Question

A long PRI (greater than 0.20 second) indicates the impulse was delayed as it passed through the atria, AV node, or AV bundle. Disturbances of AV conduction can result in prolongation of the PRI. Conditions causing such disturbances may be inflammatory, circulatory, nervous, endocrine, or pharmacological in origin. The P wave associated with a prolonged P-R interval may be normal or abnormal.

Answer 1

AV blocks, depicted in different degrees, indicate various types of delays and failures in the electrical conduction through the heart, seen as prolongations or dissociations in the PR interval on an ECG. These blocks have several possible causes, including inflammatory and pharmacological factors.

Step-by-step explanation:

A long PR interval (PRI) indicates a delay in the electrical impulse as it passes through the atria or AV conduction system. AV blocks are categorized into degrees with a first-degree AV block showing a prolonged PR interval on the ECG. In a second-degree AV block, not all P waves are followed by a QRS complex, indicating some impulses do not proceed past the AV node. A third-degree or complete AV block demonstrates no correlation between P waves and QRS complexes on an ECG. Conditions affecting AV conduction can be inflammatory, circulatory, nervous, endocrine, or pharmacological, leading to such blocks.

ECG Interpretation and AV Blocks

Common AV blocks include AV nodal and infra-Hisian blocks. The PR interval measures the time from the beginning of atrial depolarization to the beginning of ventricular depolarization and represents the conduction time, which can be delayed in these blocks. The AV node can still maintain heart function even when the SA node is blocked, acting as a pacemaker with a rate adequate to maintain consciousness.