DIAGNOSIS: Atrial Flutter with 2:1 conduction progressing to atrial flutter with 1:1 conduction in the second tracing. Left anterior fascicular block. Non-specific ST-T changes.

EXPLANATION: This 54 year old gentleman who complained of palpitations was sent to the ED by his physician via ambulance with a provisional diagnosis of ventricular tachycardia. In the first tracing, a regular narrow complex tachycardia is evident at a rate of 125. Since the QRS duration is never more than 100 msec, the origin of the tachycardia is most likely supraventricular. A very abnormal p wave axis with negative p waves in the inferior leads II, III, and aVF suggests flutter. On closer look, these negative p waves can be seen deforming the T wave after each beat as well as preceding each QRS complex at a rate exactly double the ventricular rate. The flutter rate is 250 bpm; a bit slow, but still within the range of 250-350 bpm. The axis is leftward at minus 60 degrees, and with small r waves in the inferior leads, LAFB may be diagnosed. There are diffuse mild ST-T abnormalities; these are best called non-specific and are most likely rate-related.
Flutter with 2:1 conduction is notoriously difficult to differentiate from PSVT because the typical sawtooth pattern is hidden by the QRS complexes. One must have a high default of suspicion and look carefully for an abnormal p axis. Vagal maneuvers or adenosine may transiently block the AV node and "bring out" the flutter waves. This patient however was given a bolus of lidocaine at which point the rhythm changed to that noted in the second tracing. Conduction was now 1:1 at a rate of 250 bpm! This is a somewhat less desirable way of "proving" that the tachycardia is flutter. Lidocaine is not chicken soup; it has variable effects on the AV node, sometimes slowing conduction, sometimes speeding conduction and causing cardiovascular collapse due to the increased rate. This outcome is particularly likely with rapid atrial fibrillation when wide complex Ashman beats are present and are mistaken for VPBs.
Fortunately, this patient remained stable from a cardiovascular standpoint. He was then immediately given diltiazem with a return to 2:1 conduction.. Later, procainamide was added, with eventual conversion to normal sinus rhythm 24 hours after admission.
Thanks to Dr George Kiss for the ECG tracings.

Editor: Sol Nevins MD FACEP. Faculty, Emergency Medicine Residency, Morristown Memorial Hospital, Morristown, N.J.