The Thai Journal of Veterinary Medicine


The objectives of this study were to describe (1) the form of body surface potentials for P, QRS and ST-Tcomponents using semiorthogonal ECG leads and vectorcardiograms (VCGs), (2) the instability of the QT usingcoefficient of variation compared with 3 other published methods, and (3) the frequency-domain characteristics of theQRS complex. Electrocardiograms were recorded and VCGs of P, QRS and ST-T loops were generated in frontal (Xaxisversus Y-axis), sagittal (Y-axis versus Z-axis), and horizontal (X-axis versus Z-axis) planes. Frequency-domaincomponents of the QRS complex were calculated using Fast Fourier Transform (FFT) algorithm. One of the 7 guineapigs was placed in sternal recumbency in a 1.5 T whole body scanner to identify specific cardiac structures whichproduce the QRS and ST-T. In relation to human ECGs, the guinea pig ECGs showed higher HR, and shorter P, QRS,and QT durations. The result of VCGs of the body surface in the guinea pigs suggested that the maximum vectors forP, QRS and ST-T were oriented, spatially caudad, ventrad and leftward. From NMR imaging, the guinea pig’s heartwas situated in a more nearly vertical position than the human heart. Spectral analysis of QRS demonstrated that thefrequencies which yielded the greatest powers were 44.8, 61.4 and near zero Hz in lead I, aVF, and V10, respectively.

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