Daily Archive 12.01.2019

AV conduction

AV conduction

AV conduction increases with an increase in sympathetic activity and is suppressed with an increase in the tone of the vagus nerve. Usually, during periods of patient activity, the frequency of ventricular contractions is high (up to 200 beats / min), while at rest or during sleep it decreases.

Absolutely irregular ventricular rhythm indicates the presence of AF, no matter how small or large the frequency of ventricular contractions.

Intraventricular conduction. Ventricular complexes with FP have a normal duration, except for cases of blockade of the bundle of the His, WPW syndrome or aberrant intraventricular conduction, i.e. frequency-dependent blockade of the bundle branch block. Aberrant intraventricular conduction.

Aberrant conduction is the result of different lengths of the recovery period (i.e. the exit period from the refractoriness state) in the two legs of the His bundle. An early atrial impulse can reach the ventricles at a time when one of the legs of the bundle of His is still refractory to activation after the previous cardiac cycle, while the other is already capable of conduction.

As a result, the ventricular complex will have a configuration characteristic of the blockade of the corresponding bundle of the His. Since the right leg usually has a longer refractory period, aberrant conduction usually leads to blockade of PNPG. The duration of the refractory period of the feet of the bundle of His depends on the duration of the previous cardiac cycle. Therefore, an aberration of conducting is more likely to occur when a short cycle follows a long one (the “Ashman phenomenon”). Sometimes a series of aberrant complexes can be mistakenly interpreted as paroxysmal ventricular tachycardia.

However, even if the frequency of ventricular contractions is very high, it is possible to reveal a distinct irregularity of the cardiac cycle; In addition, the question is legitimate: why during AF, there must be “jogging” of another arrhythmia?

The occurrence of atrial fibrillation. AF is usually initiated by atrial extrasystole. Sometimes TP or ABPT is transformed into fibrillation.