At that time Ringer and colleagues noticed that tap water had the ability to increase contractility of the heart, likely due to its high calcium content.
Sydney Ringer also commented on the importance of potassium ion concentration on depressing intrinsic heart rhythm.
Through a series of experiments performed on frog and canine hearts, reversible arrest was achieved with potassium ions with the consequence of ventricular fibrillation and observed myocardial necrosis.
These early experiments started nearly 50 years of work that has led to variety of perfusion strategies available today.
The main goals of hypothermic cardioplegia are: The most common procedure for accomplishing asystole is infusing cold cardioplegic solution into the coronary circulation.
This device, otherwise known as the heart-lung machine, takes over the functions of gas exchange by the lung and blood circulation by the heart.
Subsequently, the heart is isolated from the rest of the blood circulation by means of an occlusive cross-clamp placed on the ascending aorta proximal to the innominate artery.
Cardioplegia lowers the metabolic rate of the heart muscle, thereby preventing cell death during the ischemic period of time.
Chemically, the high potassium concentration present in most cardioplegic solutions decreases the membrane resting potential of cardiac cells.
[4] When extracellular cardioplegia displaces blood surrounding myocytes, the membrane voltage becomes less negative and the cell depolarizes more readily.
The depolarization causes contraction, intracellular calcium is sequestered by the sarcoplasmic reticulum via ATP-dependent Ca2+ pumps, and the cell relaxes (diastole).
When the resting potential approaches −50 mV, sodium channels are inactivated, resulting in a diastolic arrest of cardiac activity.
If partial depolarization is produced by a gradual process such as elevating the level of extracellular K+, then the gates have ample time to close and thereby inactivate some of the Na+ channels.
[10] Cardiac surgical cases were performed with the aid of a cardiopulmonary pump, without cardioplegia or other means of protecting the heart.