Factors affecting electrogram sensing in insertable cardiac monitor: Insights from surface electrocardiogram mapping analysis

Abstract

Background: Fidelity of electrogram sensing may reduce false alerts from insertable cardiac monitor (ICM). Objective: To assess impact of vector length, implant angle and patient factors on electrogram sensing using surface electrocardiogram (EKG) mapping. Methods: Twelve separate precordial single-lead surface EKGs were acquired from 150 participants at two inter-electrode distance (75mm & 45mm), three vector angles (vertical, oblique, horizontal) and in two postures (upright & supine). A subset of fifty patients also received a clinically indicated ICM implant in 1:1 ratio (Medtronic Reveal LINQ:Biotronik Biomonitor III). All EKG and ICM electrogram were analyzed by blinded investigators using DigitizeIt software. P-wave visibility threshold was set at >0.015mV. Logistic regression was used to identify factors impacting P-wave amplitude. Results: A total of 1,800 tracings from 150 participants [44.5% female, median 59 years old] were assessed. Median P- and R-wave were 45% and 53% larger with vector length of 75 vs. 45mm respectively (both p<0.001). The oblique orientation yielded the best P- and R-wave sensing while posture change did not impact on P-wave amplitude. Mixed effects modeling found that visible P-waves occur more frequently with vector length of 75mm than 45mm (86% vs. 75% respectively, p<.0001). A longer vector length improved both P-wave amplitude and visibility in all BMI categories. There was moderate correlation of P- and R-waves from the ICM electrogram to surface EKG recordings (ICC 0.74 and 0.80, respectively). Conclusion: Longer vector length and oblique implant angle yielded the best electrogram sensing and are relevant considerations for ICM implantations.