Waves, Complexes, Segments, and Intervals on EKG

Question 1

Correlate the path of cardiac electrical activity with each of the normal EKG waveforms

Answer 1

• P wave - atrial depolarization

1. Electrical impulse begins at SA node
2. Electrical impulse continues thru the atria
3. Conduction delay at the AV node

• QRS - ventricular depolarization
  
  • Q wave = first downward reflection (if first is upward, then there’s no Q wave)
  • R wave = first upward reflection
  • S wave = any downward reflection following the R wave
• T wave - ventricular repolarization

Question 2

Normal Sinus Rhythm

Answer 2

= the normal cardiac rhythm

1. Every P wave is followed by a QRS complex
2. Every QRS complex is preceded by a P wave
3. The P wave is upright in leads I, II, and III
4. The PR interval > 0.12 seconds (3 small boxes)

Question 3

Formula for calculating HR using the EKG

Answer 3

Or simply count off boxes starting from the R wave:

300—150—100—75—60—50

[1 box–2–3–4–5–6]

Question 4

PR Interval

Answer 4

Measured from the beginning of the P wave to the beginning of the QRS complex

Question 5

QRS duration

Answer 5

Measured from the beginning to the end of the QRS complex

Question 6

QT Interval

Answer 6

Measured from the beginning of the QRS complex to the beginning of the T wave.

Corrected QT interval = QT interval/ [sq root(R-R interval)]