Velocity tracking of cardiac vector loops to identify signs of stress-induced ischaemia.

Coronary artery disease (CAD) is among the leading causes of death worldwide. Initial studies require an electrocardiogram stress test often followed by cardiac imaging procedures. However, conventional indices still show insufficient diagnostic performance. We propose quaternion methods to evaluate abnormal alterations during ventricular depolarization and repolarization. Assessment was conducted during a Bruce protocol treadmill stress test and after the end of the exercise. We developed an algorithm to automatically determine the beginning and end of exercise and then, computed the angular and linear velocities. Statistical analysis for feature selection and classification between ischaemic and non-ischaemic patients was used. The most significant markers were maximum linear velocity during ventricular depolarization (p < 5E-9) and maximum angular velocity during the second half of the repolarization loop (p < 5E-16). The latter reached sensitivity / specificity pair of 78 / 92 (AUC 0.89). A linear classifier showed a trend of reduction in cardiac vector velocity in at-risk patients after the end of exercise. The sensitivity / specificity pair reached was 86 / 100. Trajectory deviations of depolarization / repolarization loops that result from ischaemia effects, could be responsible for the observed reduction in dynamic changes during exercise. Further studies could provide non-invasive complementary tools to detect CAD risk. Graphical abstract This data is mandatory, please provide.

Dynamic features of cardiac vector as alternative markers of drug-induced spatial dispersion.

INTRODUCTION: The abnormal amplification of ventricular repolarization dispersion (VRD) has long been linked to proarrhythmia risk. Recently, the measure of VRD through electrocardiogram intervals has been strongly questioned. The search for an efficient and non-invasive surrogate marker of drug-induced dispersion effects constitute an urgent research challenge. METHODS: Herein, drug-induced ventricular dispersion is generated by d-Sotalol supply in an In-vitro rabbit heart model. A cilindrical chamber simulates the thorax and a multi-electrode net is used to obtain spatial electrocardiographic signals. Cardiac vector dynamics is captured by novel velocity cardiomarkers obtained by quaternion methods. Through statistical analysis and machine learning technics, we compute potential dispersion markers that could define proarrhythmic risk. RESULTS: The cardiomarkers with the greatest statistical significance, both obtained from the electrical cardiac vector, were: the QTω, which is the difference between first and last maxima of angular velocity and λ21vT, the roundness of linear velocity. When comparing with the performance of the current standards (89%), this pair was able to correctly separate 21 out of 22 experiments achieving a performance of 95%. Moreover, the QTω computes in a much more robust basis the QT interval, the current index for drug regulation. DISCUSSION: These velocity markers circumvent the problems of accuratelly finding the fiducial points such as the always tricky T-wave end. Given the high performance they achieved, it is provided a promising outcome for future applications to the detection of anomalous changes of heterogeneity that may be useful for the purposes of torsadogenic toxicity studies.

Biomarkers of pre-existing risk of Torsade de Pointes under Sotalol treatment.

INTRODUCTION: Antiarrhythmic drugs therapies are currently going through a turning point. The high risk that exists during the treatments has led to an ongoing search for new non-invasive toxicity risk biomarkers. METHODS: We propose the use of spatial biomarkers obtained through the quaternion algebra, evaluating the dynamics of the cardiac electrical vector in a non-invasive way in order to detect abnormal changes in ventricular heterogeneity. In groups of patients with and without history of Torsade de Pointes undergoing a Sotalol challenge, we compute the radius and the linear and angular velocities of QRS complex and T-wave loops. From these signals we extract significant features in order to compute a risk patient classifier. RESULTS: Using machine learning techniques and statistical analysis, the combinations of few indices reach a pair of sensitivity/specificity of 100%/100% when separating patients with arrhythmogenic substrate. Several biomarkers not only measure drug-induced changes significantly but also observe differences in at-risk patients outperforming current standards. DISCUSSION: Alternative biomarkers were able to describe pre-existing risk of patients. Given the high levels of significance and performance, these results could contribute to a better understanding of the torsadogenic substrate and to the safe development of drug therapies.

Classification of ischemic and non-ischemic cardiac events in Holter recordings based on the continuous wavelet transform.

Holter recordings are widely used to detect cardiac events that occur transiently, such as ischemic events. Much effort has been made to detect early ischemia, thus preventing myocardial infarction. However, after detection, classification of ischemia has still not been fully solved. The main difficulty relies on the false positives produced because of non-ischemic events, such as changes in the heart rate, the intraventricular conduction or the cardiac electrical axis. In this work, the classification of ischemic and non-ischemic events from the long-term ST database has been improved, using novel spectral parameters based on the continuous wavelet transform (CWT) together with temporal parameters (such as ST level and slope, T wave width and peak, R wave peak, QRS complex width). This was achieved by using a nearest neighbour classifier of six neighbours. Results indicated a sensitivity and specificity of 84.1% and 92.9% between ischemic and non-ischemic events, respectively, resulting a 10% increase of the sensitivity found in the literature. Extracted features based on the CWT applied on the ECG in the frequency band 0.5-4 Hz provided a substantial improvement in classifying ischemic and non-ischemic events, when comparing with the same classifier using only temporal parameters. Graphical Abstract In this work it is improved the classification of ischemic and non-ischemic events. The main difficulty of ischemic detectors relies on the false positives produced because of non-ischemic events. After a preprocessing stage, temporal and spectral parameters are extracted from events of the Long Term ST Database. The novel parameters proposed in this work are extracted from the Continuous Wavelet Transform. A nearest Neighbor Classifier is used, obtaining a sensitivity and specificity of 84.1% and 92.9%, respectively.

Electrocardiogram Delineation in a Wistar Rat Experimental Model.

BACKGROUND AND OBJECTIVES: The extensive use of electrocardiogram (ECG) recordings during experimental protocols using small rodents requires an automatic delineation technique in the ECG with high performance. It has been shown that the wavelet transform (WT) based ECG delineator is a suitable tool to delineate electrocardiographic waveforms. The aim of this work is to implement and evaluate the ECG waves delineation in Wistar rats applying WT. We also describe the ECG signal of the Wistar rats giving the characteristics of its spectrum among other useful information. METHODS: We evaluated a delineator based on WT in a Wistar rat electrocardiograms database which was annotated manually by experienced observers. RESULTS: The delineation showed an "overall performance" such as sensitivity and a positive predictive value of 99.2% and 83.9% for P-wave, 100% and 99.9% for QRS complex, and 100% and 99.8% for T-wave, respectively. We also compared temporal analysis based ECG delineator with the WT based ECG delineator in RR interval, QRS duration, QT interval, and T-wave peak-to-end duration. The results showed that WT outperforms the temporal delineation technique in all parameters analyzed. CONCLUSIONS: Finally, we propose a WT based ECG delineator as a methodology to implement in a wide diversity of experimental ECG analyses using Wistar rats.

Quaternion-based study of angular velocity of the cardiac vector during myocardial ischaemia.

BACKGROUND: Early detection of acute ischaemia through non-invasive methods remains a challenge in health research. Ischaemic condition caused by a decrease in the blood supply in a cardiac region induces hypoxia and metabolic abnormalities that contribute to the electrical instability of the heart and to the development of slow conduction in damaged tissue. METHODS: Herein, a percutaneous transluminal coronary angiography (PTCA) is considered as a model of supply ischaemia. We use the concept of quaternion to develop a robust method for assessing the angular velocity of cardiac vector in the orthogonal XYZ leads obtained from 92 patients undergoing the PTCA procedure. The maxima of angular velocity in both ventricular depolarization and repolarization are combined with traditional linear velocity indexes in order to obtain a detector of ischaemic episodes (Ischaemia Detector, ID). RESULTS: ID achieves 98%/100% of sensitivity/specificity when differentiating healthy subjects from patients with early ischaemia. Furthermore, it also shows high accuracy when the comparison is made between ischaemic subjects and patients with different non-ischaemic pathologic ST-deviations which are known to cause false positives, reaching 95%/98% of sensitivity/specificity. Moreover, the study of significant reductions (p<0.001) of angular velocity components allows extraction of distinct ischaemic common features which are useful for analyzing the dependence of vectorcardiogram signal on each site of occlusion. The sensitivity of injury location reaches values of 88% (RCA), 87% (LAD) and 80% (LCx). CONCLUSIONS: The high performance of the proposed method establishes a promising outcome for application in computerized assistance in clinical practice.

Novel technique for ST-T interval characterization in patients with acute myocardial ischemia.

BACKGROUND: The novel signal processing techniques have allowed and improved the use of vectorcardiography (VCG) to diagnose and characterize myocardial ischemia. Herein, we studied vectorcardiographic dynamic changes of ventricular repolarization in 80 patients before (control) and during Percutaneous Transluminal Coronary Angioplasty (PTCA). METHODS: We propose four vectorcardiographic ST-T parameters, i.e., (a) ST Vector Magnitude Area (aSTVM); (b) T-wave Vector Magnitude Area (aTVM); (c) ST-T Vector Magnitude Difference (ST-TVD), and (d) T-wave Vector Magnitude Difference (TVD). For comparison, the conventional ST-Change Vector Magnitude (STCVM) and Spatial Ventricular Gradient (SVG) were also calculated. RESULTS: Our results indicate that several vectorcardiographic parameters show significant differences (p-value<0.05) before starting and during PTCA. Statistical minute-by-minute PTCA comparison against the control situation showed that ischemic monitoring reached a sensitivity=90.5% and a specificity=92.6% at the 5th minute of the PTCA, when aSTVM and ST-TVD were used as classifiers. CONCLUSIONS: We conclude that the sensitivity and specificity for acute ischemia monitoring could be increased with the use of only two vectorcardiographic parameters. Hence, the proposed technique based on vectorcardiography could be used in addition to the conventional ST-T analysis for better monitoring of ischemic patients.

Evaluation of ventricular repolarization dispersion during acute myocardial ischemia: spatial and temporal ECG indices.

In this work, we studied the evolution of different electrocardiogram (ECG) indices of ventricular repolarization dispersion (VRD) during acute transmural myocardial ischemia in 95 patients undergoing percutaneous coronary intervention (PCI). We studied both temporal indices of VRD (T-VRD), based on the time intervals of the ECG wave, and spatial indices of VRD (S-VRD), based on the eigenvalues of the spatial correlation matrix of the ECG. The T-wave peak-to-end interval I(TPE) index showed statistically significant differences during left anterior descending artery and right coronary artery (RCA) occlusion for almost the complete time course of the PCI procedure with respect to the control recording. Regarding S-VRD indices, we observed statistically significant increases in the ratio of second to the first eigenvalue I(T21), the ratio of the third to the first eigenvalue I(T31) and the T-wave residuum I(TWR) during RCA occlusions. We also found a statistically significant increase in the I(T31) during left circumflex artery occlusions. To evaluate the evolution of VRD indices during acute ischemia, we calculated the relative change parameter R(I) for each index I. Maximal relative changes (R(I)) during acute ischemia were found for the S-VRD indices I(T21), the first eigenvalue I(λ1) and the second eigenvalue I(λ2), with changes 64, 57 and 52 times their baseline range of variation during the control recording, respectively. Also, we found that relative changes with respect to the baseline were higher in patients with T-wave alternans (TWA) than in those without TWA. In conclusion, results suggest that I(TPE) as well as I(T21), I(T31) and I(TWR) are very responsive to dispersion changes induced by ischemia, but with a behavior which very much depends on the occluded artery.

Beat-to-beat repolarization variability measured by T wave spectral variance index in chronic infarcted animals.

BACKGROUND: Recent experimental and clinical studies have shown that beat-to-beat variability of repolarization morphology is associated with an increased risk for developing malignant ventricular arrhythmias. However, few data exist on the relationship between beat-to-beat repolarization variability and myocardial infarction itself. METHODS AND RESULTS: In the present work we tested the algorithm of T wave spectral variance (TWSV) using the two dimension fast Fourier transform, in an animal model of myocardial infarction to extend the evidences that support the existence of beat-to-beat alteration in repolarization during the chronic stage of myocardial infarction. Thirty-four New Zealand rabbits were included in the study and divided in two groups. Group I (N = 24) exposed to surgical ligation of the left anterior descendent coronary artery. Group II (N = 10) sham operated animals. The TWSV index was calculated before and after 15 and 45 days of surgery. Both groups showed significant increments in TWSV after 15 days postsurgery. However, while the sham animals return to its control value, the infarcted group exhibited values of the TWSV index that remains significantly high after 45 days of surgery, with a mean increment of 28.7% (P < 0.05 against sham). Moreover, when the infarcted group was qualitatively divided in three subgroups, according to its infarction areas, a trend was found in the correlation between the magnitude of the infarcted area and the TWSV index. CONCLUSION: This noninvasive measure confirms the presence of temporal repolarization variability associated with chronic myocardial infarction and further contributes to identify the infarcted animals.