S-ICD screening revisited: do passing vectors sometimes fail?

Area of Science:

• Cardiology
• Biomedical Engineering

Background:

• Subcutaneous implantable cardioverter-defibrillators (S-ICD) require suitable sensing vectors for safe operation.
• Cardiac over-sensing, leading to inappropriate shocks, is a common issue in S-ICD recipients.
• Dynamic variations in electrocardiogram (ECG) morphology may explain inconsistent vector eligibility.

Purpose of the Study:

• To assess the dynamic nature of S-ICD sensing vector eligibility.
• To determine the proportion of initially eligible vectors that become ineligible over time.

Main Methods:

• 24-hour ambulatory ECGs were recorded in adult ICD patients using a Holter monitor capturing all three S-ICD vectors.
• An S-ICD simulator performed automated screening at one-minute intervals.
• Eligible Vector Time (EVT) was calculated for vectors with a mean vector score > 100, representing the percentage of time the vector was deemed eligible.

Main Results:

• Of 42 analyzed vectors, 19 had a mean vector score > 100. Within this group, EVT varied significantly, with 37% of vectors having an EVT < 75%.
• A negative correlation was observed between QRS duration and EVT (r = -0.60, p = 0.007).
• No significant correlation was found between EVT and mean vector score or time to peak T wave (pTc).

Conclusions:

• S-ICD vector eligibility is not static and can fluctuate significantly over a 24-hour period.
• A substantial proportion of vectors initially considered eligible may not remain consistently so, potentially impacting S-ICD performance.
• Further research is needed to understand the clinical implications of dynamic vector eligibility on S-ICD therapy.