The enigma of myocardial preconditioning models.
Myocardial preconditioning has been reported in the hearts of many species of animals, including dogs, pigs, rabbits, rats, and anecdotally in humans. However, most studies were carried out in the regional ischemic model, although protection against global ischemic injury had been observed in rat models. Besides biochemical endpoints, the criterion of protection in regional ischemia was usually reduction in infarct size, while in global ischemia, recovery of contractile force and time-to-onset of ischemic contracture were used. We attempted to reproduce preconditioning of myocardium against global ischemic injury using an isolated perfused rabbit heart model with the rationale that global ischemia is more relevant to cardiac surgery, the rabbit model is logistically convenient, and it can be used for future comparison with the responses in immature hearts. The preconditioning was induced with 5 minutes of normothermic global ischemia followed by 10 minutes of reperfusion. The principal ischemic injury lasted 35 minutes, followed by 60 minutes of reperfusion. The control group underwent similar principal ischemic injury and reperfusion but no prior preconditioning ischemia. Results showed that there was no difference between the two groups in left ventricular resting tension, recovery in left ventricular developed pressure, contractility (dP/dt), and rate of relaxation (-dP/dt), nor were there any differences in heart rate and coronary flow rate. The reason for our negative findings is not clear, but if the results are confirmed, it will suggest that extrapolation of observations obtained from one experimental model to another should be made with caution.
Quantz
M
M
Division of Cardiovascular and Thoracic Surgery, McGill University, Montreal, Quebec, Canada.
Carsley
L
L
Shum-Tim
D
D
Tchervenkov
C
C
Chiu
R C
RC
D000818:Animals; D004195:Disease Models, Animal; D006339:Heart Rate; D006439:Hemodynamics; D066298:In Vitro Techniques; D017202:Myocardial Ischemia / Q000503:physiopathology*; D015425:Myocardial Reperfusion; D011817:Rabbits; D016277:Ventricular Function, Left