Myocardial Protection
Cardioplegia techniques and understanding
A number of different techniques as in normal cardiac surgery involving cardiopulmonary bypass are applicable. The technique of retrograde is very helpful in root surgery, especially in the setting of dissection extending down to the coronary origins.
In aortic surgery via a median sternotomy, the following general principles may be helpful:
1. Vent the heart, this is usually best done via the right superior pulmonary vein (RSPV), but LV apex and PA are other options.
2. Arrest the heart with anterograde cardioplegia, even with gross AR - clamp the vent in the RSPV until arrest occurs. If no AR is present after about 600mL switch over to retrograde and give a further 400mL. If AR is present after arrest switch over to retrograde cardioplegia and give a total of 1,000mL of cold blood.
3. When giving retrograde cardioplegia always inspect the right coronary origin, if dark blood exits using retrograde for the rest of the case is safe. However if no blood exits the RCA then intermittent anterograde cardioplegia to the RCA, but not necessarily the LCA will be needed. Always watch the coronary sinus pressure during retrograde cardioplegia, too high (>40mmHg) risks coronary sinus rupture, too low (<15mmHg) may result in inadequate cardioplegia delivery to the myocardium.
4. Give cardioplegia every 20 minutes.
In aortic surgery via a left thoracotomy, the following general principles may be helpful:
1. If left heart bypass is to be used then obviously myocardial protection is not an issue, but body must not be cooled below 32oC ish otherwise VF can occur.
2. If a circulatory arrest is to be performed, then cooling the body cools the heart, which is the mechanism of myocardial protection, then the following scenarios are possible:
a. If femoral-femoral bypass is being used some don't vent. (Must be no AR)
b. If femoral-femoral bypass is being used venting may be used performed via the PA, the LV apex or one of the pulmonary veins.