Third-degree atrioventricular block

Last updated
Third-degree atrioventricular block
Other namesComplete heart block
CompleteHeartBlock.jpg
12-lead ECG showing complete heart block
Specialty Cardiology
Symptoms Dizziness, Fainting, Shortness of breath, Sudden cardiac death
CausesFibrosis in cardiac conduction system, myocardial infarction, post-cardiac surgery, medication, vagal tone, electrolyte disturbances
Diagnostic method Electrocardiogram
Treatment Pacemaker

Third-degree atrioventricular block (AV block) is a medical condition in which the electrical impulse generated in the sinoatrial node (SA node) in the atrium of the heart can not propagate to the ventricles. [1]

Contents

Because the impulse is blocked, an accessory pacemaker in the lower chambers will typically activate the ventricles. This is known as an escape rhythm . Since this accessory pacemaker also activates independently of the impulse generated at the SA node, two independent rhythms can be noted on the electrocardiogram (ECG).

Presentation

People with third-degree AV block typically experience severe bradycardia (an abnormally low measured heart rate), hypotension, and at times, hemodynamic instability. [2]

Cause

Leads I and II demonstrating complete AV block. Note that the P waves are not related to the QRS complexes (PP interval and QRS interval both constant), demonstrating that the atria are electrically disconnected from the ventricles. The QRS complexes represent an escape rhythm arising from the ventricle. Rhythm strip showing third degree heart block.jpg
Leads I and II demonstrating complete AV block. Note that the P waves are not related to the QRS complexes (PP interval and QRS interval both constant), demonstrating that the atria are electrically disconnected from the ventricles. The QRS complexes represent an escape rhythm arising from the ventricle.
Atrial tachycardia with complete A-V block and resulting junctional escape Complete A-V block with resulting junctional escape.png
Atrial tachycardia with complete A-V block and resulting junctional escape

Many conditions can cause third-degree heart block, but the most common cause is coronary ischemia. Progressive degeneration of the electrical conduction system of the heart can lead to third-degree heart block. This may be preceded by first-degree AV block, second-degree AV block, bundle branch block, or bifascicular block. In addition, acute myocardial infarction may present with third-degree AV block. [3]

An inferior wall myocardial infarction may cause damage to the AV node, causing third-degree heart block. In this case, the damage is usually transitory. Studies have shown that third-degree heart block in the setting of an inferior wall myocardial infarction typically resolves within 2 weeks. [4] The escape rhythm typically originates in the AV junction, producing a narrow complex escape rhythm.[ citation needed ]

An anterior wall myocardial infarction may damage the distal conduction system of the heart, causing third-degree heart block. Initially demonstrated by animal studies, this is due to a stark reduction in the Kv β-subunit of the voltage-gated K+ channels in the pacemaker cells of the atrioventricular junction, causing significantly decreased propagation of ions across gap junctions between cardiac cells and thus prolonging the PR interval. [5] This is typically extensive, permanent damage to the conduction system, eliciting a necessity for a permanent pacemaker to be placed. [6] The escape rhythm typically originates in the ventricles, producing a wide complex escape rhythm.

Third-degree heart block may also be congenital and has been linked to the presence of lupus in the mother. [7] It is thought that maternal antibodies may cross the placenta and attack the heart tissue during gestation. The cause of congenital third-degree heart block in many patients is unknown. Studies suggest that the prevalence of congenital third-degree heart block is between 1 in 15,000 and 1 in 22,000 live births.[ citation needed ]

Hyperkalemia in those with previous cardiac disease [8] and Lyme disease can also result in third-degree heart block. [9]

Diagnosis

Diagnosis is largely focussed on analysis of the patients 12-lead ECG. A patient with a third-degree AV block will likely have p-waves not corresponding to QRS complexes along with bradycardia.

Treatment

Atropine is often used as a first line treatment of a third-degree heart block in the presence of a narrow QRS which indicates a nodal block, but, may have little to no effect in an infra-nodal block. [10] Atropine works by reducing vagal stimulation through the AV node but will not be effective in those who have had a previous heart transplant. [11] Other drugs may be utilized such as epinephrine or dopamine which have positive chronotropic effects and may increase the heart rate. [12] Treatment in emergency situations can involve electrical transcutaneous pacing in those who are acutely hemodynamically unstable and can be used regardless of the persons level of consciousness. [13] Sedative agents such as a benzodiazepine or opiate may be used in conjunction with transcutaneous pacing to reduce the pain caused by the intervention. [12] [13]

In cases of suspected beta-blocker overdose, the heart-block may be treated with pharmacological agents to reverse the underlying cause with the use of glucagon. In the case of a calcium channel blocker overdose treated with calcium chloride and digitalis toxicity may be treated with the digoxin immune Fab. [14]

Third-degree AV block can be treated more permanently with the use of a dual-chamber artificial pacemaker. [15] This type of device typically listens for a pulse from the SA node via lead in the right atrium and sends a pulse via a lead to the right ventricle at an appropriate delay, driving both the right and left ventricles. Pacemakers in this role are usually programmed to enforce a minimum heart rate and to record instances of atrial flutter and atrial fibrillation, two common secondary conditions that can accompany third-degree AV block. Since pacemaker correction of the third-degree block requires full-time pacing of the ventricles, a potential side effect is pacemaker syndrome, and may necessitate the use of a biventricular pacemaker, which has an additional 3rd lead placed in a vein in the left ventricle, providing more coordinated pacing of both ventricles.[ citation needed ]

The 2005 Joint European Resuscitation and Resuscitation Council (UK) guidelines [16] state that atropine is the first-line treatment especially if there were any adverse signs, namely: 1) heart rate < 40 bpm, 2) systolic blood pressure < 100 mm Hg, 3) signs of heart failure, and 4) ventricular arrhythmias requiring suppression. If these fail to respond to atropine or there is a potential risk of asystole, transvenous pacing is indicated. The risk factors for asystole include 1) previous asystole, 2) complete heart block with wide complexes, and 3) ventricular pause for > 3 seconds. Mobitz Type 2 AV block is another indication for pacing.

As with other forms of heart block, secondary prevention may also include medicines to control blood pressure and atrial fibrillation, as well as lifestyle and dietary changes to reduce risk factors associated with heart attack and stroke.

Treatment

Early treatment of atrioventricular blockade is based on the presence and severity of symptoms and signs associated with ventricular escape rhythm. Hemodynamically unstable patients require immediate medication and in most cases temporary pacing to increase heart rate and cardiac output.

Once the patient is hemodynamically stable, a potentially reversible cause should be evaluated and treated. If no reversible cause is identified, a permanent pacemaker is inserted.[ citation needed ] Most stable patients have persistent bradycardia-related symptoms and require identification and treatment of any reversible cause or permanent implantable pacemaker.

Reversible causes of complete AV block should be ruled out before the insertion of a permanent pacemaker, such as drugs that slow heart rate and which induce hyperkalemia.

Complete atrioventricular block in acute myocardial infarction should be treated with temporary pacing and revascularization. [17] [ citation needed ]

Complete atrioventricular block caused by hyperkalemia should be treated to lower serum potassium levels and patients with hypothyroidism should also receive thyroid hormone. [17]

If there is no reversible cause, the clear treatment of complete atrioventricular block is mostly permanent pacemaker placement.[ citation needed ]

Prognosis

The prognosis of patients with complete heart block is generally poor without therapy. Patients with 1st and 2nd-degree heart block are usually asymptomatic. [18]

See also

Related Research Articles

<span class="mw-page-title-main">Bradycardia</span> Heart rate below the normal range

Bradycardia is a slow resting heart rate, commonly under 60 beats per minute (BPM) as determined by an electrocardiogram. It is considered to be a normal heart rate during sleep, in young and healthy or elderly adults, and in athletes.

<span class="mw-page-title-main">Electrocardiography</span> Examination of the hearts electrical activity

Electrocardiography is the process of producing an electrocardiogram, a recording of the heart's electrical activity through repeated cardiac cycles. It is an electrogram of the heart which is a graph of voltage versus time of the electrical activity of the heart using electrodes placed on the skin. These electrodes detect the small electrical changes that are a consequence of cardiac muscle depolarization followed by repolarization during each cardiac cycle (heartbeat). Changes in the normal ECG pattern occur in numerous cardiac abnormalities, including cardiac rhythm disturbances, inadequate coronary artery blood flow, and electrolyte disturbances.

<span class="mw-page-title-main">Cardiac conduction system</span> Aspect of heart function

The cardiac conduction system(CCS) (also called the electrical conduction system of the heart) transmits the signals generated by the sinoatrial node – the heart's pacemaker, to cause the heart muscle to contract, and pump blood through the body's circulatory system. The pacemaking signal travels through the right atrium to the atrioventricular node, along the bundle of His, and through the bundle branches to Purkinje fibers in the walls of the ventricles. The Purkinje fibers transmit the signals more rapidly to stimulate contraction of the ventricles.

<span class="mw-page-title-main">First-degree atrioventricular block</span> Medical condition

First-degree atrioventricular block is a disease of the electrical conduction system of the heart in which electrical impulses conduct from the cardiac atria to the ventricles through the atrioventricular node more slowly than normal. First degree AV block does not generally cause any symptoms, but may progress to more severe forms of heart block such as second- and third-degree atrioventricular block. It is diagnosed using an electrocardiogram, and is defined as a PR interval greater than 200 milliseconds. First degree AV block affects 0.65-1.1% of the population with 0.13 new cases per 1000 persons each year.

<span class="mw-page-title-main">Second-degree atrioventricular block</span> Medical condition

Second-degree atrioventricular block is a disease of the electrical conduction system of the heart. It is a conduction block between the atria and ventricles. The presence of second-degree AV block is diagnosed when one or more of the atrial impulses fail to conduct to the ventricles due to impaired conduction. It is classified as a block of the AV node and is categorized in between first-degree and third degree blocks.

<span class="mw-page-title-main">Ventricular tachycardia</span> Medical condition of the heart

Ventricular tachycardia is a fast heart rate arising from the lower chambers of the heart. Although a few seconds of VT may not result in permanent problems, longer periods are dangerous; and multiple episodes over a short period of time are referred to as an electrical storm. Short periods may occur without symptoms, or present with lightheadedness, palpitations, or chest pain. Ventricular tachycardia may result in ventricular fibrillation (VF) and turn into cardiac arrest. This conversion of the VT into VF is called the degeneration of the VT. It is found initially in about 7% of people in cardiac arrest.

<span class="mw-page-title-main">Supraventricular tachycardia</span> Abnormally fast heart rhythm

Supraventricular tachycardia (SVT) is an umbrella term for fast heart rhythms arising from the upper part of the heart. This is in contrast to the other group of fast heart rhythms – ventricular tachycardia, which start within the lower chambers of the heart. There are four main types of SVT: atrial fibrillation, atrial flutter, paroxysmal supraventricular tachycardia (PSVT), and Wolff–Parkinson–White syndrome. The symptoms of SVT include palpitations, feeling of faintness, sweating, shortness of breath, and/or chest pain.

<span class="mw-page-title-main">AV nodal reentrant tachycardia</span> Medical condition

AV-nodal reentrant tachycardia (AVNRT) is a type of abnormal fast heart rhythm. It is a type of supraventricular tachycardia (SVT), meaning that it originates from a location within the heart above the bundle of His. AV nodal reentrant tachycardia is the most common regular supraventricular tachycardia. It is more common in women than men. The main symptom is palpitations. Treatment may be with specific physical maneuvers, medications, or, rarely, synchronized cardioversion. Frequent attacks may require radiofrequency ablation, in which the abnormally conducting tissue in the heart is destroyed.

<span class="mw-page-title-main">Bundle branch block</span> Medical condition

A bundle branch block is a defect in one of the bundle branches in the electrical conduction system of the heart.

<span class="mw-page-title-main">Right bundle branch block</span> Heart block in the right ventricle

A right bundle branch block (RBBB) is a heart block in the right bundle branch of the electrical conduction system.

<span class="mw-page-title-main">Atrioventricular block</span> Medical condition

Atrioventricular block is a type of heart block that occurs when the electrical signal traveling from the atria, or the upper chambers of the heart, to ventricles, or the lower chambers of the heart, is impaired. Normally, the sinoatrial node produces an electrical signal to control the heart rate. The signal travels from the SA node to the ventricles through the atrioventricular node. In an AV block, this electrical signal is either delayed or completely blocked. When the signal is completely blocked, the ventricles produce their own electrical signal to control the heart rate. The heart rate produced by the ventricles is much slower than that produced by the SA node.

<span class="mw-page-title-main">Ventricular escape beat</span>

In cardiology, a ventricular escape beat is a self-generated electrical discharge initiated by, and causing contraction of the ventricles of the heart; normally the heart rhythm is begun in the atria of the heart and is subsequently transmitted to the ventricles. The ventricular escape beat follows a long pause in ventricular rhythm and acts to prevent cardiac arrest. It indicates a failure of the electrical conduction system of the heart to stimulate the ventricles.

Sinoatrial arrest is a medical condition wherein the sinoatrial node of the heart transiently ceases to generate the electrical impulses that normally stimulate the myocardial tissues to contract and thus the heart to beat. It is defined as lasting from 2.0 seconds to several minutes. Since the heart contains multiple pacemakers, this interruption of the cardiac cycle generally lasts only a few seconds before another part of the heart, such as the atrio-ventricular junction or the ventricles, begins pacing and restores the heart action. This condition can be detected on an electrocardiogram (ECG) as a brief period of irregular length with no electrical activity before either the sinoatrial node resumes normal pacing, or another pacemaker begins pacing. If a pacemaker other than the sinoatrial node is pacing the heart, this condition is known as an escape rhythm. If no other pacemaker begins pacing during an episode of sinus arrest it becomes a cardiac arrest. This condition is sometimes confused with sinoatrial block, a condition in which the pacing impulse is generated, but fails to conduct through the myocardium. Differential diagnosis of the two conditions is possible by examining the exact length of the interruption of cardiac activity. If the next available pacemaker takes over, it is in the following order:

<span class="mw-page-title-main">Accelerated idioventricular rhythm</span> Medical condition

Accelerated idioventricular rhythm is a ventricular rhythm with a rate of between 40 and 120 beats per minute. Idioventricular means “relating to or affecting the cardiac ventricle alone” and refers to any ectopic ventricular arrhythmia. Accelerated idioventricular arrhythmias are distinguished from ventricular rhythms with rates less than 40 and those faster than 120. Though some other references limit to between 60 and 100 beats per minute. It is also referred to as AIVR and "slow ventricular tachycardia."

<span class="mw-page-title-main">Junctional rhythm</span> Medical condition

Junctional rhythm describes an abnormal heart rhythm resulting from impulses coming from a locus of tissue in the area of the atrioventricular node(AV node), the "junction" between atria and ventricles.

<span class="mw-page-title-main">Sinoatrial block</span> Medical condition

A sinoatrial block is a disorder in the normal rhythm of the heart, known as a heart block, that is initiated in the sinoatrial node. The initial action impulse in a heart is usually formed in the sinoatrial node and carried through the atria, down the internodal atrial pathways to the atrioventricular node (AV) node. In normal conduction, the impulse would travel across the bundle of His, down the bundle branches, and into the Purkinje fibers. This would depolarize the ventricles and cause them to contract.

<span class="mw-page-title-main">Junctional ectopic tachycardia</span> Medical condition

Junctional ectopic tachycardia (JET) is a rare syndrome of the heart that manifests in patients recovering from heart surgery. It is characterized by cardiac arrhythmia, or irregular beating of the heart, caused by abnormal conduction from or through the atrioventricular node. In newborns and infants up to 6 weeks old, the disease may also be referred to as His bundle tachycardia or congenital JET.

<span class="mw-page-title-main">Left axis deviation</span> Heart condition

In electrocardiography, left axis deviation (LAD) is a condition wherein the mean electrical axis of ventricular contraction of the heart lies in a frontal plane direction between −30° and −90°. This is reflected by a QRS complex positive in lead I and negative in leads aVF and II.

An idioventricular rhythm is a cardiac rhythm characterized by a rate of <50 beats per minute (bpm), absence of P waves and widening of the QRS complex. In cases where the heart rate is between 50 and 110 bpm, it is known as accelerated idioventricular rhythm and ventricular tachycardia if the rate exceeds 120 bpm. Causes of idioventricular rhythms are varied and can include drugs or a heart defect at birth. It is typically benign and not life-threatening.

A tachycardia-dependent bundle branch block is a defect in the conduction system of the heart, and is distinct from typical bundle branch blocks due to its reliable, reproducible onset related to an increase in the rate of cardiac contraction. Tachycardia-dependent bundle branch block can prevent both ventricles from contracting efficiently and can limit the cardiac output of the heart.

References

  1. ↑ "ECG Conduction Abnormalities" . Retrieved 2009-01-07.
  2. ↑ "Heart Block". NHS Choices. National Health Service (UK). Retrieved 25 August 2015.
  3. ↑ Knabben, V.; Chhabra, L.; Slane, M. (2022). "Third-Degree Atrioventricular Block". National Center for Biotechnology Information, U.S. National Library of Medicine. PMID   31424783 . Retrieved 3 July 2021.
  4. ↑ Sclarovsky, S; Strasberg, B; Hirshberg, A; Arditi, A; Lewin, RF; Agmon, J (July 1984). "Advanced early and late atrioventricular block in acute inferior wall myocardial infarction". American Heart Journal. 108 (1): 19–24. doi:10.1016/0002-8703(84)90539-8. PMID   6731277.
  5. ↑ Nikolaidou, T., Cai, X. J., Stephenson, R. S., Yanni, J., Lowe, T., Atkinson, A. J., Jones, C. B., Sardar, R., Corno, A. F., Dobrzynski, H., Withers, P. J., Jarvis, J. C., Hart, G., & Boyett, M. R. (2015). Congestive heart failure leads to prolongation of the PR interval and atrioventricular Junction enlargement and ion channel remodelling in the rabbit. PLOS ONE, 10(10), e0141452. https://doi.org/10.1371/journal.pone.0141452
  6. ↑ Atrioventricular block, third degree. (2012). Clinical Veterinary Advisor, 58-61. https://doi.org/10.1016/b978-1-4160-9979-6.00038-6
  7. ↑ Brucato, A; Previtali, E; Ramoni, V; Ghidoni, S (September 2010). "Arrhythmias presenting in neonatal lupus" (PDF). Scandinavian Journal of Immunology. 72 (3): 198–204. doi: 10.1111/j.1365-3083.2010.02441.x . hdl:2434/635678. PMID   20696016.
  8. ↑ Sohoni A, Perez B, Singh A (2010). "Wenckebach Block due to Hyperkalemia: A Case Report". Emerg Med Int. 2010: 879751. doi: 10.1155/2010/879751 . PMC   3200192 . PMID   22046534.
  9. ↑ Forrester, JD; Mead, P (October 2014). "Third-degree heart block associated with lyme carditis: review of published cases". Clinical Infectious Diseases. 59 (7): 996–1000. doi: 10.1093/cid/ciu411 . PMID   24879781.
  10. ↑ Tintinalli's emergency medicine : a comprehensive study guide. Tintinalli, Judith E.,, Stapczynski, J. Stephan,, Ma, O. John,, Yealy, Donald M.,, Meckler, Garth D.,, Cline, David, 1956- (Eighth ed.). New York. 2015-11-10. p. 123. ISBN   9780071794763. OCLC   915775025.{{cite book}}: CS1 maint: others (link)
  11. ↑ "Third-Degree Atrioventricular Block (Complete Heart Block) Treatment & Management: Approach Considerations, Initial Management Considerations, Atropine and Transcutaneous/Transvenous Pacing". 2018-07-05.{{cite journal}}: Cite journal requires |journal= (help)
  12. 1 2 Oxford textbook of critical care. Webb, Andrew R. (Andrew Roy),, Angus, D. C. (Derek C.), 1962-, Finfer, Simon,, Gattinoni, Luciano,, Singer, Mervyn (Second ed.). Oxford. 2016-05-26. pp. 730–735. ISBN   9780199600830. OCLC   954059445.{{cite book}}: CS1 maint: others (link)
  13. 1 2 Rosen's emergency medicine : concepts and clinical practice. Walls, Ron M.,, Hockberger, Robert S.,, Gausche-Hill, Marianne (Ninth ed.). Philadelphia, PA. 2017-03-09. p. 959. ISBN   9780323390163. OCLC   989157341.{{cite book}}: CS1 maint: others (link)
  14. ↑ "Atrioventricular block, Treatment Options". BMJ Best Practice. BMJ (British Medical Journal). Retrieved 25 August 2015.
  15. ↑ Dretzke, J.; et al. (2004). "Compared to single-chamber ventricular pacemakers, dual-chamber pacemakers may reduce the incidence of complications in people with sick sinus syndrome and atrioventricular block". The Cochrane Database of Systematic Reviews. 2004 (2): CD003710. doi:10.1002/14651858.CD003710.pub2. PMC   8095057 . PMID   15106214 . Retrieved 25 August 2015.
  16. ↑ "Peri-arrest arrhythmias". Resuscitation guidelines. Resuscitation Council UK. Retrieved 25 August 2015.
  17. 1 2 "Atrioventricular Block". The Lecturio Medical Concept Library. Retrieved 3 July 2021.
  18. ↑ Edhag O, Swahn A (1976). "Prognosis of patients with complete heart block or arrhythmic syncope who were not treated with artificial pacemakers. A long-term follow-up study of 101 patients". Acta Med Scand. 200 (6): 457–63. doi:10.1111/j.0954-6820.1976.tb08264.x. PMID   1015354.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.