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Abstract
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.
Keywords: Echocardiography, inappropriate sinus tachycardia, prenatal diagnosis, tachycardia, ultrasound imaging
How to cite this article: Introduction 
Inappropriate sinus tachycardia (IST) is characterized by unexpected sinus tachycardia (ST) at rest and during minimal physical activity. In adults, IST is defined as a sinus heart rate (HR) >100 beats/min (bpm) at rest and average 24-h HR >90 bpm, which is not due to physiological demands or conditions commonly related to increased HR.[1] However, in children, there are no specific HR cut-off values for IST.[2] However, we may consider 180–200 beats as ST and >210–300 beats as supraventricular tachycardia (SVT) in fetus. The causal mechanisms for IST remain unknown; however, increased sinus node activity and impaired neurohormonal modulation may be involved.[1],[3] Persistent tachycardia may result in nonimmune hydrops, with SVT being the most important cause. Most often, IST is benign. In utero assessment of the fetal cardiac rhythm is more frequently and easy to perform by using fetal cardiac Doppler ultrasonography even without other investigation modalities. The ventriculoatrial (VA) and atrioventricular (AV) time intervals should be measured using M-mode and Doppler ultrasonography, and the atrial and ventricular rates are similar with a one-to-one AV relationship in IST and SVT.
In this report, we describe a rare case of IST in the fetus whose mother had celiac disease (CD), drawing attention to the early onset of tachycardia. Cardiac ultrasonography enabled the assessment of the hemodynamic consequences of tachyarrhythmias and detailed anatomical cardiac examinations. The particular presentation, fetal HR up to 200 bpm during the first trimester, and scarcity of fetal reports of IST constituted challenges in this case for the diagnosis and management in utero.
Case Report A 36-year-old woman, gravida 3 para 2, was referred for fetal echocardiography due to persistent fetal tachycardia (>200 bpm) noted during the first routine obstetric ultrasound scan performed at 8 weeks of gestation. There was no history of infectious or thyroid diseases or use of any drugs, except for vitamins and minerals. The pregnant woman had CD that was diagnosed after her first pregnancy, and she was consuming a strict gluten-free diet before the present gestation. Symptoms of diarrhea, anemia, and weight loss raised the suspicion of CD, and screening was performed accordingly. She experienced a miscarriage, and her first child presented with particular tachycardia, which was treated in utero with beta-blockers, based on a postnatal diagnosis of IST.
The first fetal echocardiography examination was performed at 9 weeks of gestation using three-and four-dimensional transvaginal ultrasonography. This examination confirmed sustained tachycardia with a fetal HR ranging from 207 to 220 bpm with a one-to-one AV relationship. The variability in the fetal HR led to the diagnosis of ST, despite the HR being around 200 bpm [Figure 1]. No specific antiarrhythmic therapy was administered. The mean AV interval time at the first echocardiogram was 70 ms. The AV relationship and time intervals were assessed using the superior vena cava and left ventricular ventricular outflow Doppler recordings and AV M-mode tracings.
Figure 1: Fetal echocardiogram obtained at 9 weeks of gestation with pulse-wave Doppler tracings demonstrating tachycardia with 1:1 atrioventricular conduction using the superior vena cava and aorta view. A: Atrial contraction; V: Ventricular contraction; HR: Heart rateThe pregnant woman underwent laboratory blood evaluations. Her autoimmune workup revealed positivity for tissue transglutaminase antibodies and negativity for SSA and SSB antibodies. Serum vitamin and mineral levels and thyroid function test results were normal. Despite the presence of fetal tachycardia, the first and second morphological ultrasound findings were normal. Follow-up fetal echocardiography showed normal cardiac anatomy, and no signs of hydrops were identified. Although the increased fetal HR during gestation remained approximately 200 bpm, the HR reduced to 180–190 bpm after 30 weeks of gestation [Figure 2]. No antiarrhythmic therapy was administered in utero. An exacerbated increase in the HR during fetal movements and the unusual progression of the case drew attention to the suspected diagnosis of IST. The minimum and maximum fetal HR at 9 weeks, 2nd trimester, and 3th trimester were the following: 200 and 220, 185 and 206, and 164 and 195 bpm, respectively.
Figure 2: Simultaneous recordings of left atrial and ventricular flow waves on Doppler ultrasonography/echocardiography showing a 1:1 atrioventricular relationship with an increased heart rate in the present case. VA: Ventriculo-atrial interval time; atrioventricular: Atrioventricular interval time; HR: Heart rateAt 39 weeks of gestation, the pregnant woman underwent elective cesarean section. The female baby was born unremarkably, weighing 3130 g, with Apgar scores of 9/9 at 1 and 5 min, respectively. After birth, the first electrocardiography (ECG) showed a P wave with sinus rhythm morphology and normal PR and QT intervals [Figure 3]. Since the newborn was stable with ST (180–190 bpm), she was discharged after 3 days with no antiarrhythmic medications. In the 1st month of life, the newborn was referred to a pediatric cardiologist. The mother reported that her baby had experienced episodes of pallor and irritability, suggesting colic. Although the patient remained in a favorable condition, she exhibited tachycardia at rest, with an exaggerated increase in HR with physical activity. ECG demonstrated a sinus rhythm with an HR of 200 bpm and normal values of PR and QTc. Echocardiography revealed normal cardiac anatomy and function. A 24-h Holter ECG confirmed IST with sinus rhythm at HR of 180–200 bpm during daily activities and 110–148 bpm at rest (significantly higher values of HR during activities). Blood count and thyroid function test results were normal. Other possible causes of tachycardia, such as pheochromocytoma, were excluded. Due to the persistent tachycardia, metoprolol was administered (1 mg/kg/24 h). The patient progressed with adequate HR control, and beta-blocker treatment was maintained.
Figure 3: Electrocardiogram of the newborn in the present case with a sinus rhythm at an increased heart rate with normal P waves and normal QT intervals Discussion CD in women is associated with infertility, miscarriage, and poor pregnancy outcomes. Screening for CD should be performed in women with uninvestigated iron-deficiency anemia, gastrointestinal symptoms, autoimmune disorders, or a first-degree familial history of CD.[4],[5] The more frequent fetal and neonatal outcomes related to CD are fetal growth restriction and prematurity.[6]
IST has been described as a benign type of arrhythmia, although in adults, it is related to loss of quality of life (symptoms with minimal physical activity), and tachycardia-induced cardiomyopathy has rarely been described.[1],[3],[7] However, there are no data on the long-term follow-up of fetuses with IST, even considering the scarcity of reports of fetal IST.[8] In this report, the difficulties in determining a differential diagnosis between fetal IST and fetal SVT and their management in utero are discussed.
In general, fetal arrhythmias are detected during second or third-trimester routine obstetric ultrasound scans, and most fetal arrhythmias are benign.[9],[10] However, persistent tachycardia may result in nonimmune hydrops, with SVT being the most important cause. In utero assessment of the fetal cardiac rhythm is more frequently performed using cardiac Doppler ultrasonography if fetal ECG is not available, and fetal magnetocardiography remains an expensive method. Cardiac ultrasonography/echocardiography can provide the tools to enable the diagnosis of the type of tachycardia in most cases. The VA and AV time intervals should be measured using M-mode and Doppler ultrasonography. In ST and SVT, the atrial and ventricular rates are similar with a one-to-one AV relationship. In ST, the HR is generally <200 bpm, with some variability. In contrast, the HR usually ranges from 220 to 300 bpm in SVT.[9],[10],[11],[12] In the present study, cardiac ultrasonography enabled the assessment of the hemodynamic consequences of tachyarrhythmias and detailed anatomical cardiac examinations.
In cases of ST and SVT, the atrial and ventricular rates are similar, with a 1:1 AV relationship. However, in ST, the HR is more variable and lower (≤200 bpm) than that in SVT (HR usually ranges from 220 to 300 bpm). In the present case, as the HR was 220 bpm during the first trimester, this differentiation was initially difficult. In addition to the variability in the HR and AV relationship, measurements of the AV and VA intervals are crucial features that may enable the diagnosis of the type of fetal tachycardia. The AV and VA interval times are mechanical analogs of the PR and RP electric intervals on ECG.[9],[10],[11],[12],[13] In the present case, as the tachycardia involved the sinus, these intervals did not show any differences. In cases of SVT, the VA interval times are mostly shorter than the AV interval times (VA <AV) or even less commonly longer (VA >AV). Re-entrant SVT with a retrograde accessory electrical conduction pathway is the most common type of SVT. As retrograde conduction is rapid, the atrium is excited shortly after the ventricle, which generates a short VA time interval. Persistent junctional reciprocating tachycardia (PJRT) also known as Coumel tachycardia is a rare type of re-entrant SVT in which the re-entry pathway exhibits a slow conduction back to the atrium, resulting in a long AV interval. Atrial ectopic tachycardia, a mechanism related to atrial automatic focus, is another type of SVT with a long AV interval, similar to that in PJRT, in which the HR varies from 180 to 220 bpm.[9],[10] Chaotic or multifocal atrial tachycardia may be associated with Costello syndrome, which may be a cause of atrial tachycardia. In the present case, the AV interval was not long, and the fetus did not present with other extracardiac characteristics of Costello syndrome (nuchal thickness, polyhydramnios, short femurs and humeri, and myocardial hypertrophy).[14]
IST is characterized by a consistently high HR with an exaggerated response to minimal physical activity. It was first described by Bauernfeind, and its mechanism has not yet been clarified. It is crucial to exclude secondary causes of ST, such as hyperthyroidism, pheochromocytoma, drug screening, and diabetes mellitus with evidence of autonomic dysfunction.[1],[15] In general, the initial diagnosis occurs after adolescence or, more often, after the second decade of life. There is a scarcity of studies on IST in children, adolescents, and particularly in fetuses.[7],[16] Although IST has been considered benign arrhythmia, it may be cause of tachycardia-induced cardiomyopathy, thereby we decided to initiate antiarrhythmic medication. Postnatal drugs most commonly used for the treatment of IST are beta-blockers (atenolol, metoprolol, or propranolol) and calcium channel blockers. Recent studies in adult population have shown a favorable response to the use of ivabradine in some patients and, in those who are refractory to drug therapy, radiofrequency ablation may be an important therapeutic option.[1],[2] Since there are no strong data on the use of ivabradine in younger children with IST, beta-blocker was administered in the present patient.[7],[16]
In all cases of sustained fetal SVT or ventricular tachycardia, antiarrhythmic medications are recommended for treatment in utero, except in fetuses with SVT/VT near-term. Instead, in fetal ST, the underlying cause should be identified, and no antiarrhythmic therapy is indicated. Meanwhile, IST is an exceptional type of ST, and there is no consensus on its treatment in utero.[9],[10] In the present case, as the HR remained ≤200 bpm after the first trimester and there were no signs of heart failure, no fetal therapy was administered.
Conclusion The diagnosis of IST is extremely rare; however, it must be considered in cases of fetal tachycardia with one-to-one AV conduction beyond the expected fetal HR for gestation. The goal of treatment in cases of tachycardia in utero is to reduce the ventricular rate to tolerable levels, thereby preventing fetal hydrops. In IST, further long-term follow-up and extensive data are required to establish better management.
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The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
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Conflicts of interest
There are no conflicts of interest.
References 
Correspondence Address:
Prof. Edward Araujo Jnior
Rua Belchior De Azevedo, 156 Apto, 111 Torre Vitoria, CEP 05089-030, São Paulo
Brazil
Source of Support: None, Conflict of Interest: None
CheckDOI: 10.4103/apc.apc_130_21
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