Rhythm

puzzle

T.A. Simmers, A.A.M. Wilde

Carotid sinus clues This six-lead tracing was obtained during carotid sinus massage (CSM). The patient, a 42-year-old male, had been experiencing attacks of rapid heart rate for many years. This was one of the rare occasions that symptoms had lasted long enough for him to make it to the emergency room

in

time

for an ECG. The left part of the tracing shows a narrow QRS complex tachycardia with a 1:1 P:QRS relationship. Differential diag-

nosis ofthis arrhythmia should include: 1) circus movement tachycardia, based on the position of the P wave 'sandwiched' between two QRS complexes; as there is no preexcitation in sinus rhythm following termination of the

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tachycardia, one would have to assume a concealed bypass,

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