What is a second-degree AV block?

What is a second-degree AV block?

• A. Failure of some atrial action potentials to reach the ventricles.
• B. Complete failure of all action potentials to reach the ventricles.
• C. Prolonged PR interval with every beat.
• D. Normal conduction with occasional extra beats.

Answer: (A)

Second-degree AV block happens when conduction from the atria to the ventricles is intermittently blocked, so some atrial depolarizations (P waves) do not conduct to the ventricles and a QRS complex is skipped. This results in dropped beats on the ECG. It differs from a complete AV block, where no atrial impulses reach the ventricles at all; from a first-degree block, where every beat is conducted but the PR interval is prolonged; and from arrhythmias with extra beats, which are not about intermittent AV conduction. So the description “failure of some atrial action potentials to reach the ventricles” best fits second-degree AV block.

Second-degree AV block happens when conduction from the atria to the ventricles is intermittently blocked, so some atrial depolarizations (P waves) do not conduct to the ventricles and a QRS complex is skipped. This results in dropped beats on the ECG. It differs from a complete AV block, where no atrial impulses reach the ventricles at all; from a first-degree block, where every beat is conducted but the PR interval is prolonged; and from arrhythmias with extra beats, which are not about intermittent AV conduction. So the description “failure of some atrial action potentials to reach the ventricles” best fits second-degree AV block.