Wall stress and patterns of hypertrophy in the human left ventricle

Area of Science:

• Cardiology
• Physiology
• Biomedical Engineering

Background:

• Chronic left ventricular (LV) pressure overload typically causes concentric hypertrophy (wall thickening).
• Chronic LV volume overload typically causes eccentric hypertrophy (chamber enlargement).
• The hemodynamic factors driving these distinct hypertrophy patterns require elucidation.

Purpose of the Study:

• To investigate the role of hemodynamic factors in differential LV hypertrophy patterns.
• To measure LV wall stresses throughout the cardiac cycle in patients with pressure overload, volume overload, and controls.

Main Methods:

• Cardiac catheterization in 30 patients (6 pressure overload, 18 volume overload, 6 controls).
• Measurement of LV pressure, meridional wall stress (sigman), wall thickness (h), and radius (R) throughout the cardiac cycle.
• Calculation of the wall thickness to radius (h/R) ratio.

Main Results:

• Pressure overload normalized peak systolic wall stress due to increased wall thickness (concentric hypertrophy, increased h/R ratio).
• Volume overload did not normalize end-diastolic wall stress (eccentric hypertrophy, normal h/R ratio).
• Systolic wall stress was normalized in both overload conditions.

Conclusions:

• Hypertrophy may develop to normalize systolic wall stress but not diastolic wall stress.
• Increased systolic tension leads to myocardial fiber thickening.
• Increased diastolic tension may lead to fiber elongation, improving chamber efficiency without normalizing diastolic stress.