Information Technology Reference
In-Depth Information
I = V
−
V
, II = V
−
V
, III = V
−
V
(9.1)
LA
RA
LL
RA
LL
LA
where
L
V
,
R
V
, and
L
V
denote the potentials on the limb electrodes. The Wilson's
central terminal [
8
] is defined by the average potential from the limb electrodes:
++
.The limb leads can be visualized by a well-known Einthoven's
triangle (Fig.
9.2
) with a Wilson's central terminal “electrode” at its center. In this
way, the limb leads enable the heart to be observed in the vertical plane from angles
0°, 60°, and 120°.
(V
V
V ) / 3
LA
RA
LL
The observation angle may be refined with −30°, 90°, and −150° angles
(Fig.
9.3
) obtained from augmented limb leads, aVL, aVF, and aVR derived from
the combination of limb leads as:
I + II
II
−
(
9.2)
aVR =
−
, aVL = I
−
, aVF = II I / 2
2
2
Alternatively, augmented limb leads can be derived directly from augmented
differences between limb electrodes and Wilson's central terminal potentials. For
example, for aVR:
(
)
V
+V
+V
3
LA
RA
LL
aVR =
V
−
(9.3)
RA
2
3
= V
−
(V
+V
)/2.
RA
LA
LL
Fig. 9.3
Limb leads and their observation angles of the heart in the vertical plane
Search WWH ::
Custom Search