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This study presents a systematic comparison of different approaches to the automated selection of the principal components (PC) which optimise the detection of maternal and fetal heart beats from non-invasive maternal abdominal recordings.A public database of 75 4-channel non-invasive maternal abdominal recordings was used for training the algorithm. Four methods were developed and assessed to determine the optimal PC: (1) power spectral distribution, (2) root mean square, (3) sample entropy, and (4) QRS template. The sensitivity of the performance of the algorithm to large-amplitude noise removal (by wavelet de-noising) and maternal beat cancellation methods were also assessed. The accuracy of maternal and fetal beat detection was assessed against reference annotations and quantified using the detection accuracy score F1 [2*PPV*Se / (PPV + Se)], sensitivity (Se), and positive predictive value (PPV). The best performing implementation was assessed on a test dataset of 100 recordings and the agreement between the computed and the reference fetal heart rate (fHR) and fetal RR (fRR) time series quantified.The best performance for detecting maternal beats (F1 99.3%, Se 99.0%, PPV 99.7%) was obtained when using the QRS template method to select the optimal maternal PC and applying wavelet de-noising. The best performance for detecting fetal beats (F1 89.8%, Se 89.3%, PPV 90.5%) was obtained when the optimal fetal PC was selected using the sample entropy method and utilising a fixed-length time window for the cancellation of the maternal beats. The performance on the test dataset was 142.7 beats2/min2 for fHR and 19.9 ms for fRR, ranking respectively 14 and 17 (out of 29) when compared to the other algorithms presented at the Physionet Challenge 2013. [ABSTRACT FROM AUTHOR]

The mechanisms responsible for changes in T wave symmetry and amplitude with changes in heart rate and action potential duration were investigated. A computer model of normal left ventricular repolarization was used to simulate the T waves on the surface 12-lead ECG. The effect of heart rate changes was studied by varying the ratio between dispersion of repolarization (Disp) and action potential repolarization duration (APRD). With constant dispersion. as heart rate increases, APRD decreases and the ratio Disp/APRD increases. T waves were simulated while varying the Disp/APRD ratio from 3.6% to 100%. The T wave symmetry ratio measured from the areas either side of the peak (SRarea), the symmetry ratio from the times either side of the peak (SRtime) and the T wave amplitude (Tamplitude) were calculated from each simulated ECG. SRarea decreased from 1.42 to 0.77, SRtime from 1.75 to 1.04 and the Tamplitude increased from 0. 19 mV to 2.30 mV. The stability of results with variation in model characteristics was also investigated, by moving the heart +/- 20 mm on all three axes, rotating the heart axes by +/- 10 and by modifying all constants defining the action potential by +/- 5% and +/- 10%. T wave amplitude was sensitive to changes in heart position, as the heart was moved towards the body surface. However, T wave shape changed very little with heart position or rotation, with the SD of SRarea varying by less than 0.05 over an SRarea range of 0.65 for different values of Disp/APRD ratio. We have shown from our model that cardiac T waves increase in amplitude, and become more symmetric with their peaks becoming central as APRD shortens with increasing heart rate, agreeing with clinical observations. These results help to explain the T wave shape changes which occur when heart rate increases.