Electrical Therapy: Defibrillation, Cardioversion, and Transcutaneous Pacing

Electrical Therapy in Cardiac Emergencies

Electrical therapy uses controlled electrical current to treat life-threatening cardiac dysrhythmias. As a paramedic, you will use three distinct modalities: defibrillation, synchronized cardioversion, and transcutaneous pacing (TCP). Selecting the right modality—and applying it correctly—is one of the highest-stakes skills in prehospital care.

Defibrillation

Defibrillation delivers a high-energy, unsynchronized shock to the heart. The goal is to simultaneously depolarize a critical mass of myocardial cells, allowing the heart's natural pacemaker to resume organized electrical activity. Defibrillation is indicated for pulseless ventricular fibrillation (VF) and pulseless ventricular tachycardia (pVT)—rhythms that are chaotic and produce no effective cardiac output.

Pad placement: Place one pad on the right upper chest below the clavicle (sternal position) and the second pad on the left lateral chest wall at the mid-axillary line, at or below the level of the pectoral muscle (apex position). This anterior-lateral placement directs current through the largest mass of ventricular muscle. Avoid placing pads over implanted devices or transdermal medication patches; remove patches and wipe the skin.

Energy selection: Follow your medical director's protocols and the manufacturer's guidance for the specific device. Biphasic defibrillators typically use device-specific energy levels; if the effective dose range is unknown, use the maximum available. Monophasic defibrillators use higher energy levels by convention. Always follow local protocol.

Sequence: Power on → select energy → charge → clear the patient → deliver shock → immediately resume CPR.

Safety callout: Before delivering any shock, announce clearly: "I'm going to shock on three. One, I'm clear. Two, you're clear. Three, everybody's clear." Visually confirm no team member is touching the patient, bed, or any conductive surface. Oxygen delivery devices must be moved away from the patient's chest.

Synchronized Cardioversion

Synchronized cardioversion delivers a shock that is timed by the monitor to the R wave of the patient's QRS complex. This prevents the shock from landing on the T wave, which could induce VF—called the R-on-T phenomenon. Cardioversion is used for patients who have a pulse but are hemodynamically unstable due to a tachydysrhythmia: unstable ventricular tachycardia with a pulse, unstable atrial fibrillation, unstable atrial flutter, or unstable supraventricular tachycardia.

Recognizing instability: Signs include altered mental status, severe hypotension, acute chest pain, pulmonary edema, or other signs of shock caused by the dysrhythmia itself—not by other problems.

Procedure:

1. Attach pads and confirm the rhythm on the monitor.

2. Engage SYNC mode; the monitor will display markers (often arrows or dots) on each R wave.

3. Verify the sync markers are falling on the R wave—not the T wave.

4. Select energy (follow protocol; cardioversion typically uses lower energy than defibrillation, but specific joule values vary by rhythm and device).

5. Sedate the conscious patient if time and condition permit per protocol.

6. Charge → perform safety clearance → hold the shock button; the monitor will fire on the next sensed R wave, so there may be a brief delay.

7. Reassess rhythm and pulse immediately.

Critical point: If the patient deteriorates to pulselessness, disable SYNC mode and defibrillate immediately.

Transcutaneous Pacing (TCP)

TCP delivers repetitive low-energy electrical impulses through the chest wall to stimulate ventricular contractions. It is the first-line electrical therapy for symptomatic bradycardia that does not respond to atropine or is likely to deteriorate—such as high-degree AV blocks or sinus arrest with hemodynamic compromise.

Pad placement: Use the same anterior-lateral positions as defibrillation, or anterior-posterior placement per manufacturer guidance.

Procedure:

1. Attach pads; confirm the baseline rhythm.

2. Set the rate (typically 60–80 beats per minute as a starting point; follow protocol).

3. Set output (milliamps, mA) to the lowest setting.

4. Increase output incrementally until you see electrical capture: a wide pacing spike followed by a broad QRS complex after every spike.

5. Confirm mechanical capture by palpating a pulse that corresponds to the paced rate—do not rely on the monitor alone.

6. Once capture is achieved, increase output an additional margin above the capture threshold as directed by protocol to maintain reliable pacing.

7. Reassess the patient's hemodynamic response: blood pressure, mental status, skin signs.

Patient comfort: TCP is painful. Provide analgesia and sedation per protocol for conscious patients.

Documentation: Record the rate, output at capture, presence of electrical and mechanical capture, and patient response on your pacing record.

Overarching Safety Principles

• Clear the patient completely before every shock delivery—electrical therapy can injure rescuers.
• Never deliver a shock in a flammable or oxygen-enriched environment without moving supplemental oxygen away.
• Confirm the correct mode (SYNC vs. unsynchronized) before every energy delivery.
• Dry skin and firm pad contact reduce impedance and improve current delivery.
• Reassess the patient—rhythm and pulse—after every intervention.