Professional ECG ruler, for reading: 2 x RR (25 mm/s) 1 x RR (50 mm/s) 3 x RR (25 mm/s) 3 x RR (50 mm/s) 4 x RR (25 mm/s) Amplitudes (mV) Times, intervals (s) Conversion: heart rate - RR interval Table. heart rate - PR interval - relative QT interval
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