In order to determine the best site for A-B lead and to study the patterns of ECG and the distribution of electrical potentials, ECG were recorded from 57 sites on the body surface in 6 Japanese monkeys.
1. Distribution of electrical potentials : The transitional zone showing zero electrical potentials 'ran obliquely downwards from the left axilla to the right chest in 4 cases, and ran horizontally from left axilla, reaching to the midline and then descending on the midline towards the right inferior chest in 2 cases.
The intensification of negative electrical potentials was found in the upper part of the transitional zone on the right side of the chest or at the midline. The intensification of positive electrical potentials was found on a horizontal line of processus xiphoidus, on the left side of the midline in 5 cases. In 1 case, this was found on the right side of the processes xiphoidus.
2. Pattern of QRS complexes on the body surface : The QRS complex at the transitional zone was the RS type, showing the rS type in the upper part of the transitional zone. As the head is approached, the pattern becomes Qs or Qr type. In the lower part of the transitional zone, Rs type was seen along the transitional zone. Towards the lower chest, Rs changed to R and then to the qR type.
3. P and T waves : The transitional zones of the P and T waves obliquely descend from the left axilla, pass around the right nipple and descend down towards the right side of the chest. Both waves showed diphasic patterns in the transitional zone. In the upper part of the transitional zone, a negative wave was noted, while a positive wave was seen further down.
4. In the present study, the position of the electrode for the A-B lead in monkeys on the supine position was suggested as follows. A electrode (the apex) was generally found on a horizontal line of the processus xiphoidus, on the left side of the midline. B electrode (the base) was found on the horizontal line in the lower axilla, in the midline or the right side of the chest. However, in a supine position, as the position of the heart and distribution of electrical potentials were found in individual variation, further study was necessary as regards the position of the A-B lead.

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