What type of heart block is characterized by a progressive lengthening of the PR interval until a beat is dropped?

The type of heart block characterized by a progressive lengthening of the PR interval until a beat is dropped is known as Second-degree heart block, Type I, also referred to as Mobitz Type I or Wenckebach phenomenon. In this condition, each successive atrial impulse is progressively delayed in transmission through the AV node, reflected by an increasing PR interval. This continues until the atrial impulse fails to conduct entirely, resulting in a dropped QRS complex.

This pattern of progressive prolongation followed by a dropped beat is distinctive and helps differentiate it from other types of heart block. In first-degree heart block, there is a consistent but prolonged PR interval without dropped beats. Type II second-degree heart block, conversely, displays intermittent drops of beats without the progressive lengthening of the PR interval. Complete heart block entails a total dissociation between atrial and ventricular activity, lacking any regular pattern of lengthening PR intervals.

Understanding these characteristics is crucial for accurate EKG interpretation and appropriate clinical management of patients with heart block.