Impaired endothelium-derived hyperpolarizing factor-mediated relaxation in coronary arteries by cold storage with University of Wisconsin solution

OBJECTIVES

University of Wisconsin solution is widely used to preserve organs for transplantation, but its effect on the individual endothelium-derived relaxing factors has not been studied. This study was designed to examine the effect of cold storage of the heart with University of Wisconsin solution on relaxation mediated by the endothelium-derived hyperpolarizing factor (EDHF).

METHODS

Porcine coronary artery rings were studied in organ chambers. Relaxation in response to the EDHFs stimuli bradykinin and A23187 in U46619 (30 nmol/L)-induced precontraction after incubation with University of Wisconsin solution (either at 37 degrees C in the oxygenated organ chamber or at 4 degrees C in a refrigerator for 4 hours) was compared with the control.

RESULTS

During the incubation, the coronary tone initially increased transiently (4.8 +/- 0.8 gm) and was subsequently reduced by 10.9 +/- 1.2 gm. Under both normothermia and hypothermia, after the incubation, the relaxation mediated by EDHF significantly decreased (under normothermia: from 68.7% +/- 10.2% to 32.1% +/- 8%, n = 7, p = 0.001, for bradykinin and from 79.9% +/- 8.4% to 56.9% +/- 8.5%, n = 7, p = 0.01, for A23187; under hypothermia and hypoxia: to 18.9% +/- 5.6%, n = 9, p = 0.0005, for bradykinin and 52.7% +/- 7.5%, n = 9, p = 0.03, for A23187). The incubation at normothermia also impaired the coronary smooth muscle contractility to U46619, but this contractility was preserved by cold storage.

CONCLUSIONS

During cold storage, University of Wisconsin solution impairs the endothelium-dependent relaxation mediated by EDHF in the coronary circulation. This effect exists after the storage for at least 1 hour.

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.

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.

Coronary endothelial function in open heart surgery

1. During open heart surgery, the heart is arrested and protected by hyperkalaemic cardioplegia. The coronary endothelium may be damaged by ischaemia-reperfusion and cardioplegia. Subsequently, this may affect cardiac function immediately after cardiac surgery and cause mortality or morbidity. 2. Our studies have investigated coronary endothelial function after exposure to hyperkalaemia (K+ 20 or 50 mmol/L). Endothelium-dependent relaxation and hyperpolarization of the coronary smooth muscle and intracellular free calcium concentration in the endothelial cell were measured with regard to K+ exposure. 3. Endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation to A23187, bradykinin, and substance P in the presence of either U46619 (10 nmol/L)- or K+ (25 mmol/L)-induced contraction was reduced after exposure to either 20 or 50 mmol/L K+. 4. The hyperpolarization of the membrane potential in response to the endothelium-derived relaxing factor (EDRF) stimuli was also reduced by exposure to K+. 5. The intracellular free calcium concentration remained unchanged after exposure to hyperkalaemia. 6. We conclude that the EDHF-mediated coronary endothelial function is impaired after exposure to hyperkalaemic cardioplegia. The impairment of this function is due to the changed effect of EDHF on the smooth muscle cell, probably through partially depolarizing the membrane and affecting K+ channels rather than alteration of its biosynthesis/release in the endothelial cell. It may be of use to search for a new cardioplegia that preserves this endothelial function during open heart surgery.

Inhibition of vasoconstriction by potassium channel opener aprikalim in human conduit arteries used as bypass grafts

AIMS

Potassium channel openers (KCOs) are of potential therapeutic value. Little is known about the effect of these drugs on human conduit arteries used as coronary bypass grafts. The purpose of this study was to determine the effect of the KCO aprikalim (RP52891) on human arteries used as coronary bypass grafts with emphasis on the possible difference in the inhibitory effect on depolarizing agent-mediated rather than receptor-mediated contraction.

METHODS

Human internal mammary artery segments (IMA, n = 88) taken from 28 patients were studied. Concentration-relaxation curves for aprikalim were established in IMA precontracted with three vasoconstrictors (K+, U46619, and phenylephrine). In IMA rings incubated with aprikalim (1 or 30 microM) for 10 min concentration-contraction curves for the three vasoconstrictors were constructed.

RESULTS

Aprikalim-induced relaxation was less in K+ (37.3 +/- 6.4%) than in U46619 (80.2 +/- 7.7%, P=0.002), or phenylephrine (67.5 +/- 7.0%, P=0.038) -precontracted IMA. The EC50 for K+-(-5.40 +/- 0.12 log M) was significantly higher than that for phenylephrine (-6.43 +/- 0.30 log M, P=0.007) but not significant compared with that for U46619 (-5.81 +/- 0.11, P>0.05). Pretreatment with aprikalim depressed the contraction by phenylephrine from 140.6 +/- 27.6% to 49.3 +/- 14.1% (P=0.002) and shifted the EC50 11.0-fold higher in rings treated with 1 microM aprikalim (P=0.007). Treatment of aprikalim did not significantly reduce the K+ and U46619-induced contraction (P>0.05) but shifted the concentration-contraction curves rightward (2.8-fold higher for K+, P<0.05 and 2.2-fold higher for U46619, P<0.05).

CONCLUSIONS

This study demonstrates that aprikalim has vasorelaxant effects in human conduit arteries used as coronary artery bypass grafts contracted by a variety of vasoconstrictors and this effect is vasoconstrictor-selective with greater potency for alpha1-adrenoceptor agonists than for depolarizing agent K+. These findings provide information on the possible use of this KCO in various clinical settings.

Superiority of hyperpolarizing to depolarizing cardioplegia in protection of coronary endothelial function

OBJECTIVE

Hyperpolarizing cardioplegia has recently been proposed for myocardial protection. To compare the protective effect of hyperpolarizing cardioplegia and depolarizing (hyperkalemic) cardioplegia on coronary endothelium, we studied porcine coronary arteries in the organ chamber.

METHODS

Relaxation mediated by the endothelium-derived hyperpolarizing factor (EDHF) was used as the index of endothelial function because (1) hyperkalemia without ischemia does not impair the nitric oxide-mediated function according to previous studies and (2) EDHF relaxes vessels by hyperpolarizing the membrane potential. Therefore depolarizing cardioplegia may inhibit this function, but hyperpolarizing cardioplegia may preserve it. EDHF-mediated relaxation was induced by bradykinin and the calcium ionophore A23187 with the presence of indomethacin (7 micromol/L; INN: indometacin), a cyclooxygenase inhibitor, and N(G)-nitro-L-arginine (300 micromol), a nitric oxide biosynthesis inhibitor in U46619 (30 nmol/L)-induced precontraction. The vessels were exposed to either hyperpolarizing cardioplegic solution (the potassium-channel opener aprikalim, 0.1 mmol/L) or depolarizing cardioplegic solution (high potassium concentration, 20 mmol/L for A23187 and 50 mmol/L for bradykinin experiments) for 1 hour with a constant supply of oxygen to exclude the effect of ischemia.

RESULTS

EDHF-mediated relaxation was significantly impaired in either A23187 or bradykinin studies (80.1% +/- 7.5% vs 24.9% +/- 14.2%, p = 0.004, n = 8 in each group for A23187, and 71.4% +/- 4.7%, n = 13, vs 40.5% +/- 12.9%, n = 7, p = 0.01, for bradykinin). The effective concentration causing 50% of maximal relaxation was significantly increased in the A23187 experiments with the treatment of hyperkalemia. In contrast, in aprikalim-treated arteries, the EDHF-mediated relaxation induced by either A23187 or bradykinin was unchanged.

CONCLUSIONS

We conclude that EDHF-mediated coronary endothelial function is maximally preserved by hyperpolarizing cardioplegia but impaired by depolarizing cardioplegia. These findings support the use of hyperpolarizing cardioplegia in cardiac operations.

Comparison of nitroprusside and nitroglycerin in inhibition of angiotensin II and other vasoconstrictor-mediated contraction in human coronary bypass conduits

AIMS

To compare the effect of nitroprusside (SNP) and nitroglycerin (NTG) on angiotensin II (ANGII), endothelin-1 (ET-1), and alpha1-adrenoceptor (phenylephrine, PE)-mediated contraction in internal mammary artery (IMA).

METHODS

Human IMA segments (n=120) taken from 37 patients were studied. Concentration-relaxation curves for SNP and NTG were established in IMA precontracted with these vasoconstrictors. Concentration-contraction curves were also constructed in IMA rings incubated with SNP and NTG (0.1 and 1 microM) for 10 min.

RESULTS

Both SNP and NTG caused full relaxation with similar EC50s except NTG was four-fold more potent than SNP in PE-induced contraction (-7.92 +/- 0.06 vs -7.32 +/- 0.2 log M, mean +/- s.e. mean, P<0.01; 95% confidence interval for the difference of the means: 0.19, 1.01 log M). Pretreatment with SNP (0.1 and 1 microM) significantly depressed the contraction by ANGII from 56.6 +/- 7.7% (of 100 mM K+-contraction) to 18.3 +/- 8.6% and 3.9 +/- 2.1% (P=0.0001). In four rings treated with SNP, the contraction to ANGII was abolished whereas NTG did not depress ANGII-mediated contraction. Pretreatment with SNP (1 microM), but not NTG, significantly depressed the magnitude of the PE-induced contraction from 4.7 +/- 1.2 to 1.7 +/- 0.4 g (P<0.05). Treatment with both SNP and NTG significantly increased the EC50 (-5.09 +/- 0.17 log M, P=0.0007 for SNP and -5.40 +/- 0.06 log M, P=0.02 for NTG). Pretreatment with SNP did not significantly change either the magnitude or the EC50 of the ET-1-induced contraction.

CONCLUSIONS

SNP may be advantageous compared with NTG in preventing coronary arterial graft contraction. However, once grafts have constricted to ANGII, alpha1-adrenoceptor agonists, and ET-1, NTG may be only marginally advantageous.

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.

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.

Morphometric study of the right gastroepiploic and inferior epigastric arteries

BACKGROUND

Based on earlier observations that the thickness of the intima and structure of the media may have an impact on the long-term patency of arterial conduits and the lack of detailed histologic studies of the right gastroepiploic and inferior epigastric arteries, we subjected both vessels to morphometric analysis with emphasis on their suitability as conduits in myocardial revascularization.

METHODS

The right gastroepiploic and inferior epigastric arteries were harvested from 28 unselected individuals (mean age, 73.2 years) at autopsy, and the luminal diameter and the width of the intima and media were measured.

RESULTS

At all levels of measurement (origin, 10 cm, and 15 cm), the luminal diameter of the inferior epigastric artery was significantly smaller than that of the right gastroepiploic artery (p < 0.05). The right gastroepiploic artery demonstrated only mild intimal hyperplasia. In contrast, the inferior epigastric artery showed substantial intimal hyperplasia within the first 1-cm segment (mean, 134 +/- 131 microns versus 50 +/- 49 microns for the corresponding segment of the right gastroepiploic artery; p = 0.01). Intimal hyperplasia was only mild in the remainder of the inferior epigastric artery. In both vessels, the media was muscular with rare dispersed elastic fibers. The mean thickness of the media ranged from 380 +/- 116 microns proximally to 155 +/- 70 microns distally for the right gastroepiploic artery, and from 316 +/- 86 to 165 +/- 70 microns, respectively, for the inferior epigastric artery.

CONCLUSIONS

In myocardial revascularization, use of the right gastroepiploic artery may generally be preferable to use of the inferior epigastric artery. This recommendation is based on the larger luminal diameter of the right gastroepiploic artery as compared with the inferior epigastric artery, the significantly greater intimal hyperplasia in the first segment of the inferior epigastric artery, and the limitation that the inferior epigastric artery can be used only as a free graft. The rate of development of intimal hyperplasia in the right gastroepiploic artery, if used as an in situ coronary artery bypass graft, may be slow, approximating that of the right gastroepiploic artery in its natural environment.

Rare complication of retrograde cardioplegia: inner wall perforation of the right atrium

Retrograde cardioplegia has been widely applied with satisfactory results. This report presents a case in which the retrograde cannula was inserted into the coronary sinus by penetrating the inner wall of the right atrium rather than through the orifice of the coronary sinus. Surgeons should be cautious of this possibility, particularly in patients with a dilated right atrium in which the space between trabeculae is enlarged and the atrial tissue is friable. Under this situation, the tip of the cannula is easily caught in such a space and may penetrate the wall of the right atrium, which affects the delivery of cardioplegia.

Surgical preparation abolishes endothelium-derived hyperpolarizing factor-mediated hyperpolarization in the human saphenous vein

BACKGROUND

The impairment of the synthesis and release of endothelium-derived relaxing factors may be related to the high incidence of atherosclerosis and occlusion in saphenous vein grafts. This study focused on the effect of surgical preparation on one of the endothelium-derived relaxing factors, endothelium-derived hyperpolarizing factor, in the human saphenous vein.

METHODS

Human saphenous vein segments taken from patients undergoing coronary bypass were placed in an organ bath. A glass microelectrode was inserted into a smooth muscle cell. The membrane potential in response to acetylcholine (-9 to -5 log M) was measured in normal or surgically prepared saphenous vein with presence or absence of NG-nitro-L-arginine (300 mumol/L) and indomethacin (7 mumol/L).

RESULTS

The resting membrane potential was -71.28 +/- 1.91 mV (n = 7) with intact endothelium and -65.5 +/- 2.92 mV (n = 6, p > 0.05) without endothelium. Acetylcholine hyperpolarized membrane potential with intact endothelium (-90.57 +/- 1.48 mV, n = 7, p < 0.001), but not without endothelium (-69.67 +/- 2.93 mV, n = 6, p > 0.05). In the surgically prepared saphenous vein, acetylcholine did not hyperpolarize membrane potential (-71.83 +/- 3.84 mV versus the resting membrane potential of -69.50 +/- 3.53 mV, n = 6, p > 0.05).

CONCLUSIONS

The endothelium-derived hyperpolarizing factor plays a role in the human saphenous vein. The surgical preparation abolishes the endothelium-derived hyperpolarizing factor-mediated hyperpolarization in the saphenous vein. This study provides evidence of functional changes of endothelium by traditional surgical preparation from another point of view, and it may be related to the high incidence of occlusion in saphenous vein grafts.

Valve repair for aortic insufficiency: surgical classification and techniques

OBJECTIVE

Valve repair for aortic insufficiency may provide an alternative to aortic valve replacement in selected patients. This repair could be an attempt at permanent correction or palliation to allow the aortic annulus to grow and avoid the use of anticoagulation. Based upon a five-year experience, we proposed a classification according to valvular anatomy which could be a guide to patient and procedure selection.

METHODS

Between September 1989 and February 1995, 44 consecutive patients underwent aortic valvuloplasty for aortic incompetence at our institution. Patients' ages ranged from 19 months to 76 years with a mean of 33 years. The etiology of aortic incompetence was congenital in 30 patients, degenerative in 7 patients, rheumatic in 5 patients, and infective endocarditis in 2. Aortic valve lesions were classified into three different types: type I, aortic annular dilation (8 patients); type II, excessive aortic leaflet tissue (12 patients); and type III, restricted leaflet motion with or without deficient leaflet tissue (24 patients). Type I needed commissural plication in 7 patients; and aortic annuloplasty, which was simple in 6 patients, and pericardial-augmented in 2. Type II necessitated midleaflet excision in 11 patients and leaflet plication in 7. Type III required leaflet extension in 19 patients, leaflet replacement in 1 patient, aortic valve commissurotomy in 13 patients augmentation commissurorrhaphy in 2, leaflet shaving in 4, and repair of leaflet perforation in 2.

RESULTS

Postoperative echocardiography revealed a significant decrease in the degree of aortic incompetence. Mean follow-up was 2.6 +/- 1.4 years. There was no mortality. Patients improved as is evident by NYHA functional class postoperatively. Eight of the first 13 patients (18%) needed reoperation. Three of these reoperations were bail-out procedures, and 3 patients (7%) who underwent the leaflet extension technique were reoperated upon 19 months to 3 years later. Presently, 23 patients are without anticoagulation, 11 take aspirin and 2 receive coumadin for combined mitral procedures.

CONCLUSIONS

Aortic valve repair provides a low risk option with satisfactory intermediate-term results for the treatment of aortic insufficiency in appropriately selected patients. Patient and procedure selection may be based upon the echocardiographic anatomy of the aortic valve, and a comparative risk benefit appraisal with valve replacement.

Hyperkalemia exposure impairs EDHF-mediated endothelial function in the human coronary artery

BACKGROUND

My colleagues and I have found in the porcine coronary artery that the pathway other than the nitric oxide (NG-nitro-L-arginine [L-NNA]-sensitive) and cyclooxygenase (indomethacin-sensitive) pathways of endothelium-dependent relaxation, related to the endothelium-derived hyperpolarizing factor (K+ channel-related), are altered after exposure to hyperkalemia. The present study was designed to examine whether this effect exists in the human coronary artery.

METHODS

Coronary artery rings obtained from explanted fresh human hearts were studied in organ chambers under physiologic pressure. The endothelium-dependent relaxation in response to calcium ionophore A23187 was studied in U46619 (30 nmol/L)-induced precontraction in the presence of the cyclooxygenase inhibitor indomethacin (7 mumol/L) and the nitric oxide biosynthesis inhibitor L-NNA (300 mumol/L). The effect of incubation with 20 mmol/L K+ for 1 hour on the relaxation was examined in other coronary rings.

RESULTS

In control rings, A23187 induced a maximal relaxation of 50.7% +/- 3.2% (n = 6). After 1 hour of exposure to 20 mmol/L K+, the relaxation was reduced to 30.4% +/- 4.6% (n = 6; p = 0.005). Incubation with hyperkalemia also significantly reduced the sensitivity (increased effective concentration that caused 50% of maximal relaxation) of the indomethacin- and L-NNA-resistant relaxation (-7.37 +/- 0.17 versus -8.28 +/- 0.27 log mol/L; p = 0.019).

CONCLUSIONS

Exposure to hyperkalemia reduces the indomethacin- and L-NNA-resistant, endothelium-dependent (endothelium-derived hyperpolarizing factor-related) relaxation in the human coronary artery. This suggests that the previously proposed mechanism of coronary dysfunction after exposure to cardioplegic and organ preservation solutions in animal vessels is also valid in the human heart.

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.

Hyperkalemia alters EDHF-mediated hyperpolarization and relaxation in coronary arteries

Hyperkalemic solutions are widely used to preserve organs for transplantation and for cardiac surgery. The present study was designed to test the hypothesis that hyperkalemia may alter endothelial function through a non-nitric oxide (NO) pathway, since preliminary studies have shown that the NO pathway may not be affected. Porcine coronary artery rings were studied in organ chambers. After incubation with 20 or 50 mM K+ for 1 h, the indomethacin- and NG-nitro-L-arginine+ (L-NNA)-resistant relaxation induced by A23187 or bradykinin, which could be further inhibited by tetraethylammonium but not glibenclamide, was significantly reduced. Incubation with hyperkalemia also significantly increased the concentration eliciting 50% of the maximal response to A23187 and bradykinin. A23187-induced hyperpolarization of the membrane potential was significantly reduced by hyperkalemic incubation. However, 1-h incubation with hyperkalemia does not affect the endothelial Ca2+ concentration. We conclude that exposure to hyperkalemia reduces the indomethacin- and L-NNA-resistant endothelium-dependent relaxation and endothelium-dependent hyperpolarization. This reduction in the relaxation and hyperpolarization is related to the endothelium-derived hyperpolarizing factor by affecting its effect on the smooth muscle cell, probably through partially depolarizing the membrane, and the Ca2(+)- activated K+ channels rather than by affecting its biosynthesis and/or release in the endothelial cell. Our study may suggest a new mechanism for coronary dysfunction after exposure to hyperkalemic cardioplegia and organ preservation solutions.

Aortic valve replacement in elderly patients: influence of concomitant coronary grafting on late survival

BACKGROUND

Aortic valve replacement (AVR) has been an accepted therapy for elderly patients (> 70 years) with aortic valve disease. This study was designed to investigate the determinants of survival after the implantation of aortic valve prostheses, with emphasis on the effect of concomitant coronary artery bypass grafting on survival.

METHODS

From November 1964 to July 1994,963 elderly patients underwent isolated AVR. Long-term survival was investigated in 877 patients (70 to 94 years) who survived operation, with 92% follow-up completeness (mean +/- standard deviation, 4.5 +/- 3.9 years; maximum, 20.1 years; total, 3,920.2 patient-years), by univariate and multivariate analyses.

RESULTS

Actuarial survival was 38.1% +/- 2.8% at 10 years, 17.8% +/- 3.0% at 15 years, and 9.0% +/- 3.1% at 20 years. Eight variables (age, sex, body surface area [less or greater than 1.7 m2], period of operation, type of prosthesis, size of prosthesis, re-replacement, and concomitant coronary artery bypass grafting) were investigated with regard to long-term survival by the Kaplan-Meier method. Age, sex, and body surface area were significant. Multivariate analysis revealed that older age (p = 0.0005) and male sex (p = 0.0001) were independent variables that determined long-term survival.

CONCLUSIONS

Elderly patients may have satisfactory long-term results after AVR. Age and sex are independent determinants. Other factors (such as concomitant coronary artery bypass grafting and type of prosthesis) did not independently influence long-term survival. Coronary revascularization in elderly patients with coronary disease undergoing AVR may lead to a long-term survival similar to that in patients without coronary disease undergoing AVR.

Hyperkalemia alters endothelium-dependent relaxation through non-nitric oxide and noncyclooxygenase pathway: a mechanism for coronary dysfunction due to cardioplegia

BACKGROUND

Reported results of hyperkalemia (cardioplegia or organ preservation solutions) on endothelial function are contradictory. The endothelium-dependent relaxation is related to three major mechanisms: cyclooxygenase, nitric oxide, and endothelium-derived hyperpolarizing factor (K+ channel related). The present study was designed to test the hypothesis that hyperkalemia may alter endothelial function through non-nitric oxide and noncyclooxygenase pathways.

METHODS

Porcine coronary artery rings (5 to 10 in each group) were studied in organ chambers under physiologic pressure. After incubation with 20 or 50 mmol/L K+ for 1 hour, the response to substance P, an endothelium-dependent vasorelaxant peptide, in K+ (25 mmol/L)-induced contraction was studied in the presence of the cyclooxygenase inhibitor indomethacin (7 mumol/L), the nitric oxide biosynthesis inhibitor NG-nitro-L-arginine (L-NNA) (300 mumol/L), or the adenosine triphosphate-sensitive K(+)-channel blocker glybenclamide (3 mumol/L) in comparison with control arteries (69.8 +/- 4.6% of K+ contraction).

RESULTS

Without exposure to hyperkalemia, indomethacin (with or without glybenclamide) did not alter but L-NNA significantly reduced the relaxation (39.7% +/- 3.7%, p < 0.001). After exposure to K+, the indomethacin- and L-NNA-resistant relaxation was further reduced (7.4% +/- 3.2% for 20 mmol/L K+, p < 0.0001; or 13.5% +/- 8.4% for 50 mmol/L K+, p < 0.05, compared with rings without exposure), whereas the indomethacin- and glybenclamide-resistant relaxation was not altered. Incubation with hyperkalemia (50 mmol/L) also significantly reduced the sensitivity (increased EC50) of the indomethacin- and L-NNA-resistant relaxation (-9.75 +/- 0.06 versus -9.33 +/- 0.04 log M, p < 0.01).

CONCLUSIONS

Exposure to hyperkalemia reduces the indomethacin- and L-NNA-resistant, endothelium-dependent (endothelium-derived hyperpolarizing factor-related) relaxation. Our study may suggest a new mechanism of coronary dysfunction after exposure to hyperkalemia and open a new area for protection of coronary endothelium in cardiac surgery and for organ preservation in transplantation surgery.

Is referral source a risk factor for coronary surgery? Health maintenance organization versus fee-for-service system

We began performing coronary artery bypass grafting for a large health maintenance organization (HMO) in 1974, as the sole provider of their cardiac surgery. The outcomes of our HMO group of patients were compared with those of our patients treated on a fee-for-service (FFS) basis. The HMO system entails preintervention and multidisciplinary screening conferences and is devoid of self-referral and personal financial incentives. Since 1985, the operative mortality for HMO patients has been consistently lower than for FFS patients. There were 8483 operations during this study period: 3168 (37%) were in the HMO group, with an overall operative mortality of 2.7%, and 5315 (63%) were in the FFS group, with an operative mortality of 4.6% (p=0.00002). This difference was investigated with univariate and multivariable analyses. Sixteen factors were found to univariately affect the risk of operative mortality; for five of these risk correlates there was a significant maldistribution between the HMO and FFS patients. Logistic regression was used to explore the influence of this imbalance in risk factors. The model found seven independent risk factors (left ventricular failure, emergency coronary bypass, redo bypass, nonuse of the internal thoracic artery, unstable angina, age, and diabetes) that significantly affected operative mortality. The FFS group variable closely approached independent risk significance at p=0.059. This multivariable model explained only one third of the observed differences in actual mortality between the HMO and FFS groups. The system-wide angioplasty/coronary bypass ratio, which could not be used in a patient-specific model, was 0.6 in the HMO system and 1.5 in the FFS group. Other factors related to the operating structure of a mature, large HMO may account for the remainder of the difference. The HMO referral system, through a powerful selection process, resulted in fewer emergencies, redo bypass operations, and catheterization complications that, in turn, yielded lower operative mortality than a noncoordinated FFS system of cardiovascular management.

Potential greater than additive vasorelaxant actions of milrinone and nitroglycerin on human conduit arteries

1. The mechanism of vasorelaxation for phosphodiesterase III inhibitors is mediated by increase of cAMP whereas for nitrovasodilators, cGMP. The purpose of this study was to test the hypothesis that the phosphodiesterase III inhibitor milrinone and nitroglycerin (NTG) may have greater than additive effects in human arteries. 2. Internal mammary artery segments (IMA, n = 90) taken from 23 patients were studied in organ chambers. The effect of milrinone (3 microM), NTG (10 nM), or the combination was tested in IMA rings precontracted with potassium (K+, 25 mM) or U46619 (10 nM). Concentration-contraction curves for K+ or U46619 were established in other rings treated with milrinone (70 microM), NTG (0.1 microM), or the combination for 10 min. 3. In K(+)-induced contraction, the combination produced more relaxation (45.4%) than did either milrinone (7.9%, P < 0.05) or NTG (3.8%, P < 0.05) alone. This relaxation was significantly more than the theoretical overadditive effect (P < 0.05). Similar results were seen in U46619-induced contraction (94.1% by the combination vs 70.7% by milrinone, P < 0.05, or 36.1% by NTG, P < 0.05). Pretreatment with the combination depressed contraction to a higher extend compared with milrinone alone (P < 0.05) for the K(+)-induced contraction and to NTG alone (P < 0.05) in U46619-induced contraction. Treatment with the combination also shifted EC50 rightward and this shift was significantly more than that caused by treatment with NTG alone (P < 0.05). 4. We conclude that there is a greater than additive vasorelaxant effect of PDE III inhibitors and nitrovasodilators in human conduit arteries. This effect may be beneficial to patients undergoing coronary artery bypass grafting and to other patients requiring these vasodilators. Reduced doses of the vasodilators in concentration may be sufficient to produce vasodilatation similar to that produced by either of them alone at higher concentrations.

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.

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.

Effect of thromboxane A2 antagonist GR32191B on prostanoid and nonprostanoid receptors in the human internal mammary artery

Arterial grafts have been demonstrated to be very effective for coronary artery bypass surgery. Thromboxane A2 (TXA2) is a potent vasoconstrictor for arterial grafts. To determine whether the specific TXA2 (TP) receptor antagonist GR32191B is effective in inhibition of prostanoid or nonprostanoid receptors, we studied the effect of GR32191B in human internal mammary artery (IMA) segments, taken from coronary bypass patients, in organ chambers. In IMA precontracted with U46619 (10 nM, n = 7), prostaglandin F2 alpha (PGF2 alpha 1 microM, n = 7), or potassium chloride (K+ 25 microM, n = 6). GR32191B induced 100.0 +/- 0, 97.86 +/- 2.14, or 45.87 +/- 7.63% relaxation. In other experiments, one IMA ring taken from each patient was used as a control and others from the same patient were allocated to other groups treated with different concentrations of GR32191B [3-300 nM for U46619, 30 nM-3 microM for PGF2 alpha, 300 nM-100 microM for K+, 3 microM norepinephrine (NE), and 3 microM for 5-hydroxytryptamine (5-HT)] for 1 h before concentration-contraction curves to these vasoconstrictors (expressed as percentage of K(+)-induced contraction force) were established. Treatment with GR32191B (300 nM) significantly decreased the contraction induced by U46619 (from 306.4 +/- 22.1 to 61.9 +/- 24.9%, p < 0.01) and that induced by PGF2 alpha (from 208.2 +/- 13.5 to 1.4 +/- 1.4%, p < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

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)