Page 334 - Cardiac Nursing

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310 P A R T III / Assessment of Heart Disease
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■ Figure 15-16 (A) Frontal plane leads demonstrating LAD. See text for explanation. This is an example of
LAFB. (B) Frontal plane leads demonstrating RAD. See text for explanation. This is an example of LPFB.
0.12 second or greater and a characteristic pattern best recognized
in precordial leads V 1 and V 6 and limb leads I and aVL.
V V
Normal ventricular depolarization as recorded by leads V 1 and V 6
is illustrated in Figure 15-18. The positive electrode for V 1 is located
on the front of the chest at the fourth intercostal space to the right of
V V
the sternum, close to the right ventricle. The positive electrode for V 6
is located in the left midaxillary line at the fifth–sixth intercostal
space, close to the left ventricle. Lead V 1 records a small R wave as the
septum depolarizes from left to right toward the positive electrode. It
then records a negative deflection (S wave) as the main forces travel
away from the positive electrode toward the left ventricle, resulting in
the normal rS complex in V 1 . Lead V 6 records a small Q wave as the
V V
septum depolarizes left to right away from the positive electrode. It
then records a tall R wave as the main forces travel toward the left
ventricle, resulting in the normal qR complex in V 6 . When both ven-
V V
tricles depolarize together, the QRS width is less than 0.12 second.
■ Figure 15-17 Intraventricular conduction system. Right bundle Right Bundle-Branch Block
9
9
branch carries impulse into right ventricle. Left main bundle branch Figure 15-19A illustrates the spread of electrical forces in the ven-
divides into anterior and posterior fascicles, which carry impulse into tricles when the right bundle branch is blocked. Three separate
left ventricle. forces occur: