Question

An ECG has a scalar magnitude of 1 mV on lead II and a scalar magnitude of 0.5 mV on lead III. Calculate the scalar magnitude on lead I.

Answer 1

Answer: the scalar magnitude on lead I is 0.5 mV

Explanation:

Given that;

scalar magnitude on lead II = 1 mV

scalar magnitude on lead III = 0.5 mV

the scalar magnitude on lead I = ?

we know that;

Lead I Voltage = LA - RA -----------let this be equation 1

where LA is left arm electrode and RA is right am electrode

Also

Lead II = LL - RA

where LL is the left leg of electrode

we substitute

1 mV = LL - RA ---------------------let this be equation 2

Again

Lead III = LL - LA

we substitute

0.5 mV = LL - LA ------------------let this be equation 3

now subtract equation 3 and 2

1 mV - 0.5 mv = LL - RA - (LL - LA)

0.5 mV = LL - RA - LL + LA

0.5 mV = -RA + LA

0.5 mV = LA - RA

now taking a look at our equation 1 ( Lead I Voltage = LA - RA )

hence, Lead I Voltage = LA - RA = 0.5 mV

Therefore the scalar magnitude on lead I is 0.5 mV