CONTRIBUTION OF EACH WALL TO BIVENTRICULAR FUNCTION

Objective: Common muscle fibres encircle both ventricles and the ventricles share a common septal wall. This close anatomical association suggests that regional ischaemia and structural integrity may alter systolic function in both the right and the left ventricle. To examine this possibility, we investigated the contribution of each wall to biventricular function. Methods: Isolated hearts, obtained from anaesthetised rabbits, were perfused with physiological salt solution under constant pressure. Balloons were placed in the right and left ventricles to measure isovolumetric pressure, and pressure-volume curves were obtained. In separate sets of experiments, the left ventricular free wall, right ventricular free wall, or septum was made ischaemic, incised, or injected with glutaraldehyde, respectively. Pressure-volume curves were obtained again. Results: After left ventricular free wall ischaemia (n=11), right ventricular developed pressure decreased significantly from 27.9(SD 8.9) to 14.1(6.6) mm Hg (p<0.05), and remained depressed when the left ventricular free wall was further damaged by glutaraldehyde. Cutting the left ventricular free wall (n=6) decreased right ventricular developed pressure from 28.9(8.6) to 17.8(4.8) mm Hg (p<0.05), while reapproximating the left ventricular free wall by suturing re-established right ventricular developed pressure. After right ventricular free wall ischaemia (n=7), right ventricular developed pressure decreased from 26.8(6.6) to 24.1(5.7) mm Hg (NS) and left ventricular developed pressure was unaltered. Cutting the right ventricular free wall (n=7) had no effect on left ventricular developed pressure. Cutting the septum (n=7) had no obvious influence on right ventricular developed pressure, but dramatically decreased left ventricular developed pressure from 79.2(55.2) to 43.7(32.2) mm Hg (p<0.05). Injecting glutaraldehyde into the septum (n=7) decreased both right and left ventricular developed pressures from 22.1(8.5) to 14.0(8.8) and from 78.2(50.5) to 47.9(37.9), respectively. Conclusions: The results show that the heart should be viewed as a mechanical syncytium. The left ventricular free wall plays a critical role in right ventricular systolic function and may help to explain the right ventricular response to left ventricular ischaemia. On the other hand, in the isolated heart preparation, right ventricular free wall ischaemia has only a minimal effect on left ventricular systolic developed pressure. Altering ventricular septal function affects both right and left ventricular systolic function.