Juan Pablo Martínez

• Ph.D.
• Professor at University of Zaragoza

Objectives: Elevated heterogeneity in ventricular repolarization can promote malignant ventricular arrhythmias. During exercise, distinct ventricular cells may present different repolarization adaptation to heart-rate (HR) changes potentially increasing ventricular repolarization dispersion. An electrocar-diographic descriptor of the temporal adapt...

Background Ventricular arrhythmias (VA) risk stratification tools in individuals without known cardiovascular disease are still insufficient. Previous studies have used convolutional neural networks (CNN) to classify VA by the end of an established follow-up period using the electrocardiogram (ECG), showing a moderate performance (area under the cu...

En este trabajo evaluamos la habilidad del índice de variación morfológica basado en la deformación temporal, dw, en la clasificación de pacientes con síndrome de QT largo (SQTL) e individuos de control sanos (GC), así como pacientes con SQTL que experimentaron síncope (SQTL-S) y los que no (SQTL-NS). También se estimaron con fines comparativos el...

El objetivo de este trabajo es evaluar si un modelo de aprendizaje semisupervisado mejora el rendimiento de uno supervisado en el diagnóstico de fibrilación auricular paroxística, una tarea en la que los datos de entrenamiento son escasos y la proporción de casos está desequilibrada.

bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Background: Slower adaptation of the QT interval to sudden changes in heart rate has been identified as a risk marker of ventricular arrhythmia. The gradual changes observed in exercise stress testing facilitates the estimation of the QT-RR adaptation t...

italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Background: The T-peak-to-T-end ( $\mathrm{T}_{pe}$ ) interval has shown potential in predicting ventricular arrhythmic risk. It is an appealing index to be measured during ischemia since it is less influenced by ST-segment changes than the early part...

Background Life-threatening ventricular arrhythmias (LTVA) are a leading cause of mortality, but early identification of high-risk individuals remains a major challenge. An ECG index, TMV (T-wave morphology variations), predicts LTVA in 51,794 individuals without known cardiovascular disease from the UK Biobank (UKB) within a 10-year follow up (coh...

Variations in the dispersion of ventricular repolarization can be quantified by T-wave time-warping based index, $d_w$ . However, the early phase of the T-wave can be affected by ST-segment changes during ischemia. We hypothesized that restricting $d_{w}$ to the T-wave peak-to-end ( $T_{pe}$ ) would circumvent this limitation while still quant...

La dispersión de la repolarización ventricular reflejada en el intervalo Tpe ha mostrado potencial en la predicción del riesgo arrítmico, y no está expuesta a errores de anotación en la determinación del inicio de la onda T como consecuencia de la elevación del ST. Utilizamos el índice de variación morfológica basado en time-warping propuesto por R...

The present paper proposes an ECG simulator that advances modeling of arrhythmias and noise by introducing time-varying signal characteristics. The simulator is built around a discrete-time Markov chain model for simulating atrial and ventricular arrhythmias of particular relevance when analyzing atrial fibrillation (AF). Each state is associated w...

Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): TED2021-130459B-I00 LMP94_21 Introduction Right ventricular pacing (RVP) has been the treatment of choice for patients with atrioventricular block and sinus node disease for the last decades . It is well known that RVP ventricular may...

The adaptation lag of the QT interval after heart rate (HR) has been proposed as an arrhythmic risk marker. Most studies have quantified the QT adaptation lag in response to abrupt, step-like changes in HR induced by atrial pacing, in response to tilt test or during ambulatory recordings. Recent studies have introduced novel methods to quantify the...

Atrial fibrosis plays a key role in the initiation and progression of atrial fibrillation (AF). Atrial fibrosis is typically identified by a peak-to-peak amplitude of bipolar electrograms (b-EGMs) lower than 0.5 mV, which may be considered as ablation targets. Nevertheless, this approach disregards signal spatiotemporal information and b-EGM sensit...

Objective: T-wave alternans (TWA) manifests as beat-to-beat fluctuations of T-wave morphology on the electrocardiogram (ECG), with physiological bases not fully understood. Using a biophysical model of the ECG, we demonstrate and give explicit relations that TWA depends on the i) spatial covariance between myocytes' repolarization time and alterna...

Atrial fibrillation (AF) is the most frequent arrhythmia in clinical practice. It usually initiates as a paroxysmal activity (PxAF), with the subject having sinus rhythm, with interleaved AF episodes. The objective of the study is to evaluate the observations made by Pyotr Platonov, who hypothesized that slower conduction in the atria and the prese...

Background: T-wave (TW) morphology indices based on time-warping ( dw) have shown significant cardiovascular risk stratification value. However, errors in the location of TW boundaries may impact their prognostic power. Our aim was to test the hypothesis that a weighted time-warping function (WF) would reduce the sensitivity of dw to these errors...

We aim to provide a critical appraisal of basic concepts underlying signal recording and processing technologies applied for (i) atrial fibrillation (AF) mapping to unravel AF mechanisms and/or identifying target sites for AF therapy and (ii) AF detection, to optimize usage of technologies, stimulate research aimed at closing knowledge gaps, and de...

Resumen La morfología de la onda T (TW) se ha investigado para desarrollar marcadores de predicción de riesgo arrítmico específicos como , que cuantifica el nivel de "warping" necesario para alinear temporalmente una TW con respecto a otra de referencia a diferente ritmo cardiaco. Sin embargo, los errores de delineación de los límites de la TW pued...

Se pretende mejorar la detección del final de la onda T (Te) de la señal de electrocardiograma (ECG) grabada durante prueba de esfuerzo. Así, los puntos Te se calculan en la primera derivación transformada de los métodos PCA y piCA, y se comparan con losextraídos directamente del ECG.

La fibrosis auricular representa un papel clave en la patogenia de la fibrilación auricular, y es un factor importante para el guiado de procedimientos de ablación con catéter. Se consideran fibróticas las áreas cuyos electrogramas bipolares (b-EGMs) presentan una amplitud pico-a-pico inferior a 0.5 mV [1]. Sin embargo, la amplitud de dichas señale...

The two most common modes of death among chronic heart failure (CHF) patients are sudden cardiac death (SCD) and pump failure death (PFD). Periodic repolarization dynamics (PRD) quantifies low-frequency oscillations in the T wave vector of the electrocardiogram (ECG) and has been postulated to reflect sympathetic modulation of ventricular repolariz...

Introduction: The omnipolar electrogram method was recently proposed to try to generate orientation-independent electrograms. It estimates the electric field from the bipolar electrograms of a clique, under the assumption of locally plane and homogeneous propagation. The local electric field evolution over time describes a loop trajectory from whic...

Objective The aim of this study is to compare the performance of two electrocardiogram (ECG) lead-space reduction (LSR) techniques in generating a transformed ECG lead from which T-wave morphology markers can be reliably derived to non-invasively monitor blood potassium concentration ([K+]) in end-stage renal disease (ESRD) patients undergoing hemo...

Background: End-stage renal disease patients undergoing hemodialysis (ESRD-HD) therapy are highly susceptible to malignant ventricular arrhythmias caused by undetected potassium concentration ([K+]) variations (Δ[K+]) out of normal ranges. Therefore, a reliable method for continuous, noninvasive monitoring of [K+] is crucial. The morphology of the...

Background Atrial fibrillation (AF) is the most common supraventricular arrhythmia characterized by disorganized atrial electrical activity, maintained by localized arrhythmogenic atrial drivers. Pulmonary vein isolation (PVI) allows to exclude PV-related drivers. However, PVI is less effective in patients with additional extra-PV arrhythmogenic dr...

We investigated the ability of time-warping-based ECG-derived markers of T-wave morphology changes in time (dw) and amplitude (da), as well as their non-linear components (dwNL and daNL), and the heart rate corrected counterpart (dw,c), to monitor potassium concentration ([K+]) changes (Δ[K+]) in end-stage renal disease (ESRD) patients undergoing h...

Background: End-stage renal disease (ESRD) patients undergoing hemodyalisis therapy (HD) experience blood potassium ([K + ]) variations that are reflected on the T-wave (TW) morphology. Methods: We evaluated the performance of different lead space reduction (LSR) methods: principal component analysis (PCA), maximising the TW energy, and two derived...

Este trabajo evalúa la capacidad del índice Periodic Repolarization Dynamics (PRD) para predecir el riesgo de sufrir muerte súbita cardíaca (MSC) o muerte por fallo de bomba (MFB) en pacientes con insuficiencia cardíaca crónica (ICC).

En este trabajo se proponen marcadores no invasivos para estratificar pacientes según su riesgo de sufrir arritmias ventriculares que pueden desencadenar en muerte súbita cardiaca. Estos marcadores se basan en la respuesta del intervalo QT del ECG durante la prueba de esfuerzo, donde los cambios del ritmo cardiaco tienen un rango mayor de variación...

Atrial fibrillation (AF) is the most frequent irregular heart rhythm due to disorganized atrial electrical activity, often sustained by rotational drivers called rotors. The non-invasive localization of AF drivers can lead to improved personalized ablation strategy, suggesting pulmonary vein (PV) isolation or more complex extra-PV ablation procedur...

Atrial fibrillation (AF) is an irregular heart rhythm due to disorganized atrial electrical activity, often sustained by rotational drivers called rotors. In the present work, we sought to characterize and discriminate whether simulated single stable rotors are located in the pulmonary veins (PVs) or not, only by using non-invasive signals (i.e., t...

Background: Voltage mapping allows identifying the arrhythmogenic substrate during scar-related ventricular arrhythmia (VA) ablation procedures. Slow conducting channels (SCCs), defined by the presence of electrogram (EGM) signals with delayed components (EGM-DC), are responsible for sustaining VAs and constitute potential ablation targets. Howeve...

Ventricular arrhythmias and sudden cardiac death during long-term space missions are a major concern for space agencies. Long-duration spaceflight and its ground-based analog head-down bed rest (HDBR) have been reported to markedly alter autonomic and cardiac functioning, particularly affecting ventricular repolarization of the electrocardiogram (E...

Objective: To develop and evaluate an algorithm for the selection of the best performing QRS detections from multiple algorithms and ECG leads. Approach: The detections produced by several publicly available single-lead QRS detectors are segmented in 20 seconds consecutive windows. Then a statistical model is trained to estimate a quality metric...

Objective: To assess the effects of different durations of simulated microgravity exposure on ventricular repolarization (VR) in terms of T-wave alternans (TWA) as well as to test whether an increase in VR heterogeneity could be detected once normal gravity was restored. Approach: A total of 63 healthy volunteers were recruited in several head-d...

Patients with left bundle branch block (LBBB) are known to have a good clinical response to cardiac resynchronization therapy. However, the high number of false positive diagnosis obtained with the conventional LBBB criteria limits the effectiveness of this therapy, which has yielded to the definition of new stricter criteria. They require prolonge...

Chronic heart failure (CHF) represents one of the major public health problems that often end in sudden cardiac death (SCD). Atrial fibrillation (AF) is associated with an increased risk of SCD but nowadays there is no non-invasive method that accurately predicts that risk. The recently developed T-wave morphology restitution (TMR) index showed its...

Objective: Atrial fibrillation (AF) rhythm gives rise to an irregular response in ventricular activity, preventing the use of standard ECG-derived risk markers based on ventricular repolarization heterogeneity under this particular condition. In this study we proposed new indices to quantify repolarization variations in AF patients, assessing thei...

Widely developed for clinical screening, electrocardiogram (ECG) recordings capture the cardiac electrical activity from the body surface. ECG analysis can therefore be a crucial first step to help diagnose, understand and predict cardiovascular disorders responsible for 30% of deaths worldwide. Computational techniques, and more specifically machi...

Monitoring of ventricular premature beats (VPBs), being abundant in hemodialysis patients, can provide information on cardiovascular instability and electrolyte imbalance. In this paper, we describe a method for VPB detection which explores the signals acquired from the arterial and the venous pressure sensors, located in the extracorporeal blood c...

The aim of the Regional dossiers series is to provide a concise description of European minority languages in education. Aspects that are addressed include features of the education system, recent educational policies, main actors, legal arrangements and support structures, as well as quantitative aspects such as the number of schools, teachers, pu...

Background Sudden cardiac death (SCD) and pump failure death (PFD) are common endpoints in chronic heart failure (CHF) patients, but prevention strategies are different. Currently used tools to specifically predict these endpoints are limited. We developed risk models to specifically assess SCD and PFD risk in CHF by combining ECG markers and clini...

Construction of the models. (DOCX)

Univariable predictors of SCD in both reduced and preserved LVEF populations. (DOCX)

Multivariable predictors of SCD in both reduced and preserved LVEF populations. (DOCX)

Clinical and ECG data. (XLSX)

Definition of the dichotomized variables used to build SCD and PFD risk models. (DOCX)

Univariable predictors of PFD in both reduced and preserved LVEF populations. (DOCX)

Multivariable predictors of PFD in both reduced and preserved LVEF populations. (DOCX)

Purpose Activation mapping is used to guide ablation of idiopathic outflow tract ventricular arrhythmias (OTVAs). Isochronal activation maps help to predict the site of origin (SOO): left vs right outflow tract (OT). We evaluate an algorithm for automatic activation mapping based on the onset of the bipolar electrogram (EGM) signal for predicting t...

Background: Voltage mapping is useful in identifying the arrhythmogenic substrate in post-myocardial infarction (MI) ventricular arrhythmias (VAs). Slow conducting channels (CCs) are small bundles of viable myocardium embedded within the scar that allow reentry and promote VAs. Slow CCs elimination relies in the manual identification of them and ab...

Objective: We proposed and evaluated a method for correcting possible phase shifts provoked by the presence of ventricular premature contractions (VPCs) for a better assessment of T-wave alternans (TWA). Methods: First, we synthesized ECG signals with artificial TWA in the presence of different noise sources. Then, we assessed the prognostic value...

Objective: The aim of this work was to evaluate the potential changes in the ballistocardiogram (BCG) signal induced by different respiratory patterns and posture, by using the dynamic time warping (DTW) technique. Approach: BCG signals were recorded in a group of 20 healthy volunteers, simultaneously to the ECG. Two recordings, one in supine (S...

Objective: This study introduces a predictability framework based on the concept of Granger causality (GC), in order to analyze the activity and interactions between different intracardiac sites during atrial fibrillation (AF). Methods: GC-based interactions were studied using a three-electrode analysis scheme with multi-variate autoregressive m...

Background Patients with chronic heart failure are at high risk of sudden cardiac death (SCD). Increased dispersion of repolarization restitution has been associated with SCD, and we hypothesize that this should be reflected in the morphology of the T‐wave and its variations with heart rate. The aim of this study is to propose an electrocardiogram...