The QRS complex represents which of the following?

(Answer to Q. 1)  ANS: B
Ventricular depolarization is represented on the electrocardiogram as the QRS complex. The P wave represents atrial depolarization. The T wave represents ventricular repolarization. Threshold potential is the critical level of electrical excitation reached by any cell, causing an action poten-tial to occur.

(Answer to Q. 2)  ANS: A
The PR segment represents the time delay that occurs within the atrioventricular node and therefore represents the time between atrial and ventricular contractions. The ST segment occurs during ventricular depolarization, the QRS interval represents ventricular polarization, and the QT interval represents the time required for ventricular depolarization and repolarization to oc-cur.

(Answer to Q. 3)  ANS: D
As the electrical impulse travels through the atrioventricular node, there is a 100-ms delay in the conduction. This allows the atria to become fully depolarized and contract before ventricular ex-citation begins. This allows the atrial contraction and emptying to contribute optimally to ventric-ular filling.

(Answer to Q. 4)  ANS: B
V2 is placed in the fourth intercostal space, at the right sterna margin.

(Answer to Q. 5)  ANS: D
Electrical impulses move through a series of high-speed internodal conduction pathways between the sinoatrial and atrioventricular nodes.