Research on cardioplegic techniques used to arrest the heart for CABG surgery

This week I researched cardioplegia and its many forms. Cardioplegia is a technique that arrests the heart for on-pump CABG surgery (on-pump refers to inserting a heart-lung machine that enhances systemic circulation in the patient's body) . Cardioplegia is essential to the success of CABG surgery because it creates a still and stable environment for the surgeon to work in. Cardioplegia has many forms, including cold crystalloid cardioplegia, normothermic blood cardioplegia, hypothermic blood cardioplegia, and warm blood reperfusion. Due to the many forms of cardioplegia I organized my research into two categories, those being cold crystalloid cardioplegia (synthetic solution) and blood cardioplegia.

Cold crystalloid cardioplegia is usually administered to patient's in slightly hypothermic room conditions (28-34 °Celsius) relative to the patient's internal body temperature (37 °Celsius). Before the physician can insert the cardioplegic solution into the patient they have to cross-clamp the ascending aorta. This clamp reduces blood flow distally to the arteries and organs (such as the renal and femoral arteries) but increases blood flow proximally to the carotid and coronary arteries (the arteries that deliver blood flow to the brain and heart respectively). This effectively reduces the systemic circulation and cardiac output (amount of blood delivered to the systemic circulation per unit time) in the patient's body. A heart-lung machine is therefore cannulated into the left ventricle of the heart as well as the upper portion of the cross-clamp in order to increase systemic blood flow and meet the minimum cardiac output the patient needs to survive. Once the heart-lung machine is established, the physician cannulates the aortic root. The physician then inserts a catheter into the aortic root with a test solution to see if the aortic valve regurgitates the solution back into the aortic root. If there is aortic valve incompetence, the physician makes an incision ~2cm above the coronary ostium (opening in the wall of the blood vessel). This incision allows the test solution to drain directly into the coronary arteries and bypass the aortic valve. Once the cardioplegic delivery route is confirmed the physician then inserts the catheter with the cold crystalloid solution (approximately 4 °Celsius) into the aortic root or coronary ostium. This cold crystalloid cardioplegic solution typically arrests the heart for the duration of the surgical procedure. However, the physician has smaller doses of the solution to insert into the patient if any electrical or mechanical activity from the heart is observed. 

Blood cardioplegia: This is a solution that contains the patient's oxygenated blood (blood can be normothermic or hypothermic) with a crystalloid solution. The blood and crystalloid solution are mixed in a double-headed roller pump. This pump combines the patient's blood with a crystalloid solution in a ratio of 4:1. The newly formed blood cardioplegic solution is then sent through a heat exchanger system to determine if the solution will be warm, normothermic or hypothermic. The ascending aorta is then cross-clamped, and the aortic root and coronary ostia are cannulated as described earlier. The most interesting part of my research was learning about warm blood reperfusion. Data shows that warm blood reperfusion can repair ischemic (lack of blood flow to an organ or tissue) damage in patient's who had an acute myocardial infarction (heart attack). Warm blood reperfusion is able to repair ischemic damage in the heart by maximizing the efficacy of cellular respiration, which in turn decreases the demand for oxygen in the heart. It increases cellular respiration because the amino acids in its solution (glutamate and aspartate) restore the Krebs cycle intermediates. By restoring the intermediates, the Krebs cycle is able to continually produce GTP and NADH, which in turn are continually used by the electron transport chain to convert oxygen to water. By constantly converting oxygen to water, the continual turn of the Krebs cycle maximizes the amount of oxygen the body needs during cellular respiration. Typically the warm blood reperfusion solution is inserted via a catheter into the coronary sinus and grafts for one minute in order to repair any ischemic damage in the heart. 

The significance of my research is that warm blood reperfusion as well as all forms of blood cardioplegia are preferred to cold crystalloid cardioplegia because they perform dual beneficial functions in the patient.Those functions being they effectively stop the heart for open-heart surgery, and they repair ischemic damage in the heart that could pose problems to the patient later in life.