This type of second-degree AV block is more similar to Mobitz Type I than Mobitz Type II. The ECG shows a repeating pattern of conducted atrial impulses and completely blocked atrial impulses, often in a 2:1 or 3:1 ratio. 

Conducted atrial impulses have P waves followed by a QRS complex. Completely blocked atrial impulses have P waves without a QRS complex, i.e., a dropped beat. In second-degree AV block, advanced type, the dropped beat may occur every second atrial impulse (2:1) or every third atrial impulse (3:1). 

Conducted beats in second-degree AV blocks of the advanced type do not typically show bundle-branch block. Second-degree AV blocks do not commonly progress to complete AV block as long as there is not also a bundle-branch block. Progression to complete AV block is a concern if there is a concomitant acute inferior wall MI or digitalis overdose.

Prognosis is dependent on the rate of the atrial rhythm and the number of dropped beats. A sinus rhythm, for example, with a rate of 90 bpm and a 3:1 AV block results in a ventricular rate of only 30 bpm (ventricular bradycardia). This patient will develop significant hemodynamic instability. When a bundle-branch block is present, the patient is also more likely to progress to complete AV block. 

Second-degree AV block, advanced type, may benefit patients with concomitant atrial flutter. These patients often present with a 2:1 AV block, which inhibits the excessive ventricular rate that the flutter would otherwise drive. The interval between flutter waves and the QRS complex may be irregular due to the Wenckebach phenomenon.