J. A. Kors

QTc Dispersion Predicts Cardiac Mortality in the Elderly The Rotterdam Study

BACKGROUND Increased QTc dispersion has been associated with an increased risk for ventricular arrhythmias and cardiac death in selected patient populations. We examined the association between computerized QTc-dispersion measurements and mortality in a prospective analysis of the population-based Rotterdam Study among men and women aged > or = 55 years. METHODS AND RESULTS QTc dispersion was computed with the use of the Modular ECG Analysis System as the difference between the maximum and minimum QTc intervals in 12 and 8 leads (ie, the 6 precordial leads, the shortest extremity lead, and the median of the 5 other extremity leads). After exclusion of those without a digitally stored ECG, the population consisted of 2358 men and 3454 women. During the 3 to 6.5 years (mean, 4 years) of follow-up, 568 subjects (9.8%) died. The degree of QTc dispersion was categorized into tertiles. Data were analyzed using the Cox proportional hazards model, with adjustment for age. For QTc dispersion in 8 leads, those in the highest tertile relative to the lowest tertile had a twofold risk for cardiac death (hazard ratio, 2.5; 95% confidence interval [CI], 1.6 to 4.0) and sudden cardiac death (hazard ratio, 1.9; 95% CI, 1.0 to 3.7) and a 40% increased risk for total mortality (hazard ratio, 1.4; 95% CI, 1.2 to 1.8). Additional adjustment for potential confounders, including history of myocardial infarction, hypertension, and overall QTc, did not materially change the risk estimates. Hazard ratios for QTc dispersion in 12 leads were comparable to those found for QTc dispersion in 8 leads. CONCLUSIONS QTc dispersion is an important predictor of cardiac mortality in older men and women.

Measurement error as a source of QT dispersion: a computerised analysis

Objective To establish a general method to estimate the measuring error in QT dispersion (QTD) determination, and to assess this error using a computer program for automated measurement of QTD. Subjects Measurements were done on 1220 standard simultaneous 12 lead electrocardiograms. Design The computer program was validated against two observers on a random subset of 100 electrocardiograms. Simple laws of physics require that at least five of the six extremity leads have the same QT duration. This allows the direct assessment of the error in measuring QTD derived from five extremity leads (QTD5). It also enables ST-T amplitude dependent distributions of measurement error in determining QT duration to be established. These QT error distributions were then used to estimate the error in measuring QTD from all 12 leads (QTD12). Main outcome measures Mean and standard deviation of error in measuring QT duration, QTD5, and QTD12. Results Performance of the program was comparable to that of observers. Errors in measuring QT duration (measured QT minus reference QT) fell from a mean (SD) of 6.9 (17.1) ms for ST-T amplitudes < 50 μV to −1.4 (6.3) ms for amplitudes > 350 μV. Measurement errors of QTD5 and QTD12 were 20.4 (11.5) ms and 29.4 (14.9) ms. Conclusions The fact that no QTD can exist between five of the six extremity leads provides a means of estimating QTD measurement error. Measuring error of QT duration is dependent on ST-T amplitude. QTD measurement error is large compared with typical QTD values reported.

Adaptive Gaussian filtering in routine ECG/VCG analysis

Different types of filters are used in systems for the analysis of electrocardiograms and/or vectorcardiograms. These filters are mostly locally used to enhance the relevant signal components in order to improve the performance of one or more subtasks or modules rather than to provide filtered signals to be used in the feature extraction and classification part of the system. Filters are also used in the module dealing with the recognition of onsets and endpoints of the major components in the ECG. This paper reviews the theoretical aspects of an adaptive Gaussian filter [1], and describes the modifications that were necessary to make this filter suitable for application in the waveform-recognition module. The efficiency of the filter is demonstrated with the aid of an internationally validated database of ECGs and VCGs.

Dissociation of heart rate and ECG morphology

The authors studied thirteen healthy subjects in which identical heart rates (/spl Delta/HR<1%) could be obtained under different autonomous conditions: by increasing the angle of the legs with the horizontal plane, with tilt angles ranging from 0 till 60/spl deg/ and back, or by performing a handgrip maneuver. During all measurements the thorax was kept at a 700 angle. Heart rate increased from 65.2a/spl plusmn/9.0 (control) to 72.1/spl plusmn/8. 7 (tilt) and 72.1/spl plusmn/8.8 (handgrip) bpm. A number of vector cardiographic parameters differed significantly (P<0.05) between tilt and handgrip, e.g. QRS azimuth (-33.5/spl plusmn/15.0 vs. -22.4/spl plusmn/22.5/spl deg/), QRS duration (103/spl plusmn/10 vs. 107/spl plusmn/13 ms), maximal T vector (646/spl plusmn/200 vs. 703/spl plusmn/184 /spl mu/V), T azimuth (45.3/spl plusmn/14.5 vs. 38.6/spl plusmn/13.6/spl deg/) and the heart rate corrected QT interval (418/spl plusmn/15 vs. 435/spl plusmn/21 ms). This study demonstrates that tilt and handgrip dissociate heart rate and ventricular depolarization and repolarization.