Cardioversion and defibrillation: a nursing guide

Cardioversion and defibrillation are two distinct electrical therapies used to terminate life-threatening and hemodynamically unstable cardiac arrhythmias. Both deliver a controlled electrical current through the myocardium to depolarize the heart and allow a normal rhythm to emerge — but they differ fundamentally in timing, indication, and the clinical context in which they are used. Confusing one for the other on NCLEX is a high-stakes error. Applying synchronized cardioversion to ventricular fibrillation delays the only therapy that saves the patient. Applying unsynchronized defibrillation to a perfusing rhythm when synchronization was available risks inducing VF.

This guide covers the cardioversion-vs-defibrillation distinction, indications, energy settings, pad placement, full procedure steps, safety protocols, post-procedure monitoring, complications, and a bank of NCLEX tips drawn from the most commonly tested pitfalls. For rhythm identification background, see the cardiac arrhythmias nursing guide. For the code blue algorithm, see rapid response and code blue nursing.

Cardioversion vs defibrillation: the core distinction

This is the most testable concept in this entire skill area. Master it first.

Synchronized cardioversion vs unsynchronized defibrillation — quick reference
Feature	Synchronized cardioversion	Unsynchronized defibrillation
Shock timing	Synchronized to the R wave (delivered during QRS complex)	Delivered immediately — no synchronization
Why synchronized?	Avoids R-on-T phenomenon: shock landing on the T wave can trigger VF	No organized rhythm exists — no R wave to sync to
Rhythm requirement	Organized rhythm present (a detectable QRS complex)	No organized rhythm (VF, pulseless VT) or polymorphic VT
Patient has a pulse?	Yes — perfusing rhythm (may be hemodynamically unstable)	No pulse (pulseless arrest) — or VF
Sedation required?	Yes — always (patient must not feel the shock)	No — patient is unconscious (pulseless arrest)
CPR during procedure?	No — patient has a pulse	Yes — CPR continues until defibrillator is charged
Sync mode on defibrillator	ON — confirm sync markers on each R wave	OFF — or device resets to async after each shock
Typical first-shock energy (biphasic)	50–200 J depending on rhythm (see table below)	120–200 J (manufacturer dependent)
Indications	AFib, atrial flutter, SVT/PSVT, stable or unstable perfusing VT	VF, pulseless VT, polymorphic VT (torsades de pointes)

Why R-on-T matters

The cardiac cycle has a brief window during repolarization — the peak of the T wave — called the vulnerable period. If an electrical stimulus strikes the myocardium during this window, the partially repolarized cells can respond chaotically, triggering ventricular fibrillation. This is R-on-T phenomenon. Synchronized cardioversion avoids this by detecting the R wave and delivering the shock only during the QRS, when the myocardium is already fully depolarized. Unsynchronized defibrillation deliberately ignores this timing because in VF and pulseless VT, there is no organized R wave to detect and no functioning rhythm to protect — the goal is to terminate the chaos entirely.

Indications for synchronized cardioversion

Synchronized cardioversion is used when a patient has an organized rhythm (a detectable QRS) that is causing hemodynamic instability or has failed pharmacological management. The rhythm must be one that synchronized shock can reliably terminate.

Unstable presentations (emergent cardioversion):

Atrial fibrillation with rapid ventricular response causing hypotension, altered mental status, signs of end-organ hypoperfusion, or acute pulmonary edema
Atrial flutter with hemodynamic compromise
SVT/PSVT refractory to vagal maneuvers and adenosine
Stable or perfusing ventricular tachycardia that becomes hemodynamically unstable

Elective or semi-urgent presentations:

Persistent atrial fibrillation — rhythm control strategy (with appropriate anticoagulation or TEE to exclude thrombus)
Stable VT that has not responded to antiarrhythmics

The key clinical question: Does the patient have an organized rhythm and a pulse? If yes — and the rhythm is causing hemodynamic compromise or has failed other treatments — consider synchronized cardioversion.

Indications for defibrillation (unsynchronized)

Defibrillation is used for shockable pulseless arrest rhythms. The clinical setting is always cardiac arrest or imminent arrest.

Ventricular fibrillation (VF): chaotic electrical activity, no coordinated contraction, no pulse — the most common initial rhythm in witnessed out-of-hospital cardiac arrest
Pulseless ventricular tachycardia (pVT): organized-appearing QRS but no effective cardiac output — treat identically to VF
Polymorphic VT / torsades de pointes: treat as VF — the rhythm is too unstable to synchronize reliably; unsynchronized defibrillation is the correct choice

AEDs (automated external defibrillators) are designed for defibrillation in non-monitored settings. They analyze the rhythm automatically and determine whether a shock is advised — the operator does not select synchronized or unsynchronized mode.

Energy settings: indications and joule reference

Rhythm-specific indications and energy settings (biphasic defibrillator standard)
Rhythm	Therapy	Biphasic energy	Monophasic energy	Notes
Atrial fibrillation	Synchronized cardioversion	120–200 J initial (or per manufacturer)	200 J initial	Higher energy first — AF often requires more energy than flutter
Atrial flutter	Synchronized cardioversion	50–100 J initial	200 J	Flutter converts at lower energy than AF; escalate if no conversion
SVT / PSVT	Synchronized cardioversion	50–100 J initial	200 J	Start lower; escalate in 50 J steps if no conversion
Stable monomorphic VT	Synchronized cardioversion	100 J initial	200 J	Escalate if no conversion; if patient becomes pulseless → defibrillate
Ventricular fibrillation	Defibrillation (unsynchronized)	120–200 J (manufacturer-specific)	360 J	CPR immediately before and after; reassess every 2 min
Pulseless VT	Defibrillation (unsynchronized)	120–200 J	360 J	Same protocol as VF
Polymorphic VT / torsades	Defibrillation (unsynchronized)	120–200 J	360 J	Do NOT attempt to synchronize — rhythm too unstable; treat as VF

Biphasic vs monophasic: Biphasic defibrillators are the current standard. They deliver current in two directions (positive then negative), requiring less total energy and causing less myocardial damage than older monophasic devices. Manufacturer-specific settings vary — always follow the device manufacturer’s recommendation when displayed. Monophasic devices (360 J) are older technology but still encountered; know both.

Synchronized cardioversion: step-by-step nursing role

The nurse’s role in synchronized cardioversion spans preparation, procedure support, and post-procedure monitoring. In emergent settings, multiple steps occur simultaneously across the team.

Step 1: Confirm the clinical decision

Verify the patient has an organized rhythm with a detectable QRS
Confirm hemodynamic instability or failed pharmacological management
Identify the specific rhythm (AF, flutter, SVT, VT) — this determines energy selection

Step 2: Consent and preparation

Obtain informed consent if time allows; in emergent settings, implied consent applies
Explain the procedure to the patient if conscious — what they will feel and why
Ensure IV access is in place (required for sedation)
Establish continuous cardiac monitoring on the defibrillator
Verify a 12-lead ECG has been obtained if time permits; document baseline rhythm

Step 3: Sedation

Administer sedation and analgesia as ordered — the patient must not feel the shock
Common agents: midazolam + fentanyl (conscious sedation); propofol (elective procedures with anesthesia support)
Monitor respiratory status during sedation — have bag-valve mask available
Ensure the patient is adequately sedated before proceeding

Step 4: Oxygen and airway

Provide supplemental oxygen as needed before sedation
Remove the oxygen delivery device from the patient’s face and area before shocking — nasal cannulas and non-rebreather masks create an oxygen-enriched environment that is a fire hazard when sparks from arcing occur. Turn off oxygen flow and physically move delivery devices away from the patient

Step 5: Pad/paddle placement

Apply self-adhesive gel pads (preferred) or conductive gel if using paddles
Anterolateral (standard): right infraclavicular pad (below right clavicle, right of sternum) + left lateral chest pad (V5–V6 position, midaxillary line)
Anteroposterior (alternative): anterior pad on left precordium + posterior pad on left infrascapular region
Ensure good skin contact — press firmly, clip/shave excessive hair if needed
Do not place pads over pacemaker or ICD generator — stay at least 8 cm away

Step 6: Select synchronized mode

Press the “Sync” button on the defibrillator
Confirm sync markers appear on the monitor aligned with each R wave — do not proceed if markers are absent or misaligned
If sync markers are not aligning with the R wave, check lead placement and gain settings

Step 7: Select energy and charge

Select appropriate joule setting based on rhythm (see table above)
Charge the defibrillator
Announce to the team that you are charging

Step 8: Clear and deliver shock

Call “CLEAR” — sweep eyes from head to foot of the patient
Confirm no team member is touching the patient, bed rails, IV lines, or monitoring cables
Oxygen delivery device must be away from the patient
Deliver the shock — there may be a slight delay after the button is pressed as the device waits for the R wave
Do not release the button until the shock is delivered

Step 9: Immediate post-shock assessment

Assess rhythm on monitor immediately
Assess for pulse
If rhythm has not converted, prepare to repeat at higher energy
If rhythm converted to sinus rhythm, proceed to monitoring

Step 10: Document

Energy delivered (joules)
Number of shocks
Rhythm before and after each shock
Patient response (vital signs, level of consciousness, symptoms)
Medications administered (agent, dose, time)
Any complications (burns, hemodynamic changes, post-shock arrhythmias)

Defibrillation: nursing role (ACLS context)

Defibrillation is performed in the context of cardiac arrest — the ACLS pulseless arrest algorithm drives the sequence.

Step 1: Confirm pulselessness and initiate CPR

Verify unresponsiveness and absence of pulse (carotid pulse check ≤10 seconds)
Call for help, activate code blue
Begin high-quality CPR immediately — 100–120 compressions per minute, full chest recoil, minimize interruptions

Step 2: Attach defibrillator

Apply pads while CPR continues — do not stop compressions to place pads
Identify rhythm as soon as monitor is attached

Step 3: Identify shockable rhythm

VF or pulseless VT → proceed to defibrillation
PEA or asystole → continue CPR, identify reversible causes (H’s and T’s), do NOT shock

Step 4: Charge while CPR continues

Select energy (120–200 J biphasic, or 360 J monophasic)
Charge the defibrillator while compressions continue — do not stop CPR to charge

Step 5: Clear and deliver shock

When charged, announce “CLEAR” with visual sweep
Stop CPR briefly — confirm no one is touching patient
Ensure sync mode is OFF (verify on defibrillator display)
Deliver shock

Step 6: Resume CPR immediately

Resume CPR immediately after shock delivery — do not pause to check rhythm
Continue CPR for 2 minutes before next rhythm check
If IV/IO access available, administer epinephrine 1 mg IV/IO every 3–5 minutes during CPR

Step 7: Reassess every 2 minutes

Check rhythm every 2 minutes (during CPR pause)
Shockable rhythm persists → repeat defibrillation
Organized rhythm with pulse → post-resuscitation care
Asystole or PEA → continue CPR, H’s and T’s

Critical sync note: Some defibrillators automatically revert to unsynchronized mode after each cardioversion shock. Before repeating synchronized cardioversion, always re-select and verify sync mode. This is a common error — and a common NCLEX trap.

AED use

Automated external defibrillators are designed for use in community and non-monitored settings where rhythm analysis and mode selection are automated.

How AEDs work:

Power on the AED — follow visual and audio prompts
Attach pads to the patient (diagram on pads indicates placement)
AED analyzes the rhythm automatically — do not touch the patient during analysis
AED advises “shock advised” or “no shock advised”
If shock advised: ensure no one is touching the patient, press the shock button
Immediately resume CPR — do not wait to reassess rhythm before starting compressions
Continue CPR until the AED prompts the next analysis (every 2 minutes)

If AED says “no shock advised”:

Continue CPR immediately
The rhythm is non-shockable (PEA or asystole) — defibrillation will not help
Continue CPR until ALS personnel arrive

Pediatric considerations:

Use pediatric pads (attenuator pads) for children under 8 years or under 25 kg
Pediatric pads reduce energy delivery to age-appropriate levels
If adult pads are the only option available, use them — adult defibrillation is preferable to no defibrillation

Pad placement

Correct pad placement ensures adequate current delivery through the myocardium and affects defibrillation success.

Anterolateral (standard) placement:

Right pad: right infraclavicular area — below the right clavicle, just to the right of the sternum
Left pad: left lateral chest wall — V5–V6 position, midaxillary line, approximately at the level of the cardiac apex
Current path traverses the bulk of the ventricular myocardium

Anteroposterior (AP) placement:

Anterior pad: left precordium (over the cardiac apex)
Posterior pad: left infrascapular region — behind the heart, left of the spine
Preferred for AF cardioversion and for patients with pacemakers or ICDs (positions current delivery away from the device)
More effective for certain rhythm conversions but slightly more time-consuming to place

Pacemaker and ICD considerations:

Do not place pads directly over a pacemaker or ICD generator — minimum 8 cm clearance
Anteroposterior placement is preferred when a device is present
After cardioversion or defibrillation in patients with devices, check device function — shocks can inhibit pacemaker output or interrogate the ICD

Skin preparation:

Ensure skin is dry before applying pads — moisture reduces contact and increases arcing risk
Remove nitroglycerin patches, medication patches, or electrodes from the pad site — patches can cause burns and potentially ignite
Clip or shave dense chest hair if present — poor contact reduces current delivery and increases skin burns

For a full pacemaker safety guide, see the pacemaker nursing guide.

Safety protocols

The CLEAR protocol

Before every shock:

Announce “CLEAR” verbally and loudly
Visual sweep: move eyes from the patient’s head to their feet, confirming no team member is in contact with the patient, bed, or attached lines
Confirm:
- No hands on patient or bed rails
- No contact with IV tubing or lines connected to the patient
- Oxygen delivery device removed and flow off
- All personnel are clear
Deliver shock only after full visual confirmation

Oxygen removal — not optional

This is a high-yield NCLEX point. An oxygen-enriched environment around the patient during shock delivery is a genuine fire hazard. Sparks can arc from pads or paddles and ignite oxygen-saturated bed linens or the delivery device itself.

The requirement is specific: physically remove the oxygen delivery device from the patient’s face and surrounding area. Turning off the flow is not sufficient — residual oxygen in the mask remains concentrated. Remove the nasal cannula or non-rebreather mask entirely and move it away from the chest before shock delivery.

Wet surfaces and patches

Dry any wet skin at the pad site — moisture impairs current delivery and can cause burns or arcing
Remove all medication patches (nitroglycerin, nicotine, fentanyl) from the pad placement area before shocking

Post-shock sync mode verification

After every cardioversion shock on a biphasic defibrillator, verify whether sync mode is still active before the next shock. Many devices reset to unsynchronized mode automatically. Failing to re-select sync mode when delivering a second cardioversion shock exposes the patient to R-on-T risk.

Post-procedure monitoring

Immediate and ongoing monitoring is required after both cardioversion and defibrillation.

Post-cardioversion and post-defibrillation monitoring parameters
Parameter	Frequency	What you are looking for
Continuous cardiac monitoring	Continuous	Sustained sinus rhythm, new arrhythmias, bradycardia, AV block post-shock
12-lead ECG	Immediately post-procedure	Confirm rhythm, identify post-shock ST changes (usually transient and benign), assess for new conduction abnormalities
Vital signs (BP, HR, SpO2, RR)	Every 5 min × 30 min, then per protocol	Hemodynamic stability post-conversion; sedation effects on BP and respiratory rate
Neurological / mental status	Every 15 min until sedation cleared	Return to baseline consciousness; assess for sedation over-effect, confusion, or focal deficits
Airway and respiratory status	Continuous until sedation cleared	Adequate respiratory effort, SpO2 ≥94%; airway management if sedation causes apnea or hypoventilation
Skin at pad sites	Within 30 min of procedure	Redness, burns, blistering — uncommon with gel pads, more common with dry paddles or repeated shocks
Anticoagulation status (AF cardioversion)	Verify before and after	Adequate anticoagulation documented; initiate or continue anticoagulation post-conversion per protocol
Neurological assessment (AF cardioversion)	Post-procedure and each shift	Signs of thromboembolic stroke — new focal deficits, slurred speech, facial droop, unilateral weakness

Anticoagulation and AF cardioversion — a critical concept: Atrial fibrillation allows blood to pool in the left atrial appendage, forming thrombus. Cardioversion — even successful rhythm restoration — causes a period of atrial stunning during which clot can dislodge and embolize to the cerebral circulation. Two approaches are acceptable before elective cardioversion:

Anticoagulate for at least 3 weeks before cardioversion (and continue for at least 4 weeks after)
Perform transesophageal echocardiography (TEE) to exclude left atrial appendage thrombus, then proceed with cardioversion if no clot is found

This rule applies when AF duration is unknown or greater than 48 hours. If AF duration is confirmed under 48 hours, the thromboembolic risk is lower and cardioversion may proceed sooner, but anticoagulation is still initiated and continued post-conversion.

For monitoring protocol detail, see the cardiac monitoring and telemetry nursing guide.

Complications

Complications of cardioversion and defibrillation with nursing response
Complication	Mechanism	Nursing response
Skin burns at pad sites	High-energy current, inadequate gel, repeated shocks, dry skin	Assess pad sites after procedure; apply cool compress for comfort; document; wound care for blistering if present
Thromboembolic stroke (AF cardioversion)	Dislodgement of pre-existing LA thrombus; atrial stunning post-conversion	Verify anticoagulation adequacy before procedure; monitor neurological status post-cardioversion; report new focal deficits immediately
Post-shock bradycardia or AV block	Vagal response; conduction system effects of shock; underlying conduction disease unmasked	Continue cardiac monitoring; be prepared to administer atropine or activate transcutaneous pacing; notify provider
Transient ST elevation	Myocardial stunning from electrical shock; pericardial irritation	Obtain 12-lead ECG; compare with pre-procedure ECG; monitor for resolution — this is typically benign but must be documented and followed
Failed cardioversion (no rhythm change)	Insufficient energy, poor pad contact, underlying metabolic cause	Escalate energy for repeat attempt; check pad placement and skin contact; assess for reversible causes (electrolyte imbalance, hypoxia, acidosis)
Inadvertent induction of VF	R-on-T phenomenon if sync mode was not active or failed to detect R wave	Immediately switch to unsynchronized mode; defibrillate; begin CPR if pulseless
Aspiration (sedation-related)	Sedation-induced loss of airway protective reflexes; vomiting during procedure	Keep patient NPO before elective cardioversion; position laterally post-procedure; suction available; monitor SpO2 and respiratory rate
Pacemaker/ICD damage	Electrical current affects device programming or lead function	Use anteroposterior pad placement; notify cardiology post-procedure for device interrogation; monitor for loss of pacing or sensing

Step-by-step comparison: synchronized vs unsynchronized

Procedure comparison: synchronized cardioversion vs defibrillation
Step	Synchronized cardioversion	Defibrillation (unsynchronized)
1. Confirm indication	Organized rhythm + pulse + hemodynamic instability or failed therapy	Pulseless arrest: VF, pulseless VT, or polymorphic VT
2. CPR	Not applicable — patient has pulse	Initiate immediately; continue while charging
3. IV access + sedation	Required — sedate before shocking	Not required — patient is unconscious
4. Oxygen removal	Remove delivery device before shock	Remove delivery device before shock
5. Pad placement	Anterolateral or anteroposterior	Anterolateral (standard in arrest)
6. Sync mode	ON — verify sync markers on R waves	OFF — verify unsynchronized mode
7. Energy selection	Rhythm-specific (50–200 J biphasic)	120–200 J biphasic; 360 J monophasic
8. CLEAR protocol	Announce + visual sweep + confirm clear	Announce + visual sweep + confirm clear
9. Shock delivery	Slight delay after button press — device waits for R wave	Immediate shock on button press
10. Immediately after shock	Assess rhythm and pulse	Resume CPR immediately — 2 minutes before rhythm check
11. If no conversion/ROSC	Repeat at higher energy; re-confirm sync mode active	Resume CPR, reassess in 2 min, repeat shock if shockable
12. Post-procedure monitoring	Continuous telemetry, VS, neuro, 12-lead ECG, sedation recovery	Post-ROSC protocol: hemodynamics, 12-lead ECG, targeted temperature management if indicated

NCLEX tips

These 16 tips cover the highest-yield cardioversion and defibrillation concepts tested on NCLEX. Several have appeared in multiple practice question banks with specific wording.

VF → defibrillate, not cardiovert. Synchronized cardioversion requires an R wave to sync to. VF has no organized QRS — the device cannot synchronize. Applying cardioversion to VF delays effective treatment.
Pulseless VT = VF on NCLEX. Treat pulseless VT with unsynchronized defibrillation using the same algorithm as VF. Do not attempt to synchronize pulseless VT.
Polymorphic VT (torsades de pointes) = defibrillate. The rhythm shifts too rapidly for reliable synchronization. Treat as VF — unsynchronized defibrillation.
Stable VT → synchronized cardioversion. Stable VT with a pulse and an organized QRS is treated with synchronized cardioversion (or antiarrhythmics), not defibrillation.
Sedation is mandatory for elective cardioversion. Never shock a conscious patient without sedation. The shock is painful. Midazolam + fentanyl (or propofol under anesthesia) are the standard agents.
Remove oxygen before shocking — not just turn it off. Moving the delivery device away from the patient is required. Oxygen trapped in the mask at the patient’s face creates a fire hazard even with flow discontinued. Physical removal of the device is the correct answer.
Sync markers must appear on R waves before delivering the shock. If sync markers are absent or misaligned, the device will not synchronize correctly. Check lead placement and gain before proceeding.
Sync mode often resets to async after each shock. Before repeating synchronized cardioversion, re-select and verify sync mode. This is tested explicitly on NCLEX and in ACLS scenarios.
CPR continues while the defibrillator is charging. Compressions pause only for the brief shock delivery. This minimizes the no-flow time and is an ACLS core principle.
After defibrillation, resume CPR immediately — do not pause to assess rhythm. Resume compressions right after shock delivery and reassess rhythm after 2 minutes of CPR.
AED says “no shock advised” → continue CPR. The rhythm is PEA or asystole — non-shockable. Do not wait for a shock. Start compressions immediately and continue until ALS personnel arrive.
AF cardioversion requires anticoagulation or TEE first. If AF duration is unknown or >48 hours, anticoagulate for at least 3 weeks OR obtain TEE to exclude LAA thrombus before cardioversion. Cardioverting without this step risks embolic stroke.
Anteroposterior pad placement is preferred for pacemaker patients. Placing pads in the anterolateral position risks current passing through the device. AP placement routes current away from the generator. Minimum 8 cm clearance applies regardless of position.
Dry skin before pad placement. Wet skin at pad sites reduces current delivery and increases arcing risk. This includes sweat, water, and conductive gel from a previous pad site.
Do not place pads over medication patches. Nitroglycerin, nicotine, and other transdermal patches must be removed from pad placement sites. They can cause burns and — with nitrate patches specifically — create a fire hazard.
First action for witnessed VF in a monitored patient: Deliver defibrillation as quickly as possible. Every second of delay in defibrillation reduces survival by approximately 10%. The sequence: confirm VF on monitor → call for help → CPR → defibrillate as soon as device is available.

The cardioversion and defibrillation skill connects to several adjacent nursing competencies:

Cardiac arrhythmias nursing guide — rhythm identification for AF, flutter, SVT, VT, and VF; the prerequisite knowledge for understanding why each rhythm warrants a specific electrical therapy
Atrial fibrillation nursing — the most common indication for synchronized cardioversion; anticoagulation protocols, rate vs rhythm control strategy, CHA₂DS₂-VASc scoring
Rapid response and code blue nursing — the ACLS pulseless arrest algorithm, crash cart medications, post-ROSC care; defibrillation is one step in a larger resuscitation framework
Cardiac monitoring and telemetry nursing — post-cardioversion rhythm monitoring, telemetry strip interpretation, what to watch for after conversion to sinus rhythm
12-lead ECG nursing guide — post-cardioversion 12-lead interpretation; recognizing transient ST changes, assessing for new conduction abnormalities
Pacemaker nursing — pad placement in patients with pacemakers and ICDs, post-shock device interrogation, distinguishing pacemaker spikes on rhythm strips
Safe medication administration nursing — sedation agents used for cardioversion, dosing principles for midazolam and fentanyl, monitoring conscious sedation