The effect of ventricular systole on auricular rhythm in auriculoventricular block.

In some cases of complete A-V block the curve of the duration of P-P intervals showed a sudden dip with a gradual return, during or after the T wave. This positive chronotropic (accelerating) effect of ventricular systole is probably caused by the traction exerted on the right auricle by the contracting ventricle. Other cases showed a sudden rise in the curve of P-P intervals late in diastole, followed by a gradual return. This negative chronotropic (slowing) effect is probably caused by a vagal reflex precipitated by stimulation of the arterial pressoreceptors by the pulse wave. The interplay of these two effects determines whether the P-P intervals containing QRS will be shorter than those not containing it, or whether the relation is reversed (paradox effect).