How should I adjust the sensitivity setting on an external temporary pacemaker in a hemodynamically stable patient with secure lead attachment?

Adjusting Sensitivity on External Temporary Pacemaker

To check and adjust sensitivity on an external temporary pacemaker in a hemodynamically stable patient with secure leads, set the pacemaker rate 10-20 beats per minute below the patient's spontaneous intrinsic rate and observe for appropriate inhibition of pacemaker output. 1

Understanding Sensitivity Function

Sensitivity determines the pacemaker's ability to detect (sense) the patient's intrinsic cardiac electrical activity. The goal is to ensure the device appropriately inhibits its output when the patient has adequate spontaneous rhythm, preventing competitive pacing that could trigger dangerous arrhythmias. 1

Step-by-Step Adjustment Protocol

Initial Assessment Requirements

• Confirm the patient has spontaneous cardiac activity - sensing can only be checked when there is intrinsic rhythm in the chamber being paced. 1

• Verify mechanical capture independently of ECG - always confirm actual pulse and blood pressure, as large pacing artifacts can obscure the QRS complex and create false impressions. 2, 3

Adjustment Technique

• Program the pacemaker rate to 10-20 bpm below the patient's intrinsic ventricular rate to allow the device to sense native beats. 1, 4

• Observe for evidence of appropriate inhibition - the pacemaker should stop firing when it detects the patient's own beats. 1

• Look for absence of competitive pacing - if you see pacemaker spikes occurring simultaneously with or immediately after native QRS complexes, sensitivity is set too low (device is undersensing). 1

Optimizing Sensitivity Settings

• If undersensing occurs (pacemaker fires despite adequate intrinsic rhythm), increase the sensitivity (lower the millivolt threshold) so the device can detect smaller electrical signals. 1

• If oversensing occurs (pacemaker inappropriately inhibited by artifact or T-waves), decrease the sensitivity (higher millivolt threshold). 1

Critical Monitoring Requirements

Daily Threshold Checks

• Check pacing thresholds and generator connections daily and record results in the patient's chart to ensure reliable capture. 1, 4

• Maintain continuous cardiac monitoring for all patients with temporary pacing until the device is removed or replaced with permanent pacing. 2

Verification of Mechanical Capture

• Never rely solely on ECG evidence - the large pacing artifact may obscure or mimic the QRS complex, making it difficult to determine actual ventricular capture. 2, 3

• Use arterial pressure monitoring or pulse oximetry to confirm actual cardiac contraction and perfusion. 2, 3, 5

• Test different ECG monitoring leads to minimize pacemaker artifact and maximize QRS visualization. 3

Common Pitfalls to Avoid

Lead Position Issues

• Coronary sinus malposition can cause failure to capture at acceptable output - the lead appears to be in the right ventricle on PA radiograph but directs posteriorly (not anteriorly) on lateral view. 1

• Lead dislodgement occurs in 16% of temporary transvenous pacing cases, with 50% happening within the first 24 hours, but can occur at any time. 2

Sensitivity-Related Errors

• Do not assume stable pacing function - dislodgement and threshold changes can occur unpredictably, not just in the first 24 hours. 2

• Avoid setting sensitivity too high (too sensitive), which can cause oversensing of T-waves, muscle artifact, or electromagnetic interference, leading to inappropriate inhibition. 1

Optimal Rate Settings for Context

• Set initial pacing rate to 60-80 bpm for most patients to provide adequate circulatory support without excessive competition with intrinsic rhythm. 4

• Avoid rates below 60 bpm in symptomatic complete AV block, as this can cause hypotension, reduced cardiac output, and heart failure symptoms. 4

• Consider higher initial rates in complete AV block with hemodynamic instability (e.g., anterior MI) to preserve cardiac output. 4

Special Considerations

• Dual-chamber (DDD) pacing provides the greatest increase in resting cardiac performance and is especially advantageous in elderly patients, though this requires both atrial and ventricular sensing capability. 4, 6

• View temporary external pacing as a bridge to definitive therapy - device-related complications occur in 14-40% of cases, making prolonged use hazardous. 2

• Transcutaneous pacing has inherently variable capture and is suitable only for urgent situations pending transvenous lead placement. 3, 5