Page 83 - Critical Care Notes

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■ VVI mode: The ventricle is paced, sensed, and inhibited. The pacemaker
fires if no QRS complex is sensed. The patient’s rate is greater than the pro-
grammed rate and inhibits the pacemaker from firing. Most popular mode.
■ DVI or AV sequential mode: The atrium is paced at the programmed rate →
no ventricular activity during a certain interval → ventricle is paced.
■ DDD or fully automated mode: Senses and paces both the atrium and ven-
tricle and can inhibit either the atrium or ventricle if a patient’s native or
intrinsic beat is sensed.
■ Position I: Heart chamber paced.
■ Position II: Heart chamber where intrinsic electrical activity sensed.
■ Position II: Pacemaker response to what it senses.
■ Position IV: Presence (R) or absence (O) of rate modulation or rate respon-
siveness. Presence means that the pacemaker will alter its pacing rate to
meet metabolic demands.
■ Position V: Multisite pacing settings indicate the ability to stimulate more
than 1 site in a chamber.
■ Fixed rate pacemakers (asynchronous) discharge at a preset rate (usually
70–80 bpm) regardless of the patient’s own electrical activity.
■ Demand (synchronous) pacemakers discharge only when the patient’s HR < the
pacemaker’s preset rate.
■ Pacemakers may also be classified as temporary or permanent. Temporary
pacemakers are used in emergency situations and may serve as a bridge to
a permanent pacemaker. The pulse generator is located externally. The
pulse generator is implanted internally in permanent pacemakers.
■ Temporary pacemakers include transvenous, epicardial, transcutaneous,
and transthoracic.
■ Transvenous pacing: A lead wire is passed through the brachial, internal or
external jugular, subclavian, or femoral vein to the myocardium.
■ Epicardial pacing is used with cardiac surgical patients. Epicardial wires are
attached to the epicardium during surgery.
■ Transthoracic pacing is used as a last resort, with limited success rates. A
pacing needle is inserted directly into the anterior wall of the heart.
Transcutaneous Pacemakers
Transcutaneous pacemakers are used for noninvasive temporary pacing using
two large external electrodes. The electrodes are attached to an external pulse
generator, which operates on alternating current or battery. The generator emits
electrical pulses, which are transmitted through the electrodes and then trans -
cutaneously to stimulate ventricular depolarization when the patient’s heart rate
is slower than the rate set on the pacemaker. Used as an emergency measure,
a transcutaneous pacemaker should be used for 48–72 hr only. Electrodes
should be changed every 24 hr minimally.

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