The Christmas Tree Sign: A diagnostic tool for ECG connoisseurs
(Borrowed from The BMJ (2014): https://www.bmj.com/content/349/bmj.g7342.long)
Although sometimes challenging, ECGs can often provide invaluable information for those willing to look closely. However, we suggest a way of reading ECGs that has been neglected for more than 100 years. The following example shows its worth.
This rhythm strip from an elderly patient attending the ED of St Thomas’ Hospital, London. When the strip was turned 90° anticlockwise, however, the diagnostic “Christmas Tree Sign” became readily apparent. Reassuringly, the EP residents picked up this diagnostic marker, instantly (fig 2⇓).
The patient had Bi-Directional Ventricular Tachycardia (Bi-D VT) with underlying Dilated Cardio-Myopathy (DCM).
Bi-Directional VT is a rare arrhythmia characterised by an alternating QRS axis on a beat-to-beat basis. It is most commonly associated with severe Digitalis or Aconite toxicity. Another important Differential Diagnosis is familial Catecholaminergic Polymorphic VT (CPVT), which may be precipitated by exercise.
The proposed arrhythmia mechanism is triggered activity arising alternately from the left anterior and posterior fascicle. This results in an alternating left and right frontal-plane axis, giving rise to a typical “bidirectional” appearance.