In a third-degree AV block, how do the atrial and ventricular rates behave?

In a third-degree AV block, how do the atrial and ventricular rates behave?

• A. Atria and ventricles beat in sync
• B. Atrial rate is less than ventricular rate
• C. Atrial rate is greater than ventricular rate
• D. Atrial and ventricular rates are equal

Answer: (C)

In a third-degree AV block, also known as complete heart block, there is a complete dissociation between the atria and the ventricles. This means that impulses originating in the atria do not travel down to the ventricles. As a result, the atria and the ventricles are driven by their respective pacemakers. The atrial rate is typically dictated by the natural pacemaker of the atria, which is usually faster than the rate of the ventricular pacemaker, which is often located in the lower part of the heart, such as the Bundle of His or Purkinje fibers. In this condition, the atrial rate is generally greater than the ventricular rate due to the fact that the atria are still firing spontaneously, but the ventricles are not responding to those signals appropriately. This leads to a scenario where the atrial activity continues while the ventricular activity is slower and independent, thereby resulting in a higher atrial rate compared to the ventricular rate. This dissociation is a hallmark of third-degree AV block and is critical for correct interpretation of an ECG.

In a third-degree AV block, also known as complete heart block, there is a complete dissociation between the atria and the ventricles. This means that impulses originating in the atria do not travel down to the ventricles. As a result, the atria and the ventricles are driven by their respective pacemakers. The atrial rate is typically dictated by the natural pacemaker of the atria, which is usually faster than the rate of the ventricular pacemaker, which is often located in the lower part of the heart, such as the Bundle of His or Purkinje fibers.

In this condition, the atrial rate is generally greater than the ventricular rate due to the fact that the atria are still firing spontaneously, but the ventricles are not responding to those signals appropriately. This leads to a scenario where the atrial activity continues while the ventricular activity is slower and independent, thereby resulting in a higher atrial rate compared to the ventricular rate. This dissociation is a hallmark of third-degree AV block and is critical for correct interpretation of an ECG.