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Inappropriate Sinus Tachycardia (IST): No Longer a "Benign" Diagnosis

For those not familiar with me, a little back story. I began experiencing IST in 2013 in the 20th week of my last pregnancy at the age of 36. I had been completely healthy heart-wise for my previous pregnancies, so this came as a shock to me. Many years later, I learned that I had a familial history passed down through the women of my family of atrial fibrillation. When cardiac genetic testing happened to be ordered in late 2021, I wasn't surprised to find that I had a SCN5A genetic mutation that is known to be related to sick sinus syndrome, either slowing or exciting the sodium channels in the heart and those in the SA node in particular, an area of excitation for those of us with IST,

The heart arrhythmia was treated with an alpha beta blocker, labetolol, which was known to be relatively safe during pregnancy. I was not actually diagnosed with IST until two years later in 2015, after I had already sustained a mild stroke despite never having atrial fibrillation. It was the fall-out from my stroke and on-going frequent TIAs as well as progressive IST that was more and more limiting despite trials of every medicatioin known to treat IST and maxing out on ivabradine that forced me to consider a radiofrequency ablation when my career as a physical therapist was threatened.

While I do not regret getting the radiofrequency ablation of the SA node with balloon protection of the phrenic nerve, months later I was diagnosed with constrictive pericarditis that required open heart surgery. A sternum-malunion that caused a bone infection called osteomyelitis required 2 more chest surgeries to cure and heal the bone.

Within a year, I became short of breath with exertion again, and I was diagnosed with acquired pulmonary vein obstruction/stenosis, which is a narrowing of the pulmonary vein(s) due to scar tissue from my previous open heart surgery.

This is the backstory to my blog post called Benign, where I lamented the way IST had been minimized in all of the "trusted online medical authorities" and is blown off by physicians, like it's not important, it's no big deal, and it never leads to anything worse like stroke or transient ischemic attacks (TIAs) that I had endured. Benign by definition means "having no significant effect; harmless." But my experience was far different. Telling a patient who lost her favorite activity of distance running for life due to a mild stroke that her condition is benign is a cruel form of psychological torture, especially as I was facing life-threatening conditions as a result of the treatment required to cure my worsening IST.

In 2022, I came across a multi-disciplinary expert review article by Mayuga, et al, published in Circulation: Arrhythmia and Electrophysiology, and I was thrilled to finally read, "Clinicians are thus faced with the reality that ST, though often physiological, may be neither benign nor clinically insignificant." Finally, an admission by the medical profession that IST is not a benign diagnosis! Since I could only read the abstract due to a paywall, I messaged the author requesting the full article PDF.

The article itself is the most extensive and in-depth review of IST I have ever read and is timely, as it includes IST diagnosed in patients suffering from long COVID. It also dives deep into physiological reasons for the development of IST. One of the strengths of the article is the multi-disciplinary input from a variety of professionals,. Other notable elements of the article are the amazing figures depicting evaluation for IST, autonomic dysfunction and the SA node, classification of IST, and work-up for IST for patients with long COVID syndrome.

However, it was disappointing to read the psychologists' point of view that patients who do not have a physicologial reason for IST could simply have anxiety and be treated with cognitive behavior training. While this could be true for a very small portion of those suffering with IST (there was no evidence provided as to the number of patients or even the symptomolgy of patients who have no physiological reason for IST), this would be impossible to claim as the authors admit in this same article that the phyiolgocial etiology of IST symptoms is still in the process of being delineated. Including this information without a caveat that this is not a common presentation of IST only reaffrims the standard physician approach of mimizing and refusing to believe patient's symptoms. This leads to delays in and misdiagnosing the patient's IST as simply anxiety or panic attacks and/or leading to an ineffective treatment plan of CBT.

One other area of interst for this physical therapist (PT) is a table depicting a training and exercise program for patients with IST. There appears to be an underlying assumption by the authors that patients with IST are inactive and deconditioned. Actual patients with IST such as myself, are generally quite active prior to their symptoms starting. I recall that I was walking daily for miles with my family in addition to performing strength and conditioning exercises with my fitness clients, including doing two foot box jumps during my sixth month of pregnancy. I continued coaching my clients after IST began, but soon found that my shortness of breath and lightheadedness made it impossible for me to give client's instructions in the activities I was demonstrating, thus ending my ability to coach clients . As the frequency of my IST progressed, I found doing any physical activity lead to so many symptoms, it wasn't even worth the time to lace up my shoes to do any additional exercise other than my normal daily activities of shopping, running errands, playing with the kids, and treating my patiets. Over time, even these activities became quite limited, depending on the efficacy of my medication regime at the time.

There are no studies to date that prove that physical exercise reduces IST symptomology and improves quality of life in patients with IST. However, as a PT myself, I do believe every patient no matter the diagnosis should remain as active as possible, as there are always health benefits to exercise. However, patients with IST may read the contents of the exercise program contained in this article with a chuckle, as the feasibility is nearly if not impossible for most or perhaps all patients with IST to perform the recommended exercise intensity, duration, and progressions. The recommendations included in the article are based on the opinion of experts, not on research that proves that exercise reduces IST symptomology and improves quality of life.. Most if not all of the patients I have met with IST find that simply doing daily activities like grocery shopping, running errands, attending social events, playing with children are in and of themselves exhausting. Typically patients cannot do even these activities without significant fatigue due to symptom provocation. This makes these exercise recommendations unrealistic for the majority if not all patients with IST. I personally recommend that patients with IST work with a PT experienced in working with patients with autonomic dyscunction to tailor an exercise program that is best suited for the individual patient to have the best likelihood of symptom improvement.

Nonetheless, this article provides a major step forward for those suffering from IST and seraching for the answers that are so difficult to find about etiology, causation, and treatment to maintain qualify of life and prevent more serious problems mentioned in the article like "...cardiovascular disease, heart failure, cancer, and mortality." Never again can physicians say that IST is "benign," and thus not worthy of their time, attention, and treatment. This article is a good review of current expert knowledge and research on IST. Hopefully it will serve as a great starting point for additional research on IST to improve testing and treatment options for those so limited by this diagnosis.

Reference: Mayuga KA, et al. Sinus tachycardia: a multidisciplinary expert focused review. Circ Arrhythm Electrophys. 2022; 15(9);610-635.


Jill Murphy is a Doctor of Physical Therapy and founder of MotionWorks Physical Therapy and an advocate for patient-centered care. A Christian mom of three, she survived a seven year journey through the broken American healthcare system in search for an answer to a heart arrhythmia that appeared during pregnancy. A stroke, open heart surgery for constrictive pericarditis, and several other surgeries later, Jill is telling her story of unfailing resilience in her upcoming book, Doctor Heal Thyself.

Having grown up on a dairy farm 40 minutes from Lambeau Field, Jill is an avid Green Bay Packers and Wisconsin Badgers fan, and is up for any activity with her three children, including walking, biking, throwing the football around, hiking in scenic locales, gardening, playing piano, singing, and coaching a middle school basketball game or two.

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