Christoph Maier

Baroreflex sensitivity and heart rate variability in conscious rats with myocardial infarction

The baroreflex sensitivity (BRS) and the heart rate variability (HRV) were studied in conscious rats after myocardial infarction (MI; induced by coronary artery ligation) and after sham operation (SH). BRS was determined by linear regression of R-R interval vs. arterial pressure changes induced by nitroprusside or methoxamine (intravenous bolus). HRV was calculated from 3-min electrocardiogram recordings. Left ventricular end-diastolic pressure and plasma atrial natriuretic peptide were increased after MI; plasma norepinephrine and basal heart rate (HR) remained unchanged. At 3 and 28 days after MI, BRS was reduced as indicated by decreased reflex bradycardia (RB) (MI, 0.66 ± 0.13 and 0.78 ± 0.07 ms/mmHg; SH, 1.27 ± 0.16 and 1.48 ± 0.14 ms/mmHg, respectively; P < 0.05 MI vs. SH). At 56 days after MI, BRS was normalized. RB was unaffected by atropine 3 and 28 days after MI but reduced in all other groups. The increase of basal HR by atropine 3 and 28 days after MI was less than in all other groups. HRV (SD of mean N-N interval, coefficient of variance, low- and high-frequency power; studied at 28 and 56 days) was similar in all groups. It is concluded that BRS is transiently depressed in rats with left ventricular dysfunction after MI probably due to a reduced reflex vagal activity. Even though basal HR and HRV are unchanged after MI, a temporary attenuation of tonic vagal activity is unmasked after autonomic blockade.The baroreflex sensitivity (BRS) and the heart rate variability (HRV) were studied in conscious rats after myocardial infarction (MI; induced by coronary artery ligation) and after sham operation (SH). BRS was determined by linear regression of R-R interval vs. arterial pressure changes induced by nitroprusside or methoxamine (intravenous bolus). HRV was calculated from 3-min electrocardiogram recordings. Left ventricular end-diastolic pressure and plasma atrial natriuretic peptide were increased after MI; plasma norepinephrine and basal heart rate (HR) remained unchanged. At 3 and 28 days after MI, BRS was reduced as indicated by decreased reflex bradycardia (RB) (MI, 0.66 +/- 0.13 and 0.78 +/- 0.07 ms/mmHg; SH, 1.27 +/- 0.16 and 1.48 +/- 0.14 ms/mmHg, respectively; P < 0.05 MI vs. SH). At 56 days after MI, BRS was normalized. RB was unaffected by atropine 3 and 28 days after MI but reduced in all other groups. The increase of basal HR by atropine 3 and 28 days after MI was less than in all other groups. HRV (SD of mean N-N interval, coefficient of variance, low- and high-frequency power; studied at 28 and 56 days) was similar in all groups. It is concluded that BRS is transiently depressed in rats with left ventricular dysfunction after MI probably due to a reduced reflex vagal activity. Even though basal HR and HRV are unchanged after MI, a temporary attenuation of tonic vagal activity is unmasked after autonomic blockade.

Screening and prediction of paroxysmal atrial fibrillation by analysis of heart rate variability parameters

This study has been performed within the scope of the CinC-2001 challenge on the detection and prediction of paroxysmal atrial fibrillation (PAF) from 200 paired two-channel ECGs of 30 minutes duration. Different features of heart rate variability (HRV) describing the magnitude as well as the regularity of heart rate fluctuations and the number of supraventricular premature beats (SVPCs) and ventricular premature beats (VPCs) were investigated for their suitability with respect to the classification task using ROC analysis, classification by ranks and linear polynomial classifiers with jackknife validation. Moreover, the time courses of mean parameter values were calculated to identify possible trends. Although promising results of up to more than 80% accuracy in screening and 92% in prediction were achieved on training data, these were not reproducible on an independent test set.

Recognition and quantification of sleep apnea by analysis of heart rate variability parameters

This study was performed within the scope of the CinC-2000 challenge on detection and quantification of obstructive sleep apnea from single channel ECGs. Established statistical time domain heart rate variability (HRV) measures as well as parameters based on time delay embedding and correlation analysis are investigated for their diagnostic quality by means of receiver operating characteristics (ROC) analysis on a training set of 35 ECGs and cross validated on an independent tests set of equal size. Moreover, several feature combinations are evaluated with a second order polynomial classifier. The results indicate, that at least most of the information necessary to recognize sleep apnea is contained in the EGG. Recognition rates up to 93% for screening of apnea patients and 85.55% for minute by minute quantification are achieved.

Comparison of heart rhythm and morphological ECG features in recognition of sleep apnea from the ECG

This study addresses the problem of sleep apnea recognition on a minute-by-minute basis from single-lead ECGs recorded overnight. Analysis of heart rate fluctuations, quantified by the series of RR-intervals, is compared to analysis of ECG morphology variations, assessed using signal vectors from the QRS- and the T-wave region and projecting them onto their first principal component. The resulting series of scalar Karhunen-Loeve coefficients (KLCs) were used as descriptors of morphology. From the derived series, we calculated a measure of similarity and a spectral index in temporal segments of 5 min, and assessed their diagnostic accuracy by ROC-analysis. Although the performance for the RR-series and the similarity feature was 81%/84% sens ./spec., better results up to 87%/87% were obtained from the T-wave KLCs. It is concluded that the effects of sleep apnea on the ECG are reflected more uniformly in morphology variations of the ECG compared to heart rhythm.

Extraction of respiratory myogram interference from the ECG and its application to characterize sleep-related breathing disorders in atrial fibrillation

BACKGROUND AND PURPOSEnPresent methods to extract respiratory myogram interference (RMI) from the Holter-ECG and assess effect of supraventricular arrhythmias (SVAs) onto ECG-based detection of sleep-related breathing disorders (SRBDs) and AHI estimation.nnnMETHODSnRMI was quantified as residual energy after ECG cancellation or high-pass filtering for different windowing constellations. In 140 cases without (SET_A) and 10 cases with persistent SVAs (SET_B), respiratory polysomnogram annotations served as reference for SRDB detection from Holter-ECGs. We applied our previously published method to identify SRDBs in 1-min epochs and estimate the AHI based on joint modulations in RMI and QRS-area.nnnRESULTSnSensitivity and specificity of 0.855/0.860 in SET_A dropped to 0.831/0.75 in SET_B. A significantly higher number of wake events in SET_B likely contribute to the asymmetric decrease and is consistent with a tendency to overestimate the AHI.nnnCONCLUSIONSnDespite reduced accuracy, RMI and QRS-area appear relatively robust against SVA and promise Holter-based detection at least of medium to severe SRBDs also in patients with SVAs.

Segmentation of nocturnal Holter-ECG recordings with respect to different recumbent body positions

This paper evaluates a previously developed approach for minute-by-minute segmentation of night-time ECG recordings with respect to periods of different recumbent body positions (BPs). It is based on recurrence analysis of 8D-feature vectors aggregating the area under the QRS complex in eight Holter-ECG leads. The number and consistency of ECG-derived BPs was compared to reference BPs (45° resolution) extracted from 139 polysomnograms (PSGs, 120 subjects). The results indicate a high BP resolution for the ECG. Up to 3 ECG BPs per PSG BP were identified in 70% of the cases. In 60% of the ECGs, the fraction of inconsistent epoch assignments was ≤10%, and ≤30% of BP changes in the PSG were undetected. When adjacent PSG BPs were considered exchangeable, the results improved significantly, indicating a potentially unfavorable effect of the PSG sensor discretization and encouraging further steps towards the absolute classification of BPs at least in coarse categories.

Rhythm or morphology-which information in the ECG is more useful with respect to detection of sleep apnea?

This study investigates and compares the utility of different electrocardiographic features quantifying variability of either heart rhythm or of ECG morphology for detection of sleep apnea. For heart rhythm, the sequence of RR-intervals was analyzed. To characterize ECG morphology, signal vectors were extracted from the QRS- and the T-wave region. Their projection on the first principal component yields series of scalar coefficients which were used as parameters of morphology. From the derived series as well as from a demodulated version of these sequences, we calculated a measure of similarity as well as a spectral parameter from temporal segments of 5 minutes duration. The diagnostic accuracy of these features was evaluated by means of ROC-analysis and a second order polynomial classifier. Best results were obtained from the local similarity index of the projection coefficients from the T-wave region (sensitivity 87.2%, specificity 87.5%). A slight performance increase was achieved by considering additional features from the QRS-region and the RR-intervals (88.8%/93.1%). It is concluded that although relevant information is embedded in the heart rhythm, the variability of ECG morphology reflect apnea related patterns slightly better.

Heart rate variability analysis for patients with obstructive sleep apnea

Obstructive sleep apnea (OSA) is a common health concern associated with serious implications and increased cardiovascular morbidity and mortality. This study approaches the problem of identification OSA patients and detection of OSA phases on the basis of heart rate variability (HRV) analysis. Only a single ECG-channel is required for this purpose. We used data from the apnea ECG database:40 patients with documented OSA and 20 controls divided into a learning and a test set of equal size. Commonly used HRV measures as well as some novel parameters are tested. The results are compared by ROC-analysis and promising parameters are combined into a multidimensional vector and evaluated by means of a second order polynomial classifier. Best results are obtained from parameters calculated by time delay embedding and correlation analysis of the interbeat interval series. For the identification task, 95% sensitivity and 100% specificity are achieved on the independent test set. The detection task yields an average classification rate of almost 85%.

A system for automated analysis of RR-series applied to identification of patients with neurocardiogenic syncope

Deals with an adaptable software system for heart rate variability (HRV) analysis and its application to the clinical problem of neurocardiogenic syncope. Features here calculated from 24h-Holter recordings of 17 patients and 15 control probands. The best discrimination results (88% sensitivity, 73% specificity) between the two groups are achieved by combination of the standard deviation of intervals between normal beats (SDNN) and the standard deviation of Haar-wavelet coefficients (/spl sigma//sub WAV/) for scale 10 using a first order polynomial classifier. The prominent key features of the developed software system are discussed.

1027-45 Long QT Syndrome in Children: Evidence of Time Independent Prolongation of the Repolarization Period from Holter Recordings

The 24 hour course of prolongation of the repolarization period was measured from Holter recordings in 8 childrens (3 boys and 5 girls, 12xa0±xa05.7 years old) with documented long QT syndrome and compared to 8 recordings from age and sex matched healthy individuals. After digitization the electrocardiograms were averaged every 16 beats and the duration of the repolarization period was measured from the resulting averaged signal from the spike of the R wave to the peak of the T wave. The time resolution of this measurement was 8 ms. The resulting RT duration was corrected for the mean heart rate during the last 16 beats using the formula of BAZETT. The resulting rate corrected RTc interval was approximately 100 ms shorter than the rate corrected interval. All data were synchronized and everaged every 15 minutes for every Holter recording of patients with long QT syndrome and healthy individuals. In the group with long QT syndrome the mean RTc interval from periods of 15 minutes’ duration during 24 hour recording periods showed a remarkable small standard deviation and was 361xa0±xa08.4xa0ms, thus being almost independent from time. The corresponding value for the healthy individuals was 286xa0±xa08.4xa0ms. The mean value for the difference in RTc duration between the sick and healthy children was 75xa0±xa010.4xa0ms. The differences were highly statistically significant (pxa0lxa00.001). Conclusions 1. There is no effect of circadian rhythms on rate corrected RT duration for the children with long QT syndrome and for healthy children. 2. In childrens with long QT syndrome, the rate corrected RT duration is prolonged by a mean value of 75xa0ms representing a 26% increase as compared to the mean rate corrected RT duration in age and sex matched healthy individuals