Cardiac pacemakers are devices that regulate the heart’s rhythm, which is naturally controlled by electrical signals. When these signals malfunction, causing a heart rate that is too slow, too fast, or irregular, a pacemaker provides electrical impulses to maintain a consistent beat. This helps manage heart conditions, ensuring the heart contracts effectively and pumps blood throughout the body.
Understanding Cardiac Pacing
A pacemaker is typically implanted under the skin, with leads extending to the heart chambers. It monitors the heart’s activity and sends electrical pulses to prompt a heartbeat when needed. This is often necessary for individuals experiencing bradycardia, a condition where the heart beats too slowly.
What Asynchronous Pacing Is
Asynchronous pacing is a mode of cardiac pacing where the pacemaker delivers electrical impulses at a fixed, predetermined rate, without regard for the heart’s own intrinsic electrical activity. Unlike other pacing modes that “listen” for the heart’s natural beats, asynchronous pacing operates independently. This means the pacemaker continuously sends electrical signals at a constant interval, regardless of whether the heart is already beating. The term “asynchronous” highlights this characteristic: the pacemaker’s activity is not synchronized with, or inhibited by, the heart’s natural rhythm. This contrasts with synchronous pacing, where the device actively senses the heart’s electrical activity and adjusts its pacing accordingly.
When Asynchronous Pacing Is Employed
Asynchronous pacing is employed in scenarios where the heart’s intrinsic electrical activity is unreliable, absent, or problematic to sense. It is used during complete heart block, especially when the heart’s natural escape rhythm is unstable or too slow to sustain adequate blood flow. It is also used during surgical procedures where electromagnetic interference from surgical equipment could disrupt a synchronously operating pacemaker. In these cases, asynchronous pacing provides a stable, uninterrupted heart rate, preventing complications from rhythm disturbances. Additionally, it is used when the heart’s natural rhythm is so profoundly suppressed that relying on its intrinsic activity for pacing decisions is impractical or unsafe.
How Asynchronous Pacing Operates
Asynchronous pacing functions by delivering electrical stimuli at a constant, preset rate, regardless of any electrical activity originating from the heart itself. Common asynchronous pacing modes are identified by three-letter codes, where the third letter is always “O,” signifying no sensing or response to intrinsic cardiac activity. For example, in AOO mode, the pacemaker delivers impulses only to the atrium (A) at a fixed rate (O), without sensing the atrium’s own electrical activity (O). Similarly, VOO mode paces the ventricle (V) at a fixed rate (O), without sensing ventricular activity (O). DOO mode paces both the atrium and ventricle (D) at a fixed rate (O), without sensing either chamber’s activity (O).