Which type of AV block is characterized by a progressively prolonged PR interval until a QRS complex is dropped?

The type of AV block characterized by a progressively prolonged PR interval until a QRS complex is dropped is indeed 2nd degree AV block type I, also known as Wenckebach. In this condition, there is a gradual increase in the duration of the PR interval with each successive heartbeat, culminating in a dropped QRS complex. This pattern repeats itself in a cyclical manner.

The mechanism behind this phenomenon involves a progressive delay in conduction through the AV node. As the conduction time increases with each beat, it eventually reaches a threshold where the impulse is unable to pass through the AV node, resulting in the omission of the QRS complex. This block is typically associated with a physiological conduction disturbance and is often benign, especially in younger patients or athletes.

Understanding the distinguishing features of this type of AV block helps in identifying it on an electrocardiogram (ECG) and differentiating it from other types of heart blocks. In contrast, 1st degree AV block shows a constant PR interval with no dropped beats, 2nd degree AV block type II does not have a progressive lengthening of the PR interval and drops QRS complexes unpredictably, while complete AV block involves a complete dissociation between atrial and ventricular activity without any specific