Implantable loop recorder

Implantable loop recorder

Implantable loop recorder (ILR) is an implantable cardiac electronic device which is usually implanted subcutaneously in the pectoral region like a pacemaker. It monitors the electrocardiogram continuously, but transfers to permanent memory either on demand or when an event is sensed. It can transfer up to forty minutes of data prior to the event and one or two minutes after the event into the permanent memory which can be retrieved from the device using a wireless programmer. Modern implantable loop recorders have additional facility of transmitting data to the health care provider as well. The devices once implanted, can function up to three years depending on the battery capacity of various versions. Implantable loop recorders are very useful in evaluating symptoms that are intermittent so that it cannot be picked up by a twenty four hour Holter monitoring or a short term external loop recorder which typically records for about a week. Aniket Puri and Rohit Kumar Srivastava gave a good review of the utility of implantable loop recorders [1].

ILR has been used to detect occult atrial fibrillation in cryptogenic stroke in the TRACK-AF study [2]. Newer versions of implantable loop recorders can be called injectable loop recorders as they can be implanted using a device which delivers the ILR subcutaneously, done as an outpatient procedure [3].

Real life data outside of clinical trials on the utility of ILR in cryptogenic stroke has been provided by a retrospective study [4]. Atrial fibrillation was the most frequent arrhythmia, which was observed in 25% of patients. Bradycardias requiring a pacemaker were found in 9.4%. Ventricular tachycardia was documented in one patient.

Continuous telemonitoring with an implantable loop recorder in stable heart failure patients without other implanted devices has been studied prospectively [5]. Thirty patients had a median follow up period of 12 months. 8 patients developed subclinical atrial fibrillation with a mean burden of 65.8 min/day. One patient received a pacemaker. Overall, in 13 patients, data from the ILR led to therapeutic changes.

Role of ILR in inherited arrhythmias has also been reported in a research letter [6]. Of the 45 patients who underwent implantation 35 received an injectable ILR. Median follow up was 26.93 months. Study period was from 2009 to 2017. Remote monitoring was used for all patients after 2014. Syncope or presyncope of unclear origin was the indication for implantation in 60% of patients. 71% of patients experienced symptoms or had a silent arrhythmia documented within a median time of 5.5 months after implantation. No syncope or presyncope was associated with life threatening arrhythmias in this study. Interestingly 5 patients requested a reimplant after the device reached end of battery life as they were reassured by the possibility of longitudinal monitoring and high tolerability of the device.

References

1. Aniket Puri, Rohit Kumar Srivastava. Use of Implantable Loop Recorders to Unravel the Cause of Unexplained Syncope. Indian Pacing Electrophysiol. J. 2013;13:66-75.
2. Markus Bettin, Dirk Dechering, Simon Kochhäuser, Niklas Bode, Lars Eckardt, Gerrit Frommeyer, Florian Reinke. Extended ECG monitoring with an implantable loop recorder in patients with cryptogenic stroke: time schedule, reasons for explantation and incidental findings (results from the TRACK-AF trial). Clin Res Cardiol. 2019 Mar;108(3):309-314.
3. Santini M, Santini L, Di Fusco SA. Update on cardiac implantable electronic devices: from the injectable loop recorder to the leadless pacemaker, to the subcutaneous defibrillator. Minerva Cardioangiol. 2018 Dec;66(6):762-769. 
4. Pecha S, Wilke I, Yildirim Y, Reichenspurner H, Aydin MA. Implantable loop recorder monitoring in patients with cryptogenic stroke – Detection and treatment of different clinically relevant arrhythmias. J Electrocardiol. 2020 May-Jun;60:102-106. 
5. Kort RSS, Tuininga YS, Bosker HA, Janssen M, Tukkie R. Telemonitoring with an implantable loop recorder in outpatient heart failure care : One year follow-up report from a prospective observational Dutch multicentre study. Neth Heart J. 2019 Jan;27(1):46-51. 
6. Dwivedi A, Joza J, Malkani K, Mendelson TB, Priori SG, Chinitz LA, Fowler SJ, Cerrone M. Implantable Loop Recorder in Inherited Arrhythmia Diseases: A Critical Tool for Symptom Diagnosis and Advanced Risk Stratification. JACC Clin Electrophysiol. 2018 Oct;4(10):1372-1374.