T vector and loop characteristics in coronary artery disease and during acute ischemia

Pulmonary Hypertension Detection Non-Invasively at Point-of-Care Using a Machine-Learned Algorithm

Artificial intelligence, particularly machine learning, has gained prominence in medical research due to its potential to develop non-invasive diagnostics. Pulmonary hypertension presents a diagnostic challenge due to its heterogeneous nature and similarity in symptoms to other cardiovascular conditions. Here, we describe the development of a supervised machine learning model using non-invasive signals (orthogonal voltage gradient and photoplethysmographic) and a hand-crafted library of 3298 features. The developed model achieved a sensitivity of 87% and a specificity of 83%, with an overall Area Under the Receiver Operator Characteristic Curve (AUC-ROC) of 0.93. Subgroup analysis showed consistent performance across genders, age groups and classes of PH. Feature importance analysis revealed changes in metrics that measure conduction, repolarization and respiration as significant contributors to the model. The model demonstrates promising performance in identifying pulmonary hypertension, offering potential for early detection and intervention when embedded in a point-of-care diagnostic system.

Three-dimensional vectorcardiographic characteristics of breast cancer patients treated with chemotherapy

BACKGROUND

Patients receiving chemotherapy for breast cancer (breast cancer) may develop cardiac electrophysiological abnormalities. The aim of this study is to examined possible alterations in cardiac electrophysiological parameters detected by three-dimensional vectorcardiograms (3D-VCGs) in breast cancer patients who received chemotherapy.

METHODS

This was a prospective single-center cohort study conducted in Fourth Hospital of Hebei Medical University, China. Patients with breast cancer referred for chemotherapy from May 1, 2019, to October 1, 2019 were invited to participate in the study. 3D-VCGs and echocardiography were recorded at rest four times (baseline, after the first cycle, after third cycles and at the end of the regimen, respectively).

RESULTS

A total of 63 patients were included. Compared with baseline, decreases in 3D maximum T vector magnitude (TVM) (0.29 ± 0.10 vs. 0.25 ± 0.10 mV; p < 0.05) and 3D T/QRS ratio (0.26 ± 0.11 vs. 0.21 ± 0.11; p < 0.05) were observed by the end of chemotherapy regimen, while echocardiographic parameters showed no significant variation before and after chemotherapy (all P > 0.05). Furthermore, after third cycles, maximum TVM were correlated with LVEF except in horizontal plane (3D: r = 0.33, p < 0.01; frontal plane: r = 0.34, p < 0.01; horizontal plane: r = 0.24, p = 0.06; right side plane: r = 0.30, p = 0.02). After completion of chemotherapy, maximum TVM were also positive correlated with LVEF (3D: r = 0.33, P < 0.01; frontal plane: r = 0.32, P = 0.01; horizontal plane: r = 0.27, P = 0.03, right side plane: r = 0.38, P < 0.01).

CONCLUSIONS

Along with chemotherapy, maximum TVM and T/QRS is lower in patients with breast cancer. After third cycles and after completion of chemotherapy, there is a positive correlation between maximum TVM and LVEF. 3D-VCGs can be used to detect electrophysiological abnormalities in breast cancer patients receiving chemotherapy.

Heterogeneous Recurrence Analysis of Disease-Altered Spatiotemporal Patterns in Multi-Channel Cardiac Signals

Heart diseases alter the rhythmic behaviors of cardiac electrical activity. Recent advances in sensing technology bring the ease to acquire space-time electrical activity of the heart such as vectorcardiogram (VCG) signals. Recurrence analysis of successive heartbeats is conducive to detect the disease-altered cardiac activities. However, conventional recurrence analysis is more concerned about homogeneous recurrences, and overlook heterogeneous types of recurrence variations in VCG signals (i.e., in terms of state properties and transition dynamics). This paper presents a new framework of heterogeneous recurrence analysis for the characterization and modeling of disease-altered spatiotemporal patterns in multi-channel cardiac signals. Experimental results show that the proposed approach yields an accuracy of 96.9%, a sensitivity of 95.0%, and a specificity of 98.7% for the identification of myocardial infarctions. The proposed method of heterogeneous recurrence analysis shows strong potential to be further extended for the analysis of other physiological signals such as electroencephalogram (EEG) and electromyography (EMG) signals towards medical decision making.

Spatial indices of repolarization correlate with non-ST elevation myocardial ischemia in patients with chest pain

Mild-to-moderate ischemia does not result in ST segment elevation on the electrocardiogram (ECG), but rather non-specific changes in the T wave, which are frequently labeled as non-diagnostic for ischemia. Robust methods to quantify such T wave heterogeneity can have immediate clinical applications. We sought to evaluate the effects of spontaneous ischemia on the evolution of spatial T wave changes, based on the eigenvalues of the spatial correlation matrix of the ECG, in patients undergoing nuclear cardiac imaging for evaluating intermittent chest pain. We computed T wave complexity (TWC), the ratio of the second to the first eigenvalue of repolarization, from 5-min baseline and 5-min peak-stress Holter ECG recordings. Our sample included 30 males and 20 females aged 63 ± 11 years. Compared to baseline, significant changes in TWC were only seen in patients with ischemia (n = 10) during stress testing, but not among others. The absolute changes in TWC were significantly larger in the ischemia group compared to others, with a pattern that seemed to depend on the severity or anatomic distribution of ischemia. Our results demonstrate that ischemia-induced changes in T wave morphology can be meaningfully quantified from the surface 12-lead ECG, suggesting an important opportunity for improving diagnostics in patients with chest pain.

Effectiveness of cardiogoniometry compared with exercise-ECG test in diagnosing stable coronary artery disease in women

AIMS

To investigate the effectiveness of cardiogoniometry, a novel, non-invasive method, in diagnosing coronary artery disease (CAD) in women and compare it with exercise-ECG test, by using coronary angiography as a reference method.

METHODS

It was a single-centre, case-series study including consecutive female patients with stable angina pectoris (AP) undergoing coronary angiography. Exercise-ECG test, done according to the Bruce protocol, and cardiogoniometry were obtained prior to coronary angiography. Clinically significant CAD has been defined as one or more coronary lesions with >70% stenosis.

RESULTS

Study included 114 consecutive female patients with median age of 64.0 (58.0-71.0) years, out of which 32 (28.1%) had CAD. Cardiogoniometry yielded a total accuracy of 74.6% with a sensitivity of 75.0% (95% CI 56.6-88.5) and specificity of 74.4% (95% CI 63.6-83.4). Exercise-ECG test yielded a total accuracy of 45.1% with a sensitivity of 68.1% (95% CI 42.7-83.6) and specificity 36.6% (95% CI 25.2-50.3). Cardiogoniometry showed higher accuracy than exercise-ECG test ( P < 0.001). Pathological cardiogoniometry was associated with almost nine times higher risk for CAD (OR 8.7, 95%CI 3.4-22.3, P < 0.001), which remained significant after adjustment for age, and hypokinesia.

CONCLUSION

Cardiogoniometry is a non-invasive, easy-to-use and free-of-risk method which showed high effectiveness in diagnosing stable CAD in women and superior to exercise-ECG test. Cardiogoniometry could be introduced as a part of the diagnostic algorithm of screening women for stable CAD and is suitable for use in the primary setting, especially in women unable to undergo stress-testing.

The Value of Frontal Planar QRS-T Angle in Patients without Angiographically Apparent Atherosclerosis

OBJECTIVE

The present study was undertaken to investigate the prognostic value of the frontal planar QRS-T angle in patients without angiographically apparent coronary atherosclerosis.

SUBJECTS AND METHODS

Three hundred and seven patients with normal coronary arteries on coronary angiography were included. The absolute difference between the frontal QRS- and T-wave axes was defined as the frontal planar QRS-T angle, and patients were divided into 3 subgroups based on the frontal planar QRS-T angle (<45, 45-90, and >90°). Demographic, clinical, laboratory, and angiographic data were compared between groups. Based on the regression analysis results, patients were recategorized into 4 groups according to their luminal calibers of left main coronary artery (LMCA) and history of hypertension (HT) (nonhypertensive LMCA ≤4.13 mm, nonhypertensive LMCA >4.13 mm, hypertensive LMCA ≤4.13 mm, and hypertensive LMCA >4.13 mm).

RESULTS

The median value of the frontal planar QRS-T angle of all participants was 38°. Subjects with the widest frontal planar QRS-T angle were older (p = 0.027), were hypertensive (p = 0.001), and had higher corrected QT values (p = 0.001). Patients with the widest frontal planar QRS-T angle had larger LMCA and left anterior descending coronary artery diameters compared to subjects with a normal and borderline frontal QRS-T angle (p = 0.004 and p = 0.028, respectively). Corrected QT, HT, and LMCA diameter were found as independent predictors of the frontal planar QRS-T angle. Subjects with HT and a larger luminal caliber of LMCA had the widest frontal planar QRS-T angle.

CONCLUSION

Patients with a history of HT and a larger luminal caliber of LMCA had the widest frontal planar QRS-T angle. Since HT-induced electrophysiological changes are still not well established and we observed that changes in the luminal caliber of coronary arteries are associated with an abnormal frontal QRS-T angle, the frontal QRS-T angle could serve as a marker of ventricular repolarization heterogeneity in hypertensive patients in addition to keeping track of arrhythmic events, even before overt disease.

Prediction of Pulmonary Arterial Hypertension in Chronic Obstructive Lung Disease from Three-Dimensional Vectorcardiographic Parameters

AIM

The objective of our study was to assess diagnostic value of three-dimensional (3D) vectorcardiographic (VCG) parameters in detecting pulmonary arterial hypertension (PAH) in chronic obstructive lung disease (COLD) with and without right ventricular hypertrophy (RVH).

METHODS

The study group of 62 patients with COPD was stratified on the basis of color Doppler echocardiographic findings into three subgroups: non-PAH (n = 23), PAH without RVH (n = 22), and PAH with RVH (n = 17). Pairwise differences between the subgroups were evaluated by one-way analysis of variance, and Pearson correlation analysis was used to evaluate the significance of the correlations between pulmonary arterial systolic pressure (PASP) and various VCG parameters.

RESULTS

The azimuth of the QRS vector decreased from -24° in the non-PAH group to -62° in PAH without RVH and to -140° in PAH with RVH (P < 0.01 for pairwise differences between all three groups). Similar significant decrease was observed for the azimuth of the ventricular gradient (VG) vector. Spatial QRS/T angle increased from 69° in the non-PAH group to 115° in PAH without RVH (P < 0.01). In the PAH group with RVH, QRS/T angle was 94° (P < 0.05 for difference from the non-PAH group). There was a significant correlation between PASP and QRS/T angle (r = 0.89, P < 0.05) and between PASP and the azimuth of the VG vector (r = 0.86, P < 0.05). PASP increase from linear regression model was 0.8 mmHg for a QRS/T angle increase by 10° and 1.3 mmHg for each 10° increase in the azimuth of the VG vector.

CONCLUSION

3DVCG parameters are potentially useful for predicting PASP in COLD patients, and possibly also for differentiation between COLD patients with PAH and RVH from those without RVH.

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.

Comparison of cardiogoniometry and ECG at rest versus myocardial perfusion scintigraphy

BACKGROUND

Cardiogoniometry (CGM) is a novel resting electrocardiac method based on computer-generated three-dimensional data derived from cardiac potentials. The purpose of this study was to determine CGM's and electrocardiography's (ECG) accuracy for detecting myocardial ischemia and/or lesions in comparison with stress/rest myocardial perfusion scintigraphy (single photon emission computer tomography [SPECT]).

METHOD

A cohort of consecutively enrolled patients (n = 100) with suspected or known coronary artery disease (mean age 67.8 years, 52% female) were examined by CGM and resting ECG before stress/rest myocardial scintigraphy.

RESULTS

Pathological scintigraphy findings at adenosine stress perfusion (ASP) and/or rest were conclusively identified in 21 patients. Diagnostic sensitivity was 71% for CGM and 24% for ECG, specificity was 70% for CGM and 95% for ECG. Reversible ischemia was diagnosed in 16 of 21 patients with pathological scintigraphy results. In this subgroup, sensitivity was 67% for CGM and 25% for ECG.

CONCLUSIONS

At rest, the sensitivity of a CGM significantly surmounts that of a standard 12-lead ECG for detection of isolated myocardial ischemia or myocardial lesions revealed by scintigraphy/SPECT; specificity is in a reasonable range. CGM's ease of use and its considerable agreement with the results of myocardial scintigraphy, suggests a possible role for patient screening in the primary care setting.

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.

Instability of repolarization in LQTS mutation carriers compared to healthy control subjects assessed by vectorcardiography

BACKGROUND

Potassium channel dysfunction in congenital and acquired forms of long QT syndrome types 1 and 2 (LQT1 and LQT2) increases the beat-to-beat variability of the QT interval.

OBJECTIVE

To study about the little known variability (instability) of other aspects of ventricular repolarization (VR) in humans by using vectorcardiography.

METHODS

Beat-to-beat analysis was performed regarding vectorcardiography derived RR, QRS, and QT intervals, as well as T vector- and T vector loop-based parameters during 1-minute recordings of uninterrupted sinus rhythm at rest in 41 adult LQT1 (n = 31) and LQT2 (n = 10) mutation carriers and 41 age- and sex-matched control subjects. The short-term variability for each parameter, describing the mean orthogonal distance to the line of identity on the Poincaré plot, was calculated.

RESULTS

Mutation carriers showed significantly larger (by a factor 2) instability in most VR parameters compared to controls despite higher instantaneous heart rate variability (STVRR) in the control group. The longer the QT interval, the greater was its instability, and the instability of VR dispersion measures.

CONCLUSIONS

A greater instability of most aspects of VR already at rest seems to be a salient feature in both LQT1 and LQT2, which might pave the way for early afterdepolarizations and torsades de pointes ventricular tachycardia. In contrast, no signs of increased VR dispersion per se were observed in mutation carriers.

Comparison of cardiogoniometry and electrocardiography with perfusion cardiac magnetic resonance imaging and late gadolinium enhancement

AIMS

Cardiogoniometry (CGM) is a spatio-temporal five-lead resting electrocardiographic method utilizing automated analysis. The purpose of this study was to determine CGM's and electrocardiography (ECG)'s accuracy for detecting myocardial ischaemia and/or lesions in comparison with perfusion cardiac magnetic resonance imaging (CMRI) and late gadolinium enhancement (LGE).

METHODS AND RESULTS

Forty (n= 40) patients with suspected or known stable coronary artery disease were examined by CGM and resting ECG directly prior to CMRI including adenosine stress perfusion (ASP) and LGE. The investigators visually reading the CMRI were blinded to the CGM and ECG results. Half of the patients (n= 20) had a normal CMRI while the other half presented with either abnormal ASP and/or detectable LGE. Cardiogoniometry yielded an accuracy of 83% (sensitivity 70%) and ECG of 63% (sensitivity 35%) compared with CMRI.

CONCLUSIONS

In this pilot study CGM compares more favourably than ECG with the detection of ischaemia and/or structural myocardial lesions on CMRI.

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.

Aortic stiffness, left ventricle hypertrophy, and homogeneity of ventricle repolarization in adult dialyzed patients

AIM

Study was designed to assess relationship between aortic compliance and homogeneity of heart electrical activity in dialysis patients.

METHODS

Study group was consisted of 120 dialyzed patients; 57 (age 50,7 ± 7,1) were on continuous ambulatory peritoneal dialysis (CAPD) and 73 (age 51,6 ± 7,6) were hemodialyzed (HD). Three-dimensional vectorocardiographic (VCG) monitoring was done to assess: QRS-T(angle), T(el) and T(az). Echocardiography was performed to assess: Ao(max), Ao(min), ASI (aortic siffness index).

RESULTS

ASI in HD as well as in CAPD patients was significantly higher compared to controls [resp., 5,51 (±1,32), 5,83 (±1,41), 3,07 (±1,09)]. Cut-off value of ASI was 5,67. In HD patients strong correlations between ASI and QRS-T(angle), T(el) and T(az) were determined (resp., r = 0,429, P < 0,001; r = 0,432, P ≤ 0,001 and r = 0,387, P = 0,001). In CAPD group were significant association between ASI and QRS-T(angle), T(el) and T(az) (resp., r = 0,452, P < 0,001; r = 0,417, P < 0,001 and r = 0,390, P = 0,001). ASI was independently and markedly associated with: QRS-T(angle), T(elev), T(az), ADMA, cTnT, CRP, Total-chol, LDL-chol in HD and CAPD patients.

CONCLUSIONS

ASI and VCG indices are higher in HD and CAPD patients. Correlation between ASI and VCG parameters may reflect unfavourable influence of poor aortic compliance on the electrical activity of the heart in dialyzed patients. Hypertrophy aggravates repolarization disturbances in hemodialyzed patients.

Effect of heart rate on ventricular repolarization in healthy individuals applying vectorcardiographic T vector and T vector loop analysis

BACKGROUND

Ventricular repolarization (VR) is strongly influenced by heart rate (HR) and autonomic nervous activity, both of which also are important for arrhythmogenesis. Their relative influence on VR is difficult to separate, but might be crucial for understanding while some but not other individuals are at risk for life-threatening arrhythmias at a certain HR. This study was therefore designed to assess the "pure" effect of HR increase by atrial pacing on the ventricular gradient (VG) and other vectorcardiographically (VCG) derived VR parameters during an otherwise unchanged condition.

METHODS

In 19 patients with structurally normal hearts, a protocol with stepwise increased atrial pacing was performed after successful arrhythmia ablation. Conduction intervals were measured on averaged three-dimensional (3D) QRST complexes. In addition, various VCG parameters were measured from the QRS and T vectors as well as from the T loop. All measurements were performed after at least 3 minutes of rate adaptation of VR.

RESULTS

VR changes at HR from 80 to 120 bpm were assessed. The QRS and QT intervals, VG, QRSarea, Tarea, and Tamplitude were markedly rate dependent. In contrast, the Tp-e/QT ratio was rate independent as well as the T-loop morphology parameters Tavplan and Teigenvalue describing the bulginess and circularity of the loop.

CONCLUSIONS

In healthy individuals, the response to increased HR within the specified range suggests a decreased heterogeneity of depolarization instants, action potential morphology, and consequently of the global VR.

Electrocardiologic and related methods of non-invasive detection and risk stratification in myocardial ischemia: state of the art and perspectives

Background: Electrocardiographic methods still provide the bulk of cardiovascular diagnostics. Cardiac ischemia is associated with typical alterations in cardiac biosignals that have to be measured, analyzed by mathematical algorithms and allegorized for further clinical diagnostics. The fast growing fields of biomedical engineering and applied sciences are intensely focused on generating new approaches to cardiac biosignal analysis for diagnosis and risk stratification in myocardial ischemia.

Objectives: To present and review the state of the art in and new approaches to electrocardiologic methods for non-invasive detection and risk stratification in coronary artery disease (CAD) and myocardial ischemia; secondarily, to explore the future perspectives of these methods.

Methods: In follow-up to the Expert Discussion at the 2008 Workshop on "Biosignal Analysis" of the German Society of Biomedical Engineering in Potsdam, Germany, we comprehensively searched the pertinent literature and databases and compiled the results into this review. Then, we categorized the state-of-the-art methods and selected new approaches based on their applications in detection and risk stratification of myocardial ischemia. Finally, we compared the pros and cons of the methods and explored their future potentials for cardiology.

Results: Resting ECG, particularly suited for detecting ST-elevation myocardial infarctions, and exercise ECG, for the diagnosis of stable CAD, are state-of-the-art methods. New exercise-free methods for detecting stable CAD include cardiogoniometry (CGM); methods for detecting acute coronary syndrome without ST elevation are Body Surface Potential Mapping, functional imaging and CGM. Heart rate variability and blood pressure variability analyses, microvolt T-wave alternans and signal-averaged ECG mainly serve in detecting and stratifying the risk for lethal arrythmias in patients with myocardial ischemia or previous myocardial infarctions. Telemedicine and ambient-assisted living support the electrocardiological monitoring of at-risk patients.

Conclusions: There are many promising methods for the exercise-free, non-invasive detection of CAD and myocardial ischemia in the stable and acute phases. In the coming years, these new methods will help enhance state-of-the-art procedures in routine diagnostics. The future can expect that equally novel methods for risk stratification and telemedicine will transition into clinical routine.

Cardiogoniometric parameters for detection of coronary artery disease at rest as a function of stenosis localization and distribution

Cardiogoniometry (CGM), a spatiotemporal electrocardiologic 5-lead method with automated analysis, may be useful in primary healthcare for detecting coronary artery disease (CAD) at rest. Our aim was to systematically develop a stenosis-specific parameter set for global CAD detection. In 793 consecutively admitted patients with presumed non-acute CAD, CGM data were collected prior to elective coronary angiography and analyzed retrospectively. 658 patients fulfilled the inclusion criteria, 405 had CAD verified by coronary angiography; the 253 patients with normal coronary angiograms served as the non-CAD controls. Study patients--matched for age, BMI, and gender--were angiographically assigned to 8 stenosis-specific CAD categories or to the controls. One CGM parameter possessing significance (P < .05) and the best diagnostic accuracy was matched to one CAD category. The area under the ROC curve was .80 (global CAD versus controls). A set containing 8 stenosis-specific CGM parameters described variability of R vectors and R-T angles, spatial position and potential distribution of R/T vectors, and ST/T segment alterations. Our parameter set systematically combines CAD categories into an algorithm that detects CAD globally. Prospective validation in clinical studies is ongoing.

Right ventricular pacing-induced electrophysiological remodeling in the human heart and its relationship to cardiac memory

BACKGROUND

Right ventricular apical (RVA) pacing induces electrophysiological and structural remodeling. Cardiac memory (CM) evolves during the course of pacing and is readily apparent on electrocardiography (ECG) or vectorcardiography (VCG) when normal ventricular activation resumes.

OBJECTIVE

This study sought to assess ventricular repolarization (VR) changes during pacing and intermittent normal ventricular conduction by ECG and VCG and to determine the temporal and conformational evolution of CM.

METHODS

Twenty sick sinus patients received a dual-chamber rate-adaptive (DDD-R) pacemaker and were paced from the RVA endocardium. The pacemakers were programmed to a short AV delay to maximize ventricular preexcitation. The ECG and VCG were recorded before and 1 day after implantation, and then daily for the first week (n=6) or weekly for 5 to 8 weeks (n=14), with the pacemakers temporarily programmed to AAI (normal ventricular activation).

RESULTS

The first parameters to change were T-vector amplitude, T(area), and T(peak)-T(end) (T(p-e)), which decreased within 1 day after initiating pacing. CM became apparent between day 1 and day 3, was fully established after 1 week, and then remained stable. Signs of increased VR heterogeneity were observed as the T loop became more circular (decreased T(egenv)) and distorted (increased T(avplan)), which have previously been observed in conditions with increased risk for arrhythmias. Over weeks, VR duration was prolonged (increased QTc). In contrast, during ventricular pacing, a gradual shortening of the repolarization time was observed, suggesting a stabilizing adaptive process.

CONCLUSION

In sick sinus syndrome patients in whom ventricular pacing is indicated, switching between normal AV conduction and ventricular pacing should be minimized to avoid periods of repolarization instability.

Non-dipolar content of the T-wave as a measure of repolarization inhomogeneity in ST-elevation myocardial infarction

The non-dipolar content of the T-wave, i.e. the component of the signal, which cannot be explained by a dipolar model, has been suggested as a measure of the local repolarization inhomogeneity. Our purpose was to study the non-dipolar content of the T-wave during the initial course of ST-elevation myocardial infarction (STEMI), when local repolarization inhomogeneity presumably is markedly increased. Twelve-lead ECG was semicontinuously collected in 211 patients with STEMI, treated with a thrombolytic agent. The T-wave was processed by principal component analysis. The absolute and relative T-wave residues were used as measures of the non-dipolar content. The median values for each hour and for the entire monitoring time were computed. Changes in the parameters were closer studied in two windows, 0-10 respectively, 11-24 h after start of ECG-monitoring. The median of the absolute T-wave residue during the entire monitoring period was 25 000 units in the STEMI-group and 13 500 units in the comparison group. The median for hour 1 was 36 500 units and 28 800 units for hour 2. The decrease was greater in patients with >or=50% resolution of the ST-elevation at 60 min. The moment of change, identified by cumulative sum-method, showed no correlation to the time for 50% ST-resolution. We conclude, that patients with thrombolysed STEMI have an increased non-dipolar content of the T-wave. Resolution of the ST-elevation is associated with a decrease. The increased non-dipolar content reflects a property of the repolarization phase, which is related to but separated from the ST-elevation.

Ischemia induces aggravation of baseline repolarization abnormalities in left ventricular hypertrophy: a deleterious interaction

Epidemiological studies show that left ventricular hypertrophy (LVH) and hypertension (HT) in coronary artery disease increases the risk for cardiovascular events including sudden cardiac death (SCD). According to experimental studies, myocardial hypertrophy is associated both with altered electrophysiological properties (including prolonged repolarization) and increased vulnerability to ischemia. However, human data to support a repolarization-related mechanism for the increased SCD risk has not been provided. We therefore studied 187 patients undergoing three-dimensional vectorcardiographic monitoring during coronary angioplasty. Eight parameters reflecting different aspects of ventricular repolarization were used: 1) the ST segment (ST-VM and STC-VM), 2) the T vector (QRS-T angle, Televation, and Tazimuth), and 3) the T vector loop (Tavplan, Teigenv, and Tarea). Data collection was performed at rest and at the time of maximum ischemia during coronary occlusion. The patients were divided into three groups: 33 patients with ECG signs of LVH (18 with HT), 54 with HT but without LVH signs, and 100 patients with neither. Coronary artery disease patients with LVH not only had the most abnormal baseline repolarization (as expected) but also a significantly more pronounced repolarization response during coronary occlusion, whereas HT patients had mean parameter values between LVH patients and those without neither HT nor LVH signs. Because there is a relation between increased SCD risk and repolarization disturbances in various clinical settings, the results of the present study are in agreement with animal data and epidemiological observations, although other factors than disturbed repolarization might be of importance.

The association of spatial T wave axis deviation with incident coronary events. The ARIC cohort

Background

Although current evidence suggests that the spatial T wave axis captures important information about ventricular repolarization abnormalities, there are only a few and discordant epidemiologic studies addressing the ability of the spatial T wave axis to predict coronary heart disease (CHD) occurrence.

Methods

This prospective study analyzed data from 12,256 middle-aged African American and white men and women, from the Atherosclerosis Risk in Communities Study (ARIC). Following a standardized protocol, resting standard 12-lead, 10-second electrocardiograms were digitized and analyzed with the Marquette GE program. The median follow-up time was 12.1 years; incident coronary heart disease comprised fatal and non-fatal CHD events.

Results

The incidence rate of CHD was 4.26, 4.18, 4.28 and 5.62 per 1000 person-years respectively, across the spatial T wave axis quartiles. Among women for every 10 degrees increase in the spatial T wave axis deviation, there was an estimated increase in the risk of CHD of 1.16 (95% CI 1.04–1.28). After adjustment for age, height, weight, smoking, hypertension, diabetes, QRS axis and minor T wave abnormalities, this hazard rate ratio for women fell to 1.03 (0.92–1.14). The corresponding crude and adjusted hazard ratios for men were 1.05 (95% CI 0.96–1.15) and 0.95 (0.86–1.04) respectively.

Conclusions

In conclusion, this prospective, population-based, bi-ethnic study of men and women free of coronary heart disease at baseline shows that spatial T wave axis deviation is not associated with incident coronary events during long-term follow up. It is doubtful that spatial T wave axis deviation would add benefit in the prediction of CHD events above and beyond the current traditional risk factors.

Temporal characteristics of cardiac memory in humans: Vectorcardiographic quantification in a model of cardiac pacing

OBJECTIVES

The purpose of this study was to assess the temporal characteristics of cardiac memory in a human pacing model.

BACKGROUND

Cardiac memory is induced by periods of altered ventricular activation and in the canine pacing model develops in 2 to 3 weeks.

METHODS

Cardiac memory development (phase 1) and resolution (phase 2) was followed qualitatively (ECG) and quantitatively (vectorcardiography [VCG]) in 20 patients with symptomatic sinus bradycardia receiving DDD-R pacing at physiologic rates. During phase 1, maximum ventricular pacing in the right ventricular apical endocardium was achieved by short AV delay. ECG and VCG were recorded during normal ventricular activation prior to implantation (sinus rhythm), 1 day after and then weekly for 5 to 8 weeks during AAI pacing (n = 14, "long-term"), and daily during 1 week (n = 6, "short-term"). In phase 2, the remaining cardiac memory was related to the amount of ventricular pacing. A long AV delay was chosen to reduce ventricular pacing, and 14 patients were seen once after 4 to 5 weeks.

RESULTS

ECG and VCG showed marked changes in all patients within 1 week's pacing and remained stable during phase 1. Of the 14 long-term patients, 13 showed significant change in T vector azimuth (mean -150 degrees ) and 11 in T vector elevation (mean 63 degrees ). At the end of phase 2, a linear relation existed between remaining cardiac memory (%) and amount (%) of delivered ventricular pacing.

CONCLUSIONS

Cardiac memory developed and reached steady state within 1 week of right ventricular endocardial pacing at physiologic rates in man, was preserved in proportion to delivered ventricular pacing, and completely resolved within 1 month in its absence.