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 Table of Contents  
ORIGINAL ARTICLE
Year : 2019  |  Volume : 4  |  Issue : 2  |  Page : 68-73

Diagnostic value of implantable loop recorders in unexplained syncope patients: A single-center experience


Department of Arrhythmia, First Affiliated Hospital of Dalian Medical University, Dalian, Liaoning Province, China

Date of Submission26-Mar-2020
Date of Acceptance20-Apr-2020
Date of Web Publication15-Jun-2020

Correspondence Address:
Prof. Yingxue Dong
Department of Arrhythmia, First Affiliated Hospital of Dalian Medical University, Dalian 116011, Liaoning Province
China
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/IJHR.IJHR_5_20

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  Abstract 

Background: The role of implantable loop recorders (ILRs) in the evaluation strategy for recurrent syncope in China is limited. This study aimed to clarify the clinical usefulness of ILRs in the diagnosis and management of patients with unexplained syncope. Subjects and Methods: This was an observational cohort study in unexplained syncope patients. This retrospective study enrolled 37 patients (24 men and 13 women; mean age: 59.5 ± 19.1 years) who were implanted with ILRs and diagnosed with unexplained syncope in the First Affiliated Hospital of Dalian Medical University between January 2013 and October 2018. All patients were followed up every 3–6 months after implantation to record the patients' conditions, electrocardiogram (ECG) data, and presence of syncope. Any patients with a history of postimplantation syncope were recommended for prompt medical attention. The study was approved by the Institutional Review Board of the First Affiliated Hospital of Dalian Medical University (approval No. 2017-046) on March 22, 2017. Results: In the 37 patients, 22 (59.46%) experienced syncope within 187.73 ± 177.12 days after loop recorder implantation, including 9 cases of sinus bradycardia or sinus arrest, 6 of third-degree (advanced) atrioventricular block, 1 of ventricular tachycardia, 2 of supraventricular tachycardia, and 4 of atrial fibrillation accompanied by long RR intervals (>5 seconds). In addition, there was one syncope-free atrial fibrillation case with long RR intervals. Among all the patients, 16 were implanted with permanent pacemakers, 1 received an implantable cardioverter-defibrillator, and 2 received catheter ablation. Based on the analysis of sex, age, underlying comorbid conditions, preimplantation syncope episodes, and ECG data, syncope could be predicted from the occurrence of long RR intervals (≥2 seconds) on Holter. Conclusions: The ILR was an effective tool to establish the cause of unexplained syncope in 59.46% of the study patients and to assist these patients in medical treatment. The occurrence of long RR intervals (≥2 seconds) on Holter was an important predictor for arrhythmic syncope.

Keywords: Arrhythmia, clinical utility, implantable loop recorder, long RR interval, syncope


How to cite this article:
Yang M, Zhang R, Li G, Li D, Yin X, Gao L, Xia Y, Dong Y. Diagnostic value of implantable loop recorders in unexplained syncope patients: A single-center experience. Int J Heart Rhythm 2019;4:68-73

How to cite this URL:
Yang M, Zhang R, Li G, Li D, Yin X, Gao L, Xia Y, Dong Y. Diagnostic value of implantable loop recorders in unexplained syncope patients: A single-center experience. Int J Heart Rhythm [serial online] 2019 [cited 2020 Sep 29];4:68-73. Available from: http://www.ijhronline.org/text.asp?2019/4/2/68/286767


  Introduction Top


Syncope is a clinically common condition that affects approximately 30% of the population.[1] Syncope has varied causes and a complex underlying mechanism. In clinical practice, the cause of syncope is largely identified according to a patient's medical history, clinical manifestations, 24-hour Holter, and head-up tilt (HUT) test results. However, the causes of syncope in some patients remain unknown,[2] and a considerable proportion of these patients are eventually found to be affected by arrhythmic syncope. Studies have shown that recurrent syncope can cause a decreased quality of life, and in severe cases of falls and injuries induced by syncope episodes, it can be a life-threatening risk.[3] During loop recorder implantation, the patient is placed under local anesthesia, and an implantable loop recorder (ILR) is placed under the skin, on the left chest wall, overlying the heart. It works as an electrocardiogram (ECG) that continuously picks up electrical signals from the heart for up to 36 months. The ILR saves ECG data and intracardiac electrograms to assist the clinical diagnosis of syncope. This is especially true in attempts to establish the causes of unexplained syncope in patients.[4] Although several studies have provided ample evidence for the use of ILRs in the diagnosis of unexplained syncope as a valuable and effective tool, its application in this field is rarely reported in China. This study aims to identify the diagnostic value of ILRs for unexplained syncope in a Chinese cohort.


  Subjects and Methods Top


Subjects

This retrospective study included 37 patients who received loop recorder implantation in theFirst Affiliated Hospital of Dalian Medical University during 2013 and 2018. After excluding the possibility of neurogenic syncope, every patient was subjected to ECG, 24-hour Holter, echocardiography, CT angiography of the coronary arteries, and the HUT test. If the cause of syncope could not be determined, the patient underwent loop recorder implantation. Written informed consent was obtained from each patient. This study conforms to the principles set forth in the Declaration of Helsinki. All clinical procedures and protocols conformed to institutional guidelines and were approved by the Institutional Review Board of theFirst Affiliated Hospital of Dalian Medical University (approval No. 2017-046) on March 22, 2017.

Model, implantation and parameter settings

The Reveal XT ILRs (Medtronic, Minneapolis, MN, USA) were implanted in 26 patients, the Reveal LINQ ILR (Medtronic) was implanted in 1 patient, and the Confirm Rx ILRs (Abbott, Chicago, IL, USA) were implanted in the remaining 10 patients. Every ILR offers memory for 27 minutes of automatically sensed events (including 2 minutes for the longest detected episode(s) of atrial tachycardia/atrial fibrillation), with 30 seconds of preactivation and postactivation, respectively. In addition, the ILR can be activated manually by pressing the designated button. When relevant symptoms occur, it can store manually activated events with 6.5 minutes of preactivation and 1 minute of postactivation recording.

The optimal position for implantation must be located before implantation. It is recommended that the ILR be implanted between the first intercostal space and the fourth rib using a dermal ECG vector measurement tool. Specifically, the implantation zone is supposed to be a location between the left sternal border and the midclavicular line, which has the maximum R-wave amplitude (at least >0.3 mV) and stable R-wave patterns. The left lower parasternal region was anesthetized with lidocaine. An incision and dissection were made, and the ILR was implanted at the left chest wall. The ILR was tested before suturing. Prophylactic antibiotics were used.

Parameter settings: Tachycardia >180 beats/min in 16 consecutive cardiac cycles, bradycardia <30 beats/min during 3 beats, and RR intervals >3 seconds.

Postoperative follow-up

Surgeons who performed the loop recorder implantation operations were responsible for following up their own patients' conditions after the implantation. All patients were followed up every 3–6 months after implantation through telephone, and an outpatient visit was required after implantation to record patients' conditions, ECG data, and the presence of syncope. When syncope occurred, the patient was to promptly seek medical assistance. Real-time ECG data were collected to identify whether the syncopal attack was triggered by arrhythmia; if so, the ILR was removed to treat arrhythmia. If no arrhythmia was detected, follow-up was continued. The ILR was removed from the patient if no syncopal attacks occurred in 3 years.

Statistical analysis

Continuous variables are presented as the mean ± standard deviation and examined with an independent-samples t-test. Categorical variable data are denoted by percentage (%) and were examined with the Chi-square test. Thereafter, a multivariate regression analysis was performed to identify clinical predictors of impending syncope. The software SPSS 19.0 (IBM, Armonk, NY, USA) was used for data analysis, and P < 0.05 (two-sided) indicated statistical significance.


  Results Top


Basic clinical features

This study enrolled 37 patients with recurrent syncope and ILRs implanted, including 13 females (35.2%) and 24 males (64.8%). The mean age was 59.5 ± 19.1 (range: 40–81) years, and the average number of preimplantation syncope episodes was 3.95 ± 4.25. Among these patients, 20 had hypertension (54.0%). Long RR intervals (>2 seconds) were noted in eight (21.6%) patients before implantation, but no syncope events occurred. Details of the patients' clinical features are shown in [Table 1]. Syncope-related arrhythmia of clinical significance was observed in 22 (59.5%) patients, which was confirmed 187.73 ± 177.12 days after implantation. During the follow-up, two patients died of cancer and cerebrovascular disease. Common arrhythmic causes of syncope are shown in [Table 1] and [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5].
Table 1: Basic clinical features of the 37 patients implanted with implantable loop recorders

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Figure 1: Syncope-related arrhythmia: third-degree (advanced) atrioventricular block was recorded in six patients

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Figure 2: Syncope-related arrhythmia: ventricular tachycardia was recorded in one patient

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Figure 3: Syncope-related arrhythmia: sick sinus syndrome was recorded in nine patients

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Figure 4: Syncope-related arrhythmia: paroxysmal supraventricular tachycardia was recorded in two patients

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Figure 5: Syncope-related arrhythmia: atrial fibrillation with long RR interval was recorded in four patients

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Analysis results of predictors for recurrent syncope

Clinically significant syncope-related arrhythmia occurred in 22 patients implanted with ILRs (the positive group), and the remaining 15 patients were diagnosed as negative (the negative group). The positive group had a larger left atrial diameter and a significantly higher proportion of patients with an RR interval >2 seconds than the negative group [Table 2].
Table 2: Recurrent syncope predictors in patientsf presence and absence of syncope.related arrhythmia

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Analysis results of independent predictor for impending syncope

A multivariate regression analysis was performed to analyze the independent predictor for impending syncope. The results showed that the occurrence of long RR intervals (≥2 seconds) on Holter was an independent predictor for arrhythmic syncope [Table 3].
Table 3: Multivariate regression analysis of independent predictor for impending syncope

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Follow-up results

There were 22 cases (59.5%) of syncope-related arrhythmias, including 16 patients who were implanted with permanent pacemakers, 1 who received an implantable cardioverter-defibrillator, and 2 who received catheter ablation.


  Discussion Top


This study presents a single-center analysis concerning the diagnostic value of ILRs for unexplained syncope patients. The major findings are as follows: definitive diagnoses were made for 59.5% of the unexplained syncope patients and for 4.5% of those with syncope-free arrhythmia based on ILR-detected events, and the occurrence of long RR intervals (≥2 seconds) on Holter is an important predictor for arrhythmic syncope. The results showed that ILRs are an effective tool for the diagnosis of unexplained syncope.

Arrhythmia is a common cause of cardiac syncope. Severe bradycardia or tachycardia is associated with reduced cardiac output that induces a syncopal attack. In these cases, syncope can result in sudden death. Syncope is a clinically common condition that has a range of causes. The guidelines[5] recommend that the initial assessment for all patients presenting with syncope includes medical history, resting 12-lead ECG recording, and Holter. If no clear causes are established, an ILR (IIa) can be implanted. ILR implantation may decrease the risk of syncope-induced death and hospitalization.[6] However, there is no clear evidence showing that ILRs can reduce a syncope patient's forward death rate.[7] In a meta-analysis of five randomized controlled trials,[8],[9],[10],[11],[12] 660 unexplained syncope patients were randomly divided into two groups, with the control group receiving traditional examinations such as ECG monitoring, the HUT test, and an electrophysiological study and the experimental group undergoing ILR implantation. The results indicated that ILRs were 3.7 times more accurate than the examinations in the control group. Another meta-analysis of 9 randomized controlled trials involving 506 patients showed that in 176 cases, there was a correlation between syncope and ECG patterns (35%). According to the ILR-detected events, 56% of the patients had a history of cardiac arrest, 11% had tachycardia, and 33% had arrhythmia.[13] Researchers have noted that for those who are suspected to have syncope and who are free of high-risk factors and structural heart disease, ILRs have a detection rate of 50% for bradyarrhythmia.[14],[15],[16]

In the present study, syncope recurred on average 187.73 ± 177.12 days after ILR implantation, which is in agreement with the findings in the EaSyAS clinical study.[12] However, other studies suggest that recurrent syncope may attack 1–3 months after ILR implantation.[17],[18],[19] The present study showed that 59.5% of the patients were diagnosed with syncope using ILRs, and the most common cause was bradyarrhythmia, including atrioventricular block and long RR intervals. Some studies[20],[21],[22] have revealed that supraventricular tachycardia and ventricular tachycardia are also causes of syncope. In this study, there was one ventricular tachycardia case and two supraventricular tachycardia cases, and the patients were treated with electrophysiological study and radiofrequency ablation. Bradyarrhythmia and supraventricular tachycardia are both causes of unexplained syncope.

Brignole et al.[16] indicated that syncope episodes in patients over 65 years old were 2.7 times more common than those in other age groups, while cases of arrhythmic syncope in these patients were 3.1 times more common than those in other age groups. Prochnau et al.[23] proved that age was an independent risk factor for syncope. Ahmed et al.[24] showed that a PR interval >200 ms was an independent predictive factor of pacemaker insertion for those implanted with ILRs. Bhangu et al.[25] found that hypertension and cardiovascular disease were independent predictive factors of syncope recurrence. In this study, it was noted that an RR interval >2 seconds was a risk factor that could be used for recurrent syncope prediction.

The study presented here has two main limitations. First, it is a retrospective single-center analysis of a relatively small cohort of patients. Second, an overall RR interval >2 seconds was documented in 8 (21.6%) patients. Thus, despite the statistical significance, the relatively small number of patients with an RR interval >2 seconds may have introduced bias in the interpretation of the results.


  Conclusion Top


ILR was an effective tool to identify causes for unexplained syncope in 59.5% of the study patients and to assist this patient group in medical treatment. The occurrence of long RR intervals (≥2 seconds) on Holter was an independent predictor of arrhythmic syncope.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Institutional review board statement

The study was approved by the Institutional Review Board of theFirst Affiliated Hospital of Dalian Medical University (approval No. 2017-046) on March 22, 2017.

Declaration of patient consent

The authors certify that they have obtained all appropriate consent from patients. In the forms the patients have given their consent for 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 forms.



 
  References Top

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Ruwald MH, Ruwald AC, Jons C, Lamberts M, Hansen ML, Vinther M, et al. Evaluation of the CHADS2 risk score on short-and long-term all-cause and cardiovascular mortality after syncope. Clin Cardiol 2013;36:262-8.  Back to cited text no. 3
    
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Shen WK, Sheldon RS, Benditt DG, Cohen MI, Forman DE, Goldberger ZD, et al. 2017 ACC/AHA/HRS Guideline for the Evaluation and Management of Patients With Syncope: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society. Circulation 2017;136:e60-122.  Back to cited text no. 5
    
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Ahmed N, Frontera A, Carpenter A, Cataldo S, Connolly GM, Fasiolo M, et al. Clinical predictors of pacemaker implantation in patients with syncope receiving implantable loop recorder with or without ECG conduction abnormalities. Pacing Clin Electrophysiol 2015;38:934-41.  Back to cited text no. 24
    
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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