Question

1. On a normal ECG, a wave for atrial repolarization is not recorded. Why?

a. No repolarization of the atria occurs normally.

b. It occurs at the same time as ventricular depolarization and is masked by the QRS complex.

c. It is too small to be picked up by the recording electrodes.

2. If the duration of one cardiac cycle is 0.71 seconds, what is the heart rate?

(68.2 BPM-92.5 BPM-78 BPM-84.5 BPM)

3. Pick the answer which best explains the lag time between the start of QRS and the start of the thumb pulse.

a. It is the time the blood takes to reach the thumb.

b. It is the time it takes for the ventricles to empty and the blood to reach the thumb.

c. It is the time which includes the duration of QRS, the contraction of the ventricles and the time it takes the blood to reach the thumb.

Answer 1

1)Option B - It occurs at the same time as ventricular depolarization and is masked by the QRS complex

Atrial repolarization usually occurs after the atrial depolarization.

Atrial depolarization is marked in the ECG as the p wave. Usually the atrial repolarization is present after the P wave but it is masked by the larger QRS complex representing the ventricular depolarization.Atrial is repolarization is a low voltage wave which is masked by high voltage QRS complex.

2)Heart Rate is defined as the number of cardiac cycle occuring ina a minute of time

Here the time for one cardiac cycle is 0.71 second.

Number of times cardiac cycle occur in a minute = 60second/0.71second =84.5 Beats per minute

3)Option B -It is the time it takes for the ventricles to empty and the blood to reach the thumb.

QRS Complex of the ECG represent the ventricular depolarization.

During ventricular depolarization ,the ventricle empties the blood present in the ventricle to teh aorta and pulmonary arteries.

The blood emptied to aorta produce a pressure in the blood column of the blod vessel which gradually pases through different blood vessel and finally reaches the radial artery and produce the pulsation

A pulse is nothing but the lateral pressure exerted by the blood column on the blood vessel walls.