Chronic pressure overload hypertrophy decreases direct ventricular interaction.

We studied the relative roles of direct (via the interventricular septum) and series (via the pulmonary circulation) ventricular interaction in hearts with concentric left ventricular hypertrophy by using statistical models to analyze the transient responses in right and left ventricular pressures and dimensions to occlusions of the venae cava and pulmonary artery in five open-chest anesthetized dogs. The left ventricles of these dogs had moderate concentric hypertrophy (31% increase in mass) induced by 3 mo of renovascular hypertension [peak left ventricular pressure = 160 +/- 13 (SD) mmHg]. At end diastole we found that direct interaction was only about one-tenth as important as series interaction in determining left ventricular size with the pericardium around the heart. At end systole we found that direct interaction was about one-fifth as important as the end-systolic pressure-volume relationship in determining left ventricular size. Removing the pericardium decreased the importance of direct interaction. Direct interaction is less important in these hearts than in normal hearts, probably because the septum is thicker and, hence, less distensible. This change in the relative importance of direct ventricular interaction with hypertrophy complicates comparison of pressure-volume relationships between normal and hypertrophied hearts.