Real time microcontroller implementation of an adaptive myoelectric filter.

This paper describes a real time digital adaptive filter for processing myoelectric signals. The filter time constant is automatically selected by the adaptation algorithm, giving a significant improvement over linear filters for estimating the muscle force and controlling a prosthetic device. Interference from mains sources often produces problems for myoelectric processing, and so 50 Hz and all harmonic frequencies are reduced by an averaging filter and differential process. This makes practical electrode placement and contact less critical and time consuming. An economic real time implementation is essential for a prosthetic controller, and this is achieved using an Intel 80C196KC microcontroller.

Discrimination of antegrade and retrograde atrial depolarization by electrogram analysis.

The inability of cardiac pacemakers to selectively reject retrograde P waves limits the usefulness of dual-chamber pacemakers (because of the possibility of endless loop tachycardias) and of antitachycardia devices which use a dual-chamber sensing algorithm. In order to determine selective sensing parameters, amplitude, slew rate, and configuration of antegrade and retrograde atrial electrograms were measured in 34 patients undergoing dual-chamber pacemaker implant--31 with unipolar and three with bipolar units. All antegrade and retrograde pairs were measurably different. All 34 cases had measurable antegrade/retrograde amplitude differences; 30 of the unipolar cases (96.8%) and all bipolar cases displayed antegrade/retrograde amplitude differences of at least 0.25 mV. Thirty of the unipolar cases (96.8%) and two bipolar cases had measurable slew rate differences. Configuration differed in 14 of 31 (45.2%) of unipolar and in two bipolar cases. A combined criterion with 0.25 mV sensitivity steps (available in at least two presently available pacemakers) and 0.5 V/sec slew rate gradations (through the use of externally programmable filters) would allow the discrimination of retrograde from antegrade depolarizations in all 34 cases. With the use of amplitude and slew rate differences, it is therefore possible to reject retrograde P waves while sensing antegrade P waves with current technology.

Unipolar and bipolar right atrial appendage electrodes: comparison of sensing characteristics.

To optimize atrial sensing and reject far-field signals (i.e., ventricular potentials seen in the atrium), the atrial amplitudes of electrograms (EGMs) should be as high as possible and the ventricular amplitudes as low as possible. To compare clinical sensing results obtained with unipolar and bipolar electrodes, endocardial EGMs were recorded on a high-speed multichannel recorder with a paper speed of 200 mm/second and frequency cutoffs at 0.1 and 2,000 Hz. Forty acute unipolar and 18 acute bipolar electrodes (in different patients), three matched pairs of unipolar and bipolar electrodes, and seven coronary sinus electrodes were measured. Unipolar and bipolar right atrial appendage (RAA) electrode EGMs were compared for 1) amplitude of EGM, 2) slew rate (dv/dt); and 3) amplitude of the ventricular EGM as measured through the RAA electrode. Unipolar RAA EGMs were compared with unipolar coronary sinus EGMs. Three bipolar leads were measured as unipolar and bipolar simultaneously. Bipolar atrial EGMs had equal amplitudes (unipolar, 4.2 +/- 2.1 mV, versus bipolar, 5.9 +/- 2.5; NS), higher slew rates (unipolar, 2.6 +/- 1.6 V/second, versus bipolar, 4.4 +/- 2.1; P less than 0.005), and lower ventricular (far-field) amplitudes (unipolar, 1.1 +/- 1.1 mV, versus bipolar, 0.7 +/- 0.6; P less than 0.02) when compared with unipolar RAA electrodes. This observation was confirmed in the measurement of the matched pairs atrial/ventricular amplitude ratio (unipolar, 4.7 +/- 2.2, versus bipolar, 8.7 +/- 2.0; P less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)