Yi Gang

QT dispersion does not represent electrocardiographic interlead heterogeneity of ventricular repolarization.

QT Dispersion and Repolarization Heterogeneity. Introduction: QT dispersion (QTd, range of QT intervals in 12 ECG leads) is thought to reflect spatial heterogeneity of ventricular refractoriness. However, QTd may be largely due to projections of the repolarization dipole rather than “nondipolar” signals.

Heart rate variability in critical care medicine.

The autonomic nervous system plays an integral role in homeostasis. Autonomic modulation can frequently be altered in critically ill patients. Assessment of heart rate variability (HRV) is based on analysis of consecutive normal R-R intervals and may provide quantitative information on the modulation of cardiac vagal and sympathetic nerve input. The hypothesis that depressed HRV may occur over a broad range of critical illness and injury and may be inversely correlated with disease severity and outcome has been tested in the last decade. In this article, we review recent literature concerning assessment of HRV in patients with critical illness or injury, as well as the potential clinical implications and limitations of HRV assessment in this area.

Sample Size, Power Calculations, and Their Implications for the Cost of Thorough Studies of Drug Induced QT Interval Prolongation

Regulatory authorities require new drugs to be investigated using a so‐called “thorough QT/QTc study” to identify compounds with a potential of influencing cardiac repolarization in man. Presently drafted regulatory consensus requires these studies to be powered for the statistical detection of QTc interval changes as small as 5 ms. Since this translates into a noticeable drug development burden, strategies need to be identified allowing the size and thus the cost of thorough QT/QTc studies to be minimized. This study investigated the influence of QT and RR interval data quality and the precision of heart rate correction on the sample sizes of thorough QT/QTc studies. In 57 healthy subjects (26 women, age range 19–42 years), a total of 4,195 drug‐free digital electrocardiograms (ECG) were obtained (65–84 ECGs per subject). All ECG parameters were measured manually using the most accurate approach with reconciliation of measurement differences between different cardiologists and aligning the measurements of corresponding ECG patterns. From the data derived in this measurement process, seven different levels of QT/RR data quality were obtained, ranging from the simplest approach of measuring 3 beats in one ECG lead to the most exact approach. Each of these QT/RR data‐sets was processed with eight different heart rate corrections ranging from Bazett and Fridericia corrections to the individual QT/RR regression modelling with optimization of QT/RR curvature. For each combination of data quality and heart rate correction, standard deviation of individual mean QTc values and mean of individual standard deviations of QTc values were calculated and used to derive the size of thorough QT/QTc studies with an 80% power to detect 5 ms QTc changes at the significance level of 0.05. Irrespective of data quality and heart rate corrections, the necessary sample sizes of studies based on between‐subject comparisons (e.g., parallel studies) are very substantial requiring >140 subjects per group. However, the required study size may be substantially reduced in investigations based on within‐subject comparisons (e.g., crossover studies or studies of several parallel groups each crossing over an active treatment with placebo). While simple measurement approaches with ad‐hoc heart rate correction still lead to requirements of >150 subjects, the combination of best data quality with most accurate individualized heart rate correction decreases the variability of QTc measurements in each individual very substantially. In the data of this study, the average of standard deviations of QTc values calculated separately in each individual was only 5.2 ms. Such a variability in QTc data translates to only 18 subjects per study group (e.g., the size of a complete one‐group crossover study) to detect 5 ms QTc change with an 80% power. Cost calculations show that by involving the most stringent ECG handling and measurement, the cost of a thorough QT/QTc study may be reduced to approximately 25%‐30% of the cost imposed by the simple ECG reading (e.g., three complexes in one lead only).

Interobserver Reproducibility of QT Interval Measurement and QT Dispersion in Patients After Acute Myocardial Infarction

Background: The study evaluated interobserver differences in the classification of the T‐U wave repolarization pattern, and their influence on the numerical values of manual measurements of QT interval duration and dispersion in standard predischarge 12‐lead ECGs recorded in survivors after acute myocardial infarction.

Fractal correlation properties of R-R interval dynamics in asymptomatic relatives of patients with dilated cardiomyopathy☆

asymptomatic relatives of patients with familial dilated cardiomyopathy who have left ventricular enlargement [LVE] are at risk for progression to dilated cardiomyopathy. A novel index of the fractal correlation properties of heart rate variability (HRV), the short‐term scaling component (∝1) in detrended fluctuation analysis, is a promising prognostic tool in left ventricular dysfunction. The aim of this study was to compare values of ∝1 and conventional HRV indices in LVE relatives with dilated cardiomyopathy patients and normal controls.

Preoperative Electrocardiographic Risk Assessment of Atrial Fibrillation After Coronary Artery Bypass Grafting

Introduction: This study evaluated the role of surface ECG in assessment of risk of new‐onset atrial fibrillation (AF) after coronary artery bypass grafting surgery (CABG).