Standard 12-lead ECG exercise testing is commonly used for screening of ischemic heart disease (IHD). We studied if high-resolution body surface potential mapping (HR-BSPM) during exercise offers advantages over current standards in noninvasive evaluation of IHD. This study was carried out on 90 IHD patients and 33 healthy controls. The 67-lead HR-BSPM was recorded at rest and during exercise. Twenty-one ECG parameters including classical ST criteria were compared. The effectiveness of methods was verified based on the results of SPECT and coronary angiography. The most effective parameters in the diagnosis of IHD were: amplitude parameter ΔST60 and δT parameter showing T-wave morphology changes during exercise. The sensitivities/specificities of ΔST60 and δT parameters for the HR-BSPM were 70/69 and 59/62%, while for the standard 12-lead ECG system they were: 63/62 and 59/56%. These results demonstrate the usefulness of HR-BSPM measurements during exercise. HR-BSPM resulted in higher sensitivities and specificities compared to the standard 12-lead exercise test. The advantage was partially associated with observed ischemic changes outside standard precordial leads position that were not visible when using the standard 12-lead exercise test. This justifies research into the optimization of the number and position of ECG leads in exercise testing.

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High-Resolution Body Surface Potential Mapping in Exercise Assessment of Ischemic Heart Disease

Abstract In this study, the inverse solution with a single dipole was computed to localize the premature ventricular contraction (PVC) origin from long term multiple leads ECG measurements on fourteen patients. The stability of the obtained results was studied with respect to the preprocessing of signals used as an input to the inverse solution and the complexity of the torso model. Two methods were used for the baseline drift removal. After an averaging of the heartbeats, the influence of the retention or elimination of the remaining offset at the beginning of the PVC signal was examined. The inverse computations were performed using both homogeneous and inhomogeneous patient-specific torso models. It was shown that the remaining offset in the averaged signals at the beginning of the PVC signal had the most significant impact on the stability of the resulting position within the ventricles. Its elimination stabilizes the location of the results, decreases the sensitivity to the torso model complexity and decreases the sensitivity to the primary baseline drift removal method. The additional offset correction decreased the mean distance between the results for all patients from 17-18 mm to 1-2 mm, regardless of the baseline drift removal method or the torso model complexity.

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The Importance of ECG Offset Correction for Premature Ventricular Contraction Origin Localization from Clinical Data

Objective: Electrocardiographic imaging can provide preliminary locations of premature ventricular contraction (PVC) origins, which can lead to the shortening of the invasive radio-frequency ablation (RFA) procedure. However, PVC localization results vary significantly with respect to the equivalent cardiac source models and the level of complexity assumed in the forward model. This study aims to evaluate PVC localization based on different source and forward model assumptions. Methods: We use body surface potential (BSP) measurements from 5 patients with PVCs, indicated for RFA. Two equivalent source models (dipole-based and heart surface potential-based), and homogeneous and inhomogeneous torso geometries are used to evaluate the variability in the PVC origin. Results: Dipole-based PVC locations are in general more clustered than potential-based ones. Spatio-temporal AT estimates smooth the ATs improving the PVC localizations to be more clustered. Potential-based solutions were more sensitive to changes in the forward model than the dipole-based method. Conclusion: The AT and RRE maps provided similar information consistent with patient descriptions. Therefore, rather than specifying a single point PVC origin, these maps could guide the physicians for more accurate PVC localization.

Variability of Premature Ventricular Contraction Localization with Respect to Source and Forward Model Variation in Clinical Data

The ability of cellular automaton activation propagation heart model to simulate ventricular depolarization started in a single point was investigated using a patient-specific geometry. Body surface potential maps (BSPMs) measured during stimulation by a catheter in the right ventricle were recorded in 116 leads on the patient torso. Patient's ventricular model was used to simulate the initial depolarization started in positions close to the catheter position and corresponding BSPMs were computed. Correlations between the recorded and simulated BSPMs were computed during 20 ms at the beginning of the activation. The best mean correlation between the measured and simulated BSPMs was 0.89 or 0.91 for homogeneous or inhomogeneous torso model, respectively. The distance between the real position of the stimulating catheter and the starting points used for the best BSPMs was 23 or 22 mm. The simulations using the proposed model could serve for additional verification of the results obtained by the inverse solution when finding the origin of premature ventricular activation.

Simulation of Measured Body Surface Potential Map During Early Right Ventricular Pacing

The inverse solution using a dipole as equivalent heart generator was used for assessment of the area of the premature ventricular contraction (PVC) starting point. In two patients with frequent PVC activity, body surface maps were recorded, and the patient specific torso model was created from whole torso CT scan. The position of the assumed ectopic beat origin was computed from the first 40 ms of activation when the activated area is small. The patients also underwent intracardial electrophysiological mapping when the true origin of the PVC beat was defined as the earliest activated point. The obtained inverse results were compared with that position. The inverse solution was computed for 10 chosen ectopic beats for each patient using both, homogeneous and inhomogeneous torso models. The inverse results for both cases were within the area of the PVC beat origin. The use of the more detailed inhomogeneous torso model instead of the homogeneous one did not demonstrate an improvement of localization.

First experience with PVC localization from clinical data

In the paper, a new version of a multichannel ECG measuring system ProCardio is introduced. The system was designed for measurement, processing, and evaluation of surface electrocardiograms using up to 144 passive or active ECG electrodes. For fast and convenient placement of electrodes, self-adhesive stripes with eight electrodes are used. To minimize the capacitive coupling and guarantee maximal level of patient safety, the battery powered measuring unit is connected to the USB port of a notebook computer by an optical cable. Modular software package enables convenient ECG recording with monitoring of the signals, advanced ECG preprocessing including signal averaging or selection of extrasystoles, and computation and displaying of body surface potential maps in various formats.

J. Kadanec

Papers

ProCardio 8 — System for high resolution ECG mapping