How is a second-degree heart block (Mobitz I) typically diagnosed?

A second-degree heart block of the Mobitz I type, also known as Wenckebach, is characterized by a specific pattern observable on an electrocardiogram (ECG). The hallmark feature of this block is the progressive lengthening of the PR interval with each successive heartbeat until a QRS complex is dropped. This means that after several beats, the electrical signal fails to produce a ventricular contraction, indicated by the absence of a QRS complex after one of the P waves.

This pattern provides valuable insight into the conduction system's behavior. The progressively longer PR intervals occur due to the gradual increase in the time it takes for the electrical impulse to travel through the AV node until it fails to pass through it on one occasion, resulting in the dropped beat. Recognizing this distinctive pattern is key for accurate diagnosis and management of Mobitz I heart block, distinguishing it from other types of heart blocks and arrhythmias.

Other options do not encapsulate the defining characteristics of Mobitz I. Random dropped beats could suggest a different degree or type of block. A consistent PR interval is not indicative either, as Mobitz I specifically involves variable and increasing PR intervals. ST segment elevation is associated with other cardiac conditions, such as myocardial infarction, and