In which type of heart block would you find a fixed PR interval with a dropped beat?

The presence of a fixed PR interval with a dropped beat is characteristic of 2nd degree heart block type 2, also known as Mobitz type 2. In this type of heart block, the electrical signals from the atria to the ventricles are intermittently blocked, leading to missed ventricular contractions without any preceding lengthening of the PR interval. This results in a consistent (fixed) PR interval before the drop of the beat.

This fixed nature of the PR interval helps differentiate it from 2nd degree heart block type 1 (Mobitz type 1), where the PR interval progressively lengthens before a beat is dropped. It also distinguishes it from 1st degree heart block where all impulses are conducted but with a prolonged PR interval, and from 3rd degree heart block, where there is a complete dissociation between atrial and ventricular activity with variable PR intervals. Thus, the defining feature of a consistent PR interval with intermittent dropped beats firmly identifies 2nd degree heart block type 2.