How do you check sensitivity and capture on a dual paced epicardial pacemaker (electronic cardiac device)?

Checking Sensitivity and Capture on Dual Paced Epicardial Pacemaker

To check sensitivity and capture on a dual paced epicardial pacemaker, perform ECG monitoring with and without magnet application to assess both sensing and pacing functions, ensuring proper lead function and appropriate programming for optimal patient outcomes.

Assessment of Sensing Function (Sensitivity)

To evaluate proper sensing function:

• Obtain a non-magnet ECG strip (6-9 seconds) to determine if the patient displays intrinsic rhythm or is being intermittently or continuously paced at programmed settings 1
• Assess whether normal sensing is present for both chambers by observing if intrinsic cardiac events appropriately inhibit pacing output 1
• Characterize the underlying atrial mechanism (sinus rhythm, atrial fibrillation, atrial tachycardia) 1
• If sensing issues are suspected, different ECG monitoring leads should be tested to identify a lead that minimizes artifact and maximizes visualization of cardiac signals 1

Assessment of Capture Function

To evaluate proper capture function:

• Apply a magnet over the pacemaker to convert it to asynchronous pacing mode (typically DOO for dual chamber) 1
• Obtain a magnet-applied ECG strip (6-9 seconds) to verify effective capture of both chambers 1
• Assess the magnet rate and compare with previous values to detect any changes that might indicate battery depletion 1
• Evaluate pulse width if it is one of the elective replacement indicators for that specific pacemaker 1
• If the pacemaker has threshold testing capability (e.g., Threshold Margin Test), analyze these results to assess capture margins 1

Special Considerations for Epicardial Leads

• Epicardial leads may have different sensing and capture thresholds compared to transvenous leads, requiring careful assessment 2
• For dual-chamber epicardial systems, both atrial and ventricular leads should be individually assessed for proper function 2
• Temporary epicardial pacing wires are at higher risk for dislodgement, with rates up to 16%, making regular monitoring crucial 1

Recommended Monitoring Protocol

1. Establish baseline ECG monitoring to assess intrinsic rhythm and current pacing function 1
2. Document the programmed pacing mode (e.g., DDD, DDI, DOO) 1
3. Apply magnet to convert to asynchronous mode and assess:
   • Atrial capture - observe for consistent atrial pacing spikes followed by P waves 1
   • Ventricular capture - observe for consistent ventricular pacing spikes followed by QRS complexes 1
   • AV interval - if dual-chamber pacing, verify appropriate timing between chambers 1
4. Remove magnet and assess sensing function by observing appropriate inhibition of pacing with intrinsic beats 1
5. If sensing or capture issues are identified, consider lead repositioning or reprogramming 1

Frequency of Monitoring

• For newly implanted devices: check twice in first 6 months 3
• For established single-chamber pacemakers: check once every 12 months 3
• For established dual-chamber pacemakers: check once every 6 months 3
• Additional monitoring is necessary if the patient experiences symptoms that may reflect altered rhythm or device function 1

Common Pitfalls and Caveats

• Large pacing artifacts may obscure or mimic QRS complexes, making it difficult to determine ventricular capture 1
• Loss of pacemaker output may occur if lead wires become separated from the external pacemaker generator, batteries become depleted, or oversensing occurs 1
• Fixed low outputs may not be safe between follow-ups in pacemaker-dependent patients, even with a 100% voltage safety margin 4
• For pacemaker-dependent patients, threshold testing requires extra caution to prevent asystole 3
• Continuous ECG monitoring for 12-24 hours after implantation is recommended to detect potential complications like lead dislodgement 1