An electrocardiogram (ECG) records the heart’s electrical activity, visualizing its rhythm and function. It helps medical professionals understand how electrical signals move through the heart with each beat. During medical emergencies, especially during cardiopulmonary resuscitation (CPR), interpreting the ECG tracing becomes complex. This article explores how CPR influences the ECG, creating signals that can be mistaken for the heart’s electrical activity.
The Basics of ECG Monitoring
An ECG measures electrical changes on the skin’s surface from the heart muscle’s depolarization and repolarization. This generates a tracing that reveals the heart’s rate and rhythm.
A typical ECG tracing features distinct waves: the P wave, QRS complex, and T wave. The P wave signifies the electrical impulse spreading across the atria, causing them to contract. The QRS complex represents electrical activity spreading through the ventricles, leading to their contraction. Finally, the T wave indicates the ventricles relaxing as their electrical activity returns to a resting state.
How CPR Affects Electrical Signals
Cardiopulmonary resuscitation involves rhythmic chest compressions and ventilations to circulate blood and oxygen when the heart has stopped. These movements create physical disturbance that impacts ECG electrodes and the signals they detect. The mechanical force of compressions, patient movement during resuscitation, and even the use of a ventilator introduce electrical interference. This interference, known as artifact, appears on the ECG tracing as electrical activity not originating from the heart.
Identifying CPR Artifacts on the ECG
CPR artifacts present distinct visual characteristics on an ECG tracing, making it challenging to interpret the underlying heart rhythm. Chest compressions typically produce large, rhythmic deflections that coincide with each compression. These can appear as wide, irregular waves resembling organized electrical activity, despite being mechanical interference. Ventilation can introduce smaller, less regular movements, causing the ECG baseline to wander or fluctuate. These repetitive patterns, often occurring at the rate of compressions (around 100-120 per minute), should be recognized as external noise rather than actual cardiac electrical signals.
Interpreting the ECG During Resuscitation
Understanding CPR artifacts is important for medical professionals to avoid misinterpreting the patient’s cardiac rhythm. Artifacts can make it difficult to differentiate between underlying rhythms, such as pulseless electrical activity (PEA) or ventricular fibrillation, and the mechanical interference of CPR. Current guidelines often recommend brief pauses in chest compressions at regular intervals, typically every two minutes, to allow for accurate rhythm analysis and pulse checks. These short pauses, ideally lasting no more than 10 seconds, provide a clearer view of the ECG tracing, enabling clinicians to make informed decisions about interventions like defibrillation or medication administration. The ECG’s visual appearance during ongoing CPR can be misleading, underscoring the need for careful interpretation and strategic interruptions.