Left Epicardial vs. Best-site Right Ventricular Transvenous Pacing in Congenital Heart Block Patients: Ventricular Function Comparisons using 2 D Speckle Imaging

Background:
Pacemaker implantation is recommended in symptomatic patients with congenital complete heart block (CHB) with either an epicardial (epi) or transvenous (TV) approach depending on patient age / size. However, there is a paucity of data on updated left ventricle (LV) functional indices between the two approaches.

Objective: Our aim was to compare LV function using speckle strain imaging in patients with LV Epi vs. best site right (R) TV pacing

Methods:
This was a single center, retrospective study of patients with isolated CHB who underwent pacemaker implantation. LV epi leads were empirically placed at surgery while RTV leads were implanted based on “best site” by direct contractility (dP/dt) response. Patients with other congenital heart diseases, intrinsically abnormal LV function, or incomplete data were excluded. LV and left atrial (LA) function were assessed by 2D speckle imaging (Tomtec software) by a single reader blinded to clinical data. Global longitudinal strain (endocardium [LVendo] and myocardium [LVmyo]) were calculated from the apical 4 chamber view. LA strain was measured using the P-P gating protocol to calculate LA reservoir strain (LAres), conduit strain (LAcd) and contractile strain (LAct). Statistical analysis used the Student T-test comparing functional parameters between the two groups with p of < 0.05 considered significant.

Results:
Of the 24 patients evaluated, 16 (66.6%) were female. There were 9 (38%) patients with LV Epi and 15 (62%) patients with RV TV pacing . As expected, the mean (SD) age at Epi implant and LV function analysis were significantly (p<0.05) younger than TV pacing (2.4 (3.1) vs. 13.3 (5.4) years and (10.7 (5.5) years vs. 21.3 (6.7) years respectively. However, the follow up interval (8 years) after the pacemaker was not different between the two groups. LVendo and LVmyo were significantly (p=0.03) higher in patients with TV pacing compared to Epi pacing (Table 1). The LV end diastolic and end systolic volumes and ejection fraction (EF) were not statistically different between the groups. There was no significant difference in any of the LA function parameters between the groups.

Conclusions:
Selective RTV pacing demonstrated improved LV function as assessed by 2D speckle longitudinal strain compared to empirically-placed LV epi pacing in CHB patiens followed for comparable post-implant intervals. There were no differences in other ECHO values including EF. The better preserved LV function in endo pacing could be due to more physiological pacing. Longitudinal and larger studies are needed to evaluate the impact of difference in pacing sites in the clinical outcomes in these patients.