Dynamics of the interventricular septum in mechanical overload

To assess wall thickness dynamics of the interventricular septum, ultrasonomicrometry was directly applied to measure wall thickness of the septum as well as the left ventricular free wall thickness in open chest dogs. In the control resting state, the end-diastolic wall thickness and magnitude of the systolic thickening of the septum were essentially equal to those of the left ventricular free wall. Acute interventions, such as pressure or volume overloading on the right or left ventricle, induced the same dynamic changes in the septum as in the left ventricular free wall. To evaluate the chronic changes in wall thickness dynamics of the interventricular septum, echocardiographic studies were conducted in patients with chronic pressure or volume overload in the right or left ventricle. While sustained pressure or volume overload in the left ventricle resulted in an increase in wall thickness of both the septum and left ventricular free wall, chronic pressure overload of the right ventricle induced the hypertrophy only in the septum but not in the left ventricular free wall. Thus, the interventricular septum can be regarded as a functional part of the left ventricle, and the mechanical loading on the left ventricle will ultimately induce proportional changes in the septum and the left ventricular free wall. Although the septal function is largely independent of acute changes in right ventricular loading, a chronic effect cannot be ignored.