Abstract
Electrocardiogram (ECG) studies of drug-induced prolongation of the interval between the J point and the peak of the T wave (JTp interval) distinguished QT prolonging drugs that predominantly block the delayed potassium rectifier current from those affecting multiple cardiac repolarisation ion channel currents. Since the peak of the T wave depends on ECG lead, a “global” T peak requires to combine ECG leads into one-dimensional signal in which the T wave peak can be measured. This study aimed at finding the optimum one-dimensional representation of 12-lead ECGs for the most stable JTp measurements. Seven different one-dimensional representations were investigated including the vector magnitude of the orthogonal XYZ transformation, root mean square of all 12 ECG leads, and the vector magnitude of the 3 dominant orthogonal leads derived by singular value decomposition. All representations were applied to the median waveforms of 660,657 separate 10-s 12-lead ECGs taken from repeated day-time Holter recordings in 523 healthy subjects aged 33.5 ± 8.4 years (254 women). The JTp measurements were compared with the QT intervals and with the intervals between the J point and the median point of the area under the T wave one-dimensional representation (JT50 intervals) by means of calculating the residuals of the subject-specific curvilinear regression models relating the measured interval to the hysteresis-corrected RR interval of the underlying heart rate. The residuals of the regression models (equal to the intra-subject standard deviations of individually heart rate corrected intervals) expressed intra-subject stability of interval measurements. For both the JTp intervals and the JT50 intervals, the curvilinear regression residuals of measurements derived from the orthogonal XYZ representation were marginally but statistically significantly lower compared to the other representations. Using the XYZ representation, the residuals of the QT/RR, JTp/RR and JT50/RR regressions were 5.6 ± 1.1 ms, 7.2 ± 2.2 ms, and 4.9 ± 1.2 ms, respectively (all statistically significantly different; p < 0.0001). The study concludes that the orthogonal XYZ ECG representation might be proposed for future investigations of JTp and JT50 intervals. If the ability of classifying QT prolonging drugs is further confirmed for the JT50 interval, it might be appropriate to replace the JTp interval since with JT50 it appears more stable.
Highlights
This article concerns different methodologies for the detection of the peak of the T wave in a 12-lead electrocardiogram (ECG) with the aim of serving serial comparisons of the J to T peak (JTp) interval
The present study considered several different signal matrices of combination of ECG leads with the aim of determining a matrix that would lead to JTp interval measurements most stable for the purposes of serial comparisons
Technical suitability check based on objective noise assessment (Batchvarov et al, 2002) excluded 3,523 ECGs (0.53%) that were too noisepolluted for reasonable T peak assessment
Summary
This article concerns different methodologies for the detection of the peak of the T wave in a 12-lead electrocardiogram (ECG) with the aim of serving serial comparisons of the J to T peak (JTp) interval By this we mean situations when it needs to be investigated whether the JTp interval was changed during a certain intervention. Other needs for serial JTp comparisons might emerge, e.g., in physiologic studies of exposure to environmental changes, physical exhaustion, autonomically active provocations, etc. All such situations lead to the comparison of ECGs obtained before and after the intervention. Since the investigated intervention might change heart rate, stability of the JTp relationship to underlying heart rate is needed which, in turn, might depend of the method for the T peak detection
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