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Notes: Components of heart rate variability have attracted considerable attention in psychology and medicine and have become important dependent measures in psychophysiology and behavioral medicine. Quantification and interpretation of heart rate variability, however, remain complex issues and are fraught with pitfalls. The present report (a) examines the physiological origins and mechanisms of heart rate variability, (b) considers quantitative approaches to measurement, and (c) highlights important caveats in the interpretation of heart rate variability. Summary guidelines for research in this area are outlined, and suggestions and prospects for future developments are considered.

Notes: QT dispersion is significantly greater in patients with hypertrophic cardiomyopathy (HCM) than that in healthy subjects. Few data exist regarding the prognostic value of QT dispersion in HCM. In this study, we retrospectively investigated the association between QT dispersion and sudden cardiac death in 46 patients with HCM (mean 33.1 ±; 15.5 years, 32 men). The case group consisted of 23 HCM patients who died suddenly, and the control group consisted of 23 HCM patients who survived uneventfully during follow-up. Study patients were pair-matched for age, gender, and maximum left ventricular wall thickness. QT dispersion (maximum minus minimum QT interval) was manually measured on early 12-lead ECGs using a digitizing; board. An in-house program was used for calculating QT interval, QT dispersion, JT interval, and JT dispersion (maximum minus minimum J point to T end interval). Patients in the case group tended to have shorter RR intervals than those in the control group (777 ±; 171 vs 856 ±; 192 ms, P = 0.08). Maximum corrected QT and JT intervals did not discriminate the case group from controls (489 ±; 29 vs 479 ±; 27 ms, P = NS; 375 ±; 36 vs 366 ±; 22 ms, P = NS, respectively). Greater QT dispersion and JT dispersion were found in the case group compared with controls (74 ±; 28 vs 59 ±; 21 ms, P = 0.02 and 76 ±; 32 vs 59 ±; 26 ms, P = 0.03, respectively). The measurements of maximum QT, JT, and T peak to T end intervals, precordial QT and JT dispersion, and T peak and T end dispersion were all comparable between the two groups (P = NS for all). No systematic changes in ECG measurements were found from late ECGs of the case group compared to those from early ECGs (P = NS). No correlation between maximum left ventricular wall thickness and QT dispersion, JT dispersion, maximum QTc or JTc intervals was observed (r 〈 0.29, P 〉 0.05 for all). Our results; show that increased QT dispersion and JT dispersion is weakly associated with sudden cardiac death in the selected patients with HCM. A.N.E. 2001; 6(3):209–215

Notes: Background:Spectral techniques for the analysis of signal-averaged electrocardiogram (ECG) are superior to the standard time-domain analysis in special circumstances but none of these techniques is better than the time-domain analysis in the prospective risk stratification of survivors of myocardial infarction (Ml). Aim:This study applied wavelet decomposition of signal-averaged ECGs to prospective risk stratification of Ml survivors and compared its performance with that of conventional time-domain analysis. Methods:Eligible patients were aged 〈inlineGraphic alt="leqslant R: less-than-or-eq, slant" extraInfo="nonStandardEntity" href="urn:x-wiley:1082720X:ANEC20:les" location="les.gif"/〉 75 years without atrial fibrillation, important noncardiac disease, bundle branch block, ventricular preexcitation, permanent pacemaker, or a history of cardiac surgery. Of 754 eligible patients, signal-averaged ECG recordings were available in 551. During a 2-year follow-up, 32 patients suffered from cardiac death (CM), 21 potentially arrhythmic death, 19 sudden cardiac death (SCO), 19 developed nonfatal sustained ventricular tachycardia (VT), and 5 were resuscitated from an ECG-documented ventricular fibrillation. Signal-averaged ECG indices from both analyses were compared in patients with and without different follow-up events. The positive predictive characteristics (dependency of positive predictive accuracy on sensitivity) for predicting different follow-up events based on both modes of analysis were compared at selected levels of sensitivity. Results: Time-domain signal-averaged ECGs were strongly correlated with incidence of VT (P = 0.01). Positive wavelet analysis was more strongly correlated with this event (P 〈 0.005) and with cardiac mortality (P 〈 0.05). For all events, wavelet analysis gave higher positive predictive accuracy (PPA) than the time-domain analysis, e.g., the prediction of SCD at sensitivity of 25%, wavelet and time-domain analyses gave PPA of 20.0% and 6.5%, respectively (P 〈 10-10). Conclusion:Wavelet decomposition analysis of signal-averaged ECGs is superior to the standard time-domain analysis in predicting post-MI events. In particular, this analysis identifies not only those post-MI patients who are at high risk of nonfatal sustained VT but also those who are at risk of SCD. A.N.E. 2000;5(1):20–29

Notes: Background: The prolongation of P-wave duration has long been shown to indicate the presence of high risk for atrial fibrillation. The circadian variation of P-wave characteristics and their dynamic adaptation to heart rate changes was not tested before.Methods: To evaluate the diurnal pattern of P-wave duration, P area, and PR interval and of their linearly fitted relation with RR interval, 50 healthy volunteers (25 men, mean age 34 ± 10 years) underwent 24-hour ambulatory electrocardiographic (ECG) recording with digital 12-lead Holter recorders. The median P-wave duration, P area, and PR interval were calculated from the average 12-lead ECG constructed from each 10-second ECC recording. Single harmonic regression analysis was performed to reveal the presence of circadian variation in the aforementioned ECG parameters.Results: The P area (P 〈 0.0001, R2= 0.78), the PR interval (P 〈 0.0001, R2= 0.92), the P area / RR slope (P 〈 0.0001, R2= 0.55), and the PR/RR slope (P 〈 0.0001, R2= 0.42) showed a highly significant circadian variation while the periodic nature of P-wave duration (P = 0.016, R2= 0.32) and of the P duration / RR slope (P = 0.011, R2= 0.18) was only indicated by harmonic regression analysis.Conclusions: P-wave duration, P area, and PR interval show a significant circadian variation in healthy subjects. The relations between P area/RR,PR/ RR, and P duration/RR also demonstrate a significant diurnal pattern. A.N.E. 2001;6(2):92–97

Notes: Background: Although prolonged duration of the signal-averaged (SA) P wave has been proposed as a noninvasive marker of atrial arrhythmias, clinical value of atrial SAECG is limited, largely due to the difficulty with detection of the onset and offset of the high gain P wave. The aim of this study was to assess the reliability of automatic measurement of the atrial SAECG.Methods: Fifty-one healthy volunteers (30 men; 32 ± 8 years) underwent a session of 3 atrial and 3 ventricular SAECG recordings. Automatically detected onset and offset of SA QRS complex (QRStot) and SA P wave (Ptot) were subsequently-corrected by two independent observers. For ventricular SAECG, three conventional time-domain parameters were calculated. For atrial SAECG, the following five parameters were measured: Ptot, root mean square voltages of the entire Ptot (RMS-P) and of the terminal 40, 30, and 20 ms of Ptot. Relative errors of the different pairs of measurements were used to assess the interobserver and observer-computer variability. The Bland-Altman method was applied to express the agreement between measurements.Results: Although the mean interobserver relative errors were low for QRStot and Ptot (1.1% vs 1.5%), the observer-computer error was significantly higher for Ptot than for QRStot (1.7% vs 7.1%; P 〈 0.0001). For the voltage parameters, the lowest interobserver and observer-computer relative errors were found for RMS-P (6.6% vs 7.3%, P = ns). For RMS voltages of the terminal 40–20 ms of Ptot, relative errors exceeded 10%, but the interobserver error was significantly lower than the observer-computer error (P 〈 0.0001).Conclusion: Automatic detection of the SA P-wave onset and offset is unreliable and the atrial SAECG requires manual correction. Given a good interobserver agreement, such a correction is unlikely to introduce any significant observer-dependent bias. A.N.E. 2000; 5(2):133–138

Notes: Prolonged QT interval and QT dispersion have been reported to be associated with arrhythmogenesis in patients with cardiac disorders. However, the use of QT dispersion for risk stratification is limited by its low reproducibility. Recently, measurement of the interval between the peak and the end of the T wave (Tp-Te interval) has been suggested for detection of repolarization abnormalities, but its clinical utility has not been studied in a systematic fashion.〈section xml:id="abs1-2"〉〈title type="main"〉MethodsThis study assessed the intrasubject reproducibility of automatic measurements of QTend, QTpeak, and Tp-Te interval dispersion in 71 normal subjects and 37 patients with hypertrophic Cardiomyopathy (HC). A set of 20 ECGs (10 in supine and 10 in standing position) was evaluated in each subject. Measurements were performed automatically using an advanced commercial computer system.〈section xml:id="abs1-3"〉〈title type="main"〉ResultsHC patients showed significantly higher values of QTtend, QTpeak, Tp-Te intervals, and QTend, QTpeak dispersion compared to normal subjects (42 ± 20 vs 20 ± 12 ms and 45 ± 24 vs 33 ± 12 ms, respectively; P 〈 0.04), but no significant difference was observed in Tp-Te dispersion between both groups (32 ± 16 vs 29 ± 8 ms; NS). The reproducibility of QTend, QTpeak, and Tp-Te dispersion, expressed as coefficients of variation, was poor in both groups (14%-28% in normal subjects and 18% to 37% in HC patients).〈section xml:id="abs1-4"〉〈title type="main"〉ConclusionDespite higher values of QTend, QTpeakTp-Te intervals and QTend, QTpeak dispersion in HC patients than in normal subjects, Tp-Te dispersion was similar in both groups. The reproducibility of QTend, QTpeak, and Tp-Te dispersion was low. Automatic measurement of Tp-Tp dispersion failed to differentiate normal subjects and HC patients.

Notes: An imbalance between sympathetic and parasympathetic tone has been shown to contribute to the genesis of malignant arrhythmias after acute myocardial infarction (AMI). To assess a relationship between the magnitude of sympathoadrenal activation and the balance of autonomic input to the heart early after AMI, plasma catecholamine levels and spectral analysis of short-term heart rate variability (HRV) were evaluated on day 2 and 5 after hospital admission under standardized conditions.〈section xml:id="abs1-2"〉〈title type="main"〉MethodsThirty-two patients with AMI (27 men, 5 women, mean age 58 ± 10 years) were studied, 13 with anterior and 19 with inferior AMI. Mean left ventricular ejection fraction (LVEF), assessed by two-dimensional echocardiography, was 48%± 10%. Thirty-minute ECG recordings were performed in recumbent position, between 9–11 A.M., and edited data were used for analysis of HRV in frequency domain. The control group consisted of 9 patients (6 men, 3 women, mean age 49 ± 10 years) without a history of cardiovascular or systemic disease, who had normal findings on physical examination of the cardiovascular system, and normal 12-lead ECG. All control subjects were admitted to the hospital for eye or dermatological surgery and underwent the same study procedures according to the identical time schedule.〈section xml:id="abs1-3"〉〈title type="main"〉ResultsPlasma catecholine levels decreased significantly from day 2 to 5 of AMI, however, compared to control subjects, the only significant difference suggesting early sympathoadrenal activation in AMI patients was elevated plasma norepinephrine on day 2 (1.73 ± 1.6 vs 0.81 ± 0.7, P 〈 0.049). Among spectral components of HRV, a trend toward decrease from day 2 to 5 was found for both high frequency (HF) (123.8 ± 184.8 vs 66.7 ± 80.1 ms2, P 〈 0.03) and low frequency (LF) (293 ± 423.3 vs 164.3 ± 235.4 ms2, P 〈 0.14) components, although statistically significant only for HF components. However, the ratio between LF and HF components remained unchanged (3.4 ± 2.6 vs 3.6 ± 2.7). Significantly lower values of both LF and HF components, total power, and mean NN interval together with a tendency for a higher LF/HF ratio on day 2 were found in patients with anterior AMI as compared to those with inferior AMI or control subjects. This difference already disappeared on day 5 due to a decrease in both components of HRV in patients with inferior localization of the infarct. Patients with depressed LVEF presented with significantly lower HF components (both in absolute and relative units) while no difference was observed in the mean heart rate or in relative LF components. No significant correlations were found between LF or HF components or their ratio and either measure of sympathoadrenal activity (epinephrine, or norepinephrine and dopamine).〈section xml:id="abs1-4"〉〈title type="main"〉ConclusionThe findings of increased plasma norepinephrine levels early after AMI confirm initial sympathoadrenal activation, which was probably related to the presence of myocardial ischemia and/or necrosis per se, independently on the site of myocardial infarction and the degree of impairment of LVEF. The observed changes in spectral measures of short-term HRV assessed at supine rest under standardized conditions appear to reflect the extent of impairment of cardiac autonomic regulation rather than the magnitude of sympathoadrenal activation. Significant depression of HF

Notes: Objective: Although gender specificities of various risk factors have been well documented, risk stratification after myocardial infarction has never been compared in women and men.Methods: The power of left ventricular ejection fraction, heart rate variability, and mean RR interval computed from 24-hour Holter recordings, was compared in women and men for the prediction of cardiac mortality after an acute myocardial infarction. The study population consisted of 456 patients (108 women, 348 men) aged 50–75 years.Results: During a follow-up of 3 years, there were 41 cardiac deaths (13 women vs 28 men, P = NS). The positive predictive accuracy of left ventricular ejection fraction, heart rate variability, and mean RR interval at all sensitivity levels was higher in women than in men. For a 40% sensitivity, positive predictive accuracy of left ventricular ejection fraction was 46% in women and 16% in men (P 〈 0.05), positive predictive accuracy of mean RR interval was 90% in women and 28% in men (P 〈 0.05), and positive predictive accuracy of heart rate variability was 61% in women and 43% in men (P = NS). Mean RR interval had the highest positive predictive accuracy for cardiac mortality in women, but its superiority over heart rate variability was not statistically significant. In men, heart rate variability was the strongest predictor of mortality that was significantly more powerful than mean RR interval and left ventricular ejection fraction (P 〈 0.05).Conclusion: Increased 24-hour mean heart rate is the strongest predictor of cardiac mortality in women in whom it performs significantly better than in men. While in men, heart rate variability is a significantly better predictor of postinfarction cardiac mortality than 24-hour mean heart rate, this is not the case in women.

Notes: 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.Methods: Thirty ECGs recorded at 25 mm/s were measured by six independent observers. The observers used an adopted scheme to classify the repolarization pattern into 1 of 7 categories, based on the appearance of the T wave, and/or the presence of the U wave, and the various extent of fusion between these. In each lead with measurable QRST(U) pattern, the RR, QJ, QT-end, QT-nadir (i.e., interval between Q onset and the nadir or transition between T and U wave) and QU interval were measured, when applicable. Based on these measurements, the mean RR interval, the maximum, minimum, and mean QJ interval, QT-end and/or QT-nadir interval, and QU interval, the difference between the maximum and minimum QT interval (QT dispersion [QTD]), and the coefficient of variation of QT intervals was derived for each recording. The agreement of an individual observer with other observers in the selection of a given repolarization pattern were investigated by an agreement index, and the general reproducibility of repolarization pattern classification was evaluated by the reproducibility index. The interobserver agreement of numerical measurements was assessed by relative errors. To assess the general interobserver reproducibility of a given numerical measurement, the coefficient of variance of the values provided by all observers was computed for each ECG. Statistical comparison of these coefficients was performed using a standard sign test.Results: The results demonstrated the existence of remarkable differences in the selection of classification patterns of repolarization among the observers. More importantly, these differences were mainly related to the presence of more complex patterns of repolarization and contributed to poor interobserver reproducibility of QTD parameters in all 12 leads and in the precordial leads (relative error of 31%–35% and 34%–43%, respectively) as compared with the interobserver reproducibility of both QT and QU interval duration measurements (relative error of 3%–6%, P 〈 0.01). This observation was not explained by differences in the numerical order between QT interval duration and QTD, as the reproducibility of the QJ interval (i.e., interval of the same numerical order as QTD was significantly better (relative error of 7.5%–13%, P 〈 0.01) than that of QTD.Conclusions: Poor interobserver reproducibility of QT dispersion related to the presence of complex repolarization patterns may explain, to some extent, a spectrum of QT dispersion values reported in different clinical studies and may limit the clinical utility in this parameter.