Aberrant conduction
-
Upload
ramachandra-barik -
Category
Health & Medicine
-
view
499 -
download
5
Transcript of Aberrant conduction
ABERRANT CONDUCTIO
N
DR BARIK
DEFINITION
Alterations in QRS contour of supraventricular beats result ing from impulse transmission during periods of physiologic refractoriness and/or depressed conductivity
The supraventricular electrical impulse is conducted abnormally through the ventricular conducting system
MECHANISMS OF ABERRANCY
Premature arrival of the supraventricular impulse before full recovery
Inadequate or unequal refractoriness of conducting t issue result ing in local delay or block of dromotropism
Prolongation of Action Potential (AP) secondary to lengthiness of the preceding cycle duration
A reduced take-off potential secondary to diastole depolarization
MECHANISMS OF ABERRANCY
Failure of the refractory period to shorten in response to acceleration of the heart rate
Concealed transseptal conduction with delay or block of bundle branch conduction
Diffuse depression of Intraventricular conduction including that of specialized as well as contracti le myocardial
Unsuccessful of restitutions of transmembrane electrolyte concentration during relaxation and dilatation of the ventricles
TYPES OF ABERRATION
Type A: It is the common form and due to fascicular refractoriness.
The early impulse reach the RBB when sti l l in refractory period and it has been unable to respond and conduct
Type B: It is due to anomalous supraventricular activation
Type C: It is due to paradoxical crit ical rate
ASHMAN PHENOMENON
Gouaux-Ashman phenomenon or Ashman phenomenon is an intraventricular conduction abnormality restricted to the His-Purkinje system, caused by a change in the HR
Modulated by metabolic and electrolyte abnormalities and the effects of drugs
Relatively long cycle was fol lowed by a relatively short cycle, the beat with a short cycle often has RBBB morphology
Atrial f ibril lation( AF)
Atrial tachycardia
Premature Atrial Contractions
ASHMAN PHENOMENON
D/D-VPCS
ACCELERATION-DEPENDENT ABERRANCY
TACHYCARDIA-DEPENDENT, IN PHASE 3 ABERRANCY, OR PHASE 3 ABERRATION
Resulting from the occurrence of impaired intraventricular conduction as the heart attains a specific crit ical rate
The appearance and disappearance often depends on very small changes in cycle length
Aberrancy often appears at relatively slow rates, frequently below 75 beats/min
BRADYCARDIA-DEPENDENT, PHASE 4 ABERRANCY
Occurrence of impaired intraventricular conduction after long pauses or slowing of the heart to a crit ical rate
Due to a gradual loss transmembrane resting potential during a prolonged diastole with excitation from a less negative take-off potenial
PHASE 4 ABERRANCY
The presence of slow diastol ic depolarization which need not be enhanced;
A shift in threshold potential toward zero.
A deterioration in membrane responsiveness so that significant conduction impairment develops at -75mV instead of -65mV;
Hypopolarization ( the lost of maximum diastol ic potential)
CONCEALED INTRAVENTRICULAR CONDUCTION
Concealed Intraventricular conduction is defined as the manifestations of concealed conduction into the bundle branch system
Conduction is inferred only because of i ts inf luence on the subsequent cardiac cycle
CONCEALED INTRAVENTRICULAR CONDUCTION
Trans-septal retrograde concealed intraventricular conduction
Perpetuation of functional BBB initiated by a premature supraventricular impulse
Alternation of aberrant ventricular conduction in supraventricular bigeminy
Normalization of intraventricular conduction with acceleration or rate in bradycardia-dependent BBB
ABERRANCY SECONDARY TO DRUGS AND METABOLIC OR ELECTROLYTE DISORDERS
Hyperkalemia
Diffuse QRS complexes widening, similar to left or RBBB, associated with anterior or posterior fascicular block is seen frequently
QRS complex widening is differentiated of genuine branch blocks, the delay is f inal or middle, while in hyperkalemia is always global or diffuse
POSTEXTRASYSTOLIC ABERRATION
This variant is caused probably to slow diastolic depolarization, unequal recovery of conducting or myocardial t issue, or increased diastolic volume
ABERRANCY IN AVRT
When a bundle branch block pattern develops that is ipsi lateral to the accessory pathway that is participating in the tachycardia during ORT
VA conduction t ime prolongs as a result of the additional t ime that is required for conduction to travel from through the contralateral ventricle and septum to reach the accessory pathway
ABERRANCY IN AVRT
Prolongation of the VA interval also results in prolongation of the tachycardia cycle length unless there is a compensatory shortening of the AV interval
Prolongation oftheVA interval during a bundle branch block is diagnostic of ORT, but occurs in only 7% of patients with PSVT
Development of left bundle branch aberration with tachycardia is strongly predictive of ORT (92% positive predictive value)
ABERRANCY IN AVRT
Left bundle-branch block facil i tates induction of ORT when a left-sided accessory pathway is present and most accessory pathways are located on the left side
Induction of AV nodal reentry requires significant AV nodal delay, which makes the H1-H2 interval longer and makes aberration unl ikely