Tridamayanti A 1, Irnizarifka1,2
1Departement of Cardiology and Vascular Medicine, Faculty of Medicine, Universitas Sebelas Maret, Surakarta, Indonesia.
2Departement of Cardiology and Vascular Medicine, Faculty of Medicine, Universitas Sebelas Maret, Sebelas Maret University Hospital, Surakarta, Indonesia.
Background: 2:1 atrioventricular block can occur in either AV node (AVN) or HIS-Purkinje System (HPS) and cannot be classified into type I or type II second-degree AV block because there is only one PR segment to be examined before the dropped-beat. On the other hand, it is essential to have two consecutive conducted P waves to differentiate between type I or type II second-degree AV block. Determining those types of atrioventricular or HPS block is very important as treatments are also unlike.
Case Illustration : 56 year old diabetic woman was admitted with chief complaint of chest pain since 15 hours beforehand, accompanied with diaphoresis and near syncope. Her resting ECG revealed 2:1 AV block, with PR interval was not prolonged (0.2 sec), and ST segments were not elevated. Cardiac enzyme proved diagnosis of NSTE-ACS and 2:1 AV block. In order to define the site of block, we performed atropine challenge test. After administration of 0.5 mg atropine, ECG revealed improvement of AV conduction ratio with 3:2 Wenckebach-like manners. It indicated the location of the block was at AV node.
Discussion: Fixed 2:1 AV block poses a diagnostic dilemma because it can be difficult to determine the site of block by the surface ECG alone. The AVN is richly innervated and highly responsive to both sympathetic and vagal stimuli, whereas HPS is influenced minimally by the autonomic nervous system. Atropine or exercise can improve AVN conduction because of sympathetic stimulation and/or parasympatholysis. Therefore, atropine administration can improve AVN conduction but worsen infranodal block due to sympathetic stimulation of the sinus node and AVN without changing the HPS refractoriness.
Conclusion: This case illustrates the importance of noninvasive atropine challenge test to confirm site of 2:1 atrioventricular block, thus will guide the definite therapy.
Keyword: 2:1 atrioventricular block, atropine challenge test, wenckebach, HIS-purkinje block
Nizar MD Medical Articles 