Natural history of acute regional myocardial ischaemia revealed by infrared thermography in the canine heart.

Acute ischaemia of the left ventricular apical region has been produced by occluding for 60 min the upper mid-portion of the left anterior descending (LAD) coronary artery in the exposed heart of anaesthetized dogs. The decrease of the blood supply to this region was associated with characteristic morphologic patterns of the subepicardial temperature distribution which has been visualized with the aid of telethermography using an AGA 750 thermovision equipment. The thermographic cardiac images recorded during the progressive development and the restitution of the ischaemic events were evaluated with a new computer-assisted method developed by the authors and the results were described in composite histograms. The validity of the assumption that subepicardial cooling and warming in a particular region could be ascribed to a decrease and increase, respectively, of local flow, was substantiated by computerized simulation of myocardial heat transfer. In both the intact and the ischaemic (collateral-dependent) portions of the heart the issues of the quantitative evaluation of experimental data were indicative of important dynamic factors that elicit, depending upon some partially known individual characteristics, either compensatory adjustments in the entire myocardium (generalized vasodilation) or a demarcation of the infarct (selective flow decrease). Proofs obtained in additional experiments by administering exogenous catecholamines suggest that ischaemically transformed adrenoceptor mechanisms may play a significant role in the latter process. It was concluded that the quantitative thermographic technique developed by the authors is suitable, due to its considerable temporal and spatial resolution, for concurrent analysis of the time course and the gross morphologic details of cardiac ischaemia in vivo.