Sinoatrial block

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Mahmoud Sakr, M.D. [2]

Synonyms and keywords:; SA nodal exit block; exit block; Sino atrial exit block; Sinoatrial nodal block; sino-auricular block

Overview

Sinoatrial block is an uncommon dysrhythmia of unknown mechanism, characterized by the omission of P waves in the setting of a basic regular rhythm. It is found incidentally in normal asymptomatic subjects and in some having pre syncope or syncope. It may occur as an isolated dysrhythmia or in association with sinus bradycardia, tachycardia or, sometimes, with atrioventricular conduction disorders. ^[1]^[2]

Classification

First Degree SA Exit Block

There is a conduction delay (a slowing of conduction not a block or completion cessation in electrical conduction) in the impulse traveling from the sinus node to the atrium and there are no discernible changes on the surface EKG.

Second Degree SA Exit Block

This condition refers to intermittent conduction block (not a delay or slowing of conduction but a complete cessation of conduction) between the sinus node and the atrium.

Type I (Wenckebach Phenomenon) Sinoatrial Exit Block

This is an example of group beating. The P-P cycle (time between two P waves) is progressively shortened until there is a pause. This pause is less than twice the shortest P-P interval. The cycle is then repeated. The pause is due to the dropped P wave and measures less than twice the P-P cycle. It is similar to the behavior of the RR intervals in type I second-degree AV block.

Type II Second Degree Sinoatrial Exit Block

There is an unexpected drop of the P wave. Following this drop, there is a pause in the sinus cycle which is a multiple of the basic sinus cycle. Blocked atrial premature beats sometimes mimic second-degree sinoatrial block.

Third Degree Sinoatrial Exit Block

This SA block cannot be distinguished from sinus arrest when the sinus node ceases to fire. Under such circumstances, subsidiary pacemakers in the AV junction or ventricles may take over.

Causes

Life Threatening Causes

Life-threatening causes include conditions which may result in death or permanent disability within 24 hours if left untreated.

Common Causes

Causes by Organ System

Cardiovascular	Acute coronary syndrome, acute rheumatic fever, Andersen cardiodysrhythmic periodic paralysis, Brugada syndrome, cardiac lymphoma, cardiac tumor, cardio inhibitory syncope, congenital heart disease, congestive heart failure, coronary reperfusion therapy, dilated cardiomyopathy, hypertensive heart disease, hypertrophic cardiomyopathy, ischemic heart disease, Jervell and Lange-Nielsen syndrome, long QT syndrome, myocardial infarction, myocardial rupture, myocarditis, NSTEMI, pericarditis, Romano-Ward syndrome, sick sinus syndrome, sinus bradycardia, sinus node fibrosis, STEMI, tachycardia-bradycardia syndrome, Timothy syndrome, valvular heart disease
Chemical / poisoning	Berberine, grayanotoxin, organophosphate poisoning, parathion poisoning, pyrethroid poisoning, scorpion toxin
Dermatologic	No underlying causes
Drug Side Effect	Acetylcholine, alfentanil, amiodarone, anthracyclines, barbiturate, beta-blockers, bortezomib, bupivacaine, calcium channel blockers, cholinesterase inhibitors, clonidine, dexmedetomidine, digitalis, digoxin, diltiazem, donepezil, edrophonium, fentanyl, flecainide, granisetron, guanethidine, guanfacine, halothane, ibutilide, idarubicin, lacosamide, lidocaine, lithium^[4], magnesium, mepivacaine, mesalamine, methyldopa, mexiletine, neostigmine, nitrous oxide, pentostatin, phenothiazine, phenytoin, procainamide, propafenone, propofol, pyridostigmine, quinidine, remifentanil, rescinnamine, reserpine, rilmenidine, ropivacaine, tacrine, thiamylal, vecuronium, verapamil
Ear Nose Throat	No underlying causes
Endocrine	Diabetic ketoacidosis, thyrotoxic periodic paralysis, pheochromocytoma, profound hypothyroidism
Environmental	Berberine, hypothermia, poisonous spider bites, scorpion toxin
Gastroenterologic	No underlying causes
Genetic	Andersen cardiodysrhythmic periodic paralysis, Brugada syndrome, congenital heart disease, Emery-Dreifuss muscular dystrophy, Jervell and Lange-Nielsen syndrome, Kearns-Sayre syndrome, limb-girdle muscular dystrophy type 1B (LGMD1B), muscular dystrophy, myotonic dystrophy, Romano-Ward syndrome, Timothy syndrome
Hematologic	Hemochromatosis, multiple myeloma
Iatrogenic	Cardiac catheterization, cardiac transplantation, coronary artery bypass grafting, Fontan procedure, heart surgery, infraclavicular brachial plexus block, Maze procedure, post catheter ablation for arrhythmias
Infectious Disease	Acute rheumatic fever, Chagas disease, diptheria, Lyme disease, myocarditis, pericarditis, septic shock, sarcoidosis, systemic lupus erythematosus, tuberculosis
Musculoskeletal / Ortho	Muscular dystrophy, myotonic dystrophy, Timothy syndrome
Neurologic	Carotid sinus hypersensitivity, lateral medullary syndrome, vagal reaction
Nutritional / Metabolic	Hypermagnesemia, metabolic acidosis
Obstetric/Gynecologic	No underlying causes
Oncologic	Cardiac lymphoma, cardiac tumor, multiple myeloma, pheochromocytoma
Opthalmologic	Sjogren's syndrome
Overdose / Toxicity	Acetylcholine, amiodarone, anthracyclines, barbiturate, bortezomib, cholinesterase inhibitors, digitalis, edrophonium, nitrous oxide, phenytoin, propofol
Psychiatric	Takotsubo cardiomyopathy, severe anorexia nervosa
Pulmonary	Hypoxia, sleep apnea
Renal / Electrolyte	Acute renal failure, hyperkalemia
Rheum / Immune / Allergy	Acute rheumatic fever, sarcoidosis, Sjogren's syndrome, scleroderma
Sexual	No underlying causes
Trauma	Myocardial contusion, myocardial rupture, severe brain injury
Urologic	No underlying causes
Dental	No underlying causes
Miscellaneous	Amyloidosis

Causes in Alphabetical Order

Differentiating Sinoatrial block from other Diseases

Other types of SA nodal dysfunction are discussed in detail in other chapters on wikidoc. Follow the hyperlinks for details and those include:

Diagnosis

Treatment

Sinoatrial block principles of treatment are the same as sinus pause or sick sinus syndrome. Usually no treatment is indicated if the patient is asymptomatic. Stopping the offending drug is generally reasonable. When symptoms occur and become intolerable or life-threatening, then a permanent pacemaker would be indicated.

References

↑ GREENWOOD RJ, FINKELSTEIN D, MONHEIT R (1961). "Sinoatrial heart block with Wenckebach phenomenon". Am J Cardiol. 8: 140–6. PMID 13708372.
↑ Dighton DH (1975). "Sinoatrial block. Autonomic influences and clinical assessment". Br Heart J. 37 (3): 321–5. PMC 483972. PMID 1138735.CS1 maint: PMC format (link)
↑ Boujnah MR, Jaafari A, Boukhris B, Boussabah I, Thameur M (2000). "[Sinoatrial block induced by therapeutic doses of diltiazem. Report of 3 cases]". Tunis Med. 78 (12): 735–7. PMID 11155380.
↑ Eliasen P, Andersen M (1975). "Sinoatrial block during lithium treatment". Eur J Cardiol. 3 (2): 97–8. PMID 1183468.
↑ Bailey PL (1990). "Sinus arrest induced by trivial nasal stimulation during alfentanil-nitrous oxide anaesthesia". Br J Anaesth. 65 (5): 718–20. PMID 2248851.
↑ ^6.0 ^6.1 ^6.2 Mills TA, Kawji MM, Cataldo VD, Pappas ND, O'Meallie LP, Breaux DM; et al. (2004). "Profound sinus bradycardia due to diltiazem, verapamil, and/or beta-adrenergic blocking drugs". J La State Med Soc. 156 (6): 327–31. PMID 15688675.
↑ ^7.0 ^7.1 Lines D, Shipton EA (1991). "Severe bradycardia and sinus arrest after administration of vecuronium, fentanyl and halothane. A case report". S Afr Med J. 80 (4): 200–1. PMID 1678901.
↑ Bonvini RF, Hendiri T, Anwar A (2006). "Sinus arrest and moderate hyperkalemia". Annales De Cardiologie Et D'angéiologie. 55 (3): 161–3. PMID 16792034. Unknown parameter |month= ignored (help)
↑ Koay S, Dewan B (2013). "An unexpected Holter monitor result: multiple sinus arrests in a patient with lateral medullary syndrome". BMJ Case Rep. 2013. doi:10.1136/bcr-2012-007783. PMID 23386489.

Template:WikiDoc Sources

[pmid13708372-1] GREENWOOD RJ, FINKELSTEIN D, MONHEIT R (1961). "Sinoatrial heart block with Wenckebach phenomenon". Am J Cardiol. 8: 140–6. PMID 13708372.

[pmid1138735-2] Dighton DH (1975). "Sinoatrial block. Autonomic influences and clinical assessment". Br Heart J. 37 (3): 321–5. PMC 483972. PMID 1138735.CS1 maint: PMC format (link)

[pmid11155380-3] Boujnah MR, Jaafari A, Boukhris B, Boussabah I, Thameur M (2000). "[Sinoatrial block induced by therapeutic doses of diltiazem. Report of 3 cases]". Tunis Med. 78 (12): 735–7. PMID 11155380.

[pmid1183468-4] Eliasen P, Andersen M (1975). "Sinoatrial block during lithium treatment". Eur J Cardiol. 3 (2): 97–8. PMID 1183468.

[pmid2248851-5] Bailey PL (1990). "Sinus arrest induced by trivial nasal stimulation during alfentanil-nitrous oxide anaesthesia". Br J Anaesth. 65 (5): 718–20. PMID 2248851.

[pmid15688675-6] 6.0 ^6.1 ^6.2 Mills TA, Kawji MM, Cataldo VD, Pappas ND, O'Meallie LP, Breaux DM; et al. (2004). "Profound sinus bradycardia due to diltiazem, verapamil, and/or beta-adrenergic blocking drugs". J La State Med Soc. 156 (6): 327–31. PMID 15688675.

[pmid1678901-7] 7.0 ^7.1 Lines D, Shipton EA (1991). "Severe bradycardia and sinus arrest after administration of vecuronium, fentanyl and halothane. A case report". S Afr Med J. 80 (4): 200–1. PMID 1678901.

[pmid16792034-8] Bonvini RF, Hendiri T, Anwar A (2006). "Sinus arrest and moderate hyperkalemia". Annales De Cardiologie Et D'angéiologie. 55 (3): 161–3. PMID 16792034. Unknown parameter |month= ignored (help)

[pmid23386489-9] Koay S, Dewan B (2013). "An unexpected Holter monitor result: multiple sinus arrests in a patient with lateral medullary syndrome". BMJ Case Rep. 2013. doi:10.1136/bcr-2012-007783. PMID 23386489.

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