Cardioplegia

Excerpt

Cardioplegia is a pharmacological therapy administered during cardiac surgery to intentionally and temporarily arrest the heart. The first solution used during cardiopulmonary bypass was reported by Dr. Melrose in the early 1950s, who identified that high levels of potassium citrate induced a reversible cardiac arrest. An influx of potassium depolarizes the myocardial membrane causing contraction and thus release and subsequent sequestration of calcium ions resulting in a diastolic arrest. The resting membrane potential in myocytes is about -85 mV, and with the influx of sodium ions, depolarization occurs (membrane becomes more positive -45 to -30 mV) and thus generating an action potential that is potentiated by L-type calcium channels. These voltage-gated channels are targeted with cardioplegia to induce cardiac arrest. The persistence of potassium reduces the membrane potential and does not allow for adequate repolarization. This, in turn, creating a diastolic cardiac arrest. As the solution diffuses and there is a washout of its components along with products of anaerobic cellular metabolism, electrical activity begins to appear, and redosing of cardioplegia is required if clinically indicated. Potassium, however, is not the only ion commonly found in cardioplegia. Other ions such as calcium, sodium, and magnesium all participate in reducing contractility and preserving the myocardium. Additionally, components such as lidocaine, bicarb, and even glucose may be added for further protection.

Cardioplegia is an essential component of cardiopulmonary bypass and with the primary goal to reduce myocardial oxygen demand by creating electrical quiescence and cooling the heart to reduce the ischemic effects of being on bypass. The use of cardioplegia, in addition to being cardioprotective, also provides a relatively bloodless and motionless surgical field. There are many forms of cardioplegia ranging from the location of administration retrograde vs. antegrade as well as varying components within the solution, temperature, indications, adverse effects, pharmacokinetics, and pharmacodynamics.