Improved recording of atrial activity by modified bipolar leads derived from the 12-lead electrocardiogram.

This study investigates the use of multivariate linear regression to estimate three bipolar ECG leads from the 12-lead ECG in order to improve P-wave signal strength. The study population consisted of body surface potential maps recorded from 229 healthy subjects. P-waves were then isolated and population based transformation weights developed. A derived P-lead (measured between the right sternoclavicular joint and midway along the costal margin in line with the seventh intercostal space) demonstrated significant improvement in median P-wave root mean square (RMS) signal strength when compared to lead II (94µV vs. 76µV, p<0.001). A derived ES lead (from the EASI lead system) also showed small but significant improvement in median P-wave RMS (79µV vs. 76µV, p=0.0054). Finally, a derived modified Lewis lead did not improve median P-wave RMS when compared to lead II. However, this derived lead improved atrioventricular RMS ratio. P-wave leads derived from the 12-lead ECG can improve signal-to-noise ratio of the P-wave; this may improve the performance of detection algorithms that rely on P-wave analysis.

Fluoroscopic and electrical assessment of implantable cardioverter defibrillator leads: a prospective observational study.

BACKGROUND: Insulation defects resulting in conductor externalization (CE) have been reported in the Riata family of implantable cardioverter defibrillator (ICD) leads (St. Jude Medical, Sylmar, CA, USA). The aim of this study was to identify, prospectively, the rate of CE and outcomes following this, within a group of patients with a Riata ICD lead. METHODS: Patients with a Riata ICD lead attended for fluoroscopic screening and electrical assessment of the lead at yearly intervals between 2010 and 2012. RESULTS: One hundred and forty patients had no or borderline evidence of CE on initial assessment in 2010. These patients were prospectively followed for 3 years (304.6 patient-years). During this time, 11 patients developed definite CE, equating to an event rate of 3.6 (95% confidence intervals: 1.8-6.5) per 100 patient-years of follow-up. Of those patients developing definite CE, one patient had the ICD lead explanted (for reasons unrelated to CE) and no patients died. CE was not associated with any electrical abnormalities of the ICD lead. CONCLUSIONS: CE was observed at a rate of 3.6 per 100 patient-years of follow-up, in 140 individuals with a Riata ICD lead and no definite evidence of CE at baseline.

Fluoroscopic and electrical assessment of a series of defibrillation leads: prevalence of externalized conductors.

INTRODUCTION: Insulation defects with externalized conductors have been reported in the St. Jude Riata(®) family of defibrillation leads (St. Jude Medical, Sylmar, CA, USA). The objective of the Northern Ireland Riata(®) lead screening program was to identify insulation defects and externalized conductors by systematic fluoroscopic and electrical assessment in a prospectively defined cohort of patients. We sought to estimate the prevalence, identify risk factors, and determine the natural history of this abnormality. METHODS: All patients with a Riata(®) lead under follow-up at the Royal Victoria Hospital were invited for fluoroscopic imaging and implantable cardioverter-defibrillator lead parameter checks. Fluoroscopic images were read independently by two cardiologists and the presence of externalized conductors was classified as positive, negative, or borderline. RESULTS: One hundred and sixty-five of 212 patients with a Riata lead were evaluated by fluoroscopy and lead parameter measurements. The mean duration after implantation was 3.98+/-1.43 years. After screening 25 (15%) patients were classified as positive, 137 (83%) negative, and three (1.8%) borderline. Time since implantation (P = 0.001), presence of a single coil lead (P = 0.042), and patient age (P = 0.034) were significantly associated with externalized conductors. The observed rate of externalized conductors was 26.9% for 8-French and 4.7% for 7-French leads. No leads that were identified prospectively with externalized conductors had electrical abnormalities. Seven of 25 (28%) patients had a defective lead extracted by the end of this screening period. CONCLUSION: A significant proportion (15%) of patients with a Riata lead had an insulation breach 4 years after implantation. High-resolution fluoroscopic imaging in at least two orthogonal views is required to identify this abnormality.

WaSP-ECG: A Wave Segmentation Pretraining Toolkit for Electrocardiogram Analysis.

Introduction: Representation learning allows artificial intelligence (AI) models to learn useful features from large, unlabelled datasets. This can reduce the need for labelled data across a range of downstream tasks. It was hypothesised that wave segmentation would be a useful form of electrocardiogram (ECG) representation learning. In addition to reducing labelled data requirements, segmentation masks may provide a mechanism for explainable AI. This study details the development and evaluation of a Wave Segmentation Pretraining (WaSP) application. Materials and Methods: Pretraining: A non-AI-based ECG signal and image simulator was developed to generate ECGs and wave segmentation masks. U-Net models were trained to segment waves from synthetic ECGs. Dataset: The raw sample files from the PTB-XL dataset were downloaded. Each ECG was also plotted into an image. Fine-tuning and evaluation: A hold-out approach was used with a 60:20:20 training/validation/test set split. The encoder portions of the U-Net models were fine-tuned to classify PTB-XL ECGs for two tasks: sinus rhythm (SR) vs atrial fibrillation (AF), and myocardial infarction (MI) vs normal ECGs. The fine-tuning was repeated without pretraining. Results were compared. Explainable AI: an example pipeline combining AI-derived segmentation masks and a rule-based AF detector was developed and evaluated. Results: WaSP consistently improved model performance on downstream tasks for both ECG signals and images. The difference between non-pretrained models and models pretrained for wave segmentation was particularly marked for ECG image analysis. A selection of segmentation masks are shown. An AF detection algorithm comprising both AI and rule-based components performed less well than end-to-end AI models but its outputs are proposed to be highly explainable. An example output is shown. Conclusion: WaSP using synthetic data and labels allows AI models to learn useful features for downstream ECG analysis with real-world data. Segmentation masks provide an intermediate output that may facilitate confidence calibration in the context of end-to-end AI. It is possible to combine AI-derived segmentation masks and rule-based diagnostic classifiers for explainable ECG analysis.

3D Fabrication and Characterisation of Electrically Receptive PCL-Graphene Scaffolds for Bioengineered In Vitro Tissue Models.

Polycaprolactone (PCL) is a well-established biomaterial, offering extensive mechanical attributes along with low cost, biocompatibility, and biodegradability; however, it lacks hydrophilicity, bioactivity, and electrical conductivity. Advances in 3D fabrication technologies allow for these sought-after attributes to be incorporated into the scaffolds during fabrication. In this study, solvent-free Fused Deposition Modelling was employed to fabricate 3D scaffolds from PCL with increasing amounts of graphene (G), in the concentrations of 0.75, 1.5, 3, and 6% (w/w). The PCL+G scaffolds created were characterised physico-chemically, electrically, and biologically. Raman spectroscopy demonstrated that the scaffold outer surface contained both PCL and G, with the G component relatively uniformly distributed. Water contact angle measurement demonstrated that as the amount of G in the scaffold increases (0.75-6% w/w), hydrophobicity decreases; mean contact angle for pure PCL was recorded as 107.22 ± 9.39°, and that with 6% G (PCL+6G) as 77.56 ± 6.75°. Electrochemical Impedance Spectroscopy demonstrated a marked increase in electroactivity potential with increasing G concentration. Cell viability results indicated that even the smallest addition of G (0.75%) resulted in a significant improvement in electroactivity potential and bioactivity compared with that for pure PCL, with 1.5 and 3% exhibiting the highest statistically significant increases in cell proliferation.

Prospective Assessment of Linox Implantable Cardioverter Defibrillator Leads for Structural or Electrical Abnormalities.

INTRODUCTION: Insulation failure leading to conductor externalization (CE) of a Linox (Biotronik, Berlin, Germany) implantable cardioverter defibrillator (ICD) lead has recently been reported. The aim of this study was to assess prospectively all Linox family ICD leads implanted at our center for evidence of CE or an electrical abnormality. METHODS: All patients with a Linox family ICD lead implanted at our center, between November 2007 and March 2015, were identified and all living patients were invited to attend for fluoroscopic screening and electrical assessment of the lead. RESULTS: A total of 183 patients had a Linox family ICD lead implanted at our center. Of these, 5 patients (2.7%) had the lead extracted because of electrical failure and 2 of these leads had evidence of CE. Out of 158 living patients with a Linox family ICD lead, 111 patients attended for screening (mean age 63.1 years, 22.5% female). In this group of patients, no cases of CE or electrical abnormalities of the lead were identified. CONCLUSION: In this study evaluating 183 patients with a Linox family ICD lead implanted at a single center, 5 leads (2.7%) were explanted because of electrical failure and 2 of these leads had evidence of CE. Prospective fluoroscopic assessment of 111 Linox family ICD leads, with a mean dwell time of 31.5 months, revealed no further cases of CE.

A support vector machine for predicting defibrillation outcomes from waveform metrics.

BACKGROUND: Algorithms to predict shock success based on VF waveform metrics could significantly enhance resuscitation by optimising the timing of defibrillation. OBJECTIVE: To investigate robust methods of predicting defibrillation success in VF cardiac arrest patients, by using a support vector machine (SVM) optimisation approach. METHODS: Frequency-domain (AMSA, dominant frequency and median frequency) and time-domain (slope and RMS amplitude) VF waveform metrics were calculated in a 4.1Y window prior to defibrillation. Conventional prediction test validity of each waveform parameter was conducted and used AUC>0.6 as the criterion for inclusion as a corroborative attribute processed by the SVM classification model. The latter used a Gaussian radial-basis-function (RBF) kernel and the error penalty factor C was fixed to 1. A two-fold cross-validation resampling technique was employed. RESULTS: A total of 41 patients had 115 defibrillation instances. AMSA, slope and RMS waveform metrics performed test validation with AUC>0.6 for predicting termination of VF and return-to-organised rhythm. Predictive accuracy of the optimised SVM design for termination of VF was 81.9% (± 1.24 SD); positive and negative predictivity were respectively 84.3% (± 1.98 SD) and 77.4% (± 1.24 SD); sensitivity and specificity were 87.6% (± 2.69 SD) and 71.6% (± 9.38 SD) respectively. CONCLUSIONS: AMSA, slope and RMS were the best VF waveform frequency-time parameters predictors of termination of VF according to test validity assessment. This a priori can be used for a simplified SVM optimised design that combines the predictive attributes of these VF waveform metrics for improved prediction accuracy and generalisation performance without requiring the definition of any threshold value on waveform metrics.

An esothoracic electrode for electrophysiological studies.

A flexible polythene esothoracic electrode was passed into the stomach under light sedation. Five ring electrodes, now positioned in the lower esophagus, were used for bipolar atrial pacing and recording. Ventricular pacing was performed using a cathodic point source on the esothoracic electrode tip; the indifferent electrode (anode) was a high impedance chest pad. Parameters of atrioventricular (AV) nodal function were obtained by atrial pacing. Programmed ventricular stimulation was performed using a standard protocol. Electrophysiological parameters were subsequently determined using an endocardial approach. There was close correlation between measurements of AV node function in 48 subjects: AV Wenckebach Cycle Length (AVWCL) r(2) =.97. The degree of agreement was estimated by the mean difference delta and standard deviation of the difference sigma (AVWCL sigma = 7 ms, delta = 16 ms). Programmed ventricular stimulation was performed in 15 subjects with known or suspected ventricular tachyarrhythmias. In subjects where ventricular tachycardia was induced by using both esothoracic and endocardial approaches, the rate, morphology, and haemodynamic consequences were similar. In several cases, ventricular tachycardia was pace-terminable using overdrive esothoracic ventricular pacing. Electrophysiological parameters determined with this electrode were similar to those obtained with endocardial stimulation.