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J Thorac Cardiovasc Surg 2006;131:1344-1351
© 2006 The American Association for Thoracic Surgery

Cardiopulmonary Support and Physiology

Modeling of temperature mapping for quantitative dynamic infrared coronary angiography for intraoperative graft patency control

Jens Garbade, MD * , Cris Ullmann, Marcus Hollenstein, Markus Johannes Barten, MD, Stephan Jacobs, MD, Stefan Dhein, MD, Thomas Walther, MD, Jan Fritz Gummert, MD, Volkmar Falk, MD, Friedrich-Wilhelm Mohr, MD

Department of Cardiac Surgery, Heart Center, University of Leipzig, Leipzig, Germany.

Received for publication September 12, 2005; revisions received December 13, 2005; accepted for publication December 22, 2005.

* Address for reprints: Jens Garbade, MD, Department of Cardiac Surgery, Heart Center Leipzig, University of Leipzig, Struempellstrasse 39, 04289 Leipzig, Germany. (Email: jgmed93{at}hotmail.com).

OBJECTIVES: Intraoperative application of thermal coronary angiography based on dynamic infrared imaging leads to useful qualitative information concerning coronary artery bypass graft flow and anatomy. Additional quantitative flow estimation is desirable to detect graft failures. The aim of this study was to develop a heat-transfer model for quantitative flow estimation in an experimental setup. The first clinical results in coronary artery bypass grafting are reported.

METHODS: Dynamic infrared imaging was applied in pig hearts to collect video data of the rewarming process of the left anterior descending artery supplied by antegrade perfusion. For mathematic description, we used the dynamic enthalpy balance for open systems, and a Laplace transformation was carried out. Therefore the time constant {tau} was calculated by performing a nonlinear fit procedure on the averaged dynamic temperature curves recorded over a left anterior descending artery segment. Subsequently, left internal thoracic artery–left anterior descending artery bypass graft flow was assessed intraoperatively. Effective left anterior descending artery flow was determined by using a transit-time flowmeter.

RESULTS: Tau is a system constant and changes depending on the flow and the system capacity. Assuming system capacity to be constant, {tau} only depends on the flow. It follows from the differential equation that there is a potential relation between {tau} and the flow. An excellent comparison (R 2 = 0.968, P <.005) was demonstrated. By using the algorithms, quantitative flow estimation in pig hearts was possible. For clinical application, the formulas were applied to intraoperatively derived dynamic temperature curves with a good comparison to the actual left internal thoracic artery–left anterior descending artery flow.

CONCLUSION: The developed heat-transfer model allows for precise measurement of graft flow by using dynamic infrared imaging and can be applied for noninvasive graft flow estimation in beating-heart surgery.

Abbreviations and Acronyms CABG = coronary artery bypass grafting; DIRI = dynamic infrared imaging; LAD = left anterior descending artery; LITA = left internal thoracic artery; TCA = thermal coronary angiography; TTFM = transit-time Doppler flow measurement






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