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Inappropriate Sinus Tachycardia (IST), also known as chronic nonparoxysmal sinus tachycardia or sinus tachycardia, is primarily a condition in which the resting heart rate is elevated or uneven, commonly known as arrhythmia. IST is a type of tachycardia not very commonly seen in individuals. The cause and disease mechanism is not very well understood till date. It was identified in 1979, and is a relatively new discovery, which may be the reason why not much is known about this condition. Amongst the ones diagnosed with this condition, women in their twenties or thirties form a majority, along with women working in healthcare. The reason behind the given age group and profession being more susceptible to the disease is still unclear.

Causes
The cause of IST is still unknown, and is being studied by researchers around the world. Since this condition is a type of arrhythmia, the sinus node abnormalities may be the reason for this heart disease. The sinus node is the natural pacemaker of the heart, which controls heart rate. In the event of failure of the sinus node, the atrioventricular node (AV node) takes over. Thus, AV node blockage may also be a cause of arrhythmia. Structural changes in the sinus node have also been observed in certain cases. There is a speculation made by researchers that, the sensitivity of beta adrenergic receptors is enhanced in IST. Beta adrenergic receptors are present on cells; increase in heart rate is one of the responses observed when these receptors are sensitized. Pregnancy may be one of the reasons to cause this problem, as the heart rate increases during pregnancy. This however, is not a confirmed finding.

Symptoms
As stated earlier, the primary manifestation of IST is an elevated heart rate. Therefore, the symptoms are a result of these, which includes
  • Palpitations: Awareness of the heart beating irregularly.
  • Dyspnea
  • Fatigue and inability to perform exercises
  • Chest pain
This condition rarely causes heart attacks, but nonetheless, you have to be very cautious of other symptoms.

Diagnosis
The diagnosis of this problem usually adopts the exclusion theory. Electrocardiogram results are normal in IST. As there are no specific symptoms, it is necessary to rule out other diseases before confidently diagnosing this condition. Therefore, diseases with similar symptoms have to be excluded. These are listed as follows,
  • Hyperthyroidism
  • Anemia
  • Pheochromocytoma
  • Anxiety
  • Pulmonary embolism
Though the number of diseases to rule out are many, most of them can be identified by simple urine and blood tests. Accurate diagnosis is of utmost importance to receive correct treatment. There have been cases where patients were misdiagnosed with anxiety, however, a visit to the cardiologist or electrophysiologist will give you the appropriate diagnosis.

Treatment
Beta blockers are the first line of treatment, with IST. Calcium channel blockers and anti-arrhythmic drugs also being prescribed. This is a non-invasive treatment given to patients.

Invasive treatment includes catheter ablation, which is a surgical method, wherein, the faulty pathway responsible for the tachycardia or arrhythmia is removed. The catheter is directed towards the affected region, and with the help of high frequency impulses, arrhythmia is induced. This is how the abnormal or faulty tissue is ablated or destroyed. These cardiac ablations treatment may include
  • Sinus node modification, where a part of the sinoatrial node tissue is ablated.
  • Complete sinus node ablation, wherein, the complete tissue is ablated and is replaced with an artificial pacemaker
  • AV node ablation also necessitates the implantation of an artificial pacemaker.
  • In case you have been diagnosed with IST and are pregnant, be sure to take an appointment with a high risk OB to prevent any untoward complications during delivery.
Research on treatment options for this problem are still in its initial stages. Risking new treatments is not advisable, as not much is known about this condition. If you think you are showing the above symptoms, consult your physician and do not disregard any of the symptom as just a 'mild discomfort'.

Disclaimer: This Buzzle article is for informative purposes only, and should not be replaced for the advice of a medical professional.