A very fast wide complex tachycardia

A patient presented by EMS with non-specific symptoms.  He had a very rapid rhythm that was not converted by 6 mg, then 12 mg of adenosine.On arrival, his BP was 94/75, pulse 127.Here is his 12-lead:Wide complex, Rate 265( " Pulse " was 127, so many of these beats are not resulting in a strong enough pulse to be palpated.)What do you think?Because of the extremely fast rate, the treating physicians thought that this was atrial fib with WPW.  However, this is clearly a misdiagnosis.When the rate is so fast, it is possible to mistake a regular rhythm for an irregular one.  So one should use calipers (or mark a piece of paper and use it as calipers).  If one does this, one finds that this is perfectly regular.Atrial fibrillation is ALWAYS irregular. This cannot be atrial fibrillation.Furthermore, Atrial fibrillation with WPW always has polymorphic QRS complexes.  These complexes are all the same.What is the morphology of these QRS complexes?They are perfect LBBB complexes:  a sharp initial r-wave followed by a an S-wave that has a rapid depolarization. The rS duration is about 55 ms, which is very short (fast) and indicates that this is a supraventricular rhythm.Here are V2 and V3 magnified:The initial r-wave is about 30 ms.  If this were VT or antidromic AVRT, the r-wave would be greater than 30 ms.The rS is about 55 milliseconds.If VT, it would be greater than 70 ms.So this is a regular supraventricular fast non-sinus rhythm with LBBB.&n...
Source: Dr. Smith's ECG Blog - Category: Cardiology Authors: Source Type: blogs