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.

Triglicerydes/high-density lipoprotein ratio as a risk factor of post-Covid-19 sinus tachycardia: A retrospective study

Inappropriate sinus tachycardia (IST) is one of the manifestations of the post-COVID-19 syndrome (PCS), which pathogenesis remains largely unknown. This study aimed to identify potential risk factors for IST in individuals with PCS. The 1349 patients with PCS were included into the study. Clinical examination, 24H Holter ECG, 24H ambulatory blood pressure monitoring and biochemical tests were performed 12-16 weeks after the COVID-19 in all participants. IST was found in 69 (3.5%) individuals. In the clinical assessment IST patients were characterized by a higher age (p < 0.001) and lower prevalence of the diagnosed hypertension (p = 0.012), compared to remaining patients. Biochemical testing showed higher serum triglycerides (1.66 vs. 1.31 pmol/L, p = 0.007) and higher prevalence of a low high-density lipoprotein (HDL) cholesterol (24.6% vs. 15.2%, p = 0.035) in the IST group. Subsequently, the triglicerydes (TG)/HDL ratio, an indicator of insulin resistance, was significantly higher in the IST individuals (3.2 vs. 2.4, p = 0.005). 24H monitoring revealed a significantly higher minimum diastolic, maximum systolic and mean arterial blood pressure values in the IST group (p < 0.001 for all), suggesting a high prevalence of undiagnosed hypertension. A multivariate analysis confirmed the predictive value TG/HDL ratio >3 (OR 2.67, p < 0.001) as predictors of IST development. A receiver operating characteristic curve analysis of the relationship between the TG/HDL ratio and the IST risk showed that the predictive cut-off point for this parameter was 2.46 (area under the ROC curve = 0.600, p = 0.004). Based on these findings, one can conclude that insulin resistance seems to be a risk factor of IST, a common component of PCS.

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.

Surgery for Cardiac Arrhythmias: Past, Present, Future

There is a rich history of surgery for cardiac arrhythmias, spanning from atrial fibrillation and Wolff-Parkinson-White syndrome to inappropriate sinus tachycardia and ventricular tachycardia. This review describes the history of these operations, their evolution over time, and the current state of practice. We devote considerable time to the discussion of atrial fibrillation, the most common cardiac arrhythmia addressed by surgeons. We discuss ablation of atrial fibrillation as a stand-alone operation and as a concomitant operation performed at the time of cardiac surgery. We also discuss the emergence of newer procedures to address atrial fibrillation in the past decade, such as the convergent procedure and totally thoracoscopic ablation, and their outcomes relative to historic approaches such as the Cox maze procedure.

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.

Therapeutic Approaches to Dysautonomia in Childhood, with a Special Focus on Long COVID

BACKGROUND

Dysautonomia seems to be important for the pathophysiology of psychosomatic diseases and, more recently, for long COVID. This concept may explain the clinical symptoms and could help open new therapeutic approaches.

METHODS

We compared our data from an analysis of heart rate variability (HRV) in an active standing test in 28 adolescents who had developed an inappropriate sinus tachycardia (IST, n = 13) or postural orthostatic tachycardia syndrome (POTS, n = 15) after contracting COVID-19 disease and/or vaccination with 64 adolescents from our database who developed dysautonomia due to psychosomatic diseases prior to the COVID-19 pandemic. We prove the effects of our treatment: omega-3 fatty acid supplementation (O3-FA, n = 18) in addition to propranolol (low dose, up to 20-20-0 mg, n = 32) or ivabradine 5-5-0 mg (n = 17) on heart rate regulation and heart rate variability (HRV).

RESULTS

The HRV data were not different between the adolescents with SARS-CoV-2-related disorders and the adolescents with dysautonomia prior to the pandemic. The heart rate increases in children with POTS while standing were significantly lower after low-dose propranolol (27.2 ± 17.4 bpm***), ivabradine (23.6 ± 8.12 bpm*), and O-3-FA (25.6 ± 8.4 bpm*). The heart rate in children with IST while lying/standing was significantly lower after propranolol (81.6 ± 10.1 bpm**/101.8 ± 18.8***), ivabradine (84.2 ± 8.4 bpm***/105.4 ± 14.6**), and O-3-FA (88.6 ± 7.9 bpm*/112.1/14.9*).

CONCLUSIONS

The HRV data of adolescents with dysautonomia after COVID-19 disease/vaccination are not significantly different from a historical control of adolescents with dysautonomia due to psychosomatic diseases prior to the pandemic. Low-dose propranolol > ivabradine > omega-3 fatty acids significantly decrease elevated heart rates in patients with IST and the heart rate increases in patients with POTS and may be beneficial in these children with dysautonomia.

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.

Successful use of ivabradine in a 10-year-old patient with graft failure after heart transplantation

We encountered a paediatric case of graft failure due to antibody-mediated rejection after heart transplantation in which ivabradine was effective. Inappropriate sinus tachycardia in denervated transplanted hearts is a good indication for ivabradine administration as beta-blockers have a limited efficacy. To our knowledge, this is the first report on the effectiveness of ivabradine in a paediatric heart transplant rejection case.

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.

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.

Novel SuperMap feature of dipole charge density mapping technique offers advantages for redo catheter ablation in highly symptomatic patients with inappropriate sinus tachycardia: A case series

Ablation procedures using classical sequential mapping systems may fail to eliminate IAST. The AcQMap dipole charge density mapping technique may offer improved accuracy and has a potential added value for the ultimate success of eliminating IAST. The use of the AcQMap should be considered for redo, as well as first line therapy for patients with symptomatic IAST.

Inappropriate Sinus Tachycardia Following Viral Illness

A 67-year-old female patient with a past medical history of menopause, migraines, and gastro-esophageal disease presented with palpitation, fatigue, and shortness of breath. One month prior to her presentation, she reported having flu-like symptoms. Her EKG showed sinus tachycardia with no other abnormality. Laboratory findings, along with imaging, showed normal results. The event monitor failed to detect any arrythmias. We report a case of inappropriate sinus tachycardia secondary to viral infection as a diagnosis of exclusion.

Combined Epicardial and Endocardial Sinus Node Modification Using the Orion™ Mini-basket Mapping Catheter

In patients with inappropriate sinus tachycardia, conservative medical management targeting the relief of symptoms is the first line of therapy. Sinus node modification can offer a potential benefit in selected patients with severe, refractory inappropriate sinus tachycardia. Extensive endocardial radiofrequency (RF) ablation of the superior aspect of the sinus node complex is typically required but is often limited by the epicardial location of the sinus node and the proximity of the phrenic nerve. More recently, surgical and catheter-based epicardial approaches to the sinus node have been used to facilitate more direct access to the sinus node and mechanical displacement of the phrenic nerve from ablation target sites. In this case report, we describe a combined epicardial-endocardial sinus node modification procedure in a patient with refractory inappropriate sinus tachycardia and previous unsuccessful endocardial ablation. The Orion™ mini-basket catheter (Boston Scientific, Natick, MA, USA) was used both for mapping the sinus node and for mechanically displacing the phrenic nerve from ablation target sites, which facilitated successful ablation.

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.

A young female patient with recurrent paroxysms of inappropriate sinus tachycardia

Tachycardia is one of the most common presentations in medical practice. In most cases, it could be attributed to emotional problems, anemia, or thyroid disorders. A 16-year-old female visited primary care clinics with the complaints of palpitation for years and initially diagnosed as a case of anxiety or stress. Her condition worsened and became more symptomatic over the last few months for which investigations were done. A provisional diagnosis of pre-excitation syndrome, Lown-Ganong-Syndrome, was made. This was based on short PR interval in ECG and an attack of supraventricular tachycardia and another attack of brief atrial fibrillation in addition to the family history of her mother of having pre-excitation abnormality. She was sent to electrophysiological study where no concealed accessory pathway was confirmed, and the diagnosis of inappropriate sinus tachycardia was the final diagnosis and medical treatment was initiated.

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.

Stellate ganglion block and cardiac sympathetic denervation in patients with inappropriate sinus tachycardia

Background

Inappropriate sinus tachycardia (IST) remains a clinical challenge because patients often are highly symptomatic and not responsive to medical therapy.

Objective

To study the safety and efficacy of stellate ganglion (SG) block and cardiac sympathetic denervation (CSD) in patients with IST.

Methods

Twelve consecutive patients who had drug‐refractory IST (10 women) were studied. According to a prospectively initiated protocol, five patients underwent an electrophysiologic study before and after SG block (electrophysiology study group). The subsequent seven patients had ambulatory Holter monitoring before and after SG block (ambulatory group). All patients underwent SG block on the right side first, and then on the left side. Selected patients who had heart rate reduction ≥15 beats per minute (bpm) were recommended to consider CSD.

Results

The mean (SD) baseline heart rate (HR) was 106 (21) bpm. The HR significantly decreased to 93 (20) bpm (P = .02) at 10 minutes after right SG block and remained significantly slower at 97(19) bpm at 60 minutes. Left SG block reduced HR from 99 (21) to 87(16) bpm (P = .02) at 60 minutes. SG block had no significant effect on blood pressure or HR response to isoproterenol or exercise (all P > .05). Five patients underwent right (n = 4) or bilateral (n = 1) CSD. The clinical outcomes were heterogeneous: one patient had complete and two had partial symptomatic relief, and two did not have improvement.

Conclusion

SG blockade modestly reduces resting HR but has no significant effect on HR during exercise. Permanent CSD may have a modest role in alleviating symptoms in selected patients with IST.

Baseline intrinsic heart rate and response to ivabradine treatment in patients with inappropriate sinus tachycardia

BACKGROUND

Treatment with ivabradine became a new therapeutic alternative for patients with inappropriate sinus tachycardia (IST). The aim was to determine a relation between intrinsic heart rate (IHR) and response to ivabradine treatment.

METHODS

Twenty-seven patients (mean age 37 ± 11; 23 women) with symptomatic IST despite medical treatment were recruited into the study. Resting ECG, 24-hr ECG monitoring (24hECG), exercise treadmill test, and symptoms evaluation were performed initially and after 60 days on ivabradine. IHR was acquired at baseline after pharmacological autonomic blockade.

RESULTS

Nineteen patients (70%) were classified as abnormal IHR group (AIHR) while eight showed normal IHR (NIHR). No significant differences in ECG parameters were found between NIHR and AIHR subgroups, while baseline exercise capacity was higher in AIHR patients (10.9 vs. 9.5 METs, p < .05). Ivabradine treatment resulted in significant reduction in resting heart rate, average 24hECG heart rate, improvement in exercise capacity and reduction of symptoms in both subgroups. Nevertheless, favorable influence of ivabradine was significantly more exaggerated in AIHR subgroup (HR 116 vs. 90 bpm, av. HR 98 vs. 79 bpm, 10.9 vs. 13.6 METS, EHRA score 3.1 vs. 1.1, p < .001 for all) than in NIHR patients (HR 112 vs. 98 bpm, av. HR 97 vs. 88 bpm, 9.5 vs. 11.1 METs, EHRA score 3.1 vs. 1.9; p < .05 for all).

CONCLUSIONS

Intrinsic heart rate may be useful in predicting response to ivabradine in patients with IST. More intense response to ivabradine in patients with AIHR may be attributed to different pathophysiological mechanisms underlying IST in AIHR and NIHR groups.

Minimally invasive thoracoscopic surgery is an effective approach for treating inappropriate sinus tachycardia

INTRODUCTION

Inappropriate sinus tachycardia (IST) is characterized by increased heart rate out of proportion to normal physiologic demand. IST ablation is challenging for the electrophysiology community due to the epicardial location of the sinus node and the risk of phrenic nerve (PN) injury during catheter ablation. In this study, we investigated the safety and efficacy of a minimally invasive thoracoscopic surgery for elimination of IST.

METHODS

Patients with IST who failed medical therapy or endocardial ablation underwent minimally invasive thoracoscopic epicardial ablation. Epicardial activation mapping was performed to identify the earliest activation site and any possible migration of earliest activation along the lateral right atrium. The PN in each patient was protected by a pericardial retraction suture.

RESULTS

From 1 January 2000 to 15 June 2018, 10 patients (eight females and two males) underwent minimally invasive thoracoscopic IST ablation. Mean age of the patients was 36.7 ± 12.5 years. Mean baseline sinus rate was 113.8 ± 21.8 beats per minute. After surgery, the mean heart rate significantly decreased to 79.8 ± 8.2 at postoperative day 1 and to 75.8 ± 8.1 at day 30 (both P < .001). No in-hospital death, stroke, or PN injury occurred. One patient required reintubation, one patient developed postoperative pericarditis, and another patient had a pulmonary embolus. Median follow-up was 6 months (range, 1-50). Freedom from reintervention was 88% at 6 months.

CONCLUSION

Minimally invasive thoracoscopic ablation for IST is a safe and effective approach that preserves the phrenic nerve. Due to the possibility of IST activation site migration, continued follow-up after surgery is required.

Laser Catheter Modulation of the Sinus Node in the Treatment of Inappropriate Sinus Tachycardia: Experimental and Clinical Results

Inappropriate sinus tachycardia (IST) is a rare type of arrhythmia that is currently difficult to treat successfully. The effects of laser catheter applications aimed at the sinus nodal area were tested experimentally and the technique was used for the treatment of IST. Continuous-wave, mapping-guided 1,064 nm neodymium-doped yttrium aluminum garnet laser applications at 15 W (9.5 W/mm²) per 15 seconds (142.5 J/mm²) and an irrigation flow of 30 mL/min were aimed at the sinus nodal area in five dogs (three applications each) and one human patient (two applications) by use of an 8-French open-irrigated electrode-laser mapping and ablation (ELMA) catheter provided with three miniature pin electrodes (0.5 mm × 4.0 mm) with interelectrode distances of 2.0 mm arranged symmetrically and radially around the endhole of the catheter tip. Laser application was aimed at the largest and earliest atrial potentials recorded in the focused local electrograms 30 ms to 45 ms prior to the onset of the P-wave in the surface lead electrocardiogram. Lesions were evaluated morphometrically. Holter monitoring in the patient was performed prior to and after treatment. During laser application in the dogs, sinus nodal potential amplitudes dwindled gradually from a mean of 42 mm ± 24 mm to 5.0 mm ± 3.0 mm and sinus cycle lengths lengthened from 452 ms ± 35 ms to 634 ms ± 35 ms (p < 0.0001 for both). In the patient, electrical potential amplitudes in the local electrograms dwindled from 41.0 mm to 5.0 mm and, in the Holter monitor, heart rate decreased from 109 bpm ± 29 bpm to 79 bpm ± 26 bpm (p < 0.0001). IST ablation was painless and without complications. During a follow-up of 4.9 years, the patient was asymptomatic and her heart rate and chronotropic competence remained normal. In conclusion, ablation of IST was achieved by substrate mapping-guided laser application while using the open-irrigated EMLA catheter RytmoLas (LasCor GmbH – Laser Medical Devices, Taufkirchen, Germany). However, this is a proof-of-concept study and further research, preferably in the form of multicenter study trials, is needed for confirmation of the results.

P-Wave Amplitude and PR Changes in Patients With Inappropriate Sinus Tachycardia: Findings Supportive of a Central Mechanism

BACKGROUND

The mechanism of inappropriate sinus tachycardia (IST) remains incompletely understood.

METHODS AND RESULTS

We prospectively compared 3 patient groups: 11 patients with IST (IST Group), 9 control patients administered isoproterenol (Isuprel Group), and 15 patients with cristae terminalis atrial tachycardia (AT Group). P-wave amplitude in lead II and PR interval were measured at a lower and higher heart rate (HR1 and HR2, respectively). P-wave amplitude increased significantly with the increase in HR in the IST Group (0.16±0.07 mV at HR1=97±12 beats per minute versus 0.21±0.08 mV at HR2=135±21 beats per minute, P=0.001). The average increase in P-wave amplitude in the IST Group was similar to the Isuprel Group (P=0.26). PR interval significantly shortened with the increases in HR in the IST Group (146±15 ms at HR1 versus 128±16 ms at HR2, P<0.001). A similar decrease in the PR interval was noted in the Isuprel Group (P=0.6). In contrast, patients in the atrial tachycardia Group experienced PR lengthening during atrial tachycardia when compared with baseline normal sinus rhythm (153±25 ms at HR1=78±17 beats per minute versus 179±29 ms at HR2=140±28 beats per minute, P<0.01).

CONCLUSIONS

We have shown that HR increases in patients with IST were associated with an increase in P-wave amplitude in lead II and PR shortening similar to what is seen in healthy controls following isoproterenol infusion. The increase in P-wave amplitude and absence of PR lengthening in IST support an extrinsic mechanism consistent with a state of sympatho-excitation with cephalic shift in sinus node activation and enhanced atrioventricular nodal conduction.

Inappropriate Sinus Tachycardia Diagnosed and Treated as Depression Successfully Treated by Radiofrequency Catheter Ablation

We experienced a man in his 20s with inappropriate sinus tachycardia (IST) initially diagnosed and treated as depression who was steadily treated with radiofrequency catheter ablation (RFCA) using an EnSite™ system. The patient has remained well without any symptoms or medications, including antidepressants, for two years since the RFCA. To avoid missing IST and treating it as an emotional problem and/or mental illness such as depression, physicians - including cardiologists - should be aware of these conditions when examining patients with multiple and incapacitating complaints including palpitations and general fatigue and/or tachycardia, especially characterized by an elevated resting heart rate or a disproportionate increase in the heart rate with minimal exertion.

Ablation of Inappropriate Sinus Tachycardia: A Systematic Review of the Literature

OBJECTIVES

The goal of this study was to describe short- and long-term outcomes in all patients referred for inappropriate sinus tachycardia ablation, along with the potential complications of the intervention.

BACKGROUND

Sinus node (SN) ablation/modification has been proposed for patients refractory to pharmacological therapy. However, available data derive from limited series.

METHODS

The electronic databases MEDLINE, Embase, CINAHL, Cochrane, and Scopus were systematically searched (January 1, 1995-December 31, 2015). Studies were screened according to predefined inclusion and exclusion criteria.

RESULTS

A total of 153 patients were included. Their mean age was 35.18 ± 10.02 years, and 139 (90.8%) were female. All patients had failed to respond to maximum tolerated doses of pharmacological therapy (3.5 ± 2.4 drugs). Mean baseline heart rates averaged 101.3 ± 16.4 beats/min according to electrocardiography and 104.5 ± 13.5 beats/min according to 24-h Holter monitoring. Two electrophysiological strategies were used, SN ablation and SN modification, with the latter being used more. Procedural acute success (using variably defined pre-determined endpoints) was 88.9%. Consistently, all groups reported high-output pacing from the ablation catheter to confirm absence of phrenic nerve stimulation before radiofrequency delivery. Need of pericardial access varied between 0% and 76.9%. Thirteen patients (8.5%) experienced severe procedural complications, and 15 patients (9.8%) required implantation of a pacemaker. At a mean follow-up interval of 28.1 ± 12.6 months, 86.4% of patients demonstrated successful outcomes. The symptomatic recurrence rate was 19.6%, and 29.8% of patients continued to receive antiarrhythmic drug therapy after procedural intervention.

CONCLUSIONS

Inappropriate sinus tachycardia ablation/modification achieves acute success in the vast majority of patients. Complications are fairly common and diverse. However, symptomatic relief decreases substantially over longer follow-up periods, with a corresponding high recurrence rate.

Management of Postural Tachycardia Syndrome, Inappropriate Sinus Tachycardia and Vasovagal Syncope

Postural tachycardia syndrome (POTS), inappropriate sinus tachycardia (IST) and vasovagal syncope (VVS) are relatively common clinical syndromes that are seen by physicians in several disciplines. They are often not well recognised and are poorly understood by physicians, are associated with significant morbidity and cause significant frustration for both patients and their physicians. The 2015 Heart Rhythm Society Expert Consensus Statement on the Diagnosis and Treatment of Postural Tachycardia Syndrome, Inappropriate Sinus Tachycardia and Vasovagal Syncope provides physicians with an introduction to these disorders and initial recommendations on their investigation and treatment. Here we summarise the consensus statement to help physicians in the management of patients with these frequently distressing problems.

Postural tachycardia syndrome and inappropriate sinus tachycardia: role of autonomic modulation and sinus node automaticity

BACKGROUND

Inappropriate sinus tachycardia (IST) and postural tachycardia syndrome (POTS) are 2 disorders characterized by sinus tachycardia. It is debated whether the pathophysiology of IST and POTS results from abnormal autonomic regulation or abnormal sinus node function. We hypothesized that intrinsic heart rate (IHR) after autonomic blockade would be increased in patients with IST but not POTS.

METHODS AND RESULTS

We enrolled 48 POTS patients, 8 IST patients, and 17 healthy control (HC) subjects. Intravenous propranolol and atropine were given to block the sympathetic and parasympathetic limbs of the autonomic nervous system in order to determine the IHR. Patients with IST have a higher sympathetic contribution to heart rate when compared with POTS patients (31±13 bpm versus 12±7 bpm, P<0.001) and HC (8±4 bpm; P<0.001) and a trend to less parasympathetic contribution than POTS and HC (IST: 31±11 bpm versus POTS: 46±11 bpm versus HC: 48±11 bpm, ANOVA P=0.108). IHR was not significantly different between IST and either POTS or HC (IST: 111±11 bpm versus POTS: 108±11 bpm versus HC: 106±12 bpm, ANOVA P=0.237).

CONCLUSIONS

IST patients have more sympathetic tone when compared with either POTS or HC, but IST patients do not have abnormal sinus node automaticity. These data suggest that the treatment of IST and POTS should focus on sympatholysis, reserving sinus node modification for patients with continued debilitating symptoms after beta-blockade and possibly ivabradine.

CLINICAL TRIAL REGISTRATION URL

http://clinicaltrials.gov/. Unique identifier: NCT00262470.