HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Amram J. Cohen Lior Sasson Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Arnaudov, D. Articles by Ezra, S. Search for Related Content PubMed PubMed Citation Articles by Arnaudov, D. Articles by Ezra, S. Related Collections Related Article

Ann Thorac Surg 1996;62:1816-1819
© 1996 The Society of Thoracic Surgeons

---

Original Articles: Cardiovascular

Effect of Systemic Vasodilators on Internal Mammary Flow During Coronary Bypass Grafting

Departments of Cardiovascular Surgery and Anesthesiology, Wolfson Medical Center, Holon, and Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv University, Tel Aviv, Israel

Accepted for publication June 29, 1996.

	Abstract

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
Background. The effect of vasodilators on acute flow in the internal mammary (IMA) is unclear. Topical vasodilators show no effect on acute flow when the distal segment of the IMA is resected. The purpose of this study was to evaluate the effect of systemic vasodilators when this segment is resected.

Methods. We studied 60 patients with proximal anterior descending coronary artery lesions in whom the left IMA was harvested for grafting to the left anterior descending coronary artery. The patients were divided into six groups (n = 10), based on which of the following agents were studied: normal saline solution, nitroglycerin, nitroprusside, dobutamine, dopexamine, and amrinone. After harvesting, the IMA was trimmed as proximally as possible (and at least 3 cm proximal to the bifurcation), and free flow was measured before any pharmacologic intervention (flow 1). Systemic infusion of one of the six agents commenced. A mean of 17 ± 3.4 minutes after infusion began, with a comparable cardiac index, a second measurement of IMA flow was taken (flow 2). Hemodynamic measurements for each flow, including blood pressure, heart rate, and cardiac output, were taken.

Results. A significant increase in IMA flow was noted for those patients receiving nitroglycerin (93.5 versus 106.8 mL/min; p = 0.025), and a significant decrease in flow was noted for those receiving nitroprusside (91.0 versus 78.2 mL/min; p = 0.042). The effects remained significant when corrected for cardiac index and compared with the normal saline solution group. No other systemic agents tested significantly affected the IMA flow (dobutamine, 83.8 versus 85.0 mL/min; dopexamine, 101.8 versus 91.4 mL/min; amrinone, 75.4 versus 79 mL/min; normal saline solution, 85.8 versus 84.6 mL/min).

Conclusions. Resection of the distal segment of the IMA and the use of intravenous nitroglycerin optimizes the flow in IMA grafts.

	Introduction

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
See also page 1819.

The internal mammary artery (IMA) is the conduit of choice for bypass grafting of the anterior descending coronary artery (LAD) [1, 2]. However, perioperative spasm of the artery with insufficient early graft flow has been reported as causing perioperative morbidity [3, 4]. Controversy exists as to whether topical vasodilators applied to the IMA pedicle will reduce spasm and increase immediate flow [5, 6]. Although others have shown topical vasodilators to be effective in increasing immediate IMA flow [6], we have found this effect insignificant [5]. Recently, systemic vasodilators used in the prebypass period have been shown to increase acute IMA flow [7]. The purpose of the present study was to evaluate the effect of systemic vasodilators administered in the prebypass period on acute IMA flow in our patient population.

	Patients and Methods

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
The study included 60 patients who underwent harvesting of the IMA in preparation for coronary artery bypass grafting. Only elective operations were included in the study. Patients were selected if the target vessel for the left IMA graft was the LAD and the LAD lesion was proximal enough to allow significant shortening of the IMA pedicle. A Swan-Ganz catheter was placed in each patient for measurement of hemodynamic variables. Patients who were hemodynamically unstable or showed evidence of ischemia were excluded from the study. Patients in whom adequate hemodynamic measurements could not be obtained were also excluded from the study.

Our technique for IMA harvesting has been previously described in detail [5]. Briefly, the IMA was harvested with a wide pedicle (>2 cm) without touching the vessel. The IMA was transected as proximally as feasible, at least 3 cm proximal to the bifurcation, and fashioned for the anastomosis. It was allowed to bleed freely, and the blood volume was collected for 30 seconds. The flow per minute was then calculated (flow 1).

After the initial measurement, the IMA graft was occluded with a disposable bulldog clamp (Vascu-Statt; Scanlan International Corp, St. Paul, MN) distally just proximal to the fashioned distal tip of the IMA. Patients were divided into six groups, depending on the systemic infusion administered. The infusions included (1) nitroglycerin, 1.5 µg•kg^-1•min^-1 (Nitrocine; Schwarz Pharma AG, Monheim, Germany); (2) nitroprusside, 0.3 µg•kg^-1•min^-1 (Nipride; Roche F Hoffman SA, Bale, Switzerland); (3) dobutamine hydrochloride, 3 µg• kg^-1 •min^-1 (Dobujet; Leiras Oy, Finland); (4) dopexamine hydrochloride, 3 µg•kg^-1•min^-1 (Cardopex; Fisons, Loughborough, UK); (5) amrinone lactate, 0.5 mg•kg^-1 bolus (Inocor; Sanofi Winthrop Pharmaceuticals, New York, NY); and (6) normal saline solution (0.9% sodium chloride solution, 0.5 mL•min^-1 infusion; Travenol Laboratories [Israel] Ltd, Ashdod, Israel). The infusion was continued through the second flow measurement.

The second measurement (flow 2) was taken before placement of the venous cannula. Heart rate; arterial, systolic, and diastolic blood pressures; mean blood pressure; cardiac index (CI); and systemic vascular resistance were determined for each measurement. The time duration between flows 1 and 2 was also recorded. Any evidence of clinical instability after infusion of the vasodilators was recorded. Any clinical evidence of postoperative spasm of the IMA among these patients was noted.

Nonparametric statistics were used due to sample size. Homogeneity of the groups for the initial measurements was assured by the inclusion criteria. Kruskal-Wallis one-way analysis of variance was used to obtain overall p values. Each agent group was then compared with the control using the Mann-Whitney U rank sum test. Comparison of pretreatment and posttreatment parameters within each group was performed using the Wilcoxon sign-rank test. The reported p values are for a two-tailed test, with significance reported when p was 0.05 or less.

	Results

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
The demographic and hemodynamic data of the six groups are shown in Table 1. There was no significant difference in the groups with respect to age or sex. There was no significant difference in the first recorded heart rate between the groups. There was a significant increase in heart rate from flow 1 to flow 2 in the groups infused with nitroprusside, dobutamine, dopexamine, and amrinone. Blood pressure was similar at flow 1 for all groups. There was a significant decrease in blood pressure from flow 1 to flow 2 in the groups receiving nitroprusside and amrinone. Cardiac index at flow 1 was similar for all groups; there were no significant changes from flow 1 to flow 2.

	Comment

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
Anatomic studies of the IMA show the proximal part of the IMA to be a musculoelastic artery, the middle portion an elastic artery, and the distal segment a musculoelastic artery [8]. Physiologic studies of the IMA show the distal segment of the artery to have a highly sensitive vasoconstrictive response [9, 10]. It would be logical to assume that if the distal third of the IMA could be resected, and the middle third of the IMA could be anastamosed to the LAD, there would be less of a tendency for the IMA to spasm, and thus the beneficial influence of vasodilatory agents would be minimized. Studies that show a significant effect of topical and systemic vasodilators on flow have not stated whether the distal segment of the vessel had been resected [6, 7, 11, 12]. In a study in which the distal segment of the IMA was resected, no influence of topical vasodilators on IMA flow was noted [5].

In the present study, despite resection of the distal segment of the IMA, systemic nitroglycerin showed a significant enhancing effect on the flow in the IMA. This is consistent with recent reports that show nitroglycerin to have an equal vasodilatory effect in all segments of the IMA [10].

The negative effect on flow caused by nitroprusside in this study is worthy of comment, considering the opposite effect noted in other studies [7]. First, its mechanism of action is primarily on smooth muscle in the vessel wall. Resection of the distal portion of the IMA eliminates the section in which nitroprusside would have a major influence. Second, previous studies evaluating the effect of nitroprusside on IMA flow compared flows with similar mean blood pressures. In this study, the flows were measured with comparable CI between the two flows without compensating for a significant decrease in blood pressure between flows. In previous studies, it was probably necessary to volume load the patients after nitroprusside infusion to achieve similar blood pressures. Thus, the flow 2 measurement was probably taken with a greater CI than flow 1. Our study shows that with similar CI and the distal section of the IMA resected, nitroprusside decreases mean blood pressure and causes a deleterious effect on IMA flow, despite vasodilating the artery.

There are three significant differences between this study and our previous study [5]. In the current study (1) there is a significant decrease in the time between measurements, (2) there is a significant increase in flow 1, and (3) there is no increase in flow in the control group from flow 1 to flow 2. The reason for the decrease in time between flow measurements was a change in the time of measurement of flow 2. In our original study, flow 2 was measured after arterial and venous cannulation. This created a problem because of atrial arrythymias caused by venous cannulation, and therefore flow 2 in this study was measured before venous cannulation and placement of the retrograde cardioplegic catheter. The increased flow 1 in the present study is caused by a difference in patient selection. In our first study, we accepted all patients requiring an IMA graft to the LAD and shortened the IMA as much as possible. In this study, we chose only those patients who had proximal LAD lesions. This allowed us to shorten the IMA even further, accounting for an increase in the flow. Both factors, the shorter time between flow 1 and flow 2 and the increased initial flow, may explain why there is no difference from flow 1 to flow 2 in the present study. The concept that shortening the IMA causes increased flow beyond the physical effect of shortening the conduit requires further investigation.

The hemodynamic effects of the vasodilatory agents used during the study are significant, because all are not routinely used in patients undergoing coronary artery bypass grafting in the period before cardiopulmonary bypass. All the drugs, with the exception of nitroglycerin, caused significant tachycardia. The double product increased in those patients receiving nitroprusside, dobutamine, and dopexamine during the study. None of the drugs used increase CI significantly. Thus, all the drugs used, with the exception of nitroglycerin, appeared to increase myocardial oxygen demand in this study, without increasing oxygen supply.

In conclusion, resection of the distal segment of the IMA before anastomosis to the LAD increases flow and decreases the effect of arterial spasm on IMA flow. In patients in whom the distal IMA is resected, the use of intravenous nitroglycerin during the prebypass period increases IMA flow. Other drugs used in this study had deleterious hemodynamic effects in this setting without achieving increased flow in the IMA. In patients undergoing coronary artery bypass grafting with an IMA graft and a proximal LAD lesion, we recommend resection of as much of the distal IMA as possible and the use of intravenous nitroglycerin to achieve optimal flow in the IMA graft.

	Acknowledgments

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
This article was prepared in consultation with Diklah Geva, who prepared the statistics, and with the technical assistance of Sally Esakov.

	References

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 

1. Lytle BW, Loop FD, Cosgrove DM, Ratliff NB, Easley K, Taylor PC. Long term (5 to 12 years) serial studies of internal mammary artery and saphenous vein coronary bypass grafts. J Thorac Cardiovasc Surg 1985;89:248–58.[Abstract]
2. Loop FD, Lytle BW, Cosgrove DM, et al. Influence of the internal-mammary-artery graft on 10 year survival and other cardiac events. N Engl J Med 1986;314:1–6.[Abstract]
3. Sarabu MR, McClung JA, Fass A, Reed GE. Early postoperative spasm in the left internal mammary artery bypass grafts. Ann Thorac Surg 1987;44:195–200.
4. Barner HB. Blood flow in the internal mammary artery. Am Heart J 1973;86:570–1.[Medline]
5. Sasson L, Cohen AJ, Hauptman E, Schachner A. Effect of topical vasodilators on internal mammary arteries. Ann Thorac Surg 1995;59:494–6.
6. Cooper GJ, Wilkinson GAL, Angelini GD. Overcoming perioperative spasm of the internal mammary artery: which is the best vasodilator? J Thorac Cardiovasc Surg 1992;104:465–8.[Abstract]
7. Izzat MB, West RR, Ragoonanan C, Angelini GA. Effect of systemic vasodilators on internal mammary artery flow. J Thorac Cardiovasc Surg 1994;108:82–5.
8. Van Son JAM, Smedts F, de Wilde PCM, et al. Histological study of internal mammary artery with emphasis on its suitability as a coronary artery bypass graft. Ann Thorac Surg 1993;55:106–13.[Abstract]
9. He G-W. 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. J Thorac Cardiovasc Surg 1993;106:406–11.[Abstract]
10. He G-W, Acuff TE, Yang C-Q, Ryan WH, Mack MJ. Middle and proximal sections of the human internal mammary artery are not "passive conduits." J Thorac Cardiovasc Surg 1994;108:741–6.[Abstract/Free Full Text]
11. Okies JE, Page US, Bigelow JC, Krause AH, Salomon NW. The left internal mammary artery: the graft of choice. Circulation 1984;70(Suppl 1):213–21.
12. He G-W, Buxton BF, Rosenfeldt FL, Angus JA, Tatoulis J. Pharmacologic dilatation of the internal mammary artery during coronary bypass grafting. J Thorac Cardiovasc Surg 1994;107:1440–4.[Abstract/Free Full Text]

This article has been cited by other articles:

				M. J. Flynn, D. Winters, P. Breen, G. O'Sullivan, G. Shorten, D. O'Connell, A. O'Donnell, and T. Aherne Dopexamine increases internal mammary artery blood flow following coronary artery bypass grafting Eur. J. Cardiothorac. Surg., October 1, 2003; 24(4): 547 - 551. [Abstract] [Full Text] [PDF]

				D. Zabeeda, B. Medalion, S. Jackobshvilli, S. Ezra, A. Schachner, and A. J. Cohen Comparison of systemic vasodilators: effects on flow in internal mammary and radial arteries Ann. Thorac. Surg., January 1, 2001; 71(1): 138 - 141. [Abstract] [Full Text] [PDF]

				O. Chavanon, J.-L. Cracowski, R. Hacini, F. Stanke, M. Durand, M. Noirclerc, and D. Blin Effect of topical vasodilators on gastroepiploic artery graft Ann. Thorac. Surg., May 1, 1999; 67(5): 1295 - 1298. [Abstract] [Full Text] [PDF]

This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Amram J. Cohen Lior Sasson Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Arnaudov, D. Articles by Ezra, S. Search for Related Content PubMed PubMed Citation Articles by Arnaudov, D. Articles by Ezra, S. Related Collections Related Article