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Ann Thorac Surg 2001;71:788-793
© 2001 The Society of Thoracic Surgeons

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Original article: cardiovascular

Flow wire measurements after complete arterial coronary revascularization with T-grafts

^a Department of Cardiology, University Hospitals Homburg/Saar, Homburg/Saar, Germany
^b Department of Thoracic and Cardiovascular Surgery, University Hospitals Homburg/Saar, Homburg/Saar, Germany

Address reprint requests to Dr Markwirth, Medizinische Klinik III, Universitätskliniken des Saarlandes, Kirrberger Strasse 1, 66421 Homburg/Saar, Germany
e-mail: t.markwirth{at}gmx.de

Presented at the Thirty-sixth Annual Meeting of The Society of Thoracic Surgeons, Fort Lauderdale, FL, Jan 31–Feb 2, 2000.

	Abstract

Top Abstract Introduction Material and methods Results Comment Discussion References

 
Background. The T-graft procedure achieves complete arterial revascularization in coronary three-vessel disease. In this technique, all bypass anastomoses are supplied by the left internal mammary artery (IMA). This prospective study explores the question of whether the quantitative flow in such grafts is influenced by the pathology in the native coronary arteries.

Methods. Eighty-two patients with coronary three-vessel disease were studied after complete arterial coronary revascularization with T-grafts. Quantitative flow and coronary flow reserve were measured in the proximal IMA with a Doppler guide wire. Three groups were compared: group 1, all native coronary arteries were stenosed but patent (n = 31); group 2, one occluded native coronary vessel (n = 33); group 3, two or more occluded native coronary arteries (n = 18).

Results. Quantitative flow was significantly higher in group 3 than in group 2 at 1 week (93.9 ± 39.5 vs 75.8 ± 27.3 mL/min, p < 0.05) and 6 months postoperatively (86.0 ± 40.1 vs. 69.1 ± 35.5 mL/min, p < 0.05). Flow in group 2 was significantly (p < 0.05) higher than in group 1 (1 week: 58.0 ± 28.4 mL/min, 6 months: 55.2 ± 29.2 mL/min) in both examinations. There were no significant differences in coronary flow reserve between the three groups (1: 2.88 ± 0.97, 2: 2.84 ± 0.96, 3: 2.74 ± 0.94).

Conclusions. After complete arterial revascularization with T-grafts, the quantitative flow in the IMA is influenced by the status of the native coronary arteries. As a result of competitive flow phenomena, blood flow in the bypasses is significantly lower when the coronary arteries are affected only by stenosis.

	Introduction

Top Abstract Introduction Material and methods Results Comment Discussion References

 
The superiority of internal mammary artery (IMA) grafts to saphenous vein grafts with respect to morbidity, mortality, and long-term patency has been well established in coronary artery bypass surgery [1–3]. The use of both the left and free right IMA for revascularization of the anterior descending and circumflex coronary arteries has shown additional advantages over the use of only one IMA in combination with vein grafts [4–6]. Complete arterial revascularization appears to be reasonable to optimize surgical therapy for coronary heart disease. With the T-graft approach, complete arterial revascularization can be achieved in coronary three-vessel disease with only two arterial grafts. Tector and associates in 1994 presented the technique of T-grafting with both IMAs [7]. In this approach, the left IMA is connected to the coronary branches of the anterior wall, whereas the right IMA is anastomosed proximally to the left IMA and distally to the coronary arteries of the posterolateral and inferior wall in sequential fashion. T-grafting with the left IMA and radial artery has also been reported [8]. With this approach, complete revascularization is possible with maximum graft economy (ie, two grafts) and reduction of operative trauma and time.

In both variants of this technique, total coronary bypass flow is dependent on the flow of the left IMA. Quantitative flow measurements in such IMA grafts show a high variability [9]; in some patients, we have observed only a low resting flow volume in the IMA (< 50 mL/min) even though no graft alterations can be demonstrated angiographically. In this prospective study, we explored the question of whether quantitative flow and cardiac flow reserve in such grafts are influenced by the pathology of the native coronary arteries.

	Material and methods

Top Abstract Introduction Material and methods Results Comment Discussion References

 
The study population consisted of 82 patients (63 male, 19 female), with a mean age of 58.1 ± 8.6 years, who had undergone complete arterial coronary revascularization for coronary triple-vessel disease between May 1998 and January 1999. The operative technique has been described in a previous report [10]. Bilateral skeletonized IMAs were used as conduits in 40 patients, while the left skeletonized IMA and radial artery were utilized in 42 patients. Overall, 344 anastomoses were performed (mean 4.2 per patient). According to the status of the native coronary arteries, we divided the study population into three groups: group 1, all native coronary arteries are stenosed but patent (n = 31); group 2, patients with one occluded major coronary vessel (n = 33); group 3, two or more occluded major coronaries (n = 18).

The three groups were comparable with respect to age, gender, left ventricular function, and comorbidity (Table 1). Cardiac catheterization was performed 1 week and 6 months postoperatively after prior procurement of written informed consent. The patients did not receive calcium channel blockers in the postoperative period.

Flow recordings
Phasic coronary flow velocity was recorded in the proximal IMA graft with the use of a 0.014-inch, 12-MHz Doppler guide wire (FloWire; Cardiometrics, Inc, Mountain View, CA). The tip of the Doppler guide wire was advanced precisely 5 cm into the IMA. An optimal Doppler signal was obtained by moving the guide wire slightly into the vessel lumen and adjusting the velocity range. The final position of the guide wire was confirmed by the injection of contrast medium. Frequency analysis of the Doppler signal was carried out in real time by fast Fourier transformation with the use of a velocimeter (FloMap; Cardiometrics, Inc). After Doppler signals were recorded under baseline conditions, they were measured again after injection of adenosine (30 µg) into the IMA graft. To obtain the maximal peak velocity during hyperemia, we recorded the Doppler signals for 1 minute after the injection of adenosine. Systolic and diastolic peak velocities and the time average of the instantaneous spectral peak velocity (time-averaged peak velocity) were determined from the phasic coronary blood flow recordings. The flow volumes in the IMA graft were calculated as proposed by Doucette and associates [11], using the mean velocity and the cross-sectional area. To obtain the cross-sectional area, we measured the graft lumen diameter with the use of quantitative angiographic analysis. This was performed with an automated coronary analysis program with edge contour detection (CAAS II; Pie Medical, Maastricht, The Netherlands). The first well-opacified end-diastolic frame detected by simultaneous electrocardiogram recording was selected for analysis. The lumen diameter of the vessel at the level of the blood velocity recordings was measured by an automated contour detection algorithm. Absolute dimensions were calculated by reference to the known size of the shaft of the empty diagnostic catheter, measured 2 to 3 cm from the tip positioned within the ostium of the graft. The cross-sectional area of the graft was then computed; for this purpose, a circular cross section was assumed. Finally, the coronary flow reserve (CFR) was obtained from the ratio of maximal to baseline flow.

Statistical analysis
Data were analyzed with the use of the Statistica 5.0 for windows software package (StatSoft, 1995; StatSoft, Tulsa, OK). All data are expressed as mean values ± standard deviation (SD). Statistical analysis comparing the data was performed with paired two-tailed t testing. A p value of less than 0.05 was expected to be statistically significant.

	Results

Top Abstract Introduction Material and methods Results Comment Discussion References

 
No patients died within the first 6 months postoperatively. No myocardial infarctions occurred during this period. The hemodynamic and angiographic data are shown in Table 2. There were no significant differences with respect to these data between the three study groups. In the early postoperative angiography, 333 of 344 (97%) arterial graft anastomoses were patent. Six graft anastomoses to the right coronary artery, four to the circumflex artery, and one to the left anterior descending artery (LAD) were occluded. There was no difference between right IMA and radial artery conduits with respect to patency rate.

Quantitative angiographic analysis measurements revealed a significant (p < 0.05) higher graft lumen diameter in the 6-month examination compared with the early follow-up in all study groups (1: 3.76 ± 0.60 vs 3.20 ± 0.46 mm; 2: 3.70 ± 0.51 vs 3.26 ± 0.44 mm; 3: 3.75 ± 0.61 vs 3.29 ± 0.51 mm). There were no significant differences in lumen diameter between the three groups (p > 0.2).

The highest baseline flow volume was seen in group 3 in the early (93.9 ± 39.5 mL/min) as well as in the 6-month examination (86.0 ± 40.1 mL/min). This flow was significantly (p < 0.05) higher than in group 2 at both time points (75.8 ± 27.3 and 69.1 ± 35.5 mL/min). The baseline flow in group 1 (58.0 ± 28.4 and 55.2 ± 29.2 mL/min) was significantly (p < 0.05) lower compared with the other groups in both measurements (Fig 1).

View larger version (36K): [in this window] [in a new window]   Fig 1. Baseline flow in the IMA graft early (1 week) and late (6 months) postoperatively in the three study groups (*p < 0.05).

View larger version (39K): [in this window] [in a new window]   Fig 2. Maximum flow in the IMA graft early (1 week) and late (6 months) postoperatively in the three study groups (*p < 0.05; **p < 0.01).

View larger version (34K): [in this window] [in a new window]   Fig 3. CFR early (1 week) and late (6 months) postoperatively (**p < 0.01).

View larger version (28K): [in this window] [in a new window]   Fig 4. Baseline flow (left y-axis) and CFR (right y-axis) 1 week postoperatively compared between left IMA/right IMA (n = 40) and left IMA/radial artery T-grafts (n = 42) 1 week after revascularization.

	Comment

Top Abstract Introduction Material and methods Results Comment Discussion References

Actually, to date, no study has indicated functional limitations of IMA grafts in this configuration. In a recently published study [10], we could show that flow volume and flow reserve of the IMA are adequate for multiple coronary anastomoses. Flow data, however, exhibited a relatively high variability. The question arises as to which factors could influence flow parameters in IMA grafts in this configuration causing this high variability.

Intravascular flow wire measurements in single IMA grafts [15] have shown a correlation between the status of the native recipient LAD and the quantitative flow in the single IMA graft. After complete arterial revascularization using the T-graft technique, the anatomic situation is more complex due to numerous anastomoses being supplied by the IMA graft. One can hypothesize that the status of the native coronary arteries influences flow parameters as well in IMA T-grafts after complete arterial revascularization. Therefore, the objective of our study was to investigate whether the status of the native coronary arteries has an influence on flow parameters in IMA grafts in this configuration. Known factors influencing quantitative flow volume in coronaries are heart rate, blood pressure, left ventricular preload, and contractility [16]. These factors were comparable in our three study groups. We could show that, as a result of competitive flow phenomena, the baseline and maximum blood flow in the bypasses is significantly lower when the coronary arteries are patent and affected only by stenosis. If there is a higher flow demand (due to one ore more occluded native coronaries), the IMA is capable of meeting these higher flow requirements and the grafts have a higher flow volume. Because it is a ratio, CFR determination is substantially dependent on baseline flow values. Therefore, an augmented baseline flow may lead to a decreased flow reserve. Interestingly, in our study, there were no significant differences in CFR between the three study groups, although significantly different baseline flow volumes were measured. Even in study group 3, with the highest baseline flow volume, the CFR was not diminished when compared with the other groups.

When we compare our flow data with literature data with single IMA grafts, there is no evidence indicating functional limitation for the IMA grafts in the setting of complete arterial revascularization with T-grafts. Our study revealed a higher baseline flow volume in the left IMA when compared with literature data for single IMA grafts. In 15 patients, Gurne and associates [17] measured 38 ± 22-mL/min flow under baseline conditions using a Doppler flow wire in the early postoperative period; interestingly, the mean lumen diameter of the single IMA (2.39 ± 0.41 mm) was also lower in this study compared with our results in IMA T-grafts (3.25 ± 0.48 mm). Late postoperatively, Gurne and associates [17] noted a similar, nonsignificant decline in baseline flow in single IMA grafts; a flow of 30 ± 12 mL/min was reported 19 months after operation. This is consistent with our findings of a nonsignificant decrease in baseline flow in the 6-month examination. Thus, both early and later postoperative flow volume were more than twofold higher in IMA T-grafts compared with single IMA grafts.

The coronary flow reserve, however, is much more relevant than baseline flow, and indeed represents the most important parameter for a potential limitation of grafts or coronary vessels. In our study, we measured a CFR between 1.9 and 2 early postoperatively in the three patient groups. This is as high as reported for single IMA grafts, in which a CFR of 1.8 ± 0.3 was found in 16 patients 2 weeks postoperatively [18]. In our study, we observed a significant rise in coronary flow reserve at the 6-month follow-up compared with the early postoperative examination in all three groups. Akasaka and associates [18] showed similar results in single IMA grafts (2.6 ± 0.3) 1 year postoperatively. This is almost identical with the CFR we measured in IMA T-grafts in the 6-month examination. Thus, we could not find any evidence of flow limitation in the T-graft configuration.

The relatively low CFR values in the early postoperative period may be due to the recent surgical trauma and the resulting effects on the microvasculature. Many abnormalities of the microvasculature may diminish maximal flow capacity independently of the hemodynamic performance of the bypass conduit. In the early postoperative period, a certain degree of "stunning" is still present after bypass surgery; a restriction of the cardiac flow reserve has been described in connection with "stunned myocardium" [19].

Conclusion
As a result of competitive flow phenomena, baseline and maximum flow volume in IMA grafts after complete arterial revascularization are dependent of the status of the native coronary arteries. Even if there is a high flow demand (due to two or more occluded native coronaries), the IMA possess an adequate CFR, as high as in IMA T-grafts with lower flow volume or as reported in the literature for single IMA grafts to the LAD. Therefore, we conclude that the functional and morphological adaptation capability of the IMA is sufficient to meet the higher flow volume requirements after complete arterial revascularization with the T-graft technique.

	Discussion

Top Abstract Introduction Material and methods Results Comment Discussion References

 
DR IRVING L. KRON (Charlottesville, VA): That was an excellent study. Our group had used quantitative thallium scintigraphy many years ago to compare IMA flows with vein grafts and demonstrated, just like you did, certainly with single-vessel bypass, that the flow reserve was equivalent if not superior with internal mammary. I had two questions for you. Do you think your results would be the same in the acute phase? In other words, if someone comes to the operating room in an acutely ischemic state, would the IMA hold up in that situation? And secondly, you did not mention, but were all the grafts patent? Would slow reserve of the IMA or one of its side anastomoses possibly be reduced by 50% or less stenosis?

DR MARKWIRTH: To the first question: in the acute phase, the flow reserve is diminished due to several interfering factors. Many abnormalities of the microvasculature (eg, postischemic vasodilation of microvessels) may impair maximal flow capacity independently of the hemodynamic performance of the bypass conduit. Intraoperatively, a certain degree of "stunning" is still present and a restriction of the cardiac flow reserve has been described in connection with "stunned myocardium." We think that our measurements 1 week and 6 months after operation represent the more physiological setting for determination of flow reserve. To the second question: the patency rate of the arterial grafts in the early postoperative angiography was 97%, and in the 6-month angiography, the patency rate was 93%.

DR DAVID P. DEUTSCH (Long Beach, CA): Were any of these patients on calcium channel blockers or nitrates postoperatively?

DR MARKWIRTH: No, this was not the treatment of choice. The patients received a single dose of glycerol trinitrate during cardiac catheterization, but they did not get a special treatment of vasoactive drugs in the long-term follow-up.

	References

Top Abstract Introduction Material and methods Results Comment Discussion References

 

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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): Olaf Wendler Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Markwirth, T. Articles by Wendler, O. Search for Related Content PubMed PubMed Citation Articles by Markwirth, T. Articles by Wendler, O. Related Collections Cardiac - physiology Coronary disease