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| [[Puzzle_20075_2_072_Answer|Answer]] | | [[Puzzle_20075_2_072_Answer|Answer]] |
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| The initial four beats on the electrocardiogram are
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| compatible with sinus rhythm at a slightly irregular
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| rate. After the 4th beat an extrasystole initiates a narrow
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| QRS complex tachycardia with a cycle length of 340
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| ms (rate of ±180 beats/min). The initiating P wave
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| has a different morphology than the sinus P wave. Its
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| morphology is (also) positive in the inferior leads and
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| negative in lead aVL, indicating a left atrial superior
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| origin. The same P wave is presumably superimposed
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| on the T wave of the subsequent beats (in lead aVL the
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| negative P wave seems clearly discernable).
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| Based on the morphology of the P wave the most
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| likely diagnosis is a left atrial tachycardia, which is not
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| an uncommon finding after a MAZE procedure. An
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| alternative diagnosis could be AV nodal reentrant
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| tachycardia but this is usually initiated by an atrial
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| extrasystole with a long PR interval (the ‘slow pathway’)
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| followed by a retrograde P wave (conducted through
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| the ‘fast pathway’). The morphology and timing of
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| the P wave are not compatible with common type AV
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| nodal reentrant tachycardia or uncommon type AV
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| nodal reentrant tachycardia (the morphology in
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| particular). An orthodromic AV reentry tachycardia
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| (with a concealed bypass) is not likely either because
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| of the presumable positive P wave in the inferior leads.
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| In summary, the most likely diagnosis is a left atrial
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| tachycardia post MAZE procedure.
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