Atrioventricular block

Overview
An atrioventricular block (or AV block) is a type of heart block involving in impairment of the conduction between the atria and ventricles of the heart. It usually involves the atrioventricular node, but it can involve other structures.

Classification

 * First Degree AV Block,
 * Prolongation of PR interval
 * Second Degree AV Block also known as Mobitz I and Mobitz II
 * Type I (Wenchebach)
 * Progressive prolongation of PR before dropped beat.
 * Usually in AV node
 * Type II
 * No change in PR interval before dropped beat
 * Usually infranodal
 * Third Degree AV Block also known as complete heart block
 * No relationship between Atrial and ventricular activity.

Intrinsic Etiology

 * Congenital
 * Degenerative (Lev’s and Lenegre’s)
 * Ischemia
 * Infiltrative (Sarcoidosis, Amyloidosis, Hemochromatosis)
 * Inflammatory (systemic lupus erythematosus (SLE), Scleroderma, rheumatoid arthritis (RA))
 * Myopathic (Myotonic Dystrophy, Erbs Palsy)
 * Infectious (Lyme, Endocarditis, Chagas)
 * Trauma (Valve Replacement, Line insertions)

Extrinsic Etiology

 * Autonomic (Carotid hypersensitivity, situational, vasovagal)
 * Medications (Beta blockers, calcium-channel blocker (CCB), Digoxin, Clonidine, antiarrhythmics)
 * Hypothyroidism
 * Hypothermia
 * Neurologic
 * Electrolytes (Hyperkalemia, Hypokalemia)

Normal Variants

 * 1) PR prolongation can be found in 0.5% of healthy patients
 * 2) Second degree block type I may be seen in healthy patients during sleep
 * 3) Transient AV block can occur with vagal maneuvers

ST Elevation MI
In acute ST elevation MI:
 * First degree block occurs in 8% to 13%
 * Second degree block in 3.5% to 10%
 * Complete heart block in 2.5% to 8%

Inferior ST Elevation MI

 * Inferior ST elevation MI: AV block is more common in patients with inferior MIs (1/3rd of patients)
 * 1) In 90% of patients the inferior wall is supplied by the RCA which gives off a branch to the AV node
 * 2) As a rule the AV block is transient and normal function returns within a week of the acute episode

Anterior ST Elevation MI

 * Anterior ST elevation MI: AV block may be seen in up to 21%
 * 1) Incidence of second degree AV block and third degree AV block is 5 to 7%
 * 2) Block is the result of damage to the interventricular septum supplied by the LAD
 * 3) There is damage to the bundle branches either in the form of bilateral bundle branch block or trifascicular block
 * 4) RBBB, RBBB + LAHB, RBBB + LPHB or LBBB often appear before the development of AV block
 * 5) The PR is normal or minimally prolonged before the onset of second degree AV block or third degree AV block
 * 6) Although the AV block is usually transient, there is a relatively high incidence of recurrence or high-degree AV block after the acute event
 * 7) In addition to ischemia, fibrosis and calcification of the summit of the ventricular septum that involve the branching part of the bundle branches, may play a role in the genesis of the conduction defect.
 * 8) It used to be thought that CAD was the most frequent cause of chronic complete AV block, but it actually causes only 15% of cases

Degenerative Diseases

 * Sclerodegenerative disease of the bundle branches first described by Lenegre
 * The pathologic process is called idiopathic bilateral bundle branch fibrosis and the heart block is called primary heart block
 * This is the most common cause of chronic AV block (46%)
 * Lev described similar degenerative lesions, which he referred to as sclerosis of the left side of the cardiac skeleton. There is progressive fibrosis and calcification of the mitral annulus, the central fibrous body, the pars membranacea, the base of the aorta, and the summit of the muscular ventricular septum. Various portions of the His bundle or the bundle branches may be involved, resulting in AV block.

Hypertension

 * Chronic AV block in patients with HTN is thought to be due to CAD or sclerosis of the left side of the cardiac skeleton exacerbated by hypertension

Diseases of the Myocardium

 * Acute rheumatic fever: PR prolongation is a common (25 to 95% of cases) sign in patients with acute rheumatic fever
 * Type I second degree AV block may occur, but complete AV block is uncommon
 * usually transient, disappears when the patient recovers


 * Amyloidosis
 * Ankylosing spondylitis
 * Chagas disease
 * Dermatomyositis
 * Dilated cardiomyopathy results in various degrees of heart block are seen in 15% of patients
 * Diphtheria
 * HCM: 3% of patients with HCM will develop heart block
 * Hemochromatosis
 * Lyme disease
 * Muscular dystrophy
 * Myocarditis
 * Sarcoid
 * Scleroderma
 * SLE
 * Tumors, primary and secondary

Valvular Heart Disease
Valvular Diseases
 * Calcific aortic stenosis may be accompanied by chronic partial or complete AV block
 * There is an extension of the calcification to involve the main bundle or its bifurcation, resulting in degeneration and necrosis of the conduction tissue
 * May also occur in rheumatic mitral valve disease, but is less common
 * Occasionally, massive calcification of the mitral annulus as an aging process may cause AV block
 * May also be seen in bacterial endocarditis, especially of the aortic valve

Drugs

 * Digoxin is one of the most common causes of reversible AV block
 * When second degree AV block is induced, it is always of the Type I variety
 * When complete block occurs, the QRS complexes are narrow because the block is of the AV node
 * The ventricular response rate is more rapid than that due to organic lesions, and increased automaticity of the AV junctional pacemaker may be responsible.


 * Quinidine and Procainamide may produce slight prolongation of the PR
 * β blockers may cause AV block
 * Diltiazem and verapamil may cause AV conduction delay and PR interval prolongation

Congenital

 * Occurs in the absence of other evidence of organic heart disease
 * Site is usually proximal to the bifurcation of the His bundle, most often in the AV node
 * Narrow QRS with a rate > 40 beats per minute
 * Frequently seen in those with corrected transposition of the great vessels, and occasionally in ASDs and Ebstein's anomaly

Trauma

 * May be induced during open heart surgery in the area of AV conduction tissue
 * Seen in patients operated on for the correction of VSD, tetralogy of Fallot, and endocardial cushion defect.
 * May be due to edema, transient ischemia, or actual disruption of the conduction tissue. The block may therefore be permanent or transient.
 * Also reported with both penetrating and non-penetrating trauma of the chest

Treatment

 * Remove extrinsic causes
 * Treat reversible intrinsic causes

Acute Pharmacotherapies

 * Pharmacologic interventions (Atropine, Isoproterenol, Theophylline)

Surgery and Device Based Therapy

 * Temporary Pacing
 * Permant Pacing

Indications for Surgery and Device Based Therapy
Indications for Permanent Pacemaker in Acquired Atrioventricular Block in Adults (AHA, 1998)
 * Class I
 * Third-degree AV block plus:
 * Symptoms related to bradycardia
 * Arrhythmia or other condition requiring nodal blockers
 * Asystole > 3 seconds (while awake), ventricular rate <40
 * Neuromeuscular disease
 * Second Degree AV block plus:
 * Symptomatic Bradycardia
 * Class II
 * Asymptomatic Third-degree AV Block with HR >40
 * Asymptomatic Type II, second-degreee AV Block
 * Asymptomatic Type I, second-degree AV Block (with wide complex)
 * Class III
 * Asymptomatic Type I, second-degree AV block (with narrow complex)

==ACC / AHA Guidelines- Recommendations for Acquired Atrioventricular Block in Adults (DO NOT EDIT) == {{cquote|

Class I
1. Permanent pacemaker implantation is indicated for third-degree and advanced second-degree AV block at any anatomic level associated with bradycardia with symptoms (including heart failure) or ventricular arrhythmias presumed to be due to AV block. (Level of Evidence: C)

2. Permanent pacemaker implantation is indicated for third-degree and advanced second-degree AV block at any anatomic level associated with arrhythmias and other medical conditions that require drug therapy that results in symptomatic bradycardia. (Level of Evidence: C)

3. Permanent pacemaker implantation is indicated for third-degree and advanced second-degree AV block at any anatomic level in awake, symptom-free patients in sinus rhythm, with documented periods of asystole greater than or equal to 3.0 seconds86 or any escape rate less than 40 bpm, or with an escape rhythm that is below the AV node. (Level of Evidence: C)

4. Permanent pacemaker implantation is indicated for third-degree and advanced second-degree AV block at any anatomic level in awake, symptom-free patients with AF and bradycardia with 1 or more pauses of at least 5 seconds or longer. (Level of Evidence: C)

5. Permanent pacemaker implantation is indicated for third-degree and advanced second-degree AV block at any anatomic level after catheter ablation of the AV junction. (Level of Evidence: C)

6. Permanent pacemaker implantation is indicated for third-degree and advanced second-degree AV block at any anatomic level associated with postoperative AV block that is not expected to resolve after cardiac surgery. (Level of Evidence: C)

7. Permanent pacemaker implantation is indicated for third-degree and advanced second-degree AV block at any anatomic level associated with neuromuscular diseases with AV block, such as myotonic muscular dystrophy, Kearns-Sayre syndrome, Erb dystrophy (limb-girdle muscular dystrophy), and peroneal muscular atrophy, with or without symptoms. (Level of Evidence: B)

8. Permanent pacemaker implantation is indicated for second-degree AV block with associated symptomatic bradycardia regardless of type or site of block. (Level of Evidence: B)

9. Permanent pacemaker implantation is indicated for asymptomatic persistent third-degree AV block at any anatomic site with average awake ventricular rates of 40 bpm or faster if cardiomegaly or LV dysfunction is present or if the site of block is below the AV node. (Level of Evidence: B)

10. Permanent pacemaker implantation is indicated for second- or third-degree AV block during exercise in the absence of myocardial ischemia. (Level of Evidence: C)

Class IIa
1. Permanent pacemaker implantation is reasonable for persistent third-degree AV block with an escape rate greater than 40 bpm in asymptomatic adult patients without cardiomegaly. (Level of Evidence: C)

2. Permanent pacemaker implantation is reasonable for asymptomatic second-degree AV block at intra- or infra-His levels found at electrophysiological study. (Level of Evidence: B)

3. Permanent pacemaker implantation is reasonable for first- or second-degree AV block with symptoms similar to those of pacemaker syndrome or hemodynamic compromise. (Level of Evidence: B)

4. Permanent pacemaker implantation is reasonable for asymptomatic type II second-degree AV block with a narrow QRS. When type II second-degree AV block occurs with a wide QRS, including isolated right bundle-branch block, pacing becomes a Class I recommendation. (See Section 2.1.3, “Chronic Bifascicular Block.”) (Level of Evidence: B)

Class IIb
1. Permanent pacemaker implantation may be considered for neuromuscular diseases such as myotonic muscular dystrophy, Erb dystrophy (limb-girdle muscular dystrophy), and peroneal muscular atrophy with any degree of AV block (including first-degree AV block), with or without symptoms, because there may be unpredictable progression of AV conduction disease. (Level of Evidence: B)

2. Permanent pacemaker implantation may be considered for AV block in the setting of drug use and/or drug toxicity when the block is expected to recur even after the drug is withdrawn. (Level of Evidence: B)

Class III
1. Permanent pacemaker implantation is not indicated for asymptomatic first-degree AV block. (Level of Evidence: B) (See Section 2.1.3, “Chronic Bifascicular Block.”)

2. Permanent pacemaker implantation is not indicated for asymptomatic type I second-degree AV block at the supra-His (AV node) level or that which is not known to be intra- or infra-Hisian. (Level of Evidence: C)

3. Permanent pacemaker implantation is not indicated for AV block that is expected to resolve and is unlikely to recur (e.g., drug toxicity, Lyme disease, or transient increases in vagal tone or during hypoxia in sleep apnea syndrome in the absence of symptoms). (Level of Evidence: B)}}