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Delivery of a non-potassium modified maintenance solution to enhance myocardial protection in stressed neonatal hearts: a new approach.

OBJECTIVES
This study was undertaken to compare conventional cardioplegic strategies with a new approach that uses a modified non-potassium maintenance solution between cardioplegia doses in stressed neonatal hearts.


METHODS
Thirty-five neonatal piglets underwent 60 minutes of ventilator hypoxia (inspired oxygen fraction 8%-10%) followed by 20 minutes of ischemia on cardiopulmonary bypass. In 10 animals bypass was discontinued without further ischemia (stress control group). The other 25 received a warm blood cardioplegic induction and were separated into 5 groups. In 5 animals cardiopulmonary bypass was discontinued without further ischemia (cardioplegia control group); the remaining 20 underwent an additional 70 minutes of cold blood cardioplegic arrest. Five received only intermittent cardioplegia every 20 minutes, whereas 15 also received cold blood maintenance infusions between cardioplegic doses (integrated strategy). In 5 of these animals the blood was unmodified, whereas in 10 a modified non-potassium "cardioplegia-like" solution was delivered either antegradely (n = 5) or retrogradely (n = 5). Myocardial function was assessed by pressure-volume loops (expressed as percentage of control); vascular function was assessed by coronary vascular resistance.


RESULTS
All piglets that underwent hypoxic ischemic stress alone (controls) died. Warm induction alone (cardioplegic controls) partially repaired the stress injury. Intermittent cardioplegia preserved the depressed systolic function (end-systolic elastance 40% vs 39%), increased diastolic stiffness (255% vs 239%), reduced adenosine triphosphate (10.6 vs 12.2 microg/g tissue), and elevated coronary vascular resistance at levels identical to warm induction alone; infusing unmodified blood between cardioplegia doses (standard integrated) improved results slightly. In contrast, infusion of a cold modified solution (antegrade or retrograde) between cardioplegia doses (modified integrated) completely restored systolic function (end-systolic elastance 100% and 97%, P <.001 vs intermittent and standard integrated), only minimally increased diastolic stiffness (159% and 156%, P <.001 vs intermittent and standard integrated), restored adenosine triphosphate (18.8 and 16.6 microg/g, P <.001 vs intermittent and standard integrated), and normalized coronary vascular resistance (P <.001 vs intermittent and standard integrated). This strategy was used in 72 consecutive hypoxic patients (21 arterial switch operations, retrograde; 51 Fontan procedures, antegrade) with a 2.8% mortality.


CONCLUSIONS
Infusion of a cold modified solution between cardioplegic doses (modified integrated protection) significantly improved myocardial protection in the stressed neonatal heart, was effective delivered either antegradely or retrogradely, and was used successfully for hypoxic (stressed) pediatric patients.