Showing papers in "Annals of Noninvasive Electrocardiology in 1996"

Heart Rate Variability.: Standards of Measurement, Physiological Interpretation, and Clinical Use: Task Force of The European Society of Cardiology and the North American Society for Pacing and Electrophysiology

Abstract: Reduced heart rate variability carries an adverse prognosis in patients who have survived an acute myocardial infarction. This article reviews the physiology, technical problems of assessment, and clinical relevance of heart rate variability. The sympathovagal influence and the clinical assessment of heart rate variability are discussed. Methods measuring heart rate variability are classified into four groups, and the advantages and disadvantages of each group are described. Concentration is on risk stratification of postmyocardial infarction patients. The evidence suggests that heart rate variability is the single most important predictor of those patients who are at high risk of sudden death or serious ventricular arrhythmias.

American Heart Association Report on the Public Access Defibrillation Conference.: December 8?10, 1994

Abstract: During the past 20 years, morbidity and mortality rates for nearly all types of cardiovascular disease have declined. Progress in these areas is in stark contrast to that for sudden cardiac death, which continues unabated at a rate of approximately 1000 times per day in the United States, with little decline in incidence or improved outcome. Clearly, the problem of sudden cardiac death is best approached through prevention, but horizons in that area seem no more promising and in some respects less promising and substantially more costly than 2 decades ago. The means necessary for successful resuscitation of a patient in cardiac arrest were known by the early 1960s. Externally performed cardiopulmonary resuscitation (CPR) could maintain an “oxygen plateau” and delay permanent brain damage long enough to allow external defibrillation using direct current (DC). The possibility of long-term survival was increasingly recognized, as early anecdotal experiences accumulated into published series.1 2 3 Given the hindsight of 3 decades, the obstacles to be overcome before significant progress could be made in out-of-hospital resuscitation were formidable. First, cardiac arrest was perceived as an event that typically occurred in the hospital. In-hospital cardiac arrests are now recognized to represent only a small proportion of sudden deaths based in the community. Second, the CPR technique was known to only a limited number of hospital-based physicians. CPR is no longer restricted to hospitals or physicians; it is routinely taught to the lay public. Third, only line-powered, bulky, and awkward defibrillators were available. The first out-of-hospital defibrillation device weighed 110 lb. Contemporary external defibrillators are available that weigh less than 10 lb. The present report details progress made in achieving the goal of facilitating out-of-hospital resuscitation and specifies those areas in which further headway is needed. This effort began in 1990 with an American Heart …

Continuous Quantification of Baroreflex and Respiratory Control of Heart Rate by Use of Bivariate Autoregressive Techniques

Abstract: Background: Normal cardiovascular control involves nonstationary complex interactions between a variety of variables such as heart rate (HR), arterial blood pressure (ABP), and respiratory activity. Methods: To account for both the complexity and transient nature of these phenomena, a closed-loop bivariate and time-variant (moving window) model was implemented using autoregressive parametric techniques to identify the typical HR and ABP spectral parameters of low frequency power (LF, 0.03–0.15 Hz), high frequency power (HF, 0.15–0.45 Hz), and their ratio LF/HF. In addition, cross-parameters, such as the gain, phase, and coherent power, between HR, ABP, and changes in instantaneous lung volume (ILV) were computed in both the LF and HF regions. Results: The cross-relations included the HR baroreflex (ABP-HR, alpha), respiratory sinus arrhythmia (ILV-HR), the mechanical influence of respiration (ILV-ABP), and the mechanical feedforward of HR (HR-ABP, beta). The analyses were performed on data from a gradual tilt protocol, which simulates the physiological nonstationarities encountered in daily life. Conclusions: The results were similar to those obtained using a bivariate batch (nonmoving window) Levinson-Wiggins-Robinson algorithm, but the time-variant technique was able to provide nearly continuous parameters, allowing for a real-time continuous monitoring of circulatory control.

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

Abstract: 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.

Frequency Response Characteristics Required for Detection of T‐Wave Alternans During Ambulatory ECG Monitoring

Abstract: Background: T-wave alternans has been increasingly implicated as a potential marker of vulnerability to ventricular tachyarrhythmias in both experimental and clinical investigations. However, the suitability of ambulatory ECG (AECG) recorders for monitoring this parameter has not been systematically studied. Methods: We evaluated the frequency response characteristics and performance in monitoring a computer simulated alternans signal in three brands of amplitude-modulated (AM) and one frequency-modulated (FM) recorder and compared the results to those of the reference digital AECG unit. Results: A common feature of the AM recorders was distortion due to electronic head resonance, particularly at heart rates in the range of 60–100 beats/min. The maximum distortion of T-wave morphology by the AM units was —6% to +28%. Conclusions: We conclude that digital and FM recorders are preferable for AECG monitoring of T-wave alternans. AM recorders can be used if the distortion is not excessive.

Changes in autonomic activity preceding onset of nonsustained ventricular tachycardia.

Abstract: Background: The triggering role of the autonomic nervous system in the initiation of ventricular tachycardia has not been established. To investigate the relationship between changes in autonomic activity and the occurrence of nonsustained ventricular tachycardia (NSVT) we examined heart rate variability (HRV) during the 2-hour period preceding spontaneous episodes of NSVT. Twenty-four subjects were identified retrospectively as having had one episode of NSVT during 24-hour Holter ECC recording. Methods: We measured the mean interval between normal heats (meanRR), the standard deviation of the intervals between beats (SD), the percentage of counts of sequential intervals between normal beats with a change of >50 ms (%RR50), the logarithms of low- and high-frequency spectral components (lnLF, lnHF) of HRV for sequential 10-minute segments preceding NSVT. The correlation dimension (CDim) of HRV was calculated similarly for sequential 20-minute segments. We assessed the significance of the time-course change of each marker over the 120-minute period prior to NSVT onset. Results: MeanRR (P < 0.05), lnLF (P < 0.0001), lnHF (P < 0.0001), the natural logarithm of the ratio of LF to HF (ln[LF/HF]; P < 0.05), and CDim (P < 0.05) showed significant time-course changes during that period, while SD and %RR50 did not. MeanRR, lnLF, lnHF, and CDim all decreased prior to the onset of NSVT, whereas ln(LF/HF) increased. We divided the subjects into two groups: one consisting of 12 patients with coronary artery disease; and the second group of 12 patients without known coronary artery disease. Both groups showed significant changes (P < 0.05) of CDim, lnLF, and lnHF preceding the episodes of NSVT. Conclusions: Changes in the pattern of HRV prior to the onset of episodes of NSVT suggest that changes in autonomic activity may commonly play a role in the triggering of spontaneous episodes of NSVT in susceptible patients. The measured changes suggest a reduction in parasympathetic activity, perhaps in conjunction with an increase in sympathetic activity, may trigger NSVT.

T-Wave Alternans During Ambulatory Ischemia in Patients with Stable Coronary Disease

Abstract: Background: T-wave alternans is a marker of vulnerability to ventricular tachyarrhythmias and has been documented during myocardial ischemia associated with angioplasty, bypass graft occlusion, and episodes of Prinzmetal's variant angina. We examined whether this phenomenon was present during ambulatory ischemia in ten patients randomly selected from the placebo phase of the Angina and Silent Ischemia Study [ASIS]. Methods: The eligibility criteria for participation in the ASIS study were stable coronary disease, a positive exercise stress test, and verified ischemic episodes during ambulatory ECG (AECG) monitoring. For each patient, one ischemic episode was analyzed which met the criteria of > 2-mm ST segment depression for > 3 minutes with a relatively stable ST segment baseline of > 1 hour preceding the index episode. T-wave alternans was measured using the spectral analytical technique of complex demodulation. Results: In the stable coronary patients of the ASIS trial, we found that T-wave alternans magnitude nearly tripled from 0.27 ± 0.02 mV × ms before ischemia onset to 0.77 ± 0.08 mV × ms (P 2 mm and the ischemia-induced increase in T-wave alternans. Conclusions: We conclude that T-wave alternans often occurs in association with ambulatory ischemia. Thus, risk assessment in stable coronary patients may be enhanced by monitoring both ST segment deviation and T-wave alternans as they measure relevant but fundamentally different electrophysiological properties.

Comparison of Computerized and Standard Visual Criteria of Exercise ECG for Diagnosis of Coronary Artery Disease

Abstract: Objective: To review past and current studies of computerized exercise ECG criteria in order to establish which, if any, are superior to standard visual analysis for the diagnosis of coronary artery disease (CAD) Methods: Prior studies that compared multiple computerized ECG criteria were reviewed In addition, we investigated two sets of patients that had both exercise testing and coronary arteriography at two university-affiliated Veteran's Affairs Medical Centers Patients with previous myocardial infarction or coronary artery bypass surgery, valvular heart disease, left bundle branch block, or any diagnostic Q waves present on their resting ECGs were excluded from analysis Sensitivity and specificity values were compiled for standard visual analysis and for the following computerized ECG criteria: ST0; ST60; ST slope; ST integral; ST index; R wave adjusted ST; ST/heart rate (HR) index; Hollenberg's Treadmill exercise score; and discriminant function analysis (DFA) Results: Despite the effects of limited challenge and work-up bias, the compiled results indicate that ST measurements recorded during the time of recovery from exercise are substantially more diagnostic than those recorded at maximal exercise ST integral, ST60, and R wave adjusted ST60 during recovery are especially discriminating of CAD, while Hollenberg's treadmill exercise score is not There were inconclusive results for HR adjustments to ST depression and ST index DFA including visual analysis of the ECG consistently exhibited the greatest discriminating power of all computerized results Conclusion: Although DFA, ST integral during recovery, or ST60 during recovery exhibited improved predictive value, further research is necessary before we can clearly offer a superior alternative to standard visual analysis

Autonomic Effects on the QT Interval

Abstract: Background: This study was designed to evaluate the effects of autonomic tone on the QT interval, using conventional and heart rate independent analysis. Effects of autonomic tone on the QT interval have been studied either using rate correction formulae or during fixed rate atrial pacing, both of which have been associated with problems. Since most autonomic interventions are associated with heart rate changes, separation of “true” autonomic effects from rate related effects on the QT interval is essential. Methods: Electrocardiographic recordings were performed in 14 healthy volunteers during: (1) sympathetic stimulation (tilt, epinephrine infusion, isoproterenol infusion, and exercise); (2) β-adrenergic blockade; (3) parasympathetic blockade; (4) autonomic blockade; (5) tilt following autonomic blockade; (6) parasympathetic stimulation (phenylephrine infusion); and (7) isolated α-adrenergic stimulation (phenylephrine infusion following atropine). The QT interval was adjusted for heart rate using Bazett's formula. Heart rate independent analysis was performed between conditions with similar cycle lengths. Results: QT interval measurements were reproducible and exhibited the typical QT-RR relationship. Sympathetic stimulation decreased the RR interval and prolonged the QTc interval. Parasympathetic blockade also increased the QTc. Heart rate independent analysis of the effects of β-blockade showed a shortening of the QT (from 368.5 ± 20.5 ms to 355.9 ± 17.9 ms; n = 8). Alpha-adrenergic stimulation also decreased the QT interval from 302.4 ± 16.8 ms to 294.3 ± 17.7 ms (n = 7). Conclusion: Sympathetic stimulation prolongs the QT interval, while β-blockade shortens it. Alpha-adrenergic stimulation also shortens the QT interval. Autonomic effects on the QT interval as assessed by heart rate independent analysis may help separate the true autonomic effects from rate related effects.

Reproducibility and Comparability of Short‐ and Long‐Term Heart Rate Variability Measures in Healthy Young Men

Abstract: Background: In heart rate variability (HRV) studies, the duration of the electrocardiographic recordings may vary between 20 seconds and 24 hours. Little is known about the reproducibility or comparability of HRV measures calculated over observation periods of different duration. Methods: To assess the reproducibility and comparability of HRV measures computed from short recordings under standardized conditions and from ambulatory 24-hour recordings, 15 healthy young males were studied on three occasions. Results: The reliability coefficient (between subject variation divided by summed between and within subject variation) for 20-second intervals was low for all measures. For 5-minute intervals in supine position, but not standing position, the reliability coefficients of the standard deviation, root of mean squared successive differences, proportion of successive differences > 50 ms, and the proportion low frequency power were about 70%. The reliability coefficients of the 24-hour HRV measures were > 80% for all measures. Short- and long-term measures of heart rate and HRV appeared to be correlated, implying that these measures result in similar ranking of subjects. Conclusions: The results indicate that HRV measures based on 24-hour monitoring during regular activities are better reproducible than short-term measures under standardized conditions. A single 5-minute recording may suffice to characterize a group of persons in a population study, but, because of considerable day-to-day variation, it is not adequate for individual characterization.

Circadian Rhythms of Heart Rate Variability in Hypertrophic Cardiomyopathy

Abstract: Background: It has been hypothesized that an interaction between sympathetic nervous activity and an abnormal myocardium plays a role in the development and progression of hypertrophic cardiomyopathy (HCM) Methods: In the present study we investigated cardiac autonomic function by 24-hour spectral analysis of heart rate variability (HRV) in 18 patients with HCM, without evidence of heart failure, and 18 controls of similar age Results: We found a significant reduction of 24 hour variance in HCM patients relative to controls (15,000 ± 9480 ms2 vs 24,720 ± 12,450 ms2 respectively; p < 005) Moreover, a loss of the expected day-night changes in the low frequency (LF) spectral component (expressed in normalized units), and LF/HF ratio (HF; high frequency component) were observed in HCM patients Decreased day-night changes in LF/HF ratio were previously reported in patients with mild hypertension, uncomplicated coronary disease, and after myocardial infarction, conditions in which it seems to exist a higher than normal sympathetic activity No significant correlations were found between HRV indices and echocardiographic standard measures of systolic and diastolic function parameters Conclusions: These data are consistent with the presence of an alteration in neural modulation of heart period in HCM patients, noninvasively detectable by continuous 24 hour HRV analysis

A Prospective Study of Atrial Fibrillation After Cardiac Surgery.: Multivariate Risk Analysis Using P Wave Signal-Averaged ECG and Clinical Variables

Abstract: Background: Atrial fibrillation (AF) is a commonly encountered arrhythmia following cardiac surgery and when sustained, may be associated with significant morbidity. Methods: This large prospective investigation examined a variety of clinical and P wave signal-averaged electrocardiogram (SAECG) parameters to identify independent predictors of AF following cardiac surgery. A total of 272 patients underwent P wave SAECG recording and analysis prior to surgery. Information on their clinical, surgical, and hemodynamic characteristics as well as hospital course was collected. Patients were followed during their postoperative course with telemetry and ECGs. Results: During an observation period of up to 14 days, 79 patients (29%) developed AF 2.5 ± 1.9 days after surgery. Patients who developed AF following cardiac surgery were more likely to be older, undergo valve surgery, to have ejection fraction (EF) 140 ms (all P 140 ms and EF 140 ms and EF < 40% for the development of AF following cardiac surgery was 3.1 and 2.8, respectively, and 8.7 when combined. Conclusions: Thus, the presence of preexisting abnormal atrial substrate as detected by P wave prolongation on SAECG, and implicated by EF < 40%, clearly predicted a higher risk of AF following cardiac surgery and may provide clinicians with an effective means of identifying those at greatest risk.

Relationship Between Heart Rate Variability and Cardiovascular Risk Factors in Middle-Aged Males

Abstract: Background: Abnormal autonomic control of heart rate is associated with an inreased risk of cardiovascular morbidity and mortality. There are few population-based reports on the interindividual variation and determinants of cardiac control in healthy middle-aged males. Methods: Autonomic modulation of heart rate was studied in 172 randomly selected middle-aged males (mean age 50 ± 6 years) by measuring the heart rate variability (HRV), which was related to life style data, personality type, blood pressure, lipid analyses, results of the 2-hour glucose tolerance test and left ventricular function. Results: Large interindividual variation was observed in the standard deviation of RR intervals (mean 59 ± 20 ms; coefficient of variation (CV) 34%) compared to variation of the average heart rate (mean 76 ± 11 beats/min, CV 14%). When analyzed as normalized units, marked interindividual variation was observed in the low (CV 16%) and high frequency component (CV 37%). The total power of HRV had significant indirect univariate correlations with age, blood pressure, body mass index, 2-hour blood glucose level, fasting and 2-hour serum insulin levels, triglyceride level, and a direct correlation with left ventricular fractional shortening. In a multiple regression analysis, the total power of HRV was best predicted by age (β=−0.27, P = 0.0002), followed by the fractional shortening (β= 0.25, P = 0.0004), systolic blood pressure (/3 =−0.2 1, P = 0.005) and 2-hour insulin level (β=−0. 9, P = 0.01). Conclusions: Overall HRV has a wide interindividual variation and is related to several cardiovascular risk factors, perhaps contributing to the observed association between low HRV and cardiovascular mortality. Normalized units of HRV reflecting sympathovagal balance are unrelated to age, life style, or cardiovascular risk factors.

Late Potentials Detected by Digital Holter ECG: Reproducibility, Lead Systems, and Effects of Physical Activity

Abstract: Background: We sought to assess reproducibility, effects of various lead systems, and influence of physical activity on the results of signal-averaged ECG obtained from the digital Holter system. Late potentials are routinely recorded using specially designed electrocardiographic devices. It has been shown recently that late potentials can also be recorded and analyzed from Holter tapes, which enables to examine possible dynamic changes of late potentials in relation to transient ischemia and spontaneous ventricular arrhythmias. However, there are some technical limitations of the signal-averaged ECG analysis from Holter tapes that may be overcome by the use of digital, solid-state Holter recorders where the ECG signal is acquired directly by the computer system and analyzed in real time. Methods: The signal-averaged ECG was recorded at rest from XYZ leads and from lead system suggested by the manufacturer (Holter leads), and during moderate physical activity in 34 postin-farction patients, using a new solid-state Holter recorder. From each of these 20 minutes of recording, four consecutive ECG segments, lasting 5 minutes, were averaged, combined into vector magnitude, and analyzed using a Butterworth bidirectional filter between 40 and 250 Hz. Results: Reproducibility of signal-averaged ECG was high; the P values (ANOVA) ranged from 0.93–0.99. Of the individual signal-averaged ECG variables, reproducibility of the total QRS duration was superior to that of the terminal QRS measurements (the standard deviations of the mean relative errors were 6.3% vs 22.3% and 24.4%, respectively). There were no signifcant differences in signal-averaged ECG variables when results obtained using orthogonal XYZ leads were compared with those obtained from Holter leads. Modest physical activity (slow walk) did not alter significantly signal-averaged ECG variables. The values of the total QRS duration were more consistent than the terminal QRS measurements when two lead confgurations and recordings obtained during rest and physical activity were compared. Conclusions: Reproducibility of signal-averaged ECG analysis obtained from a digital Holter system is high, the results are similar using XYZ or Holter leads, and the signal-averaged ECG can be recorded and analyzed during minor physical activity.

Conventional Electrocardiogram in Arrhythmogenic Right Ventricular Dysplasia‐Cardiomyopathy and Idiopathic Right Ventricular Outflow Tract Tachycardia

Abstract: Objective: Arrhythmogenic right ventricular dysplasia up to now is a rare cardiomyopathic entity with certain difficulties in clinical definition of diagnostic criteria. In 42 patients with major and minor criteria of arrhythmogenic right ventricular dysplasia and 25 patients with idiopathic ventricular arrhythmia, the role of conventional ECG in the diagnosis of arrhythmogenic right ventricular dysplasia was reevaluated. Methods: In standard 12-lead ECG, QRS duration was measured in limb lead D1, and in V1-V6. A ratio of the sum of right (V2+ V3) and left (V4+ V5) was calculated. T wave inversions, Epsilon wave, and mechanisms of advancing right bundle branch block were analyzed. Results: In 39 out of 42 patients (93%) with the diagnosis of arrhythmogenic right ventricular dysplasia, a ratio of right and left precordial QRS duration of >1.2, a maximum right precordial QRS duration of > 100 ms in 10 cases (26%) and >110 ms in 29 cases (74%) could be found. Incomplete right bundle branch block with right precordial T inversions was found in one case. The ECG in two patients revealed a precordial R/S transition in V1 or V2; in all other cases, R/S transition was localized in V3 or V4. R peak time was normal (< 0.04 s) in all cases, a “notching” or “slurring” of the S wave was striking in 16 cases. T wave inversions were found in 27 cases and definite Epsilon wave in only one case. Although incomplete right bundle branch block and certain preforms could also be disclosed in four patients with idiopathic right ventricular outflow tract (RVOT) tachycardia, localized right precordial QRS prolongation could be excluded in all but one of these cases. Localized right precordial QRS duration prolongation in one case was probably due to a rotation of the heart with a precordial R/S transition between V1 and V2. Conclusion: Localized right precordial QRS prolongation in a normal precordial R/S transition: (a) seems to be the most important aspect of arrhythmogenic right ventricular dysplasia at conventional ECG, with a sensitivity of 93% and a specificity of 96% in order to distinguish idiopathic RVOT tachycardia; (b) can appear with (64%) or without (36%) secondary T wave inversions; and (c) is due to a “parietal” block sparing the specialized conducting system.

Absence of Gender Difference in Circadian Trends of QT Interval Duration

Abstract: Background: The long-term circadian behavior of the QT interval duration was comparatively evaluated in females and in males. The corrected QT interval duration is known to be longer in females than in males, and this gender difference persists after double autonomic blockade. Methods: Our population consisted of 32 young healthy subjects (16 males). Twenty-four-hour ambulatory ECG recordings were processed by QT analysis software. All sinus complexes were averaged on a 30-second time basis. The averaged template was defined by a single QT apex (QTa) interval and its mean RR interval. The circadian behavior of ventricular repolarization was assessed by the nocturnal lengthening of QTa at an identical RR interval, and by the respective diurnal and nocturnal QT/AR relationship in both genders. Results: The corrected QTa was longer in females (318 ± 20 vs 294 ± 13 ms, P = 0.0003). The correlation coefficients of the QTa/RR regression lines were >0.75, whatever the gender and the circadian period considered. In both genders, diurnal slopes were higher than nocturnal ones (0.15 ± 0.01 vs 0.09 ± 0.03 in males and 0.18 ± 0.04 vs 0.09 ± 0.05, P = NS), and the nocturnal lengthening of QTa was on the same range (25 ± 12 vs 17 ± 12 ms, P = NS). Conclusion: The longer corrected QT interval in females is not associated with a specific static or dynamic circadian behavior of QT interval.

Classification Accuracy of Electrocardiographic Criteria for Left Ventricular Hypertrophy in Normal Weight and Overweight Older Adults

Abstract: Background: We evaluated classification accuracy of ECG criteria at varying levels of left ventricular hypertrophy (LVH) severity according to echocardiographically measured left ventricular mass (LVM) adjusted to body size. Methods: The test population was derived from the Cardiovascular Health Study (CHS), a population-based sample of 5201 men and women aged 65 and older, and consisted of 1844 women and 1119 men with adequate quality ECGs and echocardiograms for LVM determination. The criteria evaluated were Sokolow-Lyon, Cornell voltage, Cornell product, Framingham modification of the Cornell voltage, and the left ventricular mass index (LVMI) of the Novacode ECG program. Results: With LVH thresholds at upper 95% normal limit for weight adjusted LVM for the CHS population and ECG thresholds adjusted for 95% specificity in normal weight and overweight subgroups, the sensitivity of ECG criteria for LVH was relatively low. It was highest (40.8%) for the Novacode LVMI in normal weight men and for the Framingham criteria (30.9%) in normal weight women, but it deteriorated for both of these criteria in the presence of obesity. The overall performance of the Cornell product and Cornell voltage criteria was least influenced by obesity. The Framingham adjustment for the Cornell voltage criteria for obesity substantially reduced their sensitivity. Conclusion: The choice of echocardiographic standard, LVH severity level and overweight in the test groups have a strong influence on ECG evaluation results.

Acceleration Spectrum Analysis: A Novel Quantitative Method for Frequenc y‐Domain Analysis of the Signal‐Averaged Electrocardiogram

Abstract: Background: Frequency-domain techniques presently used for micropotential analysis in the signal averaged ECG (SAECC) have several inherent shortcomings. For example, they depend on sensitive determination of the I-point, which becomes inaccurate in the presence of noise, or derivation of multiple, complicated statistical parameters to quantify spectral characteristics in a three-dimensional “spectral temporal map.” While these techniques are not as well accepted clinically as the conventional time-domain Simson method, the latter is not without limitations either. Although time-domain SAECG analysis has a very high negative predictive value, it has low positive predictive accuracy. Furthermore, it cannot be used to analyze SAECC data in patients with conduction delay problems, such as bundle branch block. Hence, the goal of this new frequency-domain technique is to address and solve some of these shortcomings. Methods: The Fourier transform of the second derivative signal, or “acceleration spectrum,” extracts the frequency-domain “signature” of damaged myocardium throughout the entire QRS complex, rather than from only the late potential region. The technique i s not dependent on precise endpoint or other fiducial point determination. A “spectral change index” (SCI) for quantifying variation from 50-300 Hz in the acceleration spectrum i s calculated. The characterization of the cut-off values for the SCI was based on results from a study including 50 postmyocardial infarction (post-MI) patients (25 of whom were inducible to sustained ventricular tachycardia), and 10 normal controls. Results: An SCI <20, typical of a normal, “flat” acceleration spectrum in the 50- to 300-Hz band width, may indicate undamaged myocardium, while an SCI 220 corresponding to a higher degree of spectral “fragmentation” in the same bandwidth, may indicate increased myocardial tissue damage. Using this cutoff, the sensitivity, specificity, and positive and negative predictive values for this initial study were 72%, 84%, 82%, and 75%, respectively. Conclusions: Acceleration spectrum analysis (ASA) using the SCI shows promise in predicting inducibility in post-MI patients, including those with conduction delay problems. Since it is well documented that time-domain SAECG has a high negative predictive value and a low positive predictive value, the high positive predictive value of the newly developed ASA increases the overall value of the SAECG test.

Time-Frequency Analysis of Heart Rate Variability.: Smoothed Pseudo-Wigner Distribution

Abstract: Background: The heart rate variability (HRV) signal is mainly analyzed in frequency-domain and the signal's spectrum is estimated using either Fast Fourier Transformation (FFT) or the autoregressive (AR) model. These two methods assume that the HRV signal is stationary and additionally the AR method is based on the assumption that the model is linear and the signal is monocomponent in nature. Qualities of spectral estimates are thus closely related to the validity of the above assumptions. Evidence has accumulated indicating that HRV is a multicomponent, nonlinear and nonstationary signal. Then the spectral representations currently used would yield global, approximate, and smoothed view of HRV dynamics. Methods: We applied time-frequency (TF) analysis methods, smoothed pseudo-Wigner distribution (SPWD), and spectrogram and complemented for validation by FT spectrum to the HRV signal of fifteen apparently healthy volunteers (mean age 27.2 ± 5.6 years). Short-term electrocardiograms (ECG) were recorded during supine and upright tilting positions (baseline recording). After baseline recording we induced parasympathetic, sympathetic, and total autonomic blockade correspondingly to six, nine, and four subjects. In addition, in four patients ECGs were recorded during controlled respiration. Results: SPWD and spectrogram revealed strips in frequency, or TF components, corresponding to FT components. High frequency (HF) components appeared stationary (in wide sense), with slight mean frequency shifts during spontaneous respiration, concurrent with respiratory motions. Low frequency (LF) and very low frequency (VLF) components had a nonstationary character displaying activity burst in time and interrelation in frequency. Upright tilting caused a uniform reduction in intensity and bandwidth of the HF component and enhancement of intensity and burst activity of the LF component. There was a pronounced decline of HF and LF components’intensity and decrease of HF component's bandwidth after parasympathetic blockade and total autonomic blockade, while the VLF component did not change. Sympathetic blockade was accompanied by augmentation of the LF and HF components’intensity associated with an increase in the HF component's bandwidth and the spreading of it in the region between the LF and HF. The LF component exhibited less burst activity during tilting under sympathetic blockade, as compared to baseline recordings during tilt. The VLF component's behavior did not change after sympathetic, parasympathetic, and total autonomic blockades. Conclusion: Application of TF distributions to the HRV signal offers a new representation of HRV dynamics. SPWD unveiled features in the HRV signal not available in separate time- and frequency-domains. TF components display idiosyncratic behavior patterns in time and were effected by physiological and pharmacological interventions. A.N.E. 1996;1(4):411–418

Spectral Analysis of the High Resolution QRS Complex During Exercise‐Induced Ischemia

Abstract: Background: The effect of acute myocardial infarction and regional ischemia on the frequency content of the ECG signal has been described by several investigators In the present study, the feasibility of assessing changes in the QRS spectrum during exercise testing, and whether these changes are related to the occurrence of ischemia were examined Methods: Spectral analysis of the high resolution ECGs from leads V3, V4, V5, and V6 were performed in two groups of male subjects before, during, and following treadmill exercise testing Group A included 32 coronary artery disease (CAD) patients, with arteriographically proven >75% obstruction of at least two main coronary arteries, and group B included 30 healthy subjects, without history or symptoms of CAD Signal averaging and filtering techniques were used in order to enhance the signal-to-noise ratio of the recorded ECGs The power spectrum of the averaged QRS waveform for the different stages of the exercise testing was computed using a Fast Fourier Transform, and the slope of the linear regression line was found in the frequency range 781–24992 Hz on the plot of log((amplitude)2) versus log(frequency) Results: Regression line slopes immediately after peak exercise were significantly lower for the CAD group than for the healthy subjects in 3 of the 4 examined leads No significant changes in slopes were found between the two groups at rest or during late recovery Comparing the differences between slopes at different stages of the test revealed that the difference between postexercise slope and rest slope has lower mean values for the CAD group in all four leads, with a significant difference in lead V6, and for the difference between postexercise slope and recovery slope, lower mean values were found for the CAD group in all four leads, with a significant difference in V5 and V6 Conclusions: These findings indicate that ischemic changes affect the power spectrum of the QRS complex, and result in a steeper regression line on a log-log scale

Predictive Power of Heart Rate Variability Used as a Stratifier of Cardiac Mortality After Myocardial Infarction in Patients Discharged With and Without Beta-Blocker Therapy

Abstract: Background: Depressed heart rate variability (HRV) is associated with increased risk for sudden cardiac death after myocardial infarction. Beta-blocker therapy reduces the risk of sudden cardiac death in patients with recent infarction. There is also evidence that beta-blockers improve HRV in postinfarction patients. In this study, we investigated whether the association between HRV and cardiac mortality in postinfarction patients is different in those who, on clinical grounds are and are not discharged on beta-blocker therapy. Methods: HRV was assessed from 24-hour ambulatory electrocardiograms before hospital discharge in 438 survivors of acute myocardial infarction. After the recordings, 147 patients were prescribed beta-blockers and 291 were discharged without beta-blocker therapy. The patients were followed for at least 2 years using cardiac death and arrhythmic death as clinical endpoints. Patients were dichotomized to depressed and normal HRV at the lowest 30 percentile. Results: Multivariate logistic regression analysis showed that HRV was a sigificant determinant of cardiac (P < 0.001) and arrhythmic mortality (P < 0.001) in patients who were not on beta-blocker therapy, whereas it was not a predictor of cardiac or arrhythmic mortality in patients who were taking beta-blockers. Beta-blocker therapy was associated with a significantly lower total cardiac mortality and arrhythmic mortality in patients with depressed HRV (P < 0.01 and P < 0.05, respectively). In patients with normal HRV, the reduction of mortality was smaller and remained nonsignificant. Conclusion: HRV was not a predictor of cardiac mortality in postinfarction patients who were prescribed beta-blockers before hospital discharge. In addition, beta-blocker therapy was associated with a lower cardiac mortality, particularly in patients with depressed HRV. Thus, depressed HRV might be considered as an additional indication for beta-blocker therapy in postinfarction patients.

The Clinical Significance of Nonsustained Ventricular Tachycardia in Patients with Sustained Ventricular Tachyarrhythmias

Abstract: Background: Nonsustained ventricular tachycardia (NSVT) predicts mortality in several disorders but its significance in patients with sustained ventricular tachyarrhythmias is unknown. We analyzed the clinical features and outcome associated with NSVT (>; 3 beats at >; 100 beats/min) recorded on a 48-hour Holter in the absence of antiarrhythmic drugs. Methods: Patients enrolled in the ESVEM trial (n = 486) were grouped according to the duration of the longest recorded episode of NSVT, and in the second analysis, according to frequency of recorded episodes. Assessments were on an intention-to-treat basis. Results: Patients without NSVT were more likely to have ischemic heart disease and had significantly lower frequencies of single and paired premature ventricular complexes (PVCs). There were no significant differences with respect to age, sex, presenting arrhythmia, years since last myocardial infarction, functional class, or present ejection fraction. The cumulative probabilities of arrhythmia recurrence and all-cause mortality at 4 years in patients without NSVT (60%± 7% and 32%± 6%, respectively) were not significantly different than those of patients with NSVT (63%± 3% and 41%± 3%, respectively). Cox regression models indicated that ejection fraction and functional class were significant predictors of outcome, but variables based on the presence, duration, and frequency of recorded episodes of NSVT were not. Conclusions: NSVT is common in patients with spontaneous and inducible sustained ventricular tachyarrhythmias and at least 10 PVCs/hour (ESVEM enrollment criteria), but is not a significant predictor of arrhythmia recurrence, sudden death, or all-cause mortality in patients with these characteristics.

Changes of Heart Rate Variability After Coronary Bypass Grafting

Abstract: Background: Heart rate variability (HRV) may serve as a follow-up parameter in patients with coronary artery disease undergoing percutaneous transluminal angioplasty. Several studies have shown significant changes of HRV parameters in the case of restenosis. The value of this method as a prognostic parameter in patients following coronary artery bypass grafting (CABG) is unknown. Methods: In the present study we investigated changes of HRV parameters in patients undergoing CABG to prove whether this method would predict the outcome in these patients. Twenty patients (six female, 14 male, age 51–75 years, mean 62 years) with angiographically documented coronary artery disease (1 × 1-vessel disease, 10 × 2-vessel disease, 9 × 3-vessel disease) were investigated. Eight patients had previous myocardial infarction: 3 × anterior infarction and 5 × inferior infarction. Before and after CABG 24-hour measurement of HRV was performed using Holler monitoring (elapsed time between the two measurements 218 ± 92 days). All patients underwent successful CABG with complete revascularization. The following time domain parameters were calculated: SDNN, SDNN index, SDANN, r-MSSD and pNN50. Results: These parameters showed a significant decrease after CABG (P < 0.05) except rMSSD, which was below the statistic level. The results of the patients without previous myocardial infarction suggested that the parasympathetically influenced paramenters r-MSSD and pNN50 were mainly involved, while in the subgroup with previous myocardial infarction the sympathetically influenced parameters (SDNN, SDANN) were significantly changed. Other variables such as ejection fraction or severity of coronary artery disease did not influence the HRV results. Conclusions: In contratst to patients with revascularization by PTCA, HRV does not seem to be a suitable predictive parameter in patients after successful CABG. Intrinsic operative alterations with injury of cardiac nerves may be responsible for this observation.

Adverse Prognosis of ST Depression on the Resting Electrocardiogram in Stable Patients Following Acute Myocardial Infarction.: An Analysis of the Basis for this Association

Abstract: Background: The aim of this study was to analyze the characteristics of stable patients with resting ST segment depression on the resting electrocardiogram (ECG) following an acute ischemic event (i.e., infarction or unstable angina) to better understand its association with subsequent cardiac death and nonfatal infarction. The recent Multicenter Study of Myocardial Ischemia (MSMI) demonstrated that the resting ST segment depression had an independent prognostic value. Methods: We studied clinical features, noninvasive test results and coronary arteriography findings in 99 patients with ST depression on the resting ECG and 837 patients without ST segment depression with respect to endpoints of cardiac death and hospitalization for acute myocardial infarction or unstable angina. Results: Our results showed that patients with resting ECG ST depression were significantly older with a higher incidence of hypertension, angina, claudication, and tobacco use. ST depression on the resting ECG correlated closely with ST segment depression on the 24-hour ambulatory ECG and the exercise ECG but not with redistribution on the thallium perfusion scan. Left ventricular diastolic pressure was higher and exercise duration less in patients with ST depression. Although not achieving statistical significance, patients with ST depression did show more extensive coronary disease and a lower ejection fraction. Conclusions: ECG ST depression was associated with cardiac death and nonfatal reinfarction over the follow-up period only in patients originally admitted with an acute infarction but not in patients hospitalized for unstable angina. The reason for this appears to be an association of ST depression with increased age, the presence of hypertension, the presence of more severe coronary disease, and more extensive myocardial damage.

Evaluation of Outpatient Arrhythmias and Pacemakers Utilizing Transtelephonic Monitoring Devices

Abstract: Background: The purpose of this trial was to evaluate a patient actuated transtelephonic cardiac monitoring system in order to document cardiac arrhythmias and cardiac pacemaker function. Material: Eighty-two patients were prospectively evaluated, 69 with pacemaker (group I) and 13 with symptomatic arrhythmias (group II). Two different recorders were used: a memory loop-recorder (KH) and a wrist-worn recorder (HW). Both of them were implemented using a small, portable, battery-powered transmitter, which monitors a modified V5 in KH and a lead 1 with the HW over regular nondigital pulse telephone lines. Results: In group I, 54 patients used single chamber pacemakers, 2 VDDR, and 13 used dual chamber devices. In group II, all patients included referred palpitations as their symptom. In group I, 248 registers were made using the KH and 50 with the HW. Recordings were made with KH had a 96% accuracy in the diagnosis of the ECG, while HW recordings failed to detect the QRS and the spike in 52% of the cases. Arrhythmia patients (group II) made 65 recordings with KH, all symptomatic: 28 were ventricular ectopic beats (23 isolated, 4 bigeminy, and 1 coupled ventricular ectopic beats); 9 supraventricular ectopic beats (isolated); 18 episodes of sinus tachycardia; and 10 normal sinus rhythm. Artifact was present partially in 6 other recordings, but did not affect the diagnosis. Two patients made no recordings and were excluded from the trial (group I). Conclusions: The loop-recording transtelephonic monitoring system is an excellent tool for the evaluation of patients with symptomatic arrhythmias and pacemaker. The memory KH had an excellent performance, even over regular telephone lines. The accuracy of the HW recordings was low and failed to evaluate the QRS, probably due to the direction of the AQRS vector.

The Signal‐Averaged ECG Obtained by a New Digital Holter Recording System

Abstract: Background: The implementation of signal-averaged analysis in the Holter recording may increase cost-effectiveness and enables further insights into pathophysiological links between arrhythmia genesis and time related modulating factors. This study assesses the feasibility of a new digitizing long-term recorder system to perform a signal-averaged analysis and compares the data with the results achieved by an established bedside real-time recording system. Methods: The study was performed prospectively in 22 patients. The digital recorder FD-3 obtained a 3-channel 24-hour Holter monitoring. For the signal-averaged ECG analysis, a template averaging was achieved in 5-minute periods. The interpolated sampling rate was 1024 Hz. The signal-averaged ECG by bedside real-time system was performed using the Predictor system. At 25–250 Hz and 40–250 Hz band-pass filter, 4 FD-3 epochs acquired in a 6-hour interval were chosen and the mean values of QRS, root mean square (RMS), and low amplitude signal (LAS) were compared with the data obtained by one Predictor measurement. Results: The regression analysis shows a positive correlation between the FD-3 and Predictor data of QRS, RMS, and LAS at both filter settings except for LAS at 25–250 Hz. Regarding the late potential classification, at 25–250 Hz 4 of 22 (18%) FD-3 and Predictor classifications were not coherent and at 40–250 Hz only 2 of 22 (9%) classifications did not correlate. Conclusions: The FD-3 recorder is feasible to perform a signal-averaged ECG analysis. Especially at 40–250 Hz, the late potential classification shows a concordant distribution.

Age and Gender Specific Criteria for Signal‐Averaged Electrocardiographic Parameters in Healthy Chinese Children

Abstract: Background: Detection of late potentials (LPs) using signal-averaged electrocardiograms (SAECGs) is believed to help in the prediction of malignant ventricular arrhythmias and sudden cardiac death in adults. Criteria for detection of LPs in adults may not be applicable for children, as these measurements are known to be age and sex specific. Method: SAECGs were recorded using MAC 15 ECG System. Duration of filtered QRS (TQRS), duration of high frequency, low amplitude signals in the terminal portion of QRS complex that are < 40 μV (HFLA), and root mean square voltage of the last 40 ms of the filtered QRS (RMS40) were determined for 535 healthy Chinese children, ages 6–17 years (268 males, 267 females). Results: Both mean TQRS and RMS40 were significantly different between the male and female children (TQRS: 106 ms vs 101 ms, P 12 μV. Since TQRS and RMS40 were gender specific, the criteria for male and female were: TQRS: Male 9 μV, female >17 μV. Conclusion: TQRS, HFLA, and RMS40 were shown to be age and sex specific in healthy Chinese children. The criteria for normal TQRS, HFLA and RMS40 were different from those proposed for adults, and this may be partly due to technical differences of the recording system.

A hundred years of progress in electrocardiography 1: Early contributions from Waller to Wilson

Abstract: The 1887 introduction of electrocardiography as a noninvasive investigative technique on man by Augustus Waller, and Wilhelm Einthoven's electrocardiograph from 1901 remain the two major landmarks in the 100-year history of electrocardiography. The progress in our knowledge of the mechanism and interpretation of the ECG hasevolved throughout these 100 years in a succession of relatively small steps contributed by many unsung heroes, although often even relatively minor contributions by a few dominant 'stars notably Thomas Lewis and Frank Wilson, are perceived as giant leaps. The gradual evolution of our concepts of the ECG are reviewed against the historical background of the events involved from the time of Waller's discovery to the end of the second world war.