Second degree AV block classification
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sara Zand, M.D.[2] Mohammed Salih, M.D., Cafer Zorkun, M.D., Ph.D. [3], Raviteja Guddeti, M.B.B.S. [4]
Overview
There are 4 distinct types of second degree AV block. The distinction is made between them because type 1 second-degree heart block is considered a more benign entity than the other types. In mobitz type 1 second degree AV block there is evidence of gradually PR prolongation and dropped beat and grouped beating pattern. In mobitz type 2 AV block there is suddenly dopped beats without evidence of preceding PR prolongation. In atrioventricular block with the pattern of 2:1, there is every other beat without conducting down to the ventricle. In a high-grade AV block, there are two or more consecutive P waves without conduction to the ventricle.
Classification
| Term | Classification | Definition | |
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| Atrioventricular block | First-degree atrioventricular block |
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| Second- degree atrioventricular block |
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| Third-degree atrioventricular block (complete heart block) |
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Type 1 (Mobitz I / Wenckebach)
- Type 1 second degree AV block, also known as Mobitz I or Wenckebach periodicity which is a disease of the AV node[2][3].
- Mobitz I heart block is characterized by progressive prolongation of the PR interval on the electrocardiogram (EKG) on consecutive beats followed by a blocked P wave (i.e. a 'dropped' QRS complex).
- After the dropped QRS complex, the PR interval resets and the cycle repeats.
- One of the baseline assumptions when determining if an individual has Mobitz I heart block is that the atrial rhythm has to be regular.
- If the atrial rhythm is not regular, there could be alternative explanations as to why certain P waves do not conduct to the ventricles.
- This is a benign condition for which no specific treatment is needed.
Type 2 (Mobitz II)
- Type 2 second degree AV block, also known as Mobitz II is almost always a disease of the distal conduction system (His-Purkinje System).
- Although the terms intranodal block or infrahisian block are often applied to this disorder, they are not synonymous with it.
- Infranodal block and infra-Hisian block are terms that refer to the anatomic location of the block, whereas,
- Mobitz II refers to an electrocardiographic pattern associated with block at these levels[4].
- Mobitz II heart block is characterized on a surface ECG by intermittently non-conducted P waves not preceded by PR prolongation and not followed by PR shortening.
- The medical significance of this type of AV block is that it may progress rapidly to complete heart block, in which no escape rhythm may emerge.
- In this case, the person may experience a Stokes-Adams attack, cardiac arrest, or sudden cardiac death.
- The definitive treatment for this form of AV Block is an implanted pacemaker[5][6].
Differentiating Mobitz I from Mobitz II in the Presence of a 2:1 Conduction
Likely EKG findings that help differentiate Mobitz type I from type II in the presence of a 2:1 conduction ratio include:
- Very long PR interval (> 300 msec) or narrow QRS complex - indicates the block is at the level of AV node
- Administration of atropine enhances AV nodal conduction resulting in less frequent non conducted beats - this confirms the type I Mobitz
- Mobitz I is worsened by carotid sinus massage which slows AV nodal conduction, unlike Mobitz II.
- Carotid sinus massage paradoxically eliminates infranodal block by slowing the sinus rate[7].
- Another type of classification used to classify second-degree AV block is 2:1 AV block and high-grade AV block.
- In 2:1 AV block every other atrial impulse is conducted down the ventricle.
- Higher grade blocks (eg., 3:1) unlike third degree AV block conduct few beats down the ventricle.
References
- ↑ Kusumoto, Fred M.; Schoenfeld, Mark H.; Barrett, Coletta; Edgerton, James R.; Ellenbogen, Kenneth A.; Gold, Michael R.; Goldschlager, Nora F.; Hamilton, Robert M.; Joglar, José A.; Kim, Robert J.; Lee, Richard; Marine, Joseph E.; McLeod, Christopher J.; Oken, Keith R.; Patton, Kristen K.; Pellegrini, Cara N.; Selzman, Kimberly A.; Thompson, Annemarie; Varosy, Paul D. (2019). "2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society". Circulation. 140 (8). doi:10.1161/CIR.0000000000000628. ISSN 0009-7322.
- ↑ Mangi MA, Jones WM, Napier L. PMID 29493981. Missing or empty
|title=(help) - ↑ Kashou AH, Goyal A, Nguyen T, Chhabra L. PMID 29083636. Missing or empty
|title=(help) - ↑ Li X, Xue Y, Wu H (2018). "A Case of Atrioventricular Block Potentially Associated with Right Coronary Artery Lesion and Ticagrelor Therapy Mediated by the Increasing Adenosine Plasma Concentration". Case Rep Vasc Med. 2018: 9385017. doi:10.1155/2018/9385017. PMC 5933017. PMID 29850368.
- ↑ Fu Md J, Bhatta L (2018). "Lyme carditis: Early occurrence and prolonged recovery". J Electrocardiol. 51 (3): 516–518. doi:10.1016/j.jelectrocard.2017.12.035. PMID 29275956.
- ↑ Tuohy S, Saliba W, Pai M, Tchou P (January 2018). "Catheter ablation as a treatment of atrioventricular block". Heart Rhythm. 15 (1): 90–96. doi:10.1016/j.hrthm.2017.08.015. PMID 28823599.
- ↑ Schernthaner C, Kraus J, Danmayr F, Hammerer M, Schneider J, Hoppe UC, Strohmer B (March 2016). "Short-term pacemaker dependency after transcatheter aortic valve implantation". Wien. Klin. Wochenschr. 128 (5–6): 198–203. doi:10.1007/s00508-015-0906-4. PMID 26745972.