Left ventricular hypertrophy due to volume overload versus pressure overload.

Area of Science:

• Cardiovascular Physiology
• Cardiac Remodeling
• Heart Failure Pathophysiology

Background:

• Left ventricular (LV) hemodynamic overload triggers compensatory left ventricular hypertrophy (LVH).
• The adequacy of LVH in compensating for chronic severe mitral regurgitation (MR) is debated.
• Previous studies suggest potential inadequacies in MR compensatory mechanisms.

Purpose of the Study:

• To investigate the adequacy of compensatory hypertrophy in chronic experimental MR.
• To compare the hypertrophic response and myocardial workload in MR versus aortic stenosis (AS).
• To assess the impact of MR on left ventricular contractile function.

Main Methods:

• Created chronic severe MR and aortic stenosis (AS) models in dogs.
• Matched MR and AS groups based on stroke work (SW) increase.
• Compared left ventricular weight to body weight ratio (LVBW) as an index of hypertrophy.
• Measured normalized SW (area within the stress-volume loop).
• Assessed contractile function in separate AS and MR groups with similar hypertrophy.

Main Results:

• Despite identical SW increase, AS dogs exhibited significantly greater LVH (LVBW) than MR dogs.
• Normalized SW was higher in MR dogs, indicating greater workload per unit of myocardium.
• Dogs with AS and similar hypertrophy to MR dogs had lower SW, suggesting MR requires greater overload for comparable hypertrophy.
• Contractile function was depressed in the MR group but preserved in the AS group.

Conclusions:

• The hypertrophic response to similar SW demand is less effective in MR compared to AS.
• Compensatory hypertrophy in MR is associated with impaired myocardial contractile function.
• These findings highlight the potential inadequacy of hypertrophy in mitigating hemodynamic overload in chronic MR.