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EKG Basics Practice Test
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Many phlebotomists cross-train as EKG technicians, and the fundamentals show up on every EKG/ECG certification exam. These 30 questions cover the essentials: 12-lead and precordial electrode placement, the P-QRS-T waves and what each represents, heart rate calculation, artifact and lead reversal, and common rhythms. Each answer explains the physiology and the classic setup mistakes — like swapping V1 and V2 — that distort a tracing.
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Question 1 of 30.Where is the V1 precordial (chest) electrode placed on a standard 12-lead ECG?
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Where is the V1 precordial (chest) electrode placed on a standard 12-lead ECG?
- Fourth intercostal space at the right sternal border (correct answer)
- Fourth intercostal space at the left sternal border
- Fifth intercostal space at the left midclavicular line
- Fifth intercostal space at the left midaxillary line
V1 sits in the fourth intercostal space directly at the RIGHT sternal border. The fourth intercostal space at the LEFT sternal border is V2, its mirror position, so techs commonly reverse the two; if V1 and V2 are swapped the R-wave progression across the chest is distorted and can mimic or mask an anterior infarct. The fifth-space midclavicular and midaxillary positions belong to V4 and V6, which are lower and more lateral.
Which precordial electrode is placed in the fifth intercostal space at the left midclavicular line?
- V2
- V3
- V6
- V4 (correct answer)
V4 is placed in the fifth intercostal space at the left midclavicular line, and it is actually positioned before V3 so that V3 can be centered midway between V2 and V4. V2 is one space higher at the left sternal border, and V6 is at the same fifth-space level as V4 but out at the midaxillary line. Confusing V4's landmark with V6's line shifts the electrode too far laterally and weakens the recorded voltage.
What is the correct placement for the V6 chest electrode?
- Fifth intercostal space at the left anterior axillary line
- Fifth intercostal space at the left midaxillary line (correct answer)
- Fourth intercostal space at the left sternal border
- Midway between V4 and V5
V6 belongs in the fifth intercostal space at the left MIDaxillary line, on the same horizontal level as V4 and V5. The anterior axillary line is V5's landmark, one line more forward, so mixing them up crowds the lateral leads together. The fourth-space sternal-border position is V2, and 'midway between V4 and V5' is not a defined lead position at all, so those options are distractors.
V3 does not have its own independent landmark. Where is it placed?
- Midway between V2 and V4 (correct answer)
- Midway between V4 and V5
- At the right midclavicular line
- At the left midaxillary line
V3 is placed midway between V2 and V4, which is exactly why V4 must be positioned before V3 during setup. Placing it midway between V4 and V5 would push it too low and lateral, distorting R-wave progression. The right midclavicular line and left midaxillary line describe entirely different regions (V6 uses the midaxillary line), so those choices misplace the anterior chest lead.
On a standard 12-lead ECG, which limb electrode functions as the ground (neutral) and does not directly contribute to the recorded leads?
- Left arm (LA)
- Right arm (RA)
- Left leg (LL)
- Right leg (RL) (correct answer)
The right leg (RL) electrode serves as the ground/reference and reduces electrical interference rather than generating a viewable lead. The right arm, left arm, and left leg are the three active limb electrodes that form leads I, II, III and the augmented leads. A common mistake is thinking every electrode produces a trace, but removing or mislocating the RL ground mainly introduces noise instead of changing a specific lead's shape.
How many electrodes are applied to the patient to produce a standard 12-lead ECG?
- 12 electrodes
- 10 electrodes (correct answer)
- 6 electrodes
- 4 electrodes
A 12-lead ECG uses 10 electrodes: 4 on the limbs and 6 across the chest. The machine mathematically combines the limb electrodes to derive the six frontal-plane leads (I, II, III, aVR, aVL, aVF) and reads the six chest leads directly, giving 12 views from 10 electrodes. Assuming '12 electrodes for 12 leads' is the classic error; the number of leads is a count of viewpoints, not of stickers.
Which component of the ECG waveform represents atrial depolarization?
- The P wave (correct answer)
- The QRS complex
- The T wave
- The U wave
The P wave reflects atrial depolarization, the electrical trigger for the atria to contract. The QRS complex represents ventricular depolarization, and its large size actually hides atrial repolarization. The T wave is ventricular repolarization, and the small U wave (when present) is thought to reflect late repolarization. Because the QRS is so prominent, techs sometimes attribute atrial activity to it, but the atria are seen in the P wave.
What does the QRS complex on an ECG primarily represent?
- Atrial depolarization
- Atrial repolarization
- Ventricular depolarization (correct answer)
- Ventricular repolarization
The QRS complex represents ventricular depolarization, the electrical event that drives the ventricles to pump blood. Atrial depolarization is the P wave, and ventricular repolarization is the T wave. Atrial repolarization does occur during the QRS but is buried within it because the ventricular signal is far larger, so it is never seen as its own wave.
The T wave on a normal ECG represents which electrical event?
- Ventricular repolarization (correct answer)
- Ventricular depolarization
- Atrial depolarization
- Firing of the SA node
The T wave represents ventricular repolarization, the recovery phase in which the ventricles reset electrically after contracting. Ventricular depolarization is the QRS, atrial depolarization is the P wave, and SA node firing itself is too small to appear on the surface ECG (it is inferred just before the P wave). Confusing the T wave with depolarization reverses the contraction/recovery relationship.
What is the normal duration of the PR interval in an adult?
- 0.04 to 0.10 second
- 0.20 to 0.40 second
- 0.40 to 0.60 second
- 0.12 to 0.20 second (correct answer)
A normal PR interval measures 0.12 to 0.20 second, timed from the start of the P wave to the start of the QRS; it reflects the delay as the impulse passes through the AV node. The 0.04-0.10 range is too short and roughly matches a normal QRS width, while values above 0.20 second suggest a first-degree AV block. Knowing this window helps a tech flag a prolonged interval for the interpreting provider.
A normal QRS complex in an adult has a duration of approximately:
- Less than 0.12 second (correct answer)
- 0.12 to 0.20 second
- 0.20 to 0.30 second
- Greater than 0.40 second
A normal QRS is narrow, lasting less than 0.12 second (commonly 0.06-0.10 second), because the ventricles depolarize quickly through the His-Purkinje system. The 0.12-0.20 range is the normal PR interval, not the QRS. A QRS of 0.12 second or wider is considered widened and can indicate a bundle branch block or a ventricular origin such as a PVC, which a tech should note.
At the standard ECG paper speed, how much time does one small (1 mm) box represent?
- 0.01 second
- 0.10 second
- 0.20 second
- 0.04 second (correct answer)
At the standard 25 mm/second paper speed, each small 1 mm box equals 0.04 second, and five small boxes make one large box equal to 0.20 second. The 0.20-second value describes the large box, not the small one. Knowing that one small box is 0.04 second is the basis for measuring intervals like the PR and QRS directly from the strip.
One large box on standard ECG paper (five small boxes) represents how much time?
- 0.04 second
- 0.10 second
- 0.20 second (correct answer)
- 1.0 second
One large box equals 0.20 second because it contains five small 0.04-second boxes at the standard 25 mm/second speed. The 0.04-second value is a single small box, and 1.0 second spans five large boxes. Five large boxes therefore mark one second, which is the interval techs use for quick rate estimates.
What is the standard paper speed used to record a routine 12-lead ECG?
- 10 mm per second
- 25 mm per second (correct answer)
- 50 mm per second
- 100 mm per second
The standard recording speed is 25 mm per second, which is what makes each small box equal 0.04 second and allows consistent interval measurement between machines. A speed of 50 mm/second is sometimes used to spread out complexes for detail but doubles the horizontal scale and must be labeled. Recording at the wrong speed changes every measured interval, so the tech should confirm 25 mm/second before printing.
What is the standard calibration (amplitude/gain) setting for a 12-lead ECG?
- 5 mm per millivolt
- 10 mm per millivolt (correct answer)
- 20 mm per millivolt
- 25 mm per millivolt
Standard calibration is 10 mm per millivolt, verified by the rectangular calibration pulse that should be exactly two large boxes (10 mm) tall. Halving the gain to 5 mm/mV shrinks tall complexes but understates voltage, while doubling it exaggerates amplitude; either must be labeled on the strip. If the calibration mark is not 10 mm, the tech should correct the gain so voltages are read accurately.
Which set of findings best describes normal sinus rhythm (NSR)?
- Regular rhythm, rate 60-100, with a P wave before every QRS (correct answer)
- Irregularly irregular rhythm with no identifiable P waves
- Regular rhythm at a rate over 150 with no P waves
- A chaotic baseline with no organized QRS complexes
Normal sinus rhythm is regular at 60-100 beats per minute with an upright P wave preceding each QRS and a normal PR interval, indicating the SA node is pacing normally. An irregularly irregular rhythm with absent P waves describes atrial fibrillation, and a chaotic baseline without organized QRS complexes describes ventricular fibrillation. Recognizing NSR gives the tech a baseline for spotting anything abnormal.
A tech records a rhythm that is irregularly irregular with no clearly identifiable P waves, replaced by a wavy baseline. This is most consistent with:
- Normal sinus rhythm
- Asystole
- Atrial fibrillation (correct answer)
- Sinus bradycardia
Atrial fibrillation is classically irregularly irregular with no discrete P waves, replaced by chaotic fibrillatory waves, because the atria are quivering rather than contracting in an organized way. Normal sinus rhythm would be regular with clear P waves, sinus bradycardia is a slow but regular sinus rhythm, and asystole is a flat line with no activity. A tech should flag suspected atrial fibrillation for prompt provider review.
During monitoring, the tracing suddenly becomes a chaotic, disorganized waveform with no recognizable QRS complexes and the patient is unresponsive. What should the tech recognize and do?
- Assume it is loose-lead artifact and keep watching quietly
- Treat it as ventricular tachycardia and continue the recording
- Call for help but first finish printing all 12 leads
- Recognize ventricular fibrillation and immediately summon emergency help (correct answer)
A chaotic waveform with no organized QRS in an unresponsive patient suggests ventricular fibrillation, a life-threatening rhythm that demands the tech immediately call for emergency help and activate the resuscitation response. Dismissing it as artifact wastes critical time; true VF is accompanied by clinical collapse, whereas artifact leaves the patient awake and stable. Mislabeling it as ventricular tachycardia and recording on, or delaying to finish printing all 12 leads, both postpone the lifesaving response.
On the monitor the tracing shows a nearly flat line with no P waves, QRS complexes, or T waves. Assuming leads are confirmed attached, this represents:
- Ventricular fibrillation
- Atrial fibrillation
- Asystole (correct answer)
- First-degree AV block
A flat line with no discernible electrical activity, once lead-off artifact is ruled out, represents asystole (cardiac standstill), a medical emergency requiring immediate response. Ventricular fibrillation shows a chaotic but present waveform, atrial fibrillation still has QRS complexes with an irregular pattern, and first-degree AV block has normal complexes with only a long PR interval. The tech must always confirm leads are attached before calling a flat line asystole.
Which description best characterizes a premature ventricular contraction (PVC) on the ECG?
- An early, wide, bizarre QRS not preceded by a P wave (correct answer)
- An early, narrow QRS preceded by an abnormal P wave
- A delayed QRS following a long pause and a P wave
- A P wave with no following QRS at all
A PVC appears as an early, wide, bizarre QRS complex that is NOT preceded by a P wave, because the beat originates in the ventricle rather than the atria. An early narrow QRS after an abnormal P wave describes a premature ATRIAL contraction, and a P wave with no following QRS is a dropped beat seen in AV block. Isolated PVCs are common, but frequent or grouped PVCs should be noted for the provider.
A regular sinus rhythm with a rate of 48 beats per minute and a normal P wave before each QRS is best described as:
- Sinus tachycardia
- Sinus bradycardia (correct answer)
- Atrial fibrillation
- Normal sinus rhythm
Sinus bradycardia is a regular sinus rhythm with a rate below 60 beats per minute, so 48 with normal P waves fits. Sinus tachycardia is a sinus rhythm above 100, and normal sinus rhythm falls between 60 and 100. Atrial fibrillation would be irregular with no clear P waves. Whether bradycardia matters clinically depends on symptoms, so the tech records the rate and reports it.
A regular rhythm at 120 beats per minute with an upright P wave before every QRS is best classified as:
- Normal sinus rhythm
- Sinus bradycardia
- Sinus tachycardia (correct answer)
- Ventricular fibrillation
Sinus tachycardia is a regular sinus rhythm faster than 100 beats per minute with a normal P wave before each QRS, so 120 with upright P waves qualifies. Normal sinus rhythm tops out at 100, and sinus bradycardia is below 60. Ventricular fibrillation is chaotic with no organized complexes at all. Sinus tachycardia often reflects fever, pain, anxiety, or exertion, which the tech can note as context.
A 12-lead tracing shows a slow, rolling up-and-down drift of the baseline over several beats. What is the most likely cause and correction?
- Wandering baseline from patient movement, respiration, or loose electrodes; secure electrodes and prep skin (correct answer)
- AC interference from nearby electrical equipment; unplug the device
- Somatic tremor from muscle tension; warm and reposition the patient
- A true arrhythmia that requires no correction
A slow up-and-down drift of the baseline is a wandering baseline artifact, usually caused by patient movement, breathing, or poorly adhering electrodes; the fix is to ensure electrodes are secure and the skin was properly prepped (clean, dry, oils removed). AC interference produces uniform fine spikes, not a slow drift, and somatic tremor produces rapid fuzzy spikes. Because the drift is artifact, the tech corrects it rather than reporting a false rhythm.
A tracing shows uniform, very fine, evenly spaced spikes across all leads, and there is electrical equipment running nearby. This artifact and its typical fix are:
- Wandering baseline; ask the patient to hold still
- Somatic tremor; cover the patient with a warm blanket
- AC (60-cycle) interference; move or unplug nearby electrical devices and check cable/lead connections (correct answer)
- Normal calibration signal; ignore it
Uniform, fine, regularly spaced spikes overlying the tracing are AC (electrical, 60-cycle) interference; the fix is to move or unplug nearby electrical equipment and confirm the lead wires and cables are properly connected and not crossing power cords. A wandering baseline drifts slowly, and somatic tremor produces irregular fuzzy spikes from muscle activity. The regularity and link to nearby equipment point to AC interference rather than patient-generated artifact.
A patient is cold and tense, and the tracing shows rapid, irregular, jagged fuzz on the baseline that is not a true rhythm. This is somatic tremor artifact. The best correction is to:
- Increase the paper speed to 50 mm/second
- Help the patient relax and get warm, and support the limbs so muscles are not tensed (correct answer)
- Reverse the arm electrodes
- Turn off the calibration signal
Somatic (muscle) tremor artifact comes from involuntary muscle activity when a patient is cold, tense, or uncomfortable, so the correction is to help them relax, provide warmth, and support the limbs so muscles are not straining. Changing paper speed only rescales the trace without removing the noise, reversing arm electrodes creates a different error, and the calibration signal is unrelated. Addressing the patient's comfort removes the source of the artifact.
For a routine resting 12-lead ECG, what is the standard patient position?
- Standing upright
- Sitting fully forward and leaning over a table
- Lying on the left side
- Supine, lying flat on the back (correct answer)
A routine resting ECG is recorded with the patient supine (flat on the back) with arms relaxed at the sides, or in a semi-Fowler position if the patient cannot lie flat, because a stable resting position minimizes muscle artifact. Standing or leaning forward tenses muscles and introduces noise, and side-lying shifts the heart's position relative to the chest electrodes, altering the tracing. Consistent positioning makes the recording reproducible.
Before applying chest electrodes, the tech notices the skin is oily and covered with lotion. What is the correct preparation step?
- Apply extra conductive gel over the lotion and place the electrode
- Wipe with water only and apply the electrode while still damp
- Shave the site dry with a razor without cleaning it first
- Clean the site with alcohol, let it dry, then apply the electrode (correct answer)
Oils, lotion, and dead skin raise electrical resistance, so the site should be cleaned (commonly with alcohol) and allowed to dry before the electrode is applied. Adding extra gel over lotion or applying the electrode to damp, water-only skin still leaves an oily, high-resistance surface that produces artifact, and dry-shaving with a razor abrades and can nick the skin without removing the oils. Good skin prep is the single best defense against artifact.
If the right arm and left arm electrodes are accidentally reversed, what is the most likely consequence?
- No effect, because the machine automatically corrects lead placement
- A distorted tracing (for example an inverted lead I) that can mimic pathology and require repeating the ECG (correct answer)
- The paper speed changes to 50 mm/second
- Only the chest leads are affected
Reversing the right and left arm electrodes distorts the frontal-plane leads (classically inverting lead I and swapping aVR/aVL), which can imitate genuine abnormalities and lead to a misread, so the ECG must be corrected and repeated. The machine does not know electrodes are switched and cannot self-correct, paper speed is unrelated to electrode order, and this is a limb-lead error, not a chest-lead one. Verifying correct limb placement before recording prevents this.
On the ECG grid, which measurement is read along the HORIZONTAL axis versus the VERTICAL axis?
- Horizontal measures voltage; vertical measures time
- Both axes measure time
- Horizontal measures time; vertical measures voltage (amplitude) (correct answer)
- Both axes measure voltage
On standard ECG paper the horizontal axis measures time (0.04 second per small box at 25 mm/second) and the vertical axis measures voltage/amplitude (0.1 mV per small box at 10 mm/mV calibration). Reversing them would make interval and amplitude readings meaningless. Keeping the axes straight is what lets a tech measure a PR interval horizontally and confirm the calibration pulse height vertically.
Which precordial electrode is placed at the left anterior axillary line on the same horizontal level as V4?
- V3
- V5 (correct answer)
- V6
- V2
V5 is placed at the left anterior axillary line on the same horizontal level as V4 (the fifth-space midclavicular position), so V4, V5, and V6 all sit at one level moving laterally. V6 is farther out at the midaxillary line, V3 lies between V2 and V4 on the front of the chest, and V2 is up in the fourth space at the sternal border. Placing V5 too high or on the wrong line crowds it against V4 or V6 and weakens lateral-lead accuracy.
FAQ: EKG Basics
Do phlebotomists need to know EKG?
Not for the phlebotomy exam itself, but many employers hire patient-care technicians who both draw blood and run EKGs, and cross-certifying (for example, an EKG or cardiographic technician credential) makes you far more employable. These questions cover the fundamentals every EKG certification exam tests, so you can add the skill on top of phlebotomy.
Where do the 12-lead electrodes go?
The six precordial (chest) leads are the ones people mix up: V1 sits in the fourth intercostal space at the RIGHT sternal border, V2 in the fourth intercostal space at the LEFT sternal border, V4 in the fifth intercostal space at the left midclavicular line, V3 between V2 and V4, V5 at the left anterior axillary line level with V4, and V6 at the left midaxillary line level with V4. The four limb electrodes go on the wrists and ankles. Swapping V1 and V2 — or a limb-lead reversal — distorts the tracing and can mimic or hide a real finding, which is why placement is the highest-yield topic in this drill.
What do the P, QRS, and T waves represent?
The P wave is atrial depolarization (the atria contracting), the QRS complex is ventricular depolarization (the ventricles contracting), and the T wave is ventricular repolarization (the ventricles resetting). Atrial repolarization is hidden inside the QRS. Knowing which wave maps to which event is how you reason about rhythm and rate questions instead of memorizing tracings, and every explanation in this drill walks that chain.
Are these questions taken from the real NHA CPT exam?
No. Real exam items are confidential and belong to the certifying body — be wary of any site claiming to have them. Our questions are original, written to mirror the style, difficulty, and published content outline of the exam. Scoring well here is strong evidence you are ready, not a preview of the exact questions you will see.
Is this practice test really free?
Yes. Every question, explanation, and score report on AlliedHealthTests is free, with no signup, no credit card, and no trial that expires. Retake any test as many times as you want.
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