Pulseless ventricular tachycardia pathophysiology: Difference between revisions

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__NOTOC__
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{{Pulseless ventricular tachycardia}}
{{Pulseless ventricular tachycardia}}
{{CMG}}; {{AE}}{{Aisha}} {{CZ}}
{{CMG}}; {{AE}}{{Aisha}}
==Overview==
==Overview==
Rapid abnormal [[automaticity]] and [[triggered activity]] are thought to be the main [[electrophysiological]] mechanisms of [[pulseless ventricular tachycardia]]. In abnormal automatically, the ventricular myocytes produce strong, voluntary, and recurrent depolarization and subsequent contractions at a rate that is higher than normal. This is due to a due to a decrease (ranging between -70mV and -30mV) in normal [[resting membrane potential]]. The higher the reduction in [[membrane potential]], the faster and more rapid the already abnormal [[automaticity]].<ref name="pmid4237287">{{cite journal |vauthors=Armendares S, Pérez Treviño C |title=[Congenital heart diseases in chromosome abnormalities. I. In Down's syndrome (mongolism)] |language=Spanish; Castilian |journal=Arch Inst Cardiol Mex |volume=38 |issue=6 |pages=779–91 |date=1968 |pmid=4237287 |doi= |url=}}</ref> Triggered activity is used to depict the indication of impulse in cardiac myocytes that is dependent on [[afterdepolarizations]] (an oscillation in membrane potential that occurs after repolarization). Two types of afterdepolarizations have been identified: [[Early afterdepolarizations]](EAD) and [[Delayed afterdepolarizations]] (DAD). When either of these afterdepolarizations become high enough to reach the [[membrane threshold]], they result in a spontaneous "triggered" action potential. Hence for a triggered activity to occur, at least one action potential must precede it.<ref name="pmid1855225">{{cite journal |vauthors=Buchmann A, Ruggeri B, Klein-Szanto AJ, Balmain A |title=Progression of squamous carcinoma cells to spindle carcinomas of mouse skin is associated with an imbalance of H-ras alleles on chromosome 7 |journal=Cancer Res. |volume=51 |issue=15 |pages=4097–101 |date=August 1991 |pmid=1855225 |doi= |url=}}</ref>
Rapid abnormal [[automaticity]] and [[triggered activity]] are thought to be the main [[electrophysiological]] mechanisms of [[pulseless ventricular tachycardia]]. In abnormal automatically, the ventricular myocytes produce strong, voluntary, and recurrent depolarization and subsequent contractions at a rate that is higher than normal. This is due to a due to a decrease (ranging between -70mV and -30mV) in normal [[resting membrane potential]]. The higher the reduction in [[membrane potential]], the faster and more rapid the already abnormal [[automaticity]].<ref name="pmid4237287">{{cite journal |vauthors=Armendares S, Pérez Treviño C |title=[Congenital heart diseases in chromosome abnormalities. I. In Down's syndrome (mongolism)] |language=Spanish; Castilian |journal=Arch Inst Cardiol Mex |volume=38 |issue=6 |pages=779–91 |date=1968 |pmid=4237287 |doi= |url=}}</ref> Triggered activity is used to depict the indication of impulse in cardiac myocytes that is dependent on [[afterdepolarizations]] (an oscillation in membrane potential that occurs after repolarization). Two types of afterdepolarizations have been identified: [[Early afterdepolarizations]](EAD) and [[Delayed afterdepolarizations]] (DAD). When either of these afterdepolarizations become high enough to reach the [[membrane threshold]], they result in a spontaneous "triggered" action potential. Hence for a triggered activity to occur, at least one action potential must precede it.<ref name="pmid1855225">{{cite journal |vauthors=Buchmann A, Ruggeri B, Klein-Szanto AJ, Balmain A |title=Progression of squamous carcinoma cells to spindle carcinomas of mouse skin is associated with an imbalance of H-ras alleles on chromosome 7 |journal=Cancer Res. |volume=51 |issue=15 |pages=4097–101 |date=August 1991 |pmid=1855225 |doi= |url=}}</ref>
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===Pathogenesis===
===Pathogenesis===
Pathophysiology of ventricular tachycardia can be better studied depending upon the subclass:<ref name="pmid28855272">{{cite journal |vauthors=Martin CA, Lambiase PD |title=Pathophysiology, diagnosis and treatment of tachycardiomyopathy |journal=Heart |volume=103 |issue=19 |pages=1543–1552 |date=October 2017 |pmid=28855272 |pmc=5629945 |doi=10.1136/heartjnl-2016-310391 |url=}}</ref><ref name="pmid9058854">{{cite journal |vauthors=Simons GR, Klein GJ, Natale A |title=Ventricular tachycardia: pathophysiology and radiofrequency catheter ablation |journal=Pacing Clin Electrophysiol |volume=20 |issue=2 Pt 2 |pages=534–51 |date=February 1997 |pmid=9058854 |doi=10.1111/j.1540-8159.1997.tb06209.x |url=}}</ref><ref name="pmid15137521">{{cite journal |vauthors=Brunckhorst C, Delacretaz E |title=[Ventricular tachycardia--etiology, mechanisms and therapy] |language=German |journal=Ther Umsch |volume=61 |issue=4 |pages=257–64 |date=April 2004 |pmid=15137521 |doi=10.1024/0040-5930.61.4.257 |url=}}</ref><ref name="pmid19589116">{{cite journal |vauthors=Srivathsan K, Ng DW, Mookadam F |title=Ventricular tachycardia and ventricular fibrillation |journal=Expert Rev Cardiovasc Ther |volume=7 |issue=7 |pages=801–9 |date=July 2009 |pmid=19589116 |doi=10.1586/erc.09.69 |url=}}</ref>
*The exact pathogenesis of [disease name] is not completely understood.
OR
*It is understood that [disease name] is the result of / is mediated by / is produced by / is caused by either [hypothesis 1], [hypothesis 2], or [hypothesis 3].
*[Pathogen name] is usually transmitted via the [transmission route] route to the human host.
*Following transmission/ingestion, the [pathogen] uses the [entry site] to invade the [cell name] cell.
*[Disease or malignancy name] arises from [cell name]s, which are [cell type] cells that are normally involved in [function of cells].
*The progression to [disease name] usually involves the [molecular pathway].
*The pathophysiology of [disease/malignancy] depends on the histological subtype.


==== Cellular level ====
==Genetics==
 
[Disease name] is transmitted in [mode of genetic transmission] pattern.
* Electrical reentry or abnormal [[automaticity]] is the main reason behind ventricular tachycardia.
** Myocardial scarring from any process increases the likelihood of electrical reentrant circuits.
** These circuits generally include a zone where normal electrical propagation is slowed by the scar.
** Ventricular scar formation from a prior [[Myocardial infarction|myocardial infarction (MI)]] is the most common cause of sustained monomorphic VT.
 
* VT in a structurally normal heart typically results from mechanisms such as triggered activity and enhanced [[automaticity]].
*[[Torsade de pointes]] seen in the [[Long QT syndrome|long QT syndromes]] is likely a combination of triggered activity and ventricular reentry.
 
* During VT [[cardiac output]] is reduced as a consequence of decreased ventricular filling from the rapid heart rate and the lack of properly timed or coordinated atrial contraction.
* Ischemia and [[mitral insufficiency]]  may also contribute to decreased ventricular stroke output and hemodynamic intolerance.
* Hemodynamic collapse is more likely when underlying left ventricular dysfunction is present or when heart rates are very rapid.
* Diminished [[cardiac output]] may result in diminished [[myocardial perfusion]], worsening inotropic response, and degeneration to [[Ventricular fibrillation|ventricular fibrillation (VF)]], resulting in sudden death.
* In patients with monomorphic VT, mortality risk correlates with the degree of structural heart disease. Underlying structural heart diseases such as [[ischemic cardiomyopathy]], [[dilated cardiomyopathy]], [[hypertrophic cardiomyopathy]], [[Chagas disease]], and [[Right ventricular failure|right ventricular dysplasia]] have all been associated with degeneration of monomorphic or polymorphic VT to [[VF]].
* Even without such degeneration, VT can also produce [[congestive heart failure]] and hemodynamic compromise, with subsequent morbidity and mortality.
* If VT is hemodynamically tolerated, the incessant tachyarrhythmia may cause a [[dilated cardiomyopathy]]. This may develop over a period of weeks to years and may resolve with successful suppression of the VT.


===Monomorphic Ventricular Tachycardia===
OR


* There are two reasons the morphology of the [[QRS]] does not vary in [[monomorphic ventricular tachycardia]]:
Genes involved in the pathogenesis of [disease name] include:
**A single site that generates [[cardiac arrhythmia#origin of impulse|automaticity]] of a single point in either the left or right [[ventricle]].
*[Gene1]
**A [[cardiac arrhythmia#origin of impulse|reentry]] circuit within the [[ventricle]].
*[Gene2]
*[Gene3]


===Polymorphic Ventricular Tachycardia===
OR


* Polymorphic ventricular tachycardia, on the other hand, is most commonly caused by abnormalities of [[myocardium|ventricular muscle]] repolarization.
The development of [disease name] is the result of multiple genetic mutations such as:
* The predisposition to this problem usually manifests on the [[ECG]] as a prolongation of the [[QT interval]]. [[QT prolongation]] may be congenital or acquired.
* Congenital problems include [[long QT syndrome]] and [[catecholaminergic polymorphic ventricular tachycardia]].
* Acquired problems are usually related to [[drug toxicity]] or [[electrolyte abnormalities]], but can occur as a result of [[myocardial ischemia]].
* Class III [[anti-arrhythmic]] drugs such as [[sotalol]] and [[amiodarone]] prolong the [[QT interval]] and may in some circumstances be pro-arrhythmic.
* Other relatively common drugs including some [[antibiotics]] and [[antihistamines]] may also be a danger, particularly in combination with one another.
* Problems with blood levels of [[potassium]], [[magnesium]] and [[calcium]] may also contribute. High dose [[magnesium]] is often used as an [[antidote]] in [[cardiac arrest]] protocols.


==Genetics==
*[Mutation 1]
[['''Autosomal-dominant''']] mutations in [[ryanodine receptor]] type 2 ( ryr2) have been complicated in a type of ventricular tachycardia known as [[catecholaminergic polymorphic ventricular tachycardia]].<ref name="pmid30355031">{{cite journal |vauthors=Pan X, Philippen L, Lahiri SK, Lee C, Park SH, Word TA, Li N, Jarrett KE, Gupta R, Reynolds JO, Lin J, Bao G, Lagor WR, Wehrens XHT |title=In Vivo Ryr2 Editing Corrects Catecholaminergic Polymorphic Ventricular Tachycardia |journal=Circ. Res. |volume=123 |issue=8 |pages=953–963 |date=September 2018 |pmid=30355031 |pmc=6206886 |doi=10.1161/CIRCRESAHA.118.313369 |url=}}</ref>
*[Mutation 2]
*[Mutation 3]


==Associated Conditions==
==Associated Conditions==
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*[Condition 3]
*[Condition 3]


==Gross Pathology==
On gross pathology, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].
==Microscopic Pathology==
On microscopic histopathological analysis, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].


==References==
==References==

Revision as of 14:54, 2 June 2020

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Aisha Adigun, B.Sc., M.D.[2]

Overview

Rapid abnormal automaticity and triggered activity are thought to be the main electrophysiological mechanisms of pulseless ventricular tachycardia. In abnormal automatically, the ventricular myocytes produce strong, voluntary, and recurrent depolarization and subsequent contractions at a rate that is higher than normal. This is due to a due to a decrease (ranging between -70mV and -30mV) in normal resting membrane potential. The higher the reduction in membrane potential, the faster and more rapid the already abnormal automaticity.[1] Triggered activity is used to depict the indication of impulse in cardiac myocytes that is dependent on afterdepolarizations (an oscillation in membrane potential that occurs after repolarization). Two types of afterdepolarizations have been identified: Early afterdepolarizations(EAD) and Delayed afterdepolarizations (DAD). When either of these afterdepolarizations become high enough to reach the membrane threshold, they result in a spontaneous "triggered" action potential. Hence for a triggered activity to occur, at least one action potential must precede it.[2]

In pulseless ventricular tachycardia, the combination of increased automatically and/or triggered activity leads to a rate of contraction that is too rapid to result in adequate ventricular filling during diastole. This results in deficient cardiac output, inadequate perfusion of organs, and hemodynamic collapse.[3]

Pathophysiology

Physiology

The normal physiology of [name of process] can be understood as follows:

Pathogenesis

  • The exact pathogenesis of [disease name] is not completely understood.

OR

  • It is understood that [disease name] is the result of / is mediated by / is produced by / is caused by either [hypothesis 1], [hypothesis 2], or [hypothesis 3].
  • [Pathogen name] is usually transmitted via the [transmission route] route to the human host.
  • Following transmission/ingestion, the [pathogen] uses the [entry site] to invade the [cell name] cell.
  • [Disease or malignancy name] arises from [cell name]s, which are [cell type] cells that are normally involved in [function of cells].
  • The progression to [disease name] usually involves the [molecular pathway].
  • The pathophysiology of [disease/malignancy] depends on the histological subtype.

Genetics

[Disease name] is transmitted in [mode of genetic transmission] pattern.

OR

Genes involved in the pathogenesis of [disease name] include:

  • [Gene1]
  • [Gene2]
  • [Gene3]

OR

The development of [disease name] is the result of multiple genetic mutations such as:

  • [Mutation 1]
  • [Mutation 2]
  • [Mutation 3]

Associated Conditions

Conditions associated with [disease name] include:

  • [Condition 1]
  • [Condition 2]
  • [Condition 3]

Gross Pathology

On gross pathology, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].

Microscopic Pathology

On microscopic histopathological analysis, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].

References

  1. Armendares S, Pérez Treviño C (1968). "[Congenital heart diseases in chromosome abnormalities. I. In Down's syndrome (mongolism)]". Arch Inst Cardiol Mex (in Spanish; Castilian). 38 (6): 779–91. PMID 4237287.
  2. Buchmann A, Ruggeri B, Klein-Szanto AJ, Balmain A (August 1991). "Progression of squamous carcinoma cells to spindle carcinomas of mouse skin is associated with an imbalance of H-ras alleles on chromosome 7". Cancer Res. 51 (15): 4097–101. PMID 1855225.
  3. Foglesong A, Mathew D. PMID 32119354 Check |pmid= value (help). Missing or empty |title= (help)


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