Analysis of the determining factors of detectable P-wave and amplitude of QRS complex sensed by implantable loop recorder

Introduction – Determining factors for sufficient QRS amplitude and discernible P-wave sensing in ILR are unknown. We aimed to investigate determining factors and ILR implantation angle that may improve QRS complex and P-wave sensing in ILR. Methods and Results – We retrospectively reviewed 220 patients who underwent ILR implantation or follow-up analysis. Patient demographic, clinical, echocardiography, electrocardiography, heart angle, and ILR angle data were collected as predictor variables. Associations between ILR QRS amplitude/P-wave detectability and each predictor variable were investigated. Univariate linear regression showed that ILR QRS amplitude was significantly associated with age, height, ILR angle, and QRS amplitudes of 12-Lead ECG [lead I, II, -aVR (inverted aVR), aVF, V1-V6] and Holter ECG (lead V3, V5). Among discrete variables, only left ventricular hypertrophy (LVH) affected ILR QRS amplitude (P=0.016). A multivariate linear regression analysis revealed that ILR angle (β= -0.008, P<0.001), lead -aVR amplitude (β=0.469, P=0.003), Holter lead V5 amplitude (β=0.116, p=0.049), Age (β=-0.005, P=0.014), and LVH (β=0.213, P= 0.031) were independent determinants of ILR QRS amplitude. Logistic regression revealed that heart angle significantly affected ILR P-wave detectability (β=0.12, P=0.008). Multiple logistic regression revealed that heart angle (β=0.121, P= 0.013) and lead V1 amplitude (β=28.1, P= 0.034) were independent determinants of ILR P-wave detectability. Conclusion – ILR insertion angle, lead -aVR QRS amplitude, Holter lead V5 QRS amplitude, age, and LVH are determinants of ILR QRS amplitude. Heart angle and lead V1 P-wave amplitude of 12-Lead ECG are determinants of ILR P-wave detectability.