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Ann Thorac Surg 1995;59:389-392
© 1995 The Society of Thoracic Surgeons

Color-Flow Duplex Ultrasound Assessment of Internal Thoracic Artery Graft After Coronary Bypass

Section of Cardiothoracic Surgery, William S. Middleton Memorial Veterans Hospital, University of Wisconsin School of Medicine, Madison, Wisconsin

Accepted for publication September 21, 1994.

	Abstract

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 
In an effort to develop a noninvasive method to evaluate flow characteristics of the internal thoracic artery (ITA) graft after coronary artery bypass grafting, we performed color-flow duplex ultrasound studies of the right and left ITAs of 42 patients before and 5 weeks after bypass grafting. The ITA was visualized with a duplex scanner (5.0-MHz probe) through the first or second intercostal space. We recorded the diameter, peak systolic velocity, and end-diastolic velocity for each patient. Preoperative measurements of the native ITAs were obtained easily in all patients. Postoperatively, the unused right ITA was seen in all patients. Postoperative visualization of the left ITA graft was adequate to make reliable measurements in 40 patients (95%). Postoperative end-diastolic velocities of the unused right ITA and the left ITA graft were markedly higher than the preoperative end-diastolic velocities of the native ITAs (p < 0.001). Whereas there was a marked increase in the peak systolic velocity of the postoperative unused right ITA (p < 0.05), the postoperative peak systolic velocity of the left ITA graft was significantly lower than the preoperative value (p < 0.001). We conclude that postoperative visualization of the left ITA graft is possible with the use of color-flow duplex ultrasound. Ultrasonic surveillance of postoperative ITAs may reveal ITA graft velocity abnormalities before overt graft failure is manifested in the patient who has undergone coronary artery bypass grafting.

	Introduction

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 
Invasive cardiac catheterization is the only definitive method for assessment of left internal thoracic artery (ITA) graft patency in the patient with recurrent angina, myocardial ischemia, or infarction after coronary artery bypass grafting (CABG). Noninvasive techniques such as echocardiography and ultrasonography are limited by transducer positioning, vessel curvature, and constant motion of the heart. The successful application of noninvasive Doppler spectrum analysis has been reported for the hemodynamic assessment of coarctation of the aorta [1], peripheral vascular disease [2], and unused ITA after median sternotomy [3]. Only one report [4], however, advocates the possibility of using Doppler spectrum analysis in the noninvasive hemodynamic assessment of the ITA graft after myocardial revascularization. We have successfully applied color-flow duplex ultrasound as a reliable, noninvasive screening modality for the preoperative morphologic and physiologic evaluation of the left and right ITAs for primary [5–7] and repeat [8] CABG.

In this study, our purpose was to evaluate this noninvasive ultrasonic imaging method for assessing postoperative anatomy and flow characteristics of the ITA graft in patients who had undergone CABG.

	Material and Methods

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 
The study group consisted of 42 consecutive patients who underwent elective CABG with left ITA and additional reversed saphenous vein aortocoronary grafts between September 1993 and February 1994. In every case, the left ITA was anastomosed to the left anterior descending coronary artery by one of us (C.C.C.) using the same technique. All patients were men ranging from 43 to 80 years old. Mean age was 61 ± 8.8 years.

Ultrasound transthoracic imaging of the right and left ITAs was performed on all patients at the Vascular Laboratory of the William S. Middleton Memorial Veterans Hospital (Madison, WI). These studies were done preoperatively and 5 weeks postoperatively.

This Doppler-based imaging, which has been described previously by us [5], was performed through the first or second intercostal space while the patient was in the supine position. A computerized color duplex ultrasound scanner (Quantum 2000; Siemens, Issaquah, WA) equipped with a 5.0-MHz transducer was used for all studies. The duplex probe was placed directly on the skin after application of a commercial ultrasonic gel and positioned to maintain an angle as close as possible to 60 degrees to the axis of blood flow. We measured ITA diameter (mm) and blood flow velocity (cm/s) at peak systole and end-diastole, and obtained waveforms from the right and left ITAs of each patient.

Statistical analysis was performed on the SAS statistical software program (Cary, NC), and values were expressed as the mean ± the standard deviation. Nonparametric data analysis of the preoperative and postoperative measurements was performed by use of the Wilcoxon signed-rank test. Significance was assumed when the calculated p value was 0.05 or less.

	Results

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 
Adequate ultrasonic visualization was easily obtained in all preoperative native ITAs and postoperative unused right ITAs. The preoperative waveform was triphasic with a large systolic peak followed by a much smaller diastolic component (Fig 1). Satisfactory duplex ultrasound visualization of the postoperative left ITA graft was obtained in 40 patients (95%). The postoperative Doppler waveform was converted into a biphasic waveform (Fig 2) with a decrease in the peak systolic velocity (PSV) and an increase in the end-diastolic velocity (EDV). Obesity, short neck, and pyknic constitution were possible reasons for failure of the color-flow duplex technique in visualizing the left ITA graft in 2 patients. Neither of these patients had any cardiac symptoms, and there were no clinical signs to indicate that the left ITA grafts might not be patent.

View larger version (135K): [in this window] [in a new window]   Fig 1. . Typical preoperative Doppler spectrum appearance of native left internal thoracic artery (ITA). Arrow 1 indicates peak systole; arrow 2 indicates end-diastole.

View larger version (137K): [in this window] [in a new window]   Fig 2. . Example of postoperative Doppler spectrum appearance of left internal thoracic artery (ITA) graft after myocardial revascularization. Arrow 1 indicates peak systole; arrow 2 indicates end-diastole.

	Comment

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 
The use of the ITA in myocardial revascularization is associated with a high rate of survival and freedom from cardiac-related events after CABG. In particular, a patent left ITA grafted to the left anterior descending coronary artery protects against recurrent angina and cardiac-related death [9]. However, no reliable method is available, other than invasive coronary angiography, to determine the postoperative patency of a left ITA graft.

Despite the success of accurate and reliable assessment of native ITAs using color-flow duplex ultrasound before CABG [5–8], our initial attempts to identify the left ITA graft noninvasively after CABG by that same technique were not successful. Because the left ITA was no longer in its original location in the chest wall after CABG, the left ITA graft could not be easily identified. This was due in part to the fact that ultrasound does not penetrate bone or air-filled organs, ie, lungs, and in part to the learning-curve experience. After numerous postoperative imaging studies of the left ITA graft, we were able to visualize its origin from the left subclavian artery through the first or second intercostal space.

In this study, our overall success rate of visualizing the left ITA graft was 95%, which was higher than the 47% success rate reported by van Son and associates [4]. Selective angiographic validation of Doppler-derived findings has not been done in either study. Despite the difficulty of persuading symptom-free patients after CABG to undergo coronary angiography, it is imperative that a large number of selective angiograms be performed before the ITA flow velocities can be accurately interpreted.

As shown in our previous work [5–8], the reproducibility rate for successful visualization of preoperative ITA imaging is almost 100%. In contrast, the reproducibility rate for successful identification and interrogation of postoperative ITA graft imaging by different vascular technicians has varied. In our recent study of 20 patients who had had placement of an ITA graft [10], all unused right ITAs were easily identified by all vascular technologists. Of the ten left ITA grafts selected to test reproducibility 3 months after CABG, seven were visualized adequately to record diameter and velocity measurements by two or more of the observers (70%). This is in part probably due to our learning curve with this technique. Currently, our postoperative ITA color-flow duplex studies are performed by the same vascular technician (V.M.A.), and the reproducibility rate for successful imaging of postoperative left ITA grafts is greater than 90%.

Normal arterial Doppler signals are usually biphasic or triphasic. The first sound corresponds to the high-velocity forward flow, which occurs during systole, ie, PSV. The second is of a lower frequency than the first and corresponds to reversed flow in early diastole, ie, EDV. This component is dependent on peripheral resistance and will be absent when peripheral resistance is low. The third component of the pulsed wave is of a lower frequency than the first two components and represents forward flow in late diastole. The characteristics of abnormal Doppler flow signals vary with the probe position relative to the site of stenosis or occlusion. Normal coronary blood flow as well as velocity pattern is biphasic, and the diastolic component predominates over the systolic one.

Postoperative duplex ultrasound ITA studies revealed significant changes from preoperative data in ITA waveform pattern and actual flow velocity measurements. The triphasic, mainly systolic, flow pattern of a native ITA has been well documented in prior studies dealing with preoperative ITA imaging [3, 11]. The postoperative waveform of the unused ITAs, which reflects the temporary conversion into a unidirectional systolic flow pattern with a large diastolic flow component, has been well described [3]. Our findings are consistent with those observations. For the left ITA graft anastomosed to the left anterior descending coronary artery, postoperative duplex ultrasound revealed a significant increase in diastolic flow velocity and a decrease in systolic flow velocity, thus indicating increased blood flow into the low-resistance distal coronary arterial bed and possibly indicating a patent graft. A large variation in EDV recordings is probably inherent in the duplex technique. No relationship could be demonstrated between differences in EDV and severity of left anterior descending coronary artery stenosis.

With advancements in Doppler technology, noninvasive qualitative assessment of the left ITA graft after CABG is now possible. Such high-fidelity instantaneous measurement of ITA graft size and blood flow velocities may offer the clinician the prospect of identifying phasic changes in ITA graft flow dynamics that may disclose velocity abnormalities before overt graft failure is manifested. In the future, efforts to better identify the left ITA graft, and possibly the other arterial and venous coronary grafts, should result in a clinically useful, noninvasive surveillance method to assess left ITA graft flow characteristics in the patient who has undergone CABG.

	Acknowledgments

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 
We thank Dennis M. Heisey, PhD, for statistical assistance and Wanda L. Stroyny for manuscript preparation.

	Footnotes

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 
Presented at the Sixty-seventh Scientific Session of the American Heart Association, Dallas, TX, Nov 14–17, 1994.

Address reprint requests to Dr Canver, Division of Cardiothoracic Surgery, University of Wisconsin-Madison, H4/352 Clinical Science Center, 600 Highland Ave, Madison, WI 53792-3236.

	References

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 

1. Van Son JAM, Skotnicki SH, van Asten WN, Daniels O, van Lier HJ, Lacquet LK. Quantitative assessment of coarctation in infancy by Doppler spectral analysis. Am J Cardiol 1989;63:1282–5.[Medline]
2. Van Asten WNJC, Beijneveld WJ, Pieters BR, van Lier HJ, Wijn PFF, Skotnicki SH. Assessment of aortoiliac obstructive disease by Doppler spectrum analysis of blood flow velocities in the common femoral artery at rest and during reactive hyperemia. Surgery 1991;109:633–9.[Medline]
3. Van Son JAM, Skotnicki SH, Folmer HA, van Asten WNJC. Reactive hyperemia in the nonused internal mammary artery after median sternotomy. Ann Thorac Surg 1992;54:130–3.[Abstract]
4. Van Son JAM, Skotnicki SH, Peters MBM, Pijls NHJ, Noyez L, van Asten WNJC. Noninvasive hemodynamic assessment of the internal mammary artery in myocardial revascularization. Ann Thorac Surg 1993;55:404–9.[Abstract]
5. Canver CC, Ricotta JJ, Bhayana JN, Fiedler RC, Mentzer RM Jr. Use of duplex imaging to assess suitability of the internal mammary artery for coronary artery surgery. J Vasc Surg 1991;13:294–301.[Medline]
6. Canver CC. Preoperative morphologic and physiologic as-sessment of internal thoracic arteries [Letter]. Ann Thorac Surg 1992;54:1020–1.
7. Canver CC, Zwolak RM. Preoperative evaluation of the right internal thoracic artery for coronary surgery. Ann Thorac Surg 1994;57:440–3.[Abstract]
8. Canver CC, Fiedler RC, Hoover EL, Ricotta JJ, Mentzer RM Jr. Noninvasive assessment of internal thoracic artery for reoperative coronary artery surgery. J Cardiovasc Surg (Torino) 1992;33:534–7.[Medline]
9. Acinapura AJ, Rose DM, Jacobowitz IJ, et al. Internal mammary artery bypass grafting: influence on recurrent angina and survival in 2,100 patients. Ann Thorac Surg 1989;48: 186–91.[Abstract]
10. Canver CC, Zwolak RM, Mentzer RM Jr. Noninvasive assessment of the internal thoracic artery graft after coronary bypass surgery [Abstract]. Chest 1994;106:1385.
11. Nasu M, Takagi T, Alasaka T, et al. Non-invasive Doppler technique for detection of flow velocity in left internal mammary artery grafts. Cardiovasc Surg 1994;2:207–11.[Medline]

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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): Charles C. Canver Robert M. Mentzer, Jr Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Canver, C. C. Articles by Mentzer, R. M. Search for Related Content PubMed PubMed Citation Articles by Canver, C. C. Articles by Mentzer, R. M., Jr