A fast noise-tolerant ECG feature recognition algorithm based on probabilistic analysis of gradient discontinuity.

PURPOSE: Improvement in real-time electrocardiogram (ECG) interpretation is still needed, especially for QT estimation. This paper proposes a fast algorithm for ECG feature recognition, based on locating turning points in the waveform gradient. METHODS: The algorithm places the fiducial point at the maximal value of a probabilistic decision function, assessing line intervals of best fit before and after the point and the point location relative to R-wave peaks already found. RESULTS: Fiducial points were successfully located for the 30 heartbeats annotated by a cardiologist of all 10 normal sinus rhythm records from the PhysioNet QT Database. For a given subject, the algorithm's QT estimation had superior repeatability, with intrasubject QT standard deviation just 5.42ms, 60% lower than the cardiologist's 13.57ms. Initial tests suggest immunity to noise of standard deviation up to about 9% of the signal, depending on noise type. CONCLUSIONS: The proposed algorithm is fast to calculate and noise-tolerant, and has shown improved repeatability in its QT estimation compared to a cardiologist.

Nerve-muscle activation by rotating permanent magnet configurations.

KEY POINTS: The standard method of magnetic nerve activation using pulses of high current in coils has drawbacks of high cost, high electrical power (of order 1 kW), and limited repetition rate without liquid cooling. Here we report a new technique for nerve activation using high speed rotation of permanent magnet configurations, generating a sustained sinusoidal electric field using very low power (of order 10 W). A high ratio of the electric field gradient divided by frequency is shown to be the key indicator for nerve activation at high frequencies. Activation of the cane toad sciatic nerve and attached gastrocnemius muscle was observed at frequencies as low as 180 Hz for activation of the muscle directly and 230 Hz for curved nerves, but probably not in straight sections of nerve. These results, employing the first prototype device, suggest the opportunity for a new class of small low-cost magnetic nerve and/or muscle stimulators. ABSTRACT: Conventional pulsed current systems for magnetic neurostimulation are large and expensive and have limited repetition rate because of overheating. Here we report a new technique for nerve activation, namely high-speed rotation of a configuration of permanent magnets. Analytical solutions of the cable equation are derived for the oscillating electric field generated, which has amplitude proportional to the rotation speed. The prototype device built comprised a configuration of two cylindrical magnets with antiparallel magnetisations, made to rotate by interaction between the magnets' own magnetic field and three-phase currents in coils mounted on one side of the device. The electric field in a rectangular bath placed on top of the device was both numerically evaluated and measured. The ratio of the electric field gradient on frequency was approximately 1 V m(-2) Hz(-1) near the device. An exploratory series of physiological tests was conducted on the sciatic nerve and attached gastrocnemius muscle of the cane toad (Bufo marinus). Activation was readily observed of the muscle directly, at frequencies as low as 180 Hz, and of nerves bent around insulators, at frequencies as low as 230 Hz. Nerve-muscles, with the muscle elevated to avoid its direct activation, were occasionally activated, possibly in the straight section of the nerve, but more likely in the nerve where it curved up to the muscle, at radius of curvature 10 mm or more, or at the nerve end. These positive first results suggest the opportunity for a new class of small, low-cost devices for magnetic stimulation of nerves and/or muscles.