Page 325 - Cardiac Nursing

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C HAPTER 1 5 / Electrocardiography 301
■ Figure 15-1 Cardiac conduction system. (From
Jacobson, C. [1991]. Cardiac arrhythmias and conduc-
tion abnormalities. In M. L. Patrick, S. L. Woods, R. F.
Craven, et al. [Eds.], Medical-surgical nursing [2nd ed.,
pp. 648–693]. Philadelphia: J. B. Lippincott)
P Wave ative deflection from baseline and should be less than 0.03 second
The P wave represents atrial muscle depolarization. It is normally in duration and less than 25% of the R-wave amplitude. An R wave
small, smoothly rounded, and no taller than 2.5 mm or wider is the first positive deflection from baseline. An S wave is a negative
than 0.11 second. deflection that follows an R wave. When a complex is all positive, it
is just an R wave; when it is all negative, it is called a QS. Regard-
QRS Complex less of the shape of the complex, ventricular depolarization waves
The QRS complex represents ventricular muscle depolarization. are called QRS complexes (Fig. 15-3). The width of the QRS com-
The shape of the QRS complex depends on the lead being plex represents intraventricular conduction time and is measured
recorded and the ventricular activation sequence; not all leads from the point at which it first leaves the baseline to the end of the
record all waves of the QRS complex. A Q wave is an initial neg- last appearing wave. Normal QRS width is 0.04 to 0.10 second.
Lead II
Atrial Ventricular
Depolarization P wave QRS ST T wave Depolarization
te
PR Interval Segment
■ Figure 15-2 Waves, complexes, and
e
r
intervals of the cardiac cycle in leads II QT Interval
and V 1 . VI

AV Node Ventricular
Depolarization Depolarization