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| [[Puzzle 2005_8_285 - Answer|Answer]] | | [[Puzzle 2005_8_285 - Answer|Answer]] |
| [[Image:Puzzle_2005_8_285_fig3.jpg|Figure 3|thumb]]
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| The above information should raise the suspicion of a
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| Mahaim fibre. This is an accessory pathway with AVnode-
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| like properties. Due to its decremental properties
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| preexcitation is subtle and may even be absent. The
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| Mahaim fibre only conducts in an antegrade fashion
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| and usually has a long course, extending from the free
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| wall of the right atrium across the tricuspid annulus to
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| the right bundle. Consequently, tachycardias run in
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| an antidromic direction and generally show an LBBB
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| morphology with a superior axis. Although the original
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| publications by Mahaim, who was a contemporary of
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| Wenckebach, were on nodoventricular and fasciculoventricular
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| fibres, his name survived all new insights
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| and nomenclature published thereafter and is still used
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| to paraphrase an entire family of accessory pathways
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| with AV-node-like behaviour.
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| In this patient the combination of subtle signs of
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| preexcitation in the resting ECG, absent Q wave in
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| leads I, V5 and V6, an RS in III and the wide QRS
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| tachycardia with LBBB morphology and left-axis
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| deviation is highly suggestive of the diagnosis of
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| Mahaim fibre. During invasive electrophysiological
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| testing a Mahaim fibre was identified running from the
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| anterior site of the tricuspid valve annulus to the distal
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| right bundle. The Mahaim bundle was successfully
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| ablated at the level of the annulus. The ECG shown in
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| figure 3 no longer reveals the subtle signs of abnormal
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| initial activation or preexcitation. During follow-up,
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| the patient remained free from symptoms.
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