Electrocardiogram of the Anesthetized Dog

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Abstract
There is a wide range of ecg "normality" from one dog to another, spontaneous changes occur in serial ecg on the same dog and a change of position influences some components of the ecg, T axes are among the most variable and may be in almost any direction in the frontal plane, but are more consistent in the V leads. S-T depression or elevation up to 0.20 mv in the limb leads and of 0.03 mv in the V leads may be normal for this method of securing the dog ecg. There is no predictable relationship between the mean QRS, T or S-T vector which will define the tracing as normal. Range of spontaneous changes in 10 dogs under carefully controlled conditions on 4 occasions each is described. The variability of ecg when taken with the dog in different positions is also defined. The normal range of voltages, time relationships, axes and ratios is described for 50 dogs. A reproducible and logical system of V lead electrode placement is suggested. A classification of normal tracings based on the QRS pattern for limb and V leads is presented.