ECG Anatomy and Physiology Quiz
Questions: 16 · 10 minutes
1. Which electrical event is represented primarily by the P wave?
Ventricular repolarization
AV nodal delay
Atrial depolarization
Ventricular depolarization
2. If the SA node stops initiating impulses but the AV junction remains functional, what is the most likely immediate backup mechanism?
The atrial myocardium permanently loses the ability to depolarize
The ventricular myocardium must immediately beat faster than the SA node
A slower junctional pacemaker may initiate impulses
The T wave becomes the electrical trigger for each new beat
3. What is the main physiological benefit of the normal delay at the AV node?
It allows atrial contraction to help fill the ventricles before ventricular contraction
It causes the ventricles to repolarize before they depolarize
It makes both ventricles contract before the atria
It prevents impulses from entering the atrial myocardium
4. Why is the normal ST segment usually close to the isoelectric baseline?
The atria and ventricles are both fully relaxed and electrically inactive
Only the SA node is depolarized during this period
Most ventricular myocardial cells are in a similar depolarized state, producing little net voltage difference
Atrial depolarization and ventricular repolarization cancel each other exactly
5. A medication slows conduction through the AV node while atrial and ventricular conduction remain otherwise unchanged. Which ECG measurement would most directly tend to lengthen?
PR interval
QRS duration
QT interval due only to slower ventricular repolarization
R-R interval in every case
6. An atrial impulse produces a narrow QRS complex. What does this most strongly suggest about ventricular activation?
It traveled rapidly through the His–Purkinje system
It bypassed the ventricular conduction system and spread only cell to cell
It began simultaneously throughout the ventricular muscle
It occurred during atrial repolarization without reaching the ventricles
7. Which statement best describes the normal relationship between the QRS complex and ventricular contraction?
The QRS complex is produced by ventricular contraction itself rather than electrical activity
Ventricular electrical depolarization occurs first, followed shortly by mechanical contraction
Ventricular contraction finishes before the QRS complex begins
The QRS complex represents relaxation that mechanically fills the ventricles
8. What does the T wave normally represent?
Atrial depolarization
Ventricular repolarization
Conduction through the AV node only
Ventricular depolarization
9. An ECG shows a consistently prolonged PR interval, with every P wave followed by a QRS complex. Which physiological change best fits this pattern?
Accelerated conduction through the ventricular myocardium
Simultaneous activation of the atria and ventricles by the SA node
Failure of ventricular muscle cells to repolarize
Delayed conduction from the atria through the AV conduction system
10. During sympathetic stimulation, which combination of effects is generally expected?
Slower SA node firing and slower AV nodal conduction
Faster SA node firing and faster AV nodal conduction
Faster SA node firing but complete interruption of AV conduction
No effect on pacemaker activity, but slower Purkinje conduction
11. Atrial repolarization is usually not seen as a distinct wave on a standard ECG. What best explains this?
Atrial cells do not repolarize after each beat
It occurs at exactly the same time as the P wave
Its relatively small signal is usually obscured by the QRS complex
It produces a larger signal that replaces the T wave
12. Where is the sinoatrial (SA) node normally located, and what is its primary role?
In the left ventricular wall; it triggers ventricular repolarization
In the lower interatrial septum; it delays impulses before ventricular activation
In the interventricular septum; it divides impulses between the ventricles
In the upper right atrium near the superior vena cava; it normally initiates each heartbeat
13. Cardiac muscle has a relatively long refractory period. Why is this physiologically important?
It ensures that atrial and ventricular depolarization always appear as one waveform
It prevents the cardiac conduction system from using ion channels
It allows the ventricles to remain continuously contracted between beats
It helps prevent sustained tetanic contraction, allowing relaxation and filling between beats
14. A clinician identifies the ECG waveform generated as electrical activation spreads through the ventricular myocardium. Which waveform is this?
QRS complex
PR segment
T wave
P wave
15. Which sequence best represents normal cardiac electrical conduction after an impulse begins in the SA node?
SA node → AV node → atrial myocardium → Purkinje fibers → bundle branches
SA node → Purkinje fibers → atrial myocardium → AV node → bundle branches
SA node → bundle of His → AV node → atrial myocardium → Purkinje fibers
SA node → atrial myocardium → AV node → bundle of His → bundle branches → Purkinje fibers
16. A net wave of depolarization travels toward the positive electrode of an ECG lead. What deflection is generally produced in that lead?
A flat segment because depolarization cannot generate a voltage difference
A positive deflection
A negative deflection
A deflection determined only by heart rate