Table 2.

Interatrial conduction block (IAB) types, their electrophysiological background and the corresponding ECG features.

IAB Type	Electrophysiological Background	ECG Features
first-degree (partial)	delayed conduction in the zone of BB	P-wave duration >120 ms
third-degree (advanced)	blocked conduction in the zone of BB: caudocranial, retrograde activation of the left atrium from the low right atrium (coronary sinus and to a lesser degree, the fossa ovalis)	P wave duration >120 ms with biphasic morphology (a positive initial component and a terminal negative component) in the inferior leads (II, III, aVF)
second-degree	delayed or blocked conduction in the zone of BB	transient appearance of first-degree and/or third-degree IAB pattern on the same ECG recording (atrial aberrancy)—related or not to an atrial premature beat