Explain what each of the following terms represents on an electrocardiogram (ECG).
a. P wave
b. QRS complex
c. T wave
d. P-R interval
e. S-T segment

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1. The P wave on an electrocardiogram (ECG) represents atrial depolarization, which is the electrical activity that triggers the contraction of the atria. This occurs as the sinoatrial (SA) node sends an electrical impulse through the atria.
2. The QRS complex represents ventricular depolarization, which is the electrical activity that triggers the contraction of the ventricles. It is a rapid and large deflection due to the greater muscle mass of the ventricles compared to the atria.
3. The T wave represents ventricular repolarization, which is the process of the ventricles recovering electrically after contraction. This allows the ventricles to prepare for the next cycle of depolarization and contraction.
4. The P-R interval is the time from the beginning of the P wave to the start of the QRS complex. It represents the period during which the electrical impulse travels from the atria to the ventricles via the atrioventricular (AV) node, bundle of His, and Purkinje fibers.
5. The S-T segment is the flat portion of the ECG between the end of the QRS complex and the beginning of the T wave. It represents the period when the ventricles are fully depolarized and contracting, before they begin repolarization.

Key Concepts

P Wave

The P wave on an electrocardiogram (ECG) represents atrial depolarization, which is the electrical activity that triggers the contraction of the atria. It is the first deflection in the ECG tracing and indicates the beginning of the cardiac cycle, reflecting the heart's preparation for pumping blood into the ventricles.

QRS Complex

The QRS complex signifies ventricular depolarization, which is the rapid electrical activation of the ventricles leading to their contraction. This complex is typically the most prominent feature on an ECG, consisting of three distinct waves (Q, R, and S) and is crucial for assessing the heart's rhythm and function.

T Wave

The T wave represents ventricular repolarization, the process by which the ventricles recover and prepare for the next heartbeat. It follows the QRS complex and is essential for understanding the heart's electrical recovery phase, indicating the heart's readiness for the next cycle of contraction.