Malgorzata Fereniec

Risk assessment of ventricular arrhythmia using new parameters based on high resolution body surface potential mapping.

Summary Background The effective screening of myocardial infarction (MI) patients threatened by ventricular tachycardia (VT) is an important issue in clinical practice, especially in the process of implantable cardioverter-defibrillator (ICD) therapy recommendation. This study proposes new parameters describing depolarization and repolarization inhomogeneity in high resolution body surface potential maps (HR BSPM) to identify MI patients threatened by VT. Material/Methods High resolution ECGs were recorded from 64 surface leads. Time-averaged HR BSPMs were used. Several parameters for arrhythmia risk assessment were calculated in 2 groups of MI patients: those with and without documented VT. Additionally, a control group of healthy subjects was studied. To assess the risk of VT, the following parameters were proposed: correlation coefficient between STT and QRST integral maps (STT_QRST_CORR), departure index of absolute value of STT integral map (STT_DI), and departure index of absolute value of T-wave shape index (TSI_DI). These new parameters were compared to known parameters: QRS width, QT interval, QT dispersion, Tpeak-Tend interval, total cosines between QRS complex and T wave, and non-dipolar content of QRST integral maps. Results STT_DI, TSI_DI, STT_QRST_CORR, QRS width, and QT interval parameters were statistically significant (p≤0.05) in arrhythmia risk assessment. The highest sensitivity was found for the STT_DI parameter (0.77) and the highest specificity for TSI_DI (0.79). Conclusions Arrhythmia risk is demonstrated by both abnormal spatial distribution of the repolarization phase and changed relationship between depolarization and repolarization phases, as well as their prolongation. The proposed new parameters might be applied for risk stratification of cardiac arrhythmia.

Body Surface ECG Signal Shape Dispersion

The spatial distribution of the shape of the electrocardiography (ECG) waves obtained by body surface potential mapping (BSPM) is studied, using a 64-channel high-resolution ECG system. The index associated to each lead is the shape difference between its ECG wave and a reference computed taking into account all the leads on the same column. The reference is either a selected real wave or a synthetic signal computed by integral shape averaging (ISA). Better results are obtained with the ISA signal using the distribution function method (DFM) for computing the shape difference. The spatial dispersion of ECG waves is showed to allow the separation of patients after myocardial infarction (MI) from healthy subjects. In addition, the reference signal position for each column is computed. The path linking these positions appears as an invariant, i.e., it is independent of the subject and the ECG waveThe spatial distribution of the shape of the ECG waves obtained by Body Surface Potential Mapping (BSPM) is studied, using a 64-channel High Resolution ECG system. The index associated to each lead is the shape difference between its ECG wave and a reference computed taking into account all the leads on the same column. The reference is either a real averaged wave or a synthetic signal computed by Integral Shape Averaging (ISA). Better results are obtained with the ISA signal using the Distribution Function Method (DFM) for computing the shape difference. The spatial dispersion of ECG waves is showed to allow the separation of patients after Myocardial Infarction (MI) from healthy subjects. In addition, the reference signal position for each column is computed. The path linking these positions appears as an invariant, i.e., it is independent of the subject and the ECG wave.

Spatial distribution of T-wave alternans

The aim of the study was a selection of best ECG leads to get the significant T-wave alternans signal (TWA). The group of 16 patients with implantable cardioverter-defibrillator (ICD) was examined. The 64 lead ECG system was used. Three lead sets were analyzed: 64 BSPM lead set, orthogonal lead set (XYZ) and standard 12 lead set. Patients were divided into two groups: TWA positive (TWA(+)) 5 patients and TWA negative (TWA(-)) 11 patients. In TWA(+) group mean alternans ratio was equal 5.4 (SD 8.09) and in TWA(-) group 0.73 (SD 0.26). Both standard ECG leads and XYZ leads are less sensitive to TWA than specially selected leads from 64 lead set.

Relation between depolarization and repolarization phases in body surface QRST integral map

The aim of the study was to assess the relations between QRST and STT, QRS integral maps in three groups: healthy volunteers, patients without arrhythmia and patients with implanted cardioverter-defibrillator (ICD). The obtained results showed that the mean correlation coefficient between STT and QRST integral maps was highest in the group of healthy subjects while the mean correlation coefficient between QRS and QRST integral maps was lowest in the same group of subjects. The relation of depolarization phase with repolarization phase and the influence of depolarization sequence on repolarization sequence is noticeably disrupted in patients with impaired systolic function. In such cases the QRST integral maps seems to reflect depolarization-repolarization disorder rather than only repolarization dispersion.

An Analysis of the U‐Wave and Its Relation to the T‐Wave in Body Surface Potential Maps for Healthy Subjects and MI Patients

The aim of this study was to analyze the U‐wave morphology and its relation to the T‐wave in one group of healthy subjects and in two groups of myocardial infarction (MI) patients—with and without ventricular tachycardia (VT) episodes. The context of the U‐wave origin was also discussed and the U‐wave as a potential marker of VT was investigated.

Spatial and temporal variability of ECG waveforms observed in sinus rhythm and during atrio-ventricular stimulation in a patient with implanted ICD: case study

Measurements of surface HR ECG were carried out in an unshielded environment. Signals were acquired from one patient with implanted ICD (implantable cardioverter-defibrillator) during sinus rhythm and during atrial and ventricular stimulation. QRS, STT, QRST deflection areas and T wave alternans were studied. Significant differences between two ventricular activation sequences were found in spatial distributions of QRS and STT integrals in comparison to QRST integral maps, of which spatial distribution was almost independent of activation order. Quantification of differences was done with the use of principal component analysis and correlation coefficient between deflection areas of waveforms. Departure maps were also studied. Beat to beat variations of QRS, STT and QRST deflection areas were calculated and compared to microvolt T-wave alternans test results