Inertia-Driven Mitral and Aortic Valves: The Isovolumic Myth

For the past century, the Wiggers Diagram has been universally taught as defining the phases of the cardiac cycle. However, the concepts underlying this diagram have never been fully and directly tested on intact, beating hearts.

In vivo datasets from sheep recorded left ventricular and aortic pressures and flows along with simultaneous 4-D coordinates of 30 miniature strategically placed radiopaque markers. This allowed hemodynamic synchronization with tracking of key anatomical landmarks every 16.7 msec to test Wiggers' concepts.

The Wiggers Diagram is not supported as there were no consistent isovolumic periods; the mitral valve closed anywhere during the rising phase of left ventricular pressure, and aortic valve closure and mitral valve opening were simultaneous at the end of the systolic pressure drop.

The Wiggers Diagram describes valve opening and closing solely in terms of pressure differences which can be transmitted almost instantaneously through incompressible blood in the ventricle. However, pressure differences do not open and close the valves; it is inertial flow through the valves. The present study redefines the description of the interaction between the left ventricle and its valves and shows that the periods of isovolumic contraction and relaxation are mythical concepts.