A wide QRS complex is more than 2.5 mm (100 msec) at standard settings. This can be caused by ventricular rhythms / pacing or abnormal conduction e.g. bundle branch blocks, hyperkalemia, sodium channel blockade, pre-excitation or hypothermia.
The QRS must be more than 3 mm (120 msec) to diagnose a complete bundle branch block.See also: QRS complex
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This ECG is from a man in his 60s who presented with abdominal pain dyspnoea and altered level of consciousness, in shock.
This ECG shows wide complex tachycardia with concordant ST elevation in V4-6, due to LAD occlusion. The rhythm was likely sinus tachycardia with RBBB and then LAFB mid way through the trace.