Editing Tachycardia (section)

===Differential diagnosis===
[[File:Electrocardiogram of Ventricular Tachycardia.png|thumb|12 lead [[electrocardiogram]] showing a [[ventricular tachycardia]] (VT)]]

An [[electrocardiogram]] (ECG) is used to classify the type of tachycardia. They may be classified into narrow and wide complex based on the [[QRS complex]].<ref name="ACLS2010">{{cite journal | vauthors = Neumar RW, Otto CW, Link MS, Kronick SL, Shuster M, Callaway CW, Kudenchuk PJ, Ornato JP, McNally B, Silvers SM, Passman RS, White RD, Hess EP, Tang W, Davis D, Sinz E, Morrison LJ | display-authors = 6 | title = Part 8: adult advanced cardiovascular life support: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care | journal = Circulation | volume = 122 | issue = 18 Suppl 3 | pages = S729–S767 | date = November 2010 | pmid = 20956224 | doi = 10.1161/CIRCULATIONAHA.110.970988 | doi-access = free }}</ref> Equal or less than 0.1s for narrow complex.<ref>{{cite journal | vauthors = Pieper SJ, Stanton MS | title = Narrow QRS complex tachycardias | journal = Mayo Clinic Proceedings | volume = 70 | issue = 4 | pages = 371–375 | date = April 1995 | pmid = 7898144 | doi = 10.4065/70.4.371 | doi-access = free }}</ref> Presented in order of most to least common, they are:<ref name=ACLS2010 />
* Narrow complex
** [[Sinus tachycardia]], which originates from the [[Sino-atrial node|sino-atrial (SA) node]], near the base of the [[superior vena cava]]
** [[Atrial fibrillation]]
** [[Atrial flutter]]
** [[AV nodal reentrant tachycardia]]
** [[Wolff-Parkinson-White syndrome|Accessory pathway mediated tachycardia]]
** [[Atrial tachycardia]]
** [[Multifocal atrial tachycardia]]
** [[Cardiac Tamponade]]
** [[Junctional tachycardia]] (rare in adults)
* Wide complex
** [[Ventricular tachycardia]], any tachycardia that originates in the [[Ventricle (heart)|ventricles]]
** Any narrow complex tachycardia combined with a problem with the [[Bundle branch block|conduction system]] of the heart, often termed "supraventricular tachycardia with [[Cardiac aberrancy|aberrancy]]"
** A narrow complex tachycardia with an accessory conduction pathway, often termed "supraventricular tachycardia with pre-excitation" (e.g. [[Wolff–Parkinson–White syndrome]])
** Pacemaker-tracked or pacemaker-mediated tachycardia

Tachycardias may be classified as either narrow complex tachycardias (supraventricular tachycardias) or wide complex tachycardias. Narrow and wide refer to the width of the [[QRS complex]] on the [[ECG]]. Narrow complex tachycardias tend to originate in the atria, while wide complex tachycardias tend to originate in the ventricles. Tachycardias can be further classified as either regular or irregular.{{citation needed|date=February 2021}}

====Sinus====
{{Main|Sinus tachycardia}}
{{Anchor|Reflex tachycardia}}

The body has several [[feedback mechanism]]s to maintain adequate blood flow and [[blood pressure]].  If blood pressure decreases, the heart beats faster in an attempt to raise it. This is called [[reflex]] tachycardia. This can happen in response to a decrease in blood volume (through [[dehydration]] or [[bleeding]]), or an unexpected change in [[blood flow]]. The most common cause of the latter is [[orthostatic hypotension]] (also called [[postural hypotension]]).  [[Fever]], [[hyperventilation]], [[diarrhea]] and severe [[infections]] can also cause tachycardia, primarily due to increase in [[metabolic]] demands.{{citation needed|date=February 2021}}

Upon exertion, [[sinus tachycardia]] can also be seen in some [[inborn errors of metabolism]] that result in [[Metabolic myopathy|metabolic myopathies]], such as [[Glycogen storage disease type V|McArdle's disease (GSD-V)]].<ref name="Lucia_2021">{{cite journal | vauthors = Lucia A, Martinuzzi A, Nogales-Gadea G, Quinlivan R, Reason S | title = Clinical practice guidelines for glycogen storage disease V & VII (McArdle disease and Tarui disease) from an international study group | journal = Neuromuscular Disorders | volume = 31 | issue = 12 | pages = 1296–1310 | date = December 2021 | pmid = 34848128 | doi = 10.1016/j.nmd.2021.10.006 | url = }}</ref><ref name="Scalco_2014">{{cite journal | vauthors = Scalco RS, Chatfield S, Godfrey R, Pattni J, Ellerton C, Beggs A, Brady S, Wakelin A, Holton JL, Quinlivan R | title = From exercise intolerance to functional improvement: the second wind phenomenon in the identification of McArdle disease | journal = Arquivos de Neuro-psiquiatria | volume = 72 | issue = 7 | pages = 538–41 | date = July 2014 | pmid = 25054987 | doi = 10.1590/0004-282x20140062 | url = | doi-access = free }}</ref> Metabolic myopathies interfere with the muscle's ability to create energy. This energy shortage in muscle cells causes an inappropriate rapid heart rate in response to exercise. The heart tries to compensate for the energy shortage by increasing heart rate to maximize delivery of oxygen and other blood borne fuels to the muscle cells.<ref name="Lucia_2021" />

"In McArdle's, our heart rate tends to increase in what is called an 'inappropriate' response. That is, after the start of exercise it increases much more quickly than would be expected in someone unaffected by McArdle's."<ref name="Wakelin_2017">{{Cite book | vauthors = Wakelin A |url=https://www.iamgsd.org/_files/ugd/c951b2_91a5802caa2144d5aedbb0489c1cf543.pdf |title=Living With McArdle Disease |publisher= International Assoc. of Muscle Glycogen Diseases (IAMGSD) |year=2017 |pages=15}}</ref> As skeletal muscle relies predominantly on [[glycogenolysis]] for the first few minutes as it transitions from rest to activity, as well as throughout high-intensity aerobic activity and all anaerobic activity, individuals with GSD-V experience during exercise: sinus tachycardia, [[tachypnea]], muscle fatigue and pain, during the aforementioned activities and time frames.<ref name="Lucia_2021" /><ref name="Scalco_2014" /> Those with GSD-V also experience "[[second wind]]", after approximately 6–10 minutes of light-moderate aerobic activity, such as walking without an incline, where the heart rate drops and symptoms of [[exercise intolerance]] improve.<ref name="Lucia_2021" /><ref name="Scalco_2014" /><ref name="Wakelin_2017" />

An increase in [[sympathetic nervous system]] stimulation causes the heart rate to increase, both by the direct action of [[sympathetic nerve]] fibers on the heart and by causing the [[endocrine]] system to release [[hormone]]s such as [[epinephrine|epinephrine (adrenaline)]], which have a similar effect.  Increased sympathetic stimulation is usually due to physical or psychological stress.  This is the basis for the so-called [[fight-or-flight response]], but such stimulation can also be induced by [[stimulant]]s such as [[ephedrine]], [[amphetamines]] or [[cocaine]].  Certain [[endocrine disorders]] such as [[pheochromocytoma]] can also cause epinephrine release and can result in tachycardia independent of nervous system stimulation. [[Hyperthyroidism]] can also cause tachycardia.<ref name="AmbMed2003">{{cite book | veditors = Barker RL, Burton JR, Zieve PD | title = Principles of Ambulatory Medicine | edition = Sixth | location = Philadelphia, PA | publisher = Lippinocott, Wilkins & Williams | date = 2003 | isbn = 0-7817-3486-X }}</ref> The upper limit of normal rate for sinus tachycardia is thought to be 220&nbsp;bpm minus age.{{citation needed|date=February 2021}}

=====Inappropriate sinus tachycardia=====
{{Main|Inappropriate sinus tachycardia}}

[[Inappropriate sinus tachycardia]] (IST) is a [[diagnosis of exclusion]],<ref>{{Cite journal |last1=Ahmed |first1=Adnan |last2=Pothineni |first2=Naga Venkata K. |last3=Charate |first3=Rishi |last4=Garg |first4=Jalaj |last5=Elbey |first5=Mehmet |last6=de Asmundis |first6=Carlo |last7=LaMeir |first7=Mark |last8=Romeya |first8=Ahmed |last9=Shivamurthy |first9=Poojita |last10=Olshansky |first10=Brian |last11=Russo |first11=Andrea |last12=Gopinathannair |first12=Rakesh |last13=Lakkireddy |first13=Dhanunjaya |date=21 June 2022 |title=Inappropriate Sinus Tachycardia: Etiology, Pathophysiology, and Management: JACC Review Topic of the Week |url=https://www.sciencedirect.com/science/article/pii/S0735109722048252 |journal=Journal of the American College of Cardiology |volume=79 |issue=24 |pages=2450–2462 |doi=10.1016/j.jacc.2022.04.019 |pmid=35710196 |issn=0735-1097}}</ref> a rare but benign type of cardiac arrhythmia that may be caused by a structural abnormality in the [[Sinoatrial node|sinus node]]. It can occur in seemingly healthy individuals with no history of cardiovascular disease.  Other causes may include [[Dysautonomia|autonomic nervous system deficits]], autoimmune response, or drug interactions. Although symptoms might be distressing, treatment is not generally needed.<ref>{{cite journal | vauthors = Peyrol M, Lévy S | title = Clinical presentation of inappropriate sinus tachycardia and differential diagnosis | journal = Journal of Interventional Cardiac Electrophysiology | volume = 46 | issue = 1 | pages = 33–41 | date = June 2016 | pmid = 26329720 | doi = 10.1007/s10840-015-0051-z | s2cid = 23249973 }}</ref>

====Ventricular====
{{Main|Ventricular tachycardia}}

Ventricular tachycardia (VT or V-tach) is a potentially life-threatening cardiac arrhythmia that originates in the ventricles. It is usually a regular, wide complex tachycardia with a rate between 120 and 250 beats per minute. A medically significant subvariant of ventricular tachycardia is called ''[[torsades de pointes]]'' (literally meaning "twisting of the points", due to its appearance on an EKG), which tends to result from a long QT interval.<ref>{{cite web | vauthors = Mitchell LB | date = January 2023| title = Torsades de Pointes Ventricular Tachycardia | work = Merck Manual Profesional Edition | access-date = 19 April 2019 | url = https://www.merckmanuals.com/professional/cardiovascular-disorders/arrhythmias-and-conduction-disorders/long-qt-syndrome-and-torsades-de-pointes-ventricular-tachycardia }}</ref>

Both of these rhythms normally last for only a few [[second]]s to [[minute]]s'' ([[paroxysmal tachycardia]])'', but if VT persists it is extremely dangerous, often leading to [[ventricular fibrillation]].<ref>{{cite journal | vauthors = Samie FH, Jalife J | title = Mechanisms underlying ventricular tachycardia and its transition to ventricular fibrillation in the structurally normal heart | journal = Cardiovascular Research | volume = 50 | issue = 2 | pages = 242–250 | date = May 2001 | pmid = 11334828 | doi = 10.1016/S0008-6363(00)00289-3 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Srivathsan K, Ng DW, Mookadam F | title = Ventricular tachycardia and ventricular fibrillation | journal = Expert Review of Cardiovascular Therapy | volume = 7 | issue = 7 | pages = 801–809 | date = July 2009 | pmid = 19589116 | doi = 10.1586/erc.09.69 | s2cid = 207215117 }}</ref>

====Supraventricular====
{{Main|Supraventricular tachycardia}}

This is a type of tachycardia that originates from above the ventricles, such as the atria.  It is sometimes known as paroxysmal atrial tachycardia (PAT).  Several types of supraventricular tachycardia are known to exist.<ref>{{cite web|title=Types of Arrhythmia |url= http://www.nhlbi.nih.gov/health/health-topics/topics/arr/types| work = National Heart, Lung, and Blood Institute (NHLBI) | publisher = U.S. National Institutes of Health |date=1 July 2011 |url-status=live |archive-url= https://web.archive.org/web/20150607165144/http://www.nhlbi.nih.gov/health/health-topics/topics/arr/types |archive-date=7 June 2015}}</ref>

=====Atrial fibrillation=====
[[Atrial fibrillation]] is one of the most common cardiac arrhythmias. In general, it is an irregular, narrow complex rhythm. However, it may show wide QRS complexes on the ECG if a [[bundle branch block]] is present. At high rates, the QRS complex may also become wide due to the [[Ashman phenomenon]]. It may be difficult to determine the rhythm's regularity when the rate exceeds 150 beats per minute. Depending on the patient's health and other variables such as medications taken for rate control, atrial fibrillation may cause heart rates that span from 50 to 250 beats per minute (or even higher if an [[Wolff-Parkinson-White syndrome|accessory pathway]] is present). However, new-onset atrial fibrillation tends to present with rates between 100 and 150 beats per minute.<ref>{{cite web | vauthors = Oiseth S, Jones L, Maza E |url= https://www.lecturio.com/concepts/atrial-fibrillation/ | title= Atrial Fibrillation | website= The Lecturio Medical Concept Library | date= 11 August 2020 |access-date= 3 July 2021}}</ref>

=====AV nodal reentrant tachycardia=====
[[AV nodal reentrant tachycardia]] (AVNRT) is the most common reentrant tachycardia. It is a regular [[supraventricular tachycardia|narrow complex tachycardia]] that usually responds well to the [[Valsalva maneuver]] or the drug [[adenosine]]. However, unstable patients sometimes require synchronized [[cardioversion]]. Definitive care may include [[catheter ablation]].<ref>{{cite journal | vauthors = Katritsis DG | title = Catheter Ablation of Atrioventricular Nodal Re-entrant Tachycardia: Facts and Fiction | journal = Arrhythmia & Electrophysiology Review | volume = 7 | issue = 4 | pages = 230–231 | date = December 2018 | pmid = 30588309 | pmc = 6304791 | doi = 10.15420/aer.2018.7.4.EO1 }}</ref>

=====AV reentrant tachycardia=====
[[Atrioventricular reentrant tachycardia|AV reentrant tachycardia (AVRT)]] requires an [[accessory pathway]] for its maintenance. AVRT may involve orthodromic conduction (where the impulse travels down the AV node to the ventricles and back up to the atria through the accessory pathway) or antidromic conduction (which the impulse travels down the accessory pathway and back up to the atria through the AV node). Orthodromic conduction usually results in a narrow complex tachycardia, and antidromic conduction usually results in a wide complex tachycardia that often mimics [[ventricular tachycardia]]. Most [[antiarrhythmics]] are [[contraindicated]] in the emergency treatment of AVRT, because they may paradoxically increase conduction across the accessory pathway. {{citation needed|date=April 2019}}

=====Junctional tachycardia=====
Junctional tachycardia is an [[automatic tachycardia]] originating in the AV junction. It tends to be a regular, narrow complex tachycardia and may be a sign of digitalis toxicity.<ref>{{cite journal | vauthors = Rosen KM | title = Junctional tachycardia. Mechanisms, diagnosis, differential diagnosis, and management | journal = Circulation | volume = 47 | issue = 3 | pages = 654–664 | date = March 1973 | pmid = 4571060 | doi = 10.1161/01.CIR.47.3.654 }}</ref>