22/12/2023
Myocardial Protection
In general, blood cardioplegia has become standard, with the use of various additives to reduce or buffer metabolic by-products. The addition of adenosine and lidocaine stabilizes the membrane potential of the myocardial sarcomere and allows the reduction of potassium to physiologic levels.
The cardioplegic solution is initially delivered at normothermia until myocardial arrest is achieved. The temperature is then reduced in the microplegia system, and cold cardioplegic solution is given until the myocardial temperature reaches 10°C to 15°C. Doses of cardioplegic solution are administered at 20-minute intervals to maintain this myocardial temperature. At the conclusion of the operation, a second normothermic dose of cardioplegia is administered to provide controlled rewarming and reperfusion of the myocardium.
C) Retrograde cardioplegia is preferred when there is coronary artery disease with high-grade stenoses, aortic valve or aortic root disease, mitral valve disease, or during operations on the ascending aorta.
This method has the advantage of providing uniform perfusion of the myocardium through the completely unobstructed venous system when there is coronary artery disease that may inhibit flow to some segments of the heart. A purse-string stitch is placed in the right atrium opposite the acute margin of the heart near the atrioventricular groove. An incision is made within the purse string, and a retrograde perfusion catheter is introduced into the right atrium and directed into the coronary sinus. The catheter can also be guided into the coronary sinus by placing the fingers of the right hand medial to the inferior vena cava near the posterior atrioventricular groove to monitor the catheter’s position. As the catheter enters the coronary sinus anterior to the venous uptake cannula, it is directed more cephalad to follow the course of the coronary sinus along the atrioventricular groove. The tip of the catheter is positioned at about the midpoint of the coronary sinus. Catheters with manual or self-inflating balloons are available. The pressure port is attached to an appropriate pressure monitoring device, and retrograde cardioplegia is delivered with the coronary sinus pressure about 50 mm Hg.
D) Attachment of a Y-connector to the cardioplegia system allows the tailored delivery of cardioplegic solution. In patients with high-grade coronary artery stenosis or acute occlusion of a major coronary artery with infarction, a combination of antegrade and retrograde cardioplegia delivers optimal protection of the myocardium.
The second arm of the Y-connector can also be attached to a reversed saphenous vein graft, providing unobstructed perfusion of that area of the myocardium and the measurement of pressure and flow down the graft.
📘 Cardiac Surgery, Operative Technique. Donald B. Doty, Jhon R. Doty
