Algorithm-Based Screening May Improve Patient Selection for the Subcutaneous Implantable Defibrillator.

Objectives: The study sought to describe the concept of algorithm-based screening with an external subcutaneous implantable cardioverter-defibrillator (S-ICD) to evaluate sensing using the rhythm discrimination algorithm of the device.

Background: In a proportion of patients, screening for S-ICD therapy with the dedicated screening tool results in false negative and false positive results.

Methods: Both patients who failed the standard screening and who passed with abnormal baseline ECGs were screened with an external S-ICD to evaluate sensing at rest and during exercise in all 3 sensing vectors (algorithm-based screening). Patients with adequate sensing were implanted with an S-ICD. Follow-up data regarding (in)appropriate shocks was collected.

Results: Algorithm-based screening was performed in 15 patients. Group 1 consists of 8 who failed standard screening and Group 2 consists of 7 who passed and had abnormal ECGs. Six of 8 who failed standard screening in all sensing vectors demonstrated adequate sensing with the external S-ICD and were implanted with an S-ICD. Of these 6 implanted patients in Group 1, 1 inappropriate shock was observed duration median of 17 months' follow-up and 2 episodes of ventricular fibrillation were successfully treated. Of the 7 patients in Group 2, who passed standard screening, 2 demonstrated inadequate sensing during additional screening with the external S-ICD. No appropriate or inappropriate shocks were observed in Group 2 during 10 months' follow-up.

Conclusions: Algorithm-based screening with the external S-ICD may improve patient selection and reduce the number of false positive and false negative screening results of the standard screening method.