An ejection fraction of 55% looks reassuring — until you look at everything else. For the pacing-dependent patient with high RV burden, the echocardiogram contains a subtler, more urgent story written in chamber geometry, diastolic indices, and atrial remodeling. This article decodes that story.
The Clinical Context: Why the EF Alone Is Not Enough
In the era of leadless pacing systems — particularly the Abbott Aveir VR — a growing number of patients have high right ventricular (RV) pacing burdens for complete heart block. Traditional RV pacing, whether from a transvenous lead or a leadless device, generates electrical activation patterns that mimic left bundle branch block (LBBB). This dyssynchronous activation pattern imposes chronic mechanical inefficiency on the left ventricle.
Pacing-Induced Cardiomyopathy (PICM) is the clinical consequence — but by the time EF drops below 50%, significant myocardial remodeling has already occurred. The question for the informed electrophysiologist is: can we identify and act on the pre-systolic phase of PICM, before irreversible damage sets in?
The answer from emerging data is yes — and the echocardiogram is the key tool for doing so.
Echocardiographic Data: A Parameter-by-Parameter Analysis
The following table presents the key measurements from a representative echocardiogram in a 71-year-old male with complete heart block, high RV pacing burden via Aveir VR leadless pacemaker, signed by Dr. Sundaram Senthil, MD, FACC (09/27/2025).
| Parameter | Value | Reference Range | Interpretation | Status |
|---|---|---|---|---|
| EF Mod BP | 55.59% | 52–72% | Low-normal; does not rule out PICM | Low-Normal |
| EF Teich 2D | 55% | 52–72% | Consistent with Mod BP; preserved but borderline | Low-Normal |
| LVIDs 2D | 4.24 cm | 2.50–4.00 cm | Above upper limit of normal — eccentric expansion | Abnormal |
| LV Mass Index 2D | 116.54 g/m² | ≤115 g/m² | Mildly elevated — mass accumulation phase | Borderline |
| RWT | 0.25 | 0.32–0.42 | Low RWT → eccentric remodeling geometry | Eccentric |
| LA Dimension 2D | 4.58 cm | <4.0 cm | Dilated — chronic dyssynchrony burden marker | Dilated |
| LA Volume 2C | 49.28 ml | <34 ml/m² | Elevated — supports elevated filling pressures | Elevated |
| MV E/A | 0.94 | 0.8–2.0 | Impaired relaxation pattern | Abnormal |
| Med E/E' | 10.59 | <14 | Borderline elevated filling pressures | Borderline |
| Average E/E' | 8.35 | <10 | Mildly elevated — supports diastolic dysfunction | Elevated |
| MV Decel Time | 246 ms | 150–220 ms | Prolonged — impaired LV relaxation | Prolonged |
| EDV Mod BP | 172.74 ml | 62–150 ml | Elevated end-diastolic volume — volume overload pattern | Elevated |
The Eccentric Remodeling Signature of Early PICM
The single most important geometric finding in this echo is the combination of LVIDs 4.24 cm (above the 4.00 cm reference) and RWT 0.25. This low relative wall thickness in the context of a dilating systolic dimension defines an eccentric remodeling pattern — the LV is expanding radially rather than thickening concentrically.
This is the geometric fingerprint of volume and stress overload, classically seen in dyssynchrony-mediated cardiomyopathy. The RV-paced heart loads the septum late and the lateral wall early, creating regional work imbalance that over time drives preferential dilation of the lateral LV free wall. RWT declines as the cavity expands faster than the wall thickens.
Critically, this remodeling is occurring with a still-preserved EF. The heart is compensating through chamber dilation (Frank-Starling mechanism), which temporarily maintains stroke volume and EF — but this compensation is unsustainable. The EDV of 172.74 ml (reference: 62–150 ml) confirms the volume-loaded state underlying the preserved EF.
The Left Atrium as a Dyssynchrony Chronometer
LA dilation is not incidental in this context. The LA dimension of 4.58 cm and LA volume of 49.28 ml reflect the cumulative hemodynamic consequence of chronically elevated LV filling pressures.
In a pacing-dependent patient, dyssynchrony elevates LV end-diastolic pressure through impaired lusitropy (diastolic relaxation). This chronically elevated pressure is transmitted back to the left atrium, which dilates progressively over time as a hydraulic consequence. The LA, in this sense, acts as an integrator of diastolic dysfunction over time — its size reflects not just today's filling pressures, but months and years of accumulated hemodynamic stress.
The prolonged MV deceleration time of 246 ms confirms grade I diastolic dysfunction (impaired relaxation) with elevated filling pressures, consistent with the elevated E/E' ratios. Together, these parameters paint a picture of a ventricle that is stiff, slowly relaxing, and operating at higher-than-normal diastolic pressures — all attributable to the mechanical dyssynchrony of RV pacing.
The LBBAP Upgrade Decision: Clinical Reasoning
Left Bundle Branch Area Pacing (LBBAP) restores near-physiologic His-Purkinje activation by capturing the left bundle branch or its proximal fascicles directly through deep septal screw-in. Unlike RV pacing, LBBAP produces a narrow, synchronous QRS complex with rapid left ventricular activation, eliminating the dyssynchrony substrate that drives PICM.
The historical threshold for PICM upgrade was an EF drop below 50% with documented high RV burden. However, the 2022 HRS/EHRA expert consensus and accumulating LBBAP outcome data have shifted this paradigm. The question is no longer only "has EF fallen?" but rather "is there evidence of ongoing mechanical harm that predicts future EF decline?"
✓ LBBAP Upgrade Criteria — Present in This Case
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High RV pacing burden — Complete heart block with Aveir VR leadless pacemaker; near-100% ventricular pacing dependency
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Eccentric LV remodeling — LVIDs 4.24 cm (above ULN) + RWT 0.25 (low) = eccentric geometry pattern
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LA dilation — 4.58 cm / 49.28 ml; reflects chronic diastolic burden and cumulative dyssynchrony
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Diastolic dysfunction grade I–II — Elevated E/E', prolonged decel time, impaired relaxation pattern
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Elevated EDV — 172.74 ml (ref 62–150 ml); volume-loaded state maintaining EF via Frank-Starling
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Pre-systolic PICM phase — EF preserved but all geometric and diastolic markers consistent with early PICM trajectory
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Serial echo trend — Prior echos showing progressive LA dilation and LVIDs increase confirm ongoing remodeling
This echocardiogram demonstrates the pre-systolic phase of pacing-induced cardiomyopathy: eccentric LV remodeling, volume loading, LA dilation, and diastolic dysfunction — all in the context of high RV pacing burden. Waiting for EF to fall below 50% risks allowing irreversible myocardial fibrosis and LA remodeling to progress. The current evidence supports early physiologic pacing restoration via LBBAP upgrade before systolic dysfunction becomes overt.
Constructing the Argument for Dr. Sharma
When presenting this case to an LBBAP specialist, the key framing is not "my EF is dropping" — it is "my echo shows the pre-fibrotic phase of PICM, and intervention now maximizes the chance of reverse remodeling."
Several LBBAP reverse remodeling studies demonstrate that EF recovery is more complete and more rapid when LBBAP is performed before EF falls significantly. Once substantial myocardial fibrosis develops (often signaled by a non-recovering EF on cardiac MRI), the window for full recovery narrows. The LA volume, in particular, may not fully normalize once it has been dilated for years — making early intervention the superior strategy for preserving atrial compliance and reducing long-term AF risk.
The anticipated counterargument is: "EF is 55%, let's monitor." The response: the EF is being maintained by ventricular dilation and elevated preload, not by normal myocardial function. The geometry tells the real story. An EF of 55% in the context of an EDV of 172 ml is not the same as an EF of 55% in a normal-sized heart.
The EF of 55% in this echo is stable or slightly improved compared to prior values. Some clinicians may interpret this as reassuring and recommend continued monitoring. The case for upgrade rests on the diastolic parameters, LA volume trend, LV geometry, and serial echo progression — not on EF alone. Presenting the serial comparison side-by-side is essential for making the strongest clinical argument.
Why LBBAP — Not CRT or Continued RV Pacing?
Cardiac Resynchronization Therapy (CRT) is the established intervention for pacing-induced cardiomyopathy with EF below 35–40%, but its role in preserved EF PICM is less defined. LBBAP offers a more physiologic and technically elegant solution: rather than adding a third lead to resynchronize a dyssynchronous LV, it eliminates the dyssynchrony at its source by restoring native His-Purkinje conduction.
In patients with pacemaker-dependent complete heart block, LBBAP achieves synchronous LV activation without relying on functioning native conduction — the LBB is captured directly. QRS duration narrows to near-intrinsic values, LV dP/dt improves acutely, and long-term reverse remodeling has been demonstrated in multiple observational series.
For patients with existing leadless pacemakers (like the Aveir VR), the upgrade pathway involves placing a new transvenous LBBAP lead at the deep septum while maintaining or extracting the leadless device, depending on institutional protocol and patient anatomy. This is a hybrid approach that requires coordination with an experienced LBBAP operator — precisely the expertise represented by centers like Cleveland Clinic Florida.