Radial artery has higher receptor-mediated contractility but similar endothelial function compared with mammary artery

BACKGROUND

The radial artery (RA) has been used as an alternative arterial graft for coronary artery bypass grafting, but this artery has been suggested to be spastic. Endothelin-1 (ET) and angiotensin II (AII) have been measured with increased plasma concentrations during cardiopulmonary bypass. However, whether RA is reactive to these two important receptor-mediated vasoconstrictors is unknown. Also unknown is the endothelial function of this arterial conduit. This study was designed to compare RA and the internal mammary artery regarding the contractile characteristics to ET-1 and AII and endothelial function.

METHODS

Ring segments of the RA and internal mammary artery taken from patients undergoing coronary artery bypass grafting were studied in organ chambers at a physiologic pressure. The contractility was determined from the contraction induced by ET-1 and AII as contraction force and the force normalized by circumference (g/mm). The endothelium-dependent relaxation was induced by the calcium ionophore A23187, a nonreceptor agonist, and substance P, a receptor agonist for endothelium-derived relaxing factors. Nitroglycerin was used to study the endothelium-independent relaxation.

RESULTS

Both ET-1 and AII induced a higher contraction force (9.0 +/- 0.9 g, n = 12, versus 4.5 +/- 0.4 g, n = 38, p < 0.0001 for ET and 6.5 +/- 1.9 g, n = 7, versus 1.7 +/- 0.3 g, n = 8, p = 0.015 for AII) and normalized force (0.95 +/- 0.1 g/mm versus 0.66 +/- 0.05 g/mm, p = 0.007 for ET-1 and 0.8 +/- 0.2 g/mm versus 0.2 +/- 0.05 g/mm, p < 0.01 for AII) in RA than in the internal mammary artery. There were no significant differences detected between these arteries with regard to either endothelium-dependent (to substance P and A23187) or endothelium-independent (to nitroglycerin) relaxation (p > 0.05).

CONCLUSIONS

We conclude that the human RA has a higher receptor-mediated contractility (to ET-1 and AII) but similar endothelial function compared to the internal mammary artery. The study reveals the nature of the more spastic characteristics of the RA, supports the necessity of a more active pharmacologic intervention to relieve spasm in the RA, and suggests that the similar endothelium-derived relaxing factor-mediated endothelial function of the RA compared with the internal mammary artery may be the basis for a satisfactory long-term patency.

Reactivity of the canine isolated internal mammary artery, saphenous vein, and coronary artery to constrictor and dilator substances: relevance to coronary bypass graft surgery

The internal mammary artery (IMA) and saphenous vein (SV) are used routinely in coronary artery (CA) bypass graft surgery. The IMA may develop spasm during surgery, and the SV often develops spasm during removal from the leg. We sought to determine the relative reactivity of the canine CA, IMA, and SV to potential vasoconstrictor substances and especially to determine which vasodilator agents were effective in these different blood vessels. All vessels were arranged as ring segments suspended at optimal stretch in organ baths. Glyceryl trinitrate (GTN) caused relaxation of the three vessels but was less sensitive, less potent (as determined by EC50 values), and had a reduced range of relaxation in the IMA. Papaverine was less sensitive in the IMA as compared with the CA and SV. Nifedipine, verapamil, and diltiazem were potent relaxing agents in all three vessels when precontracted by K+, but were less potent in vessels contracted by the thromboxane mimetic U46619 or phenylephrine, especially in the SV. These studies highlight the marked differences in the response of IMA and CA to constrictor and dilator agents and reinforce the notion that calcium antagonists of different chemical classes have widely differing activities in vascular tissue.

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.

Arterial grafts for coronary artery bypass grafting: biological characteristics, functional classification, and clinical choice

Various arterial grafts have been used for coronary artery bypass grafting, but a unanimous opinion on how to best use these grafts has not been formed. Arterial grafts are not uniform in their biological characteristics. Differences between the perioperative behavior of the grafts and their long-term patency may be related to different characteristics. These characteristics should be taken into account in the use of arterial grafts, some of which are subject to more active pharmacologic intervention during and after operation to obtain satisfactory results. Clinical choice of grafts must be based on the general condition of the patient, the biological characteristics of the graft, the anatomy of the coronary artery, the match between the coronary artery and the graft, and technical considerations, including antispastic management.

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)

Characteristics of adrenoceptors in the human radial artery: clinical implications

OBJECTIVES

The radial artery has been suggested to be spastic. Endogenous and exogenous catecholamines and the use of beta-blockers may be related to radial artery spasm, but the characteristics of adrenoceptors in this artery are unknown. This study was designed to characterize the alpha- and beta-adrenoceptor in the human radial artery.

METHODS

Ring segments of the radial artery (n = 59) taken from patients undergoing coronary artery bypass grafting were studied in organ chambers. Alpha-adrenoceptor agonists (norepinephrine, methoxamine, and UK14304) and antagonists (phentolamine hydrochloride [INN: phentolamine], prazosin, and yohimbine) were used to characterize the alpha-adrenoceptor. Beta-adrenoceptor function was studied in U46619-precontracted rings in response to isoproterenol (INN: isoprenaline).

RESULTS

Norepinephrine induced 6.9 +/- 0.6 gm (80.6% +/- 6.8% of the contraction by 100 mmol/L KCl), and this was almost fully inhibited by phentolamine hydrochloride (10 micromol/L, p < 0.0001). The contraction force induced by methoxamine (2.9 +/- 0.8 gm) was abolished by 0.5 micromol/L prazosin (p = 0.017). The contraction force induced by UK14304 (1.7 +/- 0.4 gm) was abolished by 1 micromol/L yohimbine. In contrast to the porcine coronary artery used as the control (fully relaxed to isoproterenol), radial artery rings did not have significant relaxation (1.1% +/- 0.8%).

CONCLUSIONS

The human radial artery is an alpha-adrenoceptor-dominant artery with little beta-adrenoceptor function. The use of beta-blockers will not likely evoke the spasm of the radial artery. Furthermore, the radial artery has a dominant alpha1-adrenoceptor function, but the postjunctional alpha2-adrenoceptor is also functional. Circulating catecholamines will mainly contract the human radial artery by activation of the alpha1-adrenoceptors and to a lesser extent also by alpha2-adrenoceptors.

Comparison of nitric oxide release and endothelium-derived hyperpolarizing factor-mediated hyperpolarization between human radial and internal mammary arteries

BACKGROUND

Arterial grafts for CABG have been used increasingly, and the radial artery (RA) has become a preferable graft, secondary to the internal mammary artery (IMA). In the present study, we investigated and compared NO release and endothelium-derived hyperpolarizing factor (EDHF)-mediated hyperpolarization for IMA and RA.

METHODS AND RESULTS

IMA and RA segments taken from CABG patients were placed in an organ chamber. An NO-sensitive electrode (to directly measure NO release) or intracellular glass microelectrode (to measure membrane potential) was used to study NO or EDHF in response to acetylcholine (ACh) and bradykinin (BK) before and after incubation with indomethacin (a cyclooxygenase inhibitor), N(G)-nitro-L-arginine (an NO synthase inhibitor), and oxyhemoglobin (an NO scavenger). The resting membrane potential of the smooth muscle cells of IMA and RA was -58+/-0.84 (n=61) and -61+/-1.3 (n=46) mV, respectively (P=0.03). BK-induced EDHF-mediated hyperpolarization in the IMA was significantly greater than that in RA (BK 10(-)(7) mol/L: -10.9+/-1.5 [n=7] versus -5.8+/-0.9 [n=6] mV, P=0.04). The basal (16.8+/-1.9 versus 11.1+/-1.0 nmol/L, n=12, P=0.02) and stimulated releases of NO in IMA were significantly greater for BK (44.3+/-4.0 versus 25.8+/-3.6 nmol/L, n=8, P=0.004) and lasting longer for ACh (9.5+/-2.0 versus 6.6+/-3.6 minutes, n=12, P=0.03) than those in RA.

CONCLUSIONS

The basal and stimulated releases of NO and EDHF-mediated hyperpolarization in the IMA are significantly greater than that in the RA. The lower capacity of NO release may contribute to the susceptibility of RA to the perioperative vasospasm and may have an impact on the long-term graft patency.

Use of verapamil and nitroglycerin solution in preparation of radial artery for coronary grafting

BACKGROUND

The radial artery (RA) has been used as an alternative arterial graft for coronary artery bypass grafting. This artery has been reported to be spastic; therefore, use of spasmolytic drugs (vasodilators) during the preparation of the RA is recommended. The combination of calcium antagonists and nitroglycerin (verapamil plus nitroglycerin, VG solution) has been suggested to be effective in other bypass grafts. This study was designed to investigate (1) the effect of the VG solution during preparation of the RA for coronary artery bypass grafting and (2) whether the effect would last for a prolonged period after topical use.

METHODS

Ring segments of the RA taken from coronary artery bypass grafting patients were studied in organ chambers at a physiologic pressure. The relaxation effect of VG (30 mumol/L verapamil and 30 mumol/L nitroglycerin, n = 5) or papaverine (30 mumol/L, n = 5) was recorded in K+ (25 mmol/L potassium chloride)-precontracted RA segments. Other segments taken from the RA were treated (n = 5) or not treated (n = 20, as the control) with the VG solution for 45 minutes before used for coronary artery bypass grafting. Both the VG-treated and nontreated segments were immersed in oxygenated Krebs solution and stored in a refrigerator at 4 degrees C for 24 hours. The contraction force to 100 mmol/L K+ was compared between the two groups.

RESULTS

The VG solution induced more rapid relaxation than papaverine (p < 0.05 from the first to the ninth minute). After 10 minutes, both solutions induced full relaxation. The contraction to K+ (100 mmol/L) in rings treated with VG solution for 45 minutes during operation was almost abolished 24 hours later (0.86 +/- 0.1 g). In contrast, the control segments (n = 20) taken from nontreated RA contracted with K+ to high force (5.0 +/- 0.6 g; p < 0.001).

CONCLUSIONS

The present study suggests that the combination of verapamil and nitroglycerin may provide a rapid onset, a complete relaxation, and a long-lasting vasorelaxant effect when used to prepare the RA for grafting. This study adds a new method to prevent RA spasm during coronary artery bypass grafting.

Risk factors for operative mortality and sternal wound infection in bilateral internal mammary artery grafting

To investigate risk factors for operative mortality and sternal infection in patients undergoing bilateral internal mammary artery grafting, we analyzed the data of 199 patients who underwent this procedure from January 1986 through June 1992. These patients were also compared with those who underwent only saphenous vein grafting (1664 cases) and those who underwent unilateral internal mammary artery grafting (3359 cases) during the same time frame. The operative mortality was 3.52% (7/199) in the patients having bilateral internal mammary artery grafting, 2.71% (91/3359) in those having unilateral internal mammary artery grafting, and 8.53% (142/1664) in the patients having saphenous vein grafting (p < 0.0001). The occurrence rate of sternal infections was 2.45% (5/199) for bilateral internal mammary artery grafting, 1.32% (13/1664) for saphenous vein grafting, and 1.19% (20/3359) for unilateral internal mammary artery grafting (p = 0.27). The univariate analysis revealed that age, history of congestive heart failure, emergency operation, ejection fraction, and aortic crossclamp time were significantly correlated with operative mortality and that obesity was correlated with sternal wound infection. Stepwise multiple logistic regression identified that old age (> or = 70 years) (p < 0.0001), long perfusion time (p < 0.0001), and emergency operation (p = 0.0004) are risk factors for operative mortality and that obesity (p = 0.0009) is the only significant risk factor for sternal wound infection. We conclude that bilateral internal mammary artery grafting does not increase operative mortality in properly selected patients. However, this procedure should be carefully chosen in elderly (> or = 70 years) patients and for emergency operation. Obese patients have a high risk for sternal infection after bilateral internal mammary artery grafting.

Up to thirty-year survival after aortic valve replacement in the small aortic root

Aortic valve replacement (AVR) in the small aortic root has been reported to be associated with obstruction of left ventricular output. This study was designed to investigate the determinants of long-term survival after the implantation of small size prostheses. From September 1961 to December 1993, 2,977 patients underwent isolated aortic valve replacement at our institution. Of these patients, 447 who were older than 18 years received small size (21 mm or less) prostheses. Long-term survival was investigated in the 404 patients who survived operation (more than 30 days) with 92% follow-up completeness (mean +/- deviation 7.1 +/- 6.4; maximum, 31 years). The age was younger than 50 years in 62 patients, 50 to 59 years in 60, 60 to 69 years in 99, 70 to 79 years in 138, and 80 to 94 years in 45; 67% were men. Thirty patients (7%) had previous AVR. Prosthesis usage included early Starr-Edwards models in 130 (32%), current Starr-Edwards (model 1260 since 1969) in 50 (12%), Carpentier-Edwards (porcine) in 113 (28%), and other prostheses in 111 patients (27%). One hundred sixteen patients (26%) had concomitant coronary artery bypass grafting (CABG). Eleven variables (age divided as above, sex, preoperative functional class, body surface area [BSA], small BSA [less than 1.6, 1.7, 1.8, or 1.9 m2], period of operation, previous AVR, type of prosthesis, size of prosthesis, concomitant CABG, and re-replacement) were investigated with regard to the long-term survival by the Kaplan-Meier method, and age, concomitant CABG, and type of prosthesis were significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Verapamil plus nitroglycerin solution maximally preserves endothelial function of the radial artery: comparison with papaverine solution

BACKGROUND

Endothelium plays a key role in graft patency. My colleagues and I have developed a verapamil+nitroglycerin solution (balanced to pH 7.4) to prepare the radial artery without mechanical distention or dilation and have reported the efficacy of its antispastic action. This study was designed to investigate whether using this solution as part of the University of Hong Kong protocol to prepare the radial artery is more efficacious than papaverine solution in preserving endothelial function.

METHODS

Ring segments of the radial artery taken from 25 patients undergoing coronary artery bypass grafting were studied in organ chambers. The endothelium-dependent relaxation, as the index of endothelial function, was examined by two mechanisms-receptor-mediated relaxation (by acetylcholine) and non-receptor-mediated relaxation (by calcium ionophore A23187) in U46619-induced contraction (10 nmol/L).

RESULTS

In the relaxation induced by either acetylcholine (27.3% +/- 5.0% [n = 7] vs 23.9% +/- 3.9% [n = 6],p = 0.6) or A23187 (62.9% +/- 6.0% [n = 13] vs 62.3% +/- 8.4% [n = 6],p = 0.96), there was no significant difference between the control radial arteries and those treated with the verapamil+nitroglycerin solution. In the papaverine-treated rings, acetylcholine-mediated relaxation was abolished (3.3% +/- 2.6% vs 23.9% +/- 3.9%,p < 0.001) and A23187-mediated relaxation was significantly reduced (39.7% +/- 5.2% vs 62.3% +/- 8.4%, p = 0.02) compared with verapamil+nitroglycerin treatment.

CONCLUSION

Use of verapamil+nitroglycerin solution to prepare the radial artery maximally preserves endothelial function. In contrast, papaverine impairs this function. Verapamil+nitroglycerin solution may be effectively and safely used to prepare the radial artery for coronary artery bypass grafting.

Contractility of the human internal mammary artery at the distal section increases toward the end. Emphasis on not using the end of the internal mammary artery for grafting

The distal section of the internal mammary artery (3 to 4 cm proximal to the bifurcation) is often used for coronary grafting. This part of the artery is more pharmacologically responsive to vasoconstrictor agents than is its midsection. The present study was designed to test the hypothesis that the reactivity of the distal section of the internal mammary artery is inversely correlated to the diameter of the artery. The distal section of the human internal mammary artery was collected from aorta-coronary bypass grafts and studied in organ baths at a length of 3 mm. At the optimal point of the length-tension curves determined by a computer-iterative fitting technique, the diameter at 100 mm Hg, the maximal contraction forces and effective concentration causing 50% of the maximal response to vasoconstrictor agents U46619, potassium chloride, alpha-adrenoceptor agonists norepinephrine, methoxamine, and phenylephrine were recorded or calculated. The maximal relaxation and 50% response to glyceryl trinitrate in phenylephrine-precontracted internal mammary artery segments were also calculated. The contraction force was standardized by the circumference (grams per millimeter). Regression analysis between contraction force and diameter revealed that the contraction force induced by U46619 and potassium chloride was inversely correlated to diameter (r2 = 0.2, p < 0.05 in U46619-induced contraction and r2 = 0.2, p < 0.01 in potassium chloride-induced contraction). The contraction force induced by norepinephrine also had a trend inversely correlated to diameter (r2 = 0.2, p = 0.07). Glyceryl trinitrate-induced relaxation was not correlated to diameter. This study demonstrated that the contractility of the distal section of the internal mammary artery is inversely correlated to the diameter; that is, the smaller the diameter, the greater the tendency for spasm to develop. This suggests that trimming off the distal end of the internal mammary artery as much as possible may be the best way to prevent graft spasm and that superior results of left internal mammary artery grafted to the left anterior descending artery or the use of a "free graft" may be related to the shorter length (distal end is trimmed off) and less contractility of the graft.

Determinants of operative mortality in reoperative coronary artery bypass grafting

Previously suggested risk factors for operative mortality in reoperative coronary artery bypass grafting are contradictory. Therefore, we analyzed our data of 622 patients who underwent reoperative bypass grafting from January 1986 through June 1993. Among these patients, 258 had saphenous vein grafts alone and 364 had internal mammary artery grafting, including unilateral (342 patients) and bilateral (22 patients) mammary artery grafting with or without additional saphenous vein grafting. Overall operative mortality was 11.4% for reoperation compared with only 3.6% for primary bypass grafting during the same time frame. To determine risk factors for mortality and the influence of internal mammary artery grafting on the outcome, we analyzed 82 variables (31 preoperative, 17 intraoperative, and 34 postoperative) by univariate analysis. Significant variables or the variables having a trend (p < 0.2) to be associated with the mortality were included in stepwise multiple logistic regression analyses. Two regression analyses were separately performed. Regression 1 only included preoperative and intraoperative variables whereas regression 2 included postoperative variables as well. The logistic regressions demonstrate that preoperative variables (low ejection fraction [p = 0.0002], old age [p = 0.003], female gender [p = 0.011], and history of arrhythmia [p = 0.023]), intraoperative variables (emergency operation [p = 0.0001] and long perfusion time [p = 0.0001]), and postoperative variables (complications) are independently associated with higher mortality. Unlike previously described results, aortic crossclamp time, route of cardioplegia, use of internal mammary artery, number of grafts, and year of operation are not associated with operative mortality. The identification of these risk factors may have important implications in further improvement of the results of reoperative coronary artery bypass grafting.

Pharmacological relaxation of the saphenous vein during harvesting for coronary artery bypass grafting

Spasm of the saphenous vein frequently occurs during harvesting from the leg and high-pressure distension is required to restore an adequate diameter for grafting. Forceful distention has been shown to damage the intima and media and may predispose to subsequent occlusion of the vein graft. Various pharmacologic vasodilators are capable of relaxing veins; in this study, we carried out a systematic investigation to determine the appropriate agents and concentrations for use during vein graft operations. In organ baths, human saphenous vein segments were contracted with potassium or a thromboxane mimetic, and vasodilator agents were then applied. Glyceryl trinitrate, 7.2 micrograms/mL, or papaverine hydrochloride, 11.9 micrograms/mL, caused 80% to 100% relaxation of contraction induced by potassium or thromboxane. Verapamil, 15.5 micrograms/mL, relaxed the potassium contraction by 100% and the thromboxane contraction by 75%. Comparison of the time course of action showed that glyceryl trinitrate had a rapid onset and a short duration of maximal action, whereas verapamil (like papaverine) had delayed onset and a long duration. A mixture of glyceryl trinitrate and verapamil combined rapid onset with long duration of action. We now use a mixture of glyceryl trinitrate and verapamil (pH 7.4) topically and intraluminally during harvesting of the saphenous vein to provide a relaxed conduit for coronary artery bypass grafting.

Weak beta-adrenoceptor-mediated relaxation in the human internal mammary artery

The function of beta-adrenoceptors in the human internal mammary artery was studied in vitro to predict the way in which the internal mammary artery graft would respond to beta-adrenergic agonists and antagonists given in the perioperative period. Ring segments of the distal internal mammary artery obtained from patients not receiving beta-blocker therapy were mounted in organ baths and isometric wall force was measured. For comparison, similar experiments were conducted on segments of canine coronary artery, a vessel known to have powerful beta-adrenoceptor function. All arteries were precontracted with potassium or the thromboxane mimetic agent, U46619, before isoproterenol cumulative concentration-relaxation curves were constructed. In the human internal mammary artery, the maximum relaxation induced by isoproterenol was only 14% of the potassium-induced contraction and 24% of the U46619-induced contraction. These responses were weak compared with 54% and 86% for beta-adrenoceptor relaxation measured in corresponding experiments in the canine coronary artery. In all experiments, propranolol antagonized the relaxation induced by isoproterenol. These studies suggested that the human internal mammary artery has only a small number of beta-adrenoceptors. We conclude that beta-adrenoceptors would contribute little to the reactivity of the human internal mammary artery graft to sympathomimetic drugs.

Spasm in Arterial Grafts in Coronary Artery Bypass Grafting Surgery

Spasm of arterial grafts in coronary artery bypass grafting surgery is still a clinical problem, and refractory spasm can occasionally be lethal. Perioperative spasm in bypass grafts and coronary arteries has been reported in 0.43% of all coronary artery bypass grafting surgery, but this may be an underestimate. Spasm can develop not only in the internal mammary artery but more frequently in the right gastroepiploic and radial artery. The mechanism of spasm can involve many pathways, particularly those involving regulation of the intracellular calcium concentration. Endothelial dysfunction also plays a role in spasm. Depending on the clinical scenario, the possibility of spasm during and after coronary artery bypass grafting should be confirmed by angiography. If present, immediate intraluminal injection of vasodilators is often effective, although other procedures such as an intraaortic balloon pump or extracorporeal membrane oxygenation may also become necessary to salvage the patient. Prevention of spasm involves many considerations, and the principles are discussed in this review article.

Aortic valve replacement: determinants of operative mortality

Contradictory results have been reported regarding risk factors for aortic valve replacement (AVR). This study was designed to investigate determinants of operative mortality for AVR with emphasis on concomitant coronary artery bypass grafting (CABG) and old age. Between January 1986 and June 1992, 371 patients with a mean age of 61.99 +/- 0.76 years underwent AVR. There were 256 men (69.0%) and 115 women (31.0%). Twenty-six patients (7.0%) were 80 years old or older, and 97 (26.1%) were between 70 and 80 years old. Of these patients, 210 (56.6%) had isolated AVR, 142 (38.3%) had concomitant CABG, and 31 (8.4%) had concomitant mitral valve operations. Twenty patients (5.4%) underwent emergency operation. There were 33 operative deaths (8.9%). Univariate analysis and stepwise multiple logistic regression analysis were used to determine the risk factors for operative mortality. In the univariate analysis, 13 preoperative variables (sex, age, history of congestive heart failure, myocardial infarction, arrhythmia, functional class, class I/II versus III/IV, four variables related to aortic valve pathology, ejection fraction, left ventricular function) and 20 perioperative variables (emergency operation, individual surgeon, myocardial protection by type and route of cardioplegia, type of prosthesis, size of prosthesis, mean size by survival, small versus large size, concomitant procedure, concomitant CABG (versus others or AVR alone), concomitant mitral valve operation (versus others or AVR alone), concomitant CABG and MV operation, aortic cross-clamp time, cardiopulmonary bypass time, use and time of insertion of intraaortic balloon pump, low cardiac output, postoperative complications) were examined.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative study on calcium channel antagonists in the human radial artery: clinical implications

OBJECTIVES

The radial artery is spastic, and calcium channel antagonists have been used clinically in the radial artery for their antispastic effects. To choose a proper calcium channel antagonist for such a purpose, we compared the in vitro antispastic effects of 4 clinically used calcium channel antagonists (nicardipine, nifedipine, verapamil, and diltiazem) in the human radial artery.

METHODS

Radial artery segments taken from patients undergoing coronary bypass operations were studied in the organ bath. The relaxation by the calcium channel antagonists was compared in the potassium-precontracted (25 mmol/L) radial artery. The inhibitory effect of the calcium channel antagonists at the clinically relevant plasma concentration and a higher concentration was also studied for the calcium channel antagonists.

RESULTS

All calcium channel antagonists induced a full relaxation (97.8%-100%, n = 5-7 for each), with higher sensitivity (P =.005, analysis of variance [ANOVA] among the calcium channel antagonists for the effective concentration of the constrictor [or dilator] agent that caused 50% of maximal contraction [or relaxation]) to nifedipine (-7.37 +/- 0. 20 log(10) M) than nicardipine (-6.43 +/- 0.39 log(10) M, P =.1), verapamil (-6.08 +/- 0.13 log(10) M, P =.03), and diltiazem (-5.87 +/- 0.07 log(10) M, P =.01). Pretreatment with the plasma concentration of the calcium channel antagonists (60 nmol/L for diltiazem and 20 nmol/L for the others) inhibited the potassium-induced contraction (n = 6 for each) by nicardipine (from 138.6% +/- 5.8% to 101.4% +/- 7.6%, P =.001) and nifedipine (to 87. 7% +/- 6.8%, P =.0003) but not by verapamil (to 140.3% +/- 15.2%, P =.9) or diltiazem (to 132.8% +/- 7.3%, P =.8), although at higher contractions (-4.5 log(10) M) all 4 calcium channel antagonists abolished the contraction.

CONCLUSIONS

Although all calcium channel antagonists have antispastic effects in the radial artery, the vessel has different sensitivities to them. Dihydropyridine derivatives may be the most potent calcium channel antiagonists and therefore are recommended for the clinical use for this purpose.

Predominant alpha 1-adrenoceptor-mediated contraction in the human internal mammary artery

alpha-Adrenoceptor agonists and antagonists are widely used perioperatively for internal mammary artery (IMA)-coronary artery bypass operations. To determine subtypes of alpha-adrenoceptors in the human IMA, we studied responses of isolated human IMA segments to alpha-adrenoceptor agonists, antagonists, and electrical stimulation in organ baths. The IMA ring segments (3 mm long) were set up at a physiologic and comparable condition according to their own length-tension curves. alpha 1-Agonist methoxamine (MO) induced 2.65 +/- 0.70 g force and alpha 1, alpha 2-agonist norepinephrine (NE) induced 4.07 +/- 0.70 g force. The contractions induced by both MO and NE were totally abolished by alpha 1-antagonist prazosin (0.1 microM) but not alpha 2-antagonist yohimbine. alpha 2-Agonist UK14304 induced only 0.39 +/- 0.17 g force, which was significantly less than that induced by MO or NE (p < 0.001). Contractions induced by electrical field stimulation (2, 10, 20 Hz) were decreased by alpha 1-antagonist prazosin 1 microM (p < 0.01) but potentiated by alpha 2-antagonist yohimbine. These results strongly suggest that in the human IMA the postjunctional alpha-adrenoceptors are predominantly of the alpha 1-subtype and therefore the alpha-adrenoceptor agonist-induced contraction and the sympathetic nerve stimulation-induced contraction is mediated mainly by activation of the alpha 1-adrenoceptors.

Determinants of operative mortality in elderly patients undergoing coronary artery bypass grafting. Emphasis on the influence of internal mammary artery grafting on mortality and morbidity

Coronary artery bypass grafting has been performed for elderly patients (> or = 70 years) with increasing frequency. From January 1986 through June 1993, 1399 elderly patients underwent isolated coronary bypass grafting. Of these patients, 823 had saphenous vein grafts alone and 576 had internal mammary artery grafting, including unilateral (n = 546) and bilateral (n = 28). Overall operative mortality was 8.86%. Operative mortality for unilateral internal mammary artery grafting (6.41%) was lower than for saphenous vein grafting only (9.96%, p = 0.021) and bilateral internal mammary artery grafting (21.43%, 6/28, p = 0.018). Fewer patients undergoing internal mammary artery grafting had postoperative complications (low cardiac output, intraaortic balloon pumping, and neurologic complications) than patients having saphenous vein grafting only. To determine risk factors for mortality and the influence of internal mammary artery grafting on the outcome, we analyzed 55 variables (27 preoperative, 15 intraoperative, and 13 postoperative) by univariate analysis. Significant variables (age, gender, height, weight, surface area, diabetes, obesity, body mass index, history of congestive heart failure, myocardial infarction, or arrhythmia, functional class, left ventricular ejection fraction, stenosis of the left anterior descending or right coronary artery, emergency operation, reoperation, number of grafts, perfusion time, and bilateral or right internal mammary artery grafting) were included in a stepwise multiple logistic regression analysis. The logistic regression demonstrates that those preoperative (history of congestive heart failure or myocardial infarction, low ejection fraction, female gender, and old age), intraoperative (long cardiopulmonary bypass time, emergency operation, reoperation, and use of right internal mammary artery grafting), and postoperative (postoperative complications) variables are independently associated with higher mortality. This study reveals the high-risk groups in elderly patients undergoing coronary bypass and suggests that a left internal mammary artery graft in combination with saphenous vein grafting may achieve a lower operative mortality and morbidity than other procedures in selected elderly patients undergoing coronary artery bypass grafting.

Risk factors for operative mortality in elderly patients undergoing internal mammary artery grafting

From January 1986 through June 1992, 512 elderly patients (70 years and older) underwent internal mammary artery grafting (IMAG). The operative mortality in these patients was 7.62% (39 of 512), which was significantly higher than that (1.97% [60 of 3,047]; p < 0.0001) in younger patients (under 70 years old). To investigate the risk factors in the elderly, the data from the 512 patients were evaluated by univariate analysis and multiple logistic regression. Of 53 variables analyzed, nine preoperative variables (age, smoking history, congestive heart failure, myocardial infarction, New York Heart Association functional class, ejection fraction, left main artery disease, stenosis of the left anterior descending artery, and reoperation), three intraoperative variables (emergency operation, bilateral IMAG, and right IMAG), and nine postoperative variables were significantly associated with the higher mortality (p < 0.05). In particular, the operative mortality was significantly higher in the patients undergoing right IMAG (21.62% [8 of 37]) than that in patients only undergoing left IMAG (6.53% [31 of 475]; p < 0.004). The significant preoperative and intraoperative variables and the variables that have a tendency for correlation (p < 0.2) to mortality were included in a stepwise multiple logistic regression. The regression analysis demonstrated that right IMAG, reoperation, history of myocardial infarction, age, left main artery disease, history of smoking, and postoperative complications are the risk factors for the elderly undergoing IMAG. Therefore, particular care should be taken in those patients scheduled to undergo IMAG. The role of right IMAG in the elderly should be further clarified before universal acceptance of the technique in these patients.

Inhibitory effects of calcium antagonists on alpha-adrenoceptor-mediated contraction in the human internal mammary artery

1. The internal mammary artery has become a preferred coronary bypass graft. Sympathomimetic amines are spasmogens for vasospasm and calcium antagonists are frequently administered drugs perioperatively. The effect of calcium antagonists on alpha-adrenoceptor-mediated contraction depends on the subtype of alpha-adrenoceptor and the type of origin of vascular smooth muscle. This study was designed to investigate the effect of calcium antagonists on alpha-adrenoceptor-mediated contraction in the IMA. 2. Human IMA segments taken from 22 patients undergoing IMA--coronary artery bypass grafting were mounted in an organ bath under the physiological pressure determined from their own length-tension curves. 3. Three ring segments were allocated into three groups. One served as a control and the others were treated with clinically related concentrations of nifedipine (20 or 200 nM) for 25 min before concentration-contraction curves to alpha 1-adrenoceptor agonist methoxamine (MO) or full alpha-adrenoceptor agonist noradrenaline (NA) were established. 4. In separate experiments, the concentration-relaxation curves to nifedipine were established in the IMA rings precontracted with MO (30 microM) or NA (10 microM). Glyceryl trinitrate (GTN, 3 microM) was added to further relax the vessels. 5. Pretreatment with nifedipine (200 nM) only slightly inhibited the MO- (1.74 +/- 0.32 vs 2.88 +/- 0.56 g) or NA- (2.43 +/- 0.66 vs 3.60 +/- 0.82 g) induced contraction without statistical significance (P > 0.05). 6. On the other hand, nifedipine only caused 34.49% relaxation in the MO-precontracted and 24.39% relaxation in the NA-precontracted IMAs. In contrast, GTN caused 76.16% (against MO, P < 0.05) or 92.22% (against NA, P < 0.0001) relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacologic dilatation of the internal mammary artery during coronary bypass grafting

Spasm of the internal mammary artery during coronary bypass grafting is a widely recognized problem during and after mobilization of the IMA. On the basis of previous laboratory studies, we have developed a buffered vasodilator solution containing glyceryl trinitrate and verapamil (pH 7.4). When tested in human internal mammary artery segments in the organ bath, this solution caused full relaxation of the segments with a 1- to 2-minute onset and a duration of action of more than 2 hours. In 31 patients undergoing internal mammary artery grafting, flow through the internal mammary artery was measured immediately after mobilization and 20 minutes later. In 10 untreated patients, flow increased by 13% from 41.8 +/- 7.1 to 47.3 +/- 7.5 ml/min (p < 0.025). In 11 patients, intraluminal injection of glyceryl trinitrate-verapamil solution into the internal mammary artery on one side caused an increase in flow of 55 +/- 10 ml/min (95%), which was greater than that caused by Ringer's solution, 22 +/- 8 ml/min (53%), in the opposite internal mammary artery (p < 0.025). In another 10 patients intraluminal injection of glyceryl trinitrate-verapamil solution in one internal mammary artery caused an increase in flow of 57.9 +/- 8.7 ml/min (107%), which was similar to that caused by papaverine solution (pH 5.2) in the opposite internal mammary artery of 45.0 +/- 12.3 ml/min (80%). We conclude that intraluminal injection of vasodilator solution is effective in dilating the IMA graft and that because of its rapid onset, long action, and neutral pH, glyceryl trinitrate-verapamil solution may be preferable to papaverine.

Depolarizing cardiac arrest and endothelium-derived hyperpolarizing factor-mediated hyperpolarization and relaxation in coronary arteries: the effect and mechanism

OBJECTIVES

Depolarizing (hyperkalemic) solutions are widely used to preserve organs for transplantation and for cardiac operations. We previously observed that exposure to hyperkalemia reduced endothelium-dependent, noncyclooxygenase- and non-nitric oxide-mediated relaxation. This study was designed to examine the mechanism of this effect with regard to K channels and the associated membrane potential changes.

METHODS

Porcine coronary artery rings were studied in organ chambers. After incubation of the tissue with 20 or 50 mmol/L doses of potassium for 1 hour, the endothelium-derived hyperpolarizing factor-mediated relaxation in the artery and the membrane hyperpolarization in a single coronary smooth muscle cell were studied.

RESULTS

The endothelium-derived hyperpolarizing factor-mediated relaxation induced by substance P, which could be significantly inhibited by the Ca(2+)-activated K channel blocker tetraethylammonium but only to a lesser extent by the adenosine triphosphate-sensitive K channel blocker glibenclamide, was significantly reduced. Substance P-induced hyperpolarization of the membrane potential was also significantly reduced by the hyperkalemic incubation with a significantly elevated resting membrane potential.

CONCLUSIONS

Depolarizing arrest reduces endothelium-derived hyperpolarizing factor-mediated membrane hyperpolarization and relaxation by affecting mainly the Ca(2+)-activated K channels and by depolarizing the membrane for a prolonged period. We suggest that this is one of the mechanisms for coronary dysfunction after exposure to depolarizing (hyperkalemic) cardioplegic and organ-preservation solutions and that, therefore, "perfect" protection of the heart or other organs should restore the endothelium-derived hyperpolarizing factor-related endothelial function.