Inappropriate sinus tachycardia

Translational Anatomy of the Sinoatrial Node: Myoarchitecture and its Relevance for Catheter Ablation: Part II: Clinical Applications

ANATOMY

Clinical applications relevant to the sinoatrial node anatomy for interventional electrophysiology procedures are reviewed.

PATHOLOGY

Inappropriate sinus tachycardia, atrial tachycardia, and superior vena cava triggers for atrial fibrillation.

IMAGING CORRELATION

Three-dimensional electroanatomic mapping, intracardiac echocardiography.

TREATMENT

Ablation guided by activation mapping and intracardiac electrograms.

TAKE-HOME MESSAGE

Understanding the anatomy of the sinoatrial node and the perinodal region provides key anatomic concepts to safely and effectively guide ablation procedures.

Advances in Cardiovascular Pharmacotherapy. II. Ivabradine, an Inhibitor of the Hyperpolarization-Activated Cyclic Nucleotide-Gated Channel

Ivabradine selectively reduces heart rate by inhibiting the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel in the sinoatrial node. Unlike other medications that produce negative chronotropic effects [beta-blockers, calcium channel blockers], ivabradine does not affect systemic, pulmonary, and coronary hemodynamics. Despite several proof-of-concept clinical studies suggesting that ivabradine may exert anti-ischemic effects, two large randomized trials did not support its use in patients with chronic stable angina. Preliminary data also did not support the use of ivabradine in patients with acute ST-segment elevation myocardial infarction or acutely decompensated heart failure. However, ivabradine improved outcome in patients with heart failure with reduced ejection fraction (HFrEF), leading to its approval by the Food and Drug Administration, but the drug failed to do so in those with heart failure with preserved ejection fraction (HFpEF). Ivabradine may also be useful in cardiac electrophysiology disorders characterized by tachycardia (e.g., inappropriate sinus tachycardia, postural orthostatic tachycardia syndrome), but it has not yet gained wide acceptance for these indications. In this article, the authors briefly review the structure and function of the cardiac HCN channel; discuss the development and actions of drugs, including ivabradine, that modulate the channel's activity; describe in detail the potential clinical applications of ivabradine in patients with coronary artery disease, HFrEF and HFpEF, and cardiac electrophysiology; comment on the adverse effects of ivabradine therapy; and finally, consider the potential anesthetic implications of ivabradine in patients undergoing noncardiac and cardiac surgery.

Endo-epicardial mapping of human sinus node in vivo: Novel electrophysiologic findings and anatomic correlations

BACKGROUND

The human sinoatrial node (SAN) pacemaker is a complex structure located at the right atrium (RA)-superior vena cava (SVC) junction.

OBJECTIVE

This study aimed to perform in vivo endocardial and epicardial electroanatomic mapping of human SAN in inappropriate sinus node tachycardia (IST) and to correlate electrical findings with anatomic observations from thoracoscopy during hybrid SAN-sparing IST ablation.

METHODS

All consecutive patients with diagnosis of symptomatic IST, refractory to or intolerant of drugs, and endocardial and epicardial mapping of SAN during hybrid ablation were included. Local activation time was defined by steepest -dV/dT on unipolar electrogram (EGM). Exit zone (EZ) was defined as the earliest activation site on endocardial and epicardial maps. Endo-epicardial delay was the time difference between the first endo-epicardial activations. Bipolar EGM morphology and SVC sleeve extension were analyzed.

RESULTS

A total of 61 patients were included. The SAN-EZ area was 1.4 ± 0.6 cm2; it was located in the superior anterior region of the RA in 46 (75.4%) patients and in the mid RA in 15 (24.6%) patients. The earliest activation occurred on epicardial SAN-EZ in all patients. The local activation time of the epicardial vs endocardial SAN-EZ was -30.8 ms vs -12.4 ms (P < .001). Endo-epicardial delay was 19.7 ms. Bipolar EGM reversed polarity at SAN-EZs was observed in 43 (70.5%) patients. SVC sleeve extension was 31.2 mm and inversely correlated with age.

CONCLUSION

The earliest SAN-EZ was found in the epicardium. Bipolar EGM reversed polarity is a novel electrophysiologic marker for SAN-EZs.

Prolonged Treatment of Inappropriate Sinus Tachycardia with Continuous Stellate Ganglion Blockade: A Case Report

Inappropriate sinus tachycardia (IST) presents challenges in diagnosis and treatment due to its unclear etiology and limited therapeutic options. This case report explores the use of continuous stellate ganglion block (CSGB) as a potential treatment avenue. A 23-year-old woman with refractory IST underwent several CSGB placements, resulting in prolonged symptom relief and decreased median heart rate. Despite the eventual recurrence of symptoms, the sustained effects of CSGB suggest its efficacy in managing IST. This report underscores the potential of CSGB as a promising therapeutic approach for IST, offering longer-lasting symptom control compared to single-injection stellate ganglion block (SGB) interventions.

Robotic-enhanced hybrid ablation for inappropriate sinus tachycardia: a world-first approach

We describe a world-first robotic ablation for inappropriate sinus tachycardia. A 26-year-old woman with refractory inappropriate sinus tachycardia underwent robotic-enhanced hybrid ablation, combining electrophysiological mapping with superior visualization and access compared to video-assisted thoracoscopic surgery (VATS) approaches. Ablations normalized the heart rate from 120 to 70 bpm. At one- and six-month follow-ups, she reported symptom resolution and improved quality of life. Holter monitoring confirmed no tachycardic episodes. This presents a promising alternative for patients who have exhausted conventional treatments, potentially revolutionizing inappropriate sinus tachycardia management.

Postural Orthostatic Tachycardia Syndrome Associated with COVID-19: A Narrative Review

Postural orthostatic tachycardia syndrome (POTS) is a complex condition marked by an atypical autonomic response to standing, leading to orthostatic intolerance and significant tachycardia without accompanying hypotension. In recent studies, a considerable number of individuals recovering from COVID-19 have been reported to experience POTS within 6 to 8 months post-infection. Key symptoms of POTS include fatigue, difficulty with orthostatic tolerance, tachycardia, and cognitive challenges. The underlying causes of POTS following COVID-19 remain unknown, with various theories proposed such as renin-angiotensin-aldosterone system (RAAS) dysregulation, hyperadrenergic reaction, and direct viral infection. Healthcare professionals should be vigilant for POTS in patients who have recovered from COVID-19 and are experiencing signs of autonomic dysfunction and use diagnostic procedures such as the tilt-up table test for confirmation. COVID-19-related POTS should be approached with a holistic strategy. Although many patients show improvement with initial non-drug treatments, for subjects who do not respond and exhibit more severe symptoms, medication-based therapies may be necessary. The current understanding of COVID-19-related POTS is limited, underscoring the need for more research to increase knowledge and enhance treatment approaches.

Intracardiac echocardiography guided anatomical ablation of the arcuate ridge for drug refractory inappropriate sinus tachycardia

INTRODUCTION

Inappropriate sinus tachycardia (IST) is a common condition with frequently not tolerated beta-blockers or ivabradine and a high rate of complication in ablation strategy; we describe an alternative anatomical approach of sinus node (SN) modulation.

METHODS

This retrospective study describes a case series of 6 patients from two centers diagnosed with symptomatic IST undergoing SN ablation.

RESULTS

The mean age was 40.6 ± 13.9 years; five of the six patients were female, 100% of patients reported heart palpitations, and 66% reported dizziness, the average heart rate (HR) on a 24-h Holter was 93.2 ± 7.9 bpm. HR during the first stage of a stress test using a standard Bruce protocol was 150 ± 70 bpm, The average HR on 24-h Holter postablation was 75 ± 5.6 bpm, the sinus rate HR during stage 1 of a Bruce protocol exercise stress test was 120 ± 10 bpm.

CONCLUSION

This is the first case series reporting the acute and long-term results of a novel anatomical approach for SN modulation to treat IST targeting the arcuate ridge (AR) under intracardiac echography (ICE) guidance. The novel anatomic ICE-guided catheter ablation approach aimed to identify the earliest activation at the AR with an extension of RF lesions toward its septal region seems effective and safe to modulate the SN in symptomatic patients with IST refractory to medical treatment.

Cardiovascular autonomic dysfunction in post-COVID-19 syndrome: a major health-care burden

Cardiovascular autonomic dysfunction (CVAD) is a malfunction of the cardiovascular system caused by deranged autonomic control of circulatory homeostasis. CVAD is an important component of post-COVID-19 syndrome, also termed long COVID, and might affect one-third of highly symptomatic patients with COVID-19. The effects of CVAD can be seen at both the whole-body level, with impairment of heart rate and blood pressure control, and in specific body regions, typically manifesting as microvascular dysfunction. Many severely affected patients with long COVID meet the diagnostic criteria for two common presentations of CVAD: postural orthostatic tachycardia syndrome and inappropriate sinus tachycardia. CVAD can also manifest as disorders associated with hypotension, such as orthostatic or postprandial hypotension, and recurrent reflex syncope. Advances in research, accelerated by the COVID-19 pandemic, have identified new potential pathophysiological mechanisms, diagnostic methods and therapeutic targets in CVAD. For clinicians who daily see patients with CVAD, knowledge of its symptomatology, detection and appropriate management is more important than ever. In this Review, we define CVAD and its major forms that are encountered in post-COVID-19 syndrome, describe possible CVAD aetiologies, and discuss how CVAD, as a component of post-COVID-19 syndrome, can be diagnosed and managed. Moreover, we outline directions for future research to discover more efficient ways to cope with this prevalent and long-lasting condition.

Novel Use of Ivabradine for Persistent Sinus Tachycardia in a Patient on Extracorporeal Life Support With Right Ventricular Dysfunction

Persistent sinus tachycardia (pST) has been associated with adverse cardiovascular events in critically ill patients. Pharmacological control of heart rate with negative inotropic agents has proven to be safe but could be potentially dangerous in patients with concomitant right ventricular (RV) dysfunction. Ivabradine, a medication devoid of negative inotropy, could be a potentially safe solution for this patient population when adequate heart rate control is desired. A 17-year-old male with a history of vaping developed acute respiratory distress syndrome (ARDS) and RV dysfunction, requiring extra corporal life support (ECLS). He suffered from pST. Given his RV dysfunction, a beta-blocker was avoided, and ivabradine was used safely with improvement of his pST. This case demonstrates the efficacy of ivabradine to reduce heart rate and avoid the use of beta-blockers for patients with RV dysfunction, which could be detrimental. Ivabradine was shown to lower the heart rate without altering hemodynamic parameters.

Cardiovascular dysautonomia in postacute sequelae of SARS-CoV-2 infection

Coronavirus disease 2019 (COVID-19) has led to a worldwide pandemic that continues to transform but will not go away. Cardiovascular dysautonomia in postacute sequelae of severe acute respiratory syndrome coronavirus 2 infection has led to persistent symptoms in a large number of patients. Here, we define the condition and its associated symptoms as well as potential mechanisms responsible. We provide a careful and complete overview of the topic addressing novel studies and a generalized approach to the management of individuals with this complex and potentially debilitating problem. We also discuss future research directions and the important knowledge gaps to be addressed in ongoing and planned studies.

Refractory Inappropriate Sinus Tachycardia Treated with Pulsed-field Ablation of the Sinus Node: A Breath of Fresh Air

The pathogenesis of inappropriate sinus tachycardia is not well understood, and the symptoms of inappropriate sinus tachycardia can be difficult to manage. Here, we present a case of inappropriate sinus tachycardia refractory to medical therapy and discuss our approach to sinus node modification by catheter ablation.

Heat and cold stress increases the risk of paroxysmal supraventricular tachycardia

Paroxysmal supraventricular tachycardia (PSVT) is a common arrhythmia in adults. Its occurrence depends on the presence of the reentry circuit and the trigger of the paroxysm. Stress, emotional factors, and comorbidities favour the occurrence of such an episode. We hypothesized that the occurrence of PSVT follows extreme thermal episodes. The retrospective analysis was based on the data collected from three hospital emergency departments in Poland (Olsztyn, Radom, and Wroclaw) involving 816 admissions for PSVT in the period of 2016-2021. To test the hypothesis, we applied the Universal Climate Thermal Index (UTCI) to objectively determine exposure to cold or heat stress. The risk (RR) for PSVT increased to 1.37 (p = 0.006) in cold stress and 1.24 (p = 0.05) in heat stress when compared to thermoneutral conditions. The likelihood of PSVT during cold/heat stress is higher in women (RR = 1.59, p< 0.001 and RR = 1.36, p = 0.024, respectively) than in men (RR = 0.64 at p = 0.088 and RR = 0.78, p = 0.083, respectively). The susceptibility for PSVT was even higher in all groups of women after exclusion of perimenopausal group of women, in thermal stress (RR = 1.74, p< 0.001, RR = 1.56, p = 0.029, respectively). Females, particularly at the perimenopausal stage and men irrespective of age were less likely to develop PSVT under thermal stress as compared to thermoneutral conditions. Progress in climate change requires searching for universal methods and tools to monitor relationships between humans and climate. Our paper confirms that the UTCI is the universal tool describing the impact of thermal stress on the human body and its high usefulness in medical researches.

Redo procedures after sinus node sparing hybrid ablation for inappropriate sinus tachycardia/postural orthostatic sinus tachycardia

AIMS

A novel sinus node (SN) sparing hybrid ablation for inappropriate sinus node tachycardia (IST)/postural orthostatic tachycardia syndrome (POTS) has been demonstrated to be an effective and safe therapeutic option in patients with symptomatic drug-resistant IST/POTS. The aim of this study was to evaluate the long-term rate of redo procedures after hybrid IST ablation and procedural strategy, outcomes and safety of redo procedures.

METHODS AND RESULTS

All consecutive patients from 2015 to 2023 were prospectively enrolled in the UZ Brussel monocentric IST/POTS registry. They were analysed if the following inclusion criteria were fulfilled: 1) diagnosis of IST or POTS, 2) symptomatic IST/POTS refractory or intolerant to drugs, and 3) hybrid SN sparing ablation performed. The primary endpoint was redo procedure. The primary safety endpoint was pacemaker (PM) implantation. A total of 220 patients undergone to hybrid IST ablation were included, 185 patients (84.1%) were treated for IST and 61 patients (27.7%) for POTS.After a follow-up of 73.3 ± 16.2 months, 34 patients (15.4%) underwent a redo. A total of 23 patients (67.6%) had a redo for IST recurrence and 11 patients (32.4%) for other arrhythmias. Pacemaker implantation was performed in 21 patients (9.5%). Nine patients (4.1%) had no redo procedure and experienced sick sinus syndrome requiring a PM. Twelve patients (5.4%) received a PM as a shared therapeutic choice combined with SN ablation procedure.

CONCLUSION

In a large cohort of patients the long-term free survival from redo procedure after hybrid IST ablation was 84.6% with a low PM implantation rate.

A gain-of-function HCN4 mutant in the HCN domain is responsible for inappropriate sinus tachycardia in a Spanish family

In a family with inappropriate sinus tachycardia (IST), we identified a mutation (p.V240M) of the hyperpolarization-activated cyclic nucleotide-gated type 4 (HCN4) channel, which contributes to the pacemaker current (If) in human sinoatrial node cells. Here, we clinically study fifteen family members and functionally analyze the p.V240M variant. Macroscopic (IHCN4) and single-channel currents were recorded using patch-clamp in cells expressing human native (WT) and/or p.V240M HCN4 channels. All p.V240M mutation carriers exhibited IST that was accompanied by cardiomyopathy in adults. IHCN4 generated by p.V240M channels either alone or in combination with WT was significantly greater than that generated by WT channels alone. The variant, which lies in the N-terminal HCN domain, increased the single-channel conductance and opening frequency and probability of HCN4 channels. Conversely, it did not modify the channel sensitivity for cAMP and ivabradine or the level of expression at the membrane. Treatment with ivabradine based on functional data reversed the IST and the cardiomyopathy of the carriers. In computer simulations, the p.V240M gain-of-function variant increases If and beating rate and thus explains the IST of the carriers. The results demonstrate the importance of the unique HCN domain in HCN4, which stabilizes the channels in the closed state.

Importance of resting heart rate

Resting heart rate is a determinant of cardiac output and physiological homeostasis. Although a simple, but critical, parameter, this vital sign predicts adverse outcomes, including mortality, and development of diseases in otherwise normal and healthy individuals. Temporal changes in heart rate can have valuable predictive capabilities. Heart rate can reflect disease severity in patients with various medical conditions. While heart rate represents a compilation of physiological inputs, including sympathetic and parasympathetic tone, aside from the underlying intrinsic sinus rate, how resting heart rate affects outcomes is uncertain. Mechanisms relating resting heart rate to outcomes may be disease-dependent but why resting heart rate in otherwise healthy, normal individuals affects outcomes remains obscure. For specific conditions, physiologically appropriate heart rate reductions may improve outcomes. However, to date, in the normal population, evidence that interventions aimed at reducing heart rate improves outcomes remains undefined. Emerging data suggest that reduction in heart rate via vagal activation and/or sympathetic inhibition is propitious.

Sinus Node Dysfunction

Sinus node dysfunction (SND) is a multifaceted disorder most prevalent in older individuals, but may also occur at an earlier age. In most cases, the SND diagnosis is ultimately established by documenting its ECG manifestations. EPS has limited utility. The treatment strategy is largely dictated by symptoms and ECG manifestations. Not infrequently, both bradycardia and tachycardia coexist in the same patients, along with other diseases common in the elderly (e.g., hypertension, coronary artery disease), thereby complicating treatment strategy. Prevention of the adverse consequences of both bradyarrhythmia and tachyarrhythmia is important to reduce susceptibility to syncope, falls, and thromboembolic complications.

Ivabradine for inappropriate sinus tachycardia-induced symptomatic Mobitz type I atrio-ventricular block: a case summary

Background

Inappropriate sinus tachycardia (IST) is characterized by a continuum of symptoms, and the aetiology of IST is imprecise. IST-induced autonomic dysfunction is well known, but IST-induced atrio-ventricular block is not reported to our knowledge.

Case summary

A 67-year-old female presented with a 4-day history of random intermittent difficulty in breathing, chest tightness, palpitations, and dizziness, with a recorded heart rate of 30 beats per minute (BPM) on home monitoring equipment. The initial electrocardiogram (ECG) demonstrated sinus rhythm with intermittent Mobitz type I second degree atrio-ventricular (AV) block, with continuous cardiac monitoring demonstrating frequent episodes of Wenckebach phenomenon throughout the day, with a sinus rate of 100-120 BPM. Echocardiogram showed no significant structural abnormalities. The patient was on bisoprolol, and hence, it was suspected Wenckebach may be due to that and so stopped. However, there was no tangible effect on rhythm 48 hours after stopping bisoprolol, leading to a suspicion of IST-induced Mobitz type I second degree AV block; and so decided to introduce ivabradine 2.5 mg twice daily. After 24 hours of Ivabradine, the patient remained in sinus rhythm with no documented episodes of Wenckebach phenomenon on cardiac monitor, a finding subsequently confirmed by 24-hour Holter monitoring. During a recent follow-up visit in clinic, the patient remained symptom-free, with an ECG demonstrating sinus rhythm at a physiological rate.

Discussion

Mobitz type I second degree AV block is usually due to reversible conduction block at the level of the AV node whereby malfunctioning AV nodal cells tend to progressively fatigue until they fail to conduct an impulse. Under conditions of increased vagal tone and autonomic dysfunction, Wenckebach occurrence will be increased. Thus, selective impulse conduction within the sinoatrial (SA) node by ivabradine to reduce beat conduction to the AV node in patients with IST/dysautonomia-induced Mobitz type I AV will reduce the occurrence of Wenckebach.

Beta-blockers in cardiac arrhythmias-Clinical pharmacologist's point of view

β-blockers is a vast group of antiarrhythmic drugs which differ in their pharmacokinetic and chemical properties. Some of them block β-adrenergic receptors selectively while the others work non-selectively. Consequently, they reduce the influence of the sympathetic nervous system on the heart, acting negatively inotropic, chronotropic, bathmotropic and dromotropic. Although they have been present in medicine since the beginning of the 1960s, they still play a crucial role in the treatment of cardiac arrhythmias. They are also first-line group of drugs used to control the ventricular rate in patients with the most common arrhythmia-atrial fibrillation. Previous reports indicate that infection with SARS-CoV-2 virus may constitute an additional risk factor for arrhythmia. Due to the aging of the population in developed countries and the increase in the number of patients with cardiac burden, the number of people suffering from cardiac arrhythmias will increase in the upcoming years. As a result the role of above-mentioned beta-blockers will remain significant. Particularly noteworthy is propranolol-the oldest beta adrenergic antagonist, which in recent years has found additional applications due to its unique properties. In this article, we reviewed the accessible literature and summarized the current guidelines on the use of beta-blockers in the treatment of cardiac arrhythmias.

Hybrid Epicardial and Endocardial Sinus-Node Sparing Ablation Therapy for Inappropriate Sinus Tachycardia: Rationale and Design of the multi-center HEAL-IST IDE trial

Background

Inappropriate sinus tachycardia (IST) is defined as resting heart rate >100 beats/min and average 24-hour heart rate >90 beats/min. It is associated with distressing symptoms and significant loss of quality of life. Drugs are not effective in symptom control of IST in up to 30% of patients. Catheter ablation of the sinus node has a high recurrence rate, and the complications are significant. Recently, a novel hybrid sinus node-sparing ablation approach for IST was described.

Objective

The objective of the Hybrid Epicardial and Endocardial Sinus Node Sparing Ablation Therapy for Inappropriate Sinus Tachycardia (HEAL-IST) investigational device exemption trial (NCT05280093) is to evaluate safety and effectiveness of the hybrid sinus node-sparing ablation procedure for the treatment of symptomatic, drug-refractory or drug-intolerant IST.

Methods

The HEAL-IST trial is a prospective, multicenter, pivotal, single-arm trial. Up to 142 subjects in up to 40 centers will be treated in the trial with a Bayesian adaptive design.

Results

Subjects will be assessed for primary safety through 30 days post-hybrid ablation procedure. The primary effectiveness endpoint will be freedom from IST at 12 months. Freedom from IST will be defined as mean heart rate of ≤90 beats/min or at least a 15% reduction in mean heart rate as compared with baseline, in the absence of new or higher dosage of previously failed medications at a 24-month follow-up assessment.

Conclusion

The HEAL-IST trial is the first multicenter trial evaluating hybrid IST ablation in patients with symptomatic IST and refractory or intolerant to drugs. The results of this study will help guide decision making regarding the best management in this population.

Three-dimensional functional anatomy of the human sinoatrial node for epicardial and endocardial mapping and ablation

The sinoatrial node (SAN) is the primary pacemaker of the human heart. It is a single, elongated, 3-dimensional (3D) intramural fibrotic structure located at the junction of the superior vena cava intercaval region bordering the crista terminalis (CT). SAN activation originates in the intranodal pacemakers and is conducted to the atria through 1 or more discrete sinoatrial conduction pathways. The complexity of the 3D SAN pacemaker structure and intramural conduction are underappreciated during clinical multielectrode mapping and ablation procedures of SAN and atrial arrhythmias. In fact, defining and targeting SAN is extremely challenging because, even during sinus rhythm, surface-only multielectrode mapping may not define the leading pacemaker sites in intramural SAN but instead misinterpret them as epicardial or endocardial exit sites through sinoatrial conduction pathways. These SAN exit sites may be distributed up to 50 mm along the CT beyond the ∼20-mm-long anatomic SAN structure. Moreover, because SAN reentrant tachycardia beats may exit through the same sinoatrial conduction pathway as during sinus rhythm, many SAN arrhythmias are underdiagnosed. Misinterpretation of arrhythmia sources and/or mechanisms (eg, enhanced automaticity, intranodal vs CT reentry) limits diagnosis and success of catheter ablation treatments for poorly understood SAN arrhythmias. The aim of this review is to provide a state-of-the-art overview of the 3D structure and function of the human SAN complex, mechanisms of SAN arrhythmias and available approaches for electrophysiological mapping, 3D structural imaging, pharmacologic interventions, and ablation to improve diagnosis and mechanistic treatment of SAN and atrial arrhythmias.

Auricular Acupressure Effect on Autonomic Responses Evoked by a Cold Pressor Test in Healthy Volunteers: A Pilot Study

Objective

This pilot study was conducted to investigate changes in the pulse rate and blood pressure in healthy volunteers after applying auricular acupressure at the "heart acupoint."

Methods

A total of 120 healthy volunteers with hemodynamic indexes within normal limits were randomly allocated into 4 groups to receive auricular acupressure treatment either at the heart acupoint of the left or the right, or in both ears, and one control group without applying auricular acupressure.

Results

Before the application of auricular acupressure, there were no statistical differences in pulse rate and blood pressure increments among the four groups during the first cold pressor test. In groups in which auricular pressure was applied, the pulse rate was significantly reduced after the application of auricular acupressure in three groups; however, no statistically significant difference was detected among the groups. Changes in blood pressure were not statistically significant in or among the different groups after applying auricular acupressure. The average recorded pulse rate values during the second cold pressor test (after auricular acupressure) were significantly lower compared to the corresponding values taken during the first cold pressor test (before auricular acupressure) (p < 0.05); however, pulse rate increments during the two cold pressor tests (with and without auricular acupressure) were similar (p > 0.05).

Conclusions

These findings suggest that auricular acupressure could be used as an adjunctive nonpharmacological method for reducing the pulse rate.

A racing heart post-Pfizer/BioNTech BNT162b2

Palpitations is one of the most common side effects experienced post-messenger-RNA COVID-19 vaccines. However, some patients experience significant symptoms and further workup needs to be considered. We present an interesting case of inappropriate sinus tachycardia in a fit gentleman who presented with worsening palpitations and elevated heart rate post-first and -second dose of the Pfizer/BioNTech vaccine.

Targeted Treatment of Inappropriate Sinoatrial Node Tachycardia Based on Electrophysiological and Structural Mechanisms

The purpose of this review is to determine the causal mechanisms and treatment of inappropriate sinoatrial tachycardia (IST), defined as a non-physiological elevation in resting heart rate. IST is defined as a resting daytime sinus rate >100 beats/minute and an average 24-hour heart rate >90 beats/minute. Potential causal mechanisms include sympathetic receptor hypersensitivity, blunted parasympathetic tone, or enhanced intrinsic automaticity within the sinoatrial node (SAN) pacemaker-conduction complex. These anomalies may coexist in the same patient. Recent ex-vivo near-infrared transmural optical imaging of the SAN in human and animal hearts provides important insights into the functional and molecular features of this complex structure. In particular, it reveals the existence of preferential sinoatrial conduction pathways that ensure robust SAN activation with electrical conduction. The mechanism of IST is debated because even high-resolution electroanatomical mapping approaches cannot reveal intramural conduction in the 3-dimensional SAN complex. It may be secondary to enhanced automaticity, intranodal re-entry, or sinoatrial conduction pathway re-entry. Different pharmacological approaches can target these mechanisms. Long-acting β blockers in IST can act on both primarily increased automaticity and dysregulated autonomic system. Ivabradine targets sources of increased SAN automaticity. Conventional or hybrid ablation may target all the described abnormalities. This review provides a state-of-the-art overview of putative IST mechanisms. In conclusion, based on current knowledge, pharmacological and ablation approaches for IST, including the novel hybrid SAN sparing ablation, are discussed.

Sinus Tachycardia: a Multidisciplinary Expert Focused Review

Sinus tachycardia (ST) is ubiquitous, but its presence outside of normal physiological triggers in otherwise healthy individuals remains a commonly encountered phenomenon in medical practice. In many cases, ST can be readily explained by a current medical condition that precipitates an increase in the sinus rate, but ST at rest without physiological triggers may also represent a spectrum of normal. In other cases, ST may not have an easily explainable cause but may represent serious underlying pathology and can be associated with intolerable symptoms. The classification of ST, consideration of possible etiologies, as well as the decisions of when and how to intervene can be difficult. ST can be classified as secondary to a specific, usually treatable, medical condition (eg, pulmonary embolism, anemia, infection, or hyperthyroidism) or be related to several incompletely defined conditions (eg, inappropriate ST, postural tachycardia syndrome, mast cell disorder, or post-COVID syndrome). While cardiologists and cardiac electrophysiologists often evaluate patients with symptoms associated with persistent or paroxysmal ST, an optimal approach remains uncertain. Due to the many possible conditions associated with ST, and an overlap in medical specialists who see these patients, the inclusion of experts in different fields is essential for a more comprehensive understanding. This article is unique in that it was composed by international experts in Neurology, Psychology, Autonomic Medicine, Allergy and Immunology, Exercise Physiology, Pulmonology and Critical Care Medicine, Endocrinology, Cardiology, and Cardiac Electrophysiology in the hope that it will facilitate a more complete understanding and thereby result in the better care of patients with ST.

Inappropriate sinus tachycardia: an examination of existing definitions

Aims

Inappropriate sinus tachycardia (IST) is a syndrome characterized by an elevated sinus rate unassociated with known physiological, pathological, or pharmacological causes. Despite published consensus documents, IST definitions appear to vary in the literature. In this study, we reviewed IST publications to evaluate IST definition variability and ascertain the degree to which consensus definitions are being adopted.

Methods and results

English-language articles in PubMed, Ovid MEDLINE, Ovid Embase, and Google Scholar published from 1 January 1970 to 1 June 2021 with the title terms ‘inappropriate sinus tachycardia,’ ‘non-paroxysmal sinus tachycardia,’ or ‘permanent sinus tachycardia’ were searched. In each, the IST definition used, qualifying characteristics, and publications cited to support each definition were recorded. We identified 138 publications meeting the search criteria. Inappropriate sinus tachycardia definitions were provided in 114 of 138 articles (83%). A majority of definitions (92/114, 81%) used distinct heart rate (HR) thresholds. Among these, the most common threshold was ≥100 beats per minute (BPM) (75/92, 82%), mainly measured at rest (54/92, 59%). Most definitions (47/92, 51%) included a second criterion to qualify for IST; these were most often an HR threshold of 90 BPM measured over 24 h by ambulatory electrocardiogram (37/47, 79%). Diagnosis of exclusion was a common criterion (75/92, 82%) but symptom status was not (41/92, 45%). The 2015 Heart Rhythm Society IST consensus was commonly cited but adopted in only 37% of definitions published after 2015.

Conclusions

Inappropriate sinus tachycardia definitions in current literature are inconsistent, and professional society consensus IST definitions have, to date, had limited impact.

Inappropriate fetal sinus tachycardia at 9 weeks of gestation

Inappropriate sinus tachycardia (IST) is characterized by an inexplicably elevated sinus heart rate (HR) at rest, with an exaggerated response to physical activity. Its etiology is unknown, and IST is more common in the middle-aged population, being rare in children and adolescents. Although a favorable long-term prognosis has been described in a small series, tachycardia-induced cardiomyopathy has rarely been associated with IST. In this report, we describe an extremely rare case of IST detected in the first trimester of gestation, focusing on reviewing important features to improve the diagnosis of the different types of tachycardia by applying fetal cardiac ultrasonography. In the case reported, the diagnosis of IST was suspected in a fetus from a pregnant woman with celiac disease, who was referred at 9 weeks of gestation with fetal tachycardia. The fetus remained hemodynamically stable until term, and the female neonate was born unremarkably. Electrocardiography in the newborn showed sinus tachycardia (ST) with normal PR and QTc intervals. Possible causes of ST were excluded, thus confirming the fetal diagnosis. The patient presented with a fast HR at rest with an exaggerated increase with minimal physical activity accompanied by irritability. Beta-adrenergic blocker therapy was initiated, and the female neonate has progressed well.

Unusual Presentation of Postprandial Sinus Tachycardia in Pregnancy

This report describes the clinical presentation and systematic workup of a 25-year-old primigravid woman presenting at 34 weeks gestation with symptoms of postprandial sinus tachycardia. Differentials included pregnancy-related inappropriate sinus tachycardia (PRIST) and swallowing-induced atrial tachycardia. PRIST has favorable outcomes for both the mother and baby, although the symptoms can be distressing and lead to the overutilization of healthcare resources. The literature describes symptom onset as sporadic with no definitive triggers, often occurring in the later trimesters of pregnancy. Swallowing-induced atrial tachycardia, which fits with postprandial symptoms seen in this patient, is a distinct entity most commonly diagnosed in middle-aged men. Management included psychosocial support and pharmacologic treatment with labetalol. The patient’s course was benign with an uncomplicated delivery at 38 weeks, complete resolution of symptoms in the postpartum period, and successful discontinuation of pharmacologic management with no relapses. Current literature on postprandial sinus tachycardia in pregnant women is limited, and the best treatment method is unknown. This report extends current knowledge on pregnancy-related postprandial sinus tachycardia and provides a framework for advances in the management of this clinical presentation.

Inappropriate Sinus Tachycardia: Etiology, Pathophysiology, and Management: JACC Review Topic of the Week

Inappropriate sinus tachycardia (IST) is a clinical syndrome that generally affects young patients and is associated with distressing symptoms. Although the most common symptom is palpitations, it can be accompanied by a myriad of symptoms, including anxiety, dizziness, presyncope, and syncope. The pathogenesis of IST is not well understood and considered multifactorial, with autonomic dysfunction being the central abnormality. IST is a diagnosis of exclusion. Management presents a clinical challenge. The overall efficacy of lifestyle modifications and medical therapy may be limited. Recent advances in catheter and surgical sinus node sparing ablation techniques have led to improvement in outcomes. In addition, increased focus has led to development of multimodality team-based interventions to improve outcomes in this group of patients. In this review, we discuss the mechanistic basis of IST, review current approaches to diagnosis, and outline contemporary therapeutic approaches.

De-novo development of fragmented QRS during a six-month follow-up period in patients with COVID-19 disease and its cardiac effects

OBJECTIVE

The aim of this study is to examine the probability of de-novo fQRS in patients with mild COVID-19 disease, as an indicator of cardiac injury.

METHODS

Data of 256 patients with normal admission electrocardiography and no comorbidities between 1.12.2020-31.12.2021, were examined retrospectively 6-month after mild COVID-19 disease. Patients were divided into two groups: fQRS+ group (n = 102) and non-fQRS group (n = 154). Relation between fQRS and other electrocardiography, echocardiographic and laboratory findings were investigated.

RESULTS

No significant difference was found between the groups among age and gender. Troponin-I and creatine kinase myocardial band values (retrospectively 9.10 ± 1.76 vs 0.74 ± 1.43, 34.05 ± 82.20 vs. 14.68 ± 4.42), COVID-19 IgG levels (45.78 ± 14.82 vs. 36.49 ± 17.68), diastolic dysfunction (39.21% vs. 15.07%), EF value (58.02 ± 1.95 vs. 64.27 ± 3.07), dyspnea (41.17% vs. 6.84%), post-COVID-19 tachycardia syndrome (19.6% vs. 2.74) were more frequent in fQRS+ group compared to non-fQRS group. The EF value was lower in the presence of fQRS in the high lateral leads (57.12 ± 1.99, 58.47 ± 1.79, p:0.018). There was a positive correlation between IgG value and endsystolic diameter, septum thickness and left atrium diameter. In multivariate analysis de-novo fQRS, dyspnea, high troponin and IgG values, diastolic dysfunction, low EF value and left atrial diameter were determined as independent risk factors for post-COVID-19 tachycardia syndrome in follow-up.

CONCLUSION

In COVID-19 disease de-novo fQRS, dyspnea, high IgG and troponin value, left atrial diameter, lower EF value, diastolic dysfunction were associated with post-COVID-19 tachycardia syndrome. The de-novo fQRS in SARS-COV-2 may be a predictor of future more important adverse cardiovascular outcomes and this should alert clinicians.

Post-COVID-19 Tachycardia Syndrome: A Distinct Phenotype of Post-Acute COVID-19 Syndrome

In this paper we highlight the presence of tachycardia in post-acute COVID-19 syndrome by introducing a new label for this phenomenon-post-COVID-19 tachycardia syndrome-and argue that this constitutes a phenotype or sub-syndrome in post-acute COVID-19 syndrome. We also discuss epidemiology, putative mechanisms, treatment options, and future research directions in this novel clinical syndrome.

Ivabradine versus bisoprolol in the treatment of inappropriate sinus tachycardia: a long-term follow-up study

AIM

The aim of our study was to compare ivabradine versus bisoprolol in the short-term and long-term treatment of inappropriate sinus tachycardia.

METHODS

From this prospective, parallel-group, open-label study, consecutive patients affected by inappropriate sinus tachycardia received ivabradine or bisoprolol and were evaluated with Holter ECG, ECG stress test, European Heart Rhythm Association score and Minnesota Living With Heart Failure Questionnaire at baseline, after 3 and 24 months.

RESULTS

Overall, 40 patients were enrolled. Baseline parameters were comparable in the ivabradine and bisoprolol subgroups. Two patients had transient phosphenes with ivabradine and two others interrupted the drug after 3 months as they planned to become pregnant. Eight individuals treated with bisoprolol experienced hypotension and weakness, which caused drug discontinuation in five of them. Ivabradine was superior to bisoprolol in reducing Holter ECG mean heart rate (HR) and mean HR during daytime at short- and long-term follow-up. Moreover, ivabradine but not bisoprolol significantly reduced Holter ECG mean HR during night-time as well as maximal and minimal HR and significantly increased the time duration and maximal load reached at ECG stress test. The quality of life questionnaires significantly improved in both subgroups.

CONCLUSION

This study suggests that ivabradine is better tolerated than bisoprolol and seems to be superior in controlling the heart rate and improving exercise capacity in a small population of individuals affected by inappropriate sinus tachycardia during a short-term and long-term follow-up.

Heart Rate in Patients with SARS-CoV-2 Infection: Prevalence of High Values at Discharge and Relationship with Disease Severity

The most common arrhythmia associated with COronaVIrus-related Disease (COVID) infection is sinus tachycardia. It is not known if high Heart Rate (HR) in COVID is simply a marker of higher systemic response to sepsis or if its persistence could be related to a long-term autonomic dysfunction. The aim of our work is to assess the prevalence of elevated HR at discharge in patients hospitalized for COVID-19 and to evaluate the variables associated with it. We enrolled 697 cases of SARS-CoV2 infection admitted in our hospital after February 21 and discharged within 23 July 2020. We collected data on clinical history, vital signs, laboratory tests and pharmacological treatment. Severe disease was defined as the need for Intensive Care Unit (ICU) admission and/or mechanical ventilation. Median age was 59 years (first-third quartile 49, 74), and male was the prevalent gender (60.1%). 84.6% of the subjects showed a SARS-CoV-2 related pneumonia, and 13.2% resulted in a severe disease. Mean HR at admission was 90 ± 18 bpm with a mean decrease of 10 bpm to discharge. Only 5.5% of subjects presented HR > 100 bpm at discharge. Significant predictors of discharge HR at multiple linear model were admission HR (mean increase = β = 0.17 per bpm, 95% CI 0.11; 0.22, p < 0.001), haemoglobin (β = −0.64 per g/dL, 95% CI −1.19; −0.09, p = 0.023) and severe disease (β = 8.42, 95% CI 5.39; 11.45, p < 0.001). High HR at discharge in COVID-19 patients is not such a frequent consequence, but when it occurs it seems strongly related to a severe course of the disease.

Sinus Node Dysfunction

Sinus node dysfunction (SND) is a multifaceted disorder most prevalent in older individuals, but may also occur at an earlier age. In most cases, the SND diagnosis is ultimately established by documenting its ECG manifestations. EPS has limited utility. The treatment strategy is largely dictated by symptoms and ECG manifestations. Not infrequently, both bradycardia and tachycardia coexist in the same patients, along with other diseases common in the elderly (e.g., hypertension, coronary artery disease), thereby complicating treatment strategy. Prevention of the adverse consequences of both bradyarrhythmia and tachyarrhythmia is important to reduce susceptibility to syncope, falls, and thromboembolic complications.

Autonomic dysfunction in SARS-COV-2 infection acute and long-term implications COVID-19 editor's page series

Abstract

The autonomic nervous system (ANS) is a complex network of nerves originating in the brain, brain stem, spinal cord, heart and extracardiac organs that regulates neural and physiological responses to internal and external environments and conditions. A common observation among patients with the 2019 Coronavirus (CoV) (SARS-severe acute respiratory syndrome CoV-2) (SARS-CoV-2) or COVID-19 [CO for corona, VI for virus, D for disease and 19 for when the outbreak was first identified (31 December 2019)] in the acute and chronic phases of the disease is tachycardia, labile blood pressure, muscular fatigue and shortness of breath. Because abnormalities in the ANS can contribute to each of these symptoms, herein a review of autonomic dysfunction in SARS-COV-2 infection is provided to guide diagnostic testing, patient care and research initiatives.

Graphic abstract

The autonomic nervous system is a complex network of nerves originating in the brain, brain stem, spinal cord, heart and extracardiac organs that regulates neural and physiological responses to internal and external environments and conditions. A common collection of signs and symptoms among patients with the 2019 Coronavirus (CoV) (SARS-severe acute respiratory syndrome CoV-2) (SARS-CoV-2) or COVID-19 [CO for corona, VI for virus, D for disease and 19 for when the outbreak was first identified (31 December 2019)] is tachycardia, labile blood pressure, muscular fatigue and shortness of breath. Abnormalities in the autonomic nervous system (ANS) can contribute to each of these identifiers, potentially offering a unifying pathobiology for acute, subacute and the long-term sequelae of SARS-CoV-2 infection (PASC) and a target for intervention.

Efficacy of medical and ablation therapy for inappropriate sinus tachycardia: A single-center experience

BACKGROUND

Effective therapy for inappropriate sinus tachycardia (IST) remains challenging with high rates of treatment failure and symptom recurrence. It is uncertain how effective pharmacotherapy and procedural therapy are long-term, with poor response to medical therapy in general.

METHODS

We retrospectively reviewed all patients with the diagnosis of IST at a tertiary academic medical center from 1998 to 2018. We extracted data related to prescribing patterns and symptom response to medical therapy and sinus node modification (SNM), assessing efficacy and periprocedural complication rates.

RESULTS

A total of 305 patients with a formal diagnosis of IST were identified, with 259 (84.9%) receiving at least one prescription medication related to the condition. Beta-blockers were the most commonly used medication (n = 245), with a majority of patients reporting no change or worsening of symptoms, and poor response was seen to other medication classes. Improvement was seen significantly more often with ivabradine than beta blockers, though the sample size was limited (p = .003). Fifty-five patients (18.0% of all IST patients), mean age 32.0 ± 9.1 years, underwent a SNM procedure, with an average of 1.8 ± 0.9 procedures per patient. Acute symptomatic improvement (<6 months) was seen in 58.2% of patients. Long-term complete resolution of symptoms was seen in 5.5% of patients, modest improvement in 29.1%, and no long-term benefit was seen in 65.5% of patients.

CONCLUSIONS

Among all medical therapies, there were high rates of treatment failure or symptom worsening in over three-quarters of patients in our study. Ivabradine was most beneficial, though the sample size was small. While most patients receiving SNM ablation for IST perceive an acute symptomatic improvement, almost two-thirds of patients have no long-term improvement, and resolution of symptoms is quite rare. AV node ablation with pacemaker implantation following lack of response to SNM offered increased success, though the sample size was limited.

Cardiovascular Disorders Mediated by Autonomic Nervous System Dysfunction

Cardiovascular disorders, such as orthostatic hypotension and supine hypertension, are common in patients with neurodegenerative synucleinopathies such as Parkinson disease (PD), and may also occur in other conditions, such as peripheral neuropathies, that result in autonomic nervous system (ANS) dysfunction. Dysfunction and degeneration of the ANS are implicated in the development of orthostatic and postprandial hypotension and impaired thermoregulation. Neurogenic orthostatic hypotension (nOH) results from sympathetic failure and is a common autonomic disorder in PD. Supine hypertension may also occur as a result of both sympathetic and parasympathetic dysfunction in conjunction with nOH in the majority of patients with PD. Management of supine hypertension in the setting of nOH can be counterintuitive and challenging. Additionally, the presence of other noncardiovascular comorbidities, such as diabetes mellitus and peripheral edema, may further contribute to the burden of disease. ANS dysfunction thus presents major healthcare implications and challenges for neurology and cardiovascular practices, necessitating an integrated neurology and cardiology management approach.

Patient Selection for Epicardial Ablation-Part I: The Role of Epicardial Ablation in Various Cardiac Disease States

Epicardial catheter ablation is most commonly performed following unsuccessful endocardial ablation. Given the frequency of epicardial substrates in certain cardiomyopathic disease states, however, a combined endocardial–epicardial approach should be considered as a primary treatment strategy. Although epicardial ablation is primarily deployed in patients with ventricular arrhythmias, the role of epicardial approaches in supraventricular tachycardias (eg, atrial fibrillation, inappropriate sinus tachycardia, and—rarely—accessory pathways) is growing, with continued advances being made.

Cardiac rhythm abnormalities - An underestimated cardiovascular risk in adult patients with Mucopolysaccharidoses

Patients with Mucopolysaccharidosis (MPS) have an increased risk of cardiovascular complications, conduction tissue abnormalities and arrhythmia; all rare but underestimated. It has been reported that conduction system defects are progressive in this group of patients and may result in sudden cardiac death. The aim of this study is to review our current practice and suggest best practice guidelines regarding the frequency of cardiac rhythm monitoring in this patient group. Seventy-seven adult MPS patients who attended metabolic clinics between 2013 and 2019 were included in this retrospective observational study. Patients were affected with different MPS types: MPS I (n = 33), MPS II (n = 16), MPS IV (n = 19), VI (n = 8) and VII (n = 1). The assessments included: 12‑lead electrocardiogram (ECG), 24-h ECG (Holter monitor), loop recorder/pacemaker interrogation assessment. Data from 12‑lead ECG (available from 69 patients) showed a variety of abnormalities: T wave inversion in a single lead III (n = 19), left ventricular hypertrophy (n = 14), early repolarization (n = 14), right axis deviation (RAD, n = 11), partial RBBB (n = 9), right bundle branch block (RBBB) (n = 1) and first degree AV block (n = 1). ECG changes of bundle branch block, RAD (left posterior fascicular block) could represent conduction tissue abnormality and equally could be related to the underlying lung tissue abnormality which is present in most of the patients with MPS. T wave abnormality in a single lead is usually insignificant in healthy individuals; however in MPS patients it could be as a result of chest shape. Among the 34 patients for who 24-hour ECG was available, sinus tachycardia was the most common rhythm noted (n = 9), followed by sinus bradycardia (n = 4), atrial fibrillation (AF) (n = 1) and atrio-ventricular nodal re-entry tachycardia (AVNRT) (n = 1). Permanent pacemaker was inserted in two patients. AF was observed in one patient with MPS II. In conclusion, we postulate that regular cardiac monitoring is required to warrant early detection of underlying conduction tissue abnormalities. In addition, 12‑lead ECG is the first line investigation that, if abnormal, should be followed up by 24-hour Holter monitoring. These findings warrant further research studies.

What Have We Learned from the European Society of Cardiology 2019 Guidelines on Supraventricular Tachycardia

Supraventricular tachycardias (SVTs) are common arrhythmic conditions in clinical practice. Increased knowledge and experience on SVTs and some unclear situations in clinical practice led the European Society of Cardiology (ESC) team to write a new guideline. In this review, we touch upon the important points in the new ESC 2019 SVT guidelines and present changing approaches and suggestions. By providing a general review on SVTs, we also mention the basic mechanism, epidemiology, and clinical presentation of SVTs, approaching narrow and wide QRS tachycardias, SVTs in special patient groups, and treatment of SVTs.

Natural history and clinical outcomes of inappropriate sinus tachycardia

BACKGROUND

Limited data are available regarding the demographics, disease associations, and long-term prognosis of patients with inappropriate sinus tachycardia (IST).

OBJECTIVE

To establish epidemiologic data for patients with IST, including symptom onset, comorbid disease, and long-term outcomes.

METHODS

We retrospectively reviewed all patients with an IST diagnosis at the Mayo Clinic (Rochester, MN) during a 20-year period (1998-2018). We extracted demographic data and clinical outcomes compared to an age and gender-matched control group with atrioventricular nodal reentry tachycardia (AVNRT).

RESULTS

Within the study period, a total of 305 patients with IST were identified (mean follow-up 3.5 years) with 92.1% female and mean age 33.2 ± 11.2 years. The most frequently identified circumstances triggering the condition included pregnancy (7.9%) and infectious illness (5.9%) while the most common comorbid conditions were depression (25.6%) and anxiety (24.6%). At diagnosis, the mean left ventricular ejection fraction (LVEF) was 62.3 ± 6.2%, with 77 patients having follow-up echocardiographic data. No significant difference in LVEF was seen after a mean 4.9 ± 4.3-year follow-up (baseline LVEF 59.8 ± 10.7% vs subsequent 61.4 ± 8.1%; P = .2971). Two deaths occurred within the study period, with one related to myocardial infarction and the other noncardiac; compared to an age and gender-matched AVNRT control group there was no excess mortality during the follow-up period.

CONCLUSIONS

In our study cohort, IST predominately affects young females with structurally normal hearts and modest coexistent psychiatric disease. In most cases of IST, a major event occurring just before or at the time of diagnosis could not be identified, although nearly 8% of patients first noted symptoms during or shortly after pregnancy. In our cohort, there was no evidence of cardiomyopathy or mortality related to IST.

Challenges in Narrow QRS Complex Tachycardia Interpretation

Several arrhythmogenic substrates may generate narrow QRS complex tachycardia, frequently encountered in clinical practice. Some narrow QRS complex tachycardias, however, are sustained by an uncommon arrhythmogenic mechanism. Although rare, these forms should be taken into account in the differential diagnosis to avoid misdiagnosis and improper patient management. Dual atrioventricular node physiology can be responsible for different uncommon forms of narrow QRS complex tachycardia, also nonreentrant in mechanism. A ventricular origin also is possible, if the tachycardia site is located in the upper ventricular septum with fast ventricular propagation to the specific conduction system and narrowing of the QRS complex.