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.

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