ECG Study Guide - Hoag Hospital Exam Practice
2026
1. Cardiac Conduc- The SA node is the heart's primary pacemaker. Electrical firing starts in the SA node,
tion: Normal Elec- then travels through the AV node, down the bundle of his and right/left bundle
tricity Pathway branches, and ends in the purkinje fibers. The final result is ventricular contractions.
2. Cardiac Conduc- The electrical pathway may become interrupted or altered depending on a pa-
tion: Interrupted tient's acute or chronic condition. If the SA node is damaged or impaired, the AV
or Altered node will initiate an electrical impulse at a rate of 40-60 beats per minute. If the AV
node is damaged or impaired, the purkinje fibers will initiate an electrical impulse
at a rate of 20-40 beats per minute.
3. Blood Flow 1) The inferior and superior vena cava returns deoxygenated blood from the body
Through the to the right atrium
Heart 2) The right atrium delivers deoxygenated blood to the right ventricle through the
tricuspid valve
3) The right ventricle pumps the deoxygenated blood through the pulmonic valve
to the pulmonary arteries. The lungs provide oxygen and "oxygenate" the blood.
4) Oxygenated blood flows through the pulmonary veins to the left atrium.
5) The left atrium delivers blood to the left ventricle through the mitral valve.
6) The left ventricle pumps oxygenated blood through the aortic valve where it is
distributed throughout the body.
4. Electricity and 1) Electrical activity, atrial contractions and ventricular contractions are intercon-
Blood Flow nected
2) If the electrical pathway is altered or impaired (i.e. atrial fibrillation, ventricular
tachycardia), the blood flow pathway is also attected.
5. P wave The P wave represents atrial contraction or depolarization
6. QRS Wave/Com- The QRS wave/complex represents ventricular contraction or depolarization
plex
7. Q wave The Q wave is the first negative deflection after the P wave
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, ECG Study Guide - Hoag Hospital Exam Practice
2026
8. R Wave The R wave is the first positive deflection after the P wave
9. S wave The S wave is the first negative deflection after the R wave
10. Normal QRS In- The normal QRS interval is 0.04 - 0.12 seconds
terval
11. T wave The T wave represents ventricular relaxation or repolarization
12. PR Interval: Mea- The PR interval is measured from the beginning of the P wave to the beginning of
surement the QRS complex
13. Normal PR Inter- The normal PR interval is 0.12 - 0.20 seconds
val
14. ST Segment The ST segment is not measured, however the shape and location should be
evaluated as pathologic conditions may be identified by an elevated or depressed
ST segment
15. QT Interval QT interval is measured from the beginning of the QRS complex to the end of the
T wave
16. Normal QT Inter- The normal QT interval is 0.33 - 0.44 seconds, but is adjusted for heart rate
val
17. When measur- 1) Measurements must be exact-when performing measurements on paper it is
ing ECG intervals best to use calipers to ensure that results are accurate
please note the 2) One small box on a six second strip is equal to 0.04 seconds
following: 3) One large box is equal to 0.20 seconds
18. The Six Second Obtain a six second tracing (30 five mm boxes) and count the number of R waves
Tracing Method that appear within that 6 second period and multiply by 10 to obtain the HR/min
*This method is the least accurate - however, it is the easiest and most appropriate
2/5
2026
1. Cardiac Conduc- The SA node is the heart's primary pacemaker. Electrical firing starts in the SA node,
tion: Normal Elec- then travels through the AV node, down the bundle of his and right/left bundle
tricity Pathway branches, and ends in the purkinje fibers. The final result is ventricular contractions.
2. Cardiac Conduc- The electrical pathway may become interrupted or altered depending on a pa-
tion: Interrupted tient's acute or chronic condition. If the SA node is damaged or impaired, the AV
or Altered node will initiate an electrical impulse at a rate of 40-60 beats per minute. If the AV
node is damaged or impaired, the purkinje fibers will initiate an electrical impulse
at a rate of 20-40 beats per minute.
3. Blood Flow 1) The inferior and superior vena cava returns deoxygenated blood from the body
Through the to the right atrium
Heart 2) The right atrium delivers deoxygenated blood to the right ventricle through the
tricuspid valve
3) The right ventricle pumps the deoxygenated blood through the pulmonic valve
to the pulmonary arteries. The lungs provide oxygen and "oxygenate" the blood.
4) Oxygenated blood flows through the pulmonary veins to the left atrium.
5) The left atrium delivers blood to the left ventricle through the mitral valve.
6) The left ventricle pumps oxygenated blood through the aortic valve where it is
distributed throughout the body.
4. Electricity and 1) Electrical activity, atrial contractions and ventricular contractions are intercon-
Blood Flow nected
2) If the electrical pathway is altered or impaired (i.e. atrial fibrillation, ventricular
tachycardia), the blood flow pathway is also attected.
5. P wave The P wave represents atrial contraction or depolarization
6. QRS Wave/Com- The QRS wave/complex represents ventricular contraction or depolarization
plex
7. Q wave The Q wave is the first negative deflection after the P wave
1/5
, ECG Study Guide - Hoag Hospital Exam Practice
2026
8. R Wave The R wave is the first positive deflection after the P wave
9. S wave The S wave is the first negative deflection after the R wave
10. Normal QRS In- The normal QRS interval is 0.04 - 0.12 seconds
terval
11. T wave The T wave represents ventricular relaxation or repolarization
12. PR Interval: Mea- The PR interval is measured from the beginning of the P wave to the beginning of
surement the QRS complex
13. Normal PR Inter- The normal PR interval is 0.12 - 0.20 seconds
val
14. ST Segment The ST segment is not measured, however the shape and location should be
evaluated as pathologic conditions may be identified by an elevated or depressed
ST segment
15. QT Interval QT interval is measured from the beginning of the QRS complex to the end of the
T wave
16. Normal QT Inter- The normal QT interval is 0.33 - 0.44 seconds, but is adjusted for heart rate
val
17. When measur- 1) Measurements must be exact-when performing measurements on paper it is
ing ECG intervals best to use calipers to ensure that results are accurate
please note the 2) One small box on a six second strip is equal to 0.04 seconds
following: 3) One large box is equal to 0.20 seconds
18. The Six Second Obtain a six second tracing (30 five mm boxes) and count the number of R waves
Tracing Method that appear within that 6 second period and multiply by 10 to obtain the HR/min
*This method is the least accurate - however, it is the easiest and most appropriate
2/5
