Editing Tachycardia (section)

====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>