High diagnostic yield of implantable loop recorders – a 5-year experience

Implantable loop recorders (ILR) provide an important tool in the investigation of symptoms including syncope, presyncope and palpitations. We aimed to review the characteristics of patients implanted with an ILR and utilise the outcomes to improve our local management of symptomatic arrhythmia. Methods: All ILR implants at a single centre over 5 years (n=183) were reviewed. ILR which had not yielded a diagnosis yet and were still being actively interrogated were excluded. We reviewed clinical notes and ILR interrogations to collect data on remaining cases. Results: Only 1 death occurred out of 183 implants during the 5 years (due to malignancy). Complication rate was 4% (2 displacements with loss of ECG sensing, 2 with discomfort necessitating removal, 1 infection and 2 keloid scars). There were 84 ILR implants and subsequent explants during 5 year follow up. 43/84(51%) were female and mean age at implant was 64 years (range 23-88). Indications for implant were syncope 62/84(74%), presyncope 21/84(25%) and palpitations 1/84(1%). All had resting ECG and echocardiography and 99% had at least one external loop recorder or 24hr Holter monitor prior to implant. ILR was able to confirm a diagnosis in 56/84(67%) of which 50(60%) had an indication for anti-bradycardia pacing and 6(7%) had clinically relevant symptomatic tachycardia. Indications for those 50 cases who required pacing were ventricular pauses or asystole in 21/84(25%), Mobitz Type 2 or complete heart block in 12(14%) and symptomatic sick sinus syndrome in 17(20%). The median time from implant of ILR to pacemaker was 140 days (range 5-976). Comparison between those who required pacing and those in whom a diagnosis could not be established, age was a significant factor in determining likelihood of pacing (mean 71yr vs 56yr, p⩽0.0001). An age >60 was associated with significant increase in likelihood of requiring pacing (p=0.001). There was no significant difference in LV systolic function (p=0.55), presence of normal ECG (p=0.11), resting sinus bradycardia (p=0.52), bundle branch block (p=0.72) or first degree heart block (p=0.31). On reviewing the 28/84(33%) cases without a diagnosis identified by ILR, all cases either had an alternative nonarrhythmogenic cause for symptoms identified 9/84(11%) or no recurrence of symptoms during the time of implant 19/84(22%). Conclusions: There was a high diagnostic yield of ILR with 60% requiring anti-bradycardia pacing and 7% with clinically relevant symptomatic tachycardia. The median time from ILR implant to pacemaker was 140 days. The LV systolic function or resting ECG (whether normal or abnormal) does not predict the need for permanent pacing. There should be a lower threshold for an ILR in those over 60 years given the greater likelihood of requiring permanent pacing. Where a diagnosis was not identified, ILR provided an excellent prognosis given all cases either had no further symptoms or a non-arrhythmogenic cause identified.