The ECG shown is diagnostic of which one of the following rhythms?
A. AF with aberrancy
The clue to this ECG is the irregular nature of the QRS complexes, although this can be difficult to detect at fast heart rates. AF with aberrancy would also be possible with an irregular rhythm, but this would have a more typical bundle branch block appearance. In a compromised patient with very short RR intervals and broad QRS complexes, pre-excited AF should be presumed. Drugs that block the AV node should be avoided in pre-excited AF as they are ineffective because fast conduction is across the pathway. Drugs which are negatively inotropic, such as calcium-channel blockers and beta-blockers can also lead to worsening haemodynamics and even death and therefore are contraindicated. Intravenous flecainide could be considered as it will slow conduction across the pathway, but this patient’s heart is going very fast with symptoms and a low BP, and therefore urgent DC cardioversion should be performed in ED resuscitation.