114
edits
Intraventricular Conduction: Difference between revisions
no edit summary
No edit summary |
No edit summary |
||
| Line 49: | Line 49: | ||
{{Box| | {{Box| | ||
;Criteria for posterior fascicular block: | ;Criteria for posterior fascicular block: | ||
:Right [[heart axis|axis | :Right [[heart axis|axis deviation]] >+120°; | ||
:Deep S in I; | :Deep S in I; | ||
:Small q in III; | :Small q in III; | ||
| Line 61: | Line 61: | ||
}} | }} | ||
Aberrancy can result from: | Aberrancy can result from: | ||
#A sudden | #A sudden increase in frequency of the heart rate that the bundles cannot conduct (phase 3 aberration) | ||
#Retrograde concealed conduction | #Retrograde concealed conduction | ||
#A slow heart rate (phase 4 aberration) | #A slow heart rate (phase 4 aberration) | ||
Right bundle branch block is most common, because the right bundle has the | Right bundle branch block is most 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 | 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 in which the refractory period of the long sequence is prolonged. | ||
===Retrograde Concealed Conduction=== | ===Retrograde Concealed Conduction=== | ||
| Line 74: | Line 74: | ||
===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 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 | 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 upward shift of the threshold membrane potential and a change in membrane responsiveness, so it is rarely seen in normal hearts. | ||
{{Box| | {{Box| | ||