Polarization and myocardial protection

Heart surgery or transplantation generally involve global ischemia, and tec hniques have been developed to protect the myocardium from ischemic and rep erfusion injury. Hyperkalemic cardioplegia has been the gold standard for m yocardial protection for years, but patients undergoing surgery almost inva riably have some postoperative dysfunction. One factor may be the depolariz ing nature of hyperkalemia, which results in continuing transmembrane fluxe s and metabolism, even during hypothermic ischemia. A potentially beneficia l alternative to hyperkalemic (depolarizing) cardioplegia is arrest in a "h yperpolarized" or "polarized" state, which maintains the myocardial membran e potential at or near the resting potential. This should minimize transmem brane 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 arre st) or the sodium-channel blocker tetrodotoxin (which induces polarized arr est), and results have been beneficial compared with the results of hyperka lemia. Additional studies are needed before experimental promise can become clinical reality. (C) 1999 Lippincott Williams & Wilkins, Inc.