ECG Case 137

At first glance, broad complexes varying in duration and amplitude may appear to represent polymorphic ventricular tachycardia (VT).

However, on closer inspection we note three features that suggest this is artefact:

• The onset is too abrupt, and there is no ‘R-on-T’ phenomenon — the apparent tachycardia begins after a T wave. Polymorphic VT is usually initiated by a premature ventricular complex (PVC) or premature atrial complex (PAC) that ‘lands’ on the preceding T wave
• The rate in the initial portion of the rhythm strip is simply too high for VT — if you look closely it is approaching 600 bpm
• Lastly, we can see QRS complexes ‘marching’ through at a rate of 60 bpm (every 5 large squares)

Most importantly, the patient was still conscious and had no change in symptoms!

Let’s compare the above example to a true case of polymorphic VT:

• There are frequent PVCs after the second, third and fourth QRS complexes. The fourth PVC lands on the preceding T wave (‘R on T’ phenomenon), triggering a run of polymorphic VT
• The rate is regular at approximately 300 bpm
• Note subsequent degeneration into ventricular fibrillation (VF)

Alarms and calls for ‘VTach’ are common for pre-hospital, emergency, and ward-based clinicians.

Artefacts generated by voluntary or involuntary movements during an ECG recording can simulate malignant arrhythmias and lead to unnecessary interventions. On the contrary, mistaking a true arrhythmia for artefact can have dire consequences.

Firstly, look at the patient. If there is no change to the clinical picture, take a closer look at the rhythm strip. An atypical onset, extremely high rates, and QRS complexes “marching” through may suggest artefact.

The presence of an unchanged pulse oximetry curve further points towards the presence of artefact.