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Ann Thorac Surg 1996;61:124-127
© 1996 The Society of Thoracic Surgeons

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Original Articles: Cardiovascular

Morphometric Analysis of the Right Gastroepiploic Artery and the Internal Mammary Artery

Escorts Heart Institute and Research Centre, New Delhi, India

Accepted for publication September 6, 1995.

	Abstract

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Background. The internal mammary artery (IMA) and the right gastroepiploic artery (RGEA) are frequently used as conduits for coronary artery bypass grafting.

Methods. Morphometric measurements and histologic characteristics of the RGEA and the IMA were studied in 25 patients undergoing coronary artery bypass grafting.

Results. External radius was found to be more in the IMA (range, 18 to 56 µm; mean, 39.56 µm) in comparison with the RGEA (range, 24 to 51 µm; mean, 32.52 µm; p < 0.01). There was no significant difference between the vessels in intimal thickness (IMA: 0.0 to 0.25 µm; mean, 0.05 µm; RGEA: 0.0 to 0.28 µm; mean, 0.09 µm), internal radius (IMA: 5 to 47 µm; mean, 28.40 µm; RGEA: 16 to 42 µm; mean, 23.56 µm), area of media (IMA: 1,690 to 3,476 µm²; mean, 2,777.52 µm²; RGEA: 1,659 to 3,600; mean, 3,012.44 µm²), intimal thickening index (IMA: 0.0 to 0.02; mean, 0.01; RGEA: 0.0 to 0.13; mean, 0.01), and medial index (IMA: 0.14 to 0.60; mean, 0.36; RGEA: 0.18 to 0.63; mean, 0.39). Histologic examination of the RGEA showed more defects in continuity of internal elastic lamina and rich smooth muscle cells in the media.

Conclusions. There was no difference in the morphometric measurements of the IMA and the RGEA except external radius, which was greater for the IMA. The histologic differences found in the RGEA may indicate an increased propensity for atherosclerosis of the RGEA as compared with the IMA. Some concern regarding the long-term patency of the RGEA in myocardial revascularization is warranted.

	Introduction

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Excellent long-term results of the internal mammary artery (IMA) as a graft for coronary artery bypass grafting (CABG) have encouraged a search for other reliable arterial conduits for total arterial revascularization. The right gastroepiploic artery (RGEA) appears to be very promising as another arterial graft to accomplish total arterial myocardial revascularization in combination with bilateral IMAs.

Suma and associates [1] have compared arteriosclerosis of the RGEA and the IMA, and found that the former has slightly more intimal thickening than the latter. In the present study we have compared morphometric measurements and histologic characteristics of the RGEA and the IMA in patients of various age groups.

	Material and Methods

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Twenty-five patients undergoing CABG in whom both IMA and RGEA were used as conduits formed the study groups. Informed consent was obtained in all the patients. Five-millimeter-long distal segments of both the IMA and the RGEA were taken just proximal to the bifurcation of IMA and RGEA in each patient. Ligaclips (Ethicon, Somerville, NJ) were applied at both the ends of these segments. The distal Ligaclip was applied first when the artery was still exposed to the systemic blood pressure, and the proximal Ligaclip was applied later. These closed IMA and RGEA segments with trapped blood inside were immersed in 4% buffered formalin. Before the IMA and RGEA segments were divided the distal ends of these vessels were bled in different bowls. The volume bled in the bowls was measured and free blood flow rate (milliliters per minute) calculated for each vessel. Flow was measured after intraluminal papaverine (0.8 mg/mL of papaverine in 0.9% normal saline solution) injection without mechanical dilation of the graft. Simultaneously radial artery pressure was recorded as an expression of central arterial pressure.

The formalin-fixed specimens of the IMA and the RGEA were processed for light microscopy. Sections of 5 µm thickness were cut and embedded in paraffin wax at 62°C. This was then stained by hematoxylin-eosin and elastic stain. Sections were cut from the midportion of the vessel segment, sufficiently far from the clip sites to ensure that the lumen was nearly circular. All the measurements were done in four axes, and the mean was taken to minimize chances of error.

Morphometric measurements were done by one of us (S.J.) using a micrometer. The perimeter of the media (PM), luminal circumference, cross-sectional area of the lumen, cross-sectional area of the media (M), external radius (Re), internal radius (Ri), intimal thickness index, media index, and intimal thickness were measured in both vessels (Fig 1).

View larger version (34K): [in this window] [in a new window]   Fig 1. . Measured and calculated variables. Measured variables were perimeter of the media (PM), area of the media (M), internal elastic lamina (IEL), and luminal area (LA). The following variables were calculated: external radius , internal radius , and luminal circumference .

Data are presented as mean ± standard deviation where appropriate. Categoric variables were compared by ² test, whereas paired and unpaired Student's t test were applied to compare the continuous variables.

	Results

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
The characteristics of patients in the IMA and the RGEA group have been compared with regard to their age, body surface area, mean arterial pressure at the time of flow measurement, internal radius, intimal thickness, area of media, intimal thickness index, and media index (Table 1). These parameters did not show any statistically significant difference between the two groups except in the external radius, which was found to be more in the IMA group (range, 18 to 56 µm; mean 39.56 µm) in comparison with the RGEA group (range, 24 to 51 µm; mean, 32.52 µm; p < 0.01). Intimal thickness was found to be more in the RGEA group (range, 0.0 to 0.28 µm; mean, 0.09 µm) than in the IMA group (range, 0.0 to 0.25 µm; mean, 0.05 µm). This, however, was not found to be statistically significant. The mean free blood flow rate of IMA was more than that of the RGEA (Table 2). Mean luminal area (± standard deviation) was 369.20 ± 164.78 µm² (range, 160 to 820 µm²) for the IMA and 339.84 ± 182.91 µm² (range, 60 to 990 µm²) for the RGEA. Comparison of the IMA and the RGEA blood flow rate in relation to their luminal area showed increased flow of both RGEA and IMA with increase in the luminal area (Fig 2).

View larger version (36K): [in this window] [in a new window]   Fig 2. . Scatter diagrams of correlation of luminal area with free blood flow of the right gastroepiploic artery (RGEA) and internal mammary artery (IMA).

	Comment

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Definite long-term superiority of the IMA graft over the saphenous venous graft has led to a constant search for finding different arterial conduits for CABG. Besides the IMA, the radial artery, splenic artery, inferior epigastric artery, and the RGEA all have been used with varying success for total arterial revascularization of the heart. In 1974 Edwards used RGEA as a direct bypass graft to the right coronary artery [2]. After that it was used infrequently for CABG for almost 10 years. In recent years it is being used more frequently, especially in patients who are suitable for total arterial revascularization. The host organ does not get compromised in dissection and division of the RGEA; therefore, it is suitable as an arterial conduit. Suma and associates [3] found that the in situ RGEA is long enough to reach the inferior ventricular wall and the circumflex and left anterior descending arteries and has a suitable diameter for CABG.

Suma and associates [1] found that in patients who had major atherosclerosis of the coronary arteries including some other side branches of aorta and the femoral arteries, the IMA was free of atherosclerosis. Comparing the atherosclerotic changes between the gastroepiploic artery (GEA) and the IMA, they found that the GEA had a slightly higher degree of atherosclerosis as compared with the IMA. In our study we have measured intimal thickening index, an indicator of atherosclerosis, and found no statistically significant atherosclerotic changes in the RGEA as compared with the IMA.

However, we have noted that the wall of the RGEA was slightly thicker than the IMA as seen by comparing the medial thickening index in the two vessels. The medial thickening index was 0.18 to 0.63 (mean, 0.39) in the RGEA group and 0.14 to 0.60 (mean, 0.36) in the IMA group. A similar observation was made by Suma and associates [4] in their study comparing wall thickness of IMA and RGEA. The RGEA is a more muscular artery compared with the IMA, which can be one of the reasons for the medial thickness index of the RGEA to be slightly more than that of the IMA.

The free blood flow of the RGEA was almost equal to that of the IMA, supporting further that the RGEA is a good arterial conduit for CABG. Analysis of free blood flow rates in relation to the luminal area of the RGEA and IMA revealed an increase in mean flow as the luminal area of the vessels increased. Mills and colleagues [5] found an increase in the flow rate as the inner diameter of RGEA increased when evaluating flow characteristics and the size of RGEA.

Larson and associates [6] found in pathologic studies that the GEA has less atherosclerotic changes as compared with the other arteries. Our study demonstrates similar results. Van Son and co-workers [7] have demonstrated that smooth muscle fibers are plentiful in the media of GEA but rare in IMA, and elastic fibers are plentiful in the media of IMA but less in GEA, which conforms to the histologic findings in the present study. Sims [8] reported that discontinuity of the internal elastic lamina causes migration of smooth muscle cells from media to intima and triggers atherosclerosis. We have also found the integrity of internal elastic lamina broken at more points in the RGEA as compared with the IMA. This may increase the probability of atherosclerosis in the RGEA, but we could not find significantly increased atherosclerosis in the RGEA as compared with the IMA in terms of morphometric measurements.

Similar observations were made by Tavilla and associates [9], who found a greater number of discontinuties in the internal elastic lamina in the muscular RGEA as compared with the IMA. This finding, however, must be interpreted with caution until further clinical studies regarding the long-term patency rate of the RGEA in myocardial revascularization have proved whether these histologic differences in the RGEA and IMA are of any concern.

Last but not least, biochemical factors such as prostacyclins, endothelial-derived relaxation factor, and other endothelial substances play a role in long-term patency of the graft [10–12]. Therefore, atherosclerosis of autologous arterial graft is not a single determinant for long-term graft patency.

We conclude from our study that the RGEA has similar morphometric characteristics as the IMA. Although we did not find any difference in morphometric characteristics of the two vessels, the histologic differences found in the RGEA may indicate an increased propensity of atherosclerosis of the RGEA as compared with the IMA. Some concern regarding the long-term patency of the RGEA in myocardial revascularization is therefore warranted until clinical trials have proved it to have as good a long-term patency as that of the IMA.

	Footnotes

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Address reprint requests to Dr Malhotra, Escorts Heart Institute and Research Centre, Okhla Rd, New Delhi 110025, India.

	References

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 

1. Suma H, Takanashi R. Arteriosclerosis of the gastroepiploic and internal thoracic arteries. Ann Thorac Surg 1990;50:413–6.[Abstract/Free Full Text]
2. Mills NL, Everson CT. Right gastroepiploic artery: a third arterial conduit for coronary artery bypass. Ann Thorac Surg 1989;47:706–11.[Abstract/Free Full Text]
3. Suma H, Fukumoto H, Takeuchi A. Coronary artery bypass grafting by utilizing in situ right gastroepiploic artery: basic study and clinical application. Ann Thorac Surg 1987;44:394–7.[Abstract/Free Full Text]
4. Suma H, Wanibuchi Y, Furuta S, Isshiki T, Yamaguchi T, Takanashi R. Comparative study between the gastroepiploic and the internal thoracic artery as a coronary bypass graft: size, flow, patency, histology. Eur J Cardiothorac Surg 1991;5:244–7.[Abstract/Free Full Text]
5. Mills NL, Hockmuth DR, Everson CT, Robart CC. Right gastroepiploic artery used for coronary artery bypass grafting: evaluation of flow characteristics and size. J Thorac Cardiovasc Surg 1993;106:579–86.[Abstract]
6. Larsen E, Johansen A, Anderson D. Gastric arteriosclerosis in elderly people. Scand J Gastroentrol 1969;4:387–9.[Medline]
7. Van Son JAM, Smedts F, Vincent JG, van Lier HJJ, Kubat K. Comparative anatomic studies of various arterial conduits for myocardial revascularization. J Thorac Cardiovasc Surg 1990;99:703–7.[Abstract]
8. Sims FH. Discontinuties in the internal elastic lamina: a comparison of coronary and internal mammary arteries. Artery 1985;13:127–42.[Medline]
9. Tavilla G, van Son JAM, Verhagen AF, Smedts F. Retrogastric versus antegastric routing and histology of the right gastroepiploic artery. Ann Thorac Surg 1992;53:1057–61.[Abstract/Free Full Text]
10. Dignan RJ, Yeh T Jr, Dyke CM, et al. Reactivity of gastroepiploic and internal mammary arteries: relevance to coronary artery bypass grafting. J Thorac Cardiovasc Surg 1992;103:116–23.[Abstract]
11. O'Neil GS, Chester AH, Schyns CJ, et al. Vascular reactivity of human internal mammary and gastroepiploic arteries. Ann Thorac Surg 1991;52:1310–4.[Abstract/Free Full Text]
12. O'Neil GS, Chester AH, Allen SP, et al. Endothelial function of human gastroepiploic artery: implications for its use as a bypass graft. J Thorac Cardiovasc Surg 1991;102:561–5.[Abstract]

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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): Rajneesh Malhotra Harinder Singh Bedi Naresh Trehan Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Malhotra, R. Articles by Trehan, N. Search for Related Content PubMed PubMed Citation Articles by Malhotra, R. Articles by Trehan, N.