The relevance of ventricular wall dynamics for the study of myocardial shortening in the intact left ventricle.

Although many studies have shown that ventricular wall dynamics are a useful estimate of global and regional ventricular function, the precise relations that exist during contraction among myocardial fiber shortening, wall dynamics, and left ventricular cavity changes have not been previously established. To study the relation among some geometric variables used to describe left ventricular contraction, we used as a model of the left ventricle a thick-walled cylinder that contracts both radially and longitudinally. From this model, it can be shown that there is a direct relation during contraction between the relative thickening of the ventricular wall and the relative shortening occurring within the wall. On the other hand, the parameters derived from left ventricular cavity changes (relative ventricular internal radius shortening, ejection fraction, normalized blood flow velocity) are determined not only by the relative shortening occurring within the ventricular wall but also by the specific geometry of the ventricle, expressed in terms of its mid-wall radius-to-wall thickness ratio. In the clinical situation, the ejection fraction may vary up to 20%, uniquely as a result of a change of this ratio. These findings further validate the use of ventricular wall dynamics for the study of ventricular function. On the other hand, the specific geometry of the ventricle must be considered in interpreting the parameters derived from left ventricular cavity changes.