Question

In a lead II ECG tracing, what does a fixed PR interval of 0.24 seconds signify regarding the conduction of an electrical impulse through the AV node?

Accepted Answer

In a lead II ECG tracing, a fixed PR interval of 0.24 seconds signifies first-degree atrioventricular (AV) block. The PR interval represents the time it takes for an electrical impulse to travel from the beginning of atrial depolarization, which is the electrical signal that triggers the upper heart chambers to contract, through the AV node, which is the specialized tissue that delays the impulse before it reaches the lower heart chambers. A normal PR interval ranges from 0.12 to 0.20 seconds. A measurement of 0.24 seconds indicates that the conduction of the impulse through the AV node is pathologically delayed. Because the PR interval is fixed, meaning it remains the same duration for every cardiac cycle, it indicates that the delay is constant and the impulse still successfully reaches the ventricles every time. Therefore, this specific measurement confirms that every atrial impulse is conducted to the ventricles but takes longer than the standard physiological duration to do so due to impaired electrical transmission within the AV node.

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In a lead II ECG tracing, what does a fixed PR interval of 0.24 seconds signify regarding the conduction of an electrical impulse through the AV node?