AM/VP in Pacemaker Terminology
AM/VP stands for Atrial Mechanical sensed-Ventricular Paced, a diagnostic counter in modern leadless pacemakers that tracks the percentage of ventricular pacing events triggered by sensed atrial mechanical contractions. 1
Understanding AM/VP Sequences
AM/VP specifically measures how often the pacemaker successfully detects atrial mechanical activity (using an accelerometer) and then delivers a ventricular pacing stimulus in response. 1 This metric serves as a surrogate marker for atrioventricular synchrony in leadless pacing systems that cannot directly sense atrial electrical activity. 1
Clinical Significance of AM/VP Percentage
In patients with high ventricular pacing burden (>90% VP), the AM/VP percentage provides a reasonable estimation of true AV synchrony, with studies showing median AM/VP of 74.7% correlating strongly with ECG-determined AV synchrony (R² = 0.764, p < 0.001). 1
The AM/VP counter is particularly important in leadless atrioventricular synchronous pacemakers (like Micra AV) where traditional atrial leads are absent, and the device must rely on sensing atrial mechanical contractions through an accelerometer (A4 signal) rather than electrical activity. 1
How AM/VP Differs from Traditional Pacing Nomenclature
Traditional pacemaker codes (like VDD or DDD) describe the pacing mode configuration, whereas AM/VP is a diagnostic metric that quantifies actual device performance in maintaining AV synchrony. 2, 1
In VDD mode (ventricular pacing in synchrony with sensed atrial activity), the device senses atrial electrical signals through a lead, while AM/VP systems sense atrial mechanical contractions through motion sensors. 2, 1
Real-World Performance Data
Real-world data from 4,384 patients programmed to VDD mode showed stable atrial sensing over time, with mean A4 amplitude (atrial mechanical signal) of 2.3 ± 1.8 m/s² at implant and 2.3 ± 1.6 m/s² at 28 weeks, demonstrating consistent AM/VP tracking capability. 1
For patients with >90% ventricular pacing need, median AM/VP percentage of 74.7% indicates that approximately three-quarters of ventricular pacing events maintain physiologic AV synchrony. 1
Clinical Caveat
The AM/VP percentage should not be confused with traditional pacing mode codes—it is a performance metric, not a programming mode, and is specific to accelerometer-based atrial sensing systems in leadless pacemakers. 1