LEAD ERRORS:Disconnected or malfunctioning limb cables

According to the Kirchhoff's law, the sum of the voltage gains and voltage drops in a closed circuit is equal to zero. In this diagram (which is not the one of the Einthoven’s triangle) Lead I + Lead II + Lead III = 0

In Einthoven’s triangle lead II is reversedTherefore I + III – II = 0 and III = II – I ( aVF = II – ½ I )

The modern digital ECG systems record and store in their database leads I and II and the six precordial chest leads. Leads III, aVR, aVL and aVF are derived from leads I and II. This reduces by 1/3 the memory space required.

“Einthoven Law”I + III - II = 0

III = II – IaVF = II – ½ I

00390a April 4, 94 11:49 Emergency Dept.

• What has happened?

Notice: Lead II is flat (no waves!)

00390a April 4, 94 11:49 Emergency Dept.

If the left-leg cable is disconnected, lead II is recorded as a straight line.The software uses lead I and this “zero signal” lead II to calculate lead III and the augmented unipolar limb leads (that obviously will be incorrect).

If the technical problem is not properly recognized, it may cause significant diagnostic errors!

The computer program’s diagnosis was: “inferior infarction”

00390a

Computer program’ statement: Inferior infarction is no longer present!.....

00390b ECG recorded 3 hrs. later! (defective cable had been replaced)

If the left-arm cable is disconnected or is non-functional, lead I is recorded as a straight line. The software uses lead II and this “zero signal” lead I to calculate lead III and the augmented unipolar limb lead (that obviously will be incorrect)

00389a

00389b ECG recorded 20 minutes later (defective cable replaced)

If the right arm cable/electrode is detached or nonfunctional,

all the limb leads record a straight line

If the left-arm cable is disconnected or is non-functional, lead I is recorded as a straight line. The software uses lead II and the “zero signal” lead I to calculate lead III and the augmented unipolar limb lead (that obviously will be incorrect).

If the left-leg cable is disconnected, lead II is recorded as a straight line.

If the right arm cable is disconnected or non-functional, all the limb leads are recorded as a straight line

SUMMARY :