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Gepubliceerd in: Netherlands Heart Journal 4/2015

Open Access 01-04-2015 | Rhythm Puzzle - Answer

What is the origin of the ectopic beat?

Gepubliceerd in: Netherlands Heart Journal | Uitgave 4/2015

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Answer

The premature depolarisation following the second QRS complex occurs late in the cardiac cycle (CL = 1000 ms) with a QRS duration of 120 ms followed by a complete compensatory pause (Fig. 1 in the Question article, doi: 10.1007/s12471-015-0655-z). The QRS complex is not preceded by a P wave, excluding an atrial ectopic origin. The amplitude of the R wave is large in leads V2–V4, suggesting an anterior axis deviation of the QRS complex in the precordial leads, which makes an AV nodal origin unlikely in the presence of a left anterior fascicular block during sinus rhythm. Since the QRS width is borderline at around 120 ms, a premature ventricular depolarisation cannot be excluded as origin of the ectopic focus. But what is the most likely explanation for this depolarisation?
Figure 1 shows the proposed mechanism of activation from a spot in the specific His-Purkinje system where the time of slow anterograde conduction over a diseased left anterior fascicle is equal to the normal conduction time of the impulse, travelling over a longer distance through the posterior fascicle and right bundle. This results in an almost synchronous activation of both right and left ventricle. Already in 1973 [1], electrophysiological investigations were performed to prove this paradoxical phenomenon of premature beats in patients with conduction disease in the left bundle branch (Fig. 1).
The second part of the question was why does the QRS complex following the first sinus beat in V1–V6 have a different QRS morphology than the other QRS complexes during sinus rhythm? Most likely this beat is a fusion beat, since the QRS complexes in leads V4–V6 are nearly identical with the ectopic focus from the diseased left anterior fascicle.
Open Access This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.
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Netherlands Heart Journal

Het Netherlands Heart Journal wordt uitgegeven in samenwerking met de Nederlandse Vereniging voor Cardiologie en de Nederlandse Hartstichting. Het tijdschrift is Engelstalig en wordt gratis beschikbaa ...

Literatuur
1.
go back to reference Massumi RA, Hilliard G, DeMaria A, Fabregas R, Lindsay AE, Amsterdam E, Mason DT. Paradoxic phenomenon of premature beats with narrow QRS the presence of bundle-branch block. Circulation 1973;47:543–53.CrossRefPubMed Massumi RA, Hilliard G, DeMaria A, Fabregas R, Lindsay AE, Amsterdam E, Mason DT. Paradoxic phenomenon of premature beats with narrow QRS the presence of bundle-branch block. Circulation 1973;47:543–53.CrossRefPubMed
Metagegevens
Titel
What is the origin of the ectopic beat?
Publicatiedatum
01-04-2015
Uitgeverij
Bohn Stafleu van Loghum
Gepubliceerd in
Netherlands Heart Journal / Uitgave 4/2015
Print ISSN: 1568-5888
Elektronisch ISSN: 1876-6250
DOI
https://doi.org/10.1007/s12471-015-0656-y

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