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Relias Dysrhythmia Basic A 2025 | 35 ECG Rhythm
Questions with Verified Answers + Diagrams | A+
Scored Pack
QUESTION 1
Rationale:
The rhythm strip presented displays an overall regular sinus rhythm with one early, wide, and bizarre
QRS complex that interrupts the normal pattern. This aberrant complex is not preceded by a P wave, and it
has a duration significantly longer than the surrounding QRS complexes — a hallmark feature of a
premature ventricular contraction (PVC).
In normal sinus rhythm, each QRS complex follows a P wave at regular intervals, and the morphology is
uniform. However, in this strip, one QRS complex appears prematurely and does not follow the same shape
or duration as the others, indicating that it originates from the ventricles rather than the atria.
, This distinguishes the rhythm from:
Sinus rhythm with PAC (D): PACs have premature P waves followed by normal-looking QRS
complexes. Here, the aberrant beat lacks a preceding P wave and is wide.
Normal sinus rhythm (C): Normal rhythm would not include premature or ectopic beats.
Sinus tachycardia (A): Although the overall rhythm is not slow, the rate is not fast enough to be
Page | 2 considered tachycardia (>100 bpm), and the irregular beat does not align with a tachycardic pattern.
PVCs are common and may be benign or related to underlying cardiac issues, especially if they occur
frequently. Recognition is key in telemetry, med-surg, and cardiac step-down settings. Patients may
experience palpitations, but often no symptoms are present. If symptomatic or frequent, further evaluation
may include electrolyte monitoring, cardiac enzymes, and ECG.
RATIONAILE
This ECG rhythm strip clearly demonstrates the characteristics of a second-degree AV block, Type I, also
known as Mobitz I or Wenckebach phenomenon. In this type of block, the PR interval progressively
lengthens with each successive beat until a P wave is not followed by a QRS complex — this is the key
diagnostic hallmark.
If you closely observe this strip:
The P waves are present and consistent.
The PR intervals get longer and longer, beat by beat.
Eventually, a QRS complex is dropped (you’ll see a P wave that isn’t followed by a QRS), and then
the cycle repeats.
This progressive conduction delay occurs at the level of the AV node, which temporarily fails to conduct the
impulse to the ventricles. After the dropped beat, the cycle resets.
, Here’s how this rhythm differs from other choices:
A. 3rd degree heart block: This shows complete dissociation between atrial and ventricular activity.
There’s no relationship between P waves and QRS — which is not the case here.
C. Sinus bradycardia: A slow but regular rhythm with consistent PR intervals and one P for each
QRS — there’s no dropped beat or PR variation.
Page | 3 D. Sinus rhythm with 1st degree AV block: This would show a consistently prolonged PR interval
(>0.20 seconds), but no dropped QRS complexes.
Mobitz I is often benign and transient, especially in athletes or during sleep, and may not require treatment
unless symptomatic (e.g., syncope, dizziness). Monitoring is key, and atropine may be considered if
symptomatic bradycardia is present.
Relias Dysrhythmia Basic A 2025 | 35 ECG Rhythm
Questions with Verified Answers + Diagrams | A+
Scored Pack
QUESTION 1
Rationale:
The rhythm strip presented displays an overall regular sinus rhythm with one early, wide, and bizarre
QRS complex that interrupts the normal pattern. This aberrant complex is not preceded by a P wave, and it
has a duration significantly longer than the surrounding QRS complexes — a hallmark feature of a
premature ventricular contraction (PVC).
In normal sinus rhythm, each QRS complex follows a P wave at regular intervals, and the morphology is
uniform. However, in this strip, one QRS complex appears prematurely and does not follow the same shape
or duration as the others, indicating that it originates from the ventricles rather than the atria.
, This distinguishes the rhythm from:
Sinus rhythm with PAC (D): PACs have premature P waves followed by normal-looking QRS
complexes. Here, the aberrant beat lacks a preceding P wave and is wide.
Normal sinus rhythm (C): Normal rhythm would not include premature or ectopic beats.
Sinus tachycardia (A): Although the overall rhythm is not slow, the rate is not fast enough to be
Page | 2 considered tachycardia (>100 bpm), and the irregular beat does not align with a tachycardic pattern.
PVCs are common and may be benign or related to underlying cardiac issues, especially if they occur
frequently. Recognition is key in telemetry, med-surg, and cardiac step-down settings. Patients may
experience palpitations, but often no symptoms are present. If symptomatic or frequent, further evaluation
may include electrolyte monitoring, cardiac enzymes, and ECG.
RATIONAILE
This ECG rhythm strip clearly demonstrates the characteristics of a second-degree AV block, Type I, also
known as Mobitz I or Wenckebach phenomenon. In this type of block, the PR interval progressively
lengthens with each successive beat until a P wave is not followed by a QRS complex — this is the key
diagnostic hallmark.
If you closely observe this strip:
The P waves are present and consistent.
The PR intervals get longer and longer, beat by beat.
Eventually, a QRS complex is dropped (you’ll see a P wave that isn’t followed by a QRS), and then
the cycle repeats.
This progressive conduction delay occurs at the level of the AV node, which temporarily fails to conduct the
impulse to the ventricles. After the dropped beat, the cycle resets.
, Here’s how this rhythm differs from other choices:
A. 3rd degree heart block: This shows complete dissociation between atrial and ventricular activity.
There’s no relationship between P waves and QRS — which is not the case here.
C. Sinus bradycardia: A slow but regular rhythm with consistent PR intervals and one P for each
QRS — there’s no dropped beat or PR variation.
Page | 3 D. Sinus rhythm with 1st degree AV block: This would show a consistently prolonged PR interval
(>0.20 seconds), but no dropped QRS complexes.
Mobitz I is often benign and transient, especially in athletes or during sleep, and may not require treatment
unless symptomatic (e.g., syncope, dizziness). Monitoring is key, and atropine may be considered if
symptomatic bradycardia is present.
