You and Your Colleague Are Medical Technicians in a Cardiac

You and your colleague are medical technicians in a cardiac function lab.You are reading the ECG of a patient and your friend is trying to capture an image of the AV valves opening using an ultrasound.At what point should you tell your friend to start recording images?

A) Just before the P wave
B) Just after the P wave
C) At the beginning of the QRS complex
D) Just before the T wave
E) After the T wave