Discussion

CRT remains a landmark therapy for HFrEF4, particularly in the context of HF with a high expected percentage of RVP5. HOT-CRT was recently shown to be safe and potentially superior to conventional CRT in the case of IVCD6. To our knowledge, ours is the first-in-human case of TV CRT-P implantation in an s-ICD patient, and also the first case of HOT-CRT in an s-ICD patient to be described in the literature. As already mentioned, this approach was chosen in order to reduce both costs and generator size, and to respect patient preferences, while ensuring possible bailout to conventional CRT-D during implantation in the event of suboptimal pQRS recognition by the s-ICD.
Many cases of the concomitant use of s-ICD and TV-PPM9,10, epicardial PPM11, epicardial CRT-P12, and HBP devices13 have been reported. In addition, there are numerous case-reports of the associated use of leadless PPM (LP) and s-ICD14. Indeed, Boston Scientific has developed a hybrid LP (EMPOWER) plus s-ICD (EMBLEM) system that is able to provide anti-bradycardia pacing and anti-tachycardia pacing together with shocks15, and which is currently under investigation (Modular ATP trial, NCT04798768). In one case, a completely leadless CRT-D system was created by using an LP (Medtronic Micra TPS) combined with a WiSE-CRT system (EBR Systems, Sunnyvale, CA) and an s-ICD16. When conventional ICD lead implantation has proved impossible, other strategies have been adopted, such as the use of a hybrid subcutaneous and trans-venous CRT-D approach using the Medtronic 6996SQ Finger subcutaneous array lead17, and ICD lead implantation in the coronary sinus in the context of CRT-D18. In one case, an s-ICD with a right parasternal electrode plus an AAI PPM was implanted19, and in another case, owing to multiple ventricular lead fractures causing inappropriate shocks, an s-ICD was implanted and the existing TV-ICD was reprogrammed as an AAI pacemaker20.
However, a few cases of device-device interaction between the s-ICD and both the TV21 and epicardial PPM22have been described. To avoid this eventuality, we chose HOT-CRT as the pacing strategy; this yielded a pQRS which was similar to the sQRS, albeit shorter. Moreover, we ensured correct pQRS recognition by the s-ICD both intra-procedurally, with the possibility of bailout to conventional CRT-D during implantation, and post-procedurally, by means of both s-ICD interrogation and the AST in multiple body positions. Of note, screening by means of the AST has been tested in patients with PPM23, HBP13 and CRT24 devices, with variable results. One group found an association between s-ICD screening and response to CRT25, which may have been due to the fact that correct pQRS identification by the s-ICD might depend on the pQRS being narrow, therefore predicting better outcomes of CRT.
In conclusion, considering that potentially up to 5.2% of s-ICD patients develop a need for permanent pacing7, we demonstrated that CRT-P, and particularly HOT-CRT implantation in an s-ICD patient, was both feasible and safe, yielding optimal electrical parameters and correct pQRS identification by the s-ICD both intra- and post-procedurally. In the event of suboptimal intra-procedural pQRS recognition by the s-ICD, bailout to conventional CRT-D is a possibility.