Case report

A 49-year-old male patient affected by ischemic heart disease leading to HFrEF and with a history of two episodes of out-of-hospital resuscitated sudden cardiac arrest (SCA) underwent s-ICD implantation by means of an EMBLEM MRI system (Boston Scientific, Massachusetts, United States). Eight months after s-ICD implantation, the patient complained of fatigue and inconstant dyspnea on moderate effort. Beta-blocker therapy had been withdrawn months earlier, owing to symptomatic sinus bradycardia. ECG showed profound sinus bradycardia with heart rate (HR) 38 bpm, PR interval of 200 msec and aspecific IVCD with spontaneous QRS (sQRS) 115 msec. Echocardiography revealed LVEF 35%, which was unaltered from 8 months before. Coronary angiography with intra-vascular ultrasound imaging excluded coronary lesions requiring invasive treatment. Continuous ECG monitoring confirmed profound sinus bradycardia with minimum HR 34 bpm and revealed episodes of II degree Mobitz type 2 AVB, requiring PPM implantation.
Considering the need for CRT4, we chose to perform CRT-P with HOT-CRT implantation and preservation of the s-ICD, rather than biventricular ICD (CRT-D) implantation and subsequent s-ICD extraction. This approach was selected for three reasons: to reduce costs; to reduce generator size and therefore the risk of pocket-related complications, owing to the small amount of subcutaneous pectoral tissue present; and in accordance with patient preference. HBP with RVP lead implantation on the His Bundle was chosen in order to guarantee correct pQRS recognition by the s-ICD, with possible bail-out to ICD lead implantation in the case of unsatisfactory intraprocedural pQRS identification by the s-ICD.
After creation of a left pre-pectoral pocket and acquisition of left subclavian vein access, an active-fixation bipolar HBP lead (Ingevity MRI 7842 59 cm, Boston Scientific) was implanted by means of SSPC3 delivery (Boston Scientific) and a pace-mapping approach, obtaining non-selective capture. A quadripolar LV lead (Acuity X4 Straight, Boston Scientific) was then implanted, after coronary sinus (CS) angiography, in an antero-lateral branch of the CS (Fig. 1 ). Correct pQRS identification by the s-ICD was established by means of intraprocedural device interrogation, and was confirmed for HBP, LVP (LV1-LV2 configuration) and biventricular pacing (BiVP), i.e. HBP with sequential LVP after 20 msec. BiVP yielded a pQRS morphology similar to that of the sQRS, albeit shorter, i.e. pQRS 100 msec vs. sQRS 115 msec (Fig 2, Fig. 3 ). A passive-fixation right atrial lead (Fineline II Sterox Atrial J Model 4480 52 cm, Boston Scientific) was implanted and the leads were then fixed to the muscle plane with silk sutures. The leads were connected to the CRT-P generator, which was placed in the pocket. Vicryl 0 and 3-0 sutures were used to close the pocket. Electrical parameters were optimal, with capture thresholds below 1 V @ 0.4 msec. The device was programmed in DDD-R 60 bpm mode, with an AV interval 150 msec, and LVP configuration LV1-LV2 with a pacing delay of 20 msec after HBP, obtaining 100% BiVP. The bipolar-to-unipolar safety switch was turned off in order to avoid accidental activation of the unipolar configuration, which is contraindicated in the presence of an s-ICD. To avoid under-sensing of the CRT-P during ventricular arrhythmias (which could lead to inappropriate pacing and therefore suboptimal recognition of arrhythmias by the s-ICD), the autosensing algorithm (Automatic Gain Control) was activated. After the procedure, QRS recognition by the s-ICD was tested again, both by device interrogation and by the automated s-ICD screening tool (AST, Boston Scientific), both of which confirmed correct pQRS identification in both the supine and standing positions (Fig. 3 ).