What is a first-degree AV block?

What is a first-degree AV block?

• A. PR prolongation with slow conduction between atria and ventricles.
• B. PR shortening with fast conduction between atria and ventricles.
• C. Complete absence of atrial activity.
• D. Intermittent drop of QRS complexes.

Answer: (A)

First-degree AV block is a consistent slowing of the electrical signal from the atria to the ventricles, shown as a longer PR interval on the ECG. Every atrial impulse still reaches the ventricles, so there is a P wave followed by a QRS, just with a delayed arrival. This prolonged PR interval with intact 1:1 conduction is exactly what the description captures. The other phrases describe different situations: PR shortening means faster conduction, not a block; absence of atrial activity would remove P waves altogether; intermittent drops of QRS indicate a higher-degree AV block where some impulses don’t get through. First-degree block is usually benign and can arise from factors like increased vagal tone or certain medications.

First-degree AV block is a consistent slowing of the electrical signal from the atria to the ventricles, shown as a longer PR interval on the ECG. Every atrial impulse still reaches the ventricles, so there is a P wave followed by a QRS, just with a delayed arrival. This prolonged PR interval with intact 1:1 conduction is exactly what the description captures. The other phrases describe different situations: PR shortening means faster conduction, not a block; absence of atrial activity would remove P waves altogether; intermittent drops of QRS indicate a higher-degree AV block where some impulses don’t get through. First-degree block is usually benign and can arise from factors like increased vagal tone or certain medications.