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===Common Causes===
===Common Causes===
The most common causes of first degree heart block are an AV nodal disease, enhanced vagal tone (for example in athletes), ,  (especially acute inferior MI), electrolyte disturbances and [[drugs]].  The drugs that most commonly cause first degree heart block are those that increase the refractory time of the [[AV node]], thereby slowing AV conduction. These include [[calcium channel blockers]], [[beta-blockers]], [[digitalis]],[[cardiac glycosides]] and anything that increases [[cholinergic]] activity such as [[cholinesterase inhibitor]]s.
* Normal variants
** [[PR prolongation]] can be found in 0.5% of healthy patients.
** Transient AV block can occur with [[vagal maneuvers]].


* Acute ST elevation MI - [[First degree block]] occurs in 8% to 13% of patients.
Enhanced vagal tone in athletes
** Inferior ST elevation [[MI]]: [[AV block]] is more common in patients with inferior [[MI]]s (1/3rd of patients).
*** In 90% of patients the inferior wall is supplied by the [[RCA]] which gives off a branch to the [[AV node]].
*** As a rule the [[AV block]] is transient and normal function returns within a week of the acute episode.
** Anterior ST elevation [[MI]]: [[AV block]] may be seen in up to 21%.
*** Block is the result of damage to the interventricular septum supplied by the [[LAD]]
*** There is damage to the bundle branches either in the form of bilateral bundle branch block or [[trifascicular block]].
*** [[RBBB]], [[RBBB]] + [[LAHB]], [[RBBB]] + [[LPHB]] or [[LBBB]] often appear before the development of [[AV block]].
*** The PR is normal or minimally prolonged before the onset of [[second degree AV block]] or [[third degree AV block]].
*** Although the [[AV block]] is usually transient, there is a relatively high incidence of recurrence or high-degree AV block after the acute event.
*** 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.


electrolyte disturbances
[[drugs]]; [[calcium channel blockers]], [[beta-blockers]], [[digitalis]],[[cardiac glycosides]], [[cholinesterase inhibitor|cholinesterase inhibitors]].
* Normal variants of [[PR prolongation]]
* [[Vagal maneuvers]]
* Acute MI - esp [[inferior MI)
* Degenerative diseases
* 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's disease]]: 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]].


* Idiopathic bilateral bundle branch fibrosis and the heart block is called primary heart block
**[[Lev's disease]]:
* Hypertension
* 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]]
* 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]]
** [[Acute rheumatic fever]]: PR prolongation is a common (25 to 95% of cases) sign in patients with [[acute rheumatic fever]]
** [[Dilated cardiomyopathy]]  
*** Usually transient, disappears when the patient recovers
** [[Dilated cardiomyopathy]] results in various degrees of heart block are seen in 15% of patients
** [[HCM]]: 3% of patients with [[HCM]] will develop heart block
** [[HCM]]: 3% of patients with [[HCM]] will develop heart block
** [[Myocarditis]]
** [[Myocarditis]]
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** May also occur in rheumatic mitral valve disease, but is less common
** 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]]
** 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]]
* May also be seen in [[bacterial endocarditis]], especially of the [[aortic valve]]
** [[Ebstein's anomaly]]  may be associated with first-degree AV block.
* [[Ebstein's anomaly]]  may be associated with first-degree AV block.


* Drugs
* Drugs

Revision as of 17:02, 21 August 2013

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2]; Raviteja Guddeti, M.B.B.S. [3] Synonyms and keywords:

Overview

Causes

Life Threatening Causes

Life-threatening conditions can result in death or permanent disability within 24 hours if left untreated.

Common Causes

Enhanced vagal tone in athletes

electrolyte disturbances drugs; calcium channel blockers, beta-blockers, digitalis,cardiac glycosides, cholinesterase inhibitors.

  • Idiopathic bilateral bundle branch fibrosis and the heart block is called primary heart 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
  • Valvular Heart Disease
    • 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
  • Ebstein's anomaly may be associated with first-degree AV block.

First degree heart block is not an absolute contraindication for the use of these drugs but caution should be maintained while using these drugs in patients with first degree block, as exposure to these drugs increases the risk of developing a higher grade block.

  • 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

Causes by Organ System

Cardiovascular AV nodal disease, Myocarditis, Acute myocardial infarction (especially acute inferior MI), Hypertension, Acute rheumatic fever, Dilated cardiomyopathy, HCM, Myocarditis, Valvular heart disease, Transposition of the great vessels, ASDs, Ebstein's anomaly, VSD, Tetralogy of Fallot, Endocardial cushion defect, Lev's disease
Chemical / poisoning No underlying causes
Dermatologic No underlying causes
Drug Side Effect Calcium channel blockers, Beta-blockers, Digitalis, Cardiac glycosides, Cholinesterase inhibitors, Quinidine, Procainamide, Disopyramide, Flecainide, Encainide, Propafenone, Amiodarone, Sotalol, Dofetilide, Ibutilide, Magnesium
Ear Nose Throat No underlying causes
Endocrine No underlying causes
Environmental No underlying causes
Gastroenterologic Hemochromatosis
Genetic No underlying causes
Hematologic No underlying causes
Iatrogenic No underlying causes
Infectious Disease Acute rheumatic fever, Chagas disease, Diphtheria, Lyme disease, Myocarditis, Tuberculosis
Musculoskeletal / Ortho Ankylosing spondylitis, Muscular dystrophy
Neurologic No underlying causes
Nutritional / Metabolic No underlying causes
Obstetric/Gynecologic No underlying causes
Oncologic No underlying causes
Opthalmologic No underlying causes
Overdose / Toxicity No underlying causes
Psychiatric No underlying causes
Pulmonary Sarcoidosis
Renal / Electrolyte No underlying causes
Rheum / Immune / Allergy Ankylosing spondylitis, Dermatomyositis, Scleroderma, SLE, Rheumatoid arthritis
Sexual No underlying causes
Trauma No underlying causes
Urologic No underlying causes
Dental No underlying causes
Miscellaneous Amyloidosis, Enhanced vagal tone (for example in athletes), Normal variants

Causes in Alphabetical Order

References


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