Left Ventricular Function Changes Induced by Moderate Hypothermia Are Rapidly Reversed After Rewarming-A Clinical...

Area of Science:

• Cardiology
• Cardiovascular Physiology
• Therapeutic Hypothermia

Background:

• Targeted temperature management (32-36°C) is crucial for neuroprotection in cardiac arrest survivors.
• The specific impact of hypothermia on myocardial function in clinical settings remains unclear.
• This study investigates the isolated effects of hypothermia on cardiac function in patients without pre-existing heart conditions.

Purpose of the Study:

• To evaluate the reversible effects of hypothermia on left ventricular diastolic and systolic function.
• To determine the tolerance of myocardial function to increased heart rate during hypothermia.
• To assess the impact of hypothermia on cardiac index and myocardial strain.

Main Methods:

• Prospective clinical study involving 20 patients undergoing ascending aorta graft-replacement.
• Left ventricular function assessed via echocardiography and hemodynamic monitoring at normothermia (36°C) and hypothermia (32°C).
• Measurements were taken at spontaneous heart rate and artificially increased heart rate (90 bpm) under comparable loading conditions.

Main Results:

• Hypothermia prolonged R-R interval and increased isovolumic relaxation time, impairing diastolic filling.
• Systolic function was preserved at spontaneous heart rate but reduced at increased heart rate due to impeded filling.
• Cardiac index decreased during hypothermia, but mixed venous oxygen saturation was maintained; function normalized post-rewarming.

Conclusions:

• Hypothermia reversibly impairs diastolic function in individuals with normal left ventricular function.
• Elevated heart rates during hypothermia exacerbate diastolic impairment and reduce systolic function.
• Myocardial function is fully restored after rewarming, suggesting hypothermia's effects are transient.