Cardiac motion and fiber shortening: the whole and its parts.

Radionuclide ventriculography findings in 24 subjects show that the ventricular blood pool motion goes from base to apex, a finding that contradicts the expectation that an apex to base relationship should exist, because excitation proceeds from apex to base. This discrepancy reflects a difference between motion caused by whole heart transmural action, and regional activity that does not require global movement. Confirmation of the radionuclide ventriculography findings was made from sonomicrometer crystals, echocardiography, and MRI that demonstrated early basal motion. During excitation, only the endocardial muscle is stimulated by the electrical impulse, but transmural motion that is needed for the endocardial motion that is detected by radionuclide ventriculography. Differences between the isometric and ejection phases are described, and there is discussion of how these findings relate to the myocardial band. The reality of twisting and downward motion of the heart observed during ejection only happens following transmural activation, a motion that exists far beyond the QRS electrical signal on the ECG.