22 12-Lead Placement Practice Questions & Answers

1. 1. A technician is applying the six chest electrodes for a standard resting 12-lead ECG. At which landmark is the V1 electrode placed?

   • A.The second intercostal space at the right edge of the manubrium
   • B.The fourth intercostal space at the left border of the sternum
   • C.The fourth intercostal space at the right border of the sternum✓ Answer
   • D.The fifth intercostal space at the right border of the sternum

   V1 sits in the fourth intercostal space immediately to the right of the sternum, directly over the interventricular septum and right ventricle; V2 is its mirror at the left sternal border in the same interspace. Shifting V1 to the left border or down one interspace changes the part of the heart the lead faces and distorts R-wave progression across the precordium.

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

2. 2. V1 and V2 are already in place. What is the correct way for the technician to locate and apply V3?

   • A.Place the V3 electrode first midway between the sternum and the left nipple in the fifth space, then V4 lateral to it
   • B.Place the V3 electrode first at the fourth intercostal space, midclavicular line, then work outward to V4, V5 and V6
   • C.Place the V3 electrode first in the third intercostal space directly above V2, then V4 two interspaces lower on that line
   • D.Place the V4 electrode first at the fifth intercostal space, midclavicular line, then V3 midway between V2 and V4✓ Answer

   V3 has no landmark of its own: it is defined as the midpoint of the line between V2 and V4, so V4 must be located first in the fifth intercostal space at the left midclavicular line. Guessing V3 before V4 is the most common precordial error and shifts the R-wave transition zone.

   Source: AHA/ACCF/HRS Standardization of the ECG, Part I (Circulation. 2007), precordial electrode positions V1-V6Report a problem with this question

3. 3. V4 has been placed in the fifth intercostal space at the left midclavicular line. Where do V5 and V6 belong?

   • A.V5 on the anterior axillary line and V6 on the midaxillary line, both level with V4✓ Answer
   • B.V5 on the midaxillary line and V6 on the posterior axillary line, level with V4
   • C.V5 on the midclavicular line and V6 on the anterior axillary line, below V4
   • D.V5 and V6 on the midaxillary line, in the fifth and sixth intercostal spaces

   V5 and V6 are carried laterally along the same horizontal plane as V4 - V5 at the anterior axillary line and V6 at the midaxillary line - so the three leads sample one transverse level of the left ventricle. Anchoring them to V4's horizontal line rather than counting ribs again keeps the low lateral leads comparable between tracings.

   Source: AHA/ACCF/HRS Standardization of the ECG, Part I (Circulation. 2007), precordial electrode positions V1-V6Report a problem with this question

4. 4. To place V1 and V2 accurately, the technician must first identify the fourth intercostal space. Which method locates it?

   • A.Palpate the clavicle, slide down to the nipple line, and count up one interspace from there
   • B.Palpate the suprasternal notch, slide down to the first rib, and count down four interspaces
   • C.Palpate the xiphoid process, slide up along the costal margin, and count up two interspaces
   • D.Palpate the sternal angle, slide laterally to the second rib, and count down two interspaces✓ Answer

   The sternal angle (angle of Louis) is the palpable ridge where the manubrium meets the body of the sternum, and the second rib articulates there; the space just below it is the second intercostal space, so counting down two more interspaces reaches the fourth. This bony landmark is findable on nearly every patient, which is why it, and not the nipple, anchors V1 and V2.

   Source: AHA/ACCF/HRS Standardization of the ECG, Part I (Circulation. 2007), locating the fourth intercostal space from the sternal angleReport a problem with this question

5. 5. On a patient with a large chest, a technician places the chest electrodes by eye, using the nipples as a guide instead of palpating the ribs. What is the most likely result on the tracing?

   • A.The chest leads flatten to a straight line, because electrodes placed by eye lose contact with the skin
   • B.The electrodes sit an interspace or two too high and too lateral, and R-wave progression is distorted✓ Answer
   • C.The electrodes record normally, because the nipple line reliably marks the fourth intercostal space
   • D.The limb leads become inverted, because the shifted chest electrodes move Wilson's central terminal

   Nipple position varies widely with body habitus, sex and age, so it is not a usable landmark; estimating by eye typically lands the electrodes an interspace or two high and too far laterally. Because each precordial lead is a positional view of the horizontal plane, that shift changes R and S amplitudes and can manufacture poor R-wave progression that mimics an anterior infarct.

   Source: AHA/ACCF/HRS Standardization of the ECG, Part I (Circulation. 2007), effect of precordial electrode displacement; NHA CET Test PlanReport a problem with this question

6. 6. A technician records a routine diagnostic resting 12-lead ECG with the arm electrodes on the upper chest and the leg electrodes on the abdomen. Why is this unacceptable for this recording?

   • A.Torso placement shifts the frontal-plane axis and alters inferior and lateral voltages, so the tracing is not comparable with a standard 12-lead✓ Answer
   • B.Torso placement leaves the right leg electrode ungrounded, so 60-cycle interference appears across all twelve leads of the recorded tracing
   • C.Torso placement reverses the polarity of the augmented leads, so aVR is recorded upright while aVL and aVF are recorded inverted
   • D.Torso placement takes two of the ten electrodes out of the circuit, so only ten of the twelve leads can actually be recorded

   Standard diagnostic limb placement is on the limbs themselves; the Mason-Likar torso arrangement used for stress testing and continuous monitoring shifts the frontal-plane axis rightward, lowers R in I and aVL and raises R in II, III and aVF. Those changes can create or erase an inferior infarct pattern, so torso placement must be labeled and is never interchangeable with a resting diagnostic 12-lead.

   Source: AHA/ACCF/HRS Standardization of the ECG, Part I (Circulation. 2007), limb electrode placement and the Mason-Likar torso modificationReport a problem with this question

7. 7. Ten electrodes are attached for a 12-lead ECG. What is the function of the electrode on the right leg?

   • A.It serves as the ground or neutral electrode, stabilizing the baseline while contributing to none of the twelve leads✓ Answer
   • B.It completes Einthoven's triangle as a fourth apex against which the frontal-plane limb leads are measured
   • C.It forms the negative pole of lead III, so lead III is recorded as the difference between the two leg electrodes
   • D.It feeds the augmented leads, supplying the reference potential from which aVR, aVL and aVF are derived

   The right-leg electrode is the ground, or right-leg drive, connection: it reduces common-mode noise and steadies the baseline, but no lead is computed from it. All twelve leads are derived from RA, LA, LL and V1-V6, which is exactly why ten electrodes yield twelve leads rather than ten.

   Source: AHA/ACCF/HRS Standardization of the ECG, Part I (Circulation. 2007), the right-leg (driven) electrodeReport a problem with this question

8. 8. A student asks how a 12-lead ECG can produce twelve tracings from only ten electrodes. Which explanation is correct?

   • A.Ten electrodes give ten leads, and the machine interpolates the two missing chest leads mathematically from V4 and V6
   • B.Six chest electrodes give six leads, and the four limb electrodes are combined in different pairings to yield six more✓ Answer
   • C.Each of the ten electrodes gives one lead, and the machine adds a second tracing of leads II and V5 for rhythm analysis
   • D.Twelve leads require twelve electrodes, so two of the chest electrodes carry a split cable that records two sites each

   A lead is a view - an electrical difference between a positive point and a reference - not a wire. Each chest electrode generates one unipolar precordial lead, while RA, LA and LL are combined into three bipolar leads (I, II, III) and three augmented leads (aVR, aVL, aVF); the right-leg electrode is the ground and generates none.

   Source: AHA/ACCF/HRS Standardization of the ECG, Part I (Circulation. 2007), derivation of the 12-lead system from 10 electrodesReport a problem with this question

9. 9. Lead II is one of the three standard bipolar limb leads. How is it recorded?

   • A.Between the left arm as positive and the right arm as negative, viewing the lateral wall
   • B.Between the left leg as positive and the left arm as negative, viewing the inferior wall
   • C.Between the left leg as positive and the right arm as negative, viewing the inferior wall✓ Answer
   • D.Between the right arm as positive and the left leg as negative, viewing the anterior wall

   The three bipolar limb leads form Einthoven's triangle: lead I runs from RA (negative) to LA (positive), lead II from RA (negative) to LL (positive) and lead III from LA (negative) to LL (positive). That geometry is why Einthoven's law holds - lead II equals lead I plus lead III - and it is how a mis-cabled limb electrode is detected.

   Source: AHA/ACCF/HRS Standardization of the ECG, Part I (Circulation. 2007), bipolar limb leads and Einthoven's triangleReport a problem with this question

10. 10. On a correctly recorded 12-lead ECG from a patient with normal anatomy, how should lead aVR appear?

    • A.Upright in adults and negative in children, because the frontal axis shifts with chest size
    • B.Predominantly upright, with a tall R wave, because aVR is the augmented view of the left arm
    • C.Isoelectric and nearly flat, because aVR is the grounded lead taken from the right-leg electrode
    • D.Predominantly negative, with the P wave, QRS complex and T wave all deflecting downward✓ Answer

    The positive pole of aVR faces the right shoulder and therefore looks into the cavity of the heart from the direction opposite the main depolarization vector, so P, QRS and T are all normally negative. An upright aVR on a resting tracing points to reversed arm electrodes or dextrocardia and should send the technician back to the cables before the tracing is filed.

    Source: AHA/ACCF/HRS Standardization of the ECG, Part I (Circulation. 2007), augmented limb leads and normal aVR orientationReport a problem with this question

11. 11. A provider asks which leads on a standard 12-lead ECG face the inferior wall of the left ventricle. Which group is it?

    • A.Leads V1 and V2 together with V3 and V4, which face the septum and front
    • B.Leads II, III and aVF, which look upward at the diaphragmatic surface✓ Answer
    • C.Leads I and aVL together with V5 and V6, which face the left lateral wall
    • D.Leads aVR, aVL and aVF, the three augmented leads of the frontal plane

    Leads II, III and aVF all have their positive pole at the left leg or foot, so they view the heart from below - the inferior or diaphragmatic surface, usually supplied by the right coronary artery. Contiguous change in those three is the classic inferior pattern, and they are also the leads whose appearance changes most when a leg electrode is misplaced.

    Source: AHA/ACCF/HRS Standardization of the ECG, Part VI: Acute Ischemia/Infarction (Circulation. 2009), contiguous lead groupingsReport a problem with this question

12. 12. Grouping the precordial leads by the wall of the left ventricle they face, which pairing is correct?

    • A.V1 and V2 face the septum, and V3 and V4 face the anterior wall✓ Answer
    • B.V1 and V2 face the anterior wall, and V3 and V4 face the septum
    • C.V1 and V2 face the lateral wall, and V5 and V6 face the septum
    • D.V3 and V4 face the inferior wall, and V5 and V6 face the septum

    V1 and V2 lie directly over the interventricular septum at the fourth intercostal space on either side of the sternum, so they are the septal leads, while V3 and V4 lie over the anterior wall of the left ventricle. V5 and V6 continue laterally as the low lateral leads and pair with I and aVL, which view the high lateral wall.

    Source: AHA/ACCF/HRS Standardization of the ECG, Part VI: Acute Ischemia/Infarction (Circulation. 2009), anatomic lead groupingsReport a problem with this question

13. 13. A tracing shows an inverted P wave, QRS and T wave in lead I with an upright aVR, while R-wave progression across V1 to V6 is entirely normal. What should the technician conclude?

    • A.The finding is a normal variant of the frontal axis, and the tracing can be mounted and sent as recorded
    • B.The patient has dextrocardia, and right-sided chest leads should be recorded and labeled before reporting
    • C.The right and left arm electrodes are reversed, and the tracing should be repeated after correcting them✓ Answer
    • D.The right leg electrode has come loose, and the tracing should be repeated after re-seating that electrode

    Swapping the arm electrodes inverts lead I and turns aVR upright, but it cannot affect the chest electrodes, so precordial R-wave progression remains normal. In true dextrocardia the chest leads also lose their normal R-wave progression, so normal progression identifies this as an acquisition error to correct and repeat rather than a finding to report.

    Source: AHA/ACCF/HRS Standardization of the ECG, Part I (Circulation. 2007), limb lead reversal versus dextrocardiaReport a problem with this question

14. 14. One limb lead on a 12-lead tracing is a nearly flat, isoelectric line while all the other leads look normal. What does this pattern most often indicate?

    • A.The 60-cycle notch filter has been switched on, so that limb lead records a completely flattened baseline
    • B.The gain has been set to half standardization, so that limb lead is recorded at a reduced amplitude
    • C.The right leg electrode has been exchanged with another limb electrode, so that lead spans two equal potentials✓ Answer
    • D.The patient moved during acquisition, so somatic tremor has cancelled the deflections in that one lead

    When the right-leg electrode and another limb electrode are exchanged, the affected lead measures the difference between two sites at essentially the same potential and records as a nearly straight line. RA/RL exchange flattens lead II and LA/RL exchange flattens lead III; the fix is to correct the cables and repeat, not to adjust the machine.

    Source: AHA/ACCF/HRS Standardization of the ECG, Part I (Circulation. 2007), limb electrode interchange involving the right-leg electrodeReport a problem with this question

15. 15. A tracing from a patient with no cardiac history shows rS complexes in V1 and V2 with inverted P waves in those leads and an abrupt break in R-wave progression. What is the most likely cause?

    • A.V1 and V2 were placed one or two intercostal spaces too high on the chest wall✓ Answer
    • B.V1 and V2 were placed one intercostal space below the true fourth space
    • C.V1 and V2 were transposed with each other across the two sternal borders
    • D.The right arm and right leg cables were transposed at the patient's side

    Electrodes at the second or third intercostal space sit over the great vessels and atria rather than the septum, producing rS complexes, inverted P waves and a false poor R-wave progression or septal infarct pattern. Because this is an acquisition error, the technician re-locates the fourth intercostal space from the sternal angle and repeats the tracing instead of reporting the finding.

    Source: AHA/ACCF/HRS Standardization of the ECG, Part I (Circulation. 2007), consequences of superior displacement of V1 and V2Report a problem with this question

16. 16. A technician notices that the R wave is taller in V3 than in V4 and that those two leads look interchanged, while every other lead is normal. What should the technician do first?

    • A.Verify the chest electrode positions and repeat the tracing before it is mounted✓ Answer
    • B.Enable the 40 Hz muscle filter and repeat the tracing to smooth the two affected leads
    • C.Mount the tracing and note on it that anterior R-wave progression appears abnormal
    • D.Switch the paper speed to 50 mm/sec and repeat, so the two leads can be compared

    Precordial electrodes applied out of order or swapped break the normally smooth growth of the R wave from V1 to V5, and a break in progression is far more often a placement error than pathology. The technician's job is to verify the electrode positions and re-record; filters and paper speed change how the tracing looks without correcting the underlying error.

    Source: NHA CET Test Plan, EKG Acquisition: lead placement and troubleshooting; AHA/ACCF/HRS Part I (Circulation. 2007)Report a problem with this question

17. 17. A provider evaluating a patient with a suspected inferior wall infarction orders a right-sided ECG. Where is the V4R electrode placed?

    • A.Fourth intercostal space at the right sternal border, as for the V1 site
    • B.Fifth intercostal space on the right midclavicular line, the mirror image of V4✓ Answer
    • C.Fifth intercostal space on the right midaxillary line, mirroring the V6 site
    • D.Fourth intercostal space on the right anterior axillary line, beside V5

    Right-sided leads mirror the standard precordial positions onto the right chest, and V4R - the fifth intercostal space in the right midclavicular line - is the single most sensitive lead for right ventricular involvement, which commonly accompanies an inferior infarction. Every right-sided lead must be clearly labeled so it is never mistaken for a standard V lead.

    Source: AHA/ACCF/HRS Standardization of the ECG, Part VI (Circulation. 2009), right-sided leads V3R-V6RReport a problem with this question

18. 18. Posterior leads V7, V8 and V9 have been ordered. Where are these three electrodes placed?

    • A.On the right chest at positions mirroring V4, V5 and V6, in the fifth right intercostal space
    • B.On the back at the midaxillary line, the midscapular line and the spinous process, level with the xiphoid
    • C.On the back below the scapulae in a horizontal row, level with the sixth thoracic vertebra of the patient
    • D.On the back at the posterior axillary line, the tip of the scapula and beside the spine, level with V6✓ Answer

    V7, V8 and V9 continue the horizontal plane of V4 to V6 around the left side of the back: V7 at the posterior axillary line, V8 at the tip of the scapula and V9 at the left paraspinal border. Keeping them in V6's horizontal plane is what makes them a true continuation of the precordial series, and they must be labeled on the tracing.

    Source: AHA/ACCF/HRS Standardization of the ECG, Part VI (Circulation. 2009), posterior leads V7-V9Report a problem with this question

19. 19. A patient scheduled for a 12-lead ECG has a below-the-knee amputation of the left leg. How should the technician place the limb electrodes?

    • A.On the left lower abdomen near the iliac crest, leaving the right leg electrode down on the ankle
    • B.On the right leg only, since the left leg electrode may be omitted whenever that limb is partly absent
    • C.On the left upper arm beside the left arm electrode, so that all four stay above the patient's waist
    • D.On the most distal remaining point of the left stump, with the right leg electrode mirrored to match✓ Answer

    The electrode goes as far distally as the remaining limb allows, and the opposite limb electrode is moved to the matching position so the frontal-plane geometry stays symmetrical. Any such modification is documented on the tracing, because unequal electrode distances from the trunk change limb-lead amplitudes and the calculated axis.

    Source: AHA/ACCF/HRS Standardization of the ECG, Part I (Circulation. 2007), limb electrode placement with amputation; NHA CET special considerationsReport a problem with this question

20. 20. A patient has had a left mastectomy, and the chest wall over the usual V4 and V5 sites is flat and scarred but the skin is intact. How should the chest electrodes be applied?

    • A.On the right chest in mirrored positions, because the left chest wall is surgically altered
    • B.One interspace lower than standard, because scar tissue conducts poorly at the usual level
    • C.At the standard landmark positions on the chest wall, with the placement noted in the record✓ Answer
    • D.Two centimetres medial to standard, so all six electrodes stay clear of the surgical scar

    Precordial positions are defined by bony landmarks - intercostal spaces and the midclavicular, anterior axillary and midaxillary lines - which breast surgery does not move, so the standard sites are used on intact skin and the tracing stays comparable with earlier and later ECGs. Shifting electrodes for convenience introduces amplitude changes that can be misread as disease; any unavoidable modification is documented.

    Source: AHA/ACCF/HRS Standardization of the ECG, Part I (Circulation. 2007), reproducibility of precordial electrode placement; NHA CETReport a problem with this question

21. 21. Electrodes keep lifting off the chest of a diaphoretic patient, and the affected leads show a wandering baseline. What should the technician do?

    • A.Move the chest electrodes to drier skin on the upper abdomen and record the tracing from there
    • B.Dry and lightly abrade the skin at each site, then apply fresh electrodes and secure the cables✓ Answer
    • C.Press the existing electrodes back down onto the damp skin and tape the lead wires to the patient
    • D.Turn on the 60-cycle notch filter and re-record, since the wander comes from electrical interference

    Moisture breaks the electrode-to-skin contact that the conductive gel depends on, and a wandering baseline is the signature of poor contact rather than of electrical interference. Drying the site, lightly abrading dead skin with gauze and applying fresh, in-date electrodes removes the cause, while filters only hide the artifact and distort waveform amplitudes.

    Source: NHA CET Test Plan, EKG Acquisition: prepare skin for electrode placement and resolve artifactsReport a problem with this question

22. 22. How does electrode placement for continuous 5-lead telemetry monitoring differ from placement for a diagnostic resting 12-lead ECG?

    • A.Telemetry puts its electrodes over bone on the back, whereas the diagnostic 12-lead uses the front of the chest
    • B.Telemetry places all five of its electrodes on the torso, whereas the diagnostic 12-lead uses the four limbs✓ Answer
    • C.Telemetry uses the same four limb positions as the 12-lead but omits all six chest electrode positions
    • D.Telemetry and the diagnostic 12-lead use identical sites, so either recording can be read as diagnostic

    Continuous monitoring puts the four limb electrodes on the torso - below the clavicles and on the lower abdomen or hips - plus one chest electrode, so the patient can move without artifact. That torso arrangement changes the frontal-plane axis and limb-lead voltages, so a monitoring strip is never a substitute for a 12-lead recorded with the electrodes on the limbs.

    Source: AHA/ACCF/HRS Standardization of the ECG, Part I (Circulation. 2007), torso electrode placement for continuous monitoringReport 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 →