---
license: other
license_name: mixed-see-licensing-section
tags:
  - ecg
  - electrocardiogram
  - lora
  - mlx
  - medical
  - ablation-study
language:
  - it
base_model:
  - mlx-community/gemma-4-e2b-it-bf16
  - mlx-community/Qwen3.5-2B-bf16
library_name: mlx
pipeline_tag: text-generation
---

# ECG interface study — four LoRA adapters, one controlled comparison

> **Research prototype. Not a medical device, not for clinical use, not validated for any patient
> population.** These adapters exist to answer a methodological question, not to read an ECG for you.
>
> Access is **gated with automatic approval**: the repository is open to read, and downloading asks
> you for an account and an acknowledgement of the line above. Approval is immediate; the gate is
> there so that nobody ends up with clinical-looking weights without having been told what they are.

This repository holds the four LoRA adapters from a study asking one question: **how much does the
way an ECG is handed to a language model matter, compared with which language model you pick?**

The answer, measured on one identical set of 1,000 patient recordings: **the interface moved
macro-averaged F1 by about 0.55; swapping model family at a fixed interface moved it by 0.085.**

## The comparison

All four adapters were trained on the **same 1,000 Chapman-Shaoxing/Ningbo recordings**, the same 11
diagnostic classes, the same LoRA shape (rank 16, scale 2.0, dropout 0, batch 1, seed 42).

One caveat about the third row, because the naming invites a wrong reading: `measures-qwen35-2b-8layer`
is **not** a smaller model. It is the same Qwen3.5-2B, whole, with LoRA attached to only the last 8 of
its 24 transformer blocks instead of all of them (`num_layers: 8` in `mlx_lm.lora` means "convert this
many blocks, counting from the last", not "truncate the network"). The choice was originally a speed
lever. What its 0.2909 measures is the cost of letting only a third of the network adapt — a property
of the training setup, not of model size. They are
evaluated on **population V**: 1,000 held-out validation recordings, one shared scoring protocol,
95 % confidence intervals from a 10,000-resample record-level bootstrap.

| folder | input the model reads | macro-F1 [95 % CI] | AUROC |
|---|---|---|---|
| `measures-gemma-4-e2b/` | 32 clinical measurements as one line of text | **0.5960** [0.5565, 0.6281] | 0.9020 |
| `measures-qwen35-2b-full/` | the same measurements | 0.5112 [0.4729, 0.5459] | 0.9262 |
| `measures-qwen35-2b-8layer/` | the same measurements, but only the last 8 of 24 blocks carry adapters | 0.2909 [0.2640, 0.3167] | 0.6563 |
| `tokens-gemma-4-e2b/` | 400 discrete codes from a learned waveform codebook | **0.0436** [0.0393, 0.0475] | — |

Reference points measured on the same 1,000 records, not in this repository: gradient boosting on the
same 32 measurements **0.6407** [0.5983, 0.6746]; a 476,819-parameter 1-D convolutional network on the
continuous waveform **0.5881** [0.5489, 0.6214]; predicting the training prevalence and nothing else
**0.1853**.

The first and last rows are the same model family and the same LoRA shape on the same recordings. Only
the interface differs — and with it two training settings that were **not** held constant, stated
plainly because they bound what the comparison proves:

| | `tokens-gemma-4-e2b` | `measures-gemma-4-e2b` |
|---|---|---|
| representation | 400 discrete codes | 32 clinical measurements as text |
| supervised decisions per example | ~1.7 | 11 |
| training length | 1 epoch (`iters: 1000`) | 10 epochs (`iters: 10000`), read out at epoch 8 |
| learning rate | 0.0001 | 0.00005 |
| `max_seq_length` | 2048 | 512 |

Because four things differ, the 0.55 swing is attributed to **the interface as a whole** — the
representation and the form of the question together — and to neither half alone. A ten-epoch re-run
of the token configuration was monitored per epoch and the collapse was still in place when it was
stopped at epoch 5.7: directional evidence that training length alone does not explain the gap, not a
completed control.

## What the token adapter is for

`tokens-gemma-4-e2b/` scores 0.0436, far **below** the 0.1853 you get by predicting class prevalence.
It is published deliberately, as the negative half of the comparison. It emits one constant answer for
every input — and not even the answer the class frequencies would recommend: the most common class in
the corpus is never emitted at all.

Three controls locate that failure in the interface rather than the architecture:

- the identical recipe, given 16 examples and 100 epochs, reproduces all 16 label sets exactly;
- a linear probe on the very same discrete codes reaches macro-F1 0.3947 (n = 4,359), so the class
  information survived the encoding;
- classical models on those codes plateau at 0.4703 at this training size, about 0.10 below what the
  continuous signal supports — so the representation was not innocent either.

**Do not read this as "language models cannot interpret ECGs."** That was never tested at an adequate
supervision budget. What was measured is that ~1.7 scored decisions per example is not enough, against
the ~330,000 the paired convolutional network received on the same 1,000 recordings.

## Usage

These are LoRA adapters for [MLX](https://github.com/ml-explore/mlx). They need their base model.

```bash
pip install mlx-lm
huggingface-cli download RandomUs666/ecg-interface-study --local-dir ecg-interface-study

python -m mlx_lm.generate \
  --model mlx-community/gemma-4-e2b-it-bf16 \
  --adapter-path ecg-interface-study/measures-gemma-4-e2b \
  --prompt "$(cat ecg-interface-study/prompts/formA_slots_system.txt)

FC 148 bpm | RR 405±85 ms | RMSSD 116 ms | battiti 25, prematuri 5 (larghi 5, stretti 0) | P presente (0.54 mV) | PR 290 ms | QRS 140 ms | QT 300 ms | QTc 487 ms | asse 50 | R V1 0.09 mV | S V1 1.30 mV" \
  --max-tokens 32 --temp 0.0
```

Expected output: **exactly 11 `SI`/`NO` tokens**, space-separated, one per class in the order given in
the system prompt. Greedy decoding (`--temp 0.0`); the reported numbers come from greedy decoding and
a frozen parser that counts unparseable output as an empty prediction set.

**The prompt is not decoration — it is the interface, and the interface is the finding.** The system
prompts are in `prompts/`, verbatim from the training data, in Italian, and the adapters expect them
as-is. `formA_slots_system.txt` drives the three `measures-*` adapters; `vq_tokens_system.txt` drives
`tokens-gemma-4-e2b`, whose output format is instead a JSON object `{"labels": [...]}`.

Each folder ships every intermediate checkpoint (`0001000_adapters.safetensors` …), so the training
trajectory can be inspected, plus `adapters.safetensors`, the final one. **The reported number for
`measures-gemma-4-e2b` is the epoch-8 checkpoint, `0008000_adapters.safetensors`, not the final one.**
Epoch 8 was selected in advance on a separate 512-record monitor; it is not established as better than
epoch 7 (difference +0.0130, CI [−0.0217, +0.0476]).

## Classes

Eleven multi-label classes, each with at least 200 training positives, covering 95.0 % of the corpus:
`ATRIAL_FIB_FLUTTER`, `AVB_FIRST_DEGREE`, `LEFT_CONDUCTION_ABNORMALITY`, `NORMAL_ECG`, `PAC`, `PVC`,
`RBBB`, `SINUS_BRADYCARDIA`, `SINUS_RHYTHM`, `SINUS_TACHYCARDIA`, `SUPRAVENTRICULAR_TACHYCARDIA`.

## Data and protocol

- **Corpus:** Chapman-Shaoxing/Ningbo, 45,152 physician-reviewed recordings at 500 Hz, via PhysioNet.
- **Splits:** 80/10/10 **by patient**, seed 42, iteratively stratified, each split frozen with a
  SHA-256 hash. The split key is the *signal-hash duplicate group*, not the record id: hashing every
  waveform found 87 groups of byte-identical duplicates in a corpus documented as one recording per
  patient, 32 of which straddled a naive split.
- **Training budget:** 1,000 recordings, a hardware ceiling rather than a choice — everything ran on
  one laptop (Apple M4 Pro, 48 GB unified memory) under a 37 GiB working-set cap.
- **Thresholds:** the language models emit hard labels, so no per-class thresholds are fitted for them.
- **Test split:** opened exactly once, for other systems. **The measurement arm has no test-set number
  at all**, and none should be invented for it. Every figure above is validation.

`results/v2_results.json` is the primary artefact behind the table: per-system scores, per-class F1,
the nine paired comparisons with bootstrap intervals and exact McNemar tests.

## Honest limits

- **One corpus, one run, one seed, one machine.** No repeated seeds, no multiple-comparison correction
  across the campaign's 28 pre-registered pairs, nine of which are not established.
- **1,000 of 34,658 available recordings.** That cut alone costs the paired convolutional network
  0.2485 macro-F1, so every number here sits far below what the data supports.
- **Representation and supervision were never crossed**, nor were training length and learning rate
  held constant (table above). The decomposition of the 0.55 swing is not available from this study.
- **Single-beat events are where every aggregate interface fails**: the best adapter here scores 0.192
  on premature ventricular complexes against 0.338 for gradient boosting on the same features.
- **Prompts and outputs are in Italian.** The adapters were never trained or tested in any other
  language.
- **The models are not calibrated**: they emit labels, not probabilities. AUROC in the table comes
  from a separate scoring path and is reported beside F1 because the two disagree — checkpoints
  spanning AUROC 0.90–0.93 span 0.51–0.60 in thresholded F1.

## What this study does not claim

- **Not** that language models cannot read ECGs.
- **Not** that a language model beats a purpose-built convolutional network. On the same 1,000
  records the difference is +0.0079 with a confidence interval of [−0.036, +0.053] and a McNemar p of
  0.67: they are indistinguishable. An earlier version of this work claimed the win; it came from a
  smaller evaluation (n = 256) in which only the language models were granted fitted thresholds, and
  it is **retracted**.
- **Not** that the language model beats gradient boosting — boosting is ahead by 0.0447, interval
  clear of zero.
- **Nothing clinical.** No sensitivity, specificity or safety claim is made or implied.

## Licensing

Mixed, and inherited — check before redistributing:

- `measures-gemma-4-e2b/` and `tokens-gemma-4-e2b/` adapt **Gemma** and are subject to the
  [Gemma Terms of Use](https://ai.google.dev/gemma/terms) and its Prohibited Use Policy.
- `measures-qwen35-2b-full/` and `measures-qwen35-2b-8layer/` adapt **Qwen**; see that model's licence.
- The training corpus is Chapman-Shaoxing/Ningbo, CC BY 4.0, obtained from PhysioNet. **No patient
  data, waveform, or derived recording is included in this repository** — only adapter weights, the
  prompt templates and aggregate results.
- Everything authored here (documentation, prompts, results JSON) : CC BY 4.0.

## Citation

An academic write-up of this study exists but is not yet public. Until then, cite this repository by
its URL and commit.