Poaching from Moffitt at VA report. Mini case of a young patient presenting with palpitations with the 1st EKG above.
Several things: Notice the extremely fast rate (>200 BPM!), wide complex, irregularly irregular rhythm, and variable QRS amplitudes and morphologies.
AFIB w/ BBB is certainly on the differential, as is VT (more commonly regular, but can look irregular with fusion/capture beats making their way down the AVN). However, notice how the QRS morphology changes. This makes AFIB w/ BBB less likely. Polymorphic VT is also less likely given that the axis of the QRS complexes does not change with this different beats!
This is a case of AFIB w/ a WPW bypass tract! Treatment of choice? Procainamide which preferentially slows the fast conduction down the bypass tract.
In this case, procainamide failed and cardioversion resulted in the second EKG. Notice the clear delta-waves in the precordial leads! (Also RBBB morphology that may have been leading to some of the QRS morphology variability in the 1st EKG).
AFIB w/ WPW is a dangerous rhythm that may degenerate into VF.
It is important to recognize as nodal blocking agents should be avoided since it would result in conduction only down the fast bypass pathway and an unstable rhythm!