Temporary Pacemaker (TPM) Lead Settings and Troubleshooting: A Practical Guide

Temporary pacemakers (TPMs) are commonly used for patients with symptomatic bradycardia, high-grade AV block, sinus node dysfunction, post-cardiac surgery conduction disturbances, acute myocardial infarction, drug-induced bradyarrhythmias, and during electrophysiology procedures.

Safe temporary pacing requires an understanding of the pacing rate, output, sensitivity, capture threshold, sensing threshold, pacing mode, and lead integrity. This article provides a practical approach to temporary pacemaker lead settings, threshold testing, and troubleshooting.

1. Basic Components of a Temporary Pacemaker System

A temporary pacing system consists of:

• Temporary pacing lead
• External pulse generator
• Connecting cable
• Battery/power source
• ECG and haemodynamic monitoring

The pacing lead has two major functions:

• Pacing: delivering an electrical stimulus to the myocardium.
• Sensing: detecting intrinsic cardiac electrical activity.

2. Important TPM Lead Settings

Parameter	Meaning	Unit
Rate	Pacing rate	ppm
Output	Electrical stimulus delivered to myocardium	mA
Sensitivity	Ability to detect intrinsic cardiac activity	mV
Capture threshold	Minimum output required for reliable myocardial capture	mA
Sensing threshold	Smallest intrinsic signal reliably detected	mV
Mode	Relationship between pacing and sensing	e.g. VVI, AAI, DDD

3. What Does ppm Mean?

In a pacing system, ppm means pulses per minute.

For example:

• 60 ppm = 60 pacing pulses per minute
• 70 ppm = 70 pacing pulses per minute
• 100 ppm = 100 pacing pulses per minute

Thus, ppm represents the programmed pacing rate of the temporary pacemaker.

4. Rate Setting

The pacing rate determines how frequently the pacemaker delivers stimulation when intrinsic cardiac activity is absent or below the programmed rate.

For example, with a ventricular demand rate of 70 ppm:

• If the intrinsic ventricular rate is above 70/min, pacing may be inhibited.
• If the intrinsic ventricular rate falls below 70/min, pacing occurs according to the programmed mode.

The appropriate rate depends on the clinical situation and the patient's underlying rhythm.

During Capture Threshold Testing

Set the pacing rate sufficiently above the intrinsic rate so that the chamber is paced consistently.

Practical approach: Set RATE at least 10 ppm above the patient's intrinsic rate.

During Sensing Threshold Testing

The pacing rate is reduced below the intrinsic rhythm so that intrinsic cardiac activity can be assessed.

Practical approach: Set RATE at least 10 ppm below the patient's intrinsic rate.

Rate reduction should only be performed when the patient's underlying rhythm is adequate and it is clinically safe to do so.

5. Output Setting

Output refers to the electrical current delivered through the pacing lead and is usually expressed in mA (milliamperes).

The output must be sufficiently high to depolarize the myocardium reliably.

The minimum output required to produce consistent myocardial depolarization is called the:

Capture Threshold

For example, if consistent ventricular capture occurs at 2 mA, the capture threshold is approximately 2 mA.

The programmed output should then provide an appropriate safety margin above the measured threshold.

A commonly used approach is to program the output at approximately 2–3 times the capture threshold.

6. Stimulation / Capture Threshold Procedure

Before performing threshold testing, ensure continuous ECG monitoring, appropriate haemodynamic monitoring, and immediate availability of resuscitation equipment.

Step 1 — Set the Rate

Set the pacing rate at least 10 ppm above the patient's intrinsic rate so that consistent pacing occurs.

Step 2 — Confirm Capture

Confirm that each pacing stimulus produces the expected cardiac response.

For ventricular pacing:

Pacing spike → QRS complex

For atrial pacing:

Pacing spike → P wave, followed by ventricular activation when AV conduction is present.

Step 3 — Decrease Output

Slowly reduce the OUTPUT while observing the ECG until capture becomes intermittent and then disappears.

Step 4 — Identify the Threshold

Slowly increase the output until consistent capture returns.

The minimum output that produces consistent capture is the stimulation/capture threshold.

Step 5 — Program an Appropriate Safety Margin

Set the output sufficiently above the measured threshold, commonly approximately 2–3 times the capture threshold, depending on the generator, lead system, and clinical circumstances.

Example:

Capture threshold = 2 mA

Programmed output = approximately 4–6 mA

Step 6 — Restore the Appropriate Rate

Return the pacing rate to the intended clinical setting.

7. Why Does the Capture Threshold Matter?

The capture threshold is not necessarily constant. It can change because of:

• Lead displacement
• Poor myocardial contact
• Local oedema
• Myocardial ischaemia
• Electrolyte abnormalities
• Hypoxaemia
• Acidosis
• Myocardial injury
• Medication effects
• Lead malfunction

An increasing capture threshold is particularly important in a pacing-dependent patient because it may precede loss of reliable capture.

8. Sensitivity Setting

Sensitivity determines how small an intrinsic cardiac electrical signal the pacemaker can detect.

Sensitivity is expressed in mV (millivolts).

IMPORTANT RULE

Lower mV = MORE sensitive

Higher mV = LESS sensitive

For example:

• 1 mV → more sensitive
• 2 mV → less sensitive than 1 mV
• 5 mV → less sensitive than 2 mV

This relationship is one of the most important concepts to remember when troubleshooting temporary pacemakers.

9. Sensing Threshold

The sensing threshold is the smallest intrinsic electrical signal that the pacemaker can reliably detect.

For example, if intrinsic ventricular activity can be reliably detected down to approximately 4 mV, the sensing threshold is approximately 4 mV.

The programmed sensitivity should provide an adequate safety margin below the measured sensing threshold.

A commonly used approach is to program sensitivity to approximately half or less of the measured sensing threshold, when appropriate for the specific generator and pacing system.

Example:

Sensing threshold = 4 mV

Programmed sensitivity = approximately 2 mV or lower

Remember: 2 mV is more sensitive than 4 mV.

10. Sensing Threshold Procedure

Step 1 — Confirm Intrinsic Rhythm

The patient should have an underlying rhythm that can safely be allowed to occur during testing.

Step 2 — Reduce the Pacing Rate

Set the pacing rate approximately 10 ppm below the intrinsic rate to allow intrinsic beats to occur.

Step 3 — Reduce Output

According to the generator-specific protocol, output may be reduced to a very low value, such as 0.1 mA, to minimize interference from pacing during assessment.

Step 4 — Decrease Sensitivity

Gradually increase the programmed mV value until the pacemaker no longer reliably senses intrinsic cardiac activity.

Step 5 — Increase Sensitivity

Gradually decrease the mV value until intrinsic cardiac activity is reliably detected again.

This value represents the sensing threshold.

Step 6 — Program a Safety Margin

Program sensitivity to a sufficiently lower mV value than the measured sensing threshold.

Step 7 — Restore the Settings

Return the rate and output to the intended clinical settings.

11. Undersensing

Undersensing occurs when the pacemaker fails to recognize intrinsic cardiac activity.

Typical Findings

Intrinsic cardiac complexes occur, but the pacemaker does not recognize them and may deliver pacing stimuli when it should have inhibited pacing.

Possible Causes

• Sensitivity programmed too low
• Excessively high mV setting
• Low intrinsic signal amplitude
• Lead displacement
• Poor lead contact
• Lead or cable problems
• Changes in intrinsic signal amplitude

Correction

Because lower mV means greater sensitivity:

Decrease the programmed mV value to increase sensitivity.

Also assess lead position, connections, cable integrity, and intrinsic signal amplitude.

12. Oversensing

Oversensing occurs when the pacemaker detects electrical signals that are not appropriate intrinsic cardiac depolarizations.

Possible Causes

• Skeletal muscle/myopotentials
• Electromagnetic interference
• T-wave sensing
• Lead fracture
• Insulation failure
• Electrical noise
• Poor connections

Oversensing may inhibit pacing and can therefore be dangerous in a pacing-dependent patient.

Correction

To make the device less sensitive:

Increase the programmed mV value.

However, do not simply change the sensitivity without investigating the underlying cause, particularly when lead malfunction or electrical noise is suspected.

13. Failure to Pace / Output Failure

In output failure, the pacing stimulus is absent.

ECG Finding

No pacing spike when pacing should occur.

Possible Causes

• Battery depletion
• Generator malfunction
• Disconnected cable
• Loose connection
• Lead fracture
• Incorrect generator settings
• Incorrect pacing mode
• Oversensing causing inappropriate inhibition
• Lead displacement

Immediate Approach

1. Assess the patient's haemodynamic status.
2. Confirm the programmed rate and mode.
3. Check the generator and battery.
4. Check all connections.
5. Confirm the correct lead is connected to the correct port.
6. Assess for oversensing.
7. Check lead integrity and position.
8. Establish reliable backup pacing if pacing is essential.

14. Failure to Capture

In failure to capture, a pacing stimulus is delivered but fails to depolarize the myocardium.

ECG Finding

Pacing spike → no expected P wave or QRS complex.

Possible Causes

• Insufficient output
• Lead displacement
• Poor myocardial contact
• Myocardial ischaemia
• Hypoxia
• Acidosis
• Electrolyte abnormalities
• Myocardial injury
• Lead malfunction

Initial Management

• Increase pacing output.
• Check lead and cable connections.
• Assess lead position.
• Reassess the capture threshold.
• Correct electrolyte and metabolic abnormalities.
• Assess for myocardial ischaemia or injury.
• Consider lead repositioning or replacement if necessary.

15. Lead Dislodgement

Lead displacement is an important cause of sudden deterioration in pacing performance.

Suspect lead displacement when there is:

• Sudden loss of capture
• Sudden increase in capture threshold
• Sudden reduction in sensing amplitude
• Intermittent pacing
• Change in lead impedance, if available
• Change in paced ECG morphology
• Recent patient movement or procedure

Lead position should be assessed clinically and with appropriate imaging when indicated.

16. Rising Capture Threshold

A progressively increasing capture threshold requires attention, especially in a pacing-dependent patient.

Time	Capture Threshold	Programmed Output
Initial	1 mA	3 mA
12 hours	2 mA	4 mA
24 hours	4 mA	6 mA

Potential causes include lead migration, myocardial oedema, ischaemia, electrolyte abnormalities, acidosis, hypoxaemia, medication effects, and problems at the lead-tissue interface.

17. Pacing Modes

VVI

• V = ventricle paced
• V = ventricle sensed
• I = pacing inhibited when ventricular activity is sensed

VVI is commonly used for ventricular demand pacing.

AAI

• Atrium paced
• Atrium sensed
• Pacing inhibited by intrinsic atrial activity

AAI requires appropriate atrial function and adequate AV conduction.

DDD

Both atrium and ventricle can be paced and sensed, allowing maintenance of AV synchrony when appropriate.

18. Practical TPM Troubleshooting Algorithm

Step 1 — Assess the Patient

Check pulse, blood pressure, mental status, oxygenation, and signs of haemodynamic compromise.

Step 2 — Look at the ECG

Ask:

Are pacing spikes present?

If NO: consider output failure, inappropriate inhibition, oversensing, battery, generator, cable, or connection problems.

If YES: ask whether each pacing spike produces the expected cardiac response.

If NO: consider failure to capture.

If intrinsic beats are present but the device does not recognize them, consider undersensing.

If pacing is unexpectedly inhibited because the generator detects unwanted electrical activity, consider oversensing.

19. Quick Troubleshooting Table

Problem	ECG Finding	Common Causes	Initial Approach
Output failure	No pacing spike	Battery, generator, cable, lead, inhibition	Check generator, battery, connections, settings
Failure to capture	Spike but no P/QRS	Low output, lead displacement, metabolic causes	Increase output; check lead and patient
Undersensing	Intrinsic beat not detected	Low sensitivity, low signal, lead problem	Decrease mV
Oversensing	Inappropriate pacing inhibition	Noise, myopotentials, T-wave, lead fracture	Increase mV and investigate cause
Rising threshold	Increasing output required	Dislodgement, oedema, ischaemia, metabolic factors	Recheck lead and capture threshold
Intermittent pacing	Variable pacing/capture	Loose connection, lead movement, threshold variation	Check entire pacing circuit

20. Daily TPM Assessment

When temporary pacing is continued, reassess the system regularly.

• Underlying rhythm
• Indication for pacing
• Rate
• Mode
• Capture
• Capture threshold
• Sensing
• Sensing threshold
• Lead position and stability
• Connections
• Battery status
• Electrolytes and metabolic status

21. Important Safety Principles

Temporary pacing should be performed with appropriate ECG and haemodynamic monitoring.

Before threshold testing, ensure that:

• The patient is clinically stable enough for brief changes in pacing.
• An adequate underlying rhythm is present when required.
• Resuscitation equipment is immediately available.
• Pacing can be immediately restored if capture or haemodynamics deteriorate.

In a pacing-dependent patient, do not deliberately reduce pacing support without an appropriate backup plan.

If capture suddenly becomes unreliable or the patient becomes unstable, prioritize immediate reliable pacing and haemodynamic stabilization over prolonged troubleshooting.

22. High-Yield Rules to Remember

RATE

Capture testing → Rate above intrinsic rate.

Sensing testing → Rate below intrinsic rate.

OUTPUT

Higher mA = stronger pacing stimulus.

Capture threshold = minimum output producing reliable capture.

Program output above the capture threshold, commonly around 2–3× depending on the system and clinical situation.

SENSITIVITY

Lower mV = MORE sensitive.

Higher mV = LESS sensitive.

UNDERSENSING

Device does not detect intrinsic beats → decrease mV.

OVERSENSING

Device detects unwanted signals → increase mV and investigate the cause.

FAILURE TO CAPTURE

Pacing spike present + no cardiac response → increase output and investigate.

OUTPUT FAILURE

No pacing spike → check generator, battery, connections, lead, mode and sensing.

Conclusion

Safe temporary pacemaker management requires a systematic understanding of rate, output, capture, sensing, and lead integrity.

The most important concepts to remember are:

• Output = strength of the pacing stimulus.
• Capture threshold = minimum output required to reliably depolarize the myocardium.
• Sensitivity = ability of the pacemaker to detect intrinsic cardiac activity.
• Lower mV = higher sensitivity.
• Undersensing → decrease mV.
• Oversensing → increase mV.
• Pacing spike without QRS/P wave → failure to capture.
• No pacing spike when pacing should occur → output failure or inappropriate inhibition.

A systematic approa