Paramedic National Registry Practice

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What does the vertical axis on an ECG represent?

Heart rate
Voltage
Time
Amplitude

The correct answer is: Voltage

The vertical axis on an ECG (electrocardiogram) represents voltage. This axis is crucial for understanding the electrical activity of the heart, as it displays the amplitude of the electrical signals generated by cardiac depolarization and repolarization. Each small square on the vertical axis typically represents 0.1 millivolts (mV), which allows healthcare providers to assess the strength of the cardiac electrical impulses. While heart rate is essential for evaluating cardiac function, it is primarily inferred from the horizontal axis, which measures time. Time is represented in milliseconds and is critical for timing the phases of the cardiac cycle, such as the intervals and segments. Amplitude, while closely related to voltage, is a broader term that may not specifically describe the vertical axis of the ECG in the same way voltage does. Thus, understanding that the vertical axis correlates directly to voltage helps in interpreting the characteristics of the heart's electrical activity accurately.