Question

Einthoven's law is best expressed as:

• A. I + III = II
• B. I - III = II
• C. I + II + III = 0
• D. I + III = aVL

Hint:

In Einthoven's triangle, lead II equals lead I plus lead III.

Answer 1

The Correct Option is A

Step 1: Einthoven's law concerns the three standard bipolar limb leads of the ECG, namely lead I, lead II and lead III, which together form Einthoven's triangle.

Step 2: The law states that if the electrical potentials of any two of these three bipolar limb leads are known at a given instant, the third can be determined mathematically by summing the first two, observing the correct positive and negative signs.

Step 3: Applying the sign convention of the triangle, the voltage in lead II equals the sum of the voltages in leads I and III. This is written as \(I + III = II\).

Step 4: Hence option a is correct. The other expressions do not satisfy the algebraic relationship among the bipolar limb leads.