Demonstration of Uneven. the infusion on myocardial temperature was insufficient

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1 Demonstration of Uneven in Patients with Coronary Lesions Rolf Ekroth, M.D., HAkan erggren, M.D., Goran Sudow, M.D., Josef Wojciechowski, M.D., o F. Zackrisson, M.D., and Goran William-Olsson, M.D. ASTRACT Low temperature is an important factor in protecting the myocardium during an operation on the heart. This can be difficult to accomplish if the cold cardioplegic solution is hindered by occlusions or stenosis of the coronary arteries. We used thermography to study myocardial temperature during infusion of cold cardioplegic solution. Slow cooling was recorded distal to coronary stenosis or occlusions, thereby indicating insufficient protection of the myocardium in these areas. Cooling the myocardium by infusion of cold cardioplegic solution into the aortic root has improved the results of cardiac operations. Coronary occlusions or stenosis can cause an uneven distribution of the cold solution and thereby produce areas of insufficient protection in the myocardium. We used thermography to demonstrate the course of events during infusion of the cardioplegic solution. Material and Methods Ten patients were investigated. Two had aortic stenosis and no coronary lesions, 1 had aortic stenosis and stenosis of the left anterior descending coronary artery and the left circumflex artery, and 7 had coronary stenosis of varying degree. After the institution of extracorporeal circulation, the aorta was cross-clamped and 1 liter of cold (4 C) cardioplegic solution was infused by gravity through a 3 mm cannula into the aortic root from a height of 1 meter above the aortic root. Infusion time was kept within 8 to 10 minutes. In 6 patients in whom the effect of From the Department of Thoracic and Cardiovascular Surgery, Department of Radiology, Sahlgrenska sjukhuset, Goteborg, Sweden. Accepted for publication Sept 27, Address reprint requests to Dr. William-Olsson, Department of Thoracic and Cardiovascular Surgery, Sahlgrenska sjukhuset, S Goteborg, Sweden. the infusion on myocardial temperature was insufficient as judged by the thermographic appearance, additional cold solution was infused. In order to obtain a frontal view of the heart with maximal exposure of the left ventricle, gauze pads were placed in the pericardium behind the ventricles and the operating table was tilted laterally toward the thermocamera (AGA thermovision 680*). The pictures recorded showed lowering temperatures as represented by increasingly darkening areas. lack areas in these studies indicated temperatures below 20 C. Thermographic pictures were taken at 60 second intervals beginning just before the start of infusion of the cardioplegic solution. To control the accuracy of the thermography, needle thermistors were used to measure myocardial temperatures at different points. Results In the 2 patients without coronary lesions, the myocardial temperature was less than 20 C after approximately 4 minutes. All 8 patients with coronary lesions had various degrees of uneven and delayed cooling of the myocardium. In 2 of them, the myocardium was cooled to less than 20 C after about 8 minutes. In 6 patients, an additional 500 ml of cardioplegic solution was infused in an attempt to lower the temperature below 20 C. This was accomplished in 3 patients, but in the other 3, a regional insufficient cooling of the myocardium prevailed (Figs 1 through 4). Eight patients had an uneventful postoperative course. Two of the patients with insufficient myocardial cooling had moderate to severe arrhythmias postoperatively. Comment It is important to achieve a uniform and sufficiently low temperature of the myocardium in AGA A, Lidingo, Sweden by Rolf Ekroth

2 342 The Annals of Thoracic Surgery Vol 29 No 4 April 1980 Fig I. (A) Thermographic picture of a heart with two stenoses in the left anterior descending coronary artery (LAD) after 1 minute of cardioplegic infusion shows that most parts of both ventricles are cold. The area around the LAD is still warm. Notice especially the apical part of the heart. The 1 corresponds to the left ventricle, 2 to the pericardium, and 3 to venous cannulas. () After 5 minutes, there is almost complete cooling of the heart except for a small apical area. Here, 1 corresponds to a small warm apical area, and 2 and 3 are the same as in IA.

3 343 Ekroth et al: Thermographic Demonstration of Uneven Myocardial Cooling 2 J I Fig 2. (A) Thermographic picture of a heart with proximal stenoses of the left anterior descending coronary artery and an obtuse margindl artery. After 3 minutes, the right ventricle is sufficiently cold while most of the left ventricle is still more than 20 C. () After 9'12 minutes, there is complete cooling of the heart's exposed surface. The 1 corresponds to the right ventricle, 2 to the pericardium, 3 to venous cannulas, 4 to the retractor, and 5 to an artifact. 3

4 344 The Annals of Thoracic Surgery Vol 29 No 4 April Fig 3. Therrnographic picture of a heart with proximal stenoses of the left anterior descending coronary artery, the left circumflex artery, and an obtuse marginal branch. (A) The thermographic appearance after 2 minutes. The right ventricle is cold but the left ventricle has a large warm area. The right ventricle is indicated by 1, and the pericardium by 2. The white area over the right ventricle is the venous cannula, indicated by 3. () The warm left ventricular area is reduced in size after 8 minutes. Measurements by a needle thermistor in this area revealed a temperature of 28 C. A needle thermistor in the septum measured a temperature of 22 C and in the right ventricular wall, 19 C. order to assure a maximal protection during ischemic cardiac arrest following aortic crossclamping. Factors that can jeopardize this are myocardial hypertrophy, which makes the standard amount of cold cardioplegic solution inadequate, or stenotic lesions of the coronary arteries, which prevent a rapid and even distribution of the perfusate. Needle thermistors have been used to control the effect of the cold cardioplegic infusion [l, 21. However, this technique gives information only from local areas. In nonmonitored parts of the myocardium, hazardous insufficient cooling can occur. The thermographic method reveals not only the temperatures over the total exposed surface of the heart [31 but also the sequential events during cooling. The temperatures at the surface should be representative of the temperature of the whole myocardium since cold cardioplegia has a protective effect throughout the myocardium. Furthermore, in our study, the thermographic appearance correlated well with the temperatures recorded by intramyocardially located thermistors. The two hearts with aortic stenosis and myocardial hypertrophy rapidly and evenly decreased in temperature. Hypertrophy alone did not appear to cause insufficient cooling when our cold cardioplegia technique was used. Coronary lesions caused a slow cooling of the myocardium, and the findings in patients with

5 345 Ekroth et al: Thermographic Demonstration of Uneven Myocardial Cooling 3 Fig 4. Thermographic picture of a heart with stenotic lesions of the three main coronary arteries. (A) After 2 minute, most of the ventricles are insufficiently cold. () Eleven minutes following a total infusion of approximately 2,300 ml of cold cardioplegic solution, most of the myocardium is still insufficiently cold. The 1 corresponds to a small cold area, 2 to the pericardium, and 3 to venous cannulas. The rest corresponds to the ventricles, which are insufficiently cold. such lesions revealed the insufficiency of using our standardized technique for cold cardioplegia. To overcome this drawback, a larger amount of cold cardioplegic solution should be used along with topical cooling. Also, injections of cold solution into the bypass graft as soon as an anastomosis is completed will help to achieve better and more reliable myocardial protection. References 1. raimbridge MV, Chayen J, itensky L, et al: Cold cardioplegia or continuous coronary perfusion? J Thorac Cardiovasc Surg 74:900, Conti VR, ertranou EG, lackstone EH, et al: Cold cardioplegia versus hypothermia for myocardial protection: randomized clinical study. J Thorac Cardiovasc Surg 76:577, Robicsek F, Masters TN, Svenson RH, et al: The application of thermography in the study of coronary blood flow. Surgery 84:858, 1978