Understanding Normal Electrocardiogram (ECG)

What is the purpose of an ECG recording?

Recording the electrical activity that initiates each heartbeat

What does the P wave in a normal ECG represent?

Electrical potential generated from depolarization of the atria before their contraction

Which part of the heart generates the QRS complex in an ECG?

Ventricles before their contraction

What causes the T wave in a normal ECG?

Potential generated from repolarization of the ventricles Signup and view all the answers

How is the P wave related to atrial contraction?

P wave immediately precedes atrial contraction Signup and view all the answers

When does ventricular contraction follow the QRS complex?

Immediately after the QRS complex Signup and view all the answers

What is the normal value of the P-Q or P-R interval on the electrocardiogram?

0.16 second Signup and view all the answers

What does the Q-T interval represent on the electrocardiogram?

The time of ventricular contraction Signup and view all the answers

Where does a cardiac action potential arise?

SA node Signup and view all the answers

What causes the 0.1-sec delay at the AV node?

Conduction slowing due to smaller fibers and fewer gap junctions Signup and view all the answers

What does the appearance of the P wave in the ECG signify?

Depolarization of atrial contractile fibers Signup and view all the answers

Why is the atrial contraction delayed at the AV node?

To allow the atria time to contract before ventricular systole begins Signup and view all the answers

When does the depolarization progress through the bundle branches, Purkinje fibers, and the entire ventricular myocardium?

About 0.2 sec after onset of the P wave Signup and view all the answers

What happens during ventricular systole?

Contraction of ventricular contractile fibers begins Signup and view all the answers

Why is atrial repolarization not usually evident in an ECG?

Atrial repolarization is masked by the larger QRS complex Signup and view all the answers

When does the repolarization of ventricular contractile fibers begin?

At the apex Signup and view all the answers

When does ventricular repolarization complete and the ventricular contractile fibers relax?

By 0.6 sec Signup and view all the answers

What happens as contraction proceeds from the apex toward the base of the heart during ventricular systole?

Blood is squeezed upward toward the semilunar valves Signup and view all the answers