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J Thorac Cardiovasc Surg 2003;126:1076-1079
© 2003 The American Association for Thoracic Surgery
Cardiopulmonary support and physiology |
a Department of Cardiology and Cardiac Surgery, "G. D'Annunzio" University, Chieti, Italy
Received for publication July 18, 2002; revisions received September 3, 2002; revisions received December 2, 2002; accepted for publication December 19, 2002.
* Address for reprints: Antonio Maria Calafiore, MD, "G. D'Annunzio" University, Division of Cardiac Surgery, c/o S. Camillo de' Lellis Hospital, via C. Forlanini, 50, 66100, Chieti, Italy
calafiore{at}unich.it
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Abstract |
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 Top Abstract Patients and methodsResultsCommentReferences |
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METHODS: In 21 patients who had Y thoracic artery grafts, the flow was measured in the main stem of the left internal thoracic artery, in the left internal thoracic artery branch, and in the right internal thoracic artery. A transit time Doppler flowmeter was used. Measurements were repeated after the injection of a bolus of 20 µg/kg dobutamine.
RESULTS: At baseline condition, the mean blood flow was 44.8 ± 24.2, 23.4 ± 11.5, and 21.4 ± 15.3 mL/min in the main stem of the left internal thoracic artery, in the left internal thoracic artery branch, and in the right internal thoracic artery, respectively. After dobutamine injection, these values increased to 93.2 ± 49.8, 46.1 ± 22.6, and 42.5 ± 31.2 mL/min, respectively. Flow reserve was 2.1 ± 0.6, 2.2 ± 0.9, and 2.1 ± 0.9 mL/min, respectively.
CONCLUSIONS: Intraoperative injection of dobutamine increases the flow in the Y thoracic graft by more than two times, not only in the main stem but also in each branch. This finding attests to the safety of Y thoracic conduits in terms of hemodynamic potential.
The present study was conceived to determine the immediate flow reserve of Y thoracic artery conduits by means of intraoperative flow measurement at rest and in stress conditions.
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Patients and methods |
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Surgical technique
The surgical technique used has been described elsewhere.5 The majority of the operations (11/21) were performed with normothermic cardiopulmonary bypass; for the others, our previously described no-pump method was used.6
Intraoperative measurements
After completion of the last anastomosis, patients were weaned from extracorporeal circulation (for those cases in which the heart-lung machine was used). Hemodynamic stabilization blood flow was measured in the main stem of the left thoracic artery (LMS) as well as in the two branches of the Y graft (left internal thoracic artery [LITA] and right internal thoracic artery [RITA], respectively) using a dedicated flowmeter (Cardiomed, Medi-Stim, Oslo, Norway). After careful evaluation of the morphologic appearance of the flowmetric curve and of the flow value, only cases in which there was a wide diastolic waveform and a mean blood flow of 10 mL/min or more were considered acceptable. All the cases in the present study fulfilled these criteria.
Mean blood flow in the LMS, LITA, and RITA was then recorded, taking care to maintain a mean arterial pressure of almost 70 mm Hg.
A 20 µg/kg dobutamine bolus (Dobutrex, Eli Lilly Italia, Sesto Fiorentino, Italy) was then injected into the patients and all the measurements were repeated when the double product (heart rate x systolic blood pressure) was greater than 10,000.
Coronary flow reserve (CRF) was obtained from the ratio of the maximum to the baseline flow in each segment where the flow was recorded.
Statistical analysis
Results are expressed as mean value ± SD unless otherwise indicated. Statistical analysis comparing two groups was performed with paired 2-tailed t testing for the mean. (SPSS software, SPSS, Inc, Chicago, Ill).
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Results |
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The LITA branch of the Y thoracic grafts was used to revascularize the left anterior descending artery, whereas the RITA was anastomosed to the obtuse marginal branch in all cases. In no case was the RITA used to graft the distal branches of the right coronary artery.
Hemodynamic and flow measurement values at baseline and after dobutamine administration are summarized in Table 3. At baseline condition, the mean blood flow in the LMS, the LITA, and the RITA was 44.8 ± 24.2, 23.4 ± 11.5, and 21.4 ± 15.3 mL/min, respectively. After dobutamine injection, these values increased to 93.2 ± 49.8, 46.1 ± 22.6, and 42.5 ± 31.2 mL/min, respectively, showing a more than twofold increase in capacity of the Y conduits in response to the moderate increase in double product caused by the dobutamine injection. CRF was 2.1 ± 0.6, 2.2 ± 0.9, and 2.1 ± 0.9 mL/min, respectively.
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All patients had a good postoperative recovery and were discharged from the hospital after a mean of 4.4 ± 1.3 days. After 23.3 ± 5.9 months from surgery, no case of clinical evidence of ischemia recurrence was reported. All the patients underwent myocardial scintigraphy that showed no ischemia in the territories grafted with both ITAs.
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Comment |
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Our group5 has shown that the adoption of Y grafts allows the performance of a greater number of anastomoses and a wider myocardial revascularization than does the use of both in situ thoracic arteries; furthermore, Y grafts do not carry any detrimental effect in terms of early clinical outcome and midterm angiographic patency.
To date, the thoracic artery is the only arterial conduit for which a solid demonstration of excellent long-term patency and clinical benefits is available (for all the others, such advantages are still only speculative). It can be hypothesized that the adoption of composite thoracic grafts can represent the optimal modality of surgical myocardial revascularization by allowing the performance of most (if not all) anastomoses using the ideal conduit.
However, the major concerns related to the widespread adoption of the composite thoracic grafts arise from the lack of substantial data on their flow capacity and the hypothesized possibility that such conduits can be unable to provide sufficient flow to two or three coronary territories, especially in the early postoperative period and in a condition of increased myocardial oxygen request.4
The present study was conceived to investigate the flow capacity of Y thoracic grafts in the period immediately after their construction. This time frame was selected because, at that moment, the thoracic artery has not yet undergone the described progressive adaptation to the postoperative increase in flow demand, so that if the possibility of a Y graft insufficiency exists, this time period should be the one of highest risk.
Our data demonstrate how, in the immediate postconstruction period, the Y thoracic conduit has the potential to augment its flow more than 2-fold in response to the moderate increase in myocardial oxygen request elicited by dobutamine injection. This happens not only in the main LMS but also in both of its branches. Although without metabolic data the presence of a subclinical degree of myocardial ischemia cannot be definitely ruled out, this wide capacity of flow increase, combined with the absence of clinical and electrocardiographic evidence of ischemia in the operating room and in the early postoperative period and the low creatine kinase MB value in all study patients, strongly argues against any possible Y graft insufficiency.
These findings are in accord with those reported by Royse and colleagues7 (who described a 2.3-fold reserve of composite thoracic and radial artery grafts intraoperatively) and by Wendler and associates8 (who found in T thoracic grafts a flow capacity of 1.85 ± 0.31 mL/min at 1 week after surgery and 2.77 ± 0.77 mL/min 6 months postoperatively). More recently, investigations performed 6 months after surgery confirmed the effectiveness of composite thoracic artery grafts after dobutamine stress echocardiography.9 Markwirth and colleagues10 found that, 6 months after surgery, flow reserve in the T thoracic graft was 2.79 ± 0.92 mL/min. It was similar to the flow reserve in the LITA radial artery T graft (2.85 ± 0.99 mL/min) and was not influenced by the presence of one or more occluded distal territories. The results of our study show that the flow reserve that can be detected in acute dobutamine stress test intraoperatively is similar to the flow reserve that can be found in the late follow-up.
From our data, it is impossible to establish whether the observed increase in thoracic artery flow is mainly a consequence of the greater myocardial oxygen demand or of the increased systolic blood pressure and cardiac output. However, as the two conditions usually coexist in clinical practice, this theoretical issue seems to have minor practical implications. Similarly, our observations do not allow us to predict the patterns of flow into the different coronary territories. However, this study was intended to evaluate the immediate flow reserve of Y thoracic artery grafts and their capacity for serving more than one coronary bed under stress condition in the immediate postoperative period and did not pretend to schematize a complex issue such as the flow dynamics of composite grafts. The relative flow distribution would be dependent on the sizes of the respective coronary beds, the sizes of the grafted vessels, and the degree of native coronary stenosis; it is likely to be different from patient to patient. The operating surgeon must carefully evaluate the anatomic and physiologic aspects of the single case to identify the eventual contraindications to Y graft adoption, independently from every theoretical attempt to schematize or predict flow dynamics.
Even though further investigations on this subject are mandatory before recommending the routine adoption of Y grafts, our observations attest to the safety of Y thoracic conduits, in terms of hemodynamic potential, and provide an objective demonstration of their flow capacity even in the immediate postoperative period.
At present, the Y thoracic graft technique should be regarded as safe and effective and probably always should be adopted in those patients who are most likely to benefit from complete thoracic artery revascularization. The Y graft is able to substantially increase its flow, not only in the LMS but also in both branches.
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Footnotes |
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References |
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This article has been cited by other articles:
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  G. Di Giammarco, M. Pano, S. Cirmeni, P. Pelini, G. Vitolla, and M. Di Mauro Predictive value of intraoperative transit-time flow measurement for short-term graft patency in coronary surgery. J. Thorac. Cardiovasc. Surg., September 1, 2006; 132(3): 468 - 474. [Abstract] [Full Text] [PDF]
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 A. M. Calafiore, L. Weltert, M. D. Mauro, G. Actis-Dato, A. L. Iaco, P. Centofanti, M. L. Torre, and F. Patane Internal mammary artery MMCTS, November 29, 2005; 2005(1129): 1008. [Abstract] [Full Text] [PDF]
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 T. Fukui, S. Takanashi, Y. Hosoda, and S. Suehiro Total Arterial Myocardial Revascularization Using Composite and Sequential Grafting With the Off-Pump Technique Ann. Thorac. Surg., August 1, 2005; 80(2): 579 - 585. [Abstract] [Full Text] [PDF]
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