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.
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 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 mechanism has been suggested as several studies have detected autoantibodies that activate beta adrenoreceptors in a portion of 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 therapy or catheter ablation are available, although it is currently difficult to treat successfully.
Symptoms reported by patients vary in frequency and severity.
Symptoms associated with IST include:
- Frequent or sustained palpitations
- Dyspnea (shortness of breath) and palpitations on exertion
- Pre-syncope (feeling as if about to faint)
- Fatigue (physical)
- Exercise intolerance
- Occasional paresthesia and cramping
- Symptoms associated with autonomic nervous system disturbance, including GI disturbance
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
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. Exercise and physical conditioning is often the most effective treatment for IST.
Some types of medication tried by cardiologists and other physicians include: beta blockers, selective sinus node If channel inhibitors (ivabradine), 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 (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).
- Supraventricular tachycardia
- Sinus tachycardia
- Postural orthostatic tachycardia syndrome
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- Dysautonomia International
- IST UK
- Inappropriate sinus tachycardia by Dr Richard N. Fogoros
- Arrhythmia Alliance
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