Rapid cooling of the heart with total liquid ventilation prevents transmural myocardial infarction following prolonged ischemia in rabbits

Study aim: Total liquid ventilation (TLV) with cooled perfluorocarbons has been demonstrated to induce an ultrafast cardioprotective cooling in rabbits. However, it remains unknown whether this technically challenging strategy would be actually more potent than a conventional external cooling after a prolonged ischemia inducing transmural myocardial infarction.

Methods: Anesthetized rabbits were randomly submitted to 60min of coronary artery occlusion (CAO) under normothermic conditions (Control group, n=7) or with cooling started at the 5th min of CAO (target left atrial temperature: 32 degrees C). Cooling procedures were either external cooling using cold blankets (EC group, n=7) or ultrafast cooling initiated by 20min of TLV (TLV group, n=6). An additional group underwent a similar ultrafast cooling protocol started at the 20th min of CAO (TLV(delayed) group, n=6). After reperfusion, all hypothermic animals were rewarmed and infarct size was assessed after 4h.

Results: In the EC group, the target temperature was reached only at 60min of CAO whereas this time-interval was dramatically reduced to 15 and 25min of CAO in TLV and TLV(delayed), respectively. Infarct sizes were significantly reduced in TLV and TLV(delayed) but not in EC groups as compared to Control (45+/-18%, 58+/-5%, 78+/-10% and 82+/-7% of the risk zone, respectively). Similar significant differences were observed for the sizes of the no-reflow zones (15+/-9%, 23+/-8%, 49+/-11% and 58+/-13% of the risk zone, respectively).

Conclusion: Cooling induced by TLV afforded a potent cardioprotection and prevented transmural infarction following prolonged and severe ischemia, even when started later than a surface cooling in rabbits.