From the Guidelines
For a patient with cardiac arrest and no pulse, presenting with tachycardia at 200 beats per minute (bpm) on electrocardiogram (ECG), immediate defibrillation is indicated, not synchronized cardioversion. This situation represents pulseless ventricular tachycardia (VT) or ventricular fibrillation (VF), which requires unsynchronized defibrillation as per ACLS protocols 1. The key distinction is the presence or absence of a pulse - no pulse means defibrillation is needed.
Defibrillation Protocol
Begin with a shock at 200 joules on a biphasic defibrillator (or 360 joules for monophasic), followed immediately by high-quality CPR for 2 minutes. After the initial shock, administer epinephrine 1 mg IV/IO every 3-5 minutes. Consider amiodarone 300 mg IV/IO for the first dose, followed by 150 mg for subsequent doses if the rhythm persists after repeated shocks.
Importance of Prompt Defibrillation
Prompt defibrillation is crucial in cardiac arrest cases, as the chances of successful defibrillation decline substantially with the passage of each minute 1. The amplitude and waveform of VF deteriorate rapidly, reflecting the depletion of high energy phosphate stores.
High-Quality CPR
High-quality CPR is fundamental to the management of all cardiac arrest rhythms, with an emphasis on minimizing pauses in CPR and optimizing chest compression rate and depth 1. The provider performing chest compressions should deliver at least 100 compressions per minute continuously without pauses for ventilation, and the provider delivering ventilations should give 1 breath every 6 to 8 seconds (8 to 10 breaths per minute).
Synchronized Cardioversion
Synchronized cardioversion is reserved for patients with a pulse who have tachyarrhythmias causing hemodynamic instability, and is not indicated in this scenario where the patient has no pulse 1. Defibrillation works by depolarizing the entire myocardium simultaneously, allowing the heart's natural pacemaker to potentially regain control of the electrical activity and restore organized contractions.
From the Research
Appropriate Intervention for Cardiac Arrest with Tachycardia
- The patient is presenting with cardiac arrest and no pulse, and has a rapid heart rate of 200 beats per minute (bpm) on electrocardiogram (ECG).
- According to the studies, defibrillation is the recommended intervention for cardiac arrest due to ventricular tachyarrhythmias 2, 3, 4, 5, 6.
- The American Heart Association recommends immediate defibrillation for patients with pulseless ventricular tachycardia or ventricular fibrillation 2.
- Synchronized cardioversion is not the initial recommended treatment for cardiac arrest with no pulse, as it is typically used for patients with a stable rhythm who are hemodynamically unstable 2.
Defibrillation Waveforms
- Biphasic defibrillation waveforms have been shown to be superior to monophasic waveforms in terminating ventricular fibrillation and ventricular tachycardia 4, 5, 6.
- Biphasic waveforms have been associated with higher success rates for defibrillation and lower energy requirements 4, 5.
- However, the evidence is not conclusive, and further studies are needed to determine the optimal defibrillation waveform for out-of-hospital cardiac arrest 6.
Post-Defibrillation Care
- After defibrillation, chest compressions should be resumed immediately, and rhythm and pulse checks should be deferred until completion of 5 compression:ventilation cycles or minimally for 2 minutes 3.
- The majority of patients remain pulseless for over 2 minutes after defibrillation, and the duration of asystole before return of pulses can be longer than 120 seconds 3.