A Multicenter Study of the Electrical Characteristics and Short-Term Outcomes of the Aveir VR Leadless Pacemaker

This multicenter study of 119 patients demonstrates that monitoring real-time electrical parameters, specifically initial current of injury increases and impedance thresholds exceeding 230 Ω, during Aveir VR leadless pacemaker implantation effectively guides site localization and predicts short-term device stability and pacing performance.

The Gist

Imagine your heart is a house with a faulty electrical system. Sometimes, the lights (heartbeats) flicker or go out because the wiring is broken. Doctors usually fix this by running a long, thin wire (a lead) from a battery pack under the skin, through a vein, and into the heart. But this is like drilling a hole in the wall to run a cable; it can be messy, risky, and leave scars.

Enter the Aveir VR, a new kind of "smart plug." It's a tiny, self-contained pacemaker (about the size of a large vitamin) that screws directly into the heart muscle. No long wires, no scars on the chest.

This study is like a field report from a team of 10 different construction crews across China who installed 119 of these smart plugs between late 2024 and early 2025. They wanted to figure out: How do we know we screwed it in just right, and not too loose or too tight?

Here is the breakdown of what they found, using simple analogies:

1. The "Map" (CEGM)

Before screwing the device in, the doctor uses a special tool to "listen" to the heart's electrical heartbeat. This is called the Commanded Electrogram (CEGM).

• The Analogy: Think of this like a GPS signal. Depending on where you are in the city (the heart), the signal sounds different.
  • If the signal looks like a big "R" wave, you are likely at the very tip (apex) of the heart.
  • If it looks like "RS," you are probably on the wall (septum).
• The Finding: The doctors realized that by just listening to the shape of this signal, they could tell exactly where they were inside the heart without needing to take an X-ray every time. It's like knowing you're in the kitchen just by the smell of coffee, rather than looking at a map.

2. The "Injury Current" (COI) - The "Squeak"

When you screw a screw into wood, you might hear a squeak or feel resistance. In the heart, when the tiny screw (helix) touches the muscle, it creates a tiny electrical "squeak" called the Current of Injury (COI).

• The Analogy: Imagine you are trying to hang a picture. You push the nail in.
  • Good: You push it in, and the nail holds tight. The "squeak" (COI) gets louder or stays steady. This means the nail is gripping the wood well.
  • Bad: You push it in, and the "squeak" gets quieter or disappears. This might mean the nail is slipping or not touching the wood properly.
• The Finding: The study found a crucial rule: The first half-turn matters most.
  • If the "squeak" (COI) gets louder in the first half-turn, the device is likely to work perfectly with low energy needs later.
  • If the "squeak" gets quieter in that first half-turn, the device might be loose, and the battery will have to work harder (high threshold) to make the heart beat.
  • Surprise: Unlike older devices where the "squeak" kept getting louder the more you screwed it in, this device sometimes stopped getting louder after the first turn. The doctors realized this is because the device gets stuck in the tiny "trabeculae" (the heart's internal muscle fibers), like a screw getting caught in a knot of wood. It's still secure, just different.

3. The "Resistance" (Impedance) - The "Grip Strength"

As the device screws in, the electrical resistance (impedance) changes.

• The Analogy: Think of this like gripping a handshake.
  • If you shake hands loosely, the connection is weak.
  • If you squeeze hard, the connection is strong.
• The Finding: The doctors found a magic number. If the electrical resistance increases by more than 230 Ohms while screwing it in, it's a very good sign that the device is gripping the heart muscle tightly and won't fall out. It's like a "grip strength test" for the pacemaker.

4. The Results

• Success Rate: 100% of the devices were successfully implanted.
• Safety: No major accidents happened (no holes in the heart, no collapsed lungs).
• Stability: The devices stayed put. The only time a doctor had to move a device was if the "grip strength" (impedance) or the "squeak" (COI) didn't look right during the first few turns.

The Bottom Line

This study gives doctors a new checklist for installing these tiny heart plugs:

1. Listen to the signal to know where you are.
2. Watch the "squeak" (COI) during the first half-turn. If it gets louder, you're on the right track. If it gets quieter, stop and move to a new spot.
3. Check the "grip" (Impedance). If the resistance jumps up by at least 230 Ohms, you have a solid hold.

By following these simple electrical clues, doctors can ensure the pacemaker is installed perfectly the first time, making the procedure safer and more effective for patients. It turns a complex surgery into a more predictable, guided process.

Technical Summary

1. Problem Statement

While leadless pacemakers (LPMs) offer a solution to complications associated with transvenous systems (e.g., lead fractures, venous occlusion, infection), existing active fixation LPMs like the Micra utilize a passive fixation mechanism that prevents the assessment of electrical parameters until after full deployment. This limitation often necessitates repeated deployments and repositioning if initial parameters are suboptimal.

The Aveir VR is a newer LPM featuring an active fixation mechanism that theoretically allows for real-time monitoring of electrical parameters (Commanded Electrogram [CEGM], Current of Injury [COI], impedance, and pacing thresholds) during the screwing-in process. However, there is a lack of comprehensive, multicenter clinical data regarding how these intraoperative electrical variations correlate with device stability and short-term outcomes. This study aims to fill that gap by analyzing these parameters to optimize implantation strategies.

2. Methodology

• Study Design: A retrospective, non-randomized, multicenter cohort study conducted across 10 centers in China.
• Population: 119 patients (mean age 70.18 years; 59.58% female) who received the Aveir VR LPM between November 2024 and May 2025. Indications included Sick Sinus Syndrome (46.2%) and Atrioventricular Block (53.8%).
• Procedure:
  • Implantation was performed via the right femoral vein.
  • Electrical data was collected at specific procedural phases: Mapping, Fixation (recorded at 0.5, 1, 1.25, and 1.5 turns), Tether Mode, and Post-Release.
  • Key Metrics Measured:
    • CEGM Morphology: (R, RS, QR, QRS, QS) to determine localization.
    • Current of Injury (COI): Measured by ST-segment elevation amplitude (mV) and Intracardiac Electrogram Duration (IED) in ms.
    • Impedance: Resistance in Ohms (Ω).
    • Pacing Threshold (PCT): Voltage required for capture at 0.4ms pulse width.
• Statistical Analysis: Used ROC curve analysis to determine predictive values for thresholds and stability, and Spearman's correlation for relationships between parameters.

3. Key Contributions

This study provides the first large-scale, real-world analysis of the dynamic electrical behavior of the Aveir VR during the active fixation process. Key technical contributions include:

1. CEGM Morphology Mapping: Establishing a correlation between CEGM waveforms and specific implantation sites (e.g., RS morphology in septal regions vs. R morphology in the apex), aiding in localization without excessive fluoroscopy.
2. COI Dynamics in Active Fixation: Challenging the traditional "more COI is better" dogma. The study found that while initial COI increases are beneficial, sustained COI increases are not always necessary for the Aveir VR due to its unique design (helix anchors, cathode acts passively).
3. Impedance as a Stability Marker: Identifying that the relative increase in impedance (rather than absolute values) is a superior predictor of device stability and low pacing thresholds.
4. Operational Thresholds: Defining specific intraoperative cut-off values (e.g., impedance increase >230 Ω) to guide operators on when to stop screwing or reposition.

4. Key Results

• Implantation Success: 100% success rate; 13 patients (10.92%) required repositioning.
• CEGM Morphology:
  • RS was the dominant morphology (57.98%), followed by R (35.29%).
  • Morphology varied significantly by location ($P < 0.0001$): Low/Mid-septum and Free Wall predominantly showed RS; the Apex predominantly showed R.
  • No significant difference in pacing thresholds was found between different CEGM morphologies.
• Current of Injury (COI) & Thresholds:
  • 0 to 0.5 Turns: 58.82% of patients showed an increase in COI. Patients with a decrease in COI during this phase had significantly higher short-term (24h) pacing thresholds ($P=0.02$).
  • 0.5 to 1 Turn: 52.94% showed further COI increases. Changes in this phase did not significantly correlate with immediate or 24-hour thresholds.
  • Conclusion: An increase in COI during the initial 0.5 turns is critical for optimal short-term thresholds.
• Impedance & Stability:
  • Predictive Value: ROC analysis showed an impedance increase of >230 Ω (from mapping to fixation) predicts lower short-term thresholds (AUC 0.634).
  • Stability Correlation: Lead stability showed a moderate positive correlation with impedance increase ($\rho=0.44, P<0.001$) but only a weak correlation with COI changes.
• Short-Term Outcomes:
  • Median 24-hour Pacing Threshold: 0.623 mV.
  • Median 24-hour Impedance: 670 Ω.
  • No significant periprocedural complications were observed.

5. Significance and Clinical Implications

• Optimized Implantation Strategy: The study suggests that operators should monitor the initial 0.5 turns closely. If COI decreases or fails to increase during this phase, immediate repositioning is advised to avoid high thresholds.
• Impedance Monitoring: Unlike previous studies focusing on absolute impedance, this paper highlights that the magnitude of impedance increase during screwing is a vital indicator of tissue contact and device stability. A threshold increase of 230 Ω serves as a practical benchmark for a secure fixation.
• Device Design Insight: The findings suggest the Aveir VR's helix acts primarily as an anchor, while the cathode tip engages trabeculations rather than penetrating deeply. This explains why COI does not always increase linearly with rotation, distinguishing it from traditional active-fixation leads.
• Localization Aid: CEGM morphology can be used as a non-invasive tool to verify implantation location, potentially reducing fluoroscopy time and contrast usage, which is particularly beneficial for patients with renal insufficiency.

In summary, this study validates the utility of real-time electrical monitoring during Aveir VR implantation, providing specific, data-driven guidelines (focusing on initial COI trends and impedance delta) to improve device stability and reduce the risk of high pacing thresholds.