So far as I know, a 12-lead ECG system is able to generate waveforms on Lead I, II, III, aVR, aVL, and aVF. A 5-lead ECG system is also able to provide all these information. So what is the difference between a 12-lead and a 5-lead ECG system? What are Lead I, II, III, aVR, aVL and aVF for? For heart rate estimation, is it feasible to analyze Lead II only? Thank you guys.