Pacemaker Heart Sounds on Auscultation
Pacemakers themselves do not produce audible sounds on cardiac auscultation—you hear the normal heart sounds (S1 and S2) that result from the paced cardiac contractions, though their timing is altered compared to native rhythm.
What You Actually Hear
When listening to a patient with a functioning pacemaker, you will hear:
- Normal S1 and S2 heart sounds generated by valve closure during the paced cardiac cycle
- No clicking, buzzing, or mechanical sounds from the pacemaker device itself
- The pacemaker generator is electronic and operates silently
Key Timing Changes with Pacing
The critical difference is in the timing of heart sounds, not their quality:
Delayed Heart Sound Timing
Research demonstrates that pacemaker-induced ventricular depolarization significantly delays the timing of cardiac events 1:
- S1 (first heart sound) is delayed by approximately 90 msec after the QRS complex compared to native conduction
- S2 (second heart sound) is delayed by approximately 70 msec
- The interval from QRS to Korotkoff sounds is markedly prolonged (QKd increases from 206 to 294 msec)
Why This Occurs
The delay results from:
- Artificial electrical activation originating from the pacing lead (typically right ventricular apex)
- Abnormal ventricular activation sequence compared to native conduction through the His-Purkinje system
- Altered mechanical contraction patterns
Clinical Implications for Auscultation
What to Listen For:
- Regular rhythm at the programmed pacing rate (if pacing continuously)
- Wide splitting of S2 may be more pronounced with right ventricular pacing due to delayed left ventricular activation
- Cannon A waves may produce audible findings if AV dissociation occurs (pacemaker syndrome)
Important Caveats:
- Pacing mode matters: Different pacing modes (VVI, DDD, AAI) produce different hemodynamic effects 2
- Underlying valve disease will still produce its characteristic murmurs
- Mitral valve prolapse clicks can change timing dramatically with pacing-induced rate and rhythm changes 3
Common Pitfall:
Do not expect to hear any sound from the pacemaker device itself. If a patient reports hearing clicking or buzzing, this is not from normal pacemaker function and warrants investigation for device malfunction, lead fracture, or myopotential sensing.
Practical Examination Approach
When examining a paced patient:
- Palpate the pulse simultaneously with auscultation to confirm 1:1 correspondence with heart sounds
- Note the rate: Should match the programmed lower rate limit if fully paced
- Assess regularity: Irregular rhythm suggests intermittent pacing, native conduction, or arrhythmia
- Listen for underlying pathology: Murmurs, rubs, and gallops are still clinically relevant
- Check for pacemaker syndrome signs: Cannon A waves, variable S1 intensity with AV dissociation
The heart sounds themselves remain physiologic—generated by valve closure—but occur with altered timing due to the artificial electrical activation sequence.