Polarization and myocardial protection.
Heart surgery or transplantation generally involve global ischemia, and techniques have been developed to protect the myocardium from ischemic and reperfusion injury. Hyperkalemic cardioplegia has been the gold standard for myocardial protection for years, but patients undergoing surgery almost invariably have some postoperative dysfunction. One factor may be the depolarizing nature of hyperkalemia, which results in continuing transmembrane fluxes and metabolism, even during hypothermic ischemia. A potentially beneficial alternative to hyperkalemic (depolarizing) cardioplegia is arrest in a "hyperpolarized" or "polarized" state, which maintains the myocardial membrane potential at or near the resting potential. This should minimize transmembrane fluxes and metabolic demand and improve myocardial protection. These alternative concepts have recently been investigated by using adenosine and potassium-channel openers (which are thought to induce hyperpolarized arrest) or the sodium-channel blocker tetrodotoxin (which induces polarized arrest), and results have been beneficial compared with the results of hyperkalemia. Additional studies are needed before experimental promise can become clinical reality.
Chambers
D J
DJ
Rayne Institute, Guy's and St Thomas' NHS Trust, St Thomas' Hospital, London, United Kingdom. david.chambers@kcl.ac.uk
D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D006348:Cardiac Surgical Procedures / Q000009:adverse effects* / Q000379:methods; D002314:Cardioplegic Solutions / Q000494:pharmacology / Q000627:therapeutic use*; D005260:Female; D006324:Heart Arrest, Induced / Q000379:methods*; D006801:Humans; D006947:Hyperkalemia / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials; D017202:Myocardial Ischemia / Q000209:etiology / Q000378:metabolism / Q000401:mortality / Q000517:prevention & control*; D009206:Myocardium / Q000378:metabolism; D020108:Nicorandil; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D011379:Prognosis; D011817:Rabbits; D015427:Reperfusion Injury / Q000378:metabolism / Q000401:mortality / Q000517:prevention & control*; D012680:Sensitivity and Specificity; D015996:Survival Rate
D015220:Calcium Channels; D002314:Cardioplegic Solutions; D015221:Potassium Channels; D020108:Nicorandil