A 68‐year‐old woman is admitted to A&E with sudden increased shortness of breath and palpitations. She is known to have angina and is complaining of chest pain, similar to her usual exertional pain.

Examination reveals that she is clammy and unwell. Her heart rate is 150–170 beats/min, and BP 88/40 mmHg. SpO₂ is 92% with reservoir bag. Her respiratory rate is 22 breaths/min and her chest has fine crepitations throughout. An ECG has been performed (Fig. 0003).

Fig. 0003.