Altered mental status, seizure, extreme hypertension, and a bizarre ECG

A middle aged woman with few serious medical issues presented with altered mental status, had a generalized tonic clonic seizure, and was found to be hypertensive and tachycardic. An ECG was recorded:What is it?The computer measures QRS duration as 126 ms.This is a regular, wide complex tachycardia, but not very wide. There are no P-waves. The QRS has 2 alternating morphologies, both of which are right bundle branch block (RBBB) in configuration, but which have different axes. Both complexes have an rSR ' in lead V1 and a wide S-wave in V6.One might suspect that the higher voltage beats are premature beats, but by my calipers, the intervals are identical. (This is critical to being certain that they are not premature beats.) Similarly, one might suspect every-other-beat pre-excitation, but no delta waves are seen.See how the S-wave in lead I alternates small, large, small, large... The large S-wave indicates right axis deviation and appears to be due to alternating left posterior fascicular block, in addition to RBBB.So this isSVT with alternating aberrancy: RBBB, then RBBB + LPFB, then RBBB, then RBBB + LPFB.....The question ofelectrical alternans came up. SVT frequently has electrical alternans but, unlike in sinus tach, it is not correlated with effusion or tamponade. In this case, it is not the typical SVT electrical alternans -- the alternans is due to alternating conduction.She spontaneously converted:Sinus tachycar...
Source: Dr. Smith's ECG Blog - Category: Cardiology Authors: Source Type: blogs