Inappropriate sinus tachycardia

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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.

Symptoms[edit]

Symptoms reported by patients vary in frequency and severity.

Symptoms associated with IST include:

Diagnosis[edit]

No formal diagnostic criteria exist. A diagnosis of Inappropriate sinus tachycardia is primarily one of exclusion and the following may be observed:

Treatment[edit]

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).

See also[edit]

References[edit]

  1. ^ Chiale, Pablo A.; Garro, Hugo A.; Schmidberg, Jorge; Sánchez, Rubén A.; Acunzo, Rafael S.; Lago, Manuel; Levy, Gabriela; Levin, Mariano (2006). "Inappropriate sinus tachycardia may be related to an immunologic disorder involving cardiac β andrenergic receptors". Heart Rhythm 3 (10): 1182–6. doi:10.1016/j.hrthm.2006.06.011. PMID 17018348. 
  2. ^ Nattel, Stanley (2006). "Inappropriate sinus tachycardia and beta-receptor autoantibodies: A mechanistic breakthrough?". Heart Rhythm 3 (10): 1187–8. doi:10.1016/j.hrthm.2006.07.019. PMID 17018349. 
  3. ^ Sato, Toshiaki; Mitamura, Hideo; Murata, Mitsushige; Shinagawa, Kaori; Miyoshi, Shunichiro; Kanki, Hideaki; Takatsuki, Seiji; Soejima, Kyoko; Miyazaki, Toshihisa (2000). "Electrophysiologic findings of a patient with inappropriate sinus tachycardia cured by selective radiofrequency catheter ablation". Journal of Electrocardiology 33 (4): 381–6. doi:10.1054/jelc.2000.9648. PMID 11099363. 
  4. ^ Zellerhoff, Stephan; Hinterseer, Martin; Felix Krull, Bastian; Schulze-Bahr, Eric; Fabritz, Larissa; Breithardt, Günter; Kirchhof, Paulus; Kääb, Stefan (2010). "Ivabradine in patients with inappropriate sinus tachycardia". Naunyn-Schmiedeberg's Archives of Pharmacology 382 (5–6): 483–6. doi:10.1007/s00210-010-0565-y. PMID 20859616. 
  5. ^ Lee, Randall J.; Kalman, Jonathan M.; Fitzpatrick, Adam P.; Epstein, Laurence M.; Fisher, Westby G.; Olgin, Jeffrey E.; Lesh, Michael D.; Scheinman, Melvin M. (1995). "Radiofrequency Catheter Modification of the Sinus Node for 'Inappropriate' Sinus Tachycardia". Circulation 92 (10): 2919–28. doi:10.1161/01.CIR.92.10.2919. PMID 7586260. 

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