Impact of right ventricular pacing site on the subcutaneous ICD sensing-a step towards personalised device therapy?

Abstract

Background: Patients with an existing subcutaneous implantable cardiac defibrillator (S-ICD) may develop a pacing indication. When transvenous pacing is not feasible, combining an S-ICD and a leadless pacemaker (LP) can be a reasonable option. There are reports of concomitant use of both devices. However, the effect of pacing on the S-ICD sensing is not well studied. We hypothesise that pacing changes R and T-wave amplitudes, causing changes in R:T ratios as perceived by a S-ICD, increasing the risk for T wave oversensing (TWO) during paced rhythm with a subsequent risk of inappropriate shocks.

Methods: This is a prospective study in patients undergoing electrophysiological studies. Participants were fitted with a Holter®, and the leads were placed to correspond to the vectors of an S-ICD. The right ventricle was paced at four positions for 10 beats each at 8 mA/2 ms. The Holter® traces were analysed, using two-way analysis of variance (ANOVA) to assess the effect of pacing on the R:T ratio.

Results: Forty-seven patients (age 56.02 ± 16.02, 72% male) were enrolled (81% structurally normal heart, 15% dilated cardiomyopathy, 2% ischaemic cardiomyopathy, and 2% adult congenital heart disease). Age, sex, and aetiology had no effect on the R:T ratio. Pacing caused significant changes in the R:T ratio. There was no significant difference in the R:T ratios between the pacing sites (p < 0.001).

Conclusions: Pacing alters the R:T ratio significantly in most patients, theoretically increasing the risk for TWO and inappropriate shocks. Tailored programming for both devices is important for concomitant use of LPs and S-ICDs.

Keywords: Cardiac implantable devices; Leadless pacemakers; Personalised medicine; Subcutaneous implantable cardiac defibrillators.

Fig. 1

Showing the typical S-ICD vectors on the left and on the right, the Holter® surface ECG positions. 1 = 1 cm infero-lateral to the xiphisternum, 2 = 14 cm superior to position 1, 3 = 5^th intercostal space, parasternal position, 4 = 6^th intercostal space left mid axillary line, 6 = Adjacent to 2, 7 = Adjacent to 4, Holter Channel A records between points 1 and 4 = surrogate of S-ICD primary vector, Holter Channel B records between points 2 and 3 = surrogate of S-ICD alternate vector, Holter Channel C records between points 6 and 7 = surrogate of S-ICD secondary vector, 5 = 5^th intercostal space right mid clavicular line = neutral electrode, Image prior to annotation © Boston Scientific Corporation or its affiliates

Fig. 2

Fluoroscopic images in the left anterior oblique (top row) and right anterior oblique (bottom row) views showing the pacing catheter placed at four different sites in the right ventricle corresponding to the potential implantation sites for the leadless pacemaker

Fig. 3

Boxplot comparing between different pacing sites and the “no pacing” group. Significant decrease was noticed in the R:T ratio when pacing in any of the selected sites. Multiple outliers were detected in all the pacing sites with nearly isoelectric T waves. Vectors A, B, and C correspond to Primary, alternate, and secondary vectors of an S-ICD, respectively

Fig. 4

An example of the effect of pacing as well as changing the pacing site on the morphology of the Holter traces corresponding to the S-ICD vectors. A, B, and C correspond to primary, alternate, and secondary vectors respectively