Which heart block is defined by a PR interval greater than 0.20 seconds and may be caused by ischemia and digitalis?

A first-degree AV block is characterized by a prolongation of the PR interval to greater than 0.20 seconds on an electrocardiogram (ECG). This condition indicates a delay in the conduction of electrical impulses through the atrioventricular (AV) node, leading to a longer than normal time between atrial depolarization and ventricular depolarization.

In the context of this block, it is important to recognize that it can be caused by various factors, including ischemia (reduced blood flow to the heart muscle) and the effects of certain medications such as digitalis. The presence of a prolonged PR interval without any dropped beats or varying PR intervals is a hallmark of first-degree AV block, making it distinct from other types of AV blocks.

In contrast, the other types of AV blocks each have unique characteristics that differentiate them from first-degree AV block. For example, second-degree AV block Type I (Wenckebach) is characterized by progressive lengthening of the PR interval followed by a dropped beat, while second-degree AV block Type II typically presents with a fixed PR interval but with occasional dropped beats. Third-degree AV block, or complete heart block, indicates a total dissociation between atrial and ventricular activity,