Intraventricular Conduction: Difference between revisions

==Left Anterior Fascicular Block (LAFB)==

;Criteria for left anterior fascicular block

:left axis deviation (<-30°)

:S > R in leads II and III

:no or very few QRS widening

In ''left anterior fascicular block'' the anterior part (fascicle) of the left bundle is slow. This results in delayed depolarisation of the upper anterior part of the left ventricle. On the ECG this results in left axis deviation. The QRS width is <0,12 seconds in isolated LAFB.

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==Left Posterior Fasicular Block (LPFB)==

;Criteria for posterior fascicular block:

:right [[heart axis|axis devation]] >+120°;  

:no or very few QRS widening;

:Right ventricular [[hypertrophy]] and previous [[Ischemia#Lateral|lateral myocardial infarction]] have been excluded

==Mechanisms of aberrant conduction==

;Aberrant ventricular conduction is defined as

:QRS widening due to delay or block in bundle branch or intramyocardial conduction<cite>wellens</cite>

Aberrancy can result from:

#A sudden fastening of the heart rate that the bundles cannot conduct (phase 3 aberration)

Phase 4 aberration only occurs after prolonged pause. During such a pause (e.g. in second degree AV block) the fibers of the Purkinje system can 'hyper'-depolarize spontaneously. As their membrane potential becomes more and more negative the conduction velocity reduces and they can even block altogether. This also requires an upwards shift of the threshold membrane potential and a change in membrane responsiveness, so it is rarely seen in normal hearts.

==References==

<biblio>

#Garcia isbn=0763722464

#wellens isbn=9781416002598

</biblio>