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Intraventricular Conduction: Difference between revisions
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=Conduction delay= | |||
[[Image:geleidingssysteem.jpg|thumb| If the conduction system is dysfunctional, the QRS widens beyond 0.12 seconds.]] | [[Image:geleidingssysteem.jpg|thumb| If the conduction system is dysfunctional, the QRS widens beyond 0.12 seconds.]] | ||
If the QRS complex is wider than 0.12 seconds this is mostly caused by a delay in the conduction tissue of one of the bundle branches: | If the QRS complex is wider than 0.12 seconds this is mostly caused by a delay in the conduction tissue of one of the bundle branches: | ||
*[[# | *[[#Left_Bundle_Branch_Block_.28LBBB.29| Left Bundle Branch Block (LBBB))]] | ||
*[[# | *[[#Right_Bundle_Branch_Block_.28RBBB.29| Right Bundle Branch Block(RBBB)]] | ||
* | *Intraventricular conduction delay | ||
A right or left axis rotation can be caused by a: | A right or left axis rotation can be caused by a: | ||
*[[# | *[[#Left_Anterior_Fascicular_Block_.28LAFB.29| Left anterior fascicular block (LAFB)]] | ||
*[[# | *[[#Left_Posterior_Fasicular_Block_.28LPFB.29| Left posterior fascicular block (LPFB)]] | ||
Sometimes this conduction delay is ''' | Sometimes this conduction delay is '''rate-dependent ''': the bundle branch block occurs only at higher heart rates and disappears at slower heart rates. | ||
{{clr}} | {{clr}} | ||
= LBBB vs RBBB = | |||
[[Image:LBTB_RBTB_en.png|thumb| A bundle branch block causes a delay in the depolarization of the right (RBBB) or left (LBBB) ventricle. In RBBB the QRS complex shows a second peak or R' in V1.]] | [[Image:LBTB_RBTB_en.png|thumb| A bundle branch block causes a delay in the depolarization of the right (RBBB) or left (LBBB) ventricle. In RBBB the QRS complex shows a second peak or R' in V1.]] | ||
Check V1 when QRS > 0 | Check V1 when QRS > 0.12 sec. | ||
When the | 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 | 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. | ||
{{clr}} | {{clr}} | ||
=Left Bundle Branch Block (LBBB)= | |||
{{:LBBB}} | {{:LBBB}} | ||
{{clr}} | {{clr}} | ||
=Right Bundle Branch Block (RBBB)= | |||
{{:RBBB}} | {{:RBBB}} | ||
=Left Anterior Fascicular Block (LAFB)= | |||
{{Box| | |||
;Criteria for | ;Criteria for Left Anterior Fascicular Block | ||
#Frontal plane axis between −45° and −90°. | |||
#qR pattern in lead aVL. | |||
#R-peak time in lead aVL of 45 ms or more. | |||
#QRS duration less than 120 ms. | |||
: | These criteria do not apply to patients with congenital heart disease in whom left-axis deviation is present in infancy. | ||
In ''left anterior fascicular block'' the anterior part (fascicle) of the left bundle is slow. This results in delayed | }} | ||
[[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 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. | |||
{{clr}} | {{clr}} | ||
=Left Posterior Fasicular Block (LPFB)= | |||
[[File:E0003194.png|thumb|A patient with [[RBBB]] and left posterior Fascicular block]] | |||
{{Box| | |||
;Criteria for posterior fascicular block: | ;Criteria for posterior fascicular block: | ||
#Frontal plane axis between 90° and 180° in adults. Owing to the more rightward axis in children up to 16 years of age, this criterion should only be applied to them when a distinct rightward change in axis is documented. | |||
#rS pattern in leads I and aVL. | |||
#qR pattern in leads III and aVF. | |||
#QRS duration less than 120 ms. | |||
: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 | ||
}} | |||
=Mechanisms of aberrant conduction= | |||
[[Image:E000573.jpg|Rate dependant left bundle branch aberration|thumb]] | |||
{{box| | |||
;Aberrant ventricular conduction is defined as | ;Aberrant ventricular conduction is defined as | ||
:QRS widening due to delay or block in bundle branch or intramyocardial conduction<cite>wellens</cite> | :QRS widening due to delay or block in bundle branch or intramyocardial conduction<cite>wellens</cite> | ||
}} | |||
# | Mechanisms of aberration: | ||
#Retrograde | #Phase 3 aberration | ||
# | #Phase 4 abberation or deceleration dependant | ||
#Acceleration dependant | |||
Right bundle branch block is | #Retrograde invasion | ||
#Fixed block | |||
Right bundle branch block is more common, because the right bundle has the longer refractory period. Left bundle branch block accounts for about 1/3rd of cases. | |||
===Phase 3 Aberration=== | ===Phase 3 Aberration=== | ||
Phase 3 aberration occurs when conduction fibers receive a new impulse, before they have fully repolarized. This can sometimes be observed at the start of paroxysmal supraventricular tachycardias or in a long-short sequence | [[File:lbbb_phase3_phase4.svg|thumb|The image explains LBBB due to phase 3 and phase 4 aberration.]] | ||
Phase 3 aberration occurs when conduction fibers receive a new impulse, before they have fully repolarized. A premature impulse is encroaching on the refractory period of the bundle branch. This is a physiological phenomenon. This can sometimes be observed at the start of paroxysmal supraventricular tachycardias or in a long-short sequence in which the refractory period of the long sequence is prolonged. This is also called Ashman phenomenon. | |||
===Phase 4 Aberration or deceleration dependant=== | |||
Phase 4 aberration only occurs after prolonged pause. During such a pause (e.g. in second degree AV block) the Purkinje fibers can depolarize spontaneously. As their membrane potential becomes more positive, the conduction velocity decreases and can even be blocked altogether. This is usually a pathological response, but can be normal at very low heart rates (e.g. 40 bpm) | |||
===Acceleration dependant=== | |||
A small increase in rhythm resulting in aberrancy due to an abnormal response of tissue that has diminished excitability. | |||
===Retrograde Concealed Conduction=== | ===Retrograde Concealed Conduction=== | ||
[[File:retrograde_concealed_conduction.svg|thumb|LBBB due to retrograde concealed conduction]] | |||
This is the most common mechanism for sustained aberrancy during tachycardia. 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. | |||
=== | ===Fixed Bundle Branch Block=== | ||
[[File:Fixed_LBBB.svg|thumb|LBBB due to fixed bundle branch block]] | |||
Complete or marked conduction delay in a bundle branch leading to complete ventricular activation over the contralateral bundle branch. | |||
{{clr}} | |||
{{Box| | |||
=References= | |||
<biblio> | <biblio> | ||
#Garcia isbn=0763722464 | #Garcia isbn=0763722464 | ||
# | #Wellens isbn=9781416002598 | ||
</biblio> | </biblio> | ||
}} | |||
[[Category:ECG Textbook]] | |||