NCLEX RN Practice Question # 661

NCLEX Examination.

Practice Question # 661.

Basics of Electrocardiography

• An electrocardiogram (ECG) reflects the electrical activity of cardiac cells and records electrical activity at a speed of 25 mm/ second.
• An electrocardiographic strip consists of horizontal lines representing seconds and vertical lines representing voltage.
• Each small square represents 0.04 second.
• Each large square represents 0.20 second.

• The P wave represents atrial depolarization.
• The PR interval represents the time it takes an impulse to travel from the atria through the atrioventricular node, bundle of His, and bundle branches to the Purkinje fibers.
• Normal PR interval duration ranges from 0.12 to 0.2 second.
• The PR interval is measured from the beginning of the P wave to the end of the PR segment.
• The QRS complex represents ventricular depolarization.
• Normal QRS complex duration ranges from 0.04 to 0.1 second.
• The Q wave appears as the first negative deflection in the QRS complex and reflects initial ventricular septal depolarization.
• The R wave is the first positive deflection in the QRS complex.
• The S wave appears as the second negative deflection in the QRS complex.
• The J point marks the end of the QRS complex and the beginning of the ST segment.
• The QRS duration is measured from the end of the PR segment to the J point.
• The ST segment represents early ventricular repolarization.
• The T wave represents ventricular repolarization and ventricular diastole.
• The U wave may follow the T wave.
• A prominent U wave may indicate an electrolyte abnormality, such as hypokalemia.
• The QT interval represents ventricular refractory time or the total time required for ventricular depolarization and repolarization.
• The QT interval is measured from the beginning of the QRS complex to the end of the T wave.
• The QT interval normally lasts 0.32 to 0.4 second but varies with the client’s heart rate, age, and gender.