LAUSR

Treatment of Brugada syndrome (BrS) with an implantable cardioverterdefibrillator (ICD) has been proven to result in a lower mortality rate for sudden cardiac death.1 The subcutaneous ICD (SICD) is an alternative device to transvenous ICD (TVICD) for the prevention of sudden cardiac death.2 It is the firstline therapeutic device, especially for young patients, without the need for pacing at the ventricles because there is a lower risk of complications associated with the leads, including vascular injury, lead fracture, or lead infection, than with the TVICD system. SICD has more oversensing than TVICD, but recent reports have shown that SICD has similar or even lower rates of inappropriate shocks compared to TVICD.3 In our case, changing the sensing vector was not sufficient to avoid inappropriate shock, but it was successfully prevented by repositioning the SICD lead downward. A 38yearold man with BrS was admitted to our hospital for SICD implantation. He neither had any symptoms nor previous episodes of syncope or cardiac arrest but had a familial history of sudden cardiac death. His 12lead electrocardiogram at rest showed fragmented QRS in leads V1 and V2, and a type I Brugada pattern following a drug provocation test using a sodium channel blocker (Figure 1). His ventricular late potentials were abnormal. During the electrophysiological study, ventricular fibrillation was induced by double extra stimulation from the right ventricle. Although risk assessment with an electrophysiological study is controversial, SICD implantation was scheduled after the patient and his family provided appropriate informed consent. Before implantation, two of the sensing vectors were applied for a screening test of the SICD system (Figure 2A). During the preimplantation screening test, two of the three sensing vectors were adequate. The SICD (EMBLEMTM️ SICD, Boston Scientific) was successfully implanted on the left side of the thorax between the serratus anterior muscle and the latissimus dorsi muscle, and the SICD lead electrode was implanted using the threeincision implant technique. The alternate sensing vector was selected because it was appropriate for immediate postoperative evaluation and the other vectors could not be used for myopotential oversensing during immediate postoperative assessment. One month later, the patient was taken to another hospital with an inappropriate ICD shock due to oversensing of P and T waves (Figure 3). Therefore, we shifted from alternate sensing vector to primary sensing vector to confirm that the effect of myopotential oversensing was reduced after 1 month postoperatively. However, after another month, an inappropriate shock occurred again due to myopotential oversensing, and upon rechecking for SICD sensing, none of the three sensing vectors was adequate (Figure 2B). Given that both primary and secondary vectors were deemed unsuitable due to myopotential oversensing, a solution to avoid inappropriate shocks was discussed. The right lead position of the sternum had not been suitable for sensing during the preoperative screening test. The patient's slender body habitus might have caused the coiling of the SICD lead located as high as the pulmonary artery. Our primary focus was sensing compliance, but we should have considered lead location more carefully using xrays. Invasive procedures were considered inevitable, and the strategy was switched to lead repositioning. Downward repositioning of the lead by 4 cm along the left costal arch was performed, which improved alternate vector sensing and reduced the risk of further inappropriate shocks. After carefully repeating the screening, we confirmed that two of the three sensing vectors were compatible at the position where the lead was moved downward (Figure 2C). The only way to obtain a high R wave was to lower the SICD lead