Inappropriate sinus tachycardia
Inappropriate Sinus Tachycardia (IST) is a rare type of cardiac arrhythmia, within the category of supraventricular tachycardia (SVT). IST may be caused by the sinus node itself having an abnormal structure or function, or it may be part of a problem called dysautonomia, a disturbance and/or failure of the autonomic nervous system. Research into the mechanism and etiology (cause) of Inappropriate Sinus Tachycardia is ongoing.
The mechanism and primary etiology of Inappropriate Sinus Tachycardia has not been fully elucidated. An autoimmune mechanism has been suggested as several studies have detected autoantibodies that activate beta adrenoreceptors in a portion of patients.[1][2] The mechanism of the arrhythmia primarily involves the sinus node and peri-nodal tissue[3] and does not require the AV node for maintenance. Treatments in the form of pharmacological therapy or catheter ablation are available, although it is currently difficult to treat successfully.
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[edit] Symptoms
Symptoms reported by patients vary in frequency and severity.
Symptoms associated with IST include:
- Frequent palpitations
- Dyspnea (shortness of breath) and palpitations on exertion
- Pre-syncope (feeling as if about to faint)
- Fatigue (physical)
- Dizziness
- Exercise intolerance
- Occasional paresthesia and cramping
- Symptoms associated with autonomic nervous system disturbance, including GI disturbance
[edit] Diagnosis
No formal diagnostic criteria exist. A diagnosis of Inappropriate sinus tachycardia is primarily one of exclusion and the following may be observed:
- Exclusion of all other causes of sinus tachycardia
- Common forms of supraventricular tachycardia (SVT) must be excluded
- Normal P wave morphology
- A resting sinus tachycardia is usually (but not always) present
- Nocturnal dip in heart rate
- Inappropriate heart rate response on exertion
- Mean heart rate in 24hrs >95bpm
- Symptoms are documented to be due to tachycardia
- Hypotension is occasionally observed
- Syncope (fainting) is occasionally reported
[edit] Treatment
IST has been treated both pharmacologically and invasively, with varying degrees of success.
Some types of medication tried by cardiologists and other physicians include: beta blockers, selective sinus node If channel inhibitors (ivabradine)[4], calcium channel blockers and antiarrhythmic agents. Some SSRI drugs are also occasionally tried and also treatments more commonly used to treat postural orthostatic tachycardia syndrome such as fludrocortisone. This approach is very much "trial-and-error". Patients with IST are often intolerant to beta blockers. A new selective sinus node inhibitor ivabradine is also being used to treat IST.
Invasive treatments include forms of catheter ablation such as sinus node modification[5] (selective ablation of the sinus node), complete sinus node ablation (with associated implantation of a permanent artificial pacemaker) and AV node ablation in very resistant cases (creation of iatrogenic complete heart block, necessitating implantation of a permanent artificial pacemaker).
[edit] See also
- Supraventricular tachycardia
- Sinus tachycardia
- Postural orthostatic tachycardia syndrome
- Dysautonomia
[edit] References
- ^ http://www.ncbi.nlm.nih.gov/pubmed/17018348
- ^ http://www.heartrhythmjournal.com/article/S1547-5271(06)01794-2/abstract
- ^ Sato T, Mitamura H, Murata M, et al. (October 2000). "Electrophysiologic findings of a patient with inappropriate sinus tachycardia cured by selective radiofrequency catheter ablation" ([dead link]). J Electrocardiol 33 (4): 381–6. doi:10.1054/jelc.2000.9648. PMID 11099363. http://linkinghub.elsevier.com/retrieve/pii/S0022073600288730.
- ^ Zellerhoff S, Hinterseer MIvabradine in patients with inappropriate sinus tachycardia. Naunyn Schmiedebergs Arch Pharmacol. 2010 Sep 22. http://www.ncbi.nlm.nih.gov/pubmed/20859616
- ^ Lee RJ, Kalman JM, Fitzpatrick AP, et al. (November 1995). "Radiofrequency catheter modification of the sinus node for "inappropriate" sinus tachycardia". Circulation 92 (10): 2919–28. PMID 7586260. http://circ.ahajournals.org/cgi/pmidlookup?view=long&pmid=7586260.
[edit] External links
[edit] Literature
Yusuf S, Camm AJ (June 2005). "Deciphering the sinus tachycardias". Clin Cardiol 28 (6): 267–76. doi:10.1002/clc.4960280603. PMID 16028460.
Still AM, Raatikainen P, Ylitalo A, et al. (March 2005). "Prevalence, characteristics and natural course of inappropriate sinus tachycardia". Europace 7 (2): 104–12. doi:10.1016/j.eupc.2004.12.007. PMID 15763524. http://europace.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=15763524.
Leon H, Guzman JC, Kuusela T, Dillenburg R, Kamath M, Morillo CA (January 2005). "Impaired baroreflex gain in patients with inappropriate sinus tachycardia". J. Cardiovasc. Electrophysiol. 16 (1): 64–8. doi:10.1046/j.1540-8167.2005.04441.x. PMID 15673390. http://www3.interscience.wiley.com/resolve/openurl?genre=article&sid=nlm:pubmed&issn=1045-3873&date=2005&volume=16&issue=1&spage=64.
Sánchez-Quintana D, Cabrera JA, Farré J, Climent V, Anderson RH, Ho SY (February 2005). "Sinus node revisited in the era of electroanatomical mapping and catheter ablation". Heart 91 (2): 189–94. doi:10.1136/hrt.2003.031542. PMC 1768731. PMID 15657230. http://heart.bmj.com/cgi/pmidlookup?view=long&pmid=15657230.
Cruz Filho FE, Maia IG, Fagundes ML, Boghossian S, Ribeiro JC (March 1998). "[Sinus node modification by catheter using radiofrequency current in a patient with inappropriate sinus tachycardia. Evaluation of early and late results]" (in Portuguese). Arq. Bras. Cardiol. 70 (3): 173–6. PMID 9674178.
Lee SH, Cheng JJ, Kuan P, Hung CR (1997). "Radiofrequency Catheter Modification of Sinus Node for Inappropriate Sinus Tachycardia: A Case Report". Chin Med J (Taipei) 60: 117–23.
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