Inappropriate sinus tachycardia (IST) is a rare type of
cardiac arrhythmia
Arrhythmias, also known as cardiac arrhythmias, heart arrhythmias, or dysrhythmias, are irregularities in the heartbeat, including when it is too fast or too slow. A resting heart rate that is too fast – above 100 beats per minute in adult ...
within the category of
supraventricular tachycardia
Supraventricular tachycardia (SVT) is an umbrella term for fast heart rhythms arising from the upper part of the heart. This is in contrast to the other group of fast heart rhythms – ventricular tachycardia, which start within the lower cha ...
(SVT). IST may be caused by the
sinus node
The sinoatrial node (also known as the sinuatrial node, SA node or sinus node) is an oval shaped region of special cardiac muscle in the upper back wall of the right atrium made up of cells known as pacemaker cells. The sinus node is approximat ...
itself having an abnormal structure or function, or it may be part of a problem called
dysautonomia
Dysautonomia or autonomic dysfunction is a condition in which the autonomic nervous system (ANS) does not work properly. This may affect the functioning of the heart, bladder, intestines, sweat glands, pupils, and blood vessels. Dysautonomia has ...
, a disturbance and/or failure of the
autonomic nervous system
The autonomic nervous system (ANS), formerly referred to as the vegetative nervous system, is a division of the peripheral nervous system that supplies internal organs, smooth muscle and glands. The autonomic nervous system is a control system t ...
. Research into the mechanism and
etiology
Etiology (pronounced ; alternatively: aetiology or ætiology) is the study of causation or origination. The word is derived from the Greek (''aitiología'') "giving a reason for" (, ''aitía'', "cause"); and ('' -logía''). More completely, e ...
(cause) of inappropriate sinus tachycardia is ongoing.
IST is viewed by most to be a benign condition in the long-term. Symptoms of IST, however, may be distracting and warrant treatment. The
heart
The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxid ...
is a strong muscle and typically can sustain the higher-than-normal heart rhythm, though monitoring the condition is generally recommended.
The mechanism and primary etiology of inappropriate sinus tachycardia has not been fully elucidated. An
autoimmune
In immunology, autoimmunity is the system of immune responses of an organism against its own healthy cells, tissues and other normal body constituents. Any disease resulting from this type of immune response is termed an " autoimmune disease" ...
mechanism has been suggested, as several studies have detected autoantibodies that activate beta adrenoreceptors in some patients.
The mechanism of the arrhythmia primarily involves the sinus node and peri-nodal tissue
and does not require the
AV node for maintenance. Treatments in the form of
pharmacological
Pharmacology is a branch of medicine, biology and pharmaceutical sciences concerned with drug or medication action, where a drug may be defined as any artificial, natural, or endogenous (from within the body) molecule which exerts a biochemi ...
therapy or
catheter ablation
Catheter ablation is a procedure used to remove or terminate a faulty electrical pathway from sections of the heart of those who are prone to developing cardiac arrhythmias such as atrial fibrillation, atrial flutter and Wolff-Parkinson-White syn ...
are available, but the condition is currently difficult to treat successfully.
Symptoms
Symptoms reported by patients vary in frequency and severity. They may include:
* Frequent or sustained
palpitations
Palpitations are perceived abnormalities of the heartbeat characterized by awareness of cardiac muscle contractions in the chest, which is further characterized by the hard, fast and/or irregular beatings of the heart.
Symptoms include a rapi ...
*
Dyspnea
Shortness of breath (SOB), also medically known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing dis ...
(shortness of breath) and palpitations on exertion
*
Tachypnea
Tachypnea, also spelt tachypnoea, is a respiratory rate greater than normal, resulting in abnormally rapid and shallow breathing.
In adult humans at rest, any respiratory rate of 1220 per minute is considered clinically normal, with tachypnea be ...
(rapid breathing)
* Pre-
syncope (feeling as if about to faint)
*
Fatigue
Fatigue describes a state of tiredness that does not resolve with rest or sleep. In general usage, fatigue is synonymous with extreme tiredness or exhaustion that normally follows prolonged physical or mental activity. When it does not resolve ...
*
Dizziness
Dizziness is an imprecise term that can refer to a sense of disorientation in space, vertigo, or lightheadedness. It can also refer to disequilibrium or a non-specific feeling, such as giddiness or foolishness.
Dizziness is a common medical ...
*
Exercise intolerance
* Occasional
paresthesia
Paresthesia is an abnormal sensation of the skin (tingling, pricking, chilling, burning, numbness) with no apparent physical cause. Paresthesia may be transient or chronic, and may have any of dozens of possible underlying causes. Paresthesias a ...
and cramping
* Symptoms associated with
autonomic nervous system
The autonomic nervous system (ANS), formerly referred to as the vegetative nervous system, is a division of the peripheral nervous system that supplies internal organs, smooth muscle and glands. The autonomic nervous system is a control system t ...
disturbance, including gastrointestinal disturbance
Diagnosis
No formal diagnostic criteria exist. A diagnosis of inappropriate sinus tachycardia is primarily one of exclusion,
[Ahmed A, Pothineni N, Charate R, et al. Inappropriate Sinus Tachycardia: Etiology, Pathophysiology, and Management. ''J Am Coll Cardiol.'' 2022 Jun, 79 (24) 2450–2462.https://doi.org/10.1016/j.jacc.2022.04.019] and the following may be observed:
* Exclusion of all other causes of
sinus tachycardia
* Common forms of
supraventricular tachycardia
Supraventricular tachycardia (SVT) is an umbrella term for fast heart rhythms arising from the upper part of the heart. This is in contrast to the other group of fast heart rhythms – ventricular tachycardia, which start within the lower cha ...
(SVT) must be excluded
* Normal P wave morphology
* A resting sinus tachycardia is usually (but not always) present
* Nocturnal dip in
heart rate
Heart rate (or pulse rate) is the frequency of the heartbeat measured by the number of contractions (beats) of the heart per minute (bpm). The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and ex ...
* Inappropriate heart rate response on exertion
* Mean heart rate in 24hrs >95 bpm
* Symptoms are documented to be due to
tachycardia
Tachycardia, also called tachyarrhythmia, is a heart rate that exceeds the normal resting rate. In general, a resting heart rate over 100 beats per minute is accepted as tachycardia in adults. Heart rates above the resting rate may be normal (su ...
*
Hypotension
Hypotension is low blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. Blood pressure is indicated by two numbers, the systolic blood pressure (the top number) and the dia ...
is occasionally observed
*
Syncope (fainting) is occasionally reported
Treatment
IST has been treated both pharmacologically and invasively, with varying degrees of success. IST, in and of itself, is not indicative of higher rates of mortality, and non-treatment is an option chosen by many if they have minimal symptoms.
Some types of medication tried by cardiologists and other physicians include:
beta blocker
Beta blockers, also spelled β-blockers, are a class of medications that are predominantly used to manage abnormal heart rhythms, and to protect the heart from a second heart attack after a first heart attack ( secondary prevention). They are a ...
s, selective sinus node I
f channel inhibitors (such as
ivabradine
Ivabradine, sold under the brand name Procoralan among others, is a medication, which is a funny current (I''f'') inhibitor, used for the symptomatic management of heart-related chest pain and heart failure. Patients who qualify for use of Iva ...
),
calcium channel blocker
Calcium channel blockers (CCB), calcium channel antagonists or calcium antagonists are a group of medications that disrupt the movement of calcium () through calcium channels. Calcium channel blockers are used as antihypertensive drugs, i.e., as ...
s, and
antiarrhythmic agent
Antiarrhythmic agents, also known as cardiac dysrhythmia medications, are a group of pharmaceuticals that are used to suppress abnormally fast rhythms ( tachycardias), such as atrial fibrillation, supraventricular tachycardia and ventricular t ...
s. Some
SSRI
Selective serotonin reuptake inhibitors (SSRIs) are a class of drugs that are typically used as antidepressants in the treatment of major depressive disorder, anxiety disorders, and other psychological conditions.
SSRIs increase the extracellu ...
drugs are also occasionally tried, as are treatments more commonly used to treat
postural orthostatic tachycardia syndrome
Postural orthostatic tachycardia syndrome (POTS) is a condition characterized by an abnormally large increase in heart rate upon standing. Symptoms may include lightheadedness, brain fog, blurred vision, weakness, fatigue, headaches, heart ...
, such as
fludrocortisone.
Invasive treatments include forms of
catheter ablation
Catheter ablation is a procedure used to remove or terminate a faulty electrical pathway from sections of the heart of those who are prone to developing cardiac arrhythmias such as atrial fibrillation, atrial flutter and Wolff-Parkinson-White syn ...
such as sinus node modification
(selective ablation of the sinus node), complete sinus node ablation (with associated implantation of a permanent
artificial pacemaker
An artificial cardiac pacemaker (or artificial pacemaker, so as not to be confused with the natural cardiac pacemaker) or pacemaker is a medical device that generates electrical impulses delivered by electrodes to the chambers of the heart eit ...
), and AV node ablation in very resistant cases (creation of
iatrogenic
Iatrogenesis is the causation of a disease, a harmful complication, or other ill effect by any medical activity, including diagnosis, intervention, error, or negligence. "Iatrogenic", ''Merriam-Webster.com'', Merriam-Webster, Inc., accessed 27 ...
complete heart block, necessitating implantation of a permanent artificial pacemaker). However, invasive treatments can also make the symptoms worse.
Differential Diagnoses
IST is primarily a
diagnosis of exclusion
A diagnosis of exclusion or by exclusion (''per exclusionem'') is a diagnosis of a medical condition reached by a process of elimination, which may be necessary if presence cannot be established with complete confidence from history, examination ...
.
Upon exertion, an inappropriate heart rate response of
sinus tachycardia can be seen in some
Inborn Errors of Metabolism that result in
metabolic myopathies, such as
McArdle Disease (GSD-V).
[Lucia A, Martinuzzi A, Nogales-Gadea G, Quinlivan R, Reason S; International Association for Muscle Glycogen Storage Disease study group. Clinical practice guidelines for glycogen storage disease V & VII (McArdle disease and Tarui disease) from an international study group. Neuromuscul Disord. 2021 Dec;31(12):1296-1310. doi: 10.1016/j.nmd.2021.10.006. Epub 2021 Oct 28. Erratum in: Neuromuscul Disord. 2022 Feb 6;: PMID: 34848128.] Rare diseases are more likely to be misdiagnosed, indeed, "Ninety percent of people with GSD V received a misdiagnosis before a corrected diagnosis (GSD VII unknown), resulting in a median diagnostic delay of 29 years, which can seriously affect QoL
uality of Life�� Of those who are misdiagnosed, 62% report being misdiagnosed more than once."
See also
*
Supraventricular tachycardia
Supraventricular tachycardia (SVT) is an umbrella term for fast heart rhythms arising from the upper part of the heart. This is in contrast to the other group of fast heart rhythms – ventricular tachycardia, which start within the lower cha ...
*
Sinus tachycardia
*
Postural orthostatic tachycardia syndrome
Postural orthostatic tachycardia syndrome (POTS) is a condition characterized by an abnormally large increase in heart rate upon standing. Symptoms may include lightheadedness, brain fog, blurred vision, weakness, fatigue, headaches, heart ...
*
Dysautonomia
Dysautonomia or autonomic dysfunction is a condition in which the autonomic nervous system (ANS) does not work properly. This may affect the functioning of the heart, bladder, intestines, sweat glands, pupils, and blood vessels. Dysautonomia has ...
*
Metabolic myopathies
References
Further reading
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{{Heart diseases
Cardiac arrhythmia