Arrhythmias - Asystole: Nursing

Cardiac arrest occurs when the heart suddenly stops pumping blood throughout the body. There are two types of cardiac arrest, asystole or cardiac flatline, and pulseless electrical activity, or PEA for short. Asystole is the most common type and refers to the total absence of electrical and mechanical activity of the heart. On the other hand, PEA occurs when there is electrical activity in the heart, but the cardiac muscle is unresponsive to stimulation; therefore, there’s no mechanical activity of the heart and pulse.

Now, let’s cover some physiology of the cardiac conduction system. The cardiac conduction system is made up of specialized myocardial cells that can create and transport electrical potential, also called an action potential. These cells have many special features, including automaticity, meaning that they can generate an impulse, excitability, which is the ability to respond to a stimulus by creating an electrical impulse, conductivity meaning they can carry the impulse to other cells, and contractility, which is the ability to shorten the length of their fibers, causing a contraction.

Now let’s look at the normal electrical conduction pathway in the heart on an ECG, which shows how the depolarization wave flows through the heart during each heartbeat. The normal electrical activity of the heart starts in the sinoatrial node or SA node, which is considered the pacemaker of the heart. Then, the impulse is conducted through the atrium, creating the P wave on an ECG. And when the atrial muscle cells get depolarized, they contract, pushing blood from the atria into the ventricles. From the atrium, electrical activity goes to the atrioventricular node, or AV node, where the impulse propagation speed slows way down; this is the PR interval on an ECG. This pause allows the atria to contract while the ventricles fill with blood. From the AV node, the depolarization wave goes through the Bundle of His, then the right and left branches of the Bundle, and finally through the Purkinje fibers, which deliver the current to the right and left ventricles, causing them to depolarize. This triggers simultaneous contraction of both ventricles, pushing blood into the systemic and pulmonary circulations, and it’s represented by the QRS complex on an ECG. Finally, the ventricles repolarize to prepare for the next cycle, which allows them to relax and fill with blood, called diastole. And on ECG, ventricular repolarization will create a T wave, while the pause between ventricular depolarization and repolarization is represented by the ST segment. Sometimes, immediately after the T wave, there’s a U wave, which represents late repolarization of the ventricles.

Now, based on the cause, asystole can be classified as primary and secondary. Primary asystole occurs when the problem is at the level of the cardiac conduction system. On the other hand, secondary asystole occurs when some other condition that is not related to the cardiac conduction system, affects the heart’s ability to fire and conduct electrical impulses. Secondary causes can be further subdivided into two main groups: 5 H’s and 5 T’s. 5 Hs include Hypoxia, or low levels of oxygen in peripheral tissues; Hypovolemia, or volume depletion; Hypothermia, or low body temperature; high concentration of Hydrogen ions, or acidosis; and finally, Hypo- or Hyperkalemia. On the flip side, 5 Ts include Toxins, cardiac Tamponade, Tension pneumothorax, pulmonary Thrombosis, and coronary Thrombosis.

Important risk factors associated with asystole include medical history of cardiovascular conditions, ventricular fibrillation or V-fib, and ventricular tachycardia or V-tach. Additionally, clients who are assigned female at birth, and children are more likely to develop asystole.

Now, moving on to pathology. Asystole typically occurs due to an abnormal ventricular rhythm, like V-fib or V-tach, which causes cessation of the electrical activity. As a result, ventricles fail to depolarize, contract, and pump blood throughout the body. When there’s not enough blood circulating through the body, there’s no oxygen for peripheral tissues, so they are left deprived. This can result in severe complications, like permanent brain damage, brain death, or even full body death.

Clinical manifestations of asystole include sudden collapse with loss of consciousness, unresponsiveness, and apnea, meaning cessation of breathing.

Upon physical assessment, the client is usually pulseless with absent heart sounds and no recordable blood pressure.