Phasic and Non-Phasic Aberrant Conduction
Report:
Sinus bradycardia, probably 46 â 50/min
SVEBs, LBBB & incomplete RBBB phasic aberrant conduction
Junctional escape beats, non-phasic aberrant conduction
Left axis deviation, possible LAHB
Comment:
The allorhythmia consists of repetitive triplets comprising a sinus beat and a SVEB followed by a junctional escape beat.
Three premature SVEBs are present. The first one has incomplete LBBB morphology, the second rSRâ incomplete RBBB morphology and the third one is only slightly aberrant, with shorter S wave than the sinus beats. S wave loss is the earliest sign of RBBB aberrancy. In all three cases, there is a long-short cycle sequence causing phasic aberrant conduction. This depends on long-short discrepancy rather than the actual rate (which determines the rate-related aberrancy).
The junctional escape beats (also SVEBs, technically) have a slightly different contour from the sinus beats. Their aberrancy is non-phasic; it is thought to arise from a different activation front reaching the bundle of His and the ventricles from a junctional focus. The value of its recognition is mostly when junctional beats are preceded by P waves â deciding whether the beats are conducted sinus or junctional ectopic beats. This is clearly not the case here, but helped in solving Case 24.
Is LAHB present? It is the commonest cause of LAD, but in this patient the small voltage, lack of secondary wave in aVR and of Rs morphology in V6 are against it.
Below (Fig 9a) is another trace, with allorhythmia broken by two successive junctional beats.
Fig 9a. The second junctional beat in the middle of the trace breaks the allorhythmia, preventing the sinus P wave inscribed at its onset (arrow) from being conducted.
Fig 10. 71 year old man with ischæmic cardiomyopathy following myocardial infarction 20 and CABGs 16 years ago.
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