Early increase in left ventricular compliance after myocardial infarction

Area of Science:

• Cardiovascular Physiology
• Biomechanical Engineering
• Cardiac Pathophysiology

Background:

• The left ventricular (LV) pressure-volume (P-V) relationship is influenced by ventricular volume, geometry, and wall stiffness.
• Assessing LV wall stiffness is crucial for understanding cardiac function and dysfunction.

Purpose of the Study:

• To develop a quantitative index for LV wall stiffness.
• To assess changes in LV wall stiffness 1 hour after acute myocardial infarction using this index.

Main Methods:

• Mathematical analysis of the isolated LV P-V relationship to derive a stiffness index (passive elastic modulus).
• Measurement of the passive elastic modulus in normal canine hearts and hearts 1 hour post-myocardial infarction.

Main Results:

• A novel passive elastic modulus (a constant from the equation dP/dV = aP + b) was developed as an index of LV wall stiffness.
• Normal canine LV passive elastic modulus was 0.099+/-0.006 cc(-1).
• In infarcted hearts, the passive elastic modulus decreased by 41% to 0.057+/-0.006 cc(-1) (P < 0.001), indicating reduced stiffness.

Conclusions:

• The passive elastic modulus is a sensitive index for detecting acute changes in LV wall stiffness.
• LV wall stiffness is significantly decreased 1 hour after acute myocardial infarction, contrary to potential later increases.
• Traditional P-V curves were less sensitive in detecting these early changes compared to the passive elastic modulus.