How is a third-degree heart block identified on an EKG?

A third-degree heart block, also known as complete heart block, is characterized by a complete dissociation between atrial and ventricular activity. This means that the electrical signals originating in the atria do not conduct to the ventricles. On an electrocardiogram (EKG), this is visually represented by independent atrial and ventricular waveforms. The P waves (representing atrial depolarization) occur at their own rate and rhythm, while the QRS complexes (representing ventricular depolarization) appear separately and also at their own rate. This dissociation indicates that the normal conduction pathway has been disrupted, preventing communication between the atria and ventricles.

In contrast, the other options represent different patterns observed in other types of heart conditions. For instance, progressive lengthening of the PR interval is associated with a second-degree heart block (specifically Type I, or Wenckebach). Complete fusion of atrial and ventricular activity typically suggests other types of arrhythmias rather than a true block. Prominent U waves following every QRS complex are not characteristic of third-degree heart block and are often associated with other electrolyte imbalances or conditions affecting the repolarization phase of the heart cycle. Understanding these distinctions is crucial for accurate E