Nursing Field Notes / Cardiovascular · Med-Surg Course
Pacemakers, ICDs & Cardioversion ⚡
Synchronized or not · what each device is for · living with one
NG-405
Cardiovascular
ADHD-friendly visual edition
The whole topic turns on one distinction: cardioversion is synchronized, defibrillation is not. Synchronized means the shock waits for the R wave. If there is no R wave to wait for, you cannot synchronize.
CardioversionSYNCHRONIZED · low energy · a pulse is present
DefibrillationNOT synchronized · high energy · V-fib or pulseless V-tach
PacemakerToo slow — it makes the heart beat
ICDToo fast and lethal — it shocks the heart back
🧨 What starts it
Four things, four jobs
- Pacemaker — for rhythms that are too slow. Symptomatic bradycardia, complete heart block, sick sinus syndrome. It fires an impulse when the heart does not.
- ICD — for rhythms that are too fast and lethal. It watches, and if it sees ventricular tachycardia or fibrillation it shocks. Many are combined with a pacemaker.
- Cardioversion — a synchronized shock, timed to the R wave, for an unstable rhythm that still has a pulse: atrial fibrillation with a rapid response, atrial flutter, SVT, or V-tach with a pulse.
- Defibrillation — an unsynchronized shock at high energy for ventricular fibrillation and pulseless ventricular tachycardia. Nothing else.
Why synchronizing matters
A shock delivered on the T wave can drive the heart into ventricular fibrillation — the R-on-T phenomenon. Synchronizing makes the machine wait for the R wave so the shock lands safely. In V-fib there is no organized R wave to find, so the machine cannot synchronize, and the correct setting is off.
Before an elective cardioversion
- Anticoagulated for 3 to 4 weeks beforehand if the atrial fibrillation has lasted more than 48 hours, or a transesophageal echo first — otherwise a clot in the atrium is thrown as a stroke.
- Hold digoxin for 48 hours — it increases the risk of a post-shock dysrhythmia.
- Signed consent, sedation, NPO, and the crash cart present.
🔎 What you will see
Doing it safely
- Confirm the rhythm and check for a pulse before choosing the mode.
- Turn the sync button ON for cardioversion, OFF for defibrillation. Check it every single time — some machines reset to off after each shock.
- “All clear” — look at the bed, look at yourself, look around, then shock. Nobody touching anything.
- Remove oxygen from the immediate area; remove nitroglycerin patches.
- Pads go at least 2.5 cm from a pacemaker or ICD, or use anterior-posterior placement.
- Resume compressions immediately after a defibrillation — do not stop to check a pulse.
Pacemaker problems on the strip
- Failure to capture — a spike with no complex after it. The impulse fired and the heart ignored it.
- Failure to sense — spikes landing where they should not, because the device cannot see the heart’s own beats. Dangerous: it can fire on a T wave.
- Failure to pace — no spikes at all when the rate is below the set rate.
- Any of these with symptoms — dizziness, syncope, a rate below the set rate — is reported.
After insertion
- Immobilize the arm on that side and avoid raising it above the shoulder for 48 hours — the lead can dislodge.
- Watch the site for bleeding, swelling and hematoma.
- Hiccups or twitching of the chest wall means a lead has moved. Report it.
- Chest x-ray to confirm lead position.
🩺 What you do
Living with a device — the teaching
- Carry the device card at all times and wear medical identification.
- Take your own pulse daily and report a rate below the set rate.
- No MRI unless the device is certified MRI-conditional. Tell every provider, including the dentist.
- Airport security: show the card, ask for a hand search, do not linger in the archway.
- Mobile phone on the opposite ear, and not carried in a breast pocket over the device.
- Microwaves, hair dryers and electric blankets are fine. Keep away from strong magnets, arc welding and large running motors.
- No contact sports and no heavy lifting on that side.
- Report: dizziness, fainting, prolonged hiccups, palpitations, swelling at the site.
ICD-specific teaching
- If it fires once and she feels well — sit or lie down, then call the cardiologist that day.
- If it fires more than once, or she feels unwell after — call emergency services.
- A bystander touching her during a shock may feel a tingle. It will not harm them.
- Driving is restricted after a shock — the rules vary, she checks locally.
- Family should learn CPR.
- Anxiety about being shocked is common and worth naming. Support groups help.
The three answers people get wrong
- V-fib is defibrillated, not cardioverted. There is no R wave to sync to.
- V-tach with a pulse is cardioverted. V-tach without a pulse is defibrillated.
- Asystole is never shocked. It is CPR and epinephrine. Shocking a flat line does nothing — check the leads and confirm in a second view.
⚡ Quick recall
CardioversionSYNCHRONIZED · low energy · a pulse is present
DefibrillationNOT synchronized · high energy · V-fib or pulseless V-tach
PacemakerToo slow — it makes the heart beat
ICDToo fast and lethal — it shocks the heart back
What is the difference between cardioversion and defibrillation?
Cardioversion is synchronized to the R wave and used when there is a pulse. Defibrillation is unsynchronized, for V-fib and pulseless V-tach.
Why can V-fib not be cardioverted?
There is no organized R wave for the machine to synchronize to.
A spike appears with no QRS after it. What is that?
Failure to capture.
How long is arm movement restricted after a pacemaker insertion?
Do not raise it above the shoulder for about 48 hours.
The ICD fires once and she feels fine. What does she do?
Sit or lie down and call the cardiologist that day.
Is asystole shocked?
No. CPR and epinephrine. Confirm the rhythm in another lead.