Mari Karsikas

T‐Wave Morphology in Short QT Syndrome

Background: Short QT syndrome (SQTS) is an inherited disorder characterized by a short QT interval and vulnerability to ventricular tachyarrhythmias. The diagnostic criteria for this syndrome are not well defined, since there is uncertainty about the lowest normal limits for the corrected QT (QTc) interval.

QRS-T morphology measured from exercise electrocardiogram as a predictor of cardiac mortality

AIMS Total cosine R-to-T (TCRT) measured from the standard 12-lead electrocardiogram (ECG) reflects the spatial relationship between depolarization and repolarization wavefronts and a low TCRT value is a marker of poor prognosis. We tested the hypothesis that measurement of TCRT or QRS/T angle from exercise ECG would provide even more powerful prognostic information. METHODS AND RESULTS The prognostic significances of TCRT and QRS/T angle were assessed from exercise ECG recordings in 1297 patients [age 56 ± 13 years (mean ± SD), 67% males] undergoing a clinically indicated bicycle stress-test and the subsequent follow-up. During an average follow-up of 45 ± 12 months, 74 patients died (5.7%); 34 (2.6%) were cardiac deaths, and 24 (1.9%) were sudden cardiac deaths. Total cosine R-to-T and QRS/T angle exhibited a correlation with the RR intervals in the total cohort, but the individual responses were variable, e.g. median correlation of TCRT-RR was 0.89 with an inter-quartile range from 0.55 to 0.98. A reduced correlation of TCRT-RR during the recovery phase of exercise ECG predicted cardiac death [adjusted heart rate (HR) 3.5, 95% confidence interval (CI): 1.8-6.8, P= 0.001] similarly as the baseline TCRT measured from ECG at rest (adjusted HR 3.4, 95% CI: 1.4-8.1, P= 0.01). The poor correlation between the TCRT-RR both during the exercise and recovery was specifically related to a risk of sudden cardiac death (adjusted HR 6.2, 95% CI: 2.1-17.8, P< 0.001). CONCLUSIONS Loss of rate-adaptation of the spatial relationship between depolarization and repolarization wavefronts is a strong predictor of cardiac death, especially of sudden cardiac death.

Dynamics and Rate‐Dependence of the Spatial Angle between Ventricular Depolarization and Repolarization Wave Fronts during Exercise ECG

Background: QRS/T angle and the cosine of the angle between QRS and T‐wave vectors (TCRT), measured from standard 12‐lead electrocardiogram (ECG), have been used in risk stratification of patients. This study assessed the possible rate dependence of these variables during exercise ECG in healthy subjects.

Functional significance of KCNH2 (HERG) K897T polymorphism for cardiac repolarization assessed by analysis of T-wave morphology.

Background: Although KCNH2 (HERG) K897T polymorphism has been shown to be associated with the QT interval measured from 12‐lead electrocardiogram (ECG), the functional significance of K897T polymorphism has been debated. The aim of this study was to test whether the K897T polymorphism of the KCNH2 (HERG) gene coding for the rapidly activating delayed rectifier K+ channel influences cardiac repolarization assessed by principal component analysis (PCA) of T‐wave morphology.

Postexercise recovery of the spatial QRS/T angle as a predictor of sudden cardiac death

BACKGROUND Postexercise measurement of heart rate (HR) recovery and QT interval dynamics provides prognostic information in various patient populations. OBJECTIVE The purpose of this study was to assess whether the measurement of the spatial relationship between the depolarization and repolarization wavefronts (total cosine R-to-T [TCRT]) during the postexercise recovery phase would yield prognostic information. METHODS The population consisted of 1297 patients (56 ± 13 years; 67% men) who performed a clinically indicated bicycle stress test. The exercise-recovery hysteresis of TCRT was quantified from the 12-lead exercise electrocardiogram by measuring the TCRT/HR loop area bounded by the exercise and first 3-minute postexercise recovery curves. The HR-corrected TCRT/HR hysteresis was calculated by dividing the area with the HR decrement during the first 3 minutes of recovery. HR recovery was measured at 1 minute postexercise recovery. End points were cardiac death and sudden cardiac death. RESULTS During an average follow-up of 45 ± 12 months, 74 patients died (5.7%); 35 (2.6%) were cardiac deaths and 24 (1.9%) were sudden cardiac deaths. Reduced TCRT/HR loop area and TCRT/HR hysteresis were associated with cardiac mortality (P <.001). After adjustments for clinical variables, including ejection fraction, TCRT/HR loop area remained an independent predictor of cardiac death (hazard ratio 5.6; 95% confidence interval 1.6-19.1; P = .007) and sudden cardiac death (10.7; 95% confidence interval 1.4-83.7; P = .024). HR recovery did not remain a significant predictor in the multivariate analysis. CONCLUSIONS Attenuated hysteresis of the depolarization and repolarization wavefronts during postexercise recovery is associated with an increased risk of cardiac and sudden cardiac death. Analysis of repolarization dynamics from exercise electrocardiogram represents a promising tool for risk stratification.

Influence of Paper Electrocardiogram Digitizing on T Wave and QRS Complex Morphology Parameters

Backround: Many morphological parameters of the electrocardiogram (ECG) can be calculated from a digital ECG and paper prints of ECG after digitizing. However, the digitizing process, including printing, scanning, ECG contour extraction, and alignment, can produce changes to the signals, reducing the reliability of some sensitive parameters of QRS complex and T wave.

New Vectorcardiographic non-planarity measure of T-wave loop improves separation between healthy subjects and myocardial infarction patients

Principal component analysis of vectorcardio-graphic T-wave loop has been shown to be a potential tool to describe the abnormality of the cardiac repolarization and to predict cardiac events in patients with cardiac disease. In this paper a new method for estimating the non-planarity of the T-wave loop is introduced and tested with healthy subjects and subjects with anterior or inferior myocardial infarction. The method is based on the resamping of T-wave data points with respect to the arc-length, the total least squares plane fitting, the identifying and reordering of the fitted axes, and decomposing the optimal rotation matrix. A recently published related measure, PCA3, was used for comparison purposes. The results showed that the non-planarity of T-wave loop increased significantly in patients with myocardial infarction compared to the healthy group. The new method separated healthy and patient groups with p-value 0.002 while PCA3 only with p-value 0.075. The new method was superior to PCA3 in separating the healthy patients from both infarction types.

Electrocardiographic abnormalities and ventricular tachyarrhythmias after myocardial infarction

Abstract Aims. To assess the association of electrocardiographic repolarization and depolarization patterns to vulnerability to ventricular tachyarrhythmias. Methods. In the present case-control study, a 12-lead ECG, signal-averaged ECG (SAECG), T-wave and QRS morphology, and T-wave alternans (TWA) were analyzed in post-MI patients with and without documented sustained ventricular tachycardia (VT) or fibrillation (VF) (VT/VF group, n=40, Non-VT/VF group, n=37, respectively) and healthy subjects (n=41). Results. The QRS complex duration, measured from standard ECG (128 ± 32 ms vs. 102 ± 21 ms, p<0.001) or SAECG (125 ± 25 ms vs. 99 ± 20 ms, p<0.001), was significantly longer in the VT/VF than Non-VT/VF group. Several T-wave morphology variables, e.g., the total cosine of the angle between the main vectors of T-wave and QRS loops (TCRT), were different in the VT/VF (−0.13 ± 0.58) and Non-VT/VF group (−0.11 ± 0.48) compared to the healthy controls (0.47 ± 0.50, p<0.001). However, there were no significant differences in any of the T-wave morphology variables including TWA between the two post-MI groups. Conclusion. Abnormalities in ventricular depolarization are more common among post-MI patients with prior VT/VF than in those without documented ventricular tachyarrhythmias. Abnormal T-wave morphology and TWA seem to reflect the heart disease rather than specifically vulnerability to VT/VF.

A Method for Robustly Determining the Relative Orientation of Vectorcardiographic Loop Structures

A robust method to determine the relative orientations of vectorcardiographic loop structures is presented.

Improving reliability of ‘Total-Cosine-R-to-T’ (TCRT) in patients with acute myocardial Infarction

The parameter TCRT (total cosine R-to-T) calculated from ECG recording has been shown to have a remarkable prognostic value as a predictor of the outcomes of the coronary artery disease and the acute myocardial infarction (AMI) patients. The TCRT is conventionally calculated using an algorithm produced by Acar et al. (1999). In this study, the reliability of the healthy group (n=25) and the AMI group (n=45). Typical problems occurred in the detection of the maximum of the T vector (9% of patients), the bounding of the R wave (18%), a comprehensive segmentation (11%), and a decreased congruence between TCRT and the spatial QRS-T angle (33%). The results show that small improvements to the basic algorithm can decrease the number of failures up to 82% in AMI data. It is concluded that segmentation properties should be improved in the basic TCRT algorithm in order to maintain the diagnostic value of TCRT in different patient data.