The normal heartbeat is generated just like clockwork by electric signals sent out from a natural pacemaker known as the sinus node. Normal individuals have heart rates of between 60-90 beats per minute. This is actually slower than the natural pacemaker of the heart, partly because there is the slowing influence of the nervous system known as vagal tone. Typically, patients with inappropriate sinus tachycardia have a resting heart rate of >100 beats/minute and not explained by other causes (such as arrhythmias like Afib with RVR or sinus arrhyhthmia). In patients with inappropriate sinus tachycardia (IST), even minimal levels of activity can result in rapid acceleration of heart rate that may cause some of those affected to severely limit their levels of activity.
Symptoms of inappropriate sinus tachycardia may include palpitations (sometimes described as heart flutter), feeling dizzy, weakness, anxiety, and a sensation of almost passing out. Interestingly the symptoms are not always associated with the resting heart rate. Whereas normally the heart rate recovers fairly rapidly after exercise, the recovery of heart rate to a normal level may be prolonged in those with inappropriate sinus tachycardia. In some people, the sinus heart rate normally increases in response to certain situations such as ingestion of caffeine, fever, anxiety etc. however this reverses when the stimulus is removed. In patients with inappropriate sinus tachycardia the increased heart rate is generally a more permanent problem. Most patients with inappropriate sinus tachycardia are young females. The good news is that the prognosis is typically benign with few long-term consequences. Although the prognosis is benign, the symptoms can be very limiting in some patients.
One of the most important aspects of evaluating someone for inappropriate sinus tachycardia is excluding other possible causes of a fast heart rate. Other arrhythmias have to be ruled out. Many commonly ingested substances such as alcohol, tobacco and caffeine are often the cause. Drugs such as methamphetamines and cocaine, as well as many commonly used medications such as those in inhalers used as breathing treatments. It’s important to rule out underlying medical conditions also when evaluating inappropriate sinus tachycardia. These include pain, fever, dehydration, high thyroid hormone levels and underlying heart conditions. It’s also important that inappropriate sinus tachycardia is differentiated from POTS syndrome that is characterized by tachycardia on standing.
Management Of Inappropriate Sinus Tachycardia
Management of inappropriate sinus tachycardia is typically centered on controlling heart rate and symptoms. Those without symptoms will generally not require treatment. Treatment is also made more difficult by the fact that controlling the heart rate may not necessarily control symptoms. Another major problem is that the therapies used to control heart rate may actually make patients more symptomatic! For this reason, when therapies are considered they should be managed by dedicated specialists. Use of medications to slow the heart rate down, such as beta-blockers, are often ineffective. Of interest, a drug called Ivabradine has recently been demonstrated to effectively lower heart rate although its utility in the setting of inappropriate sinus tachycardia requires further investigation before it can be suggested as a first line therapy. Treatments to treat associated anxiety may be helpful in some cases. Although many treatments are attempted, very few of these are proven to effectively treat IST. The use of procedure such as catheter-based treatments and even surgical treatments for inappropriate sinus tachycardia have been described however these approaches should only be used with extreme caution and only if all other approaches have failed, as the outcomes may potentially worsen. Many experts feel that conditioning by the means of exercise training is the most helpful method of treatment. My major suggestion is to ensure you are evaluated by a specialist with known interest and experience in the management of inappropriate sinus tachycardia.
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