Quality Control in ECG-based Atrial Fibrillation Screening

This thesis comprises an introductory chapter and four papers related to quality control in ECG-based atrial fibrillation (AF) screening. Atrial fibrillation is a cardiac arrhythmia characterized by an irregular rhythm and constitutes a major risk factor for stroke. Anticoagulation therapy significantly reduces this risk, and therefore, AF screening is motivated. Atrial fibrillation screening is often done using ECGs recorded outside the clinical environment. However, the higher susceptibility of such ECGs to noise and artifacts makes the identification of patients with AF challenging. The present thesis addresses these challenges at different levels in the data analysis chain. Paper I presents a convolutional neural network (CNN)-based approach to identify transient noise and artifacts in the detected beat sequence before AF detection. The results show that by inserting a CNN, prior to the AF detector, the number of false AF detections is reduced by 22.5% without any loss in the sensitivity, suggesting that the number of recordings requiring expert review can be significantly reduced. Paper II investigates the signal quality of a novel wet electrode technology, and how the improved signal quality translates to improved beat detection and AF detection performance. The novel electrode technology is designed for reduction of motion artifacts typically present in Holter ECG recordings. The novel electrode technology shows a better signal quality and detection performance when compared to a commercially available counterpart, especially when the subject becomes more active. Thus, it has the potential to reduce the review burden and costs associated with ambulatory monitoring.Paper III introduces a detector for short-episode supraventricular tachycardia (sSVT) in AF screening recordings, which has been shown to be associated with an increased risk for future AF. Therefore, the identification of subjects with suchepisodes may increase the usefulness of AF screening. The proposed detector is based on the assumption that the beats in an sSVT episode display similar morphology, and that episodes including detections of deviating morphology should be excluded. The results show that the number of false sSVT detections can be significantly reduced (by a factor of 6) using the proposed detector.Paper IV introduces a novel ECG simulation tool, which is capable of producing ECGs with various arrhythmia patterns and with several different types of noise and artifacts. Specifically, the ECG simulator includes models to generate noise observed in ambulatory recordings, and when recording using handheld recording devices. The usefulness of the simulator is illustrated in terms of AF detection performance when the CNN training in Paper I is performed using simulated data. The results show a very similar performance when training with simulated data compared to when training with real data. Thus, the proposed simulator is a valuable tool in the development and training of automated ECG processing algorithms. Together, the four parts, in different ways, contribute to improved algorithmic efficiency in AF screening

A novel method for transmission electron microscopy study of cytoplasmic fragments from preimplantation human embryos

Transmission electron microscopy (TEM) is the main tool for exploring the intracellular damage and organelle distribution. The cause of producing embryo cytoplsamic fragmentation is not completely understood. Since the fragments have detrimental effects on embryo development, the ultrastructural analysis of fragments may play an important role in fragmentation etiology and in embryo development as well. There are no studies regarding the ultrastructure of fragments in transferable embryos, because the preparation for TEM is not vital and embryos are discarded inevitably. This study aims to introduce a new method for ultrastructural evaluation of fragments without damaging the human cleaving embryos

Signal quality assessment of a novel ecg electrode for motion artifact reduction

Background: The presence of noise is problematic in the analysis and interpretation of the ECG, especially in ambulatory monitoring. Restricting the analysis to high-quality signal segments only comes with the risk of excluding significant arrhythmia episodes. Therefore, the development of novel electrode technology, robust to noise, continues to be warranted. Methods: The signal quality of a novel wet ECG electrode (Piotrode) is assessed and compared to a commercially available, commonly used electrode (Ambu). The assessment involves indices of QRS detection and atrial fibrillation detection performance, as well as signal quality indices (ensemble standard deviation and time–frequency repeatability), computed from ECGs recorded simultaneously from 20 healthy subjects performing everyday activities. Results: The QRS detection performance using the Piotrode was considerably better than when using the Ambu, especially for running but also for lighter activities. The two signal quality indices demonstrated similar trends: the gap in quality became increasingly larger as the subjects became increasingly more active. Conclusions: The novel wet ECG electrode produces signals with less motion artifacts, thereby offering the potential to reduce the review burden, and accordingly the cost, associated with ambulatory monitoring

Effects of Hybridization of Carbon and Polypropylene Short Fibers as Reinforcement on Flexural Properties of Fine Aggregate Concretes

Nowadays, the advantages of short fibers as reinforcement in cement based materials are well known. In this paper, the effect of hybridization of short polypropylene (PP) and carbon fibers on flexural properties of a fine aggregate concrete has been investigated. Samples with dimensions of  containing 2 vol% of the polypropylene and carbon fibers with 6 and 8mm length were made. The PP to carbon fiber proportion in the samples were selected as 100:0, 75:25, 50:50, 25:75 and 0:100. A four-point bending test was carried out on all the samples to investigate the flexural behaviour. It was found that the addition of carbon fibers significantly increases the flexural load (i.e. 260%). The application of PP fibers leads to a 2590% increase in the toughness compared to the control sample. It was also found that the sample with carbon to PP ratio of 75/25 shows the optimum results and it leads to 190% and 2070% increment in the flexural load and toughness, respectively, in comparison to the control sample

The role of growth factors in human sperm parameters: A review of in vitro studies

In vitro sperm preparation/incubation and cryopreservation are associated with oxidative stress as the main cause of sperm damage, and different strategies are used to improve sperm quality in in vitro conditions to treat male infertility. Growth factors (GFs) are biological molecules that play different roles in various cellular processes such as growth, proliferation, and differentiation. Many studies have shown that GFs and their receptors are expressed in the male reproductive system. In vitro supplementation of GFs to improve sperm parameters has yielded useful results. There are many studies on the effects of GFs on sperm quality improvement and subsequent assisted reproductive technology results. Hence, this study will review the in vitro results of various GFs including brain-derived neurotrophic factor, nerve growth factor, fibroblast growth factor, insulin-like growth factor I, and vascular endothelial growth factor to improve sperm quality. Key words: Growth factors, Sperm, ROS, Cryopreservation, In vitro

The Role of Microgravity in Cancer: A Dual-edge Sword

Since human beings could travel beyond the earth atmosphere, scientists started to investigate the effect of microgravity on human cells. Microgravity has different effects on normal and cancer cells, but the related mechanisms are not well-known till now. The aim of the present review is to focus on the consequences of exposing the cancer cells to reduced gravity. Some cancer cells organize three-dimensional structures under microgravity. Obviously, microgravity is an external stress, which can affect cell proliferation, apoptosis, cytoskeleton and signaling pathways. In addition, it touches immune-related components, regulates immune responses, and implicates immune cell activation. Low mutation aggregation and cancer rate in astronauts may lead to use microgravity as a therapeutic approach. However, it reduces the invasion and migration in some types of cancer cells, triggers the oncogenic signaling pathways including KRAS, and inhibits proliferation in normal lymphocytes. In conclusion, using microgravity as a therapeutic method in cancer treatment needs to be more investigated on both cancer and normal cells, and might not become true in the near future

Ultrastructure of cytoplasmic fragments in human cleavage stage embryos

Purpose: The goal of this study was to evaluate the ultrastructure of cytoplasmic fragments along with the effect of cytoplasmic fragment and perivitelline space coarse granulation removal (cosmetic microsurgery) from embryos before embryo transfer on ART outcomes. Methods: One hundred and fifty intracytoplasmic sperm injection cycles with male factor infertility were included in this prospective study. Patients were divided into three groups of case (n = 50), sham (n = 50), and control (n = 50). Embryos with 10–50 % fragmentation were included in this study. Cosmetic microsurgery and zona assisted hatching were only performed in case and sham groups respectively. Extracted fragments were evaluated ultrastructurally by transmission electron microscopy (TEM). Rates of clinical pregnancy, live birth, miscarriage, multiple pregnancies, and congenital anomaly in the three groups were also compared. Results: Micrographs from TEM showed that mitochondria were the most abundant structures found in the fragments along with mitochondria-vesicle complexes, Golgi apparatus, primary lysosomes, and vacuoles. There were no significant differences in demographic characteristics, laboratory and clinical data, or embryo morphological features between the groups. The rate of clinical pregnancy in control, sham, and case groups had no significant differences (24, 18, and 18 %, respectively). The rates of live birth, miscarriage, multiple pregnancy, and congenital anomaly were also similar between the different groups. Conclusions: Our data demonstrated that cosmetic microsurgery on preimplantation embryos had no beneficial effect on ART outcomes in unselected groups of patients. As mitochondria are the most abundant organelles found in cytoplasmic fragments, fragment removal should be performed with more caution in embryos with moderate fragmentation

INJECTION EXPERIMENTS ON ROCKS UNDER TRIAXIAL CONDITION WITH ACOUSTIC EMISSION MONITORING

This work presents the results of a series of triaxial- injection experiments carried out on two basalt cores from the Newberry geothermal field well GEO-N2 and a Mississippi lime stone. A combination of triaxial and injection experiments were performed on the cores to characterize their goemechanical properties and to better understand their response to stimulation treatment. The first GEO-N2 sample (sample A) was axially loaded to a vertical stress of 10000 psi at a strain rate of 1x10-5 strains/sec while maintaining an effective confining pressure of 3500 psi and a temperature of 90 oC. Nitrogen gas was injected at a pressure of 2000 psi. Sample didn’t fail. Then the pore pressure increased to 4500 psi resulting in an effective confining pressure of 1000 psi. However the sample still did not fail due to injection. Since the intention of the test was to create the Mohr - Coulomb envelope by performing a multistage triaxial test, the deviatoric stress did not get increased to fracture the sample and sample fractured by multistage triaxial test. The triaxial-injection test performed on the second GEO-N2 sample (sample B) same as the first GEO-N2 sample with the same procedure and configurations. For the last part of the test, the intention was to fail the rock with injection. Therefore, at the moment of the turning point on the volumetric strain curve, the axial load was held constant and the sample was fractured by injecting nitrogen gas in to it. The sample temperature was 90o C. The Mississippi lime stone sample (sample C) was axially loaded to a vertical stress of 6000 psi at a strain rate of 1x10-5 strains/sec while maintaining an effective confining pressure of 2000 psi. Nitrogen gas was injected at a pressure of 2000 psi. Sample didn’t xiv fail. Then the pore pressure increased to 3300 psi resulting in an effective confining pressure of 700 psi. However the sample still did not fail due to injection. For the last part of the test, the intention was to fail the rock with injection. Therefore, at the moment of the turning point on the volumetric strain curve, the axial load was held constant and the sample was tried to be fractured by injecting nitrogen gas in to it. However it did not fractured and sample C got fractured by compression. Fluid flow was maintained across the samples throughout the experiments while stress, strain and acoustic emissions were recorded. Rock deformation and acoustic emissions data were monitored and analyzed, and the locations of events were recorded and they correlate with the fracture location in the samples. The result showed that all three samples have high value of Young’s modulus over a 40 GPA. Sample A and B experiments were conducted at elevated temperatures to investigate the rock response to thermal stresses. Heat didn’t influence the elastic properties very much in these rocks. It is estimated that higher temperatures (>300 C) would probably create this effect. And about 0.03% strain was observed in hydrostatic heating of the sample. Sample C is from an oil field which is not hot and the tests on this sample were not performed at high temperature

False Alarm Reduction in Atrial Fibrillation Screening

Early detection of AF is essential and emphasizes the significance of AF screening. However, AF detection in screening ECGs, usually recorded by handheld and portable devices, is limited because of their high susceptibility to noise. In this study, the feasibility of applying a machine learning-based quality control stage, inserted between the QRS detector and AF detector blocks, is investigated with the aim to improve AF detection. A convolutional neural network was trained to classify the detections into either true or false. False detections were excluded and an updated series of QRS complexes was fed to the AF detector. The results show that the convolutional neural network-based quality control reduces the number of false alarms by 24.8% at the cost of 1.9% decrease in sensitivity compared to AF detection without any quality control

Identification of Transient Noise to Reduce False Detections in Screening for Atrial Fibrillation

Screening for atrial fibrillation (AF) with a handheld device for recording the ECG is becoming increasingly popular. The poorer signal quality of such ECGs may lead to false detection of AF, often caused by transient noise. Consequently, the need for expert review in AF screening can become extensive. A convolutional neural network (CNN) is proposed for transient noise identification in AF detection. The network is trained using the events produced by a QRS detector, classified into either true beat detections or false detections. The CNN and a low-complexity AF detector are trained and tested using the StrokeStop I database, containing 30-s ECGs from mass screening for AF in the elderly population. Performance evaluation of the CNN-based quality control using a subset of the database resulted in sensitivity, specificity, and accuracy of 96.4, 96.9, and 96.9%, respectively. By inserting the CNN before the AF detector, the false AF detections were reduced by 22.5% without any loss in sensitivity. The results show that the number of recordings calling for expert review can be significantly reduced thanks to the identification of transient noise. The reduction of false AF detections is directly linked to the time and cost spent on expert review