NCLEX-RN cheat sheet · Cardiovascular
Dysrhythmias and ECGs
Alarms and artifact, the main rhythms, shocks, heart blocks, devices, 12-lead placement
AI-checkedChecked by AI against current guidelines, with spot-checks by a registered nurse.
A monitor can show a deadly rhythm in a client who's fine, so the first rule of rhythms is simple: look at the client.
Download the free PDF: Dysrhythmias and ECGs, 2 pages
Two printable pages, free. No sign-up.
At a glance
Telemetry alarms
- The monitor names the rhythm, but it isn't always right. Loose electrodes and movement cause artifact, which can look just like ventricular beats.
- Any alarm: look at the client, check a pulse and output, then act on the rhythm. Then check the leads and electrodes.
- Low output: low pressure, a weak pulse, slow refill, chest pain, dizziness, confusion.
- Ventricular tachycardia, ventricular fibrillation and complete heart block can all cause cardiac arrest quickly.
The waveform
| Part | What it shows |
|---|---|
| P wave | The atria firing |
| QRS complex | The ventricles' electrical depolarization. It doesn't prove a pulse: in pulseless electrical activity, there's a rhythm but no pulse |
| T wave | The ventricles recovering, ready for the next beat |
| Regular rhythm | The spaces between beats stay the same from one beat to the next |
Sinus and atrial rhythms
| Rhythm | Looks like | Key nursing point |
|---|---|---|
| Sinus bradycardia | Normal-looking, under 60 | Can be normal in athletes. Symptoms: assess output, withhold cardiac drugs if indicated, notify the provider; atropine or pacing may be needed |
| Sinus tachycardia | Normal-looking, over 100 | Treat the cause, not the number: stress, exercise, caffeine, fever, low fluid volume, anemia, low oxygen |
| Atrial fibrillation | Irregularly irregular; no clear P waves; wavy baseline | Stroke risk: teach the warning signs, expect anticoagulation. Stable: rate or rhythm drugs; unstable: urgent synchronized cardioversion. Automatic BP can be inaccurate |
| Atrial flutter | Fast, regular sawtooth waves, about 250 to 300 a minute | Lowers output, raises stroke risk; treated much like atrial fibrillation |
| SVT | Fast; no fixed rate defines it. QRS often narrow, may be wide; P waves often hidden | Little time to fill, so output may fall: assess for low output |
Ventricular and arrest rhythms
| Rhythm | Looks like | Action |
|---|---|---|
| PVCs | An early beat from the ventricle; wide, bizarre QRS | Occasional ones are common. Frequent ones can signal a serious problem; ones from more than one spot are more dangerous. A PVC on the T wave can trigger V-tach |
| V-tach | Wide complexes, no visible P or T waves, often over 120 a minute | Is there a pulse? Pulse: synchronized cardioversion if unstable, IV antidysrhythmics if stable. No pulse: CPR and defibrillate |
| Torsades de pointes | Twisting, polymorphic V-tach with a long QT | Can turn into V-fib. Sustained: unsynchronized shock, even with a pulse |
| V-fib | Chaotic quivering; no pattern, no output | CPR, call for help, defibrillate fast; IV antidysrhythmics follow |
| Asystole | Flat line; no electrical activity | No pulse: CPR, epinephrine as ordered; check leads without pausing CPR. No shock |
| PEA | A rhythm on the monitor, but no pulse | Like asystole: CPR, airway, epinephrine, a search for reversible causes. No shock |
Heart blocks
| Block | Pattern | Usual care |
|---|---|---|
| First-degree | Long PR, over 0.2 seconds; no dropped beats | Often none |
| Second-degree, Mobitz I | PR lengthens, then a beat drops | Usually none |
| Second-degree, Mobitz II | Constant PR; beats drop without warning | Usually a permanent pacemaker; can progress to complete block |
| Third-degree (complete) | Atria and ventricles beat on their own | Permanent pacemaker if the cause can't be reversed |
Electrolytes and the ECG
| Problem | ECG change |
|---|---|
| High potassium | Peaked T waves first; higher still, a wide QRS that can slide toward a sine-wave pattern |
| Low potassium | Flat T waves, U waves, a long QT: risk of torsades |
| Low calcium or magnesium | Long QT |
| High calcium | Can shorten the QT |
Rate-slowing drugs: Before metoprolol or digoxin, check the apical pulse. Under 60: hold the drug and call the prescriber, unless other parameters are ordered.
Shock, drug or pacing?
| Situation | Usual answer |
|---|---|
| No pulse: V-fib or pulseless V-tach | CPR and defibrillation |
| A pulse, but unstable and fast | Synchronized cardioversion; sustained polymorphic V-tach gets an unsynchronized shock |
| Asystole or PEA | CPR and epinephrine, never a shock |
| Slow with symptoms, or a serious block | Atropine, or pacing |
| Stable atrial fibrillation | Rate or rhythm drugs, and anticoagulation |
Cardioversion and defibrillation
- Cardioversion: a low-energy shock timed to the QRS, for selected rhythms with a pulse (SVT, rapid atrial fibrillation or flutter, V-tach with a pulse), not torsades. Planned: consent and sedation.
- Atrial fibrillation over 48 hours, or onset unknown: an echo through the esophagus checks for clots first.
- Set the machine to synchronize; everyone stands clear.
- Defibrillation: immediate, unsynchronized; no consent needed. CPR, pads on quickly; don't touch the client while it analyzes.
- Compress while it charges; resume CPR right after the shock, for about 2 minutes before the next rhythm check.
Pacemakers and ICDs
- A pacemaker paces a slow or irregular heartbeat; an ICD can also shock a deadly rhythm back to normal. Carry the device card.
- Keep the incision dry for 4 to 5 days. Arm limits come from the surgeon, for that client and that device.
- Report wound infection, the old symptoms coming back, dizziness, breathlessness, chest pain, hiccups that won't stop, or fainting.
- Most appliances are safe. Phone on the opposite side. Distances from tools, speakers and magnets: follow the manufacturer's guidance for that model.
- Airport security: show the card. Talk to the provider before any MRI.
- ICD: report every shock. A shock and still unwell, or fainting: get emergency help.
12-lead ECG: chest leads
| Lead | Where |
|---|---|
| V1 | 4th intercostal space, right sternal border |
| V2 | 4th space, left sternal border |
| V3 | Midway between V2 and V4 |
| V4 | 5th space, midclavicular line |
| V5, V6 | Level with V4: anterior axillary line, then midaxillary line |
Who reads it: The machine's printout can't diagnose alone. A provider reads the 12-lead; trained nurses interpret rhythms, spot urgent changes and escalate. Abnormal pattern: assess the client first.
Priority and safety calls
- ★ Alarm shows V-fib, but the client is sitting up and talking: check the electrodes and leads for artifact.
- ★ Flat line, unresponsive, no pulse, leads attached: start CPR and call for help; confirmed asystole isn't shockable.
- Monomorphic V-tach with a pulse and low blood pressure is unstable: expect prompt synchronized cardioversion. A stable client may get IV antidysrhythmics first.
- New atrial fibrillation: teach stroke warning signs; expect anticoagulation.
How the NCLEX tests it
- Look at the client first, then the monitor, and assess output with every new rhythm.
- Atrial fibrillation means stroke risk and anticoagulation.
- No pulse with V-fib or V-tach: CPR and defibrillate. Unstable with a pulse: synchronized cardioversion, except polymorphic V-tach.
- Asystole and pulseless electrical activity: CPR and epinephrine, never a shock.
- Serious blocks need pacing. Follow the surgeon's arm instructions; report every ICD shock.
- V1 and V2 go in the fourth space, and V4 in the fifth, at the midclavicular line.
Practice it next
This sheet comes from Dysrhythmias, telemetry and pacemakers and Point-of-care testing, ECGs and specimens in our NCLEX-RN course. Try free practice questions, or see the lessons it was written from.
Quick self-quiz
- First-degree block: a PR interval over ___ seconds.
Show answer
0.2 - Atrial flutter: sawtooth waves of about 250 to ___ a minute.
Show answer
300 - After a shock, resume CPR for about ___ minutes before the next rhythm check.
Show answer
2 - V1 goes in the fourth intercostal space, at the ___ sternal border.
Show answer
right - Low potassium brings flat T waves and ___ waves.
Show answer
U
Sources
- Open RN, Nursing Advanced Skills, 7.4 ECG Patterns and Dysrhythmias
- Open RN, Nursing Advanced Skills, 7.5 Cardioversion and Defibrillation
- American Heart Association, Adult Advanced Life Support guidelines
- MedlinePlus, Heart pacemaker - discharge
- Open RN, Nursing Advanced Skills, Checklist: Obtain a 12-Lead ECG
More cardiovascular cheat sheets
- Heart failure NCLEX cheat sheet
- Hypertension and vascular disease NCLEX cheat sheet
- Coronary artery disease and ACS NCLEX cheat sheet
- Shock and sepsis NCLEX cheat sheet
Educational use only. This sheet is a study aid for the NCLEX-RN, not a substitute for clinical judgment, your facility’s policy or the provider’s orders. Where practice varies, follow facility policy and state law. NCLEX® and NCLEX-RN® are registered trademarks of NCSBN, which does not endorse these materials.