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J Thorac Cardiovasc Surg 1994;108:1115-1118
© 1994 Mosby, Inc.
CARDIOPULMONARY BYPASS, |
Montreal, Quebec, Canada
From the Departments of Surgery, Experimental Pathology, and Nuclear Medicine, Montreal Heart Institute, Montreal, Quebec, Canada.
Received for publication Nov. 19, 1993. Accepted for publication May 17, 1994. Address for reprints: Michel Carrier, MD, Montreal Heart Institute, 5000 Belanger St. East, Montreal, Quebec H1T 1C8, Canada.
Abstract
Perfusion of the right ventricular myocardium with retrograde infusion of cardioplegic solution through the coronary sinus has been reported to be less than optimal. To study left and right ventricular perfusion during retrograde and antegrade coronary sinus cardioplegia, we added 0.5 mCi of thallium 201 to 500 ml of hyperkaliemic crystalloid cardioplegic solution injected retrogradely into the coronary sinus at low perfusion pressure (20 to 40 mm Hg) in 14 dogs and antegradely in the ascending aorta in seven dogs. The cardioplegic solution was cold (4° C) in eight animals perfused retrogradely and warm (21° C) in 13 animals. After aortic crossclamping, the ascending aorta and the left and right ventricles were vented and cardioplegic solution was injected retrogradely into the coronary sinus. Antegrade injections were performed after aortic crossclamping and venting of the left and right ventricles and of the left and right atrium. After cardioplegic arrest, the heart was harvested, fixed, and scanned with a gamma camera. With cold retrograde cardioplegia, 82% ± 5% of the injected thallium 201 activity was identified in the myocardium—71% ± 9% for warm retrograde perfusion and 80% ± 3% for antegrade perfusion (p > 0.05). Focal areas of hypoactivity in the septum and in the right ventricular free wall were present at scintigraphic imaging in all animals receiving retrograde perfusion. In conclusion, most thallium 201 activity of cardioplegic solution injected retrogradely in the coronary sinus was identified in the myocardium, but focal areas of hypoactivity in the septum and in the right ventricular free wall were present, indicating uneven distribution. Temperature of the crystalloid solution had no effect on the myocardial distribution of the thallium 201 radiotracer in the myocardium. (J THORACCARDIOVASCSURG1994;108:1115-8)
Retrograde administration of cardioplegic solution through the coronary sinus has gained in popularity in clinical practice, and excellent results have been reported. 
1-5 The simplicity of the transatrial approach has greatly contributed to its spreading use. 6,7 However, adequate distribution of the cardioplegic solution to the septal and the right ventricular myocardium when injected by the coronary sinus route has been questioned. 8 Moreover, Lolley and Hewitt 9 reported that only 25% of the blood infused into the coronary sinus reaches the capillary bed and the myocardial cell. Therefore, myocardial distribution and capillary flow remain of concern when the retrograde route for cardioplegic administration is used.
The objective of the present study was to evaluate the myocardial distribution of cardioplegic solution injected antegradely and retrogradely through the coronary sinus and the capillary flow to the myocardial cell. On the basis of the results of current clinical experience, we hypothesized that coronary flow and myocardial distribution with the retrograde route for cardioplegia are adequate.
MATERIAL AND METHODS
Myocardial distribution and capillary flow during retrograde infusion of cardioplegic solution through the coronary sinus was studied in 14 dogs, 25 to 30 kg in body weight. The animals were anesthetized with sodium pentobarbital (30 mg/kg), and their lungs were ventilated with a Harvard respirator (Harvard Apparatus, S. Natick, Mass.). A median sternotomy was performed, and transatrial cannulation of the coronary sinus with a coronary sinus catheter (self-inflating balloon catheter, 14F, Research Medical Inc., Midvale, Utah) was done after systemic heparinization (3 mg/kg).
Thallium 201, 0.5 mCi, was added to 500 ml of hyperkalemic crystalloid cardioplegic solution containing 130 mmol of sodium, 135 mmol of chloride, 3 mmol of calcium, 28 mmol of lactate, 20 gm of mannitol, 0.17 gm of sodium bicarbonate, and 34 mEq of potassium chloride per liter. A cold crystalloid solution was used (4° C) in eight animals, and a warm solution (21° C) was infused in six animals.
Cardioplegic solution was injected retrogradely into the coronary sinus at low perfusion pressure (20 to 40 mm Hg) after ligation of the azygos vein, of the superior and inferior venae cavae, and after aortic crossclamping. The ascending aorta and the left and right ventricles were vented. Effluent solutions from vented catheters were collected and analyzed. After cardioplegic arrest and complete injection of the cardioplegic solution, the heart was harvested, soaked in polyurethane foam, cut into 7 mm thick transverse slices, and scanned with a conventional planar gamma camera (256 x 256 x 16 bit matrix 106 counts). Effluent samples were counted for 5 minutes in a gamma counter (Minaxi 5000; Packard Instrument Co., Inc., La Grange, Ill.). 10
Thallium 201 activity in the myocardium and in effluents from the left ventricle, the right ventricle, and the aorta was calculated and expressed as percent of total dose of the injected radioactive tracer.
In a group of seven dogs, myocardial distribution and capillary flow were studied during antegrade crystalloid cardioplegia (21° C) by means of the same protocol. In this group, effluent solutions from vented left and right atria and from left and right ventricles were collected and analyzed.
The data are presented as mean and standard deviation. Differences between groups were studied with the Student's t test and the analysis of variance. The level of statistical significance was established at 95%. All animals were treated in accordance with the "Guide for the Care and Use of Laboratory Animals" published by the National Institutes of Health (NIH publication No. 85-23, revised 1985).
RESULTS
Analysis of the capillary flow showed that 82% ± 5% and 71% ± 9% of total thallium 201 activity was identified in the myocardium of hearts perfused retrogradely with cold and warm cardioplegic solution, respectively (p > 0.05). Of the total thallium 201 activity, 7% ± 3% and 15% ± 6% was identified in the aortic effluent, 6% ± 2% and 10% ± 5% in the right ventricular effluent, and 3% ± 1% and 2% ± 1% in the left ventricular effluent after retrograde injection of cold and warm cardioplegic solutions, respectively (p > 0.05) (Fig. 1). No significant difference (p > 0.05) in myocardial distribution between warm and cold retrograde infusions was detected.
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Analysis of scintigraphic images of retrogradely perfused hearts showed small focal areas of hypoactivity in the septum and in the right ventricular free wall of all animals (Fig. 2). On the contrary, the distribution of thallium 201 activity in the other area of the left ventricle was found to be homogeneous. In antegradely perfused hearts the distribution of thallium 201 activity was homogeneous in both the left and the right ventricular walls
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Recent clinical experience has clearly shown that retrograde injection of cardioplegic solution through the coronary sinus is effective in protecting the myocardium during cardiac operations. 1-6 Both cold and warm retrograde cardioplegia have been used, and our study indicates that the temperature of the solution has no impact on capillary flow or on the myocardial distribution of the solution.
Several experimental studies have reported that retrograde cardioplegia results in poor perfusion of the septal and right ventricular myocardium. 8,11-13 Partington and associates 14 found that the nutritive flow to the right ventricle was significantly less than that to the left ventricle. In contrast, our study with thallium 201 scintigraphy showed only small areas of the right ventricular free wall and of the septum to be nonhomogeneously perfused with the retrograde cardioplegic infusion (Fig. 2) as compared with antegrade injection. The clinical inference of this observation is not clear. Postoperative right ventricular function was found to be similar in patients who received retrograde and in those with antegrade infusion of cardioplegic solution. 2,15 This result may be due to the volume and flow rate of cardioplegic infusions. Pan-Chik and coworkers, 16 in studying the hemodynamic significance of the coronary vein valves, suggested that the presence of competent vein valves may result in maldistribution of the retrograde cardioplegic solution, but no competent valves were encountered in dog hearts. Aronson and colleagues, 17 using intraoperative contrast echography in human hearts, demonstrated a homogeneous distribution of retrograde cardioplegic infusion to all left ventricular, septal, and even right ventricular myocardium.
It has been suggested that more than 70% of the cardioplegic solution perfused through the coronary sinus would be shunted in the right ventricle, through the thebesian vessels, and therefore that capillary and nutritive flow to the myocardium would be insufficient. 9 In our study, more than 70% of the injected thallium 201 activity was detected in the myocardium. Moreover, only 6% to 10% of the thallium 201 activity was found in the right ventricular effluent. This would indicate a high transcapillary flow and a low venous shunting with retrograde perfusion.
Thallium 201 is a radioactive tracer used to study myocardial perfusion that has the ability to accumulate in the myocardium proportionally to the rate of coronary blood flow. 18 Thallium 201 has many analogies with potassium. Both are monovalent cations, have hydrated ionic radii of similar size, and their transport involves the sodium-potassium adenosinetriphosphatase pump. 19 After intravenous injection, the myocardial thallium 201 concentration is linearly proportional to the coronary blood flow over a wide range, from about 10% up to three times normal arterial blood flow, 20,21 and its extraction efficiency is around 85%. 22
In the present study, even though the thallium 201 myocardial perfusion was retrograde in one group of animals, and under nonphysiologic physical parameters (temperature, perfusion pressure, etc.), the thallium 201 extracted by the myocardium after a single passage was comparable (71% to 82%). Thus these data suggest that most cardioplegic solution if not all was available to the myocardial cell and little was shunted through the thebesian vessels. This characteristic of the thallium 201 tracer leads to the conclusion that the capillary flow was high in the present study, because 71% to 82% of the activity was identified in the myocardium. This finding is corroborated by the results of clinical studies, whereas it is at variance with several experimental studies in which other methods have been used to assess myocardial capillary flow. Differences in the experimental approach could explain the variation in results. 23
In conclusion, retrograde infusion of cardioplegic solution through the coronary sinus results in effective perfusion of the myocardium, and only a small fraction of the cardioplegic solution is shunted through thebesian veins directly in the right ventricle. However, the focal areas of thallium 201 hypoactivity found in the septum and in the right ventricular free wall may be the result of less homogeneous distribution in some cases and remains a concern. The temperature of the cardioplegic solution had no effect on thallium 201 uptake of the myocardium.
Footnotes
Dr. Carrier is a scholar from "Le Fonds de Recherche en Santé du Québec" (FRSQ). 
References
This article has been cited by other articles:
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  A. B. Ericsson, S. Takeshima, and J. Vaage Simultaneous Antegrade And Retrograde Delivery Of Continuous Warm Blood Cardioplegia After Global Ischemia J. Thorac. Cardiovasc. Surg., March 1, 1998; 115(3): 716 - 722. [Abstract] [Full Text] [PDF]
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 M. Carrier, L. C. Pelletier, and N. R. Searle Does Retrograde Administration of Blood Cardioplegia Improve Myocardial Protection During First Operation for Coronary Artery Bypass Grafting? Ann. Thorac. Surg., November 1, 1997; 64(5): 1256 - 1262. [Abstract] [Full Text]
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M. Carrier, T. K. Leung, B. C. Solymoss, R. Cartier, Y. Leclerc, and L. C. Pelletier Clinical Trial of Retrograde Warm Blood Reperfusion Versus Standard Cold Topical Irrigation of Transplanted Hearts Ann. Thorac. Surg., May 1, 1996; 61(5): 1310 - 1314. [Abstract] [Full Text]
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A. Ardehali, H. Laks, D. C. Drinkwater Jr, R. N. Gates, and E. Kaczer Ventricular Effluent of Retrograde Cardioplegia in Human Hearts Has Traversed Capillary Beds Ann. Thorac. Surg., July 1, 1995; 60(1): 78 - 82. [Abstract] [Full Text]
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