ECG Rhythm Interpretation for NCLEX: 27 Rhythms You Need to Know
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The first time you look at an ECG strip, it might feel like Morse code. After this guide, you will be able to identify any rhythm on the NCLEX in under 10 seconds. The trick is a simple 5-step method and pattern recognition for the 27 rhythms that show up on the exam.
The 5-step ECG interpretation method
- Rate: Is it fast (over 100), slow (under 60), or normal?
- Rhythm: Is it regular or irregular?
- P waves: Are they present? One before each QRS?
- PR interval: 0.12 to 0.20 seconds (3 to 5 small boxes)?
- QRS: 0.06 to 0.12 seconds (less than 3 small boxes)?
ECG & Dysrhythmia Interpretation Bundle — 27 rhythms, 5-step method, 20 practice questions. $9.35.
Normal Sinus Rhythm (NSR)
Rate 60 to 100, regular, P before every QRS, normal PR and QRS. Baseline of a healthy heart.
Sinus bradycardia
Rate under 60, regular, P before every QRS. Symptomatic? Atropine 0.5 mg IV.
Sinus tachycardia
Rate 100 to 150, regular, P before every QRS. Treat the cause (fever, pain, dehydration).
Atrial fibrillation
Irregularly irregular, NO discernible P waves, normal QRS. Treatment: rate control (beta blockers, CCBs), rhythm control (cardioversion), anticoagulation (warfarin or DOAC).
Atrial flutter
Sawtooth flutter waves between QRS. Often 2:1 or 4:1 conduction.
SVT (Supraventricular Tachycardia)
Rate over 150, regular, P waves hidden or absent. Treatment: vagal maneuvers first, then adenosine 6 mg rapid IV push.
Premature Ventricular Contractions (PVCs)
Wide, bizarre QRS without preceding P wave. More than 6/minute or in pairs = concerning.
Ventricular tachycardia (V-tach)
Wide QRS, rate 100 to 250, regular, no P waves. Pulseless V-tach: defibrillate. With pulse: amiodarone or cardioversion.
Ventricular fibrillation (V-fib)
Chaotic, no discernible waves. Defibrillate immediately. This is a code blue.
Asystole
Flat line. CPR, epinephrine. Confirm in two leads. NOT shockable.
Pulseless Electrical Activity (PEA)
Looks like a rhythm but no pulse. Find and treat the cause (H's and T's). NOT shockable.
Heart blocks
First degree AV block
PR longer than 0.20 seconds. Usually asymptomatic.
Second degree Type I (Wenckebach)
PR gets progressively longer until a QRS is dropped.
Second degree Type II (Mobitz II)
PR is constant. Some P waves are not followed by QRS. Concerning — may need pacemaker.
Third degree (complete) heart block
P waves and QRS are completely dissociated. ALWAYS needs pacemaker.
Defibrillation vs cardioversion vs CPR
| Rhythm | Treatment |
|---|---|
| V-fib | Defibrillate (unsynchronized) |
| Pulseless V-tach | Defibrillate |
| V-tach with pulse | Cardioversion (synchronized) |
| SVT (unstable) | Cardioversion |
| AF (unstable) | Cardioversion |
| Asystole | CPR + epinephrine (no shock) |
| PEA | CPR + epinephrine + treat cause (no shock) |
The ECG & Dysrhythmia Bundle has every rhythm with practice strips. $9.35.
Frequently Asked Questions
What rhythms are shockable?
V-fib and pulseless V-tach are the only shockable rhythms. Asystole and PEA are NOT shockable.
What is the difference between defibrillation and cardioversion?
Defibrillation is unsynchronized and used for V-fib and pulseless V-tach. Cardioversion is synchronized to the R wave and used for unstable AF, atrial flutter, and V-tach with a pulse.
How do you tell V-tach from SVT?
V-tach has a wide QRS (greater than 0.12 seconds). SVT has a narrow QRS. SVT originates above the ventricles; V-tach originates in the ventricles.
What rate defines bradycardia and tachycardia?
Bradycardia is heart rate under 60 beats per minute. Tachycardia is over 100 beats per minute.