Evaluating the magnet response in deep subcutaneous implanted cardioverter defibrillator implants.

Area of Science:

• Cardiology
• Biomedical Engineering
• Medical Devices

Background:

• Subcutaneous implantable cardioverter-defibrillators (S-ICDs) rely on magnet response for therapy inhibition.
• The definition and impact of 'deep implants' on S-ICD magnet response are not well-defined by manufacturers.
• Understanding factors affecting magnet response is crucial for S-ICD management.

Purpose of the Study:

• To systematically evaluate the effect of subcutaneous tissue depth on S-ICD evoked magnet response.
• To compare the efficacy of different magnet types (bar vs. donut) in evoking a magnet response.
• To identify optimal magnet placement for reliable S-ICD magnet response.

Main Methods:

• A cohort of S-ICD patients underwent magnet response evaluation using bar and donut magnets in three zones.
• Ordinal regression models analyzed the relationship between evoked magnet response and tissue depth (TD) measured by X-ray.
• Patient audibility of the magnet response tone was recorded.

Main Results:

• Increasing tissue depth significantly decreased the odds of an evoked magnet response for both bar (OR 0.89) and donut magnets (OR 0.84).
• The donut magnet was more effective (73%) than the bar magnet (53%) in evoking a response across all zones, though not statistically significant (p=0.18).
• Placement directly over the S-ICD was most effective for the bar magnet (85%), while off-center placement was most effective for the donut magnet (100%). 23% of patients could not detect the audible tone.

Conclusions:

• A statistically significant association exists between subcutaneous tissue depth and the ability to evoke an S-ICD magnet response.
• The donut magnet demonstrates greater reliability than the bar magnet for therapy inhibition in deeper S-ICD implants.
• Optimal magnet placement varies by magnet type, and audibility of the response is a factor in patient management.