Conclusions
Real-world battery longevity of ILRs matched industry projected longevity in 99.5% of patients implanted with ILR for unexplained syncope. A battery longevity of minimum 3.5 years is recommended to maximize the diagnostic yield in this population.
Keywords: Implantable loop recorder; Battery longevity; Home monitoring
Introduction
Syncope is a form of non-traumatic, transient loss of consciousness due to hypoperfusion of the brain and can further be divided in cardiac syncope, reflex syncope or syncope due to orthostatic hypotension (1). It is a common condition (30-40% life time prevalence) (2, 3), with around 6 cases per 1000 person-years (4) and has a high rate of recurrence within the same year (up to 43%)(5). Conventional diagnostic work-up results in 30% of syncope cases remaining unexplained (2, 6), with an increased risk of recurrence and therefore trauma, or fatalities (2, 7). Digital wearables are increasingly used by patients, but are expensive (8). Diagnostic yield of Holter monitoring in patients with infrequent symptoms, is low (9). Therefore the early use of an Implantable Loop Recorder (ILR) in the diagnostic work-up of unexplained syncope, thought to be of cardiac etiology, is strongly recommended (1, 10-12). ILRs allow long-term surveillance of a single lead ECG and have been shown to be an effective tool in detecting clinically relevant arrhythmias (13-17), thereby leading to an earlier diagnosis. This early diagnosis results in less burden of further syncope (18), reduction in additional investigations, fewer hospitalization days and significant healthcare cost reduction (13, 19, 20). In a meta-analysis of five randomized controlled trials (RCTs) (660 patients), ILR implantation was 3.7 more probable of finding a diagnosis, compared to the conventional work-up (Holter, tilt testing, EP study) (13-17, 21). This way, ILR have a positive impact on survival of these patients, likely to the higher rate of device therapy (22). The median time to diagnosis, found in a large meta-analysis, is approximately 4 months (23). However, it remains unclear up to what point in time relevant arrhythmogenic diagnoses can be detected. Manufacturers of the latest generation of ILRs claim a minimum battery longevity between 2 and 4 years, but real-world data about ILR battery longevity are lacking. This study explores the battery longevity and the time relationship with the diagnostic yield of ILR implanted for unexplained syncope.
Materials and methods
Study population
This observational, prospective, single center study included all consecutive patients with unexplained syncope in whom an ILR was implanted in the period of 10/2007 – 10/2019 at the Ghent University hospital, Belgium. Inclusion was halted in 2019, since the main goal of this study was to focus on battery longevity. Patients were implanted with an ILR if syncope was suspected to be of cardiac origin and remained unexplained after a conventional diagnostic workup, in accordance with recent guidelines. (1).
ILR of different brands (Medtronic, Abbott and Biotronik) were implanted according to the preference of the referring or implanting physician. Programming of ILR was tailored to the individual patient. All ILRs were implanted in a dedicated electrophysiology lab. History, clinical information concerning the syncope event, comorbidities, ECG and laboratory results were retrieved from the electronic patient file. The study was approved by the local Ethics committee.
Follow-up and endpoints
All ILR patients underwent follow-up by remote home monitoring and regular clinical follow-up at 1 and 6 months after implant. After this initial period, the frequency of in-clinic follow-up varied between 6 to 12 months, depending on physician preference. History, clinical examination and interrogation of the ILR were routinely performed at each of the clinical follow-up consultations.
Remote monitoring alerts were checked five days a week by dedicated staff members experienced in device interrogation and follow-up. All arrhythmogenic events, potentially cause related with syncope, such as prolonged pauses (>3 seconds), type 2 2nddegree atrioventricular (AV) block or 3rd degree AV-block as well as fast supraventricular tachycardia (SVT) or ventricular tachycardia (VT) were registered and adjudicated by an electrophysiologist. Appropriate therapy was guided by the nature of the arrhythmogenic event in relation the presence or absence of symptoms. Indications for pacemaker or implantable cardioverter-defibrillator (ICD) implantation were guided by international guidelines (1, 10). Remote monitoring was also used to detect the end-of-life (EOL) status of the ILR.
Statistical analysis
Categorical variables are presented as absolute numbers (percentage). Continuous variables are expressed as mean ± standard deviation in case of Gaussian distribution or median [1st,3rd quartile] in case of non-Gaussian distribution. Normality was tested using the Shapiro-Wilk test. To compare means and medians of continuous variables among groups, the independent Student’s t-test and Mann-Whitney U test were used, respectively. In case of >2 groups, the one-way ANOVA or Kruskall-Wallis test was used where appropriate. Categorical variables were compared among groups using the Chi Squared test. Statistical significance was set at a 2-tailed probability level of <0.05. All statistical analyses were performed using SPSS software (version 28.0, IBM, Armonk, NY, US).
Results