Refractory inappropriate sinus tachycardia treated with hybrid ablation

We present a patient with medication-refractory inappropriate sinus tachycardia (IST) who was hospital-bound and successfully treated with hybrid thoracoscopic ablation.

Introduction

Inappropriate sinus tachycardia (IST) is a rare, potentially debilitating syndrome, characterised by persistent or paroxysmal sinus tachycardia in the presence of symptoms, such as palpitations, chest discomfort, dyspnoea, fatigue, or syncope.¹ It is a diagnosis of exclusion, defined by an elevated resting heart rate (HR) in the absence of an identifiable physiological cause.^1,2 Prevalence is estimated at around 1%, with a predominance in young women.² The pathogenesis remains poorly understood, but appears multi-factorial, with autonomic dysfunction a central abnormality.¹

In many individuals, IST is a self-limiting condition, albeit one that may take many months, or even years, to resolve. Managing symptoms during this prolonged course can be challenging, as medical therapy often provides limited benefit.^1,3 Catheter ablation targeting the sinus node (SN) has been attempted in severe drug-refractory cases, though procedural success and long-term outcomes remain variable.^1,3,4 More recently, a hybrid SN-sparing epicardial–endocardial technique has emerged as a promising alternative approach.^2,3

Case presentation

An 18-year-old woman presented to the emergency department with sudden-onset palpitations, chest pain, dyspnoea, diaphoresis, and overwhelming anxiety. She had returned from the US 24 hours earlier, where she had spent more than six weeks in hospital with almost daily episodes of identical symptoms. These typically occurred at rest, with no pattern or trigger. There was no history of alcohol or recreational drug use, and prior to this illness, her only medical history was mild asthma and autism spectrum disorder. However, during her admission abroad she had been diagnosed with postural orthostatic tachycardia syndrome (PoTS), supraventricular tachycardia (SVT), and non-epileptic attack disorder.

Investigations and management

A 12-lead electrocardiogram (ECG) demonstrated a narrow complex tachycardia, with a HR around 180 beats per minute (bpm), that was unresponsive to vagal manoeuvres and adenosine, given empirically for presumed re-entrant SVT. Intravenous (IV) metoprolol subsequently terminated the arrhythmia, and the patient was admitted to the acute cardiac unit. Here, further paroxysms were observed on telemetry, each characterised by an abrupt rise in HR with associated debilitating symptoms, particularly pre-syncope during ablutions. These episodes gradually resolved following administration of metoprolol, with a slow tapering of both symptoms and HR.

Transthoracic echocardiography demonstrated borderline low left ventricular (LV) systolic function with no structural abnormality. Cardiac magnetic resonance imaging (MRI) confirmed an LV ejection fraction of 52% and was otherwise unremarkable. Formal testing for PoTS was negative and a wide range of organic pathologies were excluded, including thyrotoxicosis, phaeochromocytoma, Lyme disease, and mast-cell activation syndrome.

Based on the frequency of episodes and a presumptive diagnosis of SVT, the patient was referred for an electrophysiology study with a view to ablation. This demonstrated no substrate for re-entrant tachycardia, such as atrioventricular re-entry tachycardia (AVRT) or atrioventricular node re-entry tachycardia (AVNRT), confirming a diagnosis of IST. Medical therapy was subsequently up-titrated over the following weeks with limited effect. Despite treatment with verapamil (120 mg three times daily), bisoprolol, and ivabradine (both 7.5 mg twice daily), her resting HR persisted around 100 bpm, with at least alternate-day paroxysms requiring IV boluses of metoprolol. Given the severity of her symptoms and their drug-refractory nature, she was referred for consideration of a hybrid SN modification procedure via enrolment in the HEAL-IST trial (Hybrid Epicardial and Endocardial Ablation for IST). She was deemed eligible and, at the time of writing, four months post-procedure, has had no further episodes and remains off medications.

Discussion

IST has not been shown to increase mortality and is, therefore, generally considered benign.^4,5 Nevertheless, this case detailing an 18-year-old who spent over six months in hospital highlights the considerable morbidity that can result. It also illustrates the syndrome’s frequent lack of recognition, often resulting in misdiagnosis, as occurred here. Additionally, the perceived association with psychiatric comorbidities can lead to dismissal, particularly when the condition is unresponsive to medication.^1,5 This may frustrate physicians and further contribute to patient distress.

Our patient’s clinical course also emphasises the limitations of medical therapy in IST. Ivabradine has shown the most promise, demonstrating superiority over beta blockers and calcium-channel blockers at reducing mean HR, alleviating symptoms, and improving exercise tolerance.^1,4 However, in up to 30% of patients it fails to provide adequate symptomatic control.² In such medication-resistant cases, radiofrequency catheter ablation is considered and, historically, the target of this has been the SN.¹ Success has been limited by a high rate of symptom recurrence and complications, including SN dysfunction requiring permanent pacemaker implantation.² Procedural end points and definitions of success also remain unclear, making this an even more reluctant option.^1,4 Pulsed-field ablation, a non-thermal technique that preferentially targets myocardial tissue, has recently shown promise: in one case, ablation in a pacemaker-dependent patient successfully abolished symptoms, resulting in a junctional rhythm post-procedure requiring permanent pacemaker implant,¹ while another report described symptom resolution without the need for pacing.²

In this typically young patient population, the risk of pacemaker dependency following SN ablation outweighs the potential benefits, as in our case. A novel SN-sparing hybrid thoracoscopic approach has emerged to address this therapeutic gap. The hybrid ablation requires mapping and marking the SN to avoid applying energy to the node.¹ A camera port is introduced in the fifth intercostal space, and two instrument ports are placed in the third and seventh spaces. Radiofrequency lesions are applied to isolate the superior vena cava from the right atrium, and to isolate the lateral border of the right atrium.

In the multi-centre SUSRUTA-IST (Sinus Node Sparing Hybrid Thoracoscopic Ablation Outcomes in Patients with Inappropriate Sinus Tachycardia) registry, this novel hybrid technique was compared with conventional SN ablation and demonstrated superior outcomes.³ At 12 months, only 8% of patients in the hybrid group required a repeat procedure, compared with 100% of those treated with standard SN ablation. Strikingly, 78% of patients in the hybrid arm discontinued all rate-controlling medications after a single procedure, whereas none were able to do so following SN modification. In terms of complications, most notably, only 2% of patients in the SN-sparing cohort required a permanent pacemaker, compared with 50% in the conventional group.³ Further research, such as the HEAL-IST trial, is needed to validate these early results and define the long-term safety and efficacy of this technique.

Our case underscores the importance of recognising IST, as its impact on quality of life can be profound. Furthermore, it reinforces the potential of this novel treatment to transform care in appropriate patients with treatment-refractory IST.

Key messages

• Inappropriate sinus tachycardia (IST) is increasingly recognised in clinical practice. Although usually self-limiting, a small subset of patients experience debilitating symptoms and significant morbidity
• Medical management of IST is often limited in effectiveness, with ivabradine offering the greatest benefit among conventional agents
• Catheter ablation targeting the sinus node (SN) is limited by high recurrence rates and the risk of pacemaker dependency
• A novel hybrid SN-sparing epicardial–endocardial ablation approach offers a promising option for severe, drug-refractory IST

Conflicts of interest

None declared.

Funding

None.

Patient consent

Informed consent was obtained from the patient for publication of this case report. The patient reviewed the final manuscript and confirmed they were happy with its contents.

References

1. Olshansky B, Chung MK, Zipes DP et al. Inappropriate sinus tachycardia: definition, pathophysiology, and management. J Am Coll Cardiol 2022;79:2273–92. https://doi.org/10.1016/j.jacc.2022.04.019

2. Mahida S, Patel T, Lim HS et al. Clinical profile and management of patients with inappropriate sinus tachycardia: results from a multicentre registry. Heart Rhythm Open 2023;4:100075. https://doi.org/10.1016/j.hroo.2023.100075

3. Mahida S, Sivasambu B, Dukkipati SR et al. Hybrid thoracoscopic ablation for inappropriate sinus tachycardia: results from the SUSRUTA-IST registry. Heart Rhythm 2022;19:1683–91. https://doi.org/10.1016/j.hrthm.2021.10.009

4. Marrouche NF, Beheiry S, Tomassoni G et al. Catheter modification of the sinus node for inappropriate sinus tachycardia: long-term results using a new mapping approach. Heart Rhythm 2015;12:1065–72. https://doi.org/10.1016/j.hrthm.2015.03.010

5. Man KC, Knight BP, Tse HF et al. Radiofrequency catheter ablation of inappropriate sinus tachycardia guided by activation mapping. J Cardiovasc Electrophysiol 2021;32:1561–8. https://doi.org/10.1111/jce.14288