A cardiac pacemaker is a small, implanted device designed to regulate the heart’s rhythm by delivering controlled electrical impulses. When a patient with a pacemaker is examined, auscultation—the process of listening to internal sounds, typically with a stethoscope—involves evaluating the heart’s natural sounds (S1 and S2) and any sounds produced or altered by the device itself. Listening over the chest provides direct insight into how effectively the heart is responding to the programmed electrical stimuli. Auscultation helps distinguish between normal device operation and abnormal sounds that may indicate a complication.
Understanding the Normal Pacemaker Rhythm
A properly functioning pacemaker ensures a consistent and predictable heartbeat, which is the primary auscultatory sign of a normal rhythm. The device is programmed to maintain a minimum heart rate, meaning the listener should hear a regular sequence of S1 and S2 heart sounds occurring at a steady tempo. This regularity stands in contrast to the irregular or slow rhythms that often necessitate a pacemaker implantation in the first place.
When the ventricular chamber is paced, the electrical impulse is delivered to the heart muscle slightly later than the natural system would, leading to an altered contraction pattern. This can result in a wide QRS complex on an electrocardiogram and may cause a splitting of the first heart sound (S1), as the mitral and tricuspid valves may not close at the same moment. The timing and intensity of the S1 and S2 sounds should, however, remain consistent from beat to beat, reflecting the reliable mechanical function driven by the device.
Identifying the Electrical Artifact (The Pacing Spike)
The specific sound that directly corresponds to the pacemaker’s electrical discharge is known as the pacing spike or pacemaker click. This sound is a direct result of the rapid electrical impulse traveling through the lead and stimulating the heart or surrounding tissue. It is typically described as a very faint, sharp, high-pitched clicking or “tick” sound.
This brief click occurs immediately after the electrical impulse is delivered, often preceding the S1 heart sound when the ventricle is being paced. The sound’s generation is attributed to the minute mechanical vibration created by the electrical discharge, either in the heart muscle elements beneath the electrode or by the contraction of muscles in the chest wall near the device. Though its intensity varies greatly among patients, it can occasionally be loud enough to be a prominent extra sound.
Hearing the pacing click often requires the listener to use the diaphragm of the stethoscope, which is best for detecting high-frequency sounds, and to listen carefully over the left precordium where the lead terminates. The ability to hear this click confirms that the device is successfully firing an electrical impulse. The consistent presence of the click immediately followed by a corresponding heart sound confirms both device function and successful electrical capture of the heart muscle.
Auscultation Findings Indicating Complications
Abnormal sounds heard during auscultation can serve as important warning signs of a potential pacemaker malfunction or complication. The primary concern is loss of capture, where the device fires an impulse but the heart muscle fails to contract. This is heard as an irregular or slower-than-programmed rhythm, possibly with the pacing click present but not followed by an S1/S2 complex. Similarly, a failure of the device to sense the heart’s native rhythm can lead to an irregular pattern.
A new or changing heart murmur can also suggest a complication, particularly tricuspid regurgitation. Since the pacing lead travels through the tricuspid valve to reach the right ventricle, the lead can interfere with the valve’s complete closure, causing blood to leak backward. This is auscultated as a holosystolic murmur, a sound that persists throughout the entire contraction phase of the heart.
Another finding is a pericardial friction rub, which is a coarse, grating sound heard best with the diaphragm. This sound can indicate that the pacing lead is irritating the endocardium or the pericardial sac surrounding the heart, potentially suggesting lead perforation. The presence of any new, abnormal, or irregular sound warrants immediate medical evaluation to determine the cause and ensure the device is functioning safely.