22 12-Lead Placement Practice Questions & Answers

1. 1. A technician is placing precordial electrodes for a resting 12-lead ECG. After identifying the sternal angle and counting down to the fourth intercostal space, where should the V1 electrode be applied?

   • A.Second intercostal space at the right sternal border
   • B.Fifth intercostal space at the left midclavicular line
   • C.Fourth intercostal space at the right sternal border✓ Answer
   • D.Fourth intercostal space at the left sternal border

   V1 belongs in the fourth intercostal space at the RIGHT sternal border and V2 in the same interspace at the left sternal border, so the pair straddles the sternum and faces the interventricular septum. Reversing the sides corrupts septal morphology and R-wave progression.

   Source: AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the ECG, Part I (Circulation 2007;115:1306-1324), precordial electrode positions; NHA CET Test PlanReport a problem with this question

2. 2. A student places V1, V2, then immediately places V3 before locating V4. Why is this sequence incorrect?

   • A.V3 is defined as the midpoint between V1 and V5, so V5 must be located first
   • B.V3 must always be placed in the third intercostal space, which the student skipped
   • C.V3 must be placed last, after V6, to keep the horizontal plane level
   • D.V3 is defined as the midpoint between V2 and V4, so V4 must be located first✓ Answer

   V3 has no independent anatomical landmark of its own; it is derived as the midpoint of a line between V2 and V4, so V4 (fifth intercostal space, midclavicular line) must be placed first. Guessing V3 before V4 shifts the entire anterior group and distorts R-wave progression.

   Source: AHA/ACCF/HRS ECG Standardization Part I (Circulation 2007;115:1306-1324), V3 defined as midway between V2 and V4Report a problem with this question

3. 3. A technician has placed V4 in the fifth intercostal space at the left midclavicular line. Which statement correctly describes where V5 and V6 go?

   • A.V5 and V6 at the left midaxillary line, one interspace apart from each other
   • B.V5 at the left midaxillary line and V6 at the left posterior axillary line, both level with V4
   • C.V5 in the sixth intercostal space and V6 in the seventh, following the curve of the ribs
   • D.V5 at the left anterior axillary line and V6 at the left midaxillary line, both level with V4✓ Answer

   V4, V5 and V6 must lie on one horizontal plane: V5 at the anterior axillary line and V6 at the midaxillary line, both level with V4 rather than in new interspaces. Following the rib curve upward tilts the lateral leads and destroys comparability with prior tracings.

   Source: AHA/ACCF/HRS ECG Standardization Part I (Circulation 2007;115:1306-1324), V5/V6 horizontal-plane ruleReport a problem with this question

4. 4. Rather than estimating the fourth intercostal space by eye, an experienced technician palpates a bony ridge where the manubrium meets the body of the sternum. What is the purpose of finding this landmark?

   • A.It marks the level of the apex of the heart, where V6 is placed
   • B.It identifies the second rib, from which the interspaces are counted down to the fourth✓ Answer
   • C.It marks the midclavicular line used to position V4
   • D.It identifies the fifth rib, so V4 can be placed directly on it

   The sternal angle (angle of Louis) is where the second rib attaches; sliding off it gives the second intercostal space, and counting down three more interspaces reaches the fourth. Counting from a fixed bony landmark rather than eyeballing is what makes V1/V2 reproducible between tracings and between technicians.

   Source: AHA/ACCF/HRS ECG Standardization Part I (Circulation 2007;115:1306-1324), landmark technique for locating the fourth intercostal spaceReport a problem with this question

5. 5. A new technician asks why the machine is called a 12-lead ECG when only ten electrodes are applied, and what the right leg electrode contributes. What is the correct explanation?

   • A.Ten electrodes generate twelve electrical views, and the right leg electrode is the ground/neutral that suppresses noise rather than forming a lead✓ Answer
   • B.Only six electrodes record leads, and the four limb electrodes are all grounds
   • C.Twelve electrodes are required, and the right leg electrode forms lead III
   • D.Ten electrodes generate twelve views, and the right leg electrode forms the aVF lead by itself

   A lead is a calculated view between electrodes, not a wire, so ten electrodes (four limb plus six chest) yield twelve leads. The right leg electrode contributes no vector at all; it serves as the ground/neutral that cancels common-mode interference such as 60 Hz power-line noise.

   Source: AHA/ACCF/HRS ECG Standardization Part I (Circulation 2007;115:1306-1324), lead derivation and right leg reference electrode; NHA CET Test PlanReport a problem with this question

6. 6. Einthoven's triangle is formed by the right arm, left arm and left leg electrodes. Which pairing correctly describes the bipolar limb leads?

   • A.Lead I is RA to LL, lead II is LA to LL, and lead III is RA to LA
   • B.Lead I is LA to LL, lead II is RA to LA, and lead III is RA to LL
   • C.Lead I is RA to LA, lead II is RA to LL, and lead III is LA to LL✓ Answer
   • D.Lead I is RA to RL, lead II is LA to RL, and lead III is LL to RL

   The three bipolar leads each measure the voltage difference between two corners of Einthoven's triangle: I = RA to LA, II = RA to LL, III = LA to LL, which is also why I + III = II. The right leg is not a corner of the triangle because it is the reference electrode.

   Source: Einthoven's triangle and Einthoven's law; AHA/ACCF/HRS ECG Standardization Part I (Circulation 2007;115:1306-1324)Report a problem with this question

7. 7. On an otherwise normal-appearing tracing with a rate of 76/min, regular rhythm, upright P waves preceding every QRS, PR 0.16 sec and QRS 0.08 sec, the technician notices that aVR is upright (positive). Why is this finding a red flag?

   • A.aVR views the inferior wall, so an upright aVR indicates an inferior infarction
   • B.aVR faces the cavity of the heart and is normally negative, so an upright aVR suggests the arm electrodes are reversed✓ Answer
   • C.aVR normally has no P wave, so an upright aVR indicates atrial enlargement
   • D.aVR is normally the tallest positive lead, so an upright aVR confirms correct placement

   aVR points toward the right shoulder and away from the main direction of ventricular depolarization, so its P, QRS and T deflections are normally negative. A positive aVR on an otherwise unremarkable tracing is the classic single-clue giveaway for a limb-electrode reversal, most often left arm and right arm.

   Source: AHA/ACCF/HRS ECG Standardization Part I (Circulation 2007;115:1306-1324), normal aVR polarity; lead-reversal recognitionReport a problem with this question

8. 8. A tracing shows lead I completely inverted (negative P, QRS and T), aVR upright, and aVL and aVR appearing to have swapped, yet R-wave progression across V1 through V6 is entirely normal. What does this pattern indicate?

   • A.Anterolateral myocardial infarction
   • B.True dextrocardia
   • C.Left leg and right leg electrode reversal
   • D.Left arm and right arm electrode reversal✓ Answer

   LA/RA reversal inverts lead I in its entirety, swaps II with III and aVR with aVL, and leaves aVF unchanged; because the chest electrodes were never moved, precordial R-wave progression stays normal. True dextrocardia produces the same limb-lead picture but also reversed or poor R-wave progression across the precordium, so normal progression is the discriminator.

   Source: AHA-aligned limb-lead reversal signatures (LA/RA reversal); AHA/ACCF/HRS ECG Standardization Part I (Circulation 2007;115:1306-1324)Report a problem with this question

9. 9. A technician reviews a 12-lead tracing in which lead III is completely inverted, aVL and aVF appear swapped, aVR is unchanged, and the P wave is unexpectedly larger in lead I than in lead II. Which electrode reversal best explains this?

   • A.Left arm and left leg electrode reversal✓ Answer
   • B.Right arm and right leg electrode reversal
   • C.Right arm and left leg electrode reversal
   • D.V1 and V2 electrode reversal

   LA/LL reversal inverts lead III alone, swaps I with II and aVL with aVF, and leaves aVR untouched. Because sinus atrial depolarization normally travels toward the left leg, the P wave is normally taller in II than in I; seeing the reverse is the practical bedside clue, and the resulting pattern can mimic an inferior infarct.

   Source: AHA-aligned limb-lead reversal signatures (LA/LL reversal); P-wave amplitude relationship of leads I and IIReport a problem with this question

10. 10. A monitor tech sees lead II appear as a nearly flat line while the patient is awake, talking, and has a strong radial pulse; leads I and III still show complexes. What is the most appropriate first action?

    • A.Check the electrodes and cables, since a flat single lead points to a disconnected electrode or a right leg electrode swap✓ Answer
    • B.Document asystole in the record and continue monitoring
    • C.Call a code and begin chest compressions for asystole
    • D.Increase the gain to 20 mm/mV and accept the tracing

    Asystole is a global finding, so a flat line confined to one lead while other leads show complexes is technical, not clinical. Swapping the right arm with the right leg electrode makes lead II record between two near-identical reference points and produce almost zero potential; a loose or disconnected electrode does the same, and the patient's clinical status confirms perfusion.

    Source: AHA-aligned limb-lead reversal signatures (RA/RL reversal produces a near-flat lead II); NHA CET Test Plan, artifact identification and resolutionReport a problem with this question

11. 11. During setup a technician accidentally applies the left leg electrode above the right ankle and the right leg electrode above the left ankle, with all other electrodes correct. What effect will this have on the recorded 12-lead tracing?

    • A.Essentially no detectable change, because both legs record nearly identical potentials✓ Answer
    • B.Lead I will be completely inverted
    • C.All six precordial leads will show reversed R-wave progression
    • D.Lead II will be a flat line

    The two legs sit at virtually the same electrical potential relative to the heart, so exchanging LL with RL produces no clinically detectable change in the tracing. The flat-lead reversals are the ones that pair the right leg (ground) with an ARM electrode, not the two legs with each other.

    Source: AHA-aligned limb-lead reversal signatures (LL/RL reversal is electrocardiographically silent)Report a problem with this question

12. 12. A 12-lead tracing on a healthy 30-year-old shows inverted P waves in V1 and V2, an rSr' pattern in V1, and poor R-wave progression suggesting a septal infarct. The technician suspects the V1 and V2 electrodes were placed in the second intercostal space. What should be done?

    • A.Reduce the gain to 5 mm/mV to normalize the R waves
    • B.Reposition V1 and V2 to the fourth intercostal space and repeat the tracing before it is released✓ Answer
    • C.Report the tracing as an anteroseptal myocardial infarction
    • D.Leave the electrodes and label the tracing as a Brugada pattern

    Electrodes placed one or two interspaces too high lose roughly 0.1 mV of initial R-wave amplitude per interspace and pick up atrial activity from above, which is why the P waves become negative in V1 and V2 and an rSr' or false Brugada-type pattern appears. Negative P waves in V1 and V2 are the single best clue that placement is too high, so the tech corrects the position and repeats rather than reporting pathology.

    Source: AHA/ACCF/HRS ECG Standardization Part I (Circulation 2007;115:1306-1324), effects of superior precordial electrode displacement; NHA CET Test PlanReport a problem with this question

13. 13. A patient's 12-lead shows ST elevation in leads II, III and aVF with III greater than II, and the provider requests right-sided leads. Where is the single most useful right-sided electrode, V4R, placed and what is it looking for?

    • A.Left midscapular line at the level of V6, to detect right atrial enlargement
    • B.Fourth intercostal space at the right sternal border, to detect posterior involvement
    • C.Fifth intercostal space at the right midclavicular line, to detect right ventricular involvement✓ Answer
    • D.Fifth intercostal space at the right midaxillary line, to detect septal involvement

    V4R mirrors V4 onto the right chest, sitting in the fifth intercostal space at the right midclavicular line, and it images the right ventricle directly. Inferior-wall changes in II, III and aVF often accompany right ventricular infarction, and identifying that involvement matters because those patients are preload-dependent.

    Source: AHA/ACCF/HRS ECG Standardization Part I (Circulation 2007;115:1306-1324), right-sided lead placement V3R-V6R; NHA CET Test Plan special considerationsReport a problem with this question

14. 14. A tracing shows tall R waves with ST depression in V1 through V3, and posterior leads are ordered. Where are V7, V8 and V9 placed?

    • A.V7 at the right midclavicular line, V8 at the right anterior axillary line, V9 at the right midaxillary line
    • B.V7, V8 and V9 evenly spaced across the upper back at the level of the scapular spine
    • C.V7, V8 and V9 in the sixth, seventh and eighth intercostal spaces along the left midaxillary line
    • D.V7 at the left posterior axillary line, V8 at the left midscapular line, V9 at the left paraspinal border, all level with V6✓ Answer

    The posterior leads continue the same horizontal plane as V4 through V6 around the left side of the chest: V7 at the posterior axillary line, V8 at the midscapular line near the tip of the scapula, and V9 at the left paraspinal border. Tall R waves with ST depression in V1 to V3 are the mirror image of posterior injury, which is why the back leads are added and why the patient must be turned to reach them.

    Source: AHA/ACCF/HRS ECG Standardization Part I (Circulation 2007;115:1306-1324), posterior lead placement V7-V9Report a problem with this question

15. 15. Which group of leads views the inferior surface of the heart?

    • A.II, III and aVF✓ Answer
    • B.V3 and V4
    • C.V1 and V2
    • D.I, aVL, V5 and V6

    Leads II, III and aVF all point downward toward the left leg, so together they face the inferior (diaphragmatic) wall, usually supplied by the right coronary artery. Because each lead group images one region, a single misplaced electrode produces a false regional pattern rather than a global change, which is why grouping matters when judging misplacement.

    Source: AHA/ACCF/HRS ECG Standardization Part I (Circulation 2007;115:1306-1324), lead groups and cardiac surfaces; NHA CET Test PlanReport a problem with this question

16. 16. A technician is taught to check that a suspected abnormality fits an anatomically coherent lead group before assuming pathology. Which pairing of lead group to cardiac surface is correct?

    • A.V3 and V4 are anterior, while I, aVL, V5 and V6 are lateral✓ Answer
    • B.I and aVL are inferior, while II, III and aVF are lateral
    • C.V5 and V6 are septal, while V1 and V2 are anterior
    • D.V3 and V4 are septal, while V1 and V2 are lateral

    V1 and V2 face the septum, V3 and V4 the anterior wall, and I, aVL, V5 and V6 the lateral wall, with I and aVL representing the high lateral region. Changes confined to leads that do not form an anatomically contiguous group should prompt a placement check, since a truly ischemic territory follows the coronary supply of one region.

    Source: AHA/ACCF/HRS ECG Standardization Part I (Circulation 2007;115:1306-1324), lead groups and cardiac surfacesReport a problem with this question

17. 17. A technician must record a 12-lead ECG on a woman with large breasts. What is the correct handling of the chest electrodes?

    • A.Place the electrodes on top of the breast at the standard landmarks
    • B.Move V4, V5 and V6 up two interspaces to sit above the breast
    • C.Omit V4 through V6 and record a nine-lead tracing
    • D.Place the electrodes beneath the breast tissue, directly on the chest wall at the standard landmarks, with appropriate draping✓ Answer

    Breast tissue between the electrode and the chest wall attenuates the signal and makes the position hard to reproduce, so the electrodes are placed under the breast at the standard landmarks, on the chest wall itself. Moving the landmarks upward instead would falsify the anterior and lateral leads, and privacy must still be protected with draping and explanation.

    Source: AHA/ACCF/HRS ECG Standardization Part I (Circulation 2007;115:1306-1324), electrode placement under breast tissue; NHA CET Test Plan, patient privacyReport a problem with this question

18. 18. A patient needs a 12-lead ECG but has a full-length cast on the right forearm that cannot be disturbed. What is the correct approach for the limb electrodes?

    • A.Move the right arm electrode to an accessible site above the cast and move the left arm electrode to the matching level on the opposite side, then document the modification✓ Answer
    • B.Omit the right arm electrode and record only the precordial leads
    • C.Place the right arm electrode on top of the cast and leave the left arm electrode at the wrist
    • D.Place the right arm electrode on the right leg and leave all other electrodes standard

    Electrodes cannot record through a cast or dressing, so the site is moved proximally to accessible skin, and the contralateral electrode is moved to the same level so the two arms remain symmetrical within Einthoven's triangle. Asymmetry shifts the frontal-plane axis and makes limb-lead amplitudes non-comparable, and the modification must be documented so future tracings can be matched. The same symmetry rule applies to amputations, where the residual limb or nearest torso site is used.

    Source: NHA CET Test Plan special considerations (amputations, casts/dressings); AHA/ACCF/HRS ECG Standardization Part I (Circulation 2007;115:1306-1324), symmetric limb electrode placementReport a problem with this question

19. 19. When recording an ECG on a young child, why is the V4R position commonly added or substituted for V3?

    • A.In young children the right ventricle is normally prominent and extends to the right of the sternum, so a right-sided lead adds diagnostic information✓ Answer
    • B.V4R replaces V3 so that only five chest electrodes are needed on small chests
    • C.Children have dextrocardia until about age five, so all chest leads must be mirrored
    • D.V3 cannot be located in children because the sternal angle is absent

    Right ventricular dominance is a normal developmental finding in infants and young children, and the standard left-sided precordial array under-represents it. Adding V4R (and often V3R), with appropriately sized pediatric electrodes, images the right ventricle directly, and the substitution must be labeled on the tracing.

    Source: NHA CET Test Plan, pediatric considerations; AHA/ACCF/HRS ECG Standardization Part I (Circulation 2007;115:1306-1324), right precordial leads in childrenReport a problem with this question

20. 20. A nurse asks a technician to set up five-electrode continuous telemetry on an admitted patient. Which setup is correct, and can the same electrode positions be used for a diagnostic 12-lead?

    • A.Four electrodes on the wrists and ankles plus a chest electrode; this setup is also the standard diagnostic 12-lead
    • B.Four torso electrodes plus a chest electrode at V6; this setup replaces the diagnostic 12-lead entirely
    • C.Five electrodes all placed across the precordium; they may be used for a diagnostic 12-lead if labeled
    • D.Four electrodes on the torso at the shoulders and lower trunk plus a chest electrode usually in the V1 position; torso placement is acceptable for monitoring but not for a diagnostic 12-lead✓ Answer

    In five-electrode telemetry the limb electrodes sit on the torso (arms near the outer clavicles, legs on the lower trunk above the hips) and the brown chest electrode is usually placed at V1, which is the best single lead for distinguishing wide-complex rhythms and bundle branch block. Torso placement is accepted for rhythm and rate monitoring because it resists motion artifact, but it shifts the axis and QRS morphology, so a diagnostic 12-lead still requires the limb electrodes on the limbs.

    Source: AHA/ACCF/HRS ECG Standardization Part I (Circulation 2007;115:1306-1324), torso (Mason-Likar type) limb electrode placement for monitoring; NHA CET Test Plan, telemetryReport a problem with this question

21. 21. A technician is applying a Holter monitor to a patient who will wear it for 24 hours during normal activity. Which placement practice best minimizes artifact?

    • A.Place electrodes over the pectoral and abdominal muscles so movement is captured
    • B.Place all electrodes over the diaphragm so respiration is recorded with the rhythm
    • C.Place electrodes over bony areas such as the sternum, ribs and clavicle, away from large muscle groups, and secure the wires with a stress loop✓ Answer
    • D.Place the limb electrodes at the wrists and ankles so the recording is diagnostic quality

    Ambulatory recording is dominated by motion and muscle noise, so electrodes go over bone where skin moves least and away from the pectorals and diaphragm, with the wires looped and taped so tugging does not lift the electrode. The patient is also instructed to keep a symptom diary, press the event marker when symptomatic, and not remove the electrodes.

    Source: NHA CET Test Plan, ambulatory/Holter and event monitoring and (artifact identification and resolution)Report a problem with this question

22. 22. A technician records a tracing using non-standard electrode positions because the ordering provider requested right-sided leads. What must be done before the tracing is mounted and released?

    • A.Clearly label the tracing with the modified lead positions, because automated computer interpretation is not valid when leads are moved✓ Answer
    • B.Delete the computer interpretation and add the technician's own diagnosis instead
    • C.Leave the tracing unlabeled so it can be compared directly with the standard 12-lead
    • D.Relabel the right-sided leads as V1 through V6 so the software recognizes them

    Any modified acquisition, including right-sided, posterior, torso limb placement, or an amputation or positioning adaptation, must be marked on the tracing, because interpretation criteria and the automated algorithm assume standard positions. The technician acquires and labels but does not enter a diagnosis; life-threatening findings are reported immediately to the nurse or provider per facility policy and the technician's scope of practice.

    Source: NHA CET Test Plan, mount a completed tracing and; scope of practice; AHA/ACCF/HRS ECG Standardization Part I (Circulation 2007;115:1306-1324), labeling of non-standard lead positionsReport 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 →