Question

In a standard ECG, one of the following functions of its components is not correctly interpreted.

• A. P is the contraction of only left atria.
• B. QRS complex represents ventricular contraction.
• C. T is the end of systole.
• D. P is the contraction of both atria.

Answer 1

The Correct Option is A

Let's evaluate each statement regarding the components of an ECG:

P is the contraction of only the left atria:

• This statement is incorrect. The P wave represents the depolarization of both atria (left and right). It does not specifically represent the contraction of only the left atrium. The contraction of the atria occurs after depolarization, but the P wave represents depolarization, not contraction.

QRS complex represents ventricular contraction:

• This statement is correct. The QRS complex represents the depolarization of the ventricles, which leads to ventricular contraction.

T is the end of systole:

• This statement is correct. The T wave represents ventricular repolarization, which occurs towards the end of the systole (contraction phase of the heart).

P is the contraction of both atria:

• This statement is correct. As mentioned earlier, the P wave represents the depolarization of both atria, which leads to their contraction.

The incorrect statement is A.

The correct answer is (A) : P is the contraction of only left atria..

Answer 2

An Electrocardiogram (ECG) records the electrical activity of the heart during a cardiac cycle. Different waves or complexes represent specific electrical events corresponding to depolarization (activation/contraction) and repolarization (recovery/relaxation) of the heart chambers. 

Let's analyze the interpretation of each component mentioned:

• P wave: This wave represents the electrical depolarization of the atria (both right and left). This depolarization initiates atrial contraction (atrial systole). Therefore, the statement "P is the contraction of only left atria" is incorrect because it represents the depolarization and subsequent contraction of both atria. The statement "P is the contraction of both atria" (Option 4) is the correct interpretation.
• QRS complex: This complex represents the depolarization of the ventricles. Ventricular depolarization triggers ventricular contraction (ventricular systole). Atrial repolarization also occurs during this time but is masked by the larger QRS complex. The statement "QRS complex represents ventricular contraction" is a functionally correct interpretation, as depolarization directly leads to contraction.
• T wave: This wave represents the repolarization of the ventricles. Ventricular repolarization marks the return of the ventricles to their resting state, signifying the end of ventricular contraction (systole). Therefore, the statement "T is the end of systole" is a correct interpretation.

Based on the analysis, the interpretation that is not correctly interpreted is that the P wave represents the contraction of only the left atrium.

Comparing the options:

• P is the contraction of only left atria. (Incorrect interpretation)
• QRS complex represents ventricular contraction. (Correct interpretation)
• T is the end of systole. (Correct interpretation)
• P is the contraction of both atria. (Correct interpretation)

The question asks for the function that is not correctly interpreted.

Therefore, the answer is: P is the contraction of only left atria.