A New Look at Diastole

The isovolumic period following systolic ejection is associated with untwisting of the apex that follows systolic torsion of the left ventricle, with simultaneous generation of negative pressures in the left ventricle. Previous studies have described this period as isovolumic relaxation, and have regarded the untwisting as entirely caused by restoring elastic forces. However, evidence from several sources indicates that some ventricular muscle is still contracting during this period, and that this muscle is subepicardial muscle or the ascending spiral segment of the ventricular myocardial band that extends from the apex up along the left ventricular epicardium and the right ventricular side of the septum to the root of the aorta. It is possible that diastolic dysfunction is due to defective incoordination of muscle contraction between the ascending and descending segments of this band rather than to defective passive restoring forces.