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J Thorac Cardiovasc Surg 2005;129:1192-1193
© 2005 The American Association for Thoracic Surgery
Brief Communications |
Department of Cardio-vascular and Thoracic Surgery, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Thiruvananthapuram, Kerala, India.
Received for publication June 20, 2004; revisions received September 3, 2004; accepted for publication September 22, 2004. * Address for reprints: Apurba K. Sarma, MCh, Flat No. B 2, New Faculty Building, SCT Housing Colony, Kumarapuram, Poonthi Rd, Thiruvananthapuram, Kerala, India 695 011 (E-mail: drapurbaks{at}yahoo.co.uk).
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Twisting of the aorta-coronary venous conduits is an extremely uncommon occurrence and has been reported by Roberts and colleagues1 with fatal outcome. There is a reported case of a twisted pedicled left internal thoracic artery (LITA) graft as well in which the patient survived, and the follow-up coronary angiogram revealed a patent LITA with good distal runoff.2 However, there are no published data in the English-language literature (PubMed, MEDLINE) regarding measurement of free flow from a pedicled LITA conduit in different degrees of twist. Therefore, to determine its significance on free flow, we studied the effect of varying degrees of clockwise twist of the LITA up to 360°.
Patients and methods
During the period from September 2003 through November 2003, 24 patients posted for elective coronary artery bypass grafting with standard cardiopulmonary bypass were entered into the study after approval from a departmental review committee and prior informed consent. The harvested pedicled LITA conduit was wrapped in gauze soaked in diluted papaverine and was transected after heparinization. The free flow of the LITA conduit was measured for a period of 1 minute at 0°, 180°, and 360° of clockwise twist. After each measurement, collected blood was returned to the patient through the proposed right atrial cannulation site to ensure relatively constant hemodynamics (heart rate, central venous pressure, and mean arterial blood pressure). Statistical analyses were done with the SPSS for Windows 11.0 software package (SPSS, Inc, Chicago, Ill).
Results
The mean free flow rates at twists of 0°, 180°, and 360° were 65.29 ± 16.68, 63.75 ± 16.94, and 64.74 ± 16.13 mL/min, respectively. The paired t test did not show statistical significance (P > .05) of the effect of twist on free-flow rate (Table 1). Simple linear regression analysis failed to show the influence of the hemodynamic variables on free-flow rates in the different degrees of twists.
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Twisted aorta-coronary venous grafts have been reported in fatal cases.1 Endean and coworkers,3 in an experimental study, showed thrombosis of vein graft within 4 hours at 200° twist and further reported that twist of more than 135° greatly reduces flow, leading to early graft thrombosis. We reported a case wherein the LITA conduit got twisted inadvertently 360° clockwise, but the graft remained patent and was documented with follow-up coronary angiography after 6 months.2 This occurrence stimulated us to study the influence of twist on the free flow rates of the pedicled LITA at varying degrees of clockwise twist.
This study showed no influence of the twist on LITA free flow. Why is this so? The structural tone of the arterial wall partially resists the twisting by distributing the torsion along the length of the vessel, and thus the twist acquires a spiral course4 rather than being limited to a short segment, which would otherwise compromise the flow. Second, we believe the thickness of the pedicle might not transmit the effect of the twist to the LITA proper. Furthermore, the architecture of the arterial wall and the absence of valves might play a part in keeping the lumen patent, even if there is a significant twist, and hence we see the flow in a twisted, pedicled arterial conduit.2 On the contrary, in a vein the thinner and more fragile structure renders it more sensitive to mechanical stress and makes it unable to distribute the forces of twisting along the length evenly.4 Gordon and colleagues5 reported that if rotation was applied uniformly over a 30-cm segment of (cadaver) saphenous vein, then on average, more than 2 full rotations produces collapse of the vein segment. However, we have not observed a similar effect in our study, probably because the conduit studied was a pedicled artery.
Furthermore, any twist in the rigid tube with uniform diameter increases resistance inside, thereby causing a pressure decrease and decreasing the flow through it. The thoracic artery, on the contrary, is a distensible elastic conduit (tube), and therefore on twisting, there is no significant increase in the resistance and pressure decrease, and hence there is no influence on the free flow.
This lack of variation in the free flow after a significant twist in a pedicled conduit is a unique observation. However, further research is warranted to see the short-term, as well as the long-term, hemodynamic performance of the twisted pedicled graft. We conclude that there is no significant variation in the free flow of a pedicled LITA conduit up to 360° of clockwise twist.
Acknowledgments
We thank Dr Sankara Sarma P and Mr S. Muraleedharan Nair for statistical analysis.
References
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