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Question:
How is IST (inappropriate sinus tachycardia) managed?
I'm a 36 y/o female who was diagnosed with IST in 2007 and continue to experience symptomatic episodes including fatigue, palpitations with shortness of breath, diaphoresis and presyncope. I have had an echo, EKG, EP study with no AVRNT found, blood and urine analysis. I have consulted with an endocrinologist but they weren't able to offer any further diagnostic value to my situation. I have been mostly rate controlled with beta and calcium channel blocker therapy, but have been having episodes of bradycardia in the 40's while I'm walking around and have developed more of an arrhythmia over the last 6 months, my heart rate will fluctuate from 120's to 40's without exertion within a minute's time frame. They now believe that I have chemically induced asymptomatic bradycardia and are lowering my BB dosage. I'm anticipating that my resting heart rate will climb up again and I will begin having symptomatic episodes of tachycardia. I realize the newness of my situation in the medical field, but was wondering if you have any other insight into the etiology of my condition or treatment options? If the etiology is dysautonomic or sinus node related, would a device be favored and would a device offer relief of my symptoms? Do you know if ablation long term success rates have improved over the last 5years? I've read that IST is believed to be a transient condition of sorts, is there any information on how long most people experience their symptoms before it improves and/or an intervention is attempted? Thanks in advance for your time.
submitted by Jackie from Missouri on 2/23/10
Answer:
by Texas Heart Institute cardiologist, Christopher M. Frank, MD
Inappropriate sinus tachycardia, or IST, is a recently described entity in which the heart rate is elevated over the expected range using the normal mechanism (i.e. "sinus tachycardia") in the absence of any of the expected causes (hence "inappropriate" sinus tachycardia). After causes such as thyroid disease, heart failure, anemia, fever, anxiety, panic disorder, pheochromocytoma, or any other medical causes are excluded, there does seemto be a group of patients who have sinus tachycardia without an identifiable reason. This is a poorly understood and somewhat mysterious entity; abnormalities of autonomic control, antibodies directed against betareceptors, and iron deficiency (even in the absence of anemia) have all been implicated as a possible cause of this syndrome. Alternatively, some patients appear to have localized forms of atrial tachycardia from an area "near" the sinus node, or sinus node reentry, which are intrinsic electrical abnormalities of the heart. In addition, there is some overlap with another complex and poorly understood entity called the postural orthostatic tachycardia syndrome, or POTS. For reasons that are not entirely clear, these diagnoses are more common in young women, particularly young women in health professions.
Treatment of IST is mostly empiric, and often involves a trial and error process with any one of several medications as well as a variety of lifestyle changes; as the questioner states, in many cases the syndrome seems to be transient and resolves over the course of several months. In some refractory cases, patients have benefited from catheter ablation procedures; however, as the questioner implies, the long-term success rates of such procedures are somewhat open to question, and there are no large series with long-term followup available to guide recommendations. There are certainly individual patients who have clear and long-lasting benefit from catheter procedures, although (unlike with some other arrhythmias) a trial of medical therapy for at least several weeks to months is probably wise in all patients prior to resorting to a catheter-based ablation.
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Updated February 2010
