Exercise stress test reveals ineligibility for subcutaneous implantable cardioverter defibrillator in patients with Brugada syndrome

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Brugada syndrome (BrS) is a genetic disease responsible for 4–12% of cases of sudden cardiac death (SCD).1 The syndrome is characterized by an electrocardiographic pattern of ST segment elevation with type 1 morphology in the right precordial leads V1 to V3. Most cardiac events occur in middle‐aged men.2
Symptoms often arise at rest or during sleep, in a febrile state. Lethal ventricular arrhythmias tend to occur during the recovery phase after exercise, in association with significant augmentation of ST elevation.4
A subcutaneous implantable cardioverter‐defibrillator (S‐ICD) does not require placement of leads directly into the heart, so use of these devices could avoid the complications related to the use of transvenous ICD leads. Moreover, since the incidence of lead injury increases over time after transvenous ICD implantation, use of S‐ICDs is expected to avoid troubles concerning cardiac leads,5 especially in younger patients without organic heart disease, such as patients with BrS, who do not usually need ventricular pacing.8 However, the eligibility of BrS patients for S‐ICD use is not well known, and data from a large cohort of this specific patient population have not been reported.9
The most common problem with S‐ICD systems in the real world is administration of inappropriate shocks because of T‐wave oversensing.10 To avoid this problem, the manufacturer has developed a system to identify patients who are likely to be unsuitable for S‐ICD, using supine and standing surface ECG screening templates. Moreover, ST‐T morphology shows fluctuations, particularly in high‐risk patients with BrS.11 This suggests that ECG at rest should not be considered sufficient as S‐ICD screening for patients with diurnal variations. Exercise is one of the most important factors for ST‐T fluctuations, and exercise‐induced ST‐T changes thus need to be considered when making decisions regarding S‐ICD implantation. In addition, because the specific ECG system templates proposed for determining S‐ICD eligibility are uncommon and inconvenient for actual clinical practice, parameters derived from standard 12‐lead ECG are expected to be used to eliminate clearly unsuitable patients as candidates for S‐ICD implantation.
We aimed to clarify both the eligibility of patients with BrS for S‐ICD implantation according to the surface ECG screening template at rest and the influence of exercise on ECG morphology in determining eligibility.
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