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Intraventricular Conduction: Difference between revisions
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When the "terminal force" of the QRS in V1 is below the baseline (i.e. QS wave), a LBBB is the most likely diagnosis. | When the "terminal force" of the QRS in V1 is below the baseline (i.e. QS wave), a LBBB is the most likely diagnosis. | ||
When the "terminal force" of the QRS in V1 is above the baseline (i.e. RSR' wave), it's a RBBB. | When the "terminal force" of the QRS in V1 is above the baseline (i.e. RSR' wave), it's a RBBB. | ||
If the QRS > 0.12 sec. but the morphological criteria of LBBB or RBBB do not apply, it is called ' | If the QRS > 0.12 sec. but the morphological criteria of LBBB or RBBB do not apply, it is called 'intraventriculair conduction delay', a general term. | ||
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[[Image:LAHB.png|thumb|Left anterior hemiblock]] | [[Image:LAHB.png|thumb|Left anterior hemiblock]] | ||
In ''left anterior fascicular block'' the anterior part (fascicle) of the left bundle is slow. This results in delayed | In ''left anterior fascicular block'' the anterior part (fascicle) of the left bundle is slow. This results in delayed depolarization 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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{{Box| | {{Box| | ||
;Criteria for posterior fascicular block: | ;Criteria for posterior fascicular block: | ||
: | :Right [[heart axis|axis devation]] >+120°; | ||
: | :Deep S in I; | ||
: | :Small q in III; | ||
: | :No or very few QRS widening; | ||
:Right ventricular [[hypertrophy]] and previous [[Ischemia#Lateral|lateral myocardial infarction]] have been excluded | :Right ventricular [[hypertrophy]] and previous [[Ischemia#Lateral|lateral myocardial infarction]] have been excluded | ||
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===Retrograde Concealed Conduction=== | ===Retrograde Concealed Conduction=== | ||
Phase 3 aberration is often the cause of the first wide QRS complex. However at a regular rate retrograde concealed conduction is often the sustaining mechanism. The sequence of QRS widening that is often observed is phase 3 aberration in the first premature beat. This can leave the left bundle ( | Phase 3 aberration is often the cause of the first wide QRS complex. However, at a regular rate, retrograde concealed conduction is often the sustaining mechanism. The sequence of QRS widening that is often observed is phase 3 aberration in the first premature beat. This can leave the left bundle (for example) refractory for the next complex. This next beat is conducted by the right bundle and once it reaches the apex, it is conducted retrograde by the left bundle. This can continue until a new premature ventricular complex causes a compensatory pause and 'resets' the system. | ||
===Phase 4 Aberration=== | ===Phase 4 Aberration=== | ||
Phase 4 aberration only occurs after prolonged pause. During such a pause (e.g. in second degree AV block) the fibers | Phase 4 aberration only occurs after prolonged pause. During such a pause (e.g. in second degree AV block) the Purkinje fibers can 'hyper'-depolarize spontaneously. As their membrane potential becomes more and more negative the conduction velocity decreases and can even be blocked 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. | ||
{{Box| | {{Box| | ||