Defibrillation, Cardioversion, and Pacing Practice Questions

30 multiple-choice questions on Defibrillation, cardioversion, and pacing for paramedic and EMT students, from Chapter 18 (Cardiovascular Emergencies). Read each question, pick your answer, then tap Show answer to check it and read the explanation.

30 practice questions

1. You are using a biphasic manual defibrillator on an adult in VF, and you do not know the manufacturer's recommended energy. What energy should you select?

   1. A. The maximum available
   2. B. The minimum available
   3. C. 50 J for the first shock
   4. D. 100 J then escalate
   Show answer

   Answer: A. The maximum available

   When the manufacturer's recommendation (typically 120 to 200 J) is unknown, AHA advises using the maximum available energy for biphasic defibrillation.

2. What energy is used for adult defibrillation with a monophasic defibrillator?

   1. A. 200 J
   2. B. 120 J
   3. C. 300 J
   4. D. 360 J
   Show answer

   Answer: D. 360 J

   Monophasic defibrillators deliver 360 J for all adult shocks. Biphasic devices use lower energies, typically 120 to 200 J per the manufacturer.

3. Immediately after delivering a shock for VF, what should the team do?

   1. A. Check the carotid pulse for 10 seconds
   2. B. Resume compressions without a pulse check
   3. C. Analyze the rhythm again before CPR
   4. D. Give two breaths and then check a pulse
   Show answer

   Answer: B. Resume compressions without a pulse check

   CPR should resume immediately after a shock for 2 minutes before the next rhythm check. Even when a shock succeeds, the heart rarely pumps effectively right away.

4. Why should the defibrillator be charged while compressions are still in progress?

   1. A. To increase the delivered energy
   2. B. To shorten the pre-shock pause
   3. C. To improve pad-to-skin contact
   4. D. To synchronize with the R wave
   Show answer

   Answer: B. To shorten the pre-shock pause

   Charging during compressions and pausing only for the rhythm check and shock minimizes the pre-shock pause, which is linked to better shock success.

5. Which pad placement is acceptable for adult defibrillation?

   1. A. Both pads on the left anterior chest
   2. B. Both pads on the upper back
   3. C. One pad on each upper arm
   4. D. Anterolateral or anteroposterior
   Show answer

   Answer: D. Anterolateral or anteroposterior

   AHA accepts anterolateral (right infraclavicular and left lateral chest) and anteroposterior placements. Pads must be separated so current crosses the heart.

6. You arrive to find a man in VF lying in a puddle of rainwater. Before defibrillating you should:

   1. A. Move him to a dry area and dry his chest
   2. B. Defibrillate immediately where he is lying
   3. C. Lower the energy to reduce current spread
   4. D. Place the pads on his back instead
   Show answer

   Answer: A. Move him to a dry area and dry his chest

   Water can conduct current across the skin and toward rescuers. Move the patient out of standing water and quickly dry the chest before applying pads; snow or ice is generally acceptable.

7. You press SYNC before cardioverting a patient, and the sync markers land on his tall, peaked T waves instead of the R waves. What should you do?

   1. A. Shock anyway, since having a marker on each beat is enough
   2. B. Turn sync off and use an unsynchronized shock
   3. C. Change leads or gain until markers sit on the R waves
   4. D. Double the energy to make up for the poor timing
   Show answer

   Answer: C. Change leads or gain until markers sit on the R waves

   A shock timed to the T wave can trigger VF, so before cardioverting choose a lead or ECG size where the R wave is tallest and confirm that every marker falls on the QRS. Shocking with markers on the T waves is dangerous, unsynchronized shocks are for pulseless or polymorphic rhythms, and more energy does not fix the timing.

8. Synchronized cardioversion differs from defibrillation because the shock is:

   1. A. Always lower than 25 J
   2. B. Given without any monitor
   3. C. Delivered only on a T wave
   4. D. Timed to the R wave
   Show answer

   Answer: D. Timed to the R wave

   Synchronization times the shock to the QRS complex so it avoids the relative refractory period on the T wave, where a shock could trigger VF.

9. During interfacility transport, a patient with a temporary transvenous pacemaker loses capture after being moved to the stretcher, and his rate drops to 30. What should you do?

   1. A. Turn the transvenous pacer off briefly so it resets itself
   2. B. Raise the pacer output and prepare to pace externally
   3. C. Pull back the pacing wire until capture returns
   4. D. Give adenosine to restore the paced rhythm quickly
   Show answer

   Answer: B. Raise the pacer output and prepare to pace externally

   Movement can displace a transvenous lead, causing loss of capture; increase the output per the sending team's instructions, check connections, and be ready to apply transcutaneous pacing or start a chronotropic drug. Turning the pacer off removes support, repositioning the lead is a physician procedure, and adenosine slows the heart further.

10. You have decided to cardiovert a 70-year-old whose new atrial fibrillation is causing chest pain and a BP of 76/44. Using a biphasic monitor, what first synchronized energy does the 2025 AHA cardioversion algorithm suggest for AF?

    1. A. 50 J
    2. B. 200 J
    3. C. 100 J
    4. D. 2 J/kg
    Show answer

    Answer: B. 200 J

    The 2025 AHA electrical cardioversion algorithm lists 200 J synchronized as the initial biphasic energy for atrial fibrillation (also listed for flutter), while 100 J is suggested for narrow regular rhythms and monomorphic VT; use the device's own recommendations where they differ. 50 J is too low for AF in adults, and 2 J/kg is a pediatric defibrillation dose.

11. A patient with monomorphic VT and a pulse becomes hypotensive and diaphoretic. What is the typical initial synchronized energy?

    1. A. 50 J
    2. B. 360 J
    3. C. 100 J
    4. D. 1 J/kg
    Show answer

    Answer: C. 100 J

    Unstable monomorphic VT with a pulse is typically cardioverted starting at 100 J synchronized, with stepwise increases if unsuccessful. 50 J is too low for VT, 1 J/kg is a pediatric dose, and 360 J is a defibrillation-level energy rather than the starting cardioversion energy.

12. A patient with pneumonia has sinus tachycardia at 128/min, a BP of 82/50 and confusion. Why is synchronized cardioversion not the answer?

    1. A. Cardioversion works mainly on rates above 200/min
    2. B. A rate under 150 rarely causes instability itself
    3. C. Sinus rhythms convert well to slower sinus rhythms
    4. D. He needs two doses of adenosine before a shock
    Show answer

    Answer: B. A rate under 150 rarely causes instability itself

    AHA guidance notes that heart rates below about 150/min seldom cause instability in a patient without severe heart disease; here the tachycardia is a response to sepsis, and cardioverting sinus tachycardia does nothing. Treat the underlying cause. Cardioversion is not reserved for rates above 200, sinus rhythm does not 'convert', and adenosine is not a step before treating sepsis.

13. After a synchronized cardioversion attempt fails, you plan to shock again. On many monitors, what must you check?

    1. A. That the pads have been replaced
    2. B. That the energy is lowered
    3. C. That sync mode is turned back on
    4. D. That the device is in AED mode
    Show answer

    Answer: C. That sync mode is turned back on

    Many defibrillators default back to unsynchronized mode after each shock. Re-engage sync and confirm markers on each R wave before the next shock. The energy is usually escalated rather than lowered, AED mode cannot deliver a synchronized shock, and the pads do not need replacing.

14. A conscious patient with unstable SVT is about to be cardioverted. Time and BP allow. What should be considered first?

    1. A. A 1 L normal saline bolus
    2. B. Placing a nasogastric tube
    3. C. Procedural sedation per protocol
    4. D. Atropine to prevent bradycardia
    Show answer

    Answer: C. Procedural sedation per protocol

    Cardioversion is painful, so sedation (and analgesia) should be given to a conscious patient when it will not dangerously delay treatment.

15. While preparing to defibrillate, you notice that the two pads are touching each other on a small patient's chest. Why must you reposition them?

    1. A. Current can arc across the skin and miss the heart
    2. B. The shock will be delivered at twice the set energy
    3. C. The device will switch to a synchronized shock
    4. D. The pads will measure the heart rate incorrectly
    Show answer

    Answer: A. Current can arc across the skin and miss the heart

    When pads touch or are too close, current can travel across the skin between them (arcing) instead of through the heart, reducing the chance of success and causing burns; use anterior-posterior placement on small patients. Touching pads do not double the energy, do not switch the device into sync mode, and the problem is current pathway, not rate counting.

16. Your first synchronized shock for unstable monomorphic VT with a pulse does not convert the rhythm. The patient is still hypotensive and confused. What is the next step?

    1. A. Switch to adenosine 6 mg before more shocks
    2. B. Shock again in sync mode at a higher energy
    3. C. Wait 10 minutes before shocking him again
    4. D. Begin transcutaneous pacing at 80 per minute
    Show answer

    Answer: B. Shock again in sync mode at a higher energy

    If the first synchronized shock fails, the 2025 AHA cardioversion algorithm advises escalating the energy for later attempts while checking pad contact and sync markers, and an antiarrhythmic such as amiodarone may be added. Adenosine is not effective for most VT and should not delay shocks, waiting leaves him unstable, and pacing is for slow rhythms.

17. You press the shock button to cardiovert an unstable patient in sync mode, but the device does not fire immediately. What is the correct action?

    1. A. Keep pressing until it fires on the next R wave
    2. B. Release it and switch off sync mode at once
    3. C. Press it repeatedly until a shock finally occurs
    4. D. Lift the pads off, then charge the device again
    Show answer

    Answer: A. Keep pressing until it fires on the next R wave

    In synchronized mode, the device waits to deliver the shock on the next detected R wave, so there may be a brief delay; keep the button pressed and everyone clear until it discharges. Releasing or turning off sync abandons the synchronized shock, pressing repeatedly is not how the device works, and lifting the pads off or recharging wastes time.

18. You set a transcutaneous pacer to demand mode, but the ECG cables are not connected, only the pacing pads. What is the concern?

    1. A. The pacer cannot sense the patient's own beats
    2. B. The pacer will deliver defibrillation shocks
    3. C. The pads will stop delivering their pacing current
    4. D. The pacer will fire timed to each T wave beat
    Show answer

    Answer: A. The pacer cannot sense the patient's own beats

    Many monitors need the ECG electrodes to sense intrinsic beats in demand mode; without them the pacer cannot sense and may pace asynchronously or refuse to pace, so apply both the ECG leads and the pacing pads. The pacer does not switch to defibrillation, the pads still deliver current, and it does not purposely fire on the T wave.

19. You are pacing a large patient with complete heart block. Even at the device's maximum output, there is no electrical capture. What is the best next step?

    1. A. Reposition the pads, such as anterior-posterior
    2. B. Raise the pacing rate to 120 per minute
    3. C. Switch the pacer from demand mode to fixed mode
    4. D. Lower the pacing rate to 40 per minute instead
    Show answer

    Answer: A. Reposition the pads, such as anterior-posterior

    Failure to capture at high output can be due to pad position, poor contact, a large chest wall or metabolic causes; repositioning to anterior-posterior placement, checking contact, and starting an epinephrine or dopamine infusion while correcting causes such as hyperkalemia are reasonable steps. Changing the rate up or down or switching to fixed mode does not lower the capture threshold.

20. A patient with a pacemaker was cardioverted for AF with pads placed away from the device. What should you tell the receiving hospital?

    1. A. The pacemaker will need to be removed in surgery
    2. B. No follow-up is needed after an external shock
    3. C. The device should be checked (interrogated) soon
    4. D. A magnet should be taped over it until arrival
    Show answer

    Answer: C. The device should be checked (interrogated) soon

    External shocks can rarely reset or damage a pacemaker or ICD, or raise its pacing threshold, so the device should be interrogated after cardioversion or defibrillation and the rhythm monitored closely. Surgical removal is not routine, follow-up is advised, and a magnet changes the device's function and should not be left on without medical direction.

21. A man rescued from cold water has a core temperature of 29 C (84 F), a heart rate of 36 with a pulse, and a BP of 90/56. What is the best approach to the bradycardia?

    1. A. Begin transcutaneous pacing right away
    2. B. Give atropine 1 mg, repeated up to 3 mg
    3. C. Start an epinephrine infusion first, then pace
    4. D. Rewarm him; pacing is not usually needed
    Show answer

    Answer: D. Rewarm him; pacing is not usually needed

    Bradycardia in moderate hypothermia reflects slowed metabolism and usually matches the body's reduced needs; it improves with rewarming, and pacing or drugs are rarely helpful and may provoke VF in the cold heart. Handle him gently, keep him horizontal and rewarm him. Pacing, repeated atropine and an epinephrine infusion followed by pacing are not first-line here.

22. You start transcutaneous pacing at a rate of 70/min. How do you set the current?

    1. A. Start at the highest mA available and leave it
    2. B. Increase mA until capture, then set slightly above
    3. C. Set 20 mA and leave it there
    4. D. Raise the mA until the chest muscles twitch, then stop
    Show answer

    Answer: B. Increase mA until capture, then set slightly above

    Current is increased from a low setting until consistent electrical capture is seen, then set slightly above that threshold. Pacing output is measured in milliamps, not joules. Muscle twitching appears before electrical capture and does not confirm it, a fixed low setting often fails to capture, and starting at maximum and leaving it there causes needless pain.

23. Your monitor can be used in AED mode or manual mode. For a trained paramedic during a VF arrest, what is the main advantage of manual mode?

    1. A. Higher shock energies are delivered automatically to him
    2. B. The device keeps analyzing during compressions
    3. C. It removes the need for 2-minute rhythm checks
    4. D. Shorter pauses, since you read the rhythm yourself
    Show answer

    Answer: D. Shorter pauses, since you read the rhythm yourself

    In manual mode a trained provider can recognize VF and shock quickly without waiting for automated analysis, which can shorten pre-shock pauses. It does not automatically deliver higher energies, it does not analyze during compressions, and rhythm checks are still required every 2 minutes.

24. How should mechanical capture be confirmed during transcutaneous pacing?

    1. A. Palpate a carotid pulse
    2. B. Palpate a femoral pulse
    3. C. Watch for muscle twitching
    4. D. Look for spikes on the ECG
    Show answer

    Answer: B. Palpate a femoral pulse

    Pacing makes the chest and neck muscles contract, which can be mistaken for a carotid pulse. A femoral pulse or improving BP and perfusion confirms mechanical capture.

25. You start transcutaneous pacing for a confused, hypotensive patient in complete heart block at 30/min. What initial pacing rate is typical before adjusting to his response?

    1. A. About 30 to 40 per minute
    2. B. About 100 to 120 per minute
    3. C. About 150 per minute or above
    4. D. About 60 to 80 per minute
    Show answer

    Answer: D. About 60 to 80 per minute

    Transcutaneous pacing is usually started at about 60 to 80 per minute, then the rate is adjusted to the patient's perfusion and BP while the output is set just above the capture threshold. A rate of 30 to 40 does not improve on his own rhythm, and rates of 100 or more raise oxygen demand without benefit.

26. At the start of your shift, you find that the defibrillation pads in the kit are past their expiration date. Why should they be replaced?

    1. A. Expired pads deliver twice the selected energy
    2. B. Dried gel raises resistance and reduces current
    3. C. Expired pads switch the device into sync mode
    4. D. Expired pads are acceptable for children instead
    Show answer

    Answer: B. Dried gel raises resistance and reduces current

    Pad gel dries out over time, raising resistance between the skin and pad, which can reduce the current reaching the heart and increase burns; replace expired pads during equipment checks. Expired pads do not double the energy, do not change the device mode, and are not acceptable for children instead.

27. Most transcutaneous pacers are used in demand mode. What does demand mode mean?

    1. A. The pacer fires at a fixed rate regardless of the native beats
    2. B. The pacer fires only when the operator presses the pace button
    3. C. It paces only when the native rate drops below the set rate
    4. D. The pacer adjusts its current based on the patient's demand
    Show answer

    Answer: C. It paces only when the native rate drops below the set rate

    In demand (synchronous) mode the pacer senses intrinsic beats and paces only when the rate drops below the set rate, reducing the risk of firing on a T wave.

28. Why is stacked shocking (three shocks in a row) no longer recommended for VF?

    1. A. It lowers first-shock success
    2. B. It needs a monophasic device
    3. C. It delays compressions
    4. D. It causes pad burns
    Show answer

    Answer: C. It delays compressions

    Biphasic first-shock success is high, and long pauses for repeated shocks reduce coronary perfusion. AHA recommends one shock followed by 2 minutes of CPR. Stacking does not lower first-shock success or depend on a monophasic device, and it does not cause pad burns; the issue is lost compression time.

29. Your crew has an AED on a patient being moved by stretcher. What should you do when the AED is analyzing?

    1. A. Keep moving so that compressions are not delayed
    2. B. Continue compressions during the analysis phase
    3. C. Stop all movement and avoid touching the patient
    4. D. Disconnect the pads until the stretcher stops
    Show answer

    Answer: C. Stop all movement and avoid touching the patient

    Motion and contact create artifact that can cause an AED to misread the rhythm. Pause movement and compressions during analysis.

30. A patient in pulseless VT has a large amount of chest hair, and the pads are not sticking. What is the best action?

    1. A. Increase the energy to overcome the poor contact
    2. B. Shave or rip off the hair with a spare pad
    3. C. Place the pads on the abdomen below the ribs
    4. D. Hold the pads on with a gloved hand during shock
    Show answer

    Answer: B. Shave or rip off the hair with a spare pad

    Poor contact raises impedance and can cause arcing and burns. Rapidly shave the area or rip off hair with a spare pad and apply new pads.