Beat-to-beat interplay of heart rate, ventricular depolarization, and repolarization.

To improve malignant arrhythmia risk stratification, the causal and random components of spatiotemporal dynamics of heart rate (RR distances), ventricular depolarization sequence, and repolarization disparity were studied based on body surface potential map records taken for 5 minutes, in resting, supine position on 14 healthy subjects (age range, 20-65 years) and on 6 arrhythmia patients (age range, 59-70 years). Beat-to-beat QRS and QRST integral maps, Karhunen-Loève (KL) coefficients, RR, and nondipolarity index time series were computed. Tight relationship was found between RR and QRS integrals in healthy subjects with less association in arrhythmia patients. Tight KL-domain multiple linear association (r(2) > 0.72) was found between the QRS and QRST integral dynamics (ie, depolarization sequence and repolarization disparity). Beat-to-beat probability of the generation of significant nondipolarity index spikes was proportional to the QRST KL-component standard deviations (SD(i)) and inversely proportional with the mean dipolar KL components (M(i)) of the average QRST integral map.

Importance of body surface potential field representation fidelity: analysis of beat-to-beat repolarization measurements.

OBJECTIVE: According to previous studies, the complex substrate of malignant arrhythmias needs a detailed spatio-temporal noninvasive characterization of low-amplitude dynamic changes in beat-to-beat cardiac repolarization. METHODS: Body surface potential map (BSPM) records were taken on 14 healthy male and female subjects (age 20-80 years) and on 6 ventricular arrhythmia patients, 4 of them with implanted cardioverter defibrillators (ICD). Records were taken continuously, for 5 minutes, in resting, supine position. Beat-to-beat QRST integral maps, Karhunen-Loéve coefficient time-series (KLi, i=1-12), RR and nondipolarity index (NDI) time-series were computed. RESULTS: The first order statistical properties of the spatio-temporal variability of subsequent QRST integral maps were characterized by the box and whiskers plot of their KLi components. The SD2/M2 (KLi amplitude variance/mean signal energy) values of the QRST integral maps in the normal group ranged between 0.0057 and 0.008 (i.e. 0.075=or

Noninvasive detection of repolarization changes in the heart.

OBJECTIVE: Previously reported inverse method based on dipolar representation of differences in QRST integral maps with and without manifestation of local repolarization changes has shown the ability to identify small areas in the myocardium responsible for these changes in a group of patients with coronary artery diseases underwent revascularization. The aim of this study was to verify this approach on a group of 4 healthy persons and a group of 7 patients suffering from effort angina pectoris. METHODS: Changes in QRST integral maps after nitroglycerine sublingual application were examined and single dipole best representing the difference QRST integral map was inversely computed. RESULTS: After attempted compensation of heart rate variations, changes in QRST integral maps greater than expected intra - individual variability (over 15%) were detected in 4 persons. Obtained difference integral maps could be sufficiently approximated by maps generated by single current dipole only in 2 persons with relative root mean square (rms) error less than 35%; in the rest of subjects relative rms error of the dipolar map approximation was greater than 50%. CONCLUSION: Results suggest that small repolarization changes might be detectable after nitroglycerine test, however this test did not induce detectable changes in some patients with effort angina pectoris.

The use of the SPSA method in ECG analysis.

The classification, monitoring, and compression of electrocardiogram (ECG) signals recorded of a single patient over a relatively long period of time is considered. The particular application we have in mind is high-resolution ECG analysis, such as late potential analysis, morphology changes in QRS during arrythmias, T-wave alternants, or the study of drug effects on ventricular activation. We propose to apply a modification of a classical method of cluster analysis or vector quantization. The novelty of our approach is that we use a new distortion measure to quantify the distance of two ECG cycles, and the class-distortion measure is defined using a min-max criterion. The new class-distortion-measure is much more sensitive to outliers than the usual distortion measures using average-distance. The price of this practical advantage is that computational complexity is significantly increased. The resulting nonsmooth optimization problem is solved by an adapted version of the simultaneous perturbation stochastic approximation (SPSA) method of. The main idea is to generate a smooth approximation by a randomization procedure. The viability of the method is demonstrated on both simulated and real data. An experimental comparison with the widely used correlation method is given on real data.

Extraction of intrinsic timing features of cardiac activation from body surface potential maps.

According to previous modeling studies--propagation of depolarizing wave fronts--consists of subintervals, each characterized by a smooth progression of waves through the myocardium. At the onset and end of these intervals, abrupt changes occur in the 3D pattern of activation waves (e.g. at the time of the collision of activation waves with other waves, obstacles or unexcitable myocardium and epicardial breakthrough), which manifest themselves in the surface ECG as "jumps" (high frequency notches and slurs). The timing of jumps provides diagnostic information on bioelectrical tissue properties of the heart. Findings of this study validated previous simulation results. Furthermore, essential signal processing requirements were formulated for a high-resolution body surface potential mapping technology.