Observations on the Relation Between Ventricular Activation Sequence and the Hemodynamic State

• The cardiac contraction sequence which follows the course of electrical excitation is one of the determinants of the hemodynamic state. The best known example of this rela-tion is the sequence of atrial and ventricular contraction. Hemodynamic conditions are in-fluenced by the contribution of atrial systole to ventricular filling and by the role of atrial contraction in normal closure of the atrioven-tricular valves.1 Hemodynamic effects of the activation sequence within individual cardiac chambers are also likely but are less clearly established. For example, it seems possible that the normal atrial activation and con-traction sequence advancing toward the atrioventricular valves contributes to proper expulsion of blood through these orifices. In the case of the ventricles, the relation between activation order and cardiac performance has not been defined adequately and a variety of conflicting findings have been reported. Evidence of delayed contraction of the ipsi-lateral ventricle has been found in some but not all instances of bundle branch block.2"5 In several studies different sites of ventricu-lar stimulation were associated with differ-ent intracardiac and vascular pressure levels and with different values of cardiac output.(J~s Other investigations, however, have shown no significant relation between the ventricula