Optimal protective hypothermia in arrested mammalian hearts

Area of Science:

• Cardiovascular Physiology
• Hypothermia Research
• Experimental Cardiology

Background:

• Therapeutic hypothermia (TH) recommendations lack robust experimental data.
• Defining optimal protective hypothermia (OPH) is essential for clinical application.
• Core temperatures below 29°C risk cooling injury, while hypothermia is generally considered ≤35°C.

Purpose of the Study:

• To determine the optimal target therapeutic hypothermia (TTH) range for cardiac protection during arrest.
• To investigate the effects of varying hypothermia levels on myocardial recovery post-cardiac arrest.
• To establish data from controlled experiments to support TH recommendations.

Main Methods:

• Utilized a pig cardiopulmonary bypass model for controlled cardiac arrest.
• Cooled core temperatures to 29-35°C for 20 minutes pre-arrest and 60 minutes during arrest.
• Continuously monitored left ventricular (LV) pressure, dP/dtmax, cardiac power, heart rate, cardiac output, and myocardial velocity (Vmax).

Main Results:

• Hearts cooled to 29-30.5°C showed excellent recovery (Vmax ~118%, dP/dtmax ~121% of baseline).
• Temperatures of 34-35°C resulted in poor recovery, similar to normothermia (Vmax ~56%, dP/dtmax ~24%).
• A critical inflection point around 30.5-31°C indicated the threshold for optimal protective hypothermia (OPH).

Conclusions:

• Optimal protective hypothermia (OPH) is achieved at a target therapeutic hypothermia (TTH) of approximately 31°C.
• This finding supports initiating TTH to cool core temperature to 31°C for improved cardiac recovery.
• Results align with mammalian heart data, suggesting a consistent optimal hypothermia range.