2.2 VF/pVT Management & Defibrillation Energy Protocols

2.2 VF/pVT Management & Defibrillation Energy Protocols

Ventricular Fibrillation (VF) and pulseless Ventricular Tachycardia (pVT) are the most common initial rhythms in witnessed sudden cardiac arrest. These are shockable rhythms, meaning the primary and most effective intervention is prompt electrical defibrillation. The probability of successful defibrillation and survival to hospital discharge decreases by 7% to 10% for every minute that defibrillation is delayed. Thus, rapid recognition, high-quality CPR, and timely shock delivery are paramount.

Recognition of VF and pVT

The first step in managing a shockable rhythm is accurate identification.

Ventricular Fibrillation (VF): VF is characterized by a disorganized, chaotic electrical activity in the ventricles. The ECG monitor will show irregular undulations of varying amplitudes and contours without identifiable P waves, QRS complexes, or T waves. The ventricles merely quiver, resulting in zero cardiac output and an absent pulse. VF is a life-threatening emergency that requires immediate defibrillation.

Pulseless Ventricular Tachycardia (pVT): Ventricular Tachycardia is an organized, rapid ventricular rhythm. On an ECG, it appears as wide, regular QRS complexes (monomorphic VT) or wide complexes that constantly change in shape and amplitude (polymorphic VT, such as Torsades de Pointes). While some patients with VT may have a pulse and be relatively stable, pVT presents clinically as cardiac arrest. The patient is unresponsive, apneic, and pulseless. From an ACLS algorithm perspective, pVT is treated exactly like VF.

Immediate Shock Delivery and Defibrillation Protocols

Once a shockable rhythm (VF or pVT) is identified, the immediate priority is to deliver a shock. Chest compressions should be continued while the defibrillator is charging to minimize hands-off time.

Biphasic vs. Monophasic Defibrillators

Defibrillators deliver electrical energy to depolarize a critical mass of the myocardium, halting the chaotic activity and allowing the heart's natural pacemakers to re-establish an organized rhythm.

Biphasic Defibrillators: Modern defibrillators use biphasic waveforms, which deliver current in two directions. This technology is more efficient and causes less myocardial damage than older monophasic models.

• Initial Energy Dose: The recommended initial dose for a biphasic defibrillator is typically 120 to 200 Joules (J), depending on the manufacturer's specific guidelines.
• Unknown Manufacturer Dose: If the manufacturer's recommended energy level is unknown, use the maximum available energy dose (often 200 J on many modern devices).
• Subsequent Energy Doses: For subsequent shocks, the energy level should be equivalent to or higher than the previous dose. Escalating energy (e.g., 200 J, then 300 J, then 360 J, depending on the machine's maximum) is often recommended to overcome high transthoracic impedance.

Monophasic Defibrillators: Monophasic defibrillators deliver current in only one direction. Although largely replaced by biphasic machines, they are still used in some settings.

• Energy Dose: The standard dose for a monophasic defibrillator is a single, non-escalating shock of 360 Joules for all attempts.

Clear Safety Calls

Safety is critical during defibrillation. The operator must ensure no one is touching the patient, the bed, or any connected equipment before discharging the shock. The AHA recommends a loud, clear warning sequence, such as:

1. "I am going to shock on three."
2. "One, I'm clear."
3. "Two, you're clear."
4. "Three, everybody's clear." Simultaneously, the operator must visually scan the patient from head to toe to confirm everyone is physically clear before pressing the shock button.

Immediate Post-Shock CPR

One of the most critical conceptual shifts in modern ACLS is the management of the patient immediately after a shock is delivered.

Do Not Check for a Pulse Immediately After a Shock In the past, providers often paused to check the rhythm and pulse immediately after defibrillation. This practice is now strongly discouraged. Even if defibrillation is successful at terminating VF/pVT, the heart often experiences a period of "stunning" where it beats too weakly to produce a palpable pulse or adequate blood pressure.

Resume CPR Immediately The instant the shock is delivered, the compressor must resume high-quality chest compressions, starting with the compression phase. CPR should continue uninterrupted for 2 minutes (or 5 cycles of 30:2). This immediate resumption of CPR provides necessary perfusion to the stunned myocardium, increasing the likelihood that a perfusing rhythm will eventually be established.

Rhythm Check at 2 Minutes

After 2 minutes of continuous CPR, the team should pause compressions to perform a rhythm check. This pause should ideally last less than 10 seconds.

• If the rhythm remains shockable (VF/pVT), the team will charge the defibrillator, deliver another shock, and immediately resume CPR.
• If the rhythm is non-shockable and organized, a pulse check is performed. If a pulse is present, the team transitions to Post-Cardiac Arrest Care. If no pulse is present, the team transitions to the Asystole/PEA pathway.

By adhering strictly to these protocols—rapid recognition, appropriate energy selection, safe shock delivery, and immediate post-shock CPR—providers can maximize the efficacy of defibrillation and improve the chances of survival for patients in VF or pVT.