Bradycardia pathophysiology: Difference between revisions

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==Overview==
==Overview==
It is difficult and sometimes impossible to assign a mechanism to any particular [[bradycardia]]. There are generally two types of problems that result in bradycardia: [[Sinus node dysfunction]] and [[Atrioventricular node|AV node dysfunction]]. However other pathophysiologic conditions can also result in bradycardia such as [[Acute Myocardial infarction]], [[Obstructive sleep apnea]], Exaggerated vagal activity, Increased intracranial pressure and infectious diseases such as [[Lyme disease]], [[Rocky Mountain spotted fever|rocky mountain spotted fever]], [[Chagas disease]], [[psittacosis]], [[Q fever]] and [[typhoid fever]].
[[Bradycardia]] generally results from [[sinus node dysfunction]] and [[atrioventricular node|AV node dysfunction]]. However, other pathophysiologic conditions can also result in [[bradycardia]] such as acute [[Myocardial infarction]], [[obstructive sleep apnea]], exaggerated vagal activity, increased [[intracranial pressure]], and infectious diseases such as [[Lyme disease]], [[rocky Mountain spotted fever|rocky mountain spotted fever]], [[chagas disease]], [[psittacosis]], [[Q fever]], and [[typhoid fever]].


==Pathophysiology==
==Pathophysiology==


It is difficult and sometimes impossible to assign a mechanism to any particular [[bradycardia]]. However, the underlying mechanism is not clinically relevant to treatment, which is the same in both cases of sick sinus syndrome: a permanent [[artificial pacemaker|pacemaker]].  
The underlying mechanism is not clinically relevant to the treatment.  


There are generally two types of problems that result in bradycardia:
There are generally two types of problems that result in [[bradycardia]]:
===Disorders of the [[sinus node]]===


*Impaired automaticity - Sinus node dysfunction/[[sick sinus syndrome]])<ref name="pmid6620520">{{cite journal| author=Alpert MA, Flaker GC| title=Arrhythmias associated with sinus node dysfunction. Pathogenesis, recognition, and management. | journal=JAMA | year= 1983 | volume= 250 | issue= 16 | pages= 2160-6 | pmid=6620520 | doi= | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=6620520  }} </ref>
===Disorders of the sinus node===
*Exit block - Impaired conduction of the impulse from the sinus node into the surrounding [[atrial]] tissue


===Disorders of the [[atrioventricular node]] (AV node)===
*Impaired [[automaticity]] - [[Sinus node]] dysfunction/[[sick sinus syndrome]])<ref name="pmid6620520">{{cite journal| author=Alpert MA, Flaker GC| title=Arrhythmias associated with sinus node dysfunction. Pathogenesis, recognition, and management. | journal=JAMA | year= 1983 | volume= 250 | issue= 16 | pages= 2160-6 | pmid=6620520 | doi= | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=6620520  }} </ref><ref name="BrodskyWu1977">{{cite journal|last1=Brodsky|first1=Michael|last2=Wu|first2=Delon|last3=Denes|first3=Pablo|last4=Kanakis|first4=Charles|last5=Rosen|first5=Kenneth M.|title=Arrhythmias documented by 24 hour continuous electrocardiographic monitoring in 50 male medical students without apparent heart disease|journal=The American Journal of Cardiology|volume=39|issue=3|year=1977|pages=390–395|issn=00029149|doi=10.1016/S0002-9149(77)80094-5}}</ref>


*Atrioventricular conduction disturbances ([[First degree AV block|1<sup>o</sup> AV block]], [[Second degree AV block|2<sup>o</sup> type I AV block]], [[Second degree AV block|2<sup>o</sup> type II AV block]], [[Third degree AV block|3<sup>o</sup> AV block]]) may result from impaired conduction in the [[AV node]], or anywhere below it, such as in the [[bundle of HIS]].
===Disorders of the atrioventricular node (AV node)===


[[Sinus bradycardia]] can also be seen in these pathophysiologic settings:
*[[Atrioventricular]] conduction disturbances result from impaired conduction in the [[AV node]], or anywhere below it, such as in the [[bundle of HIS]].
 
Sinus bradycardia can also be seen in these pathophysiologic settings:<ref name="pmid29630253">{{cite journal| author=| title=StatPearls | journal= | year= 2020 | volume=  | issue=  | pages=  | pmid=29630253 | doi= | pmc= | url= }}</ref><ref name="NofLuria2007">{{cite journal|last1=Nof|first1=Eyal|last2=Luria|first2=David|last3=Brass|first3=Dovrat|last4=Marek|first4=Dina|last5=Lahat|first5=Hadas|last6=Reznik-Wolf|first6=Haya|last7=Pras|first7=Elon|last8=Dascal|first8=Nathan|last9=Eldar|first9=Michael|last10=Glikson|first10=Michael|title=Point Mutation in the HCN4 Cardiac Ion Channel Pore Affecting Synthesis, Trafficking, and Functional Expression Is Associated With Familial Asymptomatic Sinus Bradycardia|journal=Circulation|volume=116|issue=5|year=2007|pages=463–470|issn=0009-7322|doi=10.1161/CIRCULATIONAHA.107.706887}}</ref>


===Acute Myocardial infarction===
===Acute Myocardial infarction===


*Patients with acute [[myocardial infarction]], especially those with the [[right coronary artery]], as it supplies the [[SA node]] are affected by [[bradycardia]].<ref name="pmid31060863">{{cite journal |vauthors=Davis WT, Montrief T, Koyfman A, Long B |title=Dysrhythmias and heart failure complicating acute myocardial infarction: An emergency medicine review |journal=Am J Emerg Med |volume=37 |issue=8 |pages=1554–1561 |date=August 2019 |pmid=31060863 |doi=10.1016/j.ajem.2019.04.047 |url=}}</ref>
*Patients with acute [[myocardial infarction]], especially those with the right [[coronary artery]], are affected by [[bradycardia]] as it supplies the [[SA node]].<ref name="pmid31060863">{{cite journal |vauthors=Davis WT, Montrief T, Koyfman A, Long B |title=Dysrhythmias and heart failure complicating acute myocardial infarction: An emergency medicine review |journal=Am J Emerg Med |volume=37 |issue=8 |pages=1554–1561 |date=August 2019 |pmid=31060863 |doi=10.1016/j.ajem.2019.04.047 |url=}}</ref>


===Obstructive sleep apnea===
===Obstructive sleep apnea===
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===Exaggerated vagal activity===
===Exaggerated vagal activity===


*Vasovagal responses may be associated with severe [[bradycardia]] due to elevated [[Parasympathetic nervous system|parasympathetic]] involvement and [[sympathetic]] suppression of the [[SA node]]. These stimuli include [[carotid sinus]] stimulation, [[vomiting]], [[coughing]], and [[Valsalva maneuver]].
*[[Vasovagal]] responses may be associated with severe [[bradycardia]] due to elevated [[Parasympathetic nervous system|parasympathetic]] involvement and [[sympathetic]] suppression of the [[SA node]]. These stimuli include [[carotid sinus]] stimulation, [[vomiting]], [[coughing]], and [[Valsalva maneuver]].


===Increased intracranial pressure===
===Increased intracranial pressure===


*Increased intracranial pressure should be excluded when [[sinus bradycardia]] arises in a patient with neurological dysfunction.[[Sinus bradycardia]] is often associated with damage to the [[cervical]] or [[thoracic]] spine, where the [[sympathetic]] denervation of the heart leaves an uncontested [[parasympathetic]] tone.<ref name="pmid7566833">{{cite journal| author=Gilson GJ, Miller AC, Clevenger FW, Curet LB| title=Acute spinal cord injury and neurogenic shock in pregnancy. | journal=Obstet Gynecol Surv | year= 1995 | volume= 50 | issue= 7 | pages= 556-60 | pmid=7566833 | doi=10.1097/00006254-199507000-00022 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=7566833  }} </ref>
*Increased intracranial pressure should be excluded when [[sinus bradycardia]] arises in a patient with neurological dysfunction. [[Sinus bradycardia]] is often associated with damage to the [[cervical]] or [[thoracic]] spine, where the [[sympathetic]] denervation of the heart leaves an uncontested [[parasympathetic]] tone.<ref name="pmid7566833">{{cite journal| author=Gilson GJ, Miller AC, Clevenger FW, Curet LB| title=Acute spinal cord injury and neurogenic shock in pregnancy. | journal=Obstet Gynecol Surv | year= 1995 | volume= 50 | issue= 7 | pages= 556-60 | pmid=7566833 | doi=10.1097/00006254-199507000-00022 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=7566833  }} </ref>


===Infectious causes===
===Infectious causes===


*Infectious agents associated with relative [[sinus bradycardia]] include [[Lyme disease]], [[Chagas disease]], [[legionella]], [[psittacosis]], [[Q fever]], [[typhoid fever]], [[typhus]], [[babesiosis]], [[malaria]], [[leptospirosis]], [[yellow fever]], [[dengue fever]], [[Viral hemorrhagic fever|viral hemorrhagic fevers]], [[trichinosis]], and [[Rocky Mountain spotted fever|Rocky Mountain Spotted fever]]. <ref name="pmid11284920">{{cite journal| author=Cunha BA| title=The diagnostic significance of relative bradycardia in infectious disease. | journal=Clin Microbiol Infect | year= 2000 | volume= 6 | issue= 12 | pages= 633-4 | pmid=11284920 | doi=10.1046/j.1469-0691.2000.0194f.x | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11284920  }} </ref><ref name="pmid15949188">{{cite journal| author=Puljiz I, Beus A, Kuzman I, Seiwerth S| title=Electrocardiographic changes and myocarditis in trichinellosis: a retrospective study of 154 patients. | journal=Ann Trop Med Parasitol | year= 2005 | volume= 99 | issue= 4 | pages= 403-11 | pmid=15949188 | doi=10.1179/136485905X36307 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15949188  }} </ref>
*[[Infection|Infectious]] agents associated with relative [[sinus bradycardia]] include [[Lyme disease]], [[Chagas disease]], [[legionella]], [[psittacosis]], [[Q fever]], [[typhoid fever]], [[typhus]], [[babesiosis]], [[malaria]], [[leptospirosis]], [[yellow fever]], [[dengue fever]], [[Viral hemorrhagic fever|viral hemorrhagic fevers]], [[trichinosis]], and [[Rocky Mountain spotted fever|Rocky Mountain Spotted fever]]. <ref name="pmid11284920">{{cite journal| author=Cunha BA| title=The diagnostic significance of relative bradycardia in infectious disease. | journal=Clin Microbiol Infect | year= 2000 | volume= 6 | issue= 12 | pages= 633-4 | pmid=11284920 | doi=10.1046/j.1469-0691.2000.0194f.x | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11284920  }} </ref><ref name="pmid15949188">{{cite journal| author=Puljiz I, Beus A, Kuzman I, Seiwerth S| title=Electrocardiographic changes and myocarditis in trichinellosis: a retrospective study of 154 patients. | journal=Ann Trop Med Parasitol | year= 2005 | volume= 99 | issue= 4 | pages= 403-11 | pmid=15949188 | doi=10.1179/136485905X36307 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15949188  }} </ref>
 
===Microscopic Pathology===
 
*On [[microscopic]] [[histopathological]] analysis,  a few patients with sinus [[bradycardia]] may show no nodal [[histopathology]], yet some [[microscopic]] findings are associated with the condition which includes the following:<ref name="pmid17646576">{{cite journal| author=Nof E, Luria D, Brass D, Marek D, Lahat H, Reznik-Wolf H | display-authors=etal| title=Point mutation in the HCN4 cardiac ion channel pore affecting synthesis, trafficking, and functional expression is associated with familial asymptomatic sinus bradycardia. | journal=Circulation | year= 2007 | volume= 116 | issue= 5 | pages= 463-70 | pmid=17646576 | doi=10.1161/CIRCULATIONAHA.107.706887 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=17646576  }}</ref><ref name="pmid15302799">{{cite journal| author=Sanders P, Kistler PM, Morton JB, Spence SJ, Kalman JM| title=Remodeling of sinus node function in patients with congestive heart failure: reduction in sinus node reserve. | journal=Circulation | year= 2004 | volume= 110 | issue= 8 | pages= 897-903 | pmid=15302799 | doi=10.1161/01.CIR.0000139336.69955.AB | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15302799  }}</ref>
**[[Nodal (protein)|Nodal]] cell reduction
**[[Nodal (protein)|Nodal]] cell and [[fibrosis]]
**[[Amyloidosis]] in the [[Nodal (protein)|nodal]] region
**[[Sinus node]] [[hypoplasia]]


==References==
==References==

Latest revision as of 14:46, 23 September 2020

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: M.Umer Tariq [2] Ibtisam Ashraf, M.B.B.S.[3]

Overview

Bradycardia generally results from sinus node dysfunction and AV node dysfunction. However, other pathophysiologic conditions can also result in bradycardia such as acute Myocardial infarction, obstructive sleep apnea, exaggerated vagal activity, increased intracranial pressure, and infectious diseases such as Lyme disease, rocky mountain spotted fever, chagas disease, psittacosis, Q fever, and typhoid fever.

Pathophysiology

The underlying mechanism is not clinically relevant to the treatment.

There are generally two types of problems that result in bradycardia:

Disorders of the sinus node

Disorders of the atrioventricular node (AV node)

Sinus bradycardia can also be seen in these pathophysiologic settings:[3][4]

Acute Myocardial infarction

Obstructive sleep apnea

Exaggerated vagal activity

Increased intracranial pressure

Infectious causes

Microscopic Pathology

References

  1. Alpert MA, Flaker GC (1983). "Arrhythmias associated with sinus node dysfunction. Pathogenesis, recognition, and management". JAMA. 250 (16): 2160–6. PMID 6620520.
  2. Brodsky, Michael; Wu, Delon; Denes, Pablo; Kanakis, Charles; Rosen, Kenneth M. (1977). "Arrhythmias documented by 24 hour continuous electrocardiographic monitoring in 50 male medical students without apparent heart disease". The American Journal of Cardiology. 39 (3): 390–395. doi:10.1016/S0002-9149(77)80094-5. ISSN 0002-9149.
  3. "StatPearls". 2020. PMID 29630253.
  4. Nof, Eyal; Luria, David; Brass, Dovrat; Marek, Dina; Lahat, Hadas; Reznik-Wolf, Haya; Pras, Elon; Dascal, Nathan; Eldar, Michael; Glikson, Michael (2007). "Point Mutation in the HCN4 Cardiac Ion Channel Pore Affecting Synthesis, Trafficking, and Functional Expression Is Associated With Familial Asymptomatic Sinus Bradycardia". Circulation. 116 (5): 463–470. doi:10.1161/CIRCULATIONAHA.107.706887. ISSN 0009-7322.
  5. Davis WT, Montrief T, Koyfman A, Long B (August 2019). "Dysrhythmias and heart failure complicating acute myocardial infarction: An emergency medicine review". Am J Emerg Med. 37 (8): 1554–1561. doi:10.1016/j.ajem.2019.04.047. PMID 31060863.
  6. Caples SM, Rosen CL, Shen WK, Gami AS, Cotts W, Adams M; et al. (2007). "The scoring of cardiac events during sleep". J Clin Sleep Med. 3 (2): 147–54. PMID 17557424.
  7. Gilson GJ, Miller AC, Clevenger FW, Curet LB (1995). "Acute spinal cord injury and neurogenic shock in pregnancy". Obstet Gynecol Surv. 50 (7): 556–60. doi:10.1097/00006254-199507000-00022. PMID 7566833.
  8. Cunha BA (2000). "The diagnostic significance of relative bradycardia in infectious disease". Clin Microbiol Infect. 6 (12): 633–4. doi:10.1046/j.1469-0691.2000.0194f.x. PMID 11284920.
  9. Puljiz I, Beus A, Kuzman I, Seiwerth S (2005). "Electrocardiographic changes and myocarditis in trichinellosis: a retrospective study of 154 patients". Ann Trop Med Parasitol. 99 (4): 403–11. doi:10.1179/136485905X36307. PMID 15949188.
  10. Nof E, Luria D, Brass D, Marek D, Lahat H, Reznik-Wolf H; et al. (2007). "Point mutation in the HCN4 cardiac ion channel pore affecting synthesis, trafficking, and functional expression is associated with familial asymptomatic sinus bradycardia". Circulation. 116 (5): 463–70. doi:10.1161/CIRCULATIONAHA.107.706887. PMID 17646576.
  11. Sanders P, Kistler PM, Morton JB, Spence SJ, Kalman JM (2004). "Remodeling of sinus node function in patients with congestive heart failure: reduction in sinus node reserve". Circulation. 110 (8): 897–903. doi:10.1161/01.CIR.0000139336.69955.AB. PMID 15302799.

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