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Department of Cardiothoracic Surgery, John Radcliffe Hospital, Oxford, OX3 9DU United Kingdom
(Email: xy.jin{at}orh.nhs.uk).
To translate compelling science into patient benefits is always a challenging process in modern medicine. The development of effective protection of the hypertrophic hearts during aortic valve replacement (AVR) has been just one of the examples. Although the cardioplegia regime, delivery route, and temperature have reached a general consensus, the clinical benefits of adding "hot shot" at the end of the AVR procedure remain an ongoing debate. The benefits of hot shot to metabolic recovery had been reported during coronary artery bypass surgery [1]. However, the randomized clinical trials reported by Edwards and colleagues [2] and by Falcoz and colleagues [3] in the AVR setting were unable to detect significant differences in cardiac enzyme release early after surgery, when the terminal hot shot was added by antegrade route to either cold blood cardioplegia or cold crystalloid cardioplegia. In this issue of The Annals of Thoracic Surgery, Ascione and colleagues [4] have taken this one step further by studying cardiac cellular metabolism profiles in a randomized trial of a small number of patients undergoing AVR for aortic stenosis, and they have produced some interesting data, although the interpretation of this data requires further deliberation.
The authors made a great leap in concluding that by adding terminal hot shot through the coronary sinus to routine antegrade cold blood cardioplegia during AVR could improve right ventricular adenosine triphosphate (ATP) preservation, but it had no effects on left ventricular ATP or lactate levels after reperfusion. This conclusion was based on the analysis of the authors by converting the ATP raw data into the percentage change from baseline and then by using a nonparametric t test. The validity of the statistical approach of the authors may be questioned by the unequal baseline. As one can see, the baseline myocardial ATP level of the left and right ventricles seemed to be approximately 27% and 31% lower in the hot shot group than those in the control group, a finding that is highly unusual for a randomized trial. It is disappointing that the authors failed to provide a sound explanation, but instead masked the issue by converting the raw data into percentage changes. If one uses simple two sample t teststo compare the raw data of two groups’ baseline, the differences in the ATP level are highly significant (p = 0.018 and 0.008 for the left and right ventricles, respectively). There was a similar pattern of differences in the ATP level between the two groups at reperfusion, although the statistic significance has reduced in regard to the left ventricle (p = 0.086), but it remained high for the right ventricle (p = 0.019). These findings are by no means conclusive, but it is believed that they have provided a good indication for using two-way analysis of variance to analyze the raw data so that the effects of cardioplegia and hot shot can be taken into consideration at the same time.
The question regarding why the baseline ATP of both ventricles was consistently different between the two apparently randomized groups is difficult to answer. Interestingly, the precise timing of insertion of the coronary sinus catheter was not documented in this article, although the normal practice is to insert it before going on bypass [5]]. If this was the case, one might speculate that the insertion of a coronary sinus catheter for the hot shot group may lead to hemodynamic disturbance and thus unintentionally drop the baseline ATP level, which did not make full recovery even with hot shot at reperfusion.
If the current study does confirm that retrograde hot shot may drop the ATP level right from the very beginning of bypass, it will add more concerns rather than enthusiasm for applying this technique in AVR. Taking together with the negative reports of using antegrade hot shot [2, 3], one has to wonder whether the theoretical benefits of hot shot will ever be demonstrated robustly in the AVR setting and why.
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