The small chill: mild hypothermia for cardioprotection?
Reducing the heart's temperature by 2-5°C is a potent cardioprotective treatment in animal models of coronary artery occlusion. The anti-infarct benefit depends upon the target temperature and the time at which cooling is instituted. Protection primarily results from cooling during the ischaemic period, whereas cooling during reperfusion or beyond offers little protection. In animal studies, protection is proportional to both the depth and duration of cooling. An optimal cooling protocol must appreciably shorten the normothermic ischaemic time to effectively salvage myocardium. Patients presenting with acute myocardial infarction could be candidates for mild hypothermia since the current door-to-balloon time is typically 90 min. But they would have to be cooled quickly shortly after their arrival. Several strategies have been proposed for ultra-fast cooling, but most like liquid ventilation and pericardial perfusion are too invasive. More feasible strategies might include cutaneous cooling, peritoneal lavage with cold solutions, and endovascular cooling with intravenous thermodes. This last option has been investigated clinically, but the results have been disappointing possibly because the devices lacked capacity to cool the patient quickly or cooling was not implemented soon enough. The mechanism of hypothermia's protection has been assumed to be energy conservation. However, whereas deep hypothermia clearly preserves ATP, mild hypothermia has only a modest effect on ATP depletion during ischaemia. Some evidence suggests that intracellular signalling pathways might be responsible for the protection. It is unknown how cooling could trigger these pathways, but, if true, then it might be possible to duplicate cooling's protection pharmacologically.
Tissier
Renaud
R
INSERM, Unité 955, Equipe 3, Créteil F-94000, France. rtissier@vet-alfort.frPublished on behalf of the European Society
Chenoune
Mourad
M
Ghaleh
Bijan
B
Cohen
Michael V
MV
Downey
James M
JM
Berdeaux
Alain
A
D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D002316:Cardiotonic Agents / Q000627:therapeutic use*; D006801:Humans; D007035:Hypothermia / Q000139:chemically induced / Q000503:physiopathology*; D023421:Models, Animal; D009203:Myocardial Infarction / Q000503:physiopathology*; D015428:Myocardial Reperfusion Injury / Q000503:physiopathology / Q000517:prevention & control; D015398:Signal Transduction / Q000502:physiology
D002316:Cardiotonic Agents; D000255:Adenosine Triphosphate