Functional Recovery After Ischemia: Warm Versus Cold Cardioplegia

Warm continuous retrograde cardioplegia has been introduced for myocardial protection during cardiac operations, particularly in the setting of acute myocardial ischemia because of its theoretical advantage of producing arrest without ischemia. To investigate the ability of warm continuous retrograde cardioplegia to provide myocardial protection after acute global ischemia, versus the more commonly used cold intermittent antegrade cardioplegia, 12 dogs were subjected to 15 minutes of normothermic global myocardial ischemia on cardiopulmonary bypass followed by 75 minutes of protected cardioplegic arrest using either warm continuous retrograde cardioplegia or cold intermittent antegrade cardioplegia. Standard blood cardioplegia at clinically used volumes and flow rates was used. Warm continuous retrograde cardioplegia animals received 30 mL/kg antegrade to induce arrest followed by 1.5 to 1.8 mL · kg−1 · min−1 retrograde at 37°C, whereas cold intermittent antegrade cardioplegia animals received 30 mL/kg antegrade to induce arrest followed by 15 mL/kg antegrade every 15 minutes at 10°C. Load-insensitive left ventricular systolic function, diastolic function, high energy nucleotides, and edema formation were assessed before and after ischemia. Results showed that myocardial preservation using clinically reported flow rates and volumes of warm continuous retrograde cardioplegia was significantly inferior to that provided by clinically used cold intermittent antegrade cardioplegia, as demonstrated by decreased preload recruitable stroke work slope (28 ± 11 versus 71 ± 6), increased α constant of the end diastolic stress-strain relationship (14.2 ± 3.0 versus 3.6 ± 1.0), decreased total nondiffusable nucleotides (40.7 ± 2.3 versus 57.4 ± 2.3 μM/g wet weight) and increased water content (82.2% ± 0.4% versus 80.4% ± 0.4%). These data demonstrate inadequate myocardial protection with clinically used flow rates of warm continuous retrograde cardioplegia in this model, supporting a cautious approach to the clinical use of warm continuous retrograde cardioplegia in the setting of acute global ischemia.