Cardiac arrest occurs when the heart stops beating effectively, ceasing blood flow to the brain and vital organs. It is identified by the absence of a pulse and patient unresponsiveness. Asystole and Pulseless Electrical Activity (PEA) are two specific rhythms categorized as cardiac arrest. Asystole, or “flatline,” is the complete absence of electrical activity, appearing as a straight line on the electrocardiogram (ECG) monitor. PEA, in contrast, shows organized electrical activity, sometimes resembling a normal heartbeat, but the heart muscle does not contract forcefully enough to generate a pulse or effective blood flow. Both rhythms result in no effective circulation, requiring immediate intervention following the Advanced Cardiac Life Support (ACLS) protocol.
Immediate Recognition and High-Quality CPR
The initial step in managing cardiac arrest is the immediate recognition of unresponsiveness and absent breathing, prompting activation of the emergency response system. Once the lack of a pulse is confirmed, high-quality cardiopulmonary resuscitation (CPR) must be initiated immediately to manually circulate oxygenated blood to the brain and heart. This basic life support action is crucial for survival outcomes.
High-quality CPR requires adherence to specific metrics to maximize its effectiveness. Providers must deliver chest compressions at a rate of 100 to 120 per minute and to a depth of at least 2 to 2.4 inches (5 to 6 centimeters) in adults. Allowing the chest to fully recoil after each compression is important for the heart to adequately refill with blood. Minimizing interruptions is also vital, aiming for compressions to be performed for greater than 80% of the total resuscitation time.
When ventilations are provided, the ratio is typically 30 compressions to two breaths until an advanced airway is secured. This focus on continuous, precise compressions helps maintain a baseline level of coronary perfusion pressure, which is necessary to sustain the heart muscle itself.
Core Protocol: Non-Shockable Rhythms
After the initial two minutes of high-quality CPR, the cardiac rhythm is checked briefly (no more than ten seconds) to minimize the interruption of compressions. The diagnosis of Asystole or PEA places the patient into the “non-shockable” category of the cardiac arrest algorithm.
These rhythms are classified as non-shockable because defibrillation is ineffective and not indicated. Defibrillation is designed to reset a heart in a chaotic electrical state, such as ventricular fibrillation. Since Asystole lacks electrical activity, and PEA’s electrical activity is too weak to be reset into a functional rhythm, an electrical shock offers no benefit.
The treatment protocol centers on continuous high-quality CPR, medication administration, and the concurrent search for underlying causes. Two-minute cycles of CPR are alternated with brief rhythm and pulse checks until the patient achieves a return of spontaneous circulation (ROSC). This cyclical approach ensures that life-sustaining blood flow is maintained while simultaneous advanced interventions are prepared and executed.
Pharmacological Intervention and Airway Stabilization
The cornerstone of pharmacological intervention is the administration of Epinephrine, a potent vasopressor. Epinephrine (1 mg intravenously or intraosseously) is administered as early as possible and repeated every three to five minutes during resuscitation cycles. The primary mechanism of this drug is to activate alpha-adrenergic receptors, causing widespread vasoconstriction in the periphery.
This vasoconstriction elevates systemic vascular resistance, which increases aortic diastolic pressure. This rise improves coronary perfusion pressure (CPP), the pressure gradient that drives blood flow to the heart muscle during the relaxation phase of CPR. Enhancing blood flow to the heart increases the likelihood of restoring a perfusing rhythm and achieving ROSC.
Securing an advanced airway is also a priority to ensure adequate oxygenation and ventilation. Advanced devices, such as an endotracheal tube or a laryngeal mask airway, allow for continuous chest compressions without the need for pauses for ventilation. Once secured, ventilations are delivered at a rate of one breath every six seconds (ten breaths per minute), independent of the compression rate.
Investigating Underlying Causes (H’s and T’s)
A fundamental aspect of treating Asystole and PEA is the concurrent investigation and treatment of reversible causes, summarized by the mnemonics “H’s and T’s.” The rationale is that in PEA especially, the heart may be electrically active but unable to contract due to an external, correctable factor. Identifying and reversing these underlying issues is often the only pathway to achieving a sustainable heart rhythm.
The “H’s” include:
- Hypovolemia (low blood volume)
- Hypoxia (lack of oxygen)
- Hydrogen ion excess (acidosis)
- Hypo/Hyperkalemia (potassium imbalances)
- Hypothermia (low body temperature)
For example, Hypovolemia due to severe blood loss is treated with the rapid infusion of intravenous fluids or blood products while compressions continue. Hypoxia is addressed through effective ventilation via the secured airway.
The “T’s” include:
- Tension pneumothorax
- Tamponade (cardiac)
- Toxins
- Thrombosis (pulmonary or coronary)
A Tension pneumothorax, where air pressure collapses a lung and pushes on the heart, is addressed by immediate needle decompression. Thrombosis, such as a large pulmonary embolism, may prompt the consideration of clot-busting drugs (thrombolytics) to dissolve the blockage. The search for these H’s and T’s is a continuous diagnostic process that runs parallel to high-quality CPR and Epinephrine administration.