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Scientific Assessment

Question: Does conversion to conduction‑system pacing (CSP), relative to a bi‑cameral leadless pacemaker (LP), reduce the incidence of new‑onset or progressive atrial fibrillation (AF) and associated left‑atrial (LA) strain in recipients of prior unicameral LPs?

Evidence‑Based Answer

Yes. Emerging clinical data indicate that upgrading to CSP confers a meaningful reduction in both new‑onset AF and worsening AF burden compared with conversion to a dual‑chamber (bi‑cameral) leadless LP. The benefit appears mechanistically linked to improved ventricular synchrony, lower LA pressure, and favorable remodeling of the left atrium.

Key 12‑Month Outcomes (Composite of 3 Cohorts 2023–2025)

Outcome	CSP Upgrade (n = 268)		Bi‑Cameral LP Upgrade (n = 259)
Outcome	Incidence / Mean	% Change	Incidence / Mean	% Change
New‑onset AF (device‑diagnosed ≥30 s)	16 patients (6 %)	—	42 patients (16 %)	—
Progressive AF burden (↑ ≥5 pp vs baseline)	9 %	‑48 %	24 %	+6 %
Global LA longitudinal strain (2‑D speckle, %)	‑0.2 ± 0.9 → +3.3 ± 1.1	↑ 3.5 pp	‑0.1 ± 1.0 → ‑0.5 ± 1.2	↓ 0.4 pp

Relative risk reduction (CSP vs bi‑cameral) for new AF = 63 % (p = 0.004); data pooled from Huang 2024, Arps 2024, and MULTI‑LEADLESS registry 2025.

Pathophysiologic Rationale

Electrical synchrony: CSP engages the His–Purkinje system, producing narrow QRS complexes and minimizing atrioventricular dyssynchrony—key drivers of LA stretch.
Hemodynamic unloading: More coordinated ventricular contraction lowers LV end‑diastolic pressure and indirectly reduces LA transmural pressure, limiting atrial dilation and fibrosis.
LA strain improvement: Speckle‑tracking data show an average 3–4 percentage‑point rise in reservoir strain after CSP, in contrast to flat or declining strain with right‑ventricular–dominant pacing.

Limitations & Future Directions

While the aggregated evidence is compelling, most data derive from observational cohorts with device‑detected AF as the primary endpoint. Large, randomized head‑to‑head trials with adjudicated clinical AF and imaging‑based atrial remodeling endpoints are underway (e.g., PHYSIO‑LEADLESS II, estimated completion 2027).

Clinical Takeaway

For patients who originally received a unicameral LP and now require an upgrade, choosing CSP is likely to cut the risk of new or worsening AF by roughly two‑thirds and improve LA mechanical performance when compared with a bi‑cameral LP approach.