Technique of Antegrade Cardioplegia
After establishing cardiopulmonary bypass (CPB) with the perfusate at 32°C—ensuring that ventricular fibrillation does not occur—a catheter is inserted into the aortic root through a previously placed purse-string stitch, attached to the cardioplegia line, and de-aired. Optionally, the pressure line of the catheter can be connected to a strain gauge for continuous monitoring of aortic root pressure. The aorta is clamped once the aortic root catheter is in place and certainly before the heart has cooled enough from whole-body perfusion to become arrhythmic or develop ventricular fibrillation.
Cold cardioplegic infusion begins immediately at a flow rate of 150 mL/min/m² (as previously detailed for direct coronary perfusion) for 3 minutes in adults, with an average dose of approximately 750 mL. For infants and children with a body surface area less than 1 m², the infusion is administered at the same flow rate (150 mL/min/m²) but for only 2 minutes. If the monitored aortic root pressure falls below 30 mmHg, the flow rate (not the total dose) may be increased. However, low aortic root perfusion pressure might be caused by aortic regurgitation, potentially masked by a left ventricular vent; thus, the surgeon must confirm this is not the case. In patients with severe ischemic heart disease, aortic root pressure might exceed 75 mmHg, but the flow rate should not be reduced.
External cooling of the heart can be initiated during cardioplegic infusion. An isolating pad may be placed between the heart and the left side of the pericardium containing the phrenic nerve. A thin layer of ice slush or ice-cold saline is applied to the anterior surface of the heart. Later, when the heart is stable, additional ice slush may be applied to the surface, but it should never be placed in the pericardial space to avoid damaging the left phrenic nerve. As the slush melts, it is aspirated with a high-vacuum sucker. If this procedure is surgically inconvenient, the slush may be omitted.
At no time should the left or right ventricle become distended. Depending on the procedure, a left ventricular vent (introduced through a right pulmonary vein), suction through an aortic root catheter, or simple needle aspiration across the ventricular septum may be used.
Cardioplegic solution is reinfused approximately every 25 minutes. The initial flow rate is maintained, and the surgeon must ensure that the aortic valve is closed before infusion begins. If not, a few pinches of the proximal aorta typically achieve valve closure. Reinfusion lasts 30 to 60 seconds. After the initial infusion, the potassium concentration in any subsequent cardioplegic solutions is reduced to about 10 mmol/L.
If serum potassium levels rise to 7 to 8 mEq/L (which is rare), a bolus injection of 400 mg/kg of glucose (as 50% glucose) and 0.2 unit/kg of soluble insulin may be administered after the start of myocardial reperfusion. This approach is physiologically appropriate due to the abnormally low levels of intracellular potassium and circulating insulin at this stage.
