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| [[Puzzle_2005_4_157_Answer|Answer]] | | [[Puzzle_2005_4_157_Answer|Answer]] |
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| The ECG shows sinus rhythm with a rate slightly below
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| 60 beats/min. The PR interval is slightly prolonged
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| (220 ms) and QRS width is normal (80 ms). The
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| electrical axis is at –30°. An old inferior myocardial
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| infarction might be present.
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| The rhythm is slightly irregular. This refers in particular
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| to the 6th P wave, which comes earlier and is
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| slightly different in morphology (most clearly seen in
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| lead III). Hence, this should be referred to as an atrial
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| extrasystole. The PR interval of this extrasystole is
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| further prolonged (360 ms). Although atrial prematurity
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| is generally followed by hampered AV-nodal
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| conduction (i.e. this is normal AV-nodal physiology),
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| a normal AV node should be expected to have recovered
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| completely from previous conduction at these
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| long coupling intervals. Hence, and as also indicated
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| by the baseline prolonged PR interval, his AV node is
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| no longer functioning optimally. The β-blocker might
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| of course be contributing to that.
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| At the most right part of the ECG a long RR
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| interval is seen. Again an atrial extrasystole is present
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| which is now blocked. The coupling interval of this
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| extrasystole is shorter than that of the first atrial extrasystole
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| and is, not unexpectedly given the significantly
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| hampered AV conduction of the first extrasystole, now
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| blocked. The PR interval of the following sinus beat
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| is within normal limits, one more argument for a
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| functional defect in a less than optimally functioning
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| AV node.
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| '''In summary: sinus rhythm with first-degree AV block, (blocked) atrial extrasystoles.'''
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