c. Sinus Tachycardia.
(1) Analysis. In sinus tachycardia, the rhythm is regular, the R-R and P-P
intervals are constant. Atrial and ventricular rates are equal to or greater than 100
beats per minute. The P wave is normal and upright with one P wave in front of every
QRS complex. The P-R interval is constant between 0.12 and 0.20 seconds, and the
QRS complex measures less than 0.12 seconds. A variety of circumstances can cause
sinus tachycardia: pain, fever, hypoxia, shock, congestive heart failure, and drugs such
as epinephrine, atropine, isoproterenol. The more rapid the heart rate, the harder the
heart works which can lead to further heart damage in AMI. Also, because there is
insufficient time between contractions for the ventricles to fill completely with blood, the
heart may not be able to pump fluid effectively when the heart rate is more than 120 to
140 beats per minute. Strenuous exercise such as jogging may cause this condition.
(2) Treatment. Treatment for sinus tachycardia is to treat the cause of this
irregularity (fever, fear, blood loss, and so forth.).
Figure 2-14. Sinus tachycardia. (file: 571f2-14.pcx)
a. Identification. The sinus node loses its pacemaking role, and the site with
the fastest rate becomes the pacemaker. In this case, the atria is the fastest
pacemaker and takes over the pacemaking role. The P wave configuration of atrial
rhythms may be flattened, notched, peaked, sawtoothed, diphasic, or upright. The QRS
complexes are narrow. Atrial arrhythmia may be caused by irritability of the heart or
escape mechanisms of the heart.
An escape mechanism is defined as an impulse from somewhere along the
conduction pathway that "escapes" to emit an electrical impulse of its own.
This electrical impulse stimulates an otherwise electrically quiet heart.