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Ann Thorac Surg 1998;66:79-81
© 1998 The Society of Thoracic Surgeons

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Original articles: cardiovascular

Assessment of internal thoracic artery graft with intraoperative color doppler ultrasonography

^a Department of Surgery II, Kochi Medical School, Kochi, Japan

Accepted for publication February 9, 1998.

Address reprint requests to Dr Oda, Department of Surgery II, Kochi Medical School, Kohasu Oko, Nankoku, Kochi, 783 Japan
e-mail: (odak{at}dtn.am400gw.kochi-ms.ac.jp)

	Abstract

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Background. Intraoperative ultrasonography has the potential to provide anatomic and functional information about internal thoracic artery (ITA) graft, but this potential has been hindered by the relatively large standard probe. In this study, we used a color Doppler microprobe to evaluate ITA grafts.

Methods. The subjects were 15 consecutive patients who underwent elective coronary artery bypass grafting either with cardiopulmonary bypass (n = 14) or without (n = 1). All patients underwent anastomosis of the left ITA to the left anterior descending artery. The ITA graft was assessed before the chest was closed, with the microprobe placed directly on the graft.

Results. A good-quality color Doppler image of the ITA graft was easily obtained in all 15 patients within a few minutes. The ITA graft function was assessed by analyzing the shape of the pulsed Doppler wave. All ITA grafts were patent, and the mean graft diameter was 1.8 ± 0.04 mm. The peak systolic velocity, peak diastolic velocity, and mean velocity were 52.0 ± 14.9 cm/s, 58.3 ± 22.4 cm/s, and 36.5 ± 10.9 cm/s, respectively. The ratio of peak diastolic velocity to peak systolic velocity was 1.24 ± 0.66. The ITA graft seemed to function well when the biphasic diastolic predominant flow appeared. The mean blood flow was 55.1 ± 22.0 mL/min.

Conclusions. Intraoperative ultrasonography using the microprobe provides adequate anatomic and hemodynamic information regarding ITA grafts. As the Doppler flow evaluation has high sensitivity and specificity, we suggest that intraoperative ultrasonography is useful for the assessment of these grafts.

	Introduction

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In the past decade, the use of the internal thoracic artery (ITA) in coronary artery bypass grafting (CABG) has become widely accepted because the rate of long-term patency is superior to that with saphenous vein graft. It is well known that the most important factor for long-term survival after CABG is a patent ITA graft at the end of the procedure [1]. The recent introduction of minimally invasive direct coronary artery bypass grafting has made it even more essential to assess the graft during the operation because of the concern about the quality of the anastomosis when performed on the beating heart [2]. Although various methods have been used to assess the ITA graft during CABG, there are no completely satisfactory methods at present.

Intraoperative ultrasonography (IOUS) has the potential to provide anatomic and functional information about the ITA graft, but its potential is hindered by the large standard transducers. Recent technological advances have led to the development of a microprobe that overcomes this limitation. In this study, we used this microprobe, which was originally developed for the purpose of spinal and spinal cord operations under a microscope, into CABG. As its crankshaft shape allows it to be manipulated in a small open chest field, it is suitable for scanning of ITA grafts.

The purpose of this study was to investigate the clinical applicability of IOUS in the assessment of ITA graft during CABG.

	Material and methods

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The ultrasound unit (SSD-200; Aloka, Tokyo, Japan) is equipped with a specially designed microprobe. The microprobe has a long holding device, which is the shape of a crankshaft. The tip of the microprobe is tilted at 60 degrees from the axis of its handle. The microprobe is 3 mm in height, 3 mm in width, and 13 mm in length (Fig 1). Although the signal-sending surface is small, B-mode, M-mode, pulsed Doppler, and color Doppler capabilities are available. The transducer frequency is 7.5 MHz, and the transducer is of a linear array type. The probe scan area is to a depth of 3 cm. Diameter as small as 0.1 mm can be measured with calipers.

View larger version (97K): [in this window] [in a new window]   Fig 1. Comparison of the standard 2.5 MHz probe (top) and the microprobe (bottom).

The ITA graft was assessed after hemodynamic conditions stabilized and before the chest was closed. The microprobe was placed directly on the ITA graft, with the aid of color Doppler flow mapping (Fig 2). After a suitable color Doppler image was obtained, the ITA graft was examined by pulsed Doppler ultrasonography. The pulsed Doppler waveform was analyzed using the computerized system supplied with the ultrasound unit. The ITA diameter was measured directly from a B-mode image. The mean blood flow values were calculated according to the following equation: . Values are expressed as the mean ± standard deviation.

View larger version (139K): [in this window] [in a new window]   Fig 2. Intraoperative assessment by the microprobe. Small arrows indicate the ITA graft, and the large arrow indicates the microprobe.

	Results

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View larger version (85K): [in this window] [in a new window]   Fig 3. The internal thoracic artery graft is clearly visualized by color Doppler imaging, and patency of the graft is easily confirmed.

View larger version (71K): [in this window] [in a new window]   Fig 4. A typical waveform for the internal thoracic artery graft showing biphasic, diastolic-predominant flow signal in the midportion of the graft (A) and systolic-predominant flow in the proximal portion (B). (D = diastole; S = systole.)

	Comment

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We consider IOUS using the microprobe to have several advantages. First, the graft patency is easily confirmed by color Doppler imaging without dissection of the ITA pedicle. Since, after the completion of the anastomosis, the ITA graft is transferred beneath the sternum, dissection of the pedicle is better avoided if possible. Second, the microprobe provides anatomic information about the ITA graft, such as whether stenosis or constriction is present, acquired by using the B-mode image. Finally, it provides functional information obtained by analyzing the waveform of the signal from the ITA graft. With all of these advantages, it is quite useful for the assessment of the ITA graft during CABG.

In recent studies, the early postoperative coronary hemodynamics and patterns of flow velocity in patients with ITA grafts were evaluated noninvasively by use of combined two-dimensional and Doppler transthoracic echocardiography [2–5]. Fusejima and associates [3] examined the pulsed Doppler flow signal in 15 patients with ITA grafts and were able to quantitate the biphasic nature of the ITA graft pattern. Flow through ungrafted ITA is principally systolic, whereas flow through grafted arteries is converted to predominantly biphasic diastolic.

The flow signals in the grafted ITA consisted of slower systolic flow velocities and faster diastolic flow velocities. Our results obtained with IOUS are in agreement with their results. In this study, all ITA grafts except one showed the typical biphasic flow pattern with a diastolic-predominant flow. Patency of the ITA grafts was confirmed soon before discharge. According to previous reports and our result, it is suggested that the ITA graft is patent when the biphasic diastolic-predominant Doppler signal is obtained [2]. The only patient who showed systolic-predominant flow required intraaortic balloon pumping during weaning from cardiopulmonary bypass. IOUS revealed that the ITA graft was patent. Postoperative angiography demonstrated patent ITA graft without any anastomotic stenosis. We speculate that systolic-predominant flow in this patient may reflect relatively minor anastomotic stenosis.

Bach and associates [6] examined 18 ITA grafts using an intravascular Doppler catheter in the proximal, middle, and distal portions. They reported a graduated transition in the phasic flow pattern from predominantly systolic velocity proximally to predominantly diastolic velocity distally. Our results accord with their results. Given this phenomenon, care should be taken as to the selection of the measurement site.

An estimated value for absolute graft flow could be obtained, on the basis of the flow-velocity signals and on the cross-sectional area of the vessel. After anastomosis, the ITA graft flow to the left anterior descending artery is reported to be approximately 50 mL/min [7–9]. Our data are generally consistent with this value. The accuracy of this estimation is limited by the relative imprecision of luminal diameter measurements. Although it has been reported that flow velocity, rather than flow volume, may be a more important determinant of graft closure, flow volume may provide additional information as to the ITA graft patency.

This preliminary study revealed the potential usefulness of IOUS with the microprobe in the assessment of ITA grafts. The features of the microprobe would make it useful for the assessment of ITA graft in not only conventional CABG, but also in minimally invasive direct coronary artery bypass grafting.

	References

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1. Loop F.D., Lytle B.W., Cosgrove D.M., 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]
2. Calafiore A.M., Di Giammarco G., Teodori G., et al. Left anterior descending coronary artery grafting via left anterior small thoracotomy without cardiopulmonary bypass. Ann Thorac Surg 1996;61:1658-1665.[Abstract/Free Full Text]
3. Fusejima K., Takahara Y., Sudo Y., Murayama H., Masuda Y., Inagaki Y. Comparison of coronary hemodynamics in patients with internal mammary artery and saphenous vein coronary artery bypass grafts: a noninvasive approach using combined two-dimensional and Doppler echocardiography. J Am Coll Cardiol 1990;15:131-139.[Abstract]
4. DeBono D.P., Samani N.J., Spyt T.J., Hartshorne T., Thrush A.J., Evans D.H. Transcutaneous ultrasound measurement of blood-flow in internal mammary artery to coronary artery grafts. Lancet 1992;339:379-381.[Medline]
5. Van Son J.A., Skotnicki S.H., Peters M.B., et al. Noninvasive hemodynamic assessment of the internal mammary artery in myocardial revascularization. Ann Thorac Surg 1993;55:404-409.[Abstract]
6. Bach R.G., Kern M.J., Donohue T.J., Aguirre F.V., Caracciolo E.A. Comparison of phasic blood flow velocity characteristics of arterial and venous coronary artery bypass conduits. Circulation 1993;88(Suppl 2):133-140.
7. Louagie Y.A.G., Haxhe J.P., Buche M., Schoevaerdts J.C. Intraoperative electromagnetic flowmeter measurements in coronary artery bypass grafts. Ann Thorac Surg 1994;57:357-364.[Abstract]
8. Takayama T., Suma H., Wanibuchi Y., et al. Doppler miniprobe to measure arterial graft flow in coronary artery bypass grafting. Ann Thorac Surg 1991;52:322-324.[Abstract]
9. Canver C.C., Dame N.A. Ultrasonic assessment of internal thoracic artery graft flow in the revascularized heart. Ann Thorac Surg 1994;58:135-138.[Abstract]

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This Article Abstract Full Text (PDF) 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): Katsushi Oda Toshiyuki Yamashiro Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Oda, K. Articles by Ogoshi, S. Search for Related Content PubMed PubMed Citation Articles by Oda, K. Articles by Ogoshi, S.