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K Hnatkova

Publications and source records attributed to K Hnatkova.

At least 37 records · Page 2Linked to original sources
PubMed1998

Wavelet decomposition analysis of the signal averaged electrocardiogram used for risk stratification of patients with hypertrophic cardiomyopathy.

AIMS: To study the predictive value of wavelet decomposition, as demonstrated by the signal-averaged ECG, in order to identify patients with hypertrophic cardiomyopathy at increased risk for malignant ventricular arrhythmias or sudden death. METHODS AND RESULTS: Two hundred and forty-six patients with hypertrophic cardiomyopathy were studied. During a mean follow-up of 68 +/- 17 months 32 patients died, of whom 17 died suddenly. Patients with sudden death, together with eight patients with a history of ventricular fibrillation (sudden death/ventricular fibrillation group) were analysed and compared to the other 221 patients as well as to a subgroup of 82 patients without a history of syncope, ventricular arrhythmias on a long-term ECG recording or a family history of sudden death. There were no differences in mean values of the four wavelet decomposition parameters among patients in the sudden death/ ventricular fibrillation group, those without sudden death/ ventricular fibrillation or patients in the low risk group. There were, however, significant differences between patients dying non-suddenly and patients being alive at the end of follow-up. Eighty-seven patients (35%) demonstrated evidence of non-sustained ventricular tachycardia on a long-term ECG. Analysis of wavelet decomposition resulted in abnormal findings in these patients more often than in those without ventricular arrhythmias. CONCLUSION: The usefulness of wavelet decomposition analysis in predicting sudden death or ventricular fibrillation is limited in patients with hypertrophic cardiomyopathy. It may, however, play a role in identifying patients at risk of dying non-suddenly and of patients with non-sustained ventricular tachycardia.

Adolescent↗
PubMed1998

Mid- and long-term similarity of ventricular response to paroxysmal atrial fibrillation: digoxin versus placebo.

The effects of digoxin on ventricular response during atrial fibrillation (AF) and consequent effects on arrhythmic symptoms have still not been fully explained. This study investigated whether the treatment by digoxin contributes to mid- and long-term stabilization of ventricular cycles in patients with paroxysmal AF. A population of 45 patients with paroxysmal AF underwent 24-hour ECG recordings during each arm of a randomized crossover trial comparing digoxin and placebo. This yielded 30 Holter recordings from 22 patients that contained AF episodes lasting in excess of 2 minutes and with acceptably low Holter noise. Each AF episode was divided into nonoverlapping segments of 30 seconds and the distribution of RR intervals in each segment was compared with the distribution of all other AF segments in the same recording using the Kolmogorov-Smirnov test. The percentage of tests that revealed significant differences at levels of P < or = 0.01, and P < or = 0.001 were sorted according to the time between the segments compared. The comparisons of these results were performed between: (a) all recordings on placebo (n = 16) and all recordings on digoxin (n = 14), and (b) between recordings on placebo and on digoxin in 8 patients in whom paired analysis was possible. Adjacent AF segments (distance 0) differed significantly only in < 30% of both recordings on placebo and on digoxin. However, with increasing the distance between segments, the proportion of the significant differences between RR interval distributions increased more with placebo than with digoxin (P < 10(-300), Chi-square test). Paired data revealed larger differences between placebo and digoxin with increasing distance between segments. Thus in patients with paroxysmal AF, digoxin leads to more reproducible patterns of ventricular cycles that may be better tolerated clinically.

Adult↗
PubMed1998

A relationship between fluctuations in heart rate and the duration of subsequent episodes of atrial fibrillation.

A relationship between autonomic tone and the onset of paroxysmal atrial fibrillation in some patients is recognised. Episodes of PAF may vary enormously in duration, however, from a few beats to many hours. Whether autonomic tone influences the duration of the episodes has been less well investigated. From a database of Holter recording taken from patients with symptomatic PAF, we identified all episodes of at least 30 seconds duration which were preceded by noise free sinus rhythm. This study examined the heart rate prior to AF onset, the change in heart rate over the final minute of sinus rhythm and the time of AF onset, and compared the data from those episodes of AF of more than 5 minutes duration to the shorter ones. Heart rate was slower before long episodes of AF, but this was found to predominantly represent data from separate recordings. A highly significant rise in heart rate was detected prior to long AF episodes compared to shorter ones. Daytime AF episodes were slightly longer than nocturnal ones. The most important finding was that longer AF episodes were typified by a heart rate acceleration. This suggests that, regardless of underlying aetiology, and increase in sympathetic tone may be important in the sustenance of episodes of PAF.

Anti-Arrhythmia Agents↗
PubMed1998

Multiparametric analysis of heart rate variability used for risk stratification among survivors of acute myocardial infarction.

A multiparametric heart rate variability analysis was performed to prove if combined heart rate variability (HRV) measures of different domains improve the result of risk stratification in patients after myocardial infarction. In this study, standard time domain, frequency domain and non-linear dynamics measures of HRV assessment were applied to 572 survivors of acute myocardial infarction. Three parameter sets each consisting of 4 parameters were applied and compared with the standard measurement of global heart rate variability HRVi. Discriminant analysis technique and t-test were performed to separate the high risk groups from the survivors. The predictive value of this approach was evaluated with receiver operator (ROC) and positive predictive accuracy (PPA) curves. Results--The discriminant analysis shows a separation of patients suffered by all cause mortality in 80% (best single parameter 74%) and sudden arrhythmic death in 86% (73%). All parameters of set 1 show a high significant difference (p < 0.001) between survivors and non-survivors based on two-tailed t-test. The specificity level of the multivariate parameter sets is at the 70% sensitivity level (ROC) about 85-90%, whereas HRVi shows maximum levels of 70%. The PPA in the all cause mortality group is at the 70% sensitivity level twice as high as the univariate HRV measure and increases to more than fourfold as high within the VT/VF group. In conclusion, in this population, the multiparametric approach with the combination of four parameters from all domains especially from NLD seems to be a better predictor of high arrhythmia risk than the standard measurement of global heart rate variability.

Arrhythmias, Cardiac↗
PubMed1998

Circadian variation in atrial fibrillation in patients with frequent paroxysms.

Determinants of the duration of episodes of atrial fibrillation (AF) in patients with paroxysmal atrial fibrillation (PAF) are poorly understood. However, autonomic tone shows circadian variation and is known to affect atrial electrophysiology. We therefore compared the duration of episodes of AF with an onset during the day (08:00-22:00) to those with an onset during the night in a database of 24-hour ECG recordings in patients with frequent symptomatic PAF. The heart rate in the 30 seconds prior to AF onset was also compared. From 42 recordings, 296 episodes of AF > 30 seconds duration and preceded by > 60 seconds sinus rhythm were identified. The 165 nocturnal episodes tended to be shorter (median = 1.15 min) than the 131 diurnal episodes (median = 1.5 min) and the distribution of nocturnal and diurnal durations was significantly different (P = 0.007; Kolgomorov-Smirnov test). This was also true in recordings containing at least 1 diurnal and at least 1 nocturnal episode. The mean heart rate prior to AF onset was lower at night (62.2 +/- 11.8 vs 75.6 +/- 16.4 beats/min; P < 0.0001 Wilcoxon test). These findings suggest that in patients with frequent symptomatic PAF, autonomic influences affect the duration of episodes of AF and has pathphysiological and therapeutic implications.

Atrial Fibrillation↗
PubMed1998

Evolution of changes in the ventricular rhythm during paroxysmal atrial fibrillation.

Changes in the RR interval within episodes of paroxysmal atrial fibrillation (PAF) have not been fully characterized. A database of 177 24-hour Holter recordings were created from patients with PAF in the CRAFT studies. PAF episodes of > or = 1 minute duration containing < or = 20% noise and preceded by > or = 1 minute of sinus rhythm with < or = 20% noise were selected. Sections of each AF episode containing 10 and 25 RR intervals were identified at the onset, middle, and termination of each episode. Descriptive characteristics (mean, SD, and RMSSD of RR intervals) were calculated within each section, and compared using a nonparametric, paired Wilcoxon test. In 25 patients (17 men, 60.6 +/- 12.2 years old), 231 episodes from 44 recordings met the selection criteria. The mean RR interval increased slightly between the onset and mid-portion of AF episodes (565.9 +/- 128.3 vs 580.3 +/- 144.7 ms, P < 0.001). The RR interval at the termination of AF was significantly greater than that at the start (627.1 +/- 156.1 vs 565.9 ms, P < 10-11) or mid-portion (627.1 +/- 156.1 vs 580.3 +/- 144.7 ms, P < 10-13). SD of the RR interval increased significantly between onset and mid-portion (111.1 +/- 60.2 vs 118.2 +/- 66.7 ms, P < 0.001) and more substantially between mid-portion and termination (118.2 +/- 66.7 vs 201.8 +/- 93.7 ms, P < 10-21). During paroxysms of AF, the mean RR interval and the variability of RR intervals increases. Termination of a paroxysm is preceded by a marked increase in RR interval variability.

Anti-Arrhythmia Agents↗
PubMed1998

Age and gender influences on rate and duration of paroxysmal atrial fibrillation.

UNLABELLED: The influence of age and gender on the character of paroxysmal atrial fibrillation (PAD) has not been described. METHODS: The heart rate (HR) during PAF in patients receiving placebo or antiarrhythmic therapy was analyzed. Data from 177 24-hour Holter recordings were analyzed to mark the onset and termination of PAF and converted into RR interval files. PAF episodes lasting at least 2 minutes and containing < or = 20% noise were included. HR during the first 30-second segment versus during the remainder of the episode, and the duration of PAF episodes were compared among groups of different ages and sex (Wilcoxon test). RESULTS: 236 episodes from 55 recordings in 32 patients (all patients: 61.4 +/- 12.8 years; men (19): 58.5 +/- 12.6 years; women (13) 65.5 +/- 12.4 years, P = ns for difference in age) fulfilled the inclusion criteria. Women had a higher mean heart rate at AF onset (123 +/- 35 beats/min vs 115 +/- 20 beats/min, P = 0.02) and during the remainder of the episode (120 +/- 25 beats/min vs 112 +/- 22 beats/min at the start, P = 0.01, and 116 +/- 26 beats/min vs 108 +/- 18 beats/min subsequently, P = 0.01). Episodes tended to be longer in women (mean 89.8 min vs 50.5 min, P = NS) and in the aged (mean 83.8 min vs 46.9 min, P = NS). CONCLUSION: PAF episodes are associated with faster heart rates and last longer in women, which may reflect differing autonomic responses to AF. A slower ventricular rate during PAF in older patients probably reflects an increasing prevalence of impaired atrioventricular conduction.

Age Factors↗
PubMed1998

Distribution of fast heart rate episodes during paroxysmal atrial fibrillation.

OBJECTIVE: To investigate the defibrillator waiting time (time between the recognition of atrial fibrillation and the actual shock) by studying paroxysmal atrial fibrillation episodes with RR intervals shorter than a certain limit (that is, episodes during which defibrillation should not be attempted). METHODS: Long term 24 hour Holter recordings from a digoxin v placebo crossover study in patients with paroxysmal atrial fibrillation were analysed. In all, 23 recordings with atrial fibrillation episodes of at least 1000 ventricular cycles and with < 20% Holter artefacts or noise were used (11 recorded on placebo and 12 on digoxin). For each recording, the mean ("mean waiting time") and maximum ("maximum waiting time") duration of continuous sections of atrial fibrillation episodes with all RR intervals shorter than a certain threshold were evaluated, ranging the threshold from 400 to 1000 ms in 10 ms steps. For each threshold, the mean and maximum waiting times were compared between recordings on placebo and on digoxin. RESULTS: Both the mean and maximum waiting times increased exponentially with increasing threshold. Practically acceptable mean waiting times less than one minute were observed with thresholds below 600 ms. There were no significant differences in mean waiting times and maximum waiting times between recordings on placebo and digoxin, and only a trend towards shorter waiting times on digoxin. CONCLUSIONS: Introduction of a minimum RR interval threshold required to deliver atrial defibrillation leads to practically acceptable delays between atrial fibrillation recognition and the actual shock. These delays are not prolonged by digoxin treatment.

Anti-Arrhythmia Agents↗
PubMed1998

Computerised measurements of QT dispersion in healthy subjects.

OBJECTIVE: To assess the stability and reproducibility of computerised QT dispersion (QTd) measurement in healthy subjects, as this is presently being incorporated into commercial electrocardiographic systems. METHODS: 70 healthy volunteers (mean (SD) age 38 (10) years, 35 men, 35 women) with a normal 12 lead electrocardiogram (ECG) were studied. From each subject, 70 ECG recordings were taken using the MAC VU ECG recorder (Marquette). In study A, 50 ECGs were recorded in each subject: 10 supine, 10 sitting, 10 standing, 10 holding breath in maximum inspiration, and 10 holding breath in maximum expiration. After a mean interval of 8 (3) days (range 7 to 23), 10 recordings in supine and 10 in the standing position were repeated in each subject (study B). On measurements made using a research version of the commercial software without manual modification, the reproducibility of QTd was assessed by coefficient of variance (CV) and relative error, and comparisons made with other ECG indices. RESULTS: (1) QTd measurements were stable and not influenced by changes in posture and respiratory cycle; (2) there was no difference in QTd measurements between men and women, or between age groups dichotomised at 35 years; (3) no correlation was found between QTd and heart rate or QT interval; (4) short term reproducibility of all QTd measurements (CV 15.6% to 43.8%) was worse than that of conventional ECG indices (CV 1.4% to 5.3%); (5) long term reproducibility of QTd measurements (relative error 27.4% to 31.0%) was also worse than that of conventional ECG indices (relative error 1.8% to 7.9%) (p < 0.0001); (6) the reproducibility of QTd measurements tended to increase when several serial recordings were averaged. CONCLUSIONS: Computerised measurements of global QTd and global QT-SD from 12 lead ECG by the MAC VU/QT Guard system are not significantly altered by changes in posture and respiration. The reproducibility of all QTd measurements is inferior to that of conventional ECG indices in healthy subjects.

Adolescent↗
PubMed1998

Use of spectral turbulence analysis for the identification of patients at high risk for ventricular fibrillation and sudden death in patients with hypertrophic cardiomyopathy.

Hypertrophic cardiomyopathy carries an increased risk of sudden death. The aim of the present study was to assess the predictive value of the signal-averaged ECG, analysed in the time domain and using a new method, spectral turbulence analysis, for the identification of high-risk patients. Two-hundred and forty-six patients with hypertrophic cardiomyopathy were studied. During a mean follow-up of 68 +/- 17 months, 17 patients died suddenly. Patients with sudden death (SD) and/or a history of ventricular fibrillation (VF; n = 25) were compared to patients without SD/VF (n = 221) and to patients without any recognised risk factors for SD (n = 82). There were no differences in mean values of the time domain or spectral turbulence parameters analysed between patients in the SD/VF group and the patients without SD/VF or in the low-risk group. It is concluded that the clinical usefulness of the signal-averaged ECG, analysed in the time domain or as spectral turbulence analysis, is limited in identifying high-risk patients with hypertrophic cardiomyopathy.

Adult↗
PubMed1997

Usefulness of signal-averaged electrocardiography in evaluation of idiopathic-dilated cardiomyopathy in families.

Family studies have confirmed that familial dilated cardiomyopathy is common and that a large proportion of relatives have mild left ventricular enlargement and therefore potentially early disease. Previous studies have shown that patients with idiopathic dilated cardiomyopathy have abnormalities of the signal-averaged electrocardiogram (ECG). We assessed the usefulness of analysis of the signal-averaged ECG in the evaluation of familial dilated cardiomyopathy. Signal-averaged electrocardiographic recordings were obtained from 58 patients with idiopathic dilated cardiomyopathy, from 161 of their relatives (35 of whom had left ventricular enlargement), and from 59 healthy subjects. Signal-averaged ECGs were analyzed using both time domain and spectral turbulence analysis techniques. The time domain and spectral turbulence analysis variables were markedly abnormal in patients with idiopathic dilated cardiomyopathy compared with relatives considered normal and healthy controls (p <0.05). Late potentials were more common in patients with idiopathic dilated cardiomyopathy (17%) and in relatives with left ventricular enlargement (20%) than in normal relatives (5%) or healthy controls (5%) (p = 0.003). Spectral turbulence analysis was abnormal in 24% of patients with idiopathic dilated cardiomyopathy, 14% of relatives with left ventricular enlargement, 6% of normal relatives, and 5% of healthy controls (p = 0.0006). The sensitivity, specificity, and positive predictive accuracy for identification of relatives with left ventricular enlargement were 20%, 95%, and 54% for time domain analysis and 14%, 94%, and 42% for spectral turbulence analysis. Similar positive predictive accuracy was achievable with spectral turbulence analysis and with time domain analysis. In conclusion, the signal-averaged ECG is frequently abnormal in patients with idiopathic dilated cardiomyopathy and relatives with left ventricular enlargement.

Adult↗
PubMed1997

Selection of dichotomy limits for multifactorial prediction of arrhythmic events and mortality in survivors of acute myocardial infarction.

AIMS: To evaluate the predictive value and optimum dichotomy limits for different combinations of prognostic indicators for the prediction of arrhythmic events and cardiac mortality in post-infarction patients. BACKGROUND: Studies of new interventions based on risk stratification after myocardial infarction have often used a single variable as a predictor of risk. However, whether the dichotomy limits of these single variables, derived from univariate analyses, should be altered when such variables are combined for the prediction of risk after myocardial infarction has not been examined. METHODS: Left ventricular ejection fraction, signal-averaged electrocardiography, heart rate variability index, mean heart rate and ventricular extrasystole frequency were recorded pre-discharge in 439 survivors of their first myocardial infarction. Arrhythmic events and cardiac mortality were recorded during 1 year (range 1-6 years) follow-up. RESULTS: During follow-up for at least 1 year, there were 25 cardiac deaths and 23 arrhythmic events. Different optimum dichotomy limits were obtained for the prediction of cardiac mortality vs arrhythmic events, for different combinations of variables, for different selected levels of sensitivity and for different numbers of variables abnormal before identification of those at risk. The dichotomy limit of the heart rate variability index for the prediction of events appeared to be the least affected by the inclusion of other variables. For example, when predicting arrhythmic events using combinations of left ventricular ejection fraction and/or heart rate variability, the optimum dichotomy limits when each variable was used alone was 32% and 18 units respectively; 43% and 18 units when either left ventricular ejection fraction or heart rate variability are required to be abnormal, and 52% and 19 units when both are required to be abnormal before identification of those at risk of arrhythmic events. CONCLUSIONS: Dichotomy limits derived from univariate analyses do not optimally predict events when used in the multivariate setting. Risk stratification can be improved by using several variables in combination and is further improved by using dichotomy limits of these variables which are different from those used in or derived from univariate analyses.

Aged↗
PubMed1997

Graphical representation of complex data--diurnal patterns of initiations of atrial fibrillation episodes.

A construction of a purpose designed graphical display is demonstrated in a study investigating the circadian distribution of patterns of RR interval sequences preceding episodes of paroxysmal atrial fibrillation (PAF). Based on a comparison with a (80%, 120%) range around the median of preceding 10 RR intervals, each RR interval is classified as normal, short, or long. Classifications of RR intervals in n-tuplets (n = 1, ...,5) preceding PAF episodes are used to compute probabilities of individual types of sequences occurring within 4-hour periods of the day (between 1 am, 5 am, 9 am, 1 pm, 5 pm, and 9 pm). Graphical representation of the data is proposed using a hierarchy of bar graphs. The graphical system has been filled with data of 327 atrial fibrillation episodes recorded in 46 24-hour ECGs in PAF patients. The graphical analysis supports a link between PAF initiation and cardiac autonomic status.

Anti-Arrhythmia Agents↗
PubMed1997

Performance of basic ventricular tachycardia detection algorithms in implantable cardioverter defibrillators: implications for device programming.

Around 20% of patients with third generation implantable cardioverter defibrillators receive inappropriate therapy, usually triggered by atrial fibrillation. This is because the criteria used for ventricular tachycardia detection by current implantable cardioverter defibrillators are based on the analysis of a sequence of RR intervals and may be inappropriately satisfied by supraventricular tachyarrhythmias. Algorithms for ventricular tachycardia detection were challenged against the full RR interval sequences from 482 spontaneous episodes of atrial fibrillation and 260 spontaneous episodes of ventricular tachycardia to determine their ability to discriminate between the arrhythmias. The sensitivities and specificities of the algorithms were calculated over a wide range of programmable parameters. For a given window length and detection interval, the most stringent algorithms, that required all beats to be classified as "fast", were more specific than those allowing a proportion of "normal" intervals, even after adjustment for differing sensitivity. These differences were less marked for faster tachycardias. Specificity increased with the detection window length to a limit of approximately 18 beats. We conclude that ventricular tachycardia is detected with the highest specificity if all beats in an analyzed sequence are required to be "fast," even after lengthening of the tachycardia detection interval to maintain sensitivity. Further improvement in algorithm performance may require the incorporation of criteria such as tachycardia onset and stability.

Algorithms↗
PubMed1997

Autonomic modulation of ventricular rate in atrial fibrillation.

This study investigated the changes in R-R interval in 23 patients (11 men and 12 women; mean age 61 yr) with persistent atrial fibrillation in response to several provocative maneuvers including active postural change, Valsalva maneuver, handgrip, and rhythm-controlled respiration. Averaged R-R intervals were shortened immediately after postural change (from 797 +/- 35 ms supine to 677 +/- 27 ms standing; P < 0.01) and recovered to the 90% level within 100 s. During Valsalva strain and handgrip, mean R-R intervals were significantly shortened (from 737 +/- 37 ms sitting to 697 +/- 38 ms in Valsalva and from 773 +/- 68 ms sitting to 701 +/- 58 ms in handgrip; both P < 0.01). During rhythm-controlled respiration, only two cases (10.5%) showed power peaks in spectrograms of moving-window-averaged R-R intervals at the frequency corresponding to respiration rhythm. The ventricular response to atrial fibrillation is influenced by an increase in sympathetic tone and a decrease in parasympathetic tone but is not necessarily influenced by the increase in parasympathetic dominance. These results suggest that even in atrial fibrillation patients, the autonomic nervous system modulates the ventricular rate via the atrioventricular node and atrial tissue.

Adult↗
PubMed1996

Use of ventricular premature complexes for risk stratification after acute myocardial infarction in the thrombolytic era.

The independent predictive role of ventricular premature complex (VPC) frequency in the stratification of mortality risk after acute myocardial infarction (AMI) was established in the prethrombolytic era by extensive multicenter trials. Thrombolysis has lead to important changes in the natural history of patients after AMI, so that reassessment of established risk factors is now required. The prognostic significance of VPCs was assessed in 680 patients, of whom 379 received early thrombolytic therapy. All patients underwent 24-hour Holter monitoring in a drug-free state between 6 and 10 days after AMI. Patients were followed up for 1 to 8 years. During the first year of follow-up, cardiac death occurred in 33 patients, sudden death in 24, and sustained ventricular tachycardia in 20. Mean VPC frequency was significantly higher in patients who died of cardiac causes, in those who died suddenly, and in those with arrhythmic events during the first year of follow-up. This was also true when patients who did and did not undergo thrombolysis were considered separately. The positive predictive accuracy of VPC frequency in predicting adverse cardiac events was greater in patients who did than did not undergo thrombolysis. At a sensitivity level of 40%, the positive predictive accuracy for cardiac mortality and arrhythmic events for the group with thrombolysis was 19.4% and 25.8%, respectively, compared with 16% and 16% for those without thrombolysis. Moreover, the highest VPC frequency for the dichotomy of patients into high-and low-risk groups was 25 VPCs/hour for patients without thrombolysis. VPC frequency appears to be more highly predictive of prognosis after AMI in patients who have undergone thrombolysis than in those who have not, but the optimal frequency for dichotomy is higher in the former.

Adult↗