What is inappropriate sinus tachycardia?

What is inappropriate sinus tachycardia?

Inappropriate sinus tachycardia (IST) is sinus tachycardia inappropriate to the clinical situation. It is defined as sinus rates above 100 beats per minute at rest or average sinus rate above 90 beats per minute over 24 hours without an underlying cause [1]. It may be either asymptomatic or sometimes associated with palpitation, shortness of breath, near syncope, chest pain, anxiety or exercise intolerance. Important secondary causes of sinus tachycardia like the use of caffeine, alcohol, nicotine, drugs of abuse like cocaine, hyperthyroidism, fever, anxiety, pain and other illnesses which can cause sinus tachycardia have to be excluded before considering IST. In addition to resting sinus tachycardia, an exaggerated response to even minimal exertion and autonomic stress are often noted in IST.

A 2015 heart rhythm society (HRS) expert consensus statement defined IST as a sinus heart rate > 100 bpm at rest (with a mean 24-hour heart rate > 90 bpm not due to primary causes) associated with distressing symptoms of palpitations [2]. Patients with postural orthostatic tachycardia syndrome (POTS) can have symptoms similar to IST. But symptoms of POTS are generally induced only by orthostatic stress while those of IST can be induced by both physiologic and emotional stresses. The expert consensus statement gives class III recommendation for sinus node modification, surgical ablation, and sympathetic denervation as a part of routine care for patients with IST.

Ivabradine has been given a class II a recommendation in the expert consensus [2]. This was based on randomized crossover study involving 21 patients. They were randomized to placebo or ivabradine for a period of weeks. Crossover was done after a washout period, for another 6 weeks. More than 70% patients reported elimination of symptoms with 47% experiencing complete elimination. There was a significant reduction in resting heart rate, standing heart rate, 24 hour heart rate and heart rate during effort. Significant increase in exercise performance was also noted. No cardiovascular adverse effects were observed in that study [3].

The HRS expert consensus mentioned that modification and ablation of sinus node, though associated with reasonably good success rates, have high rate of symptom recurrence and significant complication rates. The complications mentioned include requirement for permanent pacemaker implantation, transient or permanent phrenic nerve paralysis and transient superior vena cava syndrome. They found no agreement on the optimal approach including modification or ablation, open chest versus conventional intravascular access and mapping methods. They could not find evidence of symptomatic improvement over several years [2].

A retrospective study of IST from Mayo Clinic had 305 patients with IST between 1998 to 2018. 92.1% were females and the mean age was 33.2 ± 11.2 years [4]. They compared these patients with age and gender-matched control group with atrioventricular nodal reentry tachycardia (AVNRT). Most frequent triggering conditions were pregnancy (7.9%) and infectious illness (5.9%). No major triggering event was noted in the majority of patients. The most common comorbid conditions were depression (25.6%) and anxiety (24.6%). There was no association between IST and cardiomyopathy or mortality in that study. They found no excess mortality in IST compared with AVNRT control group.

A report on 18 patients who underwent surgical sinoatrial node isolation between 1987 and 2018 has been reported [5]. 10 patients had median sternotomy while 8 underwent minimally invasive right thoracotomy. Isolation of sinus node was done using surgical incisions, cryoablation or bipolar radiofrequency ablations. Immediate postoperative success was 100% in these cases. In the 17 patients who had a mean follow up of 11.4 ± 7.9 years, all were free of symptomatic recurrence of IST. Three of them reported occasional palpitation. Four patients were on beta-blockers and five required pacemaker implantation later. All the 8 patients who have minimally invasive isolation were in sinus rhythm at last follow up and only one of them complained of palpitation.

Ivabradine, beta-blockers and non-dihydropyridine calcium channel blockers may be useful in controlling IST. Ablative procedures are seldom advised now-a-days [1]. Historically, surgical ablation, catheter ablation of sinus node, catheter modification of sinus node and ablation of His bundle with implantation of a pacemaker were the procedures which have been tried in the past for drug refractory IST [6].

References

1. Olshansky B, Sullivan RM. Inappropriate sinus tachycardia. Europace. 2019 Feb 1;21(2):194-207. doi: 10.1093/europace/euy128. PMID: 29931244.
2. Sheldon RS, Grubb BP 2nd, Olshansky B, Shen WK, Calkins H, Brignole M, Raj SR, Krahn AD, Morillo CA, Stewart JM, Sutton R, Sandroni P, Friday KJ, Hachul DT, Cohen MI, Lau DH, Mayuga KA, Moak JP, Sandhu RK, Kanjwal K. 2015 heart rhythm society expert consensus statement on the diagnosis and treatment of postural tachycardia syndrome, inappropriate sinus tachycardia, and vasovagal syncope. Heart Rhythm. 2015 Jun;12(6):e41-63. doi: 10.1016/j.hrthm.2015.03.029. Epub 2015 May 14. PMID: 25980576; PMCID: PMC5267948.
3. Cappato R, Castelvecchio S, Ricci C, Bianco E, Vitali-Serdoz L, Gnecchi-Ruscone T, Pittalis M, De Ambroggi L, Baruscotti M, Gaeta M, Furlanello F, Di Francesco D, Lupo PP. Clinical efficacy of ivabradine in patients with inappropriate sinus tachycardia: a prospective, randomized, placebo-controlled, double-blind, crossover evaluation. J Am Coll Cardiol. 2012 Oct 9;60(15):1323-9. doi: 10.1016/j.jacc.2012.06.031. Epub 2012 Sep 12. PMID: 22981555.
4. Shabtaie SA, Witt CM, Asirvatham SJ. Natural history and clinical outcomes of inappropriate sinus tachycardia. J Cardiovasc Electrophysiol. 2020 Jan;31(1):137-143. doi: 10.1111/jce.14288. Epub 2019 Dec 1. PMID: 31749258.
5. Khiabani AJ, Greenberg JW, Hansalia VH, Schuessler RB, Melby SJ, Damiano RJ Jr. Late Outcomes of Surgical Ablation for Inappropriate Sinus Tachycardia. Ann Thorac Surg. 2019 Oct;108(4):1162-1168. doi: 10.1016/j.athoracsur.2019.03.103. Epub 2019 May 8. PMID: 31077661; PMCID: PMC6930839.
6. Lee RJ, Kalman JM, Fitzpatrick AP, Epstein LM, Fisher WG, Olgin JE, Lesh MD, Scheinman MM. Radiofrequency catheter modification of the sinus node for “inappropriate” sinus tachycardia. Circulation. 1995 Nov 15;92(10):2919-28. doi: 10.1161/01.cir.92.10.2919. PMID: 7586260.