Broad complex tachycardia: a diagnostic dilemma.

A 56 year old woman was admitted to hospital with an hour long history of palpitations. She had suVered palpitations on three occasions over the preceding 12 months, each lasting for approximately half an hour. During these episodes she felt light headed but had not lost consciousness. Past medical history was unremarkable and she was taking no drugs. On admission to hospital her symptoms had settled spontaneously and clinical examination was normal. A 12 lead ECG showed sinus rhythm and no other abnormality. Baseline blood tests, cardiac enzymes, and thyroid function tests were normal. She remained in sinus rhythm over the subsequent 24 hours and Holter monitoring was arranged as an outpatient. However, just before her discharge her symptoms returned and the heart rate was 160 beats/min and blood pressure 90/70. A 12 lead ECG was recorded which is shown in fig 1.