Inappropriate Sinus Tachycardia Patients Research Articles

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.

Reply to the Editor - Maternal inappropriate sinus tachycardia during pregnancy.

We would like to comment on the Letter to the Editor of Dr Wang on our manuscript, Management of Inappropriate Sinus Tachycardia during pregnancy (1Shah A.N. Ferreira S.W. Padanilam B.J. Prystowsky E.N. Management of inappropriate sinus tachycardia during pregnancy.Heart Rhythm O2. 2023; 4: 65-66https://doi.org/10.1016/j.hroo.2022.11.001Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar). He acknowledges that we used the standard accepted definition of inappropriate sinus tachycardia (IST) but raises the issue of whether an alternative definition of IST should be used during pregnancy. Indeed, recent data in pregnant women show that median heart rate was 82 bpm at 12 weeks gestation and rose to 91 bpm at 34.1 weeks (2Green L.J. Mackillop L.H. Salvi M. et al.Gestation-specific vital sign reference ranges in pregnancy.Obstet Gynecol. 2020; 135: 653-664Crossref PubMed Scopus (42) Google Scholar). However, the average heart rates in our patients mostly recorded in the early 2nd trimester were typically more than 100 bpm, and more importantly they were highly symptomatic with the added history of rapid and marked increases in heart rate during exertion, a classic presentation of IST. They were referred for further evaluation because their physicians considered them to have something other than the usual mild increase in heart rate with pregnancy. Dr Wang comments on the use of metoprolol to treat these very symptomatic patients, and suggests that the data on its effectiveness in non-pregnant patients remains questionable. The senior author (ENP) has a different experience and has treated scores of IST patients prior to ivabradine availability with substantial success in many using metoprolol succinate. The limiting factor for success is often the inability to use a high enough dose because some of these patients simply cannot tolerate beta-blockade therapy even at a low dose. Further, it is our experience that volume expansion and use of salt supplementation, while valuable in autonomic syndromes of hypotension, are not effective in pure IST without hypotension. Last, although one would like to avoid the use of any drug during pregnancy, metoprolol is considered safe to use if needed (3Page R.L. Joglar J.A. Caldwell M.A. et al.2015 ACC/AHA/HRS Guideline for the management of adult patients with supraventricular tachycardia: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society.Heart Rhythm. 2016; 13: e136-e221Abstract Full Text Full Text PDF PubMed Scopus (67) Google Scholar), and all our patients were treated beyond the first trimester. Risks and benefits of therapy were discussed during the shared decision making process, and all patients wanted to take metoprolol to suppress their marked symptoms. We agree that more data on IST in pregnancy, and the safety of ivabradine, would be useful and encourage others to investigate this problem. To the Editor – Maternal inappropriate sinus tachycardia during pregnancyHeart Rhythm O2PreviewShah and colleagues presented 11 patients with maternal inappropriate sinus tachycardia (IST) during pregnancy.1 Two major points are worth considering. Full-Text PDF Open Access

OBJECTIVE CARDIOVASCULAR AUTONOMIC ABNORMALITIES IN POST-ACUTE SEQUELAE OF COVID-19 (PASC): OVERALL AND SEX-BASED PREVALENCE

OBJECTIVE CARDIOVASCULAR AUTONOMIC ABNORMALITIES IN POST-ACUTE SEQUELAE OF COVID-19 (PASC): OVERALL AND SEX-BASED PREVALENCE

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

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. 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. 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. 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.

Abstract 16505: Sinus Node Sparing Surgical Hybrid Thoracoscopic Ablation for Inappropriate Sinus Tachycardia: Results of a Prospective Multicenter Registry (the Susruta Registry)

Background: Medical treatment for inappropriate sinus tachycardia (IST) remains suboptimal. Radiofrequency Sinus node Modification (RFSM) has been used for managing drug-refractory symptomatic IST. Although, acute success is reasonable, it is faced with high complications and recurrence rates. A novel Sinus Node sparing surgical thoracoscopic hybrid ablation (SUSRUTA) has been recently proposed. Objective: To report outcomes of SUSRUTA for IST patients from a prospective multicenter registry. Methods: This is a multicenter, prospective registry of patients who received SUSRUTA which is SN sparing hybrid ablation using surgical thoracoscopic video-assisted epicardial ablation comprised of a RF bipolar clamp which was used for sparing the SN region (identified by endocardial 3D mapping) and isolation of superior and inferior vena cava with creation of a lateral line across the crista terminalis during IST with isoproterenol challenge. Gaps in the epicardial lesion set are filled in by endocardial RFA. Patients were treated with post op Colchicine and were enrolled in cardiac rehabilitation program. Results: Of the 139 patients, mean age was 26±4 yrs, 91% women and mean duration of IST was 40±21.5 months. 90% were on ivabradine, 86% on beta-blocker, 77% on calcium channel blocker and 77% were on class IC antiarrhythmic agent. Heart rate post-procedure was significantly lower when compared with pre-procedure (110±10 vs. 64±11 bpm, p&lt;0.0001). After a blanking period of 3 months, normal sinus rhythm was restored in 100% of patients in the hybrid group. Postop pericarditis was the most common complication in 80%(severe-4%), severe bradycardia (HR &lt;35 bpm) in 5%, pneumothorax 3.5% and pleural effusion requiring drainage in 2.1% of cases. One patient required a permanent pacemaker. Hospital length of stay was 4.5±0.8 days. At 1041±541 days follow up 94.5% (131/139) were free of symptoms after a single procedure and the 8 patients required a redo-RF catheter ablation.95% patients are off all preprocedural rate controlling medications Conclusion: SUSRUTA appears to be efficacious and safe for the treatment of symptomatic drug resistant IST.

Prevalence of inappropriate sinus tachycardia and the comparison of the heart rate variability characteristics with propensity score-matched controls.

Inappropriate sinus tachycardia (IST) is a syndrome characterized by an elevated resting heart rate with distressing symptoms and no secondary cause of sinus tachycardia. This study was conducted to evaluate both the prevalence of IST among symptomatic patients and heart rate variability (HRV) characteristics. The records of all consecutive symptomatic patients who had undergone 24-hour Holter monitoring between September 2015 and November 2016 at a single center were retrospectively evaluated. IST was defined as a 24-hour mean heart rate (HR) of ≥90 beats/minute and a resting HR of ≥100 beats/minute in the absence of any secondary cause of sinus tachycardia. All of the study data related to clinical characteristics, symptoms, concomitant diseases, and Holter electrocardiogram parameters were obtained from the electronic hospital records. A propensity age- and sex-matched control group was selected from a non-IST patient cohort. A total of 1865 consecutive patients were evaluated and 32% were excluded due to an inadequate Holter recording period or insufficient quality, atrial fibrillation episodes, atrioventricular block, or >1% atrial or ventricular extrasystoles. Among 1265 patients with sinus rhythm, 4.98% (n=63) had IST. The IST patients were younger (39.6±17.4 vs. 50.2±17.2 years; <0.001), and female gender was more prominent (60.3% vs. 43.8%; p=0.009). All of the time and frequency domain parameters of HRV except the low frequency/high frequency ratio were significantly reduced in the IST group compared with the propensity-matched controls. The IST prevalence among symptomatic patients in sinus rhythm was 4.98%. IST was primarily seen in younger women, and they had diminished time and frequency domain HRV parameters.

Inappropriate sinus tachycardia – symptom and heart rate reduction with ivabradine: pooled analysis of prospective studies

Objective: Inappropriate sinus tachycardia (IST), is a debilitating condition despite currently available treatment. Ivabradine, a selective sinus node blocker, has been used off-label to treat IST. We therefore systematically reviewed the literature and analyzed the quality of existing data and calculated sample size estimates for adequately powered studies. Methods: We included all available trials, open label prospective studies studies with ivabradine, specifically for IST among subjects with no structural heart disease with a minimum follow-up period of > 2 weeks. Heart rate and symptom reduction with ivabradine were estimated based on results of subjective change in symptoms assessed by data instruments used in the studies. All studies were assessed for quality using two validated checklists scoring the quality of studies. Sample size estimates for future studies were calculated based on the magnitude of symptom reduction encountered after treatment with ivabradine. Results: Nine studies met study criteria, culminating in 145 patients pooled with the majority being women (> 70%). All studies were small, most inadequately powered. All studies reported a decrease in maximum and/or mean resting heart rate with ivabradine. Symptom reduction demonstrated either complete or considerable amelioration. Most studies were at least of moderate quality. Excellent consistency of study quality was gauged by both data-quality tools and narrow limits of agreement between these tools. Calculated sample size estimates for adequately powered studies with a placebo effects of 30 and 50% was 56 and 242 patients respectively. Conclusions: Although ivabradine is effective in reducing heart rate and symptoms in IST patients, none of the studies were adequately powered to account for the expected placebo effect on symptoms. A multicenter-randomized, placebo controlled active comparative study with a beta-blocker is needed to confirm these findings. This is relevant given the ivabradine’s potential teratogenic effect as many IST patients are females of childbearing potential.

Inappropriate sinus tachycardia–symptom and heart rate reduction with ivabradine: A pooled analysis of prospective studies

Inappropriate sinus tachycardia (IST) is debilitating despite available treatment. Off-label use of ivabradine for IST prompted this systematic analysis of existing data quality and sample size estimates for adequately powered studies. To determine clinical efficacy of ivabradine in IST from pooled prospective studies. Analysis included ivabradine studies for IST participants without structural heart disease and with follow-up of ≥2 weeks. Heart rate and symptom reduction with ivabradine were estimated based on results of subjective change in symptoms assessed by various data instruments used in each study. Studies were assessed for quality using validated checklists. Sample sizes were calculated based on the magnitude of symptom reduction encountered after treatment with ivabradine. Nine studies met criteria, culminating in 145 patients pooled. Most patients were women (≥70%). Studies were small and not adequately powered, and all reported a decrease in maximum or mean resting heart rate or both, with complete or considerable amelioration of symptoms with ivabradine. Most studies had moderate quality with excellent consistency of study quality and narrow limits of agreement between the quality checklists. Sample size estimates for adequately powered studies with various placebo effects and comparisons with β-blockade are reported. Ivabradine effectively reduces heart rate and symptoms in IST, but no study was adequately powered to account for the expected placebo effect on symptoms. A multicenter, randomized, placebo-controlled, active, comparative study with a β-blocker is needed for confirmation. This is especially relevant given the ivabradine's potential teratogenic effect, as many IST patients are females of childbearing potential.

A gain-of-function mutation in the cardiac pacemaker HCN4 channel increasing cAMP sensitivity is associated with familial Inappropriate Sinus Tachycardia.

Aims Inappropriate Sinus Tachycardia (IST), a syndrome characterized by abnormally fast sinus rates and multisystem symptoms, is still poorly understood. Because of the relevance of HCN4 channels to pacemaker activity, we used a candidate-gene approach and screened IST patients for the presence of disease-causing HCN4 mutations. Methods and results Forty-eight IST patients, four of whom of known familial history, were enrolled in the study. We initially identified in one of the patients with familial history the R524Q mutation in HCN4. Investigation extended to the family members showed that the mutation co-segregated with IST-related symptoms. The R524Q mutation is located in the C-linker, a region known to couple cAMP binding to channel activation. The functional relevance of the mutation was investigated in heterologous expression systems by patch-clamp experiments. We found that mutant HCN4 channels were more sensitive to cAMP than wild-type channels, in agreement with increased sensitivity to basal and stimulated adrenergic input and with a faster than normal pacemaker rate. The properties of variant channels indicate therefore that R524Q is a gain-of-function mutation. Increased channel contribution to activity was confirmed by evidence that when spontaneously beating rat newborn myocytes were transfected with R524Q mutant HCN4 channels, they exhibited a faster rate than when transfected with wild-type HCN4 channels. Conclusion This is the first report of a gain-of-function HCN4 mutation associated with IST through increased sensitivity to cAMP-dependent activation.

Differences in cardiac autonomic function contributes to heart rate abnormalities in POTS and IST.

Our objective was to examine the differences in cardiac autonomic function in Postural Tachycardia Syndrome (POTS) versus inappropriate sinus tachycardia (IST). Subjects (IST, n = 8; POTS, n = 12) were studied using standard measurements of the autonomic reflex screen, baroreflex function and spectral analysis. Data was compared to age/gender-matched controls (n = 20). The components of the autonomic reflex screen did not differ between groups. The exception was the significant but expected difference in postural heart rate increment on head-up tilt in POTS (47.9 ± 13.8; n = 12) compared to IST (30.9 ± 9.7; n = 8; p = 0.008). Accordingly the Orthostatic Intolerance Scale showed significantly greater orthostatic symptoms in POTS (2.6 ± 0.5; n = 12) versus IST patients (0.4 ± 0.5; n = 8; p < 0.001). Conversely, IST patients had a significantly higher resting heart rate (96 ± 12; n = 8) when compared to POTS patients (73 ± 12; n = 12; p = 0.001). There was a significant difference in vagal baroreflex sensitivity (BRSv) in POTS (8.21 ± 2.3, n = 12) compared to IST patients (5.30 ± 2.94, n = 8, p = 0.036) during the Valsalva maneuver. Only POTS subjects showed a significant increase in sympathovagal balance (LF/HF) with tilt (FFT, 8.29 ± 6.38; AR, 7.84 ± 5.24) compared to the supine position (FFT, 2.25 ± 1.75; AR, 1.99 ± 1.38; p < 0.05) for both frequency domains. Differences in cardiac autonomic function contribute to changes in positional and non-positional heart rate in postural tachycardia syndrome versus inappropriate sinus tachycardia. These findings shed further light on the autonomic dysfunction underlying POTS and IST.

Epicardial/Endocardial Sinus Node Ablation After Failed Endocardial Ablation for the Treatment of Inappropriate Sinus Tachycardia

Success of endocardial sinus node (SN) ablation for refractory inappropriate sinus tachycardia (IST) is limited by the epicardial location of the SN and potential damage to the phrenic nerve (PN). An epicardial approach may overcome these limitations. IST patients who failed endocardial ablation underwent an epicardial approach. Percutaneous pericardial access was obtained with a double wire technique for PN protection (i.e., with a balloon catheter), if needed. Earliest sinus activation was mapped and ablated with remapping for changes in P-wave morphology or sinus rate. The endpoint was total SN ablation (patients with atrial pacing [AP]); otherwise the target was a >25% decrease in sinus rate and inversion of P-wave axis. Five patients (all female, age 36 ± 4 years) underwent ablation. Two had prior AP, and 1 elected to have SN ablation and pacemaker during the same procedure. Three had prior endocardial ablation limited by PN proximity. Baseline sinus rate was 119 ± 20 bpm. After 35.2 ± 21.3 lesions (22.4 ± 21.7 epicardial, 12.8 ± 21.3 endocardial), 4 were in junctional rhythm, 1 in atrial rhythm at 90 bpm. This latter patient had symptom recurrence and underwent combined minimally invasive surgical/catheter SN cryoablation. Atrial tachycardia subsequently occurred and was successfully ablated. The only significant complication was pericarditis (3 patients). At last follow-up (30.4 ± 18.4 months), all had symptom resolution. Two were AP >99%, 1 was AP 54%. Two remain in ectopic atrial rhythm with controlled rates. Combined epicardial/endocardial SN ablation is a viable approach for patients with severely symptomatic IST after a failed endocardial attempt.

Long term outcomes of ivabradine in inappropriate sinus tachycardia patients: appropriate efficacy or inappropriate patients?

Long term outcomes of ivabradine in inappropriate sinus tachycardia patients: appropriate efficacy or inappropriate patients?

Noninvasive Assessment of Autonomic Cardiovascular Activity in Patients With Inappropriate Sinus Tachycardia

Inappropriate sinus tachycardia (IST) is a clinical syndrome characterized by excessive resting heart rate (HR) or disproportional HR increase during exercise. The etiology of IST has not been fully elucidated and remains controversial. The aim of the present study was to assess autonomic function by means of noninvasive tests and commonly available electrocardiographic methods in a series of consecutive patients with symptomatic IST. Twenty-four patients (37 ± 12 years; 20 women) with IST were enrolled. Six cardiovascular reflex tests were performed: (1) HR variation during slow deep breathing, (2) 30-to-15 ratio during active standing, (3) blood pressure response to standing, (4) cold face test, (5) Valsalva maneuver, and (6) blood pressure response to sustained handgrip. Intrinsic HR was calculated and compared with HR after pharmacologic denervation. Additionally, spontaneous baroreflex sensitivity and 24-hour HR variability indices were analyzed. In IST patients, intrinsic HR was significantly higher compared with control subjects. Most cardiovascular autonomic tests revealed abnormal or borderline results, particularly those reflecting mainly parasympathetic function. The spontaneous baroreflex gain was significantly reduced in IST patients. After controlled orthostatic stress and during Valsalva maneuver, impaired baroreflex function was observed. The sympathovagal balance from HR variability was preserved, but altered activity in both bands of frequency domain analysis was recorded. In conclusion, IST is a heterogenic syndrome with enhanced sinus node automaticity modulated by complex alterations of autonomic tone.

Long‐Term Outcomes of Ivabradine in Inappropriate Sinus Tachycardia Patients: Appropriate Efficacy or Inappropriate Patients

Inappropriate sinus tachycardia (IST) is characterized by persistent and disproportional elevation of heart rate (HR). Ivabradine has been successfully used in some patients. Twenty-four patients (18 women, 41 ± 13 year olds) were diagnosed with IST according to current guidelines criteria. Patients were treated with 5-7.5 mg of ivabradine twice a day. Twenty-four-hour Holter recordings and the SF-36 Health Survey were performed at 6 months to evaluate both HR control and clinical status. Holter recordings before and after 6 months on treatment showed a significant reduction in the average maximal HR of 155 ± 18 beats/min versus 132 ± 16 beats/min, mean HR of 97 ± 6 beats/min versus 79 ± 8 beats/min (mean daytime HR of 103 ± 8 beats/min vs 84 ± 10 beats/min) and minimal HR of 58 ± 12 beats/min versus 48 ± 7 beats/min (Wilcoxon analysis, P < 0.05). The SF-36 mean score showed a significant improvement on ivabradine treatment (57 ± 23 vs 76 ± 20), with a better physical and mental status scores (56 ± 25 vs 74 ± 22 and 58 ± 24 vs 78 ± 18, respectively) (Wilcoxon analysis, P < 0.001). Mean dose of ivabradine was 5.8 ± 1.4 mg. No episodes of severe bradycardia or syncope were reported. After 1 year, patients were asked to stop treatment to reevaluate the situation. Twenty patients were on treatment and only 10 patients accepted to stop ivabradine. Only two patients (20%) remained on IST criteria. IST patients treated with ivabradine showed both HR normalization and quality-of-life improvement maintained in the long-term follow-up. Stopping ivabradine after 1 year unexpectedly showed that HR remained in the normal limits in 80% of the patients.

Ivabradine for inappropriate sinus tachycardia: another piece of evidence

This editorial refers to ‘Metoprolol succinate vs. ivabradine in the treatment of inappropriate sinus tachycardia in patients unresponsive to previous pharmacological therapy’ by P. Ptaszynski et al. , on page 116 Prevalence of inappropriate sinus tachycardia (IST) defined by heart rate criteria is estimated to be 1.2% in the middle-aged population.1 Its clinical presentation with polymorphic symptoms of variable intensity, sometimes including debilitating palpitations and general incapacity, is fortunately much less common. Pathophysiological background of this infrequent entity remains poorly understood and several investigations led to rather controversial results.2 Enhanced intrinsic automaticity of the sinus node and/or impairment of cardiac autonomic regulation were suggested. Inappropriate sinus tachycardia has also been linked to the presence of beta-receptor stimulating autoantibodies.3 The clinical features of IST significantly overlap with postural orthostatic tachycardia syndrome, so that extracardiac autonomic system abnormalities may play an important role. For all these reasons, a multidisciplinary model in managing IST patients was proposed.4 Beta-blockers are the cornerstone of pharmacological therapy for IST that may be replaced by or combined with non-dihydropyridine calcium channel blockers. Since this therapy is ineffective or associated with intolerable side effects in approximately one-third of patients, radiofrequency catheter modification of sinus nodal region has been proposed. This approach should be reserved for highly symptomatic patients who are refractory to medical therapy because ablation has no clear acute endpoint and may be associated with significant complications. Also long-term outcomes were disappointing.4 Due to the ‘systemic’ nature of IST, invasive procedure may, however, identify a considerable proportion of associated non-IST arrhythmias that can be cured by radiofrequency ablation more successfully.5 …

Usefulness of Non-contact Mapping for Radiofrequency Catheter Ablation of Inappropriate Sinus Tachycardia: New Procedural Strategy and Long-term Clinical Outcome

The present study evaluated the clinical benefits of a new therapeutic method of radiofrequency catheter ablation (RFCA) using an EnSite system for inappropriate sinus tachycardia (IST). Six patients with debilitating IST underwent RFCA using EnSite. Using the beta-adrenergic blocker and agonist, the heart rate was controlled between 70 to 150 bpm before and after the RFCA. The areas of the breakout sites (BOSs) were clearly distinguished between those from the normal P-wave zones during rates of less than 100 bpm and those from more upper rate sites during rates of more than 100 bpm using the EnSite system, in accordance with the appearance of tall P-waves (tall P-wave zone) in the IST patients. This was selected as the target for ablation. After the RFCA, the BOSs observed during heart rates of more than 100 bpm moved completely from the tall P-wave zone to the normal P-wave zone in the IST patients. The total number of heart beats and average heart beat on the 24-h Holter monitoring decreased statistically from that before the RFCA to that after, and no adverse heart rate responses was observed after the RFCA. Before the RFCA, the brain natriuretic peptide was elevated, New York Heart Association functional class was worse, and there was an impaired exercise tolerance observed with exercise electrocardiogram testing. The RFCA for the IST significantly improved those parameters. This new therapeutic method for IST using EnSite is effective and produces clinical benefits.

Prevalence, characteristics and natural course of inappropriate sinus tachycardia

To study the prevalence, characteristics and natural course of inappropriate sinus tachycardia (IST). The prevalence and characteristics of IST were evaluated in a random sample of 604 middle-aged subjects. Seven of the subjects (1.16%) fulfilled the contemporary diagnostic criteria of IST. The systolic (147+/-11 mmHg vs. 130+/-13 mmHg, P<0.001) and diastolic ambulatory blood pressures (92+/-7 mmHg vs. 81+/-8 mmHg, P<0.001) were higher among the subjects with IST than among the controls. The other laboratory, echocardiographic and personality measurements, with the exception of the hostility score (10+/-2 vs. 8+/-3, P<0.001), revealed no differences between the groups. The natural course and prognosis of the disorder was assessed among the subjects fulfilling the IST criteria and nine previously diagnosed IST patients. During a mean follow-up of 6.0+/-2.4 years, none of the subjects developed any clinical or echocardiographic evidence of structural heart disease despite ongoing palpitations, and there was no significant reduction in the 24-h average HR (9+/-2 bpm vs. 89+/-8 bpm, P=0.204). The prevalence of IST in a middle-aged population was higher than previously assumed. Despite the chronic nature of the disorder, the prognosis of IST was benign. The causal relationship between IST and hypertension and/or hostile personality type remains speculative.

Impaired Baroreflex Gain in Patients with Inappropriate Sinus Tachycardia

The aim of this study was to determine the characteristics of heart rate variability (HRV), blood pressure variability (BPV), and baroreflex gain (BRG) at rest and during orthostatic stress in patients with clinical criteria of inappropriate sinus tachycardia (IST). Beat-to-beat HRV and BPV, measured by time- and frequency-domain methods, and noninvasive BRG, calculated by cross-spectral analysis, were obtained during 10 minutes both at rest and during the stabilization phase (5-15 min) of orthostatic stress at 60 degrees in 8 patients with clinical criteria of IST and 9 healthy volunteers (CON). IST patients had a higher resting mean heart rate (78.8 +/- 5.3 vs 58.5 +/- 4.2 beats/min, P=0.01) and mean blood pressure (90.4 +/- 2.4 vs 72.0 +/- 4.2 mmHg; P=0.002). RMSSD, pNN50m, and BRG were significantly reduced in IST patients at rest. BRG during orthostatic stress (7.2 +/- 0.8 vs 20.3 (2.4 ms/mmHg, P <0.01) was significantly reduced in IST patients. Delta BRG (-16.9%+/- 11 vs -50.1%+/- 5, P=0.02) was markedly blunted during orthostatic stress in IST patients. BRG was markedly impaired both at rest and during orthostatic stress in IST patients. This alteration may be responsible for the higher resting heart rate and mean blood pressures seen at rest and may facilitate tachycardia during orthostatic stress. A primary alteration in sinus node automaticity coupled with impaired BRG determines heart rate response to orthostatic stress in patients with IST.

Electrophysiologic findings of a patient with inappropriate sinus tachycardia cured by selective radiofrequency catheter ablation

Radiofrequency catheter ablation (RFCA) for inappropriate sinus tachycardia (IST) is associated with a high recurrence rate and sometimes requires pacemaker implantation, especially after extensive ablation. We report a patient with drug-refractory IST who was successfully treated by selective RFCA to the 2 earliest activation sites. During tachycardia, the earliest atrial activation preceded the surface P wave by 50 ms or more, whereas it was only 27 ms for the rest of the right atrium after ablation. Our patient had the longest activation period during tachycardia among the reported patients. In IST patients, a longer activation time at the site of the earliest atrial activation may imply that the abnormality is confined to a small area within the sinus node and may predict the efficacy of selective RFCA.

Mechanism of 'inappropriate' sinus tachycardia. Role of sympathovagal balance.

"Inappropriate" sinus tachycardia (IST) is an uncommon and poorly defined atrial tachycardia characterized by inappropriate tachycardia and exaggerated acceleration of heart rate with "normal" P wave. The mechanism of this tachycardia is unknown. The purpose of the present study was to determine the role of autonomic balance in the genesis of IST. Six female patients aged 23 to 38 years with IST and 10 age- and sex-matched control subjects were assessed with the following autonomic function tests: (1) sympathovagal balance to the sinus node assessed by calculating the LF/HF (low frequency/high frequency) ratio using power spectral analysis both in the supine position and after 10 minutes of head-up tilt to 60 degrees, (2) cardiovagal reflex assessed by cold face test (CFT), (3) beta-adrenergic sensitivity as determined by calculating isoproterenol dose-response curves and isoproterenol chronotropic dose 25 (CD25), and (4) intrinsic heart rate (IHR) assessed after autonomic blockade with atropine 0.04 mg/kg and propranolol 0.2 mg/kg administered as an intravenous bolus. No significant differences in the LF/HF ratio both in the supine position (2.8 +/- 0.3 versus 2.6 +/- 0.4) and during upright tilt (8.7 +/- 1.3 versus 8.5 +/- 0.5) were observed between control subjects and IST patients. Cardiovagal response to CFT was markedly depressed in all patients (6.3% IST patients versus 24.2% control subjects, P < .001). beta-Adrenergic hypersensitivity to isoproterenol was noted in all patients (mean CD25, 0.29 +/- 0.10 microgram IST patients versus 1.27 +/- 0.4 microgram control subjects; P < .001), and high IHR was noted in all cases. The patients were treated with high doses of beta-blockers with adequate short-term control. Radiofrequency catheter ablation of the sinus node area was performed in one drug-refractory patient. These findings suggest that the mechanism leading to IST is related to a primary sinus node abnormality characterized by a high IHR, depressed efferent cardiovagal reflex, and beta-adrenergic hypersensitivity.