Ventricular fibrillation induced by atrial threshold search: a case report

Area of Science:

• Cardiology
• Electrophysiology
• Medical Devices

Background:

• Implantable cardioverter defibrillators (ICDs) are crucial for preventing sudden cardiac death from ventricular arrhythmias.
• However, device algorithms, including automatic threshold searches, can paradoxically induce malignant arrhythmias.
• This case highlights a rare complication associated with ICD function.

Observation:

• A 72-year-old man experienced syncope, leading to the discovery of ventricular fibrillation (VF) on ICD interrogation.
• The VF episode initiated immediately following an automatic atrial threshold search.
• The patient had a history of heart failure, necessitating a CRT-D device.

Findings:

• The most likely cause of the VF was the atrial threshold test, as no other etiology was identified.
• Disabling the Atrial Capture Management feature resolved the issue, with no recurrence of ventricular arrhythmias.
• The mechanism may involve a shift to right ventricular-only pacing during the test, increasing repolarization dispersion.

Implications:

• This case emphasizes the importance of careful ICD programming and monitoring of automatic features.
• Awareness of potential proarrhythmic effects of threshold testing is crucial for patient safety.
• Newer ICD models may incorporate safeguards to prevent such complications during threshold measurements.