Page 693 - Cardiac Nursing

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C HAPTER 2 8 / Pacemakers and Implantable Defibrillators 669
Care of Epicardial Leads. Epicardial leads exit through the 1. Verify that the patient is in a paced rhythm; pacing rate may
chest and unless they are being used for pacing, they are usually need to be temporarily increased to override an intrinsic
coiled and placed in a gauze dressing until needed. The exit site rhythm.
should be kept clean and dry according to established hospital 2. Watch the cardiac monitor continuously while gradually de-
policies on exit site care. Epicardial leads are easily dislodged, so creasing output.
care must be taken when handling them so as not to pull them 3. Note when loss of capture occurs (pacing spike not followed by
out. Use of a pacing cable is recommended to prevent the need to appropriate waveform: P wave for atrial pacing, QRS for ven-
strap the temporary pacemaker directly to the patient’s body. The tricular pacing).
leads and pacing cable must be securely taped to the chest to pre- 4. Gradually turn output up until 1:1 capture resumes—this is
vent dislodgement of epicardial leads. Because the exposed metal the stimulation threshold.
end of the leads is a direct route for electrical current from the en- 5. Set the output two- to three-times higher than threshold to en-
vironment to conduct directly to the heart, care must be taken to sure adequate safety margin; for example, if consistent capture
insulate the leads to prevent cardiac arrhythmias, especially VF is regained at 2 mA, then set the output at 4 to 6 mA.
(see section “Electrical Safety,” for more information).
Sensitivity Threshold Testing. The sensitivity threshold is
Electrical Safety. A temporary pacing lead provides a direct the minimum voltage of intrinsic cardiac activity that can be
pathway for stray electrical current to reach the heart without the sensed by the pacemaker. The pacemaker becomes more sensitive
protective resistance of the skin. Even a very small electrical cur- (can sense smaller signals) as the number on the sensitivity control
rent can initiate atrial fibrillation or VF if it is conducted directly gets smaller (see section “Sensing,” for further explanation).
to the heart by pacing leads. Sensitivity testing can be performed only if the patient has a
Some considerations for electrical safety when caring for pa- hemodynamically stable underlying rhythm. If the patient is com-
tients with temporary pacing leads include: pletely pacemaker-dependent or has a very slow underlying rate,
then do not perform sensitivity threshold testing. The procedure
1. Wear gloves when handling pacing leads. for performing a sensitivity threshold test is as follows:
2. Make sure that all connections between the pulse generator and
pacing cable and between pacing cable and pacing leads are 1. Verify that the patient has an intrinsic rhythm (is not being
tight and inserted completely into their receptacles so no metal paced); this may require temporarily decreasing the pacing rate
is exposed. to allow the underlying rhythm to emerge.
3. If using a pacing cable with an alligator clip connector, then wrap 2.Slowly decrease the pacemaker’s sensitivity (by increasing the
a glove around the connections in such a way that they are sepa- number on the sensitivity control) while watching the sense in-
rated and insulated from each other and from the environment. dicator light on the pulse generator or watching the cardiac
4. Cover exposed metal ends of pacing leads that are not in use monitor.
with some type of insulating material. a. The sense indicator light flashes with each sensed P wave
a. Wrap a glove around the ends of transvenous leads and tape (for atrial sensing) or QRS (for ventricular sensing).
loosely. b. Pacing remains inhibited and there are no pacing spikes seen
b. Place the ends of epicardial leads in a glove (or cut a finger on the monitor as long as sensing continues.
from a glove and place them inside) or place the metal end 3. Note when the sense indicator fails to flash with each P wave or
of each individual lead in a needle cover, small syringe, or QRS and when pacing spikes begin to appear in competition
some other insulating material. with the intrinsic rhythm; this is the sensitivity threshold.
5. Keep dressings over pacing lead insertion sites dry; wet dress- 4. Set the sensitivity at one-half of the identified threshold to en-
ings conduct electricity more easily. sure an adequate safety margin; for example, if the threshold is
6. Make sure all electrical equipment in the room is grounded and 5 mV, then set the sensitivity at 2.5 mV.
in good working order.
7. Be aware of your own body’s static electricity, especially if your Evaluating Pacemaker Function
unit is carpeted.
a. Never let the pacing system be the first thing you touch This section is directed primarily at temporary pacemakers be-
when entering a patient’s room. cause nurses can interact more directly with them than with per-
b. Be especially careful when using slider boards to transfer pa- manent pacemakers. The same concepts apply to permanent pace-
tients into and out of bed, because they generate static elec- makers, but corrective measures require the use of a pacemaker
tricity. programmer or an actual surgical procedure to reposition pacing
leads or replace the pulse generator.
Stimulation Threshold Testing. The stimulation threshold Evaluation of pacemaker function requires knowledge of the
is the minimum pacemaker output necessary to capture the heart mode of pacing expected (e.g. VVI, AAI, DDD); the minimum
consistently. The contact of the pacing lead with the myocardium rate of the pacemaker, or pacing interval; and any other pro-
causes local tissue edema and inflammation that impedes the de- grammed parameters in the pacemaker. The basic functions of a
livery of current to the myocardium. Peak thresholds occur ap- pacemaker include stimulus release, capture, and sensing, and
proximately 3 to 4 weeks after permanent lead placement, and they should be evaluated for both temporary and permanent pace-
chronic stable thresholds are usually reached at approximately 3 makers. Stimulus release refers to pacemaker output, or the ability
months. Stimulation threshold testing with a temporary pacing of the pacemaker to generate and release a pacing impulse. Cap-
system should be performed every shift to ensure an adequate ture is the ability of the pacing stimulus to cause depolarization of
safety margin for capture. The procedure for performing a stimu- the chamber being paced. Sensing is the ability of the pacemaker
lation threshold test is as follows: to recognize and respond to intrinsic electrical activity in the