COMPREHENSIVE BASIC
ARRHYTHMIA STUDY GUIDE:
ESSENTIAL QUESTIONS AND
ANSWERS WITH DETAILED
RATIONALES FOR THE SENTARA
COMPETENCY EXAMINATION
ECG Fundamentals & Measurements
1. What does the P wave represent on an ECG?
Answer: Atrial depolarization (contraction)
Rationale: The P wave reflects the electrical impulse spreading
through the atria from the SA node .
2. What does the QRS complex represent?
Answer: Ventricular depolarization (contraction)
Rationale: The QRS complex represents the electrical impulse
traveling through the bundle branches and Purkinje fibers, causing
ventricular contraction .
3. What does the T wave represent?
Answer: Ventricular repolarization (relaxation)
, Rationale: The T wave represents the recovery phase of the ventricles
as they repolarize after contraction .
4. What is the normal duration of the PR interval?
Answer: 0.12 – 0.20 seconds
Rationale: A PR interval >0.20 seconds indicates first-degree AV
block .
5. What is the normal duration of the QRS complex?
Answer: 0.06 – 0.12 seconds
Rationale: A QRS duration >0.12 seconds indicates a bundle branch
block or a ventricular origin of the rhythm .
6. What is the normal duration of the QT interval?
Answer: 0.32 – 0.44 seconds
Rationale: The QT interval represents the total time for ventricular
depolarization and repolarization .
7. How many seconds is one small square on ECG paper?
Answer: 0.04 seconds
Rationale: Each small square represents 0.04 seconds when the ECG
runs at standard speed (25 mm/sec) .
8. How many seconds is one large square on ECG paper?
Answer: 0.20 seconds
Rationale: One large square contains 5 small squares: 5 × 0.04
seconds = 0.20 seconds .
9. What is the "300 method" for calculating heart rate?
, Answer: Count the number of large squares between two R waves
and divide 300 by that number
Rationale: If the R-R interval is 4 large squares, rate = 300 ÷ 4 = 75
bpm .
10. What is the "1500 method" for calculating heart rate?
Answer: Count the number of small squares between two R waves
and divide 1500 by that number
Rationale: This method works best for regular rhythms .
Sinus Rhythms
11. What are the characteristics of Normal Sinus Rhythm?
Answer: Regular rhythm, rate 60-100 bpm, upright uniform P waves
before each QRS, PR interval 0.12-0.20 seconds, QRS <0.12 seconds
Rationale: Normal sinus rhythm originates in the SA node with
consistent P wave morphology and constant 1:1 P-to-QRS
relationship .
12. What is the rate range for Sinus Bradycardia?
Answer: Less than 60 bpm
Rationale: Sinus bradycardia shares identical electrical features with
normal sinus rhythm except that the rate slows below 60 beats per
minute due to increased vagal tone or SA node depression .
13. What is a normal physiologic cause of sinus bradycardia?
Answer: Athletic conditioning / high vagal tone
, Rationale: Well-conditioned athletes often have resting heart rates
below 60 bpm due to increased stroke volume and high vagal tone.
This is a normal physiologic adaptation .
14. What is the characteristic rate for Sinus Tachycardia?
Answer: Greater than 100 bpm (typically 100-150 bpm)
Rationale: Sinus tachycardia is a sinus rhythm with a rate greater than
100 bpm. Common causes include fever, anxiety, exercise,
dehydration, and hyperthyroidism .
15. What is the appropriate treatment for asymptomatic sinus
bradycardia?
Answer: Continue monitoring; no immediate treatment required
Rationale: In asymptomatic patients, treatment is not indicated—
monitoring is sufficient. Atropine and transcutaneous pacing are
reserved for symptomatic bradycardia .
16. What is the primary treatment priority for sinus tachycardia?
Answer: Identify and treat the underlying cause
Rationale: Sinus tachycardia is a compensatory response to
underlying physiological stressors. The priority is treating the cause
(fever, pain, dehydration, anxiety, hypoxia) rather than the rhythm
itself .
17. What characterizes Sinus Arrhythmia?
Answer: An irregular rhythm varying with respiration, featuring
normal P waves and a heart rate between 60 and 100 beats per
minute
ARRHYTHMIA STUDY GUIDE:
ESSENTIAL QUESTIONS AND
ANSWERS WITH DETAILED
RATIONALES FOR THE SENTARA
COMPETENCY EXAMINATION
ECG Fundamentals & Measurements
1. What does the P wave represent on an ECG?
Answer: Atrial depolarization (contraction)
Rationale: The P wave reflects the electrical impulse spreading
through the atria from the SA node .
2. What does the QRS complex represent?
Answer: Ventricular depolarization (contraction)
Rationale: The QRS complex represents the electrical impulse
traveling through the bundle branches and Purkinje fibers, causing
ventricular contraction .
3. What does the T wave represent?
Answer: Ventricular repolarization (relaxation)
, Rationale: The T wave represents the recovery phase of the ventricles
as they repolarize after contraction .
4. What is the normal duration of the PR interval?
Answer: 0.12 – 0.20 seconds
Rationale: A PR interval >0.20 seconds indicates first-degree AV
block .
5. What is the normal duration of the QRS complex?
Answer: 0.06 – 0.12 seconds
Rationale: A QRS duration >0.12 seconds indicates a bundle branch
block or a ventricular origin of the rhythm .
6. What is the normal duration of the QT interval?
Answer: 0.32 – 0.44 seconds
Rationale: The QT interval represents the total time for ventricular
depolarization and repolarization .
7. How many seconds is one small square on ECG paper?
Answer: 0.04 seconds
Rationale: Each small square represents 0.04 seconds when the ECG
runs at standard speed (25 mm/sec) .
8. How many seconds is one large square on ECG paper?
Answer: 0.20 seconds
Rationale: One large square contains 5 small squares: 5 × 0.04
seconds = 0.20 seconds .
9. What is the "300 method" for calculating heart rate?
, Answer: Count the number of large squares between two R waves
and divide 300 by that number
Rationale: If the R-R interval is 4 large squares, rate = 300 ÷ 4 = 75
bpm .
10. What is the "1500 method" for calculating heart rate?
Answer: Count the number of small squares between two R waves
and divide 1500 by that number
Rationale: This method works best for regular rhythms .
Sinus Rhythms
11. What are the characteristics of Normal Sinus Rhythm?
Answer: Regular rhythm, rate 60-100 bpm, upright uniform P waves
before each QRS, PR interval 0.12-0.20 seconds, QRS <0.12 seconds
Rationale: Normal sinus rhythm originates in the SA node with
consistent P wave morphology and constant 1:1 P-to-QRS
relationship .
12. What is the rate range for Sinus Bradycardia?
Answer: Less than 60 bpm
Rationale: Sinus bradycardia shares identical electrical features with
normal sinus rhythm except that the rate slows below 60 beats per
minute due to increased vagal tone or SA node depression .
13. What is a normal physiologic cause of sinus bradycardia?
Answer: Athletic conditioning / high vagal tone
, Rationale: Well-conditioned athletes often have resting heart rates
below 60 bpm due to increased stroke volume and high vagal tone.
This is a normal physiologic adaptation .
14. What is the characteristic rate for Sinus Tachycardia?
Answer: Greater than 100 bpm (typically 100-150 bpm)
Rationale: Sinus tachycardia is a sinus rhythm with a rate greater than
100 bpm. Common causes include fever, anxiety, exercise,
dehydration, and hyperthyroidism .
15. What is the appropriate treatment for asymptomatic sinus
bradycardia?
Answer: Continue monitoring; no immediate treatment required
Rationale: In asymptomatic patients, treatment is not indicated—
monitoring is sufficient. Atropine and transcutaneous pacing are
reserved for symptomatic bradycardia .
16. What is the primary treatment priority for sinus tachycardia?
Answer: Identify and treat the underlying cause
Rationale: Sinus tachycardia is a compensatory response to
underlying physiological stressors. The priority is treating the cause
(fever, pain, dehydration, anxiety, hypoxia) rather than the rhythm
itself .
17. What characterizes Sinus Arrhythmia?
Answer: An irregular rhythm varying with respiration, featuring
normal P waves and a heart rate between 60 and 100 beats per
minute
