more effectively by Carmeda BioActive Surface than by Duraflo II.

Hypertension increases the contractions to sumatriptan in the human internal mammary artery

BACKGROUND

The internal mammary artery is the graft of choice for myocardial revascularization. The tendency to spasm increases toward the distal end of the internal mammary artery, which is the portion generally used for anastomosis. The distal internal mammary artery is more pharmacologically responsive to 5-hydroxytryptamine and several other vasoconstrictor agents than its midsection.

METHODS

We examined the effects of 5-hydroxytryptamine and a 5-hydroxytryptamine1-like receptor agonist sumatriptan on internal mammary artery segments (length, 3-4 mm) obtained from patients undergoing coronary artery bypass grafting. To unmask a 5-hydroxytryptamine1-like receptor-mediated contractile response, threshold concentrations of potassium chloride were used.

RESULTS

5-Hydroxytryptamine induced concentration-dependent contractions in all, quiescent and potassium chloride precontracted, preparations. Sumatriptan induced marked contraction in some of the quiescent internal mammary artery rings, whereas it elicited marked and concentration-dependent contractions in all of the preparations given a moderate tone by a threshold concentration of potassium chloride. The sensitivity to sumatriptan was higher in potassium chloride-precontracted distal arteries than it was for the quiescent distal segments. Additionally, the sensitivity to and the efficacy of sumatriptan were much more markedly potentiated by precontraction in the preparations taken from hypertensive patients.

CONCLUSIONS

The more marked potentiation of the responses in arteries from hypertensive patients may be one of the factors influencing the patency rates.

Inhibition of vasoconstriction by phosphodiesterase III inhibitor milrinone in human conduit arteries used as coronary bypass grafts

We wished to determine the effect of phosphodiesterase III (PDE III) inhibitor milrinone on human arteries used as coronary bypass grafts. Human internal mammary artery segments (IMA, n = 109) taken from 25 patients were studied. Concentration-relaxation curves for milrinone were established in IMA precontracted with four vasoconstrictors [K+, endothelin-1 (ET-1), U46619, and phenylephrine (PE)]. In IMA rings incubated with therapeutic plasma concentrations of milrinone (7 and 70 microM) for 10 min, concentration-contraction curves for the four vasoconstrictors were constructed. Milrinone caused a complete relaxation in U46619, ET-1, PE (100%), or K+ (97.7%)-precontracted IMA. The EC50 value was higher against K+ (-5.31 +/- 0.27 log M) than PE (-6.20 +/- 0.25 log M, p = 0.036) or endothelin-1 (-6.41 +/- 0.28 log M, p = 0.018). Pretreatment with milrinone decreased the contraction induced by ET-1 from 186.0 +/- 23.3 to 66.9 +/- 9.6% (p = 0.002) and that induced by PE from 140.6 +/- 27.6 to 54.1 +/- 7.0% (p = 0.03) and shifted the EC50 7.6-fold higher (p = 0.003). Treatment of milrinone reduced the K+ and U46619 contraction (p < 0.05) at lower concentrations (between 10 and 80 mM for K+ and -8.5 and -7.5 log M for U46619) and shifted the concentration-contraction curves rightward (2.56-fold higher for K+, p < 0.0001; 3.18-fold higher for U46619, p = 0.007). Denudation of endothelium did not affect the milrinone-induced relaxation. These results demonstrate that milrinone is a potent vasodilator of human conduit arteries used as coronary bypass grafts and may have a slight selectivity with greater potency to receptor stimulants than to the depolarizing agent K+. The results may prove a particular indication for milrinone for use in patients receiving arterial grafts for coronary bypass.

5-HT1-like receptor-mediated contraction in the human internal mammary artery

We wished to characterize the 5-hydroxytryptamine (5-HT) receptors mediating vasoconstriction in the human internal mammary artery (IMA). Segments of the IMA obtained from patients undergoing coronary by-pass surgery were suspended in an organ bath and exposed to 5-HT and sumatriptan (SUM), a 5-HT1-like receptor agonist, in the presence and absence of potassium chloride (KCl) and angiotensin II. 5-HT induced concentration-dependent contractions in all quiescent and pre-contracted preparations. SUM induced small contractions in 70% of quiescent IMA rings, whereas it elicited marked and concentration-dependent contractions in all of the preparations given a moderate tone by a threshold concentration of KCl and angiotensin II. The efficacy of SUM was higher in precontracted arteries. Concentration-effect curves (CEC) of 5-HT and SUM were not affected by the 5-HT3-receptor antagonist tropisetron (1 microM). The nonselective antagonist, methiothepin (30 nM), shifted the CEC of SUM to the right. 5-HT2A-receptor antagonist, ketanserin (1 microM) inhibited responses to 5-HT, whereas it affected only the responses to the smaller concentrations of SUM. When methiothepin (30 nM) was applied in the presence of ketanserin (1 microM), a further inhibition in the responses to 5-HT was observed. These results suggest that 5-HT1-like receptors mediate the contractile action of SUM and contribute to that of 5-HT in IMA.

Which is the graft of choice for the right coronary and posterior descending arteries? Comparison of the right internal mammary artery and the right gastroepiploic artery

BACKGROUND

The graft of choice for the left anterior descending coronary artery is the left internal mammary artery because of superior long-term patency. However, controversy exists regarding the graft of choice for the right coronary artery and for the posterior descending branch.

METHODS AND RESULTS

Two types of pedicled arterial grafts were used for the right coronary and the posterior descending arteries in patients undergoing coronary bypass surgery between January 1991 and September 1994. Group A comprised 114 patients with a right internal mammary artery (RIMA) graft, and group B consisted of 127 patients with an in situ right gastroepiploic artery (R-GEA) graft. Mean age was 56.9 years in group A and 63.3 years in group B; 7.9% (9 of 114) and 33.9% (43 of 127) were diabetics in groups A and B, respectively. Overall mortality was 2.6% (3 deaths) for group A and 3.9% (5 deaths) for group B (P = NS). However, the prevalence of perioperative myocardial infarction in the right coronary artery distribution was significantly higher for group A (5.3%, or 6 of 114) than for group B (0.8%, or 1 of 127; P < .05), and the reoperation rate for graft failure (from 0 to 12 months after surgery) was significantly higher for the RIMA (4.4%, or 5 of 114) than for the R-GEA (0%; P < .05). Also, the prevalence of deep sternal wound infection in diabetics was significantly higher in group A (22.2%, or 2 of 9) than in group B (4.6%, or 2 of 43; P < .05).

CONCLUSIONS

Our preliminary results suggest that the failure rate of the RIMA graft is significantly higher, especially if used as a pedicled graft to the posterior descending artery. The risk of sternal wound complications is greater in diabetics if both internal mammary arteries are used for grafting. Therefore, the R-GEA graft is preferred in diabetics and whenever the posterior descending artery is the target vessel.

Comparison among arterial grafts and coronary artery. An attempt at functional classification

Various arterial conduits have been used for coronary artery bypass grafting. However, arterial grafts are not uniform either in anatomy or in function. Some conduits are more spastic than others and there may be possible differences in long-term patency rates. The diverse biologic characteristics promote a necessity of classification of arterial grafts, which may facilitate the understanding of surgeons of biologic characteristics of various arterial grafts and provide a scientific basis for searching for new grafts. Another important issue is the comparison of reactivity between arterial grafts and coronary arteries. In this study, we aim to compare the pharmacologic reactivity among the human arteries (grafts and coronary arteries) and to classify arterial grafts. Segments of three arterial grafts (gastroepiploic, internal mammary, and inferior epigastric) taken from patients undergoing coronary artery bypass grafting and coronary arteries taken from explanted hearts were studied in organ baths for the contraction to four vasoconstrictors (endothelin-1, thromboxane A2 mimetic U46619, full adrenoceptor agonist norepinephrine, and depolarizing agent potassium) under physiologic pressure. The diameter of the four arteries at a pressure of 100 mm Hg was similar (p > 0.05). However, the gastroepiploic artery contracted to higher forces (9.41 +/- 2.0 gm for endothelin, 11.79 +/- 1.85 gm for U46619, 13.54 +/- 2.7 gm for norepinephrine, and 11.11 +/- 1.97 gm for potassium) than did the coronary artery and internal mammary artery (p < 0.05) for all the tested vasoconstrictors and higher than the inferior epigastric artery for potassium and norepinephrine (p < 0.05). There was no significant difference among the other three arteries (internal mammary artery, inferior epigastric artery, and coronary artery) regarding the maximal contraction force to any vasoconstrictor. No difference was detected in regard to the sensitivity (effective concentration causing 50% of the maximal response) to the vasoconstrictors among the four arteries. This study reveals that among the arterial grafts and the coronary artery, the gastroepiploic artery has the highest contractility to various vasoconstrictors. On the basis of our findings and physiologic and embryologic knowledge we propose a classification for arterial grafts: type I (somatic arteries), type II (splanchnic arteries), and type III (limb arteries). Types II and III are prone to spasm because of higher contractility whereas type I arteries are usually less spastic. This classification may have important clinical implications for the understanding of arterial graft spasm or patency and may be useful in the search for new grafts.

Overview of the nature of vasoconstriction in arterial grafts for coronary operations

Many vasoconstrictors (spasmogens) may cause arterial graft spasm; however, there is lack of an overview of the nature of vasoconstriction in grafts. This study was designed to investigate the response of three major arterial grafts currently used for coronary artery bypass grafting to various vasoconstrictor substances. Segments of three arterial grafts (gastroepiploic [GEA], n = 28; internal mammary [IMA], n = 213; inferior epigastric [IEA], n = 24) taken from patients undergoing coronary artery bypass grafting were studied in organ baths under a physiologic pressure. Cumulative concentration-contraction curves were established for the following vasoconstrictor substances: endothelin-1, U46619, prostaglandin F2 alpha, norepinephrine, methoxamine, phenylephrine, 5-hydroxytryptamine, and potassium chloride (K+). In IMA, the highest contraction force was induced by U46619 (5.69 +/- 0.48 g), endothelin-1 (4.43 +/- 0.4 g), PGF2 alpha (6.29 +/- 1.42 g), and K+ (4.58 +/- 0.5 g). Internal mammary artery is highly sensitive to endothelin-1 (EC50, -8.13 +/- 0.08 log M) and U46619 (EC50, -8.21 +/- 0.21 log M) (lower than any other vasoconstrictors, p < 0.001). Next sensitive vasoconstrictors were PGF2 alpha and norepinephrine. 5-Hydroxytryptamine induced significantly higher contraction force in the IMA without endothelium (2.8 +/- 0.64 g versus 1.4 +/- 0.23 g, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)