22 Rhythm Identification Practice Questions & Answers

1. 1. A 6-second rhythm strip is recorded at the standard paper speed of 25 mm/sec. It contains 11 QRS complexes, each 0.08 sec wide. The R-R interval varies continuously between 12 and 28 small boxes with no repeating pattern, no organized upright P wave precedes any QRS complex, and the baseline between complexes is fine and undulating. What is the ventricular rate?

   • A.125 beats/min
   • B.75 beats/min
   • C.54 beats/min
   • D.110 beats/min✓ Answer

   Because the R-R interval is not constant, the rhythm is irregular and only the 6-second method is valid: count the QRS complexes in the 6-second strip and multiply by 10, giving 11 x 10 = 110 beats/min. The 1500 method applied to a single R-R pair would give 125 (1500/12) or 54 (1500/28) depending on which pair was measured, which is exactly why that method is reserved for regular rhythms.

   Source: NHA CET Test Plan — calculate heart rate; 6-second method required for irregular rhythmsReport a problem with this question

2. 2. A rhythm strip recorded at 25 mm/sec shows a constant R-R interval of exactly 20 small boxes, an upright uniform P wave before every QRS complex, a PR interval of 0.16 sec, and a QRS duration of 0.08 sec. Using the R-R interval (1500) method, what is the heart rate?

   • A.75 beats/min✓ Answer
   • B.100 beats/min
   • C.80 beats/min
   • D.60 beats/min

   At 25 mm/sec each small box is 0.04 sec, so there are 25 small boxes per second and 1500 per minute; dividing 1500 by the number of small boxes between two consecutive R waves gives the rate, and 1500/20 = 75 beats/min. The method is valid here only because the R-R interval is constant.

   Source: NHA CET Test Plan — R-R interval method; standard paper speed 25 mm/sec, small box = 0.04 secReport a problem with this question

3. 3. A regular rhythm strip recorded at 25 mm/sec shows R waves falling exactly 3 large boxes apart, with a uniform upright P wave before each QRS, a PR interval of 0.14 sec, and a QRS duration of 0.06 sec. Using the large-box (300) sequence method, what is the heart rate?

   • A.100 beats/min✓ Answer
   • B.150 beats/min
   • C.75 beats/min
   • D.60 beats/min

   Each large box represents 0.20 sec, so there are 300 large boxes in one minute and the rate equals 300 divided by the number of large boxes between R waves: 300/3 = 100 beats/min. This is the same logic behind the memorized sequence 300-150-100-75-60-50, in which the third large box lands on 100.

   Source: NHA CET Test Plan — sequencing method; large box = 0.20 sec at 25 mm/secReport a problem with this question

4. 4. A technician must report a heart rate from a strip in which the R-R interval changes from beat to beat with no repeating pattern and no two consecutive R-R intervals are the same. Which rate-determination method is the appropriate choice for this tracing?

   • A.Subtract the patient's age from 220
   • B.Divide 1500 by the small boxes between the first two R waves
   • C.Count the QRS complexes in a 6-second strip and multiply by 10✓ Answer
   • D.Divide 300 by the large boxes between the first two R waves

   The 1500 and 300 methods both assume that one measured R-R interval represents every cycle, so they are only valid when the rhythm is regular; on an irregular rhythm they report the rate of a single pair of beats rather than the true average. Counting all QRS complexes across a full 6 seconds and multiplying by 10 averages the whole strip, which is why it is the required method for irregular rhythms. The 220-minus-age formula estimates maximum predicted heart rate for stress testing and is not a rate-measurement method.

   Source: NHA CET Test Plan — 6-second method, R-R interval method, sequencing; maximum predicted HR formulaReport a problem with this question

5. 5. EKG paper is running at the standard speed of 25 mm/sec. How many large boxes are contained in the 6-second segment used for the 6-second rate method?

   • A.25 large boxes
   • B.60 large boxes
   • C.15 large boxes
   • D.30 large boxes✓ Answer

   At 25 mm/sec one small box (1 mm) equals 0.04 sec and one large box (5 mm) equals 0.20 sec, so 5 large boxes make 1 second and 6 seconds spans 30 large boxes. This is why the hash marks printed along the top of most strips fall every 15 large boxes, marking 3-second intervals.

   Source: NHA CET Test Plan supporting knowledge — EKG graph paper units; 25 mm/sec, small box 0.04 sec, large box 0.20 secReport a problem with this question

6. 6. A strip is recorded with the paper speed set to 50 mm/sec instead of the standard setting. The rhythm is regular with a constant R-R interval of 20 small boxes, an upright P wave before each QRS, and a QRS that measures 6 small boxes in width on this tracing. What is the actual heart rate?

   • A.75 beats/min
   • B.100 beats/min
   • C.150 beats/min✓ Answer
   • D.60 beats/min

   The constants 1500 and 300 are derived from a paper speed of 25 mm/sec; doubling the speed to 50 mm/sec halves the time value of every box, so each small box now represents 0.02 sec and the constant becomes 3000. The R-R interval is therefore 20 x 0.02 = 0.40 sec, giving 60/0.40 = 150 beats/min, and the QRS that looks 6 boxes wide actually measures only 0.12 sec. Reflexively applying 1500/20 would yield the wrong answer of 75.

   Source: NHA CET Test Plan supporting knowledge — paper speed and calibration; 1500/300 constants assume 25 mm/secReport a problem with this question

7. 7. A tracing recorded at 25 mm/sec shows uniform, repetitive, saw-edged atrial deflections that march out regularly with a P-to-P interval of 5 small boxes and no flat isoelectric baseline between them. Narrow QRS complexes (0.08 sec) occur regularly after every fourth atrial deflection, with an R-R interval of 20 small boxes. What is the ATRIAL rate?

   • A.150 beats/min
   • B.75 beats/min
   • C.300 beats/min✓ Answer
   • D.100 beats/min

   Atrial rate is measured P-to-P and ventricular rate R-to-R, and they must be reported separately whenever not every atrial impulse conducts. Here 1500/5 = 300 for the atrial rate, while 1500/20 = 75 is the ventricular rate produced by 4:1 conduction; 75 is the classic wrong answer when the question asks for the atrial rate.

   Source: NHA CET Test Plan and E — separate atrial and ventricular rate determination in atrial flutterReport a problem with this question

8. 8. A strip recorded at 25 mm/sec shows an R-R interval that is constant within one small box at a rate of 72, a rounded upright P wave of identical shape before every QRS complex in a 1:1 relationship, a PR interval of 0.16 sec, and a QRS duration of 0.08 sec. How should this rhythm be identified?

   • A.Accelerated junctional rhythm
   • B.Sinus tachycardia
   • C.Sinus arrhythmia
   • D.Normal sinus rhythm✓ Answer

   Normal sinus rhythm requires all five criteria to be met at once: rate 60-100, regular R-R, a uniform upright P wave before every QRS in a 1:1 ratio, a PR interval of 0.12-0.20 sec, and a QRS under 0.12 sec, all of which this tracing satisfies. Sinus arrhythmia would show a varying R-R, sinus tachycardia a rate above 100, and an accelerated junctional rhythm would lack the upright preceding P wave.

   Source: NHA CET Test Plan — sinus rhythm criteria; PR 0.12-0.20 sec, QRS under 0.12 secReport a problem with this question

9. 9. A strip recorded at 25 mm/sec shows a regular R-R interval of 33 small boxes, a uniform upright P wave preceding every QRS complex in a 1:1 relationship, a PR interval of 0.16 sec, and a QRS duration of 0.08 sec. How should this rhythm be identified?

   • A.Junctional escape rhythm
   • B.Idioventricular rhythm
   • C.Sinus bradycardia✓ Answer
   • D.Sinus arrest

   1500/33 gives a rate of about 45, and every other criterion matches normal sinus rhythm, so the only abnormality is the rate below 60, which defines sinus bradycardia. A junctional escape rhythm at 40-60 would have an absent, inverted, or retrograde P wave rather than an upright one, an idioventricular rhythm would show a wide QRS of 0.12 sec or more with no P waves, and sinus arrest requires a missing P-QRS-T cycle rather than a uniformly slow regular rhythm.

   Source: NHA CET Test Plan — sinus bradycardia: all sinus criteria with rate under 60Report a problem with this question

10. 10. A strip recorded at 25 mm/sec on a healthy 19-year-old shows an R-R interval that shortens and lengthens smoothly and cyclically in time with the patient's breathing, ranging from 68 to 92 beats/min. Each QRS complex is preceded by an upright P wave of identical shape, the PR interval is constant at 0.16 sec, and the QRS duration is 0.08 sec. How should this rhythm be identified?

    • A.Sinus arrhythmia✓ Answer
    • B.Atrial fibrillation
    • C.Wandering atrial pacemaker
    • D.Atrial flutter with variable conduction

    Every sinus criterion is preserved except the regularity, and the variation is phasic and cyclical with respiration, which defines sinus arrhythmia and is a normal variant in young patients. Atrial fibrillation is the classic over-call, but it has no discernible P waves and is irregularly irregular with no pattern; wandering atrial pacemaker requires at least three different P morphologies with varying PR intervals, and this tracing has one uniform P shape and a fixed PR.

    Source: NHA CET Test Plan and E — sinus arrhythmia: sinus criteria with phasic respiratory R-R variationReport a problem with this question

11. 11. A strip recorded at 25 mm/sec shows a perfectly regular R-R interval of 8 small boxes, a QRS duration of 0.08 sec, and no discernible P wave before any QRS complex; the T waves appear slightly peaked and distorted, and the monitor recorded the rhythm starting abruptly from a preceding rate of 80. How should this rhythm be identified?

    • A.Atrial flutter with 2:1 conduction
    • B.Monomorphic ventricular tachycardia
    • C.Sinus tachycardia
    • D.Supraventricular tachycardia✓ Answer

    The rate is 1500/8 = about 188, the rhythm is perfectly regular, the QRS is narrow, the onset was abrupt, and the P waves are not visible because they are buried in the preceding T waves, which is the classic picture of supraventricular tachycardia. Sinus tachycardia normally stays below about 150 in adults, accelerates and slows gradually, and keeps a visible P before each QRS; ventricular tachycardia requires a wide QRS of 0.12 sec or more.

    Source: NHA CET Test Plan — supraventricular tachycardia: regular, narrow QRS, 150-250, abrupt onset, P waves hidden in TReport a problem with this question

12. 12. A 6-second strip recorded at 25 mm/sec contains 13 QRS complexes, each 0.08 sec wide. No P waves can be identified anywhere on the tracing, the baseline between complexes wavers coarsely and continuously, and the R-R interval varies unpredictably from 8 to 19 small boxes with no repeating grouping. How should this rhythm be identified?

    • A.Atrial fibrillation with rapid ventricular response✓ Answer
    • B.Multifocal atrial tachycardia
    • C.Atrial flutter with variable conduction
    • D.Sinus arrhythmia

    Absent P waves plus a wavering baseline plus an irregularly irregular R-R with a narrow QRS is atrial fibrillation, and because the 6-second count gives 13 x 10 = 130 beats/min, it is described as having a rapid ventricular response (a rate under 100 would be called controlled). Multifocal atrial tachycardia is also irregularly irregular but requires at least three distinct P wave shapes, atrial flutter shows uniform repetitive atrial deflections at roughly 250-350, and sinus arrhythmia keeps a uniform upright P before every QRS.

    Source: NHA CET Test Plan and E — atrial fibrillation: no discernible P, irregularly irregular, narrow QRS; RVR when ventricular rate over 100Report a problem with this question

13. 13. A strip recorded at 25 mm/sec shows uniform, repetitive, saw-edged atrial deflections marching out regularly at a P-to-P interval of 5 small boxes with no flat baseline between them. Every second atrial deflection is followed by a narrow QRS complex of 0.08 sec, producing a regular ventricular R-R interval of 10 small boxes. How should this rhythm be identified?

    • A.Atrial fibrillation
    • B.Atrial flutter with 2:1 conduction✓ Answer
    • C.Sinus tachycardia
    • D.Supraventricular tachycardia

    Uniform repetitive atrial waves at 1500/5 = 300 per minute with no isoelectric baseline between them identify atrial flutter, and a fixed 2:1 conduction ratio yields a regular ventricular rate of 1500/10 = 150. Supraventricular tachycardia is the common trap because both are regular and narrow at about 150, but SVT shows no organized atrial activity at all; atrial fibrillation would be irregularly irregular with a chaotic rather than uniform atrial baseline.

    Source: NHA CET Test Plan — atrial flutter: atrial rate ~250-350, regular ventricular response with fixed conduction ratioReport a problem with this question

14. 14. A strip recorded at 25 mm/sec shows an R-R interval that is constant at 20 small boxes for every cycle except one: a single beat arrives after only 13 small boxes. That early beat is preceded by a P wave of a different shape riding on the previous T wave, its PR interval is 0.14 sec, its QRS is 0.08 sec, and the interval to the next normal beat is 22 small boxes, less than two full underlying cycles. How should the regularity of this tracing be described?

    • A.Regularly irregular with group beating
    • B.Regular with a premature atrial complex✓ Answer
    • C.Irregularly irregular
    • D.Regular with a premature ventricular complex

    A tracing whose R-R is constant except at the site of a single early beat is reported as regular with a premature complex, not as an irregular rhythm. The early beat has its own abnormally shaped P wave and a narrow QRS, so it originated in the atria, and the shorter-than-compensatory pause that follows (less than two full cycles) is the non-compensatory pause typical of a PAC, in contrast to the full compensatory pause that usually follows a PVC.

    Source: NHA CET Test Plan and E — premature atrial complex; non-compensatory pause vs full compensatory pause after a PVCReport a problem with this question

15. 15. A strip recorded at 25 mm/sec shows alternating beats: every other complex is a normal-looking beat with an upright P wave, a PR of 0.16 sec, and a QRS of 0.08 sec, while each intervening complex arrives early, is 0.14 sec wide and bizarre in shape with no preceding P wave and a T wave deflected opposite the QRS. All of the early complexes are identical to one another in shape, and each is followed by a pause so that the interval between the normal beats surrounding it equals two full underlying R-R cycles. How is this pattern named?

    • A.Premature ventricular complexes occurring as couplets
    • B.Multifocal premature ventricular complexes in bigeminy
    • C.Unifocal premature ventricular complexes in bigeminy✓ Answer
    • D.Premature atrial complexes in bigeminy

    An early, wide, bizarre QRS with no preceding P wave, an oppositely deflected T wave, and a full compensatory pause is a premature ventricular complex; when one occurs as every other beat the pattern is bigeminy, and because all of the ectopic complexes share an identical shape they arise from a single focus and are unifocal. Multifocal PVCs would differ in shape from one another, a couplet is two PVCs back to back, and a PAC would be narrow with an abnormal P wave.

    Source: NHA CET Test Plan — PVC morphology and patterns: unifocal vs multifocal, bigeminy, couplet, compensatory pauseReport a problem with this question

16. 16. A strip recorded at 25 mm/sec shows a regular R-R interval of 34 small boxes with a QRS duration of 0.08 sec. No upright P wave appears before any QRS complex; instead a small inverted deflection follows each QRS in lead II. How should this rhythm be identified?

    • A.Sinus bradycardia
    • B.Idioventricular rhythm
    • C.Junctional escape rhythm✓ Answer
    • D.Atrial fibrillation

    A regular narrow-complex rhythm at 1500/34 = about 44 with a retrograde (inverted) P wave following each QRS in lead II is a junctional escape rhythm, whose intrinsic rate is 40-60; the inverted P reflects atrial depolarization traveling backward from the AV junction. The most common error is to answer atrial fibrillation whenever no upright P is seen, but atrial fibrillation is irregularly irregular while junctional rhythms are regular; an idioventricular rhythm would have a wide QRS of 0.12 sec or more.

    Source: NHA CET Test Plan — junctional rhythms: narrow QRS, absent/inverted/retrograde P, escape rate 40-60Report a problem with this question

17. 17. A strip recorded at 25 mm/sec shows a regular R-R interval at a rate of 78, with an upright uniform P wave before every QRS complex in a 1:1 relationship, a QRS duration of 0.08 sec, and a PR interval that measures a constant 0.26 sec on every beat. How should this tracing be identified?

    • A.Second-degree AV block, Mobitz II
    • B.Sinus rhythm with first-degree AV block✓ Answer
    • C.Second-degree AV block, Mobitz I (Wenckebach)
    • D.Normal sinus rhythm

    Every P wave is followed by a QRS and the rhythm is regular, so no beats are dropped; the only abnormality is a PR interval that is constant but longer than the normal 0.12-0.20 sec range, which defines first-degree AV block superimposed on an otherwise normal sinus rhythm. Mobitz I requires the PR to lengthen progressively until a QRS is dropped and Mobitz II requires intermittently dropped QRS complexes, neither of which occurs here.

    Source: NHA CET Test Plan and E — first-degree AV block: every P conducted, PR constant and greater than 0.20 secReport a problem with this question

18. 18. A strip recorded at 25 mm/sec shows P waves that are uniform and march out regularly at 88 per minute. The PR interval measures 0.16 sec, then 0.24 sec, then 0.32 sec, and the next P wave is not followed by a QRS complex at all; the sequence then repeats, the R-R intervals shorten progressively within each group, and every conducted QRS is 0.08 sec wide. How should this rhythm be identified?

    • A.First-degree AV block
    • B.Second-degree AV block, Mobitz I (Wenckebach)✓ Answer
    • C.Second-degree AV block, Mobitz II
    • D.Third-degree (complete) AV block

    Progressive lengthening of the PR interval on successive beats until one P wave fails to conduct, followed by repetition of the cycle, is the defining sequence of Mobitz I; the resulting pattern of grouped beating makes the rhythm regularly irregular rather than randomly irregular. Mobitz II drops beats without any change in the PR interval, first-degree block never drops a beat, and in complete block there is no consistent PR relationship at all.

    Source: NHA CET Test Plan — second-degree AV block type I: progressive PR prolongation with a dropped QRS, group beatingReport a problem with this question

19. 19. A strip recorded at 25 mm/sec shows uniform P waves marching out regularly at 80 per minute. Every conducted beat has a PR interval of exactly 0.18 sec with no beat-to-beat variation, but at irregular points a P wave appears with no QRS following it, so there are more P waves than QRS complexes; the conducted QRS complexes measure 0.13 sec. How should this rhythm be identified?

    • A.Second-degree AV block, Mobitz II✓ Answer
    • B.Second-degree AV block, Mobitz I (Wenckebach)
    • C.Sinus arrest
    • D.Third-degree (complete) AV block

    A constant PR interval on every conducted beat with intermittently dropped QRS complexes and more P waves than QRS complexes is Mobitz II, and the wide conducted QRS reflects the block being located below the AV node, which is why this type is considered more serious and may progress. Mobitz I is excluded because the PR does not lengthen before the drop, complete block is excluded because a fixed PR relationship still exists on conducted beats, and sinus arrest is excluded because the P waves continue on time.

    Source: NHA CET Test Plan — second-degree AV block type II: constant PR with intermittently dropped QRS, more P waves than QRSReport a problem with this question

20. 20. A strip recorded at 25 mm/sec shows uniform P waves marching out regularly at 88 per minute and wide QRS complexes of 0.14 sec marching out regularly at 36 per minute. The two are completely independent: some P waves fall just before a QRS, some land inside a QRS, and some sit on top of a T wave, and no PR interval can be measured consistently. How should this rhythm be identified?

    • A.Second-degree AV block, Mobitz II
    • B.Sinus bradycardia with first-degree AV block
    • C.Atrial fibrillation with a slow ventricular response
    • D.Third-degree (complete) AV block✓ Answer

    In complete heart block no atrial impulse reaches the ventricles, so the P-P interval is regular, the R-R interval is regular, the atrial rate exceeds the ventricular rate, and the two march independently with no fixed PR interval. The wide escape QRS at 36 indicates a ventricular escape pacemaker (intrinsic rate 20-40) rather than a junctional one, which would be narrow at 40-60; Mobitz II still has a measurable constant PR on conducted beats, and atrial fibrillation would have no P waves and an irregular R-R.

    Source: NHA CET Test Plan — third-degree AV block: AV dissociation, regular P-P and R-R, atrial rate exceeds ventricular rateReport a problem with this question

21. 21. While a technician is obtaining a routine tracing, the monitor shows a regular rhythm at 190 per minute in which every QRS complex is 0.16 sec wide, uniform in shape and bizarre, with no P waves visible and T waves deflected opposite the QRS. The technician looks up and finds the patient unresponsive with no palpable carotid pulse. What should the technician do first?

    • A.Complete the full 12-lead tracing so the physician has a diagnostic record
    • B.Reposition the chest electrodes to rule out artifact before acting
    • C.Document the finding in the chart and report it to the nurse at the end of the recording
    • D.Call for help immediately, activate the facility's emergency response, and begin CPR✓ Answer

    Three or more consecutive wide, uniform QRS complexes at 100-250 per minute with no P waves is monomorphic ventricular tachycardia, and an unresponsive patient with no pulse makes it a pulseless arrest requiring immediate help and chest compressions. The governing principle is that the patient is always treated before the tracing: finishing a recording, hunting for artifact, or deferring the report all delay resuscitation, and the technician's role is to recognize, summon help, and start CPR, not to interpret or treat definitively.

    Source: NHA CET Test Plan — take appropriate action when life-threatening arrhythmias are identified; CPR/BLS responseReport a problem with this question

22. 22. A monitor lead shows chaotic, irregular deflections of continuously varying amplitude in which no P waves, QRS complexes, or T waves can be identified and no rate can be measured. The patient is sitting upright, talking, and visibly shivering, and the other displayed leads show a regular narrow-complex rhythm at 76 with an upright P wave before each QRS. What is the most appropriate action?

    • A.Document the tracing as ventricular fibrillation and continue the recording
    • B.Call a code and prepare for immediate defibrillation for ventricular fibrillation
    • C.Document the tracing as asystole and report it at the end of the study
    • D.Assess the patient and the electrode connections, treat the pattern as muscle tremor artifact, and warm the patient before repeating the tracing✓ Answer

    A lethal rhythm must always be correlated with the patient before it is named, because ventricular fibrillation produces immediate unresponsiveness and pulselessness, and this patient is awake and talking. Somatic (muscle) tremor from shivering is the classic mimic of ventricular fibrillation, and the fact that the disturbance appears in only one lead while the others show an organized rhythm confirms an acquisition problem rather than an arrhythmia. The same rule applies in reverse to a flat line, which must be verified in a second lead and with the patient before asystole is reported, since a disconnected lead can mimic it.

    Source: NHA CET Test Plan — artifact identification (somatic tremor, lead disconnection); — verify lethal rhythms with the patient and a second leadReport 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 →