This physiological observation explains the mechanisms behind P-P interval variations in complete A-V block, highlighting the roles of mechanical traction and vagal reflexes.
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May clarify P-P interval behavior in AV block; hypothesis-generating and requires prospective validation before clinical application.
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).
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Rosenbaum et al. (1955) studied this question.
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