A Cascaded Quantized Spiking Neural Network for Real-Time ECG Arrhythmia Detection on Edge Hardware

Wearable ECG monitors enable continuous cardiac surveillance, but most still rely on cloudbasedanalysis with limited on-device support for multi-class arrhythmia detection. Spikingneural networks (SNNs) are promising for low-power edge inference, yet it remains unclearhow class-imbalance loss design interacts with RR-interval features in directly trainedquantized SNNs, and FPGA validation in this setting is largely unexplored. We proposea quantized convolutional spiking neural network (QCSNN) for real-time arrhythmiadetection on resource-constrained hardware. The model uses a dual-head architecture thatjointly trains binary and four-class classifiers, subsequently reorganized into a cascadedpipeline that routes only abnormal beats to the second stage. At inference, beats classifiedas Normal exit at Stage 1; only beats classified as Abnormal are routed to the four-classhead, so the bulk of the inference cost is absorbed by Stage 1. We evaluate two loss functions,Cross-Entropy and Focal Loss, under four RR-feature routing strategies. Without RRfeatures, Focal Loss improves macro F1 by 2.3–2.5% over Cross-Entropy (mean Δ = +0.013in Stage-2 macro F1; Wilcoxon two-sided p = 0.031). With RR features, this advantagelargely disappears (Wilcoxon two-sided p ≥ 0.219 at all RR routings); meanwhile, RRfeatures at the strongest routing improve Stage-2 macro F1 by +0.028 to +0.034 dependingon loss function—a gain that exceeds the entire Focal-Loss-over-Cross-Entropy advantage,suggesting that RR features provide discriminative information that compensates for classimbalance at the input level. Based on clinically prioritized sensitivity, the CE:RR→Bothconfiguration was deployed on a PYNQ-Z2 FPGA, achieving 99.02% cascaded accuracy,11.54 ms per-beat latency, and 0.33Waccelerator power—a 31.66× power reduction and4.01× energy reduction versus GPU inference, within 1% macro F1. These results demonstratequantized SNNs as a practical solution for real-time edge arrhythmia monitoringthat operates independently of cloud connectivity—removing the network-dependentlatency, connectivity-dropout failure modes, and continuous-transmission energy burdenthat constrain current wearable monitors and, to our knowledge, represent one of the firstsystematic studies of loss-function/RR-feature interactions in directly trained SNN arrhythmiaclassification and one of the first FPGA deployments of a fully quantized, directlytrained SNN for multi-class ECG arrhythmia detection. All code generated and used inthis study has been made publicly available.