Normal Amplitude for Pacemaker Leads
Modern bipolar pacemaker stimulus outputs are typically very small in amplitude (often too small to be reliably detected on standard ECG) and short in duration (<0.5 ms), which fundamentally differs from the larger amplitude signals measured for intrinsic cardiac depolarization. 1
Pacemaker Spike Characteristics on ECG
The amplitude of pacemaker spikes on surface ECG is not standardized because:
- Modern bipolar pacemaker stimulus outputs have very small amplitudes that are often too small to be recognized on standard ECG recordings 1
- Pacemaker stimulus outputs are generally shorter in duration than 0.5 ms, requiring oversampling at 1000-15,000 samples per second for reliable detection 1
- The very small amplitudes of modern bipolar pacemaker stimulus outputs present a detection problem that requires resolution without artificially enhancing signals 1
Measured Lead Performance Parameters (Not Spike Amplitude)
What clinicians actually measure and optimize are the electrical performance characteristics of the pacemaker lead system, not the spike amplitude on surface ECG:
Ventricular Lead Parameters
Acute (at implantation):
- Pacing threshold: 0.4 ± 0.2 V at 0.5 ms pulse width (range 0.1-1.2 V) 2
- R wave sensing amplitude: 13 ± 5 mV (range 3-28 mV) 2
- Lead impedance: 576 ± 161 ohms (range 262-1200 ohms) 2
Chronic (12-18 months):
- Pacing threshold: 0.15 ± 0.10 ms at 1.5 V output 3
- R wave amplitude: >7.5 ± 2.4 mV 3
- Lead impedance: 497 ± 105 ohms 3
Atrial Lead Parameters
Acute (at implantation):
Chronic (12 months):
- Pacing threshold: 0.18 ± 0.10 ms at 1.5 V output 3
- P wave amplitude: 3.3 ± 0.9 mV 3
- Lead impedance: 500 ± 65 ohms 3
Clinical Targets for Optimal Lead Performance
Acceptable acute implantation values:
- Pacing threshold <0.5 V at 0.5 ms pulse duration 2
- R wave amplitude >10 mV for ventricular leads 2
- P wave amplitude >1.5 mV for atrial leads 4
- Lead impedance 400-1200 ohms 3, 2
Programming recommendations:
- Use 2:1 safety margin in terms of charge (double the threshold charge) 5
- Optimize output amplitude to 1.0 V when possible to maximize battery longevity 5
- Patients capturing at 0.5 V should be programmed to 1.0 V; those capturing at 1.5 V should be programmed to 2.0 V 5
Important Clinical Caveats
There is no correlation between low pacing thresholds and high R wave amplitudes - locations with excellent capture thresholds may not have optimal sensing characteristics 2. Each parameter must be evaluated independently during lead positioning.
Distal lead placement in cardiac veins produces superior performance compared to proximal placement, with significantly lower pacing thresholds (0.8 ± 0.2 V vs 1.8 ± 0.8 V) and higher R wave amplitudes (13.1 ± 4.5 mV vs 9.3 ± 6.5 mV) 6.
ECG machines should incorporate separate representation of detected pacemaker stimulus outputs into one row of the standard output tracing to aid identification, rather than artificially increasing amplitude 1. Low-amplitude pacemaker stimulus outputs should not be artificially enhanced because this distorts the recorded ECG 1.