Per-Recording Fidelity Guarantees for Wearable ECG Compression by Encoder-Side Verification

In a wearable electrocardiograph (ECG), sending one bit over a short-range radio consumes about two thousand times the energy of one arithmetic operation, so battery life depends mainly on compression. Existing compressors are tuned once on a development set and applied to each recording the device later encounters, so fidelity can only be reported as an average, which conceals the recordings that were damaged. On the MIT-BIH ECG Compression Test Database the transform family achieves 23.15x while an automatic reader detects only 82.0% of the QRS complexes. We observe that the encoder retains the original signal, so it can decompress its own output before transmission, compare the beats detected in that reconstruction with the beats it started from, and reject any attempt that moves or loses a beat, retrying at a finer setting. Each recording is then compressed as much as it can tolerate, instead of as much as the least tolerant recording in the database allows, so the coder also achieves higher ratios. Over 162 recordings it obtains 14.81x with all beats preserved, compared with 6.49x at 99.3% beat retention for the published family, and it extends a 225 mA h cell from 304 to 631 days, with verification taking 9 percent of the power budget. Two further measurements limit what any coder can gain. Noise accounts for 87% to 96% of the bits used by a strong neural coder, and that coder is three orders of magnitude less energy-efficient than a linear predictor. Verifying fidelity inside the encoder allows ambulatory monitoring to be audited one recording at a time.