What is the appropriate workup for an Automatic Implantable Cardioverter-Defibrillator (AICD) firing?

Workup for AICD Firing

When an AICD fires, immediately interrogate the device to determine whether the shock was appropriate (true ventricular arrhythmia) or inappropriate (supraventricular arrhythmia, lead malfunction, or electromagnetic interference), as this distinction fundamentally directs all subsequent management. 1

Immediate Device Interrogation

• Perform device interrogation urgently to review stored electrograms, event logs, sensing parameters, and therapy delivery details 1
• Examine the stored electrograms to distinguish ventricular tachycardia/fibrillation from supraventricular tachycardia, sinus tachycardia, atrial fibrillation with rapid ventricular response, or lead noise 1
• Review battery status, lead impedances, and sensing thresholds to identify device malfunction 1
• Document the number of shocks delivered, as multiple shocks (>5) are associated with increased psychological distress and may indicate electrical storm 1

Clinical Assessment for Appropriate Shocks

If device interrogation confirms appropriate therapy for ventricular arrhythmia:

• Obtain 12-lead ECG to assess for acute ischemic changes, QT prolongation, or new conduction abnormalities 1
• Draw cardiac biomarkers (troponin) to evaluate for acute myocardial infarction or ongoing ischemia as a trigger 1
• Check complete metabolic panel focusing on potassium and magnesium levels, as electrolyte abnormalities are reversible triggers for ventricular arrhythmias 2
• Assess for precipitating factors: recent medication changes (especially antiarrhythmic drugs), drug non-compliance, new medications that prolong QT interval, or substance use 1
• Review thyroid function if not recently checked, as thyroid dysfunction can precipitate arrhythmias 1

Evaluation for Ischemia

• If troponin is elevated or ECG shows ischemic changes, proceed urgently to coronary angiography with revascularization if indicated, as acute ischemia is a reversible cause 1
• For patients with known coronary disease and appropriate shocks without clear acute ischemia, consider stress testing or coronary angiography to evaluate for progressive disease 1
• Sustained ventricular arrhythmias occurring >48 hours post-MI in the absence of ongoing ischemia represent a different substrate than acute ischemic arrhythmias 1

Assessment for Structural Heart Disease Progression

• Obtain echocardiography to assess left ventricular ejection fraction, new wall motion abnormalities, valvular disease progression, or development of cardiomyopathy 1
• Consider cardiac MRI if non-ischemic cardiomyopathy is suspected or to identify arrhythmogenic substrate, particularly in patients with recurrent appropriate shocks 1
• Evaluate for heart failure decompensation with BNP/NT-proBNP, chest X-ray, and clinical examination, as worsening heart failure increases arrhythmia risk 1

Management of Inappropriate Shocks

If device interrogation reveals inappropriate therapy:

• Identify the specific cause: atrial fibrillation with rapid ventricular response, sinus tachycardia, lead fracture/noise, T-wave oversensing, or electromagnetic interference 1
• Reprogram detection parameters to reduce inappropriate shock risk (adjust rate cutoffs, use enhanced detection algorithms, enable SVT discriminators) 1
• For atrial arrhythmias causing inappropriate shocks, initiate rate control or rhythm control strategies and consider upgrading to dual-chamber ICD if not already present 1
• Evaluate lead integrity with impedance measurements and chest X-ray; lead fracture or dislodgment requires surgical revision 1

Antiarrhythmic Therapy Optimization

For patients with appropriate shocks indicating recurrent ventricular arrhythmias:

• Optimize beta-blocker therapy as first-line antiarrhythmic strategy, as beta-blockers reduce arrhythmia burden and are associated with improved outcomes 1, 2
• Consider adding amiodarone for recurrent ventricular arrhythmias despite beta-blockade, particularly in patients with multiple appropriate shocks 1
• Evaluate for catheter ablation in patients with recurrent monomorphic VT, especially those with ischemic cardiomyopathy and well-defined substrate 1
• Surgical ablation may be considered in highly selected patients with refractory VT after failed catheter ablation, particularly those with discrete aneurysms 1

Psychological Assessment

• Screen for anxiety and depression, which occur in 8-63% and 5-41% of ICD patients respectively, with highest rates in those experiencing multiple shocks 1
• Assess for post-traumatic stress disorder, particularly in patients with recent multiple shocks or pre-existing psychological distress 1
• Provide psychological support and consider referral to mental health services, as assessment and treatment of psychological distress should be integral to clinical management 1

Device Programming Optimization

• Review and optimize detection zones to minimize inappropriate therapies while maintaining appropriate detection 1
• Enable antitachycardia pacing (ATP) for ventricular tachycardia zones, as ATP successfully terminates 78-90% of VT episodes and reduces painful shocks 1
• Consider programming longer detection times for faster VT zones if clinically tolerated to reduce inappropriate shocks 1
• Ensure appropriate programming of SVT discriminators in single-chamber devices or utilize dual-chamber sensing if available 1

Common Pitfalls to Avoid

• Do not assume all shocks are appropriate without device interrogation—inappropriate shocks occur at a rate of 3.7% per year and require different management 3
• Avoid attributing appropriate shocks solely to "breakthrough arrhythmia" without evaluating for reversible causes like ischemia, electrolyte abnormalities, or medication non-compliance 1, 2
• Do not discharge patients with electrical storm (≥3 appropriate shocks in 24 hours) without addressing the underlying trigger and optimizing antiarrhythmic therapy 1
• Recognize that ICD shocks themselves may worsen heart failure and increase mortality risk, emphasizing the importance of shock reduction strategies 1