Adenosine-Induced Preconditioning of Human Myocardium?

To the Editor: Although the article by Leesar and coworkers in the June 3, 1997, issue of Circulation1 concludes that “adenosine preconditions human myocardium,” in our opinion their investigation in 30 patients undergoing balloon angioplasty (PTCA) and pretreatment with normal saline or adenosine (2 mg/min for 10 minutes) merely allows them to reiterate their introductory statement that “to the best of our knowledge, evidence that adenosine can precondition human myocardium in vivo is still lacking.” First of all, the fact that there have been recent studies demonstrating reduced signs of myocardial ischemia during repeated balloon inflations does not necessarily suggest the existence of ischemic preconditioning in the conventional, ie, biochemical, sense. As long as the contribution of the gradual opening of collateral channels with successive balloon occlusions is not accounted for in the observed phenomenon of attenuated myocardial ischemia, ischemic “preconditioning” may be not a biochemical but a biophysical process of collateral recruitment due to the temporally increasing effect of a pressure gradient across the anastomoses between the nonstenotic donor vessel and the occluded recipient vessel. Hence, the finding that such a thing as ischemic preconditioning, in the normally used sense of the word, exists in humans is very controversial and is inversely associated with whether or not the authors accounted for collaterals.2 Second, and considering the effects of adenosine on the resistance and conductance vessels of the coronary circulation, it is similarly disputable whether there is such a thing as adenosine-induced preconditioning or whether the phenomenon of mitigated myocardial ischemia during coronary occlusion on adenosine administration is actually pharmacologically induced collateral recruitment. After all, exogenously administered adenosine is known to …