APEX Cardiac Rhythms Question and
answers already passed 2026/2027
What are the 3 internodal tracts that connect the SA to the AV node? - correct answer Anterior =
Bachmann bundle (extends to LA)
Middle = Wenckebach
Posterior = Thorel
Conduction velocity of SA and AV nodes - correct answer 0.02 - 0.1 m/sec (slow)
Conduction velocity of myocytes - correct answer 0.3 -1 m/sec (intermediate speed)
Conduction velocity of His bundle, bundle branches, purkinje fibers - correct answer 1-4 m/sec (fast)
Conduction velocity is a function of what 3 things - correct answer 1. Resting membrane potential
2. Amplitude of the action potential
3. Rate of change in membrane potential during phase 0 (Initial depolarization)
Conduction velocity is affected by what 5 things - correct answer 1. Ischemia
2. ANS tone
3. Hyperkalemia (closure of fast Na channels due to significantly increased membrane potential)
4. Acidosis
5. Antiarrythmics
,List and describe the 4 major accessory pathways - correct answer 1. James fiber: Atrium → AV node
2. Atrio-hisian fiber: Atrium → His bundle
3. Kent's bundle: Atrium → Ventricle
4. Mahaim bundle: AV Node → Ventricle
Phase 0 of the cardiac action potential correlates to what event, EKG piece, and ion movement? -
correct answer Depolarization
QRS
Na+ influx
Phase 1 of the cardiac action potential correlates to what event, EKG piece, and ion movement? -
correct answer Initial repolarization
QRS
Cl- influx
K+ efflux
Phase 2 of the cardiac action potential correlates to what event, EKG piece, and ion movement? -
correct answer Plateau
ST segment
Ca+2 influx
K+ efflux
,Phase 3 of the cardiac action potential correlates to what event, EKG piece, and ion movement? -
correct answer Final repolarization
T wave
K+ efflux
Phase 4 of the cardiac action potential correlates to what event, EKG piece, and ion movement? -
correct answer Resting phase
End of T wave --> next QRS
Na+ efflux (Na/K pump restores RMP)
The absolute refractory period occurs between which points on the EKG? What does it mean? - correct
answer Absolute refractory period: no stimulus can depolarize the cell.
Extends from the Q wave to the first 1/3 of T wave
Define the relative refractory period and identify where it occurs on the EKG - correct answer A larger
than normal stimulus is required to depolarize the myocyte. Occurs in last 2/3 of T wave.
What are the Bipolar leads? - correct answer I, II, III
What are the limb leads? - correct answer aVR, aVL, aVF
What are the precordial leads? - correct answer V1, V2, V3, V4, V5, V6
, Describe the electrical events associated with each part of the EKG - correct answer
P wave
Duration & Amplitude - correct answer 0.08 - 0.12 sec
< 2.5 mm
PR interval
Duration - correct answer 0.12 - 0.20 seconds
What condition can depress the PR interval? - correct answer pericarditis
Q wave
Duration & Amplitude - correct answer < 0.04 seconds
< 0.4 - 0.5 mm
What 3 variations of the Q wave could be indicative of an MI? - correct answer amplitude > 1/3 of R
wave
duration > 0.04 seconds
answers already passed 2026/2027
What are the 3 internodal tracts that connect the SA to the AV node? - correct answer Anterior =
Bachmann bundle (extends to LA)
Middle = Wenckebach
Posterior = Thorel
Conduction velocity of SA and AV nodes - correct answer 0.02 - 0.1 m/sec (slow)
Conduction velocity of myocytes - correct answer 0.3 -1 m/sec (intermediate speed)
Conduction velocity of His bundle, bundle branches, purkinje fibers - correct answer 1-4 m/sec (fast)
Conduction velocity is a function of what 3 things - correct answer 1. Resting membrane potential
2. Amplitude of the action potential
3. Rate of change in membrane potential during phase 0 (Initial depolarization)
Conduction velocity is affected by what 5 things - correct answer 1. Ischemia
2. ANS tone
3. Hyperkalemia (closure of fast Na channels due to significantly increased membrane potential)
4. Acidosis
5. Antiarrythmics
,List and describe the 4 major accessory pathways - correct answer 1. James fiber: Atrium → AV node
2. Atrio-hisian fiber: Atrium → His bundle
3. Kent's bundle: Atrium → Ventricle
4. Mahaim bundle: AV Node → Ventricle
Phase 0 of the cardiac action potential correlates to what event, EKG piece, and ion movement? -
correct answer Depolarization
QRS
Na+ influx
Phase 1 of the cardiac action potential correlates to what event, EKG piece, and ion movement? -
correct answer Initial repolarization
QRS
Cl- influx
K+ efflux
Phase 2 of the cardiac action potential correlates to what event, EKG piece, and ion movement? -
correct answer Plateau
ST segment
Ca+2 influx
K+ efflux
,Phase 3 of the cardiac action potential correlates to what event, EKG piece, and ion movement? -
correct answer Final repolarization
T wave
K+ efflux
Phase 4 of the cardiac action potential correlates to what event, EKG piece, and ion movement? -
correct answer Resting phase
End of T wave --> next QRS
Na+ efflux (Na/K pump restores RMP)
The absolute refractory period occurs between which points on the EKG? What does it mean? - correct
answer Absolute refractory period: no stimulus can depolarize the cell.
Extends from the Q wave to the first 1/3 of T wave
Define the relative refractory period and identify where it occurs on the EKG - correct answer A larger
than normal stimulus is required to depolarize the myocyte. Occurs in last 2/3 of T wave.
What are the Bipolar leads? - correct answer I, II, III
What are the limb leads? - correct answer aVR, aVL, aVF
What are the precordial leads? - correct answer V1, V2, V3, V4, V5, V6
, Describe the electrical events associated with each part of the EKG - correct answer
P wave
Duration & Amplitude - correct answer 0.08 - 0.12 sec
< 2.5 mm
PR interval
Duration - correct answer 0.12 - 0.20 seconds
What condition can depress the PR interval? - correct answer pericarditis
Q wave
Duration & Amplitude - correct answer < 0.04 seconds
< 0.4 - 0.5 mm
What 3 variations of the Q wave could be indicative of an MI? - correct answer amplitude > 1/3 of R
wave
duration > 0.04 seconds
