Infarct Size Reduction by Ischemic Preconditioning Is a Monophasic, Short-Lived Phenomenon in Anesthetized Pigs.

Area of Science:

• Cardiovascular Physiology
• Myocardial Ischemia and Reperfusion Injury

Background:

• Controversy exists regarding the duration of infarct size reduction following ischemic preconditioning across different species.
• The existence of a late protective phase, or "second window," after 24 hours remains debated.

Purpose of the Study:

• To evaluate the time course of infarct size reduction after ischemic preconditioning in an open-chest pig model.
• To determine if a late protective "second window" of preconditioning is present at 24 hours in pigs.

Main Methods:

• Six groups of anesthetized pigs underwent a 1-hour coronary artery occlusion followed by 2-hour reperfusion.
• Preconditioning involved two 10-minute ischemia episodes with varying reperfusion intervals (30 minutes to 24 hours) before sustained occlusion.
• Infarct size was quantified using p-nitrobluetetrazolium and expressed as a percentage of the area at risk.

Main Results:

• Ischemic preconditioning significantly reduced infarct size compared to controls (25.6% vs. 71.3%, P <.001).
• Extending reperfusion intervals to 60, 90, 300 minutes, and 24 hours did not maintain infarct size reduction (P = NS vs. control).
• No significant late protection was observed at 24 hours post-preconditioning.

Conclusions:

• The infarct size-limiting effects of ischemic preconditioning are transient in the pig model, lasting less than 1 hour.
• Unlike other species, a late "second window" of protection was not detected at 24 hours in this study.
• Ischemic preconditioning demonstrates a monophasic protective effect in anesthetized pigs.