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DIAGNOSIS: Paroxysmal Supraventricular Tachycardia [PSVT]. Non-specific ST-T changes.
EXPLANATION: With a normal axis and narrow complexes of normal appearance in this regular tachycardia at a rate of more than 200 bpm, one might think that this is a garden variety PSVT. However, this example occurred in a 75 year old woman with no prior history of arrhythmia. Her BP was 100/palp and her only complaint was that of palpitations [any wonder]. Certainly in this age group atrial flutter, atrial fibrillation, and ectopic atrial tachyarrhythmias would be more common and should not be missed. However, there is a feature of interest here which may help to pinpoint the diagnosis and thus suggest the appropriate treatment. Note the retrograde [inverted] P waves peaking out from the terminal portion of the QRS complexes, especially well seen in the inferior leads II, III, and aVF. These so-called pseudo S waves suggest A-V nodal re-entry. In about two thirds of A-V nodal re-entry, the retrograde P is buried in the QRS, in the remaining one third, as in this case, it makes its appearance just after the QRS. If the retrograde P occurs significantly after the QRS, one must think of the concealed bypass conduction syndromes, such as Wolf-Parkinson-White (WPW) and Lowne-Ganong Levine (LGL). These compose about 10%-30% of re-entrant tachycardias. In ectopic atrial tachycardias, the P wave also appears significantly beyond the QRS. In atrial flutter, as we have seen, the atrial rate would be between 250 and 350 bpm with [hopefully] 2:1 or slower conduction and saw-toothed flutter waves apparent in the inferior leads. In atrial fibrillation, the ventricular response would be irregularly irregular. In this patient, the arrhythmia transiently broke after adenosine, and was terminated with intravenous diltiazem. The rate related ST-T changes, best seen in the lateral precordial leads, gradually resolved after conversion to sinus rhythm.
Editor: Sol Nevins MD FACEP. Faculty, Emergency Medicine Residency, Morristown Memorial Hospital, Morristown, N.J.