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Ann Thorac Surg 1997;63:1041-1043
© 1997 The Society of Thoracic Surgeons

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Original Article: Cardiovascular

Assessment of Internal Thoracic Artery Vasoreactivity in Response to Sublingual Nitroglycerin

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

Accepted for publication October 28, 1996.

	Abstract

Top Footnotes Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
Background. We have previously shown the feasibility of assessing internal thoracic artery (ITA) size and blood flow hemodynamics before and after coronary artery bypass grafting using color-flow duplex ultrasound. This noninvasive method would be an ideal diagnostic tool for the evaluation of ITA graft status after therapeutic interventions in a patient with angina after coronary artery bypass grafting. The purpose of this study was to investigate the effects of nitroglycerin on the diameter and blood flow velocities of the left native ITA before coronary artery bypass grafting and the ITA graft postoperatively.

Methods. The study consisted of 24 male patients (mean age, 59 ± 2.3 years) who had undergone elective coronary artery bypass grafting using a left ITA graft to the left anterior descending artery, with additional saphenous vein grafts. Color-flow duplex ultrasound (5.0-MHz transducer) was used for both the preoperative imaging of native ITAs and the postoperative study of ITA grafts before patient discharge. Repeated-measures analysis of variance was used to compare measurements of the ITA size and flow velocities (peak systolic velocity and end-diastolic velocity) at 5, 10, and 15 minutes after a single dose of sublingual nitroglycerin (0.4 mg) with the baseline values obtained without nitroglycerin.

Results. The preoperative native left ITA and the postoperative left ITA graft diameters responded to sublingual nitroglycerin by showing a rapid and significant increase beginning at 5 minutes and lasting up to 15 minutes (p = 0.0001). Sublingual nitroglycerin caused the peak systolic velocity of the native left ITA to be augmented at 5 minutes (p = 0.0002), and this effect was still apparent at 10 minutes (p = 0.0001) and 15 minutes (p = 0.0192). However, postoperative left ITA graft peak systolic velocities remained unaffected by the sublingual nitroglycerin (p = not significant).

Conclusions. We conclude that instantaneous noninvasive measurement of ITA graft size and blood flow velocities after a therapeutic drug intervention may be clinically useful, particularly in a post–coronary artery bypass grafting patient with recurrent angina.

	Introduction

Top Footnotes Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
In the past, invasive cardiac catheterization was considered the sole definitive method for evaluating the patency of a left internal thoracic artery (ITA) graft in a patient with recurrent angina, myocardial ischemia, or infarction after coronary artery bypass grafting (CABG). With advancements in ultrasound technology, however, the noninvasive qualitative assessment of the left ITA graft after CABG became possible [1, 2]. Such high-fidelity, instantaneous measurement of ITA graft size and blood flow velocities may offer the clinician the ability to identify phasic changes in ITA graft flow dynamics. We have previously shown that the ultrasonic surveillance of postoperative ITAs may reveal ITA graft velocity abnormalities before overt graft failure is manifested in a patient who has undergone CABG [1]. Another clinically beneficial application of this noninvasive surveillance method would be to assess the effect of therapeutic drug interventions on ITA graft blood flow in a post-CABG patient with recurrent angina. To test this hypothesis, we investigated the effects of nitroglycerin (NTG) on the size and blood flow characteristics of the native ITA and ITA graft in patients who had undergone CABG.

	Patients and Methods

Top Footnotes Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
The study group consisted of 24 consecutive patients who underwent elective CABG with left ITA and additional reversed saphenous vein aortocoronary grafts between January 1995 and December 1995. In every case the left ITA was harvested as a pedicle and was anastomosed to the left anterior descending coronary artery by the same surgeon (C.C.C.) using the same technique. All patients were male and ranged in age from 38 to 78 years. The mean age was 59 ± 2.3 years.

Ultrasound transthoracic imaging of the 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 before and after NTG administration to image the native left ITAs before CABG and the ITA grafts postoperatively before patient discharge.

This Doppler-based imaging method, which we have described previously [3–6], was performed through the first or second intercostal space with the patient supine. A computerized color-flow 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 patient's skin after the 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 the ITA diameter (in millimeters) and blood flow velocity (in centimeters per second) at peak systole and end-diastole and obtained waveforms from the left ITAs of each patient. Measurements of the size and blood flow velocities of the ITAs at 5, 10, and 15 minutes after a single dose of sublingual NTG (0.4 mg) were compared with baseline values obtained before the administration of NTG.

Statistical analysis was performed using the SAS statistical software program (SAS Institute, Cary, NC), and values were expressed as the mean ± the standard deviation. Data analysis for the preoperative and postoperative measurements was performed using the repeated-measures analysis of variance. Significance was assumed when the calculated p value was 0.05 or less.

	Results

Top Footnotes Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
Adequate ultrasonic visualization of all preoperative native left ITAs and postoperative left ITA grafts was easily obtained. The preoperative waveform was triphasic with a large systolic peak followed by a much smaller diastolic component (Fig 1). The postoperative Doppler waveform was converted into a biphasic waveform (Fig 2) with a decrease in the peak systolic velocity and an increase in the end-diastolic velocity.

View larger version (96K): [in this window] [in a new window]   Fig 1. . Typical preoperative Doppler spectrum appearance of native left internal thoracic artery (LITA). Arrow 1 indicates peak systole; arrow 2 indicates end-diastole.

View larger version (84K): [in this window] [in a new window]   Fig 2. . Example of postoperative Doppler spectrum appearance of left internal thoracic artery (LITA) graft after myocardial revascularization. Arrow 1 indicates decreased peak systolic velocity; arrow 2 indicates increased end-diastolic velocity.

	Comment

Top Footnotes Abstract Introduction Patients and Methods Results Comment Acknowledgments References

The effects of various vasoactive agents on the size and blood flow rate of ITAs have been of great interest to many investigators. Conceptually such a tool should be able to provide objective information about drug-induced ITA graft flow alterations in patients and this information could be used to influence the use of the various coronary vasodilators used worldwide for the treatment of post-CABG recurrent angina. This study demonstrated that the native ITA responds to a single dose of sublingual NTG by increasing the diameter and peak systolic velocity of the vessel. In contrast, the lack of similar vasoreactive response by the left ITA graft may be explained either by the fact that the dose of NTG was insufficient or its oral administration ineffective or by the fact that, after harvesting, the ITA graft becomes insensitive to the vasodilatory effects of sublingual NTG.

We decided to study sublingual NTG because of its common use in the treatment of coronary artery disease, its rapid effect when given sublingually, its ease of administration by the vascular technician, and its relatively harmless nature for the study patients. One limitation of this study is that some of the patients were being treated with antianginal beta-blockers or calcium-channel blockers or with antihypertensive medications, or combinations of these, before operation, and their influence on the observed effects of NTG cannot be adequately assessed. However, another study is currently under way that addresses this issue. In addition, selective angiographic validation of Doppler-derived findings was not done in our study. Despite the difficulty in persuading symptom-free patients to undergo coronary angiography after CABG, it is desirable that many such selective angiograms be performed so that the ITA flow velocities shown by color-flow duplex ultrasound can be accurately interpreted.

In summary, the in vivo noninvasive assessment of ITA size and blood flow velocities in response to a therapeutic drug intervention is possible through the use of the color-flow duplex ultrasound. The information about the ITA graft flow and size provided by this noninvasive technique may allow coronary vasodilator therapy to be optimized, particularly in the post-CABG patient with recurrent angina. Future efforts should be directed toward investigating the effects of other common cardiac drugs on ITA characteristics before and after CABG.

	Acknowledgments

Top Footnotes Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
We are grateful for the work of Dennis M. Heisey, PhD, in the statistical analysis of the data and for the assistance of Wanda L. Stroyny in the preparation of the manuscript.

	Footnotes

Top Footnotes Abstract Introduction Patients and Methods Results Comment Acknowledgments References

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

	References

Top Footnotes Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 

1. Canver CC, Armstrong VM, Nichols RD, Mentzer RM Jr. Color-flow duplex ultrasound assessment of internal thoracic artery graft after coronary bypass. Ann Thorac Surg 1995;59:389–92.[Abstract/Free Full Text]
2. Crowley JJ, Shapiro LM. Noninvasive assessment of left internal mammary artery graft patency using transthoracic echocardiography. Circulation 1995;92(Suppl 2):25–30.[Abstract/Free Full Text]
3. 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]
4. Canver CC. Preoperative morphologic and physiologic assessment of internal thoracic arteries [Letter]. Ann Thorac Surg 1992;54:1020–1.
5. 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 1992;33:534–7.[Medline]
6. Canver CC, Zwolak RM. Preoperative evaluation of the right internal thoracic artery for coronary surgery. Ann Thorac Surg 1994;57:440–3.[Abstract]
7. Acinapura AJ, Rose KM, 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]

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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 Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Canver, C. C. Articles by Nichols, R. D. Search for Related Content PubMed PubMed Citation Articles by Canver, C. C. Articles by Nichols, R. D.