Final answer:
The AH <> HA method is used during electrophysiological studies to differentiate subtypes of AVNRT by examining the conduction times between the atrium, the AV node, and His bundle.
Step-by-step explanation:
The AH <> HA method can be used to help differentiate different types of Atrioventricular Nodal Reentrant Tachycardia (AVNRT). This type of method is not directly applicable for diagnosing AVNRT subtypes, but instead refers to the intervals measured during an electrophysiological study. In AVNRT, there are usually two pathways within the AV node: a fast pathway and a slow pathway. By analyzing the conduction times (AH interval representing conduction from the atrium to the His bundle via the slow pathway, and HA interval representing retrograde conduction from the His bundle to the atrium via the fast pathway), physicians can specify the subtype of AVNRT.
In contrast, AV blocks, classified into first, second, and third degrees, are characterized by conduction delays or blocks between the SA and AV nodes, as evidenced by the ECG intervals but are not typically assessed by AH/HA intervals. First-degree AV block shows a prolonged PR interval. Second-degree AV block shows P waves not followed by a QRS complex intermittently, and third-degree AV block presents a complete disassociation between P waves and QRS complexes. Thus, the differentiation of AV block types and AVNRT subtypes relies on specific ECG findings and, in the case of AVNRT, potentially intracardiac electrophysiological study intervals.