PO-03-082 EFFECT OF IMPLANTABLE LOOP RECORDER INSERTION SITE ON P WAVE AMPLITUDE

Abstract

Implantable loop recorders (ILRs) are increasingly utilised for rhythm monitoring, including in the diagnosis of atrial fibrillation and other atrial arrhythmias. A larger P wave amplitude may assist in improving arrhythmia diagnosis. Current manufacturer guidelines for ILR insertion suggest a left 4th intercostal space (ICS) insertion, without prior mapping of R waves or P waves. However, recent data using surface mapping suggests that P wave sensing may be improved by altering the implant site to a higher ICS. To determine the effect of ILR insertion in the 3rd or 4th ICS on ILR sensing parameters. We reviewed the medical records and remote monitoring transmissions of 117 patients who underwent Medtronic ILR insertion at our institution. Both LINQ I and LINQ II devices were included. All devices were implanted in the left parasternal 3rd or 4th ICS using surface anatomical landmarks, at a 45-60 degree angle to the sternum. The choice of ICS was at the discretion of the implanting physician. P wave, T wave, R wave (base to positive peak), S wave (base to negative peak) and peak-to-peak QRS amplitudes were measured on the using electronic calipers, which were calibrated using the included voltage marker. Patients were excluded if the presenting electrocardiogram showed atrial fibrillation. Of the 117 patients, 77 (66%) had LINQ II and 40 (34%) had LINQ I devices. The median age was 65 years (IQR 43-75 years) and 63 (54%) were male. Sixty-nine (59%) devices were inserted in the 3rd ICS. The majority of devices were inserted for investigation of syncope (61%). A 3rd ICS implant location was associated with a higher mean P wave amplitude (0.037±0.016 vs 0.026±0.012mV, p<0.001). Mean R wave amplitude was smaller (0.24±0.24 vs 0.38±0.37mV, p=0.009) but there was no difference in mean peak-to-peak QRS amplitude (0.58±0.35vs 0.60+0.39mV, p=0.74) or mean T wave amplitude (0.12±0.08 vs 0.12±0.10mV, p=0.82). The mean QRS / P amplitude ratio was significantly lower with 3rd ICS implants (16±8.5 vs 24±13.9, p<0.001). Two patients had undetectable P waves and both had devices in the 4th ICS. One patient with a 3rd ICS device had peak-to-peak QRS amplitude of 0.09mV and intermittent T wave oversensing was noted. Insertion of ILRs in the 3rd ICS as opposed to the 4th ICS resulted in significantly higher P wave amplitude without a reduction of overall QRS amplitude.