Myocardial temperature variation: effect on regional function and coronary flow in dogs

Area of Science:

• Cardiovascular Physiology
• Myocardial Thermoregulation

Background:

• Understanding the direct impact of regional myocardial temperature on cardiac function is crucial for managing cardiac conditions.
• Previous research has not fully elucidated the precise relationship between localized temperature variations and ventricular performance under controlled hemodynamic conditions.

Purpose of the Study:

• To investigate the effect of controlled regional myocardial temperature changes on ventricular function and coronary blood flow.
• To establish the relationship between midwall temperature and myocardial contractility in a beating heart model.

Main Methods:

• Utilized a canine right heart bypass preparation with controlled preload, afterload, and heart rate.
• Manipulated regional myocardial temperature in the left-anterior descending coronary artery (LAD) territory using a heat exchanger.
• Measured segment lengths with sonomicrometry and monitored midmyocardial temperature with fast thermistors.
• Assessed coronary blood flow and distribution using 9-micron microspheres.

Main Results:

• Regional systolic shortening decreased by 42.2% at 41°C and increased by 23.3% at 31°C, relative to normothermia (38°C).
• No significant alterations in coronary blood flow or distribution were observed across the tested temperatures.
• Pressure-length area, a measure of contractility, varied inversely with myocardial temperature.

Conclusions:

• Demonstrated a reversible, inverse relationship between midwall myocardial temperature and ventricular function.
• These findings highlight the sensitivity of myocardial contractility to temperature changes, independent of alterations in coronary perfusion.