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| [[Puzzle_2007_5_198_Answer|Answer]] | | [[Puzzle_2007_5_198_Answer|Answer]] |
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| The left part of the ECG shows a narrow complex
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| tachycardia with a rate of 200 beats/min (RR interval
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| 320 ms). At first glance a P wave is not clearly discernable.
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| After five cycles, the tachycardia suddenly stops
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| and four multiform complexes are seen without any P
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| waves. These complexes should be regarded as a polymorphic
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| ventricular tachycardia, which is not uncommon
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| after an adenosine-terminated supraventricular
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| tachycardia.<cite>Tan</cite> A fifth complex is preceded by a P wave.
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| The subsequent four complexes are morphologically
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| similar, all show a widened QRS complex and all are
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| immediately preceded by a P wave. The initial phase
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| of the QRS complex is slurred and positive in all available
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| leads. Sinus rhythm continues thereafter with
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| gradual abbreviation of the QRS complex until a 120
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| msec wide QRS complex remains. A close look reveals
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| that the PQ interval remains short and that the initial
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| phase of these QRS complexes is still slurring.
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| All tachycardias that include the AV node in their
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| circuit are sensitive to adenosine. This includes AV
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| nodal reentrant tachycardia and AV reentrant tachycardia.
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| Conduction through the AV node is temporarily
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| blocked by adenosine and the fact that AV conduction
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| is still present (the four similar wide QRS complexes
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| preceded by a P wave) suggests the presence of an
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| alternative AV connection. (i.e. a Kent bundle). After
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| restoration of the AV node both pathways are used.
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| Hence, the initial polymorphic ventricular tachycardia
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| is followed by restoration of sinus rhythm, initially
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| exclusively conducted over an accessory pathway,
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| followed by preexcitation and normal AV conduction.
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| Figure 2 shows the ECG during sinus rhythm. A
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| discrete Δ wave is clearly visible. The morphology of
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| the Δ wave suggests a left posterior Kent bundle.
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| '''Conclusion: Wolff-Parkinson-White syndrome with an orthodromic circus movement tachycardia and under the influence of adenosine temporarily exclusive preexcitation.'''
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| ==References==
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| <biblio>
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| #Tan pmid=11341081
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| </biblio>
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