When faced with a patient with a BCT, the default position should be to assume that the arrhythmia is ventricular in origin until proved otherwise, particularly if the patient is over the age of 35 with a history of ischaemic heart disease or congestive cardiac failure.

However, tachycardias with a supraventricular origin can present as a BCT when associated with aberrant conduction or a pre-existing bundle branch block. The ECG shows atrial flutter and right bundle branch block – note the rate is in excess of 200 bpm.

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