Atrioventricular Nodes, Blocks, and Pacemaker Selection

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Table of Contents

Introduction
Atrioventricular Blocks: Types and Classification
First Degree Av Block
Second Degree Av Blocks
Third Degree Av Blocks
Complete Third-Degree Av Block With or Without Symptoms
Conclusion
References

Introduction

The atrioventricular node is part of the hearts conduction system located in the atrial septum. Its purpose is to connect the electrical systems of the atria and ventricles, providing electrical resistance from the atria and the built-in pacemaker in its absence (Heaton and Goyal, 2020). The AV node can cause pathological conditions provoked by a violation of electrical conductivity and will slow down the heartbeat. In the assignment, the topics of types and classification of atrioventricular blocks and a critical analysis of pacemakers by guidelines were considered.

Atrioventricular Blocks: Types and Classification

Atrioventricular (AV) heart block violates conduction from the atria to the ventricles through the AV connection. Such a disorder occurs when the atrial impulse is delayed or does not enter the ventricles. The three types of AV block are 1st, 2nd and 3rd degree. The second-degree block is further divided into Mobitz Type I AV blocks, also known as Wenckebach, and Type II AV block.

First Degree Av Block

Atrioventricular block of the first degree is a condition of abnormally low conductivity through the AV node. This is determined by ECG changes that include a PR interval of more than 0.20 without disruption of atrioventricular conduction with a normal measurement of the PR interval from 0.12 seconds to 0.20 seconds (Oldroyd, Rodriguez, and Makaryus, 2020). This condition usually proceeds asymptomatically, without significant complications and is detected only on a conventional ECG. For the vast majority of patients, no treatment is required, except for the usual monitoring of the deterioration of conduction delay.

Second Degree Av Blocks

With Wenckebach block or Mobitz type I AV block, there is a violation of conduction through the AV node so that a QRS complex may not accompany some P waves. Second-degree type I AV block occurs when the conduction inside the AV node itself is delayed. This does not necessarily indicate a congenital conduction disorder and rarely requires the implantation of a pacemaker. Type I AV block of the second degree can be caused by AV-blocking drugs or increased nerve tone. AV block of type II of the second degree indicates a significant violation of conductivity in this His-Purkinje system and is irreversible. Mobitz type ll block can potentially progress to complete heart block and, if not recognized, lead to death (Mangi et al., 2021). The second degree or incomplete AV block occurs with intermittent ventricular conduction disorder. That is, P-waves are sometimes associated with QRS complexes. This often happens according to the usual P:QRS scheme with ratios of 2:1. 3:2, 4:3, 5:4, and so on.

Third Degree Av Blocks

Third degree atrioventricular block, also called complete heart block (CHB), indicates a total loss of communication between the atria and the ventricles (Knabben, Chhabra, and Slane, 2021). It is a cardiac arrhythmia resulting from a defect in the cardiac conduction system, which leads to complete dissociation of the heart rhythm. The ventricular evacuation mechanism can occur anywhere from the lower part to the Purkinje system with a bundle of branches.

Complete Third-Degree Av Block With or Without Symptoms

A complete third-degree AV block entails many symptoms, some of which may pose a danger to the patients life. The most common symptoms are shortness of breath, attacks of dizziness or nausea, syncope or congestive heart failure (Wang et al., 2018). It is worth noting that similar symptoms are also characteristic of people with less severe forms of heart block, but in general they are less affected by them.

There is an underutilization of the excellent AIR pacing regimen for symptomatic SND. Evidence-based practice currently confirms that material-based pricing reduces the frequency of atrial fibrillation and that continuous right ventricular pacing increases the risk of heart failure progression. Therefore, all attempts are recommended to avoid unnecessary packing of the right ventricle by implementing strategies to maintain normal ventricular activation (Sidhu and Marine, 2020).

Conclusion

The choice and use of pacemakers will also be influenced by the improvement of technologies (Kusumoto et al., 2019). In the nearest future, it may lead to a new stratification of the target patient population and lower costs for simpler pacemakers, which will increase the number of target patients receiving pacemakers.

References

Bonikowske, A.R., Barout, A., Fortin-Gamero, S., Lara, M.I.B., Kapa, S. and Allison, T.G. (2019) Frequency and characteristics of exercise-induced second-degree atrioventricular block in patients undergoing stress testing. Journal of Electrocardiology, 54, pp. 54-60.

Heaton, J. and Goyal, A. (2020) Atrioventricular node. In StatPearls [Internet]. StatPearls Publishing.

Higuchi, S., Goldschlager, N. and Gerstenfeld, E.P. (2021) Atrioventricular Block With Narrow and Wide QRS: The Pause That Refreshes. Circulation, 144(15), pp. 1262-1264.

Knabben, V., Chhabra, L. and Slane, M. (2021) Third-Degree Atrioventricular Block. In StatPearls [Internet]. StatPearls Publishing.

Knight, B.P. and Hoekstra, J. (2022) Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation. In StatPearls [Internet]. StatPearls Publishing

Kusumoto, F.M., Schoenfeld, M.H., Barrett, C., Edgerton, J.R., Ellenbogen, K.A., Gold, M.R., Goldschlager, N.F., Hamilton, R.M., Joglar, J.A., Kim, R.J. and Lee, R. (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. Journal of the American College of Cardiology, 74(7), pp. 51-156.

Mangi, M.A., Jones, W.M., Mansour, M.K. and Napier, L. (2021) Atrioventricular block second-degree. In StatPearls [Internet]. StatPearls Publishing.

Oldroyd, S.H., Rodriguez, B.S.Q. and Makaryus, A.N. (2021) First degree heart block. In StatPearls [Internet]. StatPearls Publishing.

Sidhu, S. and Marine, J.E. (2020) Evaluating and managing bradycardia. Trends in cardiovascular medicine, 30(5), pp. 265-272.

Wang, Q., Shang, Y., Li, S., Wu, Y., Wang, C. and Yan, X. (2018) Complete heart block in systemic sclerosis: A case report and literature review. Medicine, 97(46).

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