Residual strain changes with left ventricular pressure in the developing heart

Residual stress and strain can result from mechanically induced growth and may help to optimize a tissue´s load-bearing ability. We hypothesized that left ventricular (LV) residual strain changes after chronic pressure overload or underload in the stage 29 (6-d) embryonic chick. Stage 21 (3.5-d) chicks were treated with either conotruncal banding or extraembryonic verapamil drip until stage 29. LV pressure was measured in ovo. A transverse basal section through both ventricles was removed and a radial cut made in the LV wall to give zero-stress configuration. Opening angle, a measure of circumferential residual strain, was measured at interior, mid-wall, and exterior positions. Peak systolic pressures in control, banded, and verapamil-treated hearts were 4.73±0.58, 7.32±0.88 (p<0.001 vs control), and 3.70±0.30 mmHg (p<0.001). Maximum and minimum dP/dt also changed significantly after both interventions. End diastolic pressures were similar in all. Heart rates were similar in control and banded but lowered after verapamil treatment. Opening angles were 42.0°±9.7°, 69.3°±12.2° (p<0.001), and 31.3°±8.1° (p<0.01). These increases and decreases in residual strain with increases and decreases in LV pressure may help normalize myocardial stress and strain.