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J Thorac Cardiovasc Surg 1995;109:595-597
© 1995 Mosby, Inc.

LETTERS TO THE EDITOR

Myocardial rewarming during normothermic cardiopulmonary bypass

I. A. Regragui, FRCS, M. B. Izzat, FRCS, A. J. Bryan, FRCS, G. D. Angelini, FRCS

Department of Cardiac Surgery
University of Bristol
Bristol, United Kingdom

To the Editor:

We read with interest the recent paper by Bert and Singh Go 1 on right ventricular function after normothermic versus hypothermic cardiopulmonary bypass with multidose cold blood cardioplegia in patients undergoing myocardial revascularization. They observed a greater rewarming of the heart with normothermic perfusion which, however, did not compromise right ventricular function.

We have recently investigated, as part of a prospective randomized study, the contribution of cardiopulmonary bypass (CPB) perfusion temperature to myocardial rewarming during the arrest period with cold crystalloid cardioplegia. Sixty patients (55 men, mean age 60.1 ± 7.1 [standard deviation] years) undergoing coronary artery bypass grafting were randomized to either hypothermic (28° C), moderately hypothermic (32° C), or normothermic (37° C) CPB perfusion. Except for the conduct of the CPB, the intraoperative management of all patients was similar. Anesthesia was standardized, and the surgical technique included aortic and two-stage venous cannulation. An aortic root vent was used in all patients. Hypothermic and moderately hypothermic CPB was conducted with perfusate at appropriate temperature to reach a nasopharyngeal temperature of 28 degrees or 32° C, respectively. Patients in the normothermic group were actively rewarmed to 37° C throughout the period of CPB. Perfusion pressure was maintained at 50 to 60 mm Hg and flow at 1.8 L/m2 per minute for the hypothermic group, 2.0 L/m2 per minute for the moderately hypothermic group, and 2.4 L/m2 per minute for the normothermic group. Rewarming in the hypothermic and moderately hypothermic groups was commenced at the completion of all distal anastomoses.

After aortic crossclamping, electromechanical arrest was obtained with the antegrade infusion of 1000 ml of cold (6° to 8° C) St Thomas' Hospital No. 1 crystalloid cardioplegic solution (Martindale, Essex, United Kingdom). The myocardium was also cooled topically with 1000 ml of ice-cold (6° to 8° C) saline solution. An additional 300 ml of cardioplegic solution was administered after the initial 30 minutes of crossclamping or whenever electrical activity was seen on the electrocardiogram monitor.

Myocardial temperature was measured in triplicate with an 18 mm, 22-gauge thermocouple temperature probe (Mallinckrodt Medical, St Louis, Mo) from the interventricular septum, 1 cm medially and halfway down the course of the left anterior descending coronary artery immediately after the first dose of cardioplegic solution, before any supplementary dose of cardioplegic solution (if administered), and just before removal of the aortic crossclamp. Distal anastomoses were completed within a single aortic crossclamping period. There was no significant difference in patients' demographic and operative data in the three groups (GoTable I). No deaths occurred in the patients studied, although one patient had a perioperative myocardial infarct (hypothermic group).


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  		Table I. Demographic and operative data (data expressed as mean ± standard deviation)
 
All three groups had comparable degrees of cooling after the first dose of cardioplegic solution. The temperatures recorded before the supplementary doses of cardioplegic solution were also similar, as was the time between the two infusions (Fig. 1). There were no statistically significant differences among the three groups in the total volume of cardioplegic solution administered, the final temperature recorded before the removal of the aortic crossclamp, or the aortic crossclamp time (Fig. 1). The calculated rate of myocardial rewarming was 0.29° ± 0.13 degrees C/min for the hypothermic group, 0.28° ± 0.12 degrees C/min for the moderately hypothermic group, and 0.25° ± 0.16° C/min for the normothermic group (all not significant).



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  		Fig. 1. Intraoperative data. T1, Myocardial temperature after initial (1 L) dose of cardioplegic solution; T2, myocardial temperature before supplementary (300 ml) dose of cardioplegic solution; T3, myocardial temperature before removal of aortic crossclamp; T1-T2, time between T1 and T2 recordings; XCLAMP, aortic crossclamp time; PLEG. VOL., total volume of cardioplegic solution. Open columns, hypothermic CPB (28° C); light dotted columns, moderately hypothermic CPB (32° C); dark dotted columns, normothermic CPB (37° C).

 
Direct-current cardioversion for ventricular fibrillation on removal of the aortic crossclamp was required in 35% of patients in the normothermic group, significantly less than in the moderately hypothermic (60%) or the hypothermic (80%) groups (both p < 005). There was no significant difference in inotropic support required on discontinuation of CPB in the three groups (see GoTable I). One patient from the hypothermic group required the use of the intraaortic balloon pump after the operation. Intensive care and hospital stay were similar in the three groups (see GoTable I).

The data show that myocardial rewarming is not influenced by the CPB perfusion temperature in patients undergoing myocardial revascularization when cold crystalloid cardioplegic solution is used to maintain electromechanical arrest. Although Bert and Singh Go 1 observed enhanced myocardial rewarming with normothermic CPB when the myocardial temperature was measured after the construction of each distal anastomosis, it is worth noting that this difference narrowed gradually as extra doses of cardioplegic solution were given. Indeed, there was no statistically significant difference between the final myocardial temperatures measured in both groups. Despite the reduced volume of cardioplegic solution used in our study compared with the protocol adopted by Bert and Singh, Go 1 only one patient had an intraoperative myocardial infarction, and the overall need for inotropic support was minimal.

In conclusion, the results of our study support the view that a systemic perfusion temperature of 28° to 37° C has no influence on myocardial rewarming during intermittent antegrade cold crystalloid cardioplegic arrest.

12/8/58954

References

  1. Bert AA, Singh AK. Right ventricular function after normothermic versus hypothermic cardiopulmonary bypass. J Thorac Cardiovasc Surg 1993;106:988-96.[Abstract]



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