NHA EKG Technician (CET) — All Questions

A technician measures the distance from the beginning of the P wave to the beginning of the QRS complex on a strip and counts four small boxes. What is the PR interval, and is it normal?

• a.0.04 second, which is shorter than normal
• b.0.16 second, which is normal✓
• c.0.08 second, which is normal
• d.0.40 second, which is longer than normal

Each small box equals 0.04 second at the standard paper speed of 25 mm/sec, so four small boxes equal 0.16 second. The normal PR interval is 0.12 to 0.20 second, so 0.16 second falls in range. The 0.04 and 0.08 answers miscount the boxes, and 0.40 second would require ten small boxes and would indicate a first-degree AV block.

What is the normal duration of the QRS complex in an adult?

• a.0.20 to 0.36 second
• b.Greater than 0.44 second
• c.0.12 to 0.20 second
• d.Less than 0.12 second✓

A normal QRS is under 0.12 second (fewer than three small boxes) because the ventricles depolarize rapidly through the bundle branches and Purkinje fibers. The 0.12 to 0.20 second range describes the PR interval, not the QRS. Values of 0.20 second or more suggest a bundle branch block or a beat that started in the ventricles, and 0.44 second is a QT-interval reference, not a QRS value.

Using the 300 method on a regular rhythm, a technician counts four large boxes between two consecutive R waves. What is the heart rate?

• a.150 beats per minute
• b.75 beats per minute✓
• c.100 beats per minute
• d.60 beats per minute

The 300 method divides 300 by the number of large boxes between R waves, so 300 divided by 4 equals 75 beats per minute. Sixty would require five large boxes, 100 would require three, and 150 would require two. The method only works when the rhythm is regular, because it assumes every R-R interval is the same.

A patient has an irregular rhythm. The technician counts 11 QRS complexes in a six-second strip. What is the approximate heart rate?

• a.11 beats per minute
• b.110 beats per minute✓
• c.66 beats per minute
• d.22 beats per minute

The six-second method multiplies the number of QRS complexes in six seconds by 10, giving 11 times 10, or about 110 beats per minute. This estimate is the preferred method for irregular rhythms because the 300 and 1500 methods assume equal R-R intervals. Multiplying by 2 or 6 instead of 10 gives the wrong scaling, since six seconds is one tenth of a minute.

What electrical event does the P wave represent on an EKG tracing?

• a.Atrial repolarization
• b.Atrial depolarization✓
• c.Ventricular depolarization
• d.Ventricular repolarization

The P wave is the small rounded deflection produced when the impulse from the SA node spreads across both atria and depolarizes them, which triggers atrial contraction. Ventricular depolarization produces the QRS complex, and ventricular repolarization produces the T wave. Atrial repolarization does occur, but it is buried inside the much larger QRS complex and is not normally visible.

A technician is explaining a tracing to a student and points to the rounded wave that follows each QRS complex. What does this wave represent?

• a.Depolarization of the ventricles
• b.Conduction delay at the AV node
• c.Repolarization of the ventricles✓
• d.Contraction of the atria

The T wave follows the QRS and represents ventricular repolarization, the recovery phase in which the ventricular cells return to their resting electrical state. Ventricular depolarization is the QRS itself. The AV node delay is represented by the flat segment within the PR interval, and atrial contraction follows the P wave.

Using the 1500 method, a technician counts 20 small boxes between two consecutive R waves on a regular strip. What is the heart rate?

• a.50 beats per minute
• b.75 beats per minute✓
• c.300 beats per minute
• d.100 beats per minute

The 1500 method divides 1500 by the number of small boxes between R waves: 1500 divided by 20 equals 75 beats per minute. The number 1500 is used because there are 1500 small boxes in one minute at 25 mm/sec. This method is the most precise of the calculation methods, but like the 300 method it requires a regular rhythm.

Which set of findings meets the criteria for normal sinus rhythm?

• a.Rate 80, irregularly irregular, no P waves, QRS 0.08 second
• b.Rate 80, regular, upright P before each QRS, PR 0.16, QRS 0.08 second✓
• c.Rate 112, regular, upright P before each QRS, PR 0.16, QRS 0.08 second
• d.Rate 52, regular, inverted P after each QRS, PR not measurable

Normal sinus rhythm requires a rate of 60 to 100, a regular rhythm, one upright P wave in front of every QRS, a PR interval of 0.12 to 0.20 second, and a QRS under 0.12 second. The choice at 112 meets every one of those criteria except the rate, which makes it sinus tachycardia rather than normal sinus rhythm. Absent P waves with an irregularly irregular ventricular response describes atrial fibrillation. A rate of 52 with P waves inverted after the QRS points to a junctional rhythm, in which the impulse starts below the atria and travels backward through them.

A sleeping athlete on telemetry shows a regular rhythm at 52 beats per minute with an upright P wave before each narrow QRS and a PR interval of 0.16 second. How should this rhythm be identified?

• a.Normal sinus rhythm
• b.Sinus bradycardia✓
• c.Junctional escape rhythm
• d.Second-degree AV block

Every measurement is normal except the rate, which is below 60, so the rhythm is sinus bradycardia. Normal sinus rhythm requires a rate of at least 60. A junctional escape rhythm would show absent or inverted P waves, and a second-degree AV block would show P waves that are not all followed by a QRS complex.

A patient with a fever of 103 degrees Fahrenheit has a regular rhythm at 124 beats per minute with an upright P wave before every narrow QRS. What is this rhythm?

• a.Sinus tachycardia✓
• b.Ventricular tachycardia
• c.Atrial flutter
• d.Supraventricular tachycardia

Sinus tachycardia is a sinus rhythm faster than 100 beats per minute, and it is a normal response to fever, pain, exercise, anxiety, or dehydration. Supraventricular tachycardia is usually faster than 150 and the P waves are hidden. Atrial flutter shows sawtooth flutter waves, and ventricular tachycardia produces wide QRS complexes with no P waves.

A pediatric strip shows upright P waves before every narrow QRS, a PR interval of 0.14 second, and R-R intervals that shorten with inhalation and lengthen with exhalation. What is this rhythm?

• a.Wandering atrial pacemaker
• b.Sinus arrhythmia✓
• c.Second-degree AV block, Mobitz I
• d.Atrial fibrillation

Sinus arrhythmia is a sinus rhythm whose only abnormality is an irregularity that varies with the breathing cycle, and it is a normal finding in children and young adults. Atrial fibrillation would have no identifiable P waves and an irregularly irregular rhythm. Wandering atrial pacemaker shows at least three different P wave shapes, and Mobitz I shows progressively lengthening PR intervals with a dropped QRS.

A strip shows no identifiable P waves, a wavy chaotic baseline, narrow QRS complexes, and R-R intervals that vary from beat to beat with no pattern. What is this rhythm?

• a.Atrial flutter
• b.Ventricular fibrillation
• c.Sinus arrhythmia
• d.Atrial fibrillation✓

Atrial fibrillation is described as irregularly irregular with no discernible P waves and a fibrillatory baseline, while the QRS stays narrow because conduction below the AV node is normal. Sinus arrhythmia still has clear P waves. Atrial flutter has organized sawtooth waves, and ventricular fibrillation has no QRS complexes at all.

A monitor strip shows a sawtooth baseline with regular atrial waves at about 300 per minute and a QRS after every fourth sawtooth wave. What is this rhythm?

• a.Atrial flutter with 4:1 conduction✓
• b.Coarse atrial fibrillation
• c.Sinus tachycardia with artifact
• d.Second-degree AV block, 4:1

Atrial flutter produces uniform sawtooth flutter waves, classically at 250 to 350 per minute, and the AV node blocks most of them so only every second, third, or fourth impulse reaches the ventricles. That physiologic filtering is normal protection and is not called second-degree AV block, which is a conduction defect occurring at ordinary atrial rates. Coarse atrial fibrillation has a chaotic, constantly changing baseline instead of identical repeating waves, and sinus tachycardia shows discrete P waves that stop at the QRS rather than marching straight through it.

An otherwise regular sinus strip contains one early beat with a P wave shaped differently from the others, followed by a normal narrow QRS and then a pause. What is the early beat?

• a.Escape beat
• b.Premature atrial contraction✓
• c.Premature ventricular contraction
• d.Premature junctional contraction

A premature atrial contraction arrives early and comes from an irritable site in the atria, so its P wave looks different from the sinus P waves but the QRS remains narrow because conduction to the ventricles is normal. A premature ventricular contraction would be wide and bizarre with no P wave. A junctional premature beat has an inverted or absent P wave, and an escape beat arrives late rather than early.

A patient reports sudden palpitations. The strip shows a perfectly regular narrow-complex rhythm at 180 beats per minute with P waves that cannot be identified. What is the most likely rhythm?

• a.Accelerated junctional rhythm
• b.Ventricular tachycardia
• c.Supraventricular tachycardia✓
• d.Sinus tachycardia

Supraventricular tachycardia is a regular narrow-complex rhythm, usually 150 to 250 beats per minute, in which the P waves are buried in the preceding T waves and cannot be seen. Sinus tachycardia usually stays under 160 and has visible P waves that speed up gradually. Ventricular tachycardia has wide QRS complexes, and an accelerated junctional rhythm runs about 60 to 100.

A strip shows a regular rhythm at 45 beats per minute with narrow QRS complexes and inverted P waves appearing immediately after each QRS. What is this rhythm?

• a.Junctional escape rhythm✓
• b.Idioventricular rhythm
• c.First-degree AV block
• d.Sinus bradycardia

When the junction takes over as pacemaker, the atria depolarize backward, so the P wave is inverted and may fall before, during, or after the QRS; at 40 to 60 beats per minute this is a junctional escape rhythm. Sinus bradycardia has upright P waves before the QRS. An idioventricular rhythm has wide QRS complexes at 20 to 40, and first-degree AV block has upright P waves with a long PR interval.

What is the inherent rate range of the AV junction when it functions as the heart's pacemaker?

• a.40 to 60 beats per minute✓
• b.20 to 40 beats per minute
• c.60 to 100 beats per minute
• d.100 to 150 beats per minute

The AV junction fires at an inherent rate of 40 to 60 beats per minute and takes over when the SA node fails or slows. The SA node is the primary pacemaker at 60 to 100, and the ventricular Purkinje network is the last-resort pacemaker at 20 to 40. A junctional rhythm faster than 60 is called accelerated junctional, and above 100 it is junctional tachycardia.

A sinus rhythm strip contains a single early beat that is wide and bizarre, has no preceding P wave, and has a T wave that points opposite to the QRS. What is the beat?

• a.Somatic tremor artifact in one lead
• b.Premature ventricular contraction✓
• c.Ventricular paced beat with capture
• d.Premature atrial contraction with aberrancy

A premature ventricular contraction originates below the bundle of His, so the impulse spreads muscle cell to muscle cell rather than through the fast conduction system, producing a wide bizarre QRS with no preceding P wave and a T wave that points opposite the QRS. A premature atrial contraction conducted with aberrancy is the genuinely competing answer: it is also early and wide, but it is preceded by its own early P wave, which this beat lacks. A paced beat carries a sharp pacing spike immediately in front of it, and tremor artifact rides on top of the baseline without replacing a beat or resetting the cycle.

A monitor alarms and the strip shows a regular wide-complex rhythm at 170 beats per minute with no visible P waves. The patient is unresponsive. What rhythm is displayed?

• a.Supraventricular tachycardia
• b.Sinus tachycardia with a bundle branch block
• c.Ventricular tachycardia✓
• d.Atrial flutter

Ventricular tachycardia is three or more consecutive PVCs at a rate above 100, appearing as a regular run of wide, uniform complexes without P waves, and it is a lethal rhythm when the patient has no pulse. Supraventricular tachycardia is narrow. Atrial flutter shows sawtooth waves, and while a rate-related bundle branch block can widen a sinus tachycardia, an unresponsive patient with this tracing must be treated as ventricular tachycardia and help summoned at once.

A telemetry strip suddenly shows chaotic, irregular waves of varying height with no identifiable P waves, QRS complexes, or T waves. What should the technician do first?

• a.Reposition the electrodes and print a new strip
• b.Immediately check the patient and call for emergency help✓
• c.Ask the patient to lie still and stop talking
• d.Chart the finding and continue monitoring

That description is ventricular fibrillation, a lethal rhythm in which the ventricles quiver and produce no cardiac output, so the technician must verify the patient at the bedside and activate the emergency response without delay. Documenting and waiting wastes the minutes that determine survival. Repositioning electrodes or asking the patient to hold still is the response to suspected artifact, and artifact is ruled out the moment the patient is found unresponsive and pulseless.

A monitor shows a nearly flat line with no waveforms in two different leads and the patient is unresponsive with no pulse. What is this rhythm?

• a.Loose lead artifact
• b.Ventricular fibrillation
• c.Idioventricular rhythm
• d.Asystole✓

Asystole is the absence of all electrical activity, appearing as a flat or nearly flat line, and it must be confirmed in more than one lead before it is accepted as true. Ventricular fibrillation still shows chaotic deflections, and an idioventricular rhythm shows wide slow complexes. A loose lead can mimic a flat line, which is exactly why the finding is confirmed in a second lead and at the bedside.

A strip shows wide QRS complexes at a regular rate of 32 beats per minute with no P waves. What is this rhythm called?

• a.Agonal artifact
• b.Junctional escape rhythm
• c.Idioventricular rhythm✓
• d.Sinus bradycardia

When the ventricles become the pacemaker of last resort, they fire at their inherent rate of 20 to 40 beats per minute and produce wide complexes without P waves, which is an idioventricular rhythm. A junctional escape rhythm runs 40 to 60 with narrow complexes. Sinus bradycardia has upright P waves and narrow QRS complexes, and this tracing is an organized rhythm rather than artifact.

A regular strip at 68 beats per minute has one upright P wave before every narrow QRS, and every PR interval measures 0.28 second. What is this rhythm?

• a.Normal sinus rhythm at a rate of 68
• b.Second-degree AV block, Mobitz type II
• c.Third-degree AV block with a junctional escape
• d.Sinus rhythm with a first-degree AV block✓

A PR interval that is constant but longer than 0.20 second defines first-degree AV block, in which every impulse still reaches the ventricles but is delayed. Normal sinus rhythm requires a PR of 0.12 to 0.20 second, so 0.28 second rules it out. Mobitz II drops beats without lengthening the PR, and this strip drops nothing. In third-degree block with a junctional escape, the P waves and QRS complexes march at independent rates, so no PR interval would measure the same value twice, let alone every time.

A strip shows PR intervals of 0.18, 0.24, 0.32 second, then a P wave with no QRS after it, and the pattern repeats. What is this rhythm?

• a.First-degree AV block with a sinus pause
• b.Second-degree AV block, Mobitz type II
• c.Second-degree AV block, Mobitz I (Wenckebach)✓
• d.Third-degree AV block with variable PR intervals

Mobitz I, also called Wenckebach, shows the PR interval getting progressively longer until one P wave is not conducted and a QRS is dropped, after which the cycle starts over. Mobitz II also drops beats, but the conducted PR intervals stay constant, which is the single feature that separates the two here. First-degree block never drops a beat at all, so pairing it with a pause misreads the dropped QRS as a sinus problem. In third-degree block the PR intervals vary randomly because the atria and ventricles are unrelated, rather than lengthening in an orderly sequence.

A strip shows a constant PR interval of 0.20 second on conducted beats, but every third P wave is suddenly not followed by a QRS complex. What is this rhythm?

• a.Premature atrial contractions that are not conducted
• b.Second-degree AV block, Mobitz II✓
• c.Second-degree AV block, Mobitz I
• d.Sinus arrhythmia

Mobitz II is identified by dropped QRS complexes with no warning and PR intervals that remain constant on the beats that do conduct. Mobitz I would show the PR lengthening before the drop. Sinus arrhythmia never drops a QRS, and non-conducted premature atrial contractions arrive early with abnormal P waves rather than on schedule.

A strip shows a regular ventricular rhythm at 40 beats per minute with wide QRS complexes, regular P waves at 80 per minute, and no consistent relationship between the P waves and the QRS complexes. What is this rhythm?

• a.Sinus bradycardia with premature atrial contractions
• b.Second-degree AV block, Mobitz I
• c.Junctional escape rhythm
• d.Third-degree (complete) AV block✓

In third-degree AV block nothing crosses the AV node, so the atria and ventricles beat independently: the P-P interval is regular, the R-R interval is regular, and the PR interval constantly changes. Mobitz I still conducts most beats with a lengthening PR. Sinus bradycardia keeps one P wave tied to each QRS, and a pure junctional escape rhythm would not show a separate faster atrial rate marching through the tracing.

A strip shows a sharp, narrow vertical spike immediately before each wide QRS complex at a regular rate of 70. What does this indicate?

• a.Sixty-cycle AC interference
• b.A ventricular paced rhythm✓
• c.Somatic tremor artifact
• d.A premature ventricular contraction pattern

A pacemaker spike is a thin vertical line marking the electrical impulse delivered by the device; a spike followed by a wide QRS indicates ventricular capture. AC interference appears as a uniform fuzzy band across the whole tracing rather than a single spike per beat. Premature ventricular contractions occur early and irregularly without spikes, and somatic tremor causes erratic jagged baseline movement.

A monitor alarms for ventricular fibrillation, but the technician finds the patient sitting up, alert, and brushing her teeth, and a regular narrow-complex rhythm is visible between the chaotic sections. What is the most likely explanation?

• a.Pacemaker malfunction
• b.Intermittent true ventricular fibrillation
• c.Third-degree AV block
• d.Muscle movement artifact✓

An alert, talking patient cannot be in ventricular fibrillation, and the presence of underlying normal complexes marching through the chaos identifies the tracing as motion artifact. True ventricular fibrillation has no organized QRS complexes anywhere and produces immediate unresponsiveness. AV block and pacemaker failure both produce organized, measurable patterns rather than chaotic noise tied to the patient's activity.

Which group of rhythms is considered immediately life-threatening and requires the technician to summon help right away?

• a.Sinus bradycardia, sinus tachycardia, and sinus arrhythmia
• b.First-degree AV block, atrial flutter, and premature atrial contractions
• c.Junctional rhythm, wandering atrial pacemaker, and paced rhythm
• d.Ventricular fibrillation, pulseless ventricular tachycardia, and asystole✓

Ventricular fibrillation, pulseless ventricular tachycardia, and asystole produce no effective cardiac output, so survival depends on immediate recognition and activation of the emergency response. The sinus rhythms in the first choice are common and often benign. First-degree block, flutter, and premature atrial beats need reporting but not emergency action, and junctional or paced rhythms usually maintain perfusion.

What does the QT interval measure on an EKG tracing?

• a.The delay of the impulse at the AV node
• b.The time between two consecutive R waves
• c.Atrial depolarization plus repolarization
• d.Ventricular depolarization plus repolarization✓

The QT interval is measured from the start of the QRS complex to the end of the T wave and represents the full cycle of ventricular depolarization and recovery; it normally occupies less than half of the R-R interval and generally measures under about 0.44 second at normal rates. Atrial depolarization is the P wave, and atrial repolarization is buried inside the QRS and is not measured. The AV nodal delay lies inside the PR interval, and the R-R interval measures rate and regularity.

A strip shows a normal sinus beat followed by a wide bizarre beat, then another sinus beat followed by another wide bizarre beat, repeating throughout the strip. What is this pattern called?

• a.Ventricular bigeminy✓
• b.Ventricular tachycardia
• c.Ventricular trigeminy
• d.A couplet

Bigeminy means every other beat is a premature ventricular contraction, alternating one normal beat and one PVC. Trigeminy is a PVC every third beat. A couplet is two PVCs in a row, and three or more consecutive PVCs at a rate above 100 constitute ventricular tachycardia.

Which premature ventricular contraction pattern is considered most dangerous because it can trigger ventricular tachycardia or fibrillation?

• a.An interpolated PVC between two normal beats
• b.A unifocal PVC that is late in the cycle
• c.A PVC followed by a full compensatory pause
• d.A PVC that lands on the T wave of the preceding beat✓

A PVC falling on the T wave, called the R-on-T phenomenon, arrives during the vulnerable relative refractory period of repolarization and can precipitate ventricular tachycardia or fibrillation. Unifocal PVCs that arrive later in the cycle are the least worrisome type. An interpolated PVC does not disturb the underlying rhythm, and a compensatory pause is a normal feature of most PVCs rather than a warning sign.

An otherwise normal sinus strip contains one early narrow beat with an inverted P wave right in front of it and a PR interval of 0.08 second. What is this beat?

• a.Premature atrial contraction
• b.Premature ventricular contraction
• c.Sinus escape beat
• d.Premature junctional contraction✓

A premature junctional contraction comes from the AV junction, so the atria depolarize retrograde and produce an inverted P wave with a short PR of less than 0.12 second, while the QRS stays narrow. A premature atrial contraction has an upright though differently shaped P wave with a normal PR. A PVC is wide with no P wave, and an escape beat comes late, not early.

What is the correct way to determine whether a ventricular rhythm is regular?

• a.March out the R-to-R intervals and check that they stay equal✓
• b.Compare the height of each R wave from one beat to the next
• c.March out the P-to-P intervals, since the atria govern the rate
• d.Check that every PR interval measures less than 0.20 second

Ventricular regularity is judged by marching out the R-to-R intervals with calipers or a paper edge and checking whether they stay the same. Marching out P-to-P intervals is a real measurement, but it reports ATRIAL regularity, and the two differ whenever conduction fails: in complete heart block the P-to-P intervals can be perfectly regular while the ventricles are not. R wave height reflects voltage and lead placement rather than timing, and measuring PR intervals evaluates AV conduction.

On standard EKG paper running at 25 mm/sec, how far apart are the vertical time markers printed at the top of the strip used for the six-second method?

• a.One second apart, so six intervals equal six seconds
• b.Six seconds apart, so one interval equals six seconds
• c.Half a second apart, so twelve intervals equal six seconds
• d.Three seconds apart, so two intervals equal six seconds✓

EKG paper is marked at three-second intervals, which equals 15 large boxes, so a six-second strip spans two marked intervals or 30 large boxes. Each large box is 0.20 second and each small box is 0.04 second at the standard 25 mm/sec speed. The other spacings do not correspond to how standard EKG paper is printed.

Where is the V1 electrode placed for a 12-lead EKG?

• a.Fifth intercostal space, right sternal border
• b.Fourth intercostal space, right sternal border✓
• c.Fifth intercostal space, left midclavicular line
• d.Fourth intercostal space, left sternal border

V1 sits in the fourth intercostal space at the right sternal border, and it is located by walking down from the sternal angle to the second rib, then counting the second, third, and fourth spaces. The fourth space at the left sternal border is V2. The fifth space at the left midclavicular line is V4, and there is no standard chest lead at the fifth space on the right sternal border.

A technician has correctly placed V1. Where does the V2 electrode go?

• a.Fifth intercostal space, left anterior axillary line
• b.Fourth intercostal space, left sternal border✓
• c.Directly below V1 in the fifth intercostal space
• d.Midway between V1 and V4

V2 is placed in the fourth intercostal space at the left sternal border, directly across the sternum from V1. The electrode placed midway between V2 and V4 is V3, and V3 is always positioned after V4 is located. The fifth space at the left anterior axillary line is V5.

Which chest electrode is placed in the fifth intercostal space at the left midclavicular line?

• a.V4✓
• b.V3
• c.V5
• d.V6

V4 is placed in the fifth intercostal space at the left midclavicular line, and it is located before V3 because V3 is defined as the midpoint between V2 and V4. V5 goes at the left anterior axillary line and V6 at the left midaxillary line, both level with V4 rather than following the rib spaces.

After placing V1, V2, and V4, where should the technician place V3?

• a.Midway between V2 and V4 on a straight line✓
• b.At the left anterior axillary line level with V4
• c.Directly below V2 in the fifth intercostal space
• d.Midway between V1 and V2 at the same level

V3 sits on a straight line halfway between V2 and V4, which is exactly why V4 is placed before V3 rather than in numerical order. Halfway between V1 and V2 would land on the sternum, over bone rather than over the heart. Dropping straight down from V2 ignores the diagonal that the chest wall follows as it curves toward the axilla, and the left anterior axillary line at the level of V4 is the position for V5.

A technician is placing V5 on a 12-lead EKG. Which description is correct?

• a.Fifth intercostal space, left midaxillary line
• b.Fourth intercostal space, left anterior axillary line
• c.Left anterior axillary line, on the same horizontal level as V4✓
• d.Sixth intercostal space, left anterior axillary line

V5 is placed at the left anterior axillary line on the same horizontal plane as V4 rather than by counting rib spaces, because the chest wall curves and the horizontal alignment keeps V4, V5, and V6 comparable. The midaxillary line at that level is V6. Counting to the sixth space or the fourth space would place the electrode too low or too high.

Where is the V6 electrode placed?

• a.Right midaxillary line, level with V4
• b.Left midaxillary line, level with V4 and V5✓
• c.Posterior axillary line, level with V4
• d.Left midclavicular line, sixth space

V6 is placed at the left midaxillary line on the same horizontal plane as V4 and V5, completing the left lateral view of the heart. The posterior axillary line is one space further back and is used for the additional posterior lead V7, not for V6. The right midaxillary line looks at the heart from the wrong side of the chest, and dropping to the sixth space at the midclavicular line abandons the horizontal plane that V4, V5, and V6 share.

Where should the limb electrodes be placed for a standard 12-lead EKG?

• a.On fleshy, non-muscular areas of the arms and lower legs, positioned symmetrically✓
• b.On the bony prominences of the wrists and ankles for the best signal
• c.On the upper chest and abdomen for all four limb leads
• d.Anywhere convenient, since limb lead position does not affect the tracing

Limb electrodes belong on flat, fleshy areas of the arms and lower legs, placed symmetrically on the right and left, because bone conducts poorly and muscle bellies generate tremor artifact. Torso placement is acceptable only for continuous monitoring or when a limb is missing, and it must be documented because it alters the tracing. Limb position does affect amplitude and axis, so it is never arbitrary.

A 12-lead tracing shows an inverted P wave, inverted QRS, and inverted T wave in lead I, while the chest leads look normal. What is the most likely cause?

• a.The left arm and left leg electrodes are reversed
• b.The V1 and V2 chest electrodes are reversed
• c.The right arm and left arm electrodes are reversed✓
• d.The right leg ground electrode is loose

Reversing the right and left arm electrodes flips the polarity of lead I, producing a globally negative complex in that lead while the chest leads, which do not depend on arm placement, remain normal. Swapping the left arm and left leg electrodes is the closest competitor and does disturb the frontal-plane leads, but it exchanges leads I and II and inverts lead III, so lead I still records an upright complex. Reversing V1 and V2 distorts only those two chest leads, and a loose right leg ground electrode produces baseline wander or noise rather than inversion.

A tracing shows a uniform, thick, fuzzy baseline with small spikes occurring exactly 60 times per second across all leads. What is the most likely cause?

• a.AC interference from nearby powered equipment✓
• b.Deep respiration moving the chest wall electrodes
• c.Electrodes that have dried out and lost contact
• d.A resting tremor of the patient's hands

Sixty-cycle interference is alternating current picked up from nearby electrical devices, cords, or fluorescent lights, and it produces a perfectly regular fuzzy band at exactly 60 hertz in every affected lead. The giveaway is the word exactly: no physiologic source repeats at a fixed 60 per second. A resting tremor produces irregular jagged spikes at a slower and varying rate, deep respiration causes a slow rolling baseline rather than fine spikes, and dried electrodes produce erratic noise or a flat trace confined to the leads they belong to.

An anxious, cold patient produces a tracing with irregular jagged spikes that obscure the small waveforms. What artifact is this and what is the best first correction?

• a.AC interference; move the patient cable away from power cords
• b.Wandering baseline; coach the patient to breathe slowly
• c.Somatic tremor; warm the patient and support the limbs✓
• d.Loose electrode; reapply the chest electrodes

Somatic tremor is muscle-movement artifact from shivering, tension, or involuntary motion, and the first correction is to warm the patient, support the arms and legs on the bed, and coach the patient to relax. Wandering baseline is a slow rolling drift rather than jagged spikes. AC interference is a uniform 60-cycle band that does not vary with how tense the patient is, and a loose electrode disturbs only the leads that electrode contributes to rather than the whole tracing.

A tracing shows the baseline slowly drifting up and down in a wave pattern that matches the patient's breathing. What should the technician check first?

• a.Whether the standardization pulse is set to 20 mm/mV
• b.Whether the patient is holding a deep breath during the whole run
• c.Whether the electrodes are loose, dried out, or over lotion✓
• d.Whether the arm and leg electrodes are reversed

A wandering baseline is usually caused by poor electrode contact from loose tabs, dried gel, body lotion, oils, or sweat, so the first check is the skin and the electrodes themselves. Respiration genuinely contributes to the drift, which is what makes breath-holding tempting, but it treats a symptom, cannot be sustained through a full 12-lead, and leaves the bad contact in place. Paper speed and standardization change the size or spacing of the complexes without causing drift, and lead reversal changes polarity rather than making the baseline roll.

What does the standardization mark on an EKG tracing indicate when it is 10 mm tall?

• a.Each large box on the paper represents 10 milliseconds
• b.The patient's voltage is ten times the normal range
• c.The paper is running at 10 mm per second
• d.One millivolt produces a 10 millimeter deflection✓

Standard calibration is 10 mm per millivolt, printed as a rectangular standardization mark two large boxes tall at the start of the tracing, so amplitudes can be compared between machines and over time. Paper speed is a separate setting, and the standard is 25 mm/sec rather than 10. The mark says nothing about the patient's own voltage, and each large box represents 0.20 second, not 10 milliseconds.

At the standard paper speed, how much time does one small box represent, and what is that speed?

• a.0.04 second at 50 mm/sec
• b.0.20 second at 25 mm/sec
• c.0.04 second at 25 mm/sec✓
• d.0.10 second at 25 mm/sec

Standard EKG paper runs at 25 millimeters per second, so each 1 mm small box equals 0.04 second and each 5 mm large box equals 0.20 second. The 0.20 second value belongs to the large box, not the small one. A speed of 50 mm/sec is a special setting used to spread out very fast rhythms, and 0.10 second does not correspond to any standard box.

How much time and voltage does one large box on standard EKG paper represent?

• a.0.50 second and 5 millimeters of height
• b.0.20 second and 5 millimeters of height✓
• c.0.04 second and 1 millimeter of height
• d.0.10 second and 10 millimeters of height

A large box is five small boxes across and five tall, so it represents 0.20 second horizontally and 5 millimeters, or 0.5 millivolt, vertically at standard calibration. The 0.04 second and 1 millimeter values describe a small box. The 0.10 and 0.50 second values do not match standard paper, where five large boxes equal one second.

A patient has a hairy chest and oily skin. What is the correct skin preparation before applying chest electrodes?

• a.Wipe with a povidone-iodine swab and apply the electrodes wet
• b.Shave the whole chest with a razor and apply lotion afterward
• c.Clip hair at each site, cleanse with alcohol, dry, then abrade lightly✓
• d.Apply the electrodes over the hair and press them down firmly

Good skin prep means clipping excess hair only at the electrode sites, cleansing with alcohol to remove oils, allowing the skin to dry completely, and lightly abrading with dry gauze to lower skin resistance. Applying electrodes over hair or onto wet skin gives poor contact and a wandering baseline. Lotion insulates the skin rather than helping it conduct, and shaving the whole chest with a razor is unnecessary and risks nicks that break the skin barrier.