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Quizzes > Health & Medicine

6 second ECG quiz for supraventricular rhythm strips

Quick, free 6 sec ECG strip practice. Instant results.

Editorial: Review CompletedCreated By: Saurabh SumanUpdated Aug 28, 2025
Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art illustration for rhythm strip interpretation quiz on golden yellow background

This 6 second ECG quiz helps you interpret supraventricular rhythm strips quickly and with confidence. You will practice spotting P waves, timing intervals, and distinguishing sinus rhythm, SVT, atrial flutter, and atrial fibrillation, with instant feedback on each strip. For broader review, try our cardiac rhythm quiz, warm up with the ecg quiz for beginners, or compare ventricular patterns in idioventricular rhythm ecg.

On a 6-second ECG strip there are 7 QRS complexes. What is the approximate heart rate?
70 beats per minute
120 beats per minute
42 beats per minute
84 beats per minute
In a 6-second strip, multiply the number of QRS complexes by 10 to approximate beats per minute: 7 × 10 = 70 bpm. This is the standard quick?rate calculation.
A rhythm strip shows regular P waves before each QRS complex, a PR interval of 0.16 seconds, and a rate of 90 bpm. What is the rhythm?
Junctional rhythm
Sinus rhythm
Atrial tachycardia
Atrial flutter
Regular P waves before every QRS with a normal PR interval (0.12 - 0.20 s) and rate of 60 - 100 bpm confirms sinus rhythm. This distinguishes it from other SVTs.
A narrow QRS complex (?120 ms) on a 6-second strip suggests which origin of rhythm?
Complete heart block
Ventricular origin
Supraventricular origin
Pericardial effusion
Narrow QRS complexes under 120 ms indicate the impulse travels through the normal His-Purkinje system, consistent with supraventricular rhythms. Wide QRS suggests ventricular origin or aberrancy.
What is the normal PR interval duration in a sinus rhythm?
0.20 - 0.28 seconds
0.08 - 0.12 seconds
0.28 - 0.35 seconds
0.12 - 0.20 seconds
The PR interval normally ranges from 0.12 to 0.20 seconds (3 - 5 small boxes). Prolongation indicates first-degree AV block.
How many large 5-mm (0.2 sec) boxes equal 6 seconds on an ECG strip?
35 boxes
30 boxes
25 boxes
20 boxes
Each large box is 0.2 seconds. To represent 6 seconds, 6 ÷ 0.2 = 30 large boxes are required. This helps you quickly identify 6-second segments for rate calculation.
Beat-to-beat variation in P-wave morphology with a rate less than 60 bpm most likely indicates:
Multifocal atrial tachycardia
Sinus bradycardia
Wandering atrial pacemaker
Atrial fibrillation
Wandering atrial pacemaker shows P waves of varying shapes due to shifts in pacemaker focus, typically with a rate under 60 bpm. MAT is similar but with rate over 100 bpm.
If the RR interval on a 6-second strip measures 0.6 seconds consistently, what is the ventricular rate?
120 beats per minute
60 beats per minute
80 beats per minute
100 beats per minute
Rate = 60 ÷ RR interval (in seconds). Thus 60 ÷ 0.6 = 100 bpm. This method is used for regular rhythms.
Sawtooth-shaped atrial waves ("flutter waves") most commonly indicate:
Junctional tachycardia
SVT
Atrial flutter
Atrial fibrillation
Flutter waves are rapid, regular atrial depolarizations at ~250 - 350 bpm, seen best in leads II, III, aVF. This pattern defines atrial flutter.
An irregularly irregular ventricular rhythm with absent discrete P waves is diagnostic of:
Atrial fibrillation
Sinus arrhythmia
Multifocal atrial tachycardia
Atrial flutter with variable block
An irregularly irregular rhythm without identifiable P waves is classic for atrial fibrillation. MAT shows P waves of multiple morphologies and flutter has sawtooth waves.
Atrial flutter at an atrial rate of 300 bpm with 2:1 conduction produces a ventricular rate of:
75 beats per minute
200 beats per minute
150 beats per minute
100 beats per minute
With 2:1 conduction, every other atrial beat is conducted. So 300 ÷ 2 = 150 bpm for the ventricles. This is a common flutter conduction ratio.
Which finding is diagnostic of multifocal atrial tachycardia (MAT)?
Absent P waves
Sawtooth atrial waves
At least three different P-wave morphologies and rate >100 bpm
Regular narrow QRS at 150 bpm
MAT requires ?3 distinct P-wave shapes and tachycardia (>100 bpm). It's often seen in COPD exacerbations.
Adenosine is most useful to both diagnose and terminate which SVT?
Atrial flutter
Sinus tachycardia
AV nodal reentrant tachycardia (AVNRT)
Multifocal atrial tachycardia
Adenosine briefly blocks AV nodal conduction, terminating AVNRT and revealing underlying atrial activity. It usually does not terminate flutter or MAT.
In orthodromic AV reentrant tachycardia (AVRT), the atrial depolarization (P wave) is usually seen:
Hidden in the PR segment
Before each QRS complex
Simultaneously with the QRS
Immediately after the QRS complex in the ST segment
In orthodromic AVRT, conduction travels down the AV node and returns retrograde via the accessory pathway, so P waves appear shortly after each QRS, often in the ST segment.
Which feature on a rhythm strip indicates a junctional escape rhythm?
Multiple P-wave morphologies
Absent or inverted P waves with narrow QRS and rate 40 - 60 bpm
Sawtooth atrial waves
PR intervals lengthening until a beat drops
Junctional escape arises in AV node at 40 - 60 bpm; P waves may be absent, inverted, or after QRS, and QRS remains narrow.
A premature atrial contraction (PAC) is identified by:
A wide QRS preceded by a normal P wave
Regularly irregular RR intervals without P waves
No P wave and a compensatory pause
An early beat with an abnormal P-wave followed by a normal QRS
A PAC originates in atrium outside the SA node, producing an early P wave of different morphology, usually with a narrow QRS and a noncompensatory pause.
Which characteristic differentiates paroxysmal SVT from sinus tachycardia?
Rate always below 140 bpm
Abrupt onset and termination
Presence of discernible P waves before every QRS
Gradual changes in rate
Paroxysmal SVTs start and stop suddenly due to reentry circuits. Sinus tachycardia accelerates and decelerates gradually with physiologic triggers.
Which ECG lead is most sensitive for detecting atrial activity such as flutter or atrial tachycardia?
V1
Lead I
aVR
Lead III
Lead V1 is located over the right atrium and best captures atrial depolarizations, making it ideal for identifying flutter waves and subtle P-waves.
An automatic atrial tachycardia often shows which phenomenon on a rhythm strip?
Abrupt onset and termination
Fixed PR interval shortening
Sawtooth atrial waves
Gradual warm-up and cool-down of rate
Automatic atrial tachycardia is driven by enhanced automaticity and shows gradual acceleration and deceleration ('warm-up' and 'cool-down'), unlike reentrant SVTs.
Which finding distinguishes typical (counterclockwise) atrial flutter from atypical flutter?
Positive P waves in leads II, III, aVF
Variable PR intervals
Complete AV dissociation
Negative flutter waves in V1
Typical counterclockwise atrial flutter shows negative sawtooth waves in V1 due to activation moving away from that lead. Atypical forms have different atrial circuits and wave morphologies.
Concealed conduction in atrial flutter can cause which pattern on the ventricular response?
Progressive PR prolongation
Irregular ventricular response despite constant atrial rate
Regular narrow complex tachycardia
Fixed 2:1 conduction
Concealed conduction occurs when non-conducted flutter waves partially penetrate the AV node, altering subsequent conduction and producing irregular ventricular rhythms despite constant atrial rates.
Digitalis toxicity can produce which supraventricular arrhythmia?
Multifocal atrial tachycardia
Typical atrial flutter
AV nodal reentrant tachycardia
Atrial tachycardia with block
Digitalis toxicity often causes atrial tachycardia with block, characterized by ectopic atrial beats with 2:1 or variable AV block. This is a hallmark sign in digoxin overdose.
How can you differentiate orthodromic from antidromic AV reentrant tachycardia on a rhythm strip?
Orthodromic has narrow QRS, antidromic has wide QRS
Orthodromic has no P waves, antidromic has P before QRS
Antidromic shows sawtooth waves
Only antidromic responds to adenosine
Orthodromic AVRT uses the AV node antegrade, producing narrow QRS, while antidromic conducts antegrade over the accessory pathway causing wide QRS complexes.
Which ECG feature indicates a second-degree AV block (Mobitz II) in the context of atrial flutter?
Variable QRS morphology
Progressive PR lengthening before a dropped beat
Fixed dropped QRS complexes without PR changes
Atrial rate < 100 bpm
Mobitz II block shows sudden nonconducted P waves with constant PR intervals on conducted beats. In flutter, every nth flutter wave fails to conduct with no PR change.
Dual AV nodal physiology as the mechanism for AVNRT is suggested by:
Gradual onset of tachycardia over several seconds
Sawtooth atrial activity
Sudden change in cycle length with PVC initiating tachycardia
Absence of retrograde P waves
A PVC can block the fast pathway and allow conduction via the slow pathway, initiating reentrant circuit in AVNRT. Sudden initiation by PVC suggests dual nodal pathways.
Esophageal ECG leads are used to better visualize which component?
Bundle branch block patterns
Left atrial and atrial appendage activity
ST-segment elevation
Ventricular repolarization
Esophageal leads lie close to the left atrium, enhancing atrial signal amplitude to detect flutter waves or atrial tachycardia that may be concealed on surface ECG.
Which finding differentiates atrial fibrillation with slow ventricular response from junctional escape rhythm?
Irregularly irregular rhythm versus regular escape rhythm
Fixed PR intervals
P wave inverted in lead II
Presence of sawtooth waves
AF with slow response remains irregularly irregular due to variable conduction, whereas junctional escape is a regular rhythm with consistent intervals.
Carotid sinus massage is most likely to terminate which arrhythmia?
AV nodal reentrant tachycardia (AVNRT)
Atrial flutter with 2:1 block
Atrial tachycardia
Multifocal atrial tachycardia
Carotid sinus massage increases vagal tone to AV node, interrupting reentrant circuits in AVNRT. It rarely terminates atrial tachycardia or flutter.
Which pacing maneuver can help distinguish atrial tachycardia from AVNRT?
Isoproterenol infusion accelerating atrial rate
Atrial overdrive pacing advancing the tachycardia without affecting VA interval
Ventricular pacing terminating tachycardia
Carotid massage slowing ventricular rate
Atrial overdrive pacing that captures the atrium and resets the tachycardia without altering VA interval indicates an atrial focus rather than AV nodal reentry.
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Study Outcomes

  1. Analyze 6 sec strip metrics -

    Calculate heart rate, measure intervals, and assess rhythm regularity on any 6 sec strip to establish a solid foundation for ECG interpretation.

  2. Interpret supraventricular rhythm strip characteristics -

    Recognize P-wave morphology, PR interval consistency, and narrow QRS complexes to accurately identify common supraventricular rhythms.

  3. Differentiate idioventricular rhythm strips -

    Distinguish idioventricular patterns by spotting wide QRS complexes, absent P waves, and slow rates compared to supraventricular rhythms.

  4. Identify agonal rhythm strip indicators -

    Spot critical agonal features such as extreme bradycardia, irregular complexes, and gradually widening QRS to anticipate urgent clinical intervention.

  5. Apply systematic strip interpretation -

    Use a step-by-step framework to approach each 6 sec strip quiz, ensuring consistent analysis from rate calculation to waveform evaluation.

  6. Evaluate clinical implications of arrhythmias -

    Assess how findings on supraventricular, idioventricular, or agonal rhythm strips impact patient management and treatment decisions.

Cheat Sheet

  1. Rate Calculation Using a 6-Second Strip -

    To quickly estimate heart rate on a 6 sec strip, count the number of QRS complexes and multiply by 10. This method is endorsed by the American Heart Association for rapid assessment of supraventricular rhythm strip recordings. For example, 8 complexes on a 6 sec strip equate to a heart rate of 80 bpm.

  2. P Wave Morphology and Atrial Origin -

    Examine P wave shape and axis in lead II to determine atrial focus; upright, rounded P waves suggest sinus origin according to ACC guidelines. Abnormal P waves (e.g., peaked or notched) can indicate ectopic atrial rhythms or atrial enlargement. Mnemonic tip: "P before QRS means atrial first," reinforcing supraventricular labeling.

  3. PR Interval and AV Conduction Assessment -

    Measure the PR interval from the start of the P wave to the start of the QRS complex; a normal range is 120 - 200 ms per Cardiac Electrophysiology Society standards. Prolongation hints at first-degree AV block, while varying PR intervals may signal Mobitz types I or II. Recognizing these nuances refines interpretation of both supraventricular and idioventricular rhythm strips.

  4. QRS Duration: Narrow vs. Wide Complex Rhythms -

    A QRS width under 120 ms typically denotes a supraventricular rhythm strip, whereas durations above 120 ms suggest aberrant conduction or ventricular origin, like idioventricular rhythm strips. The Cleveland Clinic emphasizes this criterion to distinguish SVT from life-threatening ventricular beats. Remember: "Slim QRS is SV, fat QRS is ventricular or aberrant."

  5. Differentiating Agonal, Idioventricular, and Supraventricular Rhythms -

    Agonal rhythm strip patterns show irregular, slow complexes with widening QRS and minimal P waves, indicating dying heart activity per ACLS protocols. Idioventricular rhythm strips feature regular but slow rates (20 - 40 bpm) without preceding P waves, while supraventricular rhythms have rates above 50 bpm and preserved P - QRS relationships. Use the mnemonic "No P, Slow Wide = Idio/Agonal" to guide your interpretation.

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