An electrocardiogram (ECG) records the electrical signals generated by the heart, providing a visual representation of its rhythm and function, typically displayed as P-QRS-T complexes. Cardiopulmonary Resuscitation (CPR) is a manual technique involving rhythmic chest compressions used to circulate blood when the heart stops. When electrical monitoring and forceful mechanical intervention occur simultaneously, the sensitive ECG equipment records the heart’s underlying electrical activity alongside the physical disturbance caused by CPR. The resulting tracing is a complex mix of the true heart rhythm and confusing electrical noise known as artifact.
The Electrical Landscape of Cardiac Arrest
Before compressions begin, the ECG displays the underlying electrical problem causing cardiac arrest. These non-perfusing rhythms fall into three categories, each requiring a different treatment approach. Ventricular Fibrillation (VF) is a chaotic, disorganized electrical storm where the ventricles quiver instead of contracting effectively. On the ECG, VF appears as an erratic, wavy line with no recognizable complexes.
Pulseless Electrical Activity (PEA) shows an organized rhythm on the monitor, but the patient lacks a pulse because the electrical activity is disconnected from the heart’s mechanical pumping action. Asystole, or a “flat line,” represents a complete cessation of electrical activity, showing the absence of any discernible P, QRS, or T waves.
The Visual Impact of Chest Compressions
The moment chest compressions begin, the ECG tracing changes drastically due to a phenomenon called CPR compression artifact. This artifact is a form of electrical interference created by the mechanical force applied to the patient’s chest. The physical act of pressing down on the chest wall and releasing pressure causes significant movement of the torso, which in turn displaces the ECG electrodes attached to the skin. This mechanical movement generates a chaotic, high-frequency signal that is picked up by the sensitive monitoring equipment.
The artifact often appears as a regular, jagged, or wavy line that is superimposed over the patient’s true heart rhythm. Since compressions are performed at a rate of 100 to 120 times per minute, the artifact frequently presents as an almost periodic waveform corresponding to the frequency of the compressions. The appearance of this artifact is highly variable, changing with the quality and consistency of the compressions or changes in the patient’s position. In some cases, the mechanical artifact can closely resemble a true, shockable heart rhythm like Ventricular Fibrillation. This visual similarity can pose a significant problem for automated external defibrillators (AEDs) or medical professionals, as the artifact can mask or mimic the life-threatening rhythm.
Differentiating Artifact from True Heart Rhythm
Distinguishing the CPR artifact from the heart’s underlying electrical activity is a practical challenge in resuscitation, as delivering a defibrillating shock while compressions are ongoing is ineffective and unnecessary if the rhythm is non-shockable. Medical guidelines emphasize the importance of minimizing interruptions in chest compressions to maintain blood flow to the brain and heart. However, a brief pause is necessary to accurately assess the true rhythm and determine the next step.
This necessary assessment is known as the “rhythm check” or “pulse check pause,” and it is performed every two minutes during resuscitation. During this short interval, chest compressions are intentionally stopped, and the monitor is observed for no more than ten seconds. When the mechanical motion ceases, the CPR artifact immediately disappears from the screen, revealing the patient’s underlying electrical rhythm, such as VF, PEA, or Asystole.
If the rhythm check reveals a shockable rhythm, the team can prepare the defibrillator. If the rhythm is non-shockable, the focus remains on continuing high-quality compressions and administering medications. Recognizing the chaotic, rhythmic electrical noise as merely an artifact of the manual intervention ensures that appropriate, life-saving measures are delivered based on the actual state of the patient’s heart.