Transvenous permanent pacemaker (PPM) implantation is an available option for Fontan patients with sinus node dysfunction (SND). However, the thrombogenic potential of leads within the Fontan baffle is unknown.

To compare the clot burden in Fontan patients with a transvenous atrial PPM to those without a PPM and those with an epicardial PPM.

This was a retrospective cohort study of all transvenous PPM implantations in Fontan patients followed at our institution (2000-2018). We performed frequency matching on Fontan type and age group. Primary outcome was identification of intracardiac clot, pulmonary embolism, or embolic stroke.

Of 1,920 Fontan patients, 58 patients with a median age 23 yrs (IQR 25-75 14-33) at time of transvenous PPM implantation and 174 matched subjects formed our cohort. The type of Fontan performed in case subjects was as follows: RA-PA or RA-RV conduit (54%), lateral tunnel (43%), and extracardiac (3%). The cumulative incidence of clot was highest in patients with transvenous PPM followed by patients with epicardial PPM and no PPM (1.2 vs. 0.87 vs. 0.67 per 100 person-years of follow-up respectively). In multivariable analysis, anticoagulation and/or antiplatelet therapy were protective against clot and resulted in reduction of clot risk by 3-fold (IRR 0.33, 95% CI [0.21-0.53], p<0.001).

In a large cohort of Fontan patients matched for age and Fontan type, patients with transvenous PPM had a higher but not statistically significant incidence of clot compared to those with no PPM and epicardial PPM. Patients treated with warfarin/aspirin had lower clot risk.