The Study To Access The Anatomical Feasibility Of Implanting Extravascular ICD In The Substernal Space

Objective: To reveal the substernal space of Chinese population and to assess the anatomical feasibility of implanting extravascular ICD lead in the substernal space in patients with and without prior median sternotomy,we measured the distance from the sternum to the heart by computed tomography images and quantified the relationship between the sternum and the heart,which could provide reference for guiding the delivery of the lead and promoting the development of the delivery tools for EV-ICD.Methods: The high quality CT images from 20 patients with prior median sternotomy(S-group,75% male,aged 72.10 ± 7.08 years)and 20 patients without prior median sternotomy(NS-group,75% male,aged 70.10±12.35years)were enrolled from July 2018 to December 2019 in our hospital.The distance from the sternum to the epicardium was measured from CT images by 3D Slicer software.The measurement area was segmented into4 regions using the xiphisternal joint as the anatomic landmark.In each transverse view,we measured the distance from the sternum to the heart on the lines which were along the midline and ±10 mm lateral to the midline sternum.Finally,the average measurement data were analyzed statistically.Results: The average distances from the sternum to the heart in Region1,Region 2,Region 3 and Region 4 were 5.18±4.90mm、5.06±4.14mm、9.39 ± 6.65 mm 、 13.77 ± 9.66 mm respectively for S-group,whereas the average distances from the sternum to the heart in Region 1,Region 2,Region 3 and Region 4 were 7.29±4.55mm、8.71±7.28mm、13.75±6.73mm、19.34±9.53 mm respectively for NS-group.No statistically significant difference of the distance from the sternum to the heart was observed in each region for patients with and without prior median sternotomy(P>0.05).In each region,there was no statistically significant difference of the distance from the sternum to the heart in patients of different postoperative years for S-group(P>0.05).Conclusions: The experience with prior median sternotomy has no significant effect on the distance from the sternum to the heart.There is still viable space for lead position even in this specific patient group with prior median sternotomy.In terms of anatomical space,it is feasible to implant the defibrillating lead of EV-ICD in the substernal space.Measuring the distance from the sternum to the heart based on CT images is helpful to quantify the relationship between the sternum and the heart and to reveal the substernal space of Chinese population.