22 Heart Anatomy & Conduction Practice Questions & Answers

1. 1. A technician is tracing the path of one normal impulse through the heart. After the impulse leaves the AV node, which sequence does it follow before it reaches the ventricular myocardium?

   • A.Bundle of His, then the right and left bundle branches, then the Purkinje fibers✓ Answer
   • B.Internodal pathways, then Bachmann's bundle, then the Purkinje fibers
   • C.Left bundle branch, then back through the AV node, then the bundle of His
   • D.Purkinje fibers, then the bundle of His, then the bundle branches

   The normal conduction sequence is SA node, internodal atrial pathways and Bachmann's bundle, AV node, bundle of His, right and left bundle branches, Purkinje fibers, ventricular myocardium. The internodal pathways and Bachmann's bundle carry the impulse across the atria before the AV node, so they cannot come after it, and the Purkinje fibers are the last structure, not the first, because they distribute the impulse to the working ventricular muscle.

   Source: NHA CET Test Plan, Core Knowledge: basic anatomy and physiology of the heart (cardiac conduction sequence), applied in arrhythmia identificationReport a problem with this question

2. 2. Where is the SA node located, and why does it normally control the heart rate?

   • A.In the interventricular septum just below the tricuspid valve, because it is closest to the bundle of His
   • B.On the epicardial surface of the left ventricle near the apex, because the left ventricle has the thickest muscle
   • C.In the upper posterior wall of the right atrium near the opening of the superior vena cava, because it has the fastest rate of automaticity✓ Answer
   • D.At the junction of the left atrium and the pulmonary veins, because oxygenated blood arrives there first

   Whichever pacemaker site depolarizes spontaneously the fastest controls the heart, and the SA node's intrinsic rate of 60 to 100 per minute is faster than the AV junction (40 to 60) or the ventricles (20 to 40). Its position high in the right atrium is also why normal atrial depolarization spreads downward and to the left, producing an upright P wave in lead II.

   Source: NHA CET Test Plan, Core Knowledge: anatomy and physiology of the heart (SA node as dominant pacemaker; intrinsic rates)Report a problem with this question

3. 3. A monitor shows a regular rhythm at 45 beats per minute with no upright P waves in front of the QRS complexes, and the QRS complexes measure 0.08 second. Which pacemaker site is most likely controlling the ventricles?

   • A.The SA node, discharging slowly as sinus bradycardia
   • B.A ventricular focus, escaping at its intrinsic rate of 20 to 40 per minute
   • C.The AV junction, escaping at its intrinsic rate of 40 to 60 per minute✓ Answer
   • D.An atrial ectopic focus firing at 60 to 80 per minute

   A QRS of 0.08 second is narrow, which means the impulse reached the ventricles through the normal His-Purkinje system and therefore started at or above the AV junction; a ventricular focus would have to spread muscle-to-muscle and would widen the QRS to 0.12 second or more. The absence of upright preceding P waves rules out the SA node and an atrial focus, and the rate of 45 falls squarely in the junctional escape range of 40 to 60.

   Source: NHA CET Test Plan, junctional arrhythmias with core knowledge of intrinsic escape rates and QRS widthReport a problem with this question

4. 4. The AV node holds the impulse for roughly a tenth of a second before passing it on. What is the physiologic purpose of that delay?

   • A.It gives the ventricles time to finish filling, including the atrial kick, before they depolarize and contract✓ Answer
   • B.It keeps the Purkinje fibers from overriding the SA node as pacemaker
   • C.It allows the atria to finish repolarizing so the T wave is not buried
   • D.It allows the coronary arteries to fill during systole

   The AV nodal delay appears on the tracing as the PR segment and exists so that atrial contraction can deliver the final portion of ventricular filling, commonly about 20 to 30 percent of the total, before ventricular depolarization begins. A second benefit is protective: the slow-conducting AV node blocks many impulses when the atrial rate is very fast, limiting the ventricular response. Coronary perfusion actually occurs during diastole, not systole.

   Source: NHA CET Test Plan, Core Knowledge: cardiac cycle and conduction (AV nodal delay, atrial kick)Report a problem with this question

5. 5. On a normal tracing, the P wave represents which cardiac event?

   • A.Repolarization of the ventricles
   • B.Depolarization of the atria✓ Answer
   • C.Conduction through the right and left bundle branches
   • D.The force of atrial contraction

   An ECG records electrical events only, so the P wave is atrial depolarization, the electrical stimulus that then triggers atrial contraction a moment later. The tracing cannot measure how forcefully the atria squeeze, and conduction through the bundle branches is part of the QRS, not the P wave. A normal P wave is less than 0.12 second wide and no more than 2.5 mm tall, and it is upright in lead II when the SA node is pacing.

   Source: AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram, Part I (P wave = atrial depolarization; normal P duration and amplitude)Report a problem with this question

6. 6. A student asks which part of the tracing shows atrial repolarization. What is the correct answer?

   • A.It produces the ST segment
   • B.It produces the T wave
   • C.It has no separate visible wave because it is buried within the QRS complex✓ Answer
   • D.It produces the U wave that follows the T wave

   Atrial repolarization does generate a small wave, sometimes called the Ta wave, but it occurs at the same time as ventricular depolarization and the atrial muscle mass is far smaller than the ventricular mass, so the much larger QRS complex masks it completely. The T wave is ventricular repolarization and the U wave is late repolarization of the Purkinje fibers, so neither belongs to the atria.

   Source: AHA/ACCF/HRS ECG Standardization, Part I (atrial repolarization wave obscured by the QRS complex)Report a problem with this question

7. 7. A technician needs to identify the portion of the tracing that corresponds to the AV nodal delay by itself, with no wave included. Which portion is that?

   • A.The TP segment, measured from the end of the T wave to the beginning of the next P wave
   • B.The QT interval, measured from the beginning of the QRS complex to the end of the T wave
   • C.The PR interval, measured from the beginning of the P wave to the beginning of the QRS complex
   • D.The PR segment, measured from the end of the P wave to the beginning of the QRS complex✓ Answer

   By definition an interval includes a wave while a segment is the flat line between waves, so the PR interval (normal 0.12 to 0.20 second) contains atrial depolarization plus the AV delay, whereas the PR segment is the delay alone. That distinction matters clinically because a prolonged PR interval can come from slowed atrial conduction or from the AV node, and only the segment isolates the nodal component.

   Source: AHA/ACCF/HRS ECG Standardization, Part I (definitions of ECG intervals versus segments; PR interval 0.12-0.20 s)Report a problem with this question

8. 8. A rhythm strip shows a regular rate of 72, an upright P wave before every QRS, a PR interval of 0.16 second, and a QRS duration of 0.14 second. What does the widened QRS most likely indicate?

   • A.A bundle branch block delaying conduction through one ventricle✓ Answer
   • B.A first-degree AV block
   • C.A junctional rhythm with retrograde atrial conduction
   • D.A ventricular escape rhythm taking over the heart

   An upright P wave before every QRS with a PR interval inside the normal 0.12 to 0.20 second range proves the impulse started in the SA node and crossed the AV node normally, so the problem must lie below the AV node. When one bundle branch is blocked, the two ventricles depolarize one after the other instead of simultaneously, which stretches the QRS to 0.12 second or more; a first-degree block would show a long PR with a narrow QRS, and a ventricular or junctional rhythm would not have normally related sinus P waves.

   Source: AHA/ACCF/HRS ECG Standardization, Part III (intraventricular conduction disturbances: QRS >= 0.12 s with normal PR)Report a problem with this question

9. 9. The T wave on a normal ECG represents which event?

   • A.Repolarization of the atria
   • B.Depolarization of the ventricles
   • C.Repolarization of the ventricles✓ Answer
   • D.Mechanical relaxation of the ventricles during filling

   The T wave is the electrical recovery of the ventricular cells, not a mechanical event. Ventricular depolarization travels from endocardium to epicardium while repolarization travels the opposite way, epicardium to endocardium, and those two reversals cancel out so the normal T wave points in the same direction as the QRS, usually upright in most leads and negative in aVR.

   Source: AHA/ACCF/HRS ECG Standardization, Part I (T wave = ventricular repolarization; epicardial-to-endocardial repolarization sequence)Report a problem with this question

10. 10. What does the QT interval measure?

    • A.Ventricular repolarization only
    • B.Total ventricular depolarization plus repolarization✓ Answer
    • C.Atrial depolarization plus ventricular depolarization
    • D.The delay of the impulse within the AV node

    The QT interval runs from the beginning of the QRS complex to the end of the T wave, so it spans the whole ventricular electrical cycle: depolarization (the QRS) followed by repolarization (the ST segment and T wave). Because it shortens as heart rate rises and lengthens as rate falls, it is normally corrected for rate before it is judged, and an abnormally long QT leaves cells vulnerable to torsades de pointes.

    Source: AHA/ACCF/HRS ECG Standardization, Part IV (QT interval definition: onset of QRS to end of T wave)Report a problem with this question

11. 11. When evaluating the ST segment, the technician uses the J point as the reference. What is the J point?

    • A.The junction where the QRS complex ends and the ST segment begins✓ Answer
    • B.The peak of the R wave
    • C.The beginning of the P wave
    • D.The point where the descending T wave returns to baseline

    The ST segment is the electrically quiet stretch between the end of ventricular depolarization and the start of ventricular repolarization, corresponding to the plateau phase of the action potential, and it is normally at the isoelectric baseline. The J point marks exactly where that segment starts, which is why any ST elevation or depression is judged at the J point relative to the baseline rather than somewhere farther along the curve.

    Source: AHA/ACCF/HRS ECG Standardization, Part I (J point defined as the QRS-ST junction; ST segment measured relative to the isoelectric baseline)Report a problem with this question

12. 12. A technician notices a small rounded deflection that follows the T wave and is separate from it. What does this wave represent?

    • A.Repolarization of the AV node
    • B.Early depolarization of the atria
    • C.Late repolarization of the Purkinje fibers, which becomes prominent with hypokalemia or bradycardia✓ Answer
    • D.Delayed closure of the mitral valve

    That deflection is the U wave, attributed to the final, late repolarization of the Purkinje system after the bulk of the ventricular muscle has already recovered. It is normally tiny or invisible, so a prominent U wave is a clue to low potassium or to a slow rate, and because the ECG records electrical signals it can never show a valve opening or closing.

    Source: AHA/ACCF/HRS ECG Standardization, Part I (U wave; prominent U waves with hypokalemia and bradycardia)Report a problem with this question

13. 13. Which portion of the tracing represents electrical diastole and is considered the truest isoelectric baseline?

    • A.The QT interval
    • B.The R-R interval
    • C.The ST segment
    • D.The TP segment, from the end of the T wave to the beginning of the next P wave✓ Answer

    Between the end of the T wave and the next P wave the heart is electrically at rest, with no depolarization or repolarization occurring anywhere, so the stylus sits on the true zero line. That makes the TP segment the reference against which ST deviation is compared; the QT interval and R-R interval are measurements of time, not flat reference lines, and the ST segment is the very thing being measured.

    Source: AHA/ACCF/HRS ECG Standardization, Part I (TP segment as the isoelectric reference for ST-segment deviation)Report a problem with this question

14. 14. On ECG paper recorded at the standard paper speed, what do one small box and one large box represent on the horizontal axis?

    • A.0.02 second and 0.10 second
    • B.0.1 millivolt and 0.5 millivolt
    • C.0.20 second and 1.00 second
    • D.0.04 second and 0.20 second✓ Answer

    The horizontal axis is time and the standard paper speed is 25 mm per second, so 1 mm (one small box) equals 1 divided by 25, or 0.04 second, and a large box of five small boxes equals 0.20 second. Five large boxes therefore equal one full second. The values 0.1 and 0.5 millivolt belong to the vertical axis, which measures voltage at the standard sensitivity of 10 mm per millivolt.

    Source: AHA/ACCF/HRS ECG Standardization, Part I (standard recording conventions: 25 mm/s paper speed, 10 mm/mV gain)Report a problem with this question

15. 15. A technician reviews a tracing and sees that the calibration mark is only 5 mm tall instead of the usual 10 mm. What effect does this have on the recording?

    • A.Every complex is recorded twice as wide, so intervals appear prolonged
    • B.Every complex is recorded at half its true amplitude, so the small deflections reflect a machine setting rather than pathology✓ Answer
    • C.Each small box now represents 0.02 second instead of 0.04 second
    • D.Every complex is recorded at twice its true amplitude

    The standardization mark shows how the machine's gain is set: at standard sensitivity a 1 millivolt signal produces a 10 mm deflection, so a 5 mm mark means half standard, or 5 mm per millivolt, and all vertical deflections are halved. Gain affects only amplitude; the time value of each box depends on paper speed, which has not changed, so durations such as the PR interval and QRS width are still measured normally.

    Source: AHA/ACCF/HRS ECG Standardization, Part I (standardization signal 10 mm/mV; half-standard recording halves amplitude)Report a problem with this question

16. 16. On a regular sinus rhythm at 68 beats per minute recorded at standard paper speed, every P wave is followed by a QRS complex and the PR interval measures exactly 6 small boxes. What is the PR duration and what does it suggest?

    • A.0.24 second, which is longer than normal and consistent with a first-degree AV conduction delay✓ Answer
    • B.0.12 second, which is normal
    • C.0.30 second, which indicates complete AV block
    • D.0.20 second, the upper limit of normal

    Each small box is 0.04 second at the standard 25 mm per second, so 6 times 0.04 equals 0.24 second, which exceeds the normal range of 0.12 to 0.20 second. Because every P wave still conducts to a QRS, the impulse is only delayed at the AV node rather than blocked; in complete AV block the P waves and QRS complexes would march independently with no fixed PR relationship at all.

    Source: AHA/ACCF/HRS ECG Standardization, Part I and Part III (0.04 s per small box at 25 mm/s; normal PR 0.12-0.20 s; first-degree AV block defined as PR > 0.20 s with every P conducted)Report a problem with this question

17. 17. What ion movement produces the rapid upstroke of depolarization in a ventricular muscle cell?

    • A.Slow influx of calcium into the cell
    • B.Rapid efflux of potassium out of the cell
    • C.Rapid influx of sodium into the cell✓ Answer
    • D.Active transport by the sodium-potassium pump

    A resting myocyte is polarized with a negative interior and sodium concentrated outside; when fast sodium channels open, sodium rushes in and flips the interior positive, which is depolarization. Calcium entering more slowly sustains the plateau and couples the electrical event to contraction, potassium leaving the cell produces repolarization, and the sodium-potassium pump restores the gradients afterward rather than creating the upstroke.

    Source: NHA CET Test Plan, Core Knowledge: cardiac cell electrophysiology (polarization, depolarization, repolarization and ion movement)Report a problem with this question

18. 18. A premature ventricular complex lands on the downslope of the preceding T wave. Which period of the cardiac cycle is this, and why is it dangerous?

    • A.The plateau phase, when calcium entry sustains contraction
    • B.The absolute refractory period, when no stimulus of any strength can depolarize the cells
    • C.The isoelectric TP segment, when the heart is electrically at rest
    • D.The relative refractory period, the vulnerable period in which a strong enough stimulus can capture partially recovered cells and trigger ventricular tachycardia or fibrillation✓ Answer

    During the absolute refractory period, which spans the QRS through roughly the peak of the T wave, the cells cannot respond at all, but on the T wave's downslope they are only partially repolarized, so some fibers can be excited while neighbors cannot. That patchwork of recovered and unrecovered tissue sets up re-entry, which is why an R-on-T premature ventricular complex can degenerate into ventricular tachycardia or fibrillation.

    Source: NHA CET Test Plan, Core Knowledge: refractory periods of cardiac cells (absolute versus relative refractory period; vulnerable period)Report a problem with this question

19. 19. A monitor displays an organized narrow-complex rhythm at 70 beats per minute, but the patient has no palpable pulse. What does this demonstrate about the ECG?

    • A.The ECG records electrical activity only, and depolarization does not guarantee effective mechanical contraction, so the patient must always be assessed for a pulse✓ Answer
    • B.The presence of a T wave proves the ventricles contracted
    • C.A narrow QRS confirms that cardiac output is adequate
    • D.The monitor must be running at half standard calibration

    Depolarization is the electrical trigger for contraction, but the muscle can fail to respond, so a normal-looking complex on the screen says nothing about whether blood actually moved. This is why cardiac output, contractile force and valve function require assessment such as pulse checks, blood pressure or echocardiography, and why a rhythm must always be correlated with the patient rather than treated on the monitor alone.

    Source: NHA CET Test Plan, Core Knowledge: electrical activity versus mechanical activity of the heart (pulseless electrical activity)Report a problem with this question

20. 20. Which sequence correctly traces blood from the right ventricle to the aorta?

    • A.Right ventricle, pulmonary veins, lungs, pulmonary artery, left atrium, mitral valve, left ventricle, aorta
    • B.Right ventricle, pulmonic valve, pulmonary artery, lungs, pulmonary veins, left atrium, mitral valve, left ventricle, aortic valve, aorta✓ Answer
    • C.Right ventricle, aortic valve, aorta, lungs, left atrium, left ventricle
    • D.Right ventricle, tricuspid valve, pulmonary artery, lungs, pulmonary veins, left ventricle, aorta

    Blood always leaves a ventricle through a semilunar valve and enters a ventricle through an atrioventricular valve, so the right ventricle empties through the pulmonic valve and the left ventricle through the aortic valve. The pulmonary artery is the exception that carries deoxygenated blood away from the heart and the pulmonary veins are the exception that return oxygenated blood to the left atrium, and the tricuspid valve is the inlet to the right ventricle, not its outlet.

    Source: NHA CET Test Plan, Core Knowledge: basic anatomy of the heart (chambers, valves and path of blood flow)Report a problem with this question

21. 21. A patient with ischemic changes in leads II, III and aVF develops sinus bradycardia and AV block. Which anatomic relationship best explains this combination?

    • A.The right coronary artery supplies the inferior wall and, in most people, the AV node and the SA node, so reduced flow there affects both the wall and nodal conduction✓ Answer
    • B.The left circumflex artery supplies both the inferior wall and the AV node
    • C.The left anterior descending artery supplies the inferior wall and the AV node
    • D.The pulmonary artery supplies the conduction system with oxygenated blood

    Leads II, III and aVF face the inferior wall, which is right coronary artery territory in most hearts, and the same vessel typically supplies the AV node and often the SA node as well. That shared blood supply is why inferior ischemia so commonly presents together with sinus slowing and AV conduction block, while the left anterior descending feeds the septum and anterior wall and the circumflex feeds the lateral wall.

    Source: NHA CET Test Plan, ischemia/injury/infarction variances with core knowledge of coronary circulation and anatomic lead groups (inferior = II, III, aVF)Report a problem with this question

22. 22. Why is lead II most often chosen for continuous rhythm monitoring?

    • A.It is the only lead that records mechanical contraction as well as electrical activity
    • B.It looks directly at the posterior wall of the heart
    • C.It is a unipolar lead and is therefore unaffected by electrode placement
    • D.Its axis roughly parallels the normal direction of depolarization from the SA node toward the apex, so P waves and QRS complexes are most clearly upright✓ Answer

    Because the SA node sits high in the right atrium and the wave of depolarization travels downward and to the left toward the apex, a lead whose positive electrode lies at the left leg records that wave coming almost straight at it, which yields the tallest, most reliably upright P wave for judging atrial activity. Lead II is a bipolar limb lead, and no ECG lead can record mechanical contraction; the posterior wall requires additional leads such as V7 through V9.

    Source: NHA CET Test Plan, lead placement with core knowledge of Einthoven's triangle and cardiac axis; AHA/ACCF/HRS ECG Standardization, Part I (limb lead orientation)Report a problem with this question

Practice questions based on the NHA Certified EKG Technician (CET) test plan, the standard 12-lead electrode positions defined by anatomical landmark, and durable cardiac electrophysiology. CET is a mark of the National Healthcareer Association; this site is not affiliated with or endorsed by NHA. An EKG technician records tracings and does not diagnose. Always follow your facility's policies, your state's scope of practice, and the direction of the ordering provider. About the CET exam →