Vectorcardiography Research Articles

Individualization of a vectorcardiographic model by a particle swarm optimization

Abstract This paper presents the application of a bio-inspired method for optimizing a lifelike vectorcardiographic (VCG) model. During the model estimation, a Particle Swarm Optimization (PSO) seeks the optimal combination of all parameters that maximize the correlation coefficient (r) and minimize the Mean Squared Error (MSE) between the synthetic and directly measured VCG leads. The proposed method was tested on 52 different VCG records annotated as a healthy control (HC) from PTB database. 156 models were individualized without any previous analysis of the waves of the original records. The PSO method automatically provides very realistic models with a correlation coefficient r > 0.995 and MSE

A review of beat-to-beat vectorcardiographic (VCG) parameters for analyzing repolarization variability in ECG signals.

Elevated ventricular repolarization lability is believed to be linked to the risk of ventricular tachycardia/ventricular fibrillation. However, ventricular repolarization is a complex electrical phenomenon, and abnormalities in ventricular repolarization are not completely understood. To evaluate repolarization lability, vectorcardiography (VCG) is an alternative approach where the electrocardiographic (ECG) signal can be considered as possessing both magnitude and direction. Recent research has shown that VCG is advantageous over ECG signal analysis for identification of repolarization abnormality. One of the key reasons is that the VCG approach does not rely on exact identification of the T-wave offset, which improves the reproducibility of the VCG technique. However, beat-to-beat variability in VCG is an emerging area for the investigation of repolarization abnormality though not yet fully realized. Therefore, the purpose of this review is to explore the techniques, findings, and efficacy of beat-to-beat VCG parameters for analyzing repolarization lability, which may have potential utility for further study.

Cardiac memory in cardiac resynchronization therapy: A vectorcardiographic comparison of biventricular and left ventricular pacing

Introduction“Cardiac memory” (CM) refers to a change in repolarization induced by an altered pathway of activation, manifested after resumption of spontaneous ventricular activation (SVA). AimsTo investigate for the first time in humans the effects of left ventricular (LV) pacing on CM development through vectorcardiography (VCG). MethodsWe studied 28 patients with heart failure (HF) and left bundle branch block (LBBB) treated with cardiac resynchronization therapy (CRT). Fourteen patients underwent biventricular (BIV) stimulation; the other 14 underwent LV stimulation only. VCG was acquired during SVA at baseline and during AAI and DDD pacing immediately after and 7 and 90days after the implant. ResultsAt baseline, in both groups, the QRS and T vectors angles were those specific of LBBB pattern.During DDD pacing, QRS vector angle changed to the right and upward in BIV patients while no significant differences were observed in LV patients.During AAI pacing, T vector angle changed significantly in BIV patients, following the direction of the paced QRS and amplitude significantly increased. In LV patients no significant differences in T vector angles were observed. Only T vector amplitude significantly increased at 7days (p=0.03) and at 90days (p=0.008 vs baseline). ConclusionIn patients with LBBB, BIV pacing induces cardiac memory development as a significant change in T vector magnitude and angle, while LV pacing doesn’t induce significant modifications in QRS and T vector angles and CM is manifested only as a significant T vector amplitude change.

The synthesized vectorcardiogram resembles the measured vectorcardiogram in patients with dyssynchronous heart failure

BackgroundThe use of vectorcardiography (VCG) has regained interest, however, original Frank-VCG equipment is rare. This study compares the measured VCGs with those synthesized from the 12-lead electrocardiogram (ECG) in patients with heart failure and conduction abnormalities, who are candidate for cardiac resynchronization therapy (CRT). MethodsIn 92 CRT candidates, Frank-VCG and 12-lead ECG were recorded before CRT implantation. The ECG was converted to a VCG using the Kors method (Kors-VCG) and the two methods were compared using correlation and Bland–Altman analyses. ResultsVariables calculated from the Frank- and Kors-VCG showed correlation coefficients between 0.77 and 0.90. There was a significant but small underestimation by the Kors-VCG method, relative bias ranging from −1.9%±4.6% (QRS-T angle) to −9.4%±20.8% (T area). ConclusionThe present study shows that it is justified to use Kors-VCG calculations for VCG analysis, which enables retrospective VCG analysis of previously recorded ECGs in studies related to CRT.

Methods for derivation of orthogonal leads from 12-lead electrocardiogram: A review

Vectorcardiography (VCG), as an alternative to standard 12-lead electrocardiography (ECG), represents the electrical activity of the heart. Previous studies on VCG document that VCG criteria for the diagnosis of, for example, myocardial infarction (MI), ventricular hypertrophy and ischemic diseases, are superior to the corresponding 12-lead ECG criteria. Its use in clinical practice is not common because it requires the placement of additional electrodes. However, VCG leads can be derived from standard ECG by using mathematical transformations.This paper reviews the published works on transformation techniques for derivation VCG from 12-lead ECG, their historical evolution and their importance in today's clinical practice. Different kinds of criteria for evaluation accuracy of transformations are briefly described and the accuracy of individual techniques discussed.

Abstract 11981: ECG-Derived Vectorcardiography Identifies Disease and Genotype Status in Hypertrophic Cardiomyopathy

Introduction: Vectorcardiography (VCG) has clinical prognostic and diagnostic value in various disease states. Hypertrophic cardiomyopathy is a disease state which can lead to sudden cardiac death, where genotype status has been shown to predict worse outcomes.. Hypothesis: We set out to determine the utility of vectorcardiographic parameters in one of the largest genotyped cohorts of patients with hypertrophic cardiomyopathy (HCM) and to determine whether they can identify genotype status. Methods: Between 1997 and 2007, research based genetic testing was performed on 1053 patients with HCM (60% males; mean age at diagnosis 44.4 years); yield of genetic testing was 34%. Of these, 967 had ECG’s appropriate for computerized derivation of VCG parameters including the spatial mean and peaks QRS-T angles, spatial ventricular gradient and the spatial QRS, QT, and Tpeak-Tend (TpTe) intervals. Results were compared against those from a group of healthy control subjects (N=418).Subsequent genotype positive versus negative comparisons were performed using paired student T-tests or Mann-Whitney U-tests as appropriate. Results: Spatial peaks and spatial mean QRS-T angles were significantly higher in HCM patients (129.3±26.4 and 121.8±38.6 degrees, respectively) than in controls (25.0±15.0 and 43.0±-21.0 degrees, respectively, p<0.001). Sensitivities for HCM, based on cutoff values of 2 standard deviations above the mean values reported for control patients, were 84.5% and 81.5% for spatial peaks and spatial mean QRS-T angles, respectively. VCG predicted genotype status as genotype positive patients had significantly higher spatial peaks (132.4±-29.2 vs. 127.9±24.8 degrees; p = 0.02) and spatial mean (129.7±33.8 vs. 117.6±40.3 degrees; p<0.001) QRS-T angles, spatial TpTe (118.0±40.8 vs. 107.9±48.7 ms; p<0.001) as well as significantly lower spatial ventricular gradients (0.059±0.044 vs. 0.067±0.04; p<0.001). Conclusions: Patients with HCM can be distinguished from normal subjects through the study of the spatial QRS-T angle. Whether incorporation of spatial peaks QRS-T angle to pre-existing genetic test prediction tools will further improve prediction of genotype status remains to be determined.

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

BackgroundThe 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). MethodsWe 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. ResultsOur 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. ConclusionsWe 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.

Computer-Based Vectorcardiograph for Research Purposes

The vectorcardiography (VCG) represents the cardiac electric field by vectors and provides a better morphological interpretation of the cardiac electrical field. The main objective of this paper has been to describe our VCG device that has been determined for scientific research and for the clinical diagnosis of heart diseases. We have designed the hardware as a small portable device and the software that measures data saved in a raw form accessible for further processing. The main contribution is in the new way of common mode reduction (driven right leg circuit). The designed device has a great potential thanks to the new methods of interpretation and automatic signal evaluation an also thanks to the small procurement price. DOI: http://dx.doi.org/10.5755/j01.eee.19.9.5650

Baseline vectorcardiography as a predictor of invasively determined acute hemodynamic response to cardiac resynchronization therapy

Identifying potential responders to cardiac resynchronization therapy (CRT) may be sometimes difficult and time consuming. Searching for a simple method, we chose vectorcardiography (VCG) for our study. The aim was to evaluate whether a VCG parameter can be used to predict invasively measured acute hemodynamic changes after CRT onset. Baseline VCG data were prospectively recorded just before initiation of CRT in a series of 126 consecutive patients (♂74 %, DCMP 60 %, ICMP 40 %, NYHA class III 100 %, QRS width 161 ± 27 ms, LV-EF 25 ± 6.5 %) prior to implantation at our specialized center. The time interval (TI) between the maximum vector and the end of the vector loop (initial description by Koglek W.) was correlated with acute hemodynamic change after CRT onset. Positive response to CRT was defined as an increase in dp/dt max >10 % or pulse pressure >5 %. According to these invasive hemodynamic parameters, 25 patients (20 %) were defined as non-responders. Using ROC analysis, the threshold value of the TI for responders was found to be 64 ms. TI is a predictor of acute hemodynamic response with a sensitivity of 96 %, a specificity of 76 %, a positive predictive value of 94 %, and a negative predictive value of 79 %. More non-responders are identified by TI than by using conventional QRS width in the 12-lead surface ECG. TI is a new method of evaluation based on baseline VCG analysis. It may be a useful diagnostic test for predicting acute hemodynamic response to CRT.

Cardiac Syndrome X Electrocardiographic Patterns Using Signal-Averaged Orthogonal Leads and VCG Indices

Cardiac syndrome X (CSX) is a clinical condition, characterized by angina, positive stress test and negative coronary angiography. Myocardial ischemia is suggested to influence the ischemic changes in the electrocardiogram (ECG), observed during stress test. The aim of this study, is to obtain CSX patterns of the high-resolution vectorcardiographic (VCG) loops in the horizontal (H), frontal (F) and right sagittal (RS) planes of the Frank corrected orthogonal leads (X,Y, Z), and to assess their similarity with the reference VCG loops of normal subjects. The results suggest that CSX VCG profile in resting state could be considered as a variant of the normal profile; however, it contains some VCG changes seen in the ischemic heart disease.

Vectorcardiography analysis of the repolarization response to pharmacologically induced autonomic nervous system modulation in healthy subjects

Autonomic nervous system activity is essential for regulation of ventricular repolarization (VR) and plays an important role in several arrhythmogenic conditions. This study in 31 healthy adult subjects (16 men, 15 women) evaluated the VR response to pharmacologically modulated autonomic nervous system activity applying vectorcardiography (VCG) analysis. During continuous VCG recording, 0.01-0.1 μg·kg(-1)·min(-1) isoprenaline (Iso) was infused at an increasing flow rate until three targeted heart rates (HR) were reached. After Iso washout, one intravenous bolus of 0.04 mg/kg atropine was given followed by an intravenous bolus of 0.2 mg/kg propranolol. A 5-min steady-state VCG recording was analyzed for each of the seven phases (including baseline 1 and 2). Furthermore, during the first 4 min following atropine, six periods of 10-s VCG were selected for subanalysis to evaluate the time course of change. The analysis included QRS, QT, and T-peak to T-end intervals, measures of the QRS and T vectors and their relation, as well as T-loop morphology parameters. By increasing HR, Iso infusion decreased HR dependent parameters reflecting total heterogeneity of VR (T area) and action potential morphology (ventricular gradient). In contrast, Iso prolonged QT HR corrected according to Bazett and increased the T-peak to T-end-to-QT ratio to levels observed in arrhythmogenic conditions. HR acceleration after atropine was accompanied by a transient paradoxical QT prolongation and delayed HR adaptation of T area and ventricular gradient. In addition to the expected HR adaptation, the VR response to β-adrenoceptor stimulation with Iso and to muscarinic receptor blockade with atropine thus included alterations previously observed in congenital and acquired long QT syndromes, demonstrating substantial overlap between physiological and pathophysiological electrophysiology.

Left atrial volume index as a predictor of ventricle repolarization abnormalities in adult dialyzed patients

This study was performed to investigate the relationship between left atrium (LA) volume index (LAVI) and left ventricle electrical activity presumably repolarization in end-stage renal disease patients. Study group was consisted of 120 dialyzed patients divided into two subgroups: 57 (age 50.7 ± 7.1) were on continuous ambulatory peritoneal dialysis (CAPD) and 73 (age 51.6 ± 7.6) were hemodialyzed (HD). All patients were undergoing three-dimensional vectorcardiographic (VCG) monitoring to assess parameters concerning T vector: QRS-T angle, Tel, and Taz. Standard echocardiography was performed to assess: LAmax, LAshort, LAlong. LAVI was calculated due to formula: LAVI = (π/6X [LAmax × LAshort × LAlong])/m2. LAVI in HD as well as in CAPD patients was significantly higher compared with controls (respectively: 36.29 ± 10.92; 36.41 ± 11.06; 20.64 ± 6.77 mL/m2). The calculated cutoff value of LAVI was 36.32 mL/m2. In HD patients, the strong correlations between LAVI and QRS-T angle and Tel were determined (respectively: r = 0.407, P < 0.001 and r = 0.359, P = 0.006). Similarly in CAPD group were significant associations between LAVI and QRS-T angle and Tel (respectively: r = 0.423, P < 0.001 and r = 0.374, P = 0.004). The QRS-T angle, Tel and Taz are independently and markedly associated with LAVI in both HD and CAPD patients. LAVI and VCG indices are higher in both HD and CAPD patients. Correlation between QRS-T angle and LAVI may reflect unfavorable influence on the electrical activity of the heart in dialyzed patients with left ventricle diastolic dysfunction. LAVI cutoff value is useful biomarker for stratification of ventricle repolarization disturbances in those patients.

MRI of Arterial Flow Reserve in Patients with Intermittent Claudication: Feasibility and Initial Experience

ObjectivesThe aim of this work was to develop a MRI method to determine arterial flow reserve in patients with intermittent claudication and to investigate whether this method can discriminate between patients and healthy control subjects.MethodsTen consecutive patients with intermittent claudication and 10 healthy control subjects were included. All subjects underwent vector cardiography triggered quantitative 2D cine MR phase-contrast imaging to obtain flow waveforms of the popliteal artery at rest and during reactive hyperemia. Resting flow, maximum hyperemic flow and absolute flow reserve were determined and compared between the two groups by two independent MRI readers. Also, interreader reproducibility of flow measures was reported.ResultsResting flow was lower in patients compared to controls (4.9±1.6 and 11.1±3.2 mL/s in patients and controls, respectively (p<0.01)). Maximum hyperemic flow was 7.3±2.9 and 16.4±3.2 mL/s (p<0.01) and the absolute flow reserve was 2.4±1.6 and 5.3±1.3 mL/s (p<0.01), respectively in patients and controls. The interreader coefficient of variation was below 10% for all measures in both patients and controls.ConclusionsQuantitative 2D MR cine phase-contrast imaging is a promising method to determine flow reserve measures in patients with peripheral arterial disease and can be helpful to discriminate patients with intermittent claudication from healthy controls.

Vectorcardiography shows cardiac memory and repolarization heterogeneity after ablation of accessory pathways not apparent on ECG

BackgroundPacing induced cardiac memory is an established phenomenon, but following successful WPW ablation, cardiac memory was present on ECG in variable proportions of patients depending on accessory pathway (AP) location. We hypothesized that vectorcardiography (VCG), which is more sensitive than ECG, would show cardiac memory after WPW ablation independent of AP location. MethodsThirty-six patients were followed after successful AP ablation, 11 with overt posteroseptal (PS), 13 with overt left-sided (LS) and 12 with concealed APs (controls). VCGs were recorded the day before and after the procedure, ≥once/week for 6–8weeks and after ≥3months. T vector and T-vector loop parameters were analyzed and compared. ResultsAfter ablation of overt APs, there was a correlation between the directions of the preexcited maximum QRS-vector and the post-ablation maximum T-vector, confirming the presence of cardiac memory. Ablation of overt APs was followed by cardiac memory apparent in different directions. Thus, ablation of PS APs was followed by most pronounced changes in T-vector elevation and LS APs with significant changes only in T-vector azimuth. Cardiac memory disappeared within a month in >80% of cases. Furthermore, T-vector loop morphology changes suggested a period of repolarization heterogeneity immediately after ablation of overt APs. ConclusionsAccording to VCG analysis cardiac memory was present after ablation of overt APs independent of location as consistently as after ventricular pacing, and disappeared within a similar time frame during normal ventricular activation. In addition, signs of transient repolarization heterogeneity were observed after ablation of overt APs.

Noninvasive vectorcardiographic evaluation of pulmonary vein–atrial reconnection after pulmonary vein isolation for atrial fibrillation

Although pulmonary vein (PV)-left atrium (LA) reconnection is associated with recurrence of atrial fibrillation (AF) in patients who undergo pulmonary vein isolation (PVI), no noninvasive method for evaluating PV reconnection has yet been established. The purpose of this study was to examine whether PV-LA reconnection could be detected noninvasively by analyzing the change of P-loop configuration by vectorcardiography (VCG). The study included 80 patients with paroxysmal AF (8 female; mean age 58 ± 10 years) who underwent PVI. VCG was prospectively analyzed by recording during the procedure (before and after PVI) and 1 year after the procedure to noninvasively evaluate PV-LA reconnection. All patients showed a significant antero-leftward shift in the middle portion of the P loop on the horizontal plane of VCG, with an increase of the area within the P loop after the initial PVI (2.4 ± 1.7 vs 4.6 ± 2.7 × 10(3) mV(2), P <.001). Sixty-three (78.8%) patients without AF recurrence demonstrated no remarkable change in the P-loop area after 16 ± 11 months of follow-up (4.4 ± 2.7 vs 4.1 ± 2.5 × 10(3) mV(2), P = .51), whereas 17 (21.2%) patients with AF recurrence demonstrated P-loop reversion to the preprocedural P-loop morphology, with a decrease of P-loop area (5.6 ± 2.7 vs 3.2 ± 1.7 × 10(3) mV(2), P <.001). Change of the P loop on VCG was associated with subsequent PV-LA reconnection. VCG is helpful as a noninvasive method for detecting PV-LA reconnection after PVI for paroxysmal AF.

Transient repolarization instability following the initiation of cardiac resynchronization therapy

Cardiac resynchronization therapy (CRT) may cause changes in ventricular repolarization (VR), particularly in the initial phase of treatment. This study investigated the effect of CRT cessation and re-initiation on parameters of VR duration and heterogeneity at different paced heart rates. Cardiac resynchronization therapy was inactivated for 2 weeks in 16 treatment responders to CRT. QT and JT intervals were measured on the surface electrocardiogram at 60, 70, and 80 bpm (randomized order) and vectorcardiography (VCG) was performed with CRT 'on' (day 0), 'off' (day 0, 1, 7, and 14) and after CRT re-initiation (day 14, 15, 16, and 21). On day 0 ('on') and 14 ('off') echocardiography, the 6 min walking distance and brain natriuretic peptide were assessed. The QT interval at baseline (CRT 'on'), measured at 60, 70, and 80 bpm, was 482 ± 31, 468 ± 37, and 457 ± 39 ms, respectively, and decreased by 5, 5, and 6% during the first week following CRT cessation (all P< 0.05). Immediately after re-initiation on day 14, it increased again by 20 ± 18 (4%; P< 0.05), 34 ± 39 (8%; P< 0.01), and 16 ± 38 ms (4%, ns) followed by a gradual decrease towards previous 'off' levels. Similar changes were observed for the JT interval. Ventricular repolarization duration was significantly shortened by increasing the paced heart rate from 60 to 70 and 80 bpm. Vectorcardiography parameters reflecting VR gradients (ST-vector magnitude, Tarea, and Tavplan) increased significantly (by 31, 45, and 71%) after CRT cessation. A similar but non-significant pattern was observed after CRT re-initiation. The increase in repolarization duration and gradients observed after CRT initiation suggests a transient state of VR instability that can be attenuated by programming of higher paced heart rates during the initial phase of treatment.

When deriving the spatial QRS-T angle from the 12-lead electrocardiogram, which transform is more frank: regression or inverse dower?

The use of vectorcardiography (VCG) has regained interest, however, original Frank-VCG equipment is rare. This study compares the measured VCGs with those synthesized from the 12-lead electrocardiogram (ECG) in patients with heart failure and conduction abnormalities, who are candidate for cardiac resynchronization therapy (CRT).In 92 CRT candidates, Frank-VCG and 12-lead ECG were recorded before CRT implantation. The ECG was converted to a VCG using the Kors method (Kors-VCG) and the two methods were compared using correlation and Bland–Altman analyses.Variables calculated from the Frank- and Kors-VCG showed correlation coefficients between 0.77 and 0.90. There was a significant but small underestimation by the Kors-VCG method, relative bias ranging from − 1.9% ± 4.6% (QRS-T angle) to − 9.4% ± 20.8% (T area).The present study shows that it is justified to use Kors-VCG calculations for VCG analysis, which enables retrospective VCG analysis of previously recorded ECGs in studies related to CRT.

Diagnostic utility of the spatial versus individual planar QRS-T angles in cardiac disease detection

Introduction We compared the diagnostic utility of various planar QRS-T angles to that of the spatial QRS-T angle in detecting various cardiac diseases. Materials and Methods Electrocardiographic (ECG) and derived vectorcardiographic (VCG) data were analyzed from 370 patients with imaging-proven cardiac disease (coronary artery disease, hypertrophic cardiomyopathy, or left ventricular systolic dysfunction) and 210 apparently healthy controls. The areas under the curve (AUC) of the Receiver Operating Characteristic (ROC) for distinguishing cardiac health from disease for each disease condition were statistically compared for the spatial mean QRS-T angle versus the ECG-derived frontal and VCG-derived frontal, left sagittal and horizontal planar QRS-T angles. Results The AUC ROC of the spatial mean QRS-T angle, which ranged from 0.801 ± 0.035 to 0.987 ± 0.007 depending on the specific comparison, was always significantly greater than that of the ECG frontal planar QRS-T angle (range from 0.680 ± 0.043 to 0.796 ± 0.045) and usually significantly greater than that of all other QRS-T angles for the diseases studied. Discussion The spatial mean QRS-T angle is statistically significantly more diagnostically powerful than the ECG-derived frontal planar QRS-T angle and also generally more diagnostically powerful than all VCG-derived planar QRS-T angles in detecting cardiac disease. The ECG frontal planar QRS-T angle should not be considered an adequate diagnostic substitute for the spatial QRS-T angle.

Non-invasive Electrophysiology I

Non-invasive Electrophysiology I

Clinical determinants of electrocardiographic and spatial vectorcardiographic descriptors of ventricular repolarization in healthy children.

Although the association of repolarization alterations to the development of life-threatening ventricular arrhythmias has received considerable research attention, there is paucity of data regarding what may be considered as normal, especially in children. To define electrocardiographic (ECG) and vectorcardiographic (VCG) descriptors of ventricular repolarization in healthy school-age children, 12-lead digital ECGs were obtained from 646 children (348 males/298 females, mean age 8.54 ± 1.86 years). All QT intervals were measured manually using the digitally stored ECGs. Orthogonal X, Y, and Z leads were reconstructed from the standard 12-lead ECGs and the maximal amplitudes of the spatial QRS and T vectors were calculated, as well as the spatial QRS-T angle. The mean heart rate was 95.3 ± 15.8 bpm and the QRS duration was 83.4 ± 9.3 ms. Mean QT interval was 334.1 ± 24.2 ms and the corrected QT interval was 436.5 ± 23.8 ms (Bazzet) and 404.3 ± 19.4 ms (Fridericia). Although the uncorrected maximum and mean QT intervals were significantly higher in boys (P values 0.011 and 0.009, respectively), there was no difference in the rate-corrected QT interval. The spatial QRS and T-vector amplitudes were 1512.0 ± 365.7 μV and 478.8 ± 149.3 μV, respectively. The spatial QRS-T angle was 14.1 ± 8.0 degrees. Although the mean QT interval showed significant increase with age (P = 0.014), all VCG parameters did not show significant variance with age. A range of ECG and VCG descriptors of ventricular repolarization was determined in a large sample of healthy school-age children to provide a data basis of normal values for future reference.