Introduction: Following a cardiac arrest, many patients still die or suffer severe damage to the heart even when the best CPR is delivered. Reintroduction of blood flow at the start of CPR may cause additional injury to the heart beyond that caused by the systemic ischemia itself. Ventilation with the noble gas argon early during CPR has been shown to improve hemodynamic outcome in pigs in vivo that have suffered an experimentally induced cardiac arrest. We tested if the protective effect of argon prevails in vitro when administered as a post-conditioning stimulus early during reoxygenation (R) following hypoxia (H) of isolated cardiomyocytes.
Hypothesis: Argon (65%) protects isolated cardiomyocytes against hypoxia/reoxygenation (H/R; simulated ischemia/reperfusion [I/R]) injury.
Methods: Human cardiomyocytes (80-90% confluent) were stabilized for 2 hrs in regular complete media and 30% O2, 65% N2, 5% CO2 before undergoing 4 hrs hypoxia (serum & glucose-free media, 0.01% O2) followed by 2 hrs reoxygenation with regular complete media and 30% O2, 65% N2, 5% CO2. Argon-treated cells received 30% O2, 65% argon, 5% CO2 as the post-conditioning stimulus for the first 10 or 30 minutes of the 2 hr reoxygenation. Endpoints were cell number, viability (mitochondrial dehydrogenase activity), and injury (lactate dehydrogenase [LDH] release). Statistics: ANOVA and SNK post hoc comparisons, p<0.05 (two-tailed) *vs control/normoxia, n = 4 experiments.
Results: There was a significant decrease in cell number and viability, as well as a significant increase in LDH release, following H/R compared to control/normoxia. The use of argon during the first 10 or 30 minutes of the reoxygenation did not provide protection against the H/R-induced decrease in cell number and viability, nor the increase in LDH release. In addition, argon had no effect on control/normoxic cells.
Conclusion: These findings suggest that, in contrast to the in vivo studies of global I/R during CA, the noble gas argon, when given as a post-conditioning stimulus for a short time during early reoxygenation, does not attenuate H/R (simulated I/R) injury at the cellular (cardiomyocyte) level, but requires mechanisms present in vivo to improve outcome.