NONPHARMACOLOGIC TREATMENTS

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•ability to change modes automatically

•ability to mimic the normal physiologic cardiac cycle, maintaining AV synchrony

•ability to sense and pace the atria and ventricles at the same time according to the intrinsic atrial rate and the maximal rate limit.

Home, home on the rate range

Unlike other pacemakers, the DDD pacemaker is set with a rate range, rather than a single critical rate. It senses atrial activity and ensures that the ventricles track or respond to each atrial stimulation, thereby maintaining normal AV synchrony.

Firing and pacing

The DDD pacemaker fires when the ventricle doesn’t respond on its own, and it paces the atria when the atrial rate falls below the lower set rate. (See Evaluating a DDD pacemaker rhythm strip.) In a patient with a high atrial rate, a safety mechanism allows the pacemaker to follow the intrinsic atrial rate only as far as a preset upper limit. That limit is usually set at about 130 beats/minute and helps to prevent the ventricles from tracking atrial fibrillation, atrial tachycardia, or atrial flutter.

Evaluating pacemakers

Now you’re ready to find out if your patient’s pacemaker is working correctly. To do this, follow the procedure described below.

1. Read the records

First, determine the pacemaker’s mode and settings. If your patient had a permanent pacemaker implanted before admission, ask him whether he has a wallet card from the manufacturer that notes the mode and settings.

If the pacemaker was recently implanted, check the patient’s records for information. Don’t check only the ECG tracing—you might misinterpret it if you don’t know the pacemaker type.

2. Look at the leads

Next, review the patient’s 12-lead ECG. If it isn’t available, examine lead V1 or MCL1 instead. If there is only one ventricular lead, it is usually in the right ventricle. Therefore, expect a negatively deflected paced QRS complex here, just as with a left bundlebranch block. An upright QRS complex may mean that the

Evaluating a DDD pacemaker rhythm strip

Look for these possible events when examining a rhythm strip showing the activities of a DDD pacemaker:

•Intrinsic rhythm—No pacemaker activity occurs because none is needed.

•Intrinsic P wave followed by a ventricular pacemaker spike—The pacemaker is tracking the atrial rate and ensuring a ventricular response.

•Pacemaker spike before a P wave, then an intrinsic ventricular QRS complex—The atrial rate is falling below the lower rate limit, causing the atrial channel to fire. Normal conduction to the ventricles then ensues.

•Pacemaker spike before a P wave and a pacemaker spike before the QRS complex—No intrinsic activity occurs in either the atria or the ventricles.

leadwire is out of position, perhaps even perforating the septum and lodging in the left ventricle.

3. Scrutinize the spikes

Then select a monitoring lead that clearly shows the pacemaker spikes. Make sure the lead you select doesn’t cause the cardiac monitor to mistake a spike for a QRS complex and then doublecount the heart rate monitor. This may cause the alarm to go off, falsely signaling a high heart rate. If the monitor has a “paced mode,” select this mode to reduce errors.

4. Mull over the mode

When looking at the ECG tracing of a patient with a pacemaker, consider the pacemaker mode. Then interpret the paced rhythm. Does it match what you know about the pacemaker?

5. Unravel the rhythm

Look for information that tells you which chamber is paced. Is there capture? Is there a P wave or QRS complex after each atrial or ventricular spike? Or do the P waves and QRS complexes stem from intrinsic activity?

Look for information about the pacemaker’s sensing ability. If intrinsic atrial or ventricular activity is present, what’s the pacemaker’s response? Look at the rate. What’s the pacing rate per minute? Is it appropriate given the pacemaker settings? Although you can determine the rate quickly by counting the number of complexes in a 6-second ECG strip, a more accurate method is to count the number of small boxes between complexes and divide this into 1,500.

Troubleshooting problems

Malfunction of a pacemaker can lead to arrhythmias, hypotension, and syncope. (See When a pacemaker malfunctions, page 188.) Common problems with pacemakers that can lead to low cardiac output and loss of AV synchrony include:

•failure to capture

•failure to pace

•undersensing

•oversensing.

Failure to capture

Failure to capture is indicated on an ECG by a pacemaker spike without the appropriate atrial or ventricular response—a spike without a complex. Think of failure to capture as the pacemaker’s inability to stimulate the chamber.

Check out these 5 procedure points to find out if your patient’s pacemaker is working correctly.

Failure to capture

•If the patient’s condition has changed, notify the practitioner and ask for new settings. Be prepared to initiate cardiopulmonary resuscitation (CPR) if needed.

•If pacemaker settings have been altered by the patient or someone else, return them to their correct positions. Make sure the face of the pacemaker is covered with its plastic shield. Remind the patient not to touch the dials.

•If the heart still doesn’t respond, carefully check all connections. You can also increase the milliampere setting slowly (according to your facility’s policy or the practitioner’s orders), turn the patient from side to side, or change the battery. Keep in mind that the practitioner may order a chest X-ray to determine the position of the electrode.

Failure to pace

•If the pacing or indicator light flashes, check the connections to the cable and the position of the pacing electrode in the patient (done by X-ray).

•If the pulse generator is turned on but the indicators aren’t flashing, change the battery. If that doesn’t help, use a different pulse generator.

•Decrease the sensitivity by increasing the millivolts. The pacemaker may be inhibiting pacing due to oversensing electrical activity from another heart chamber or muscle.

•Make sure atropine is available in case the patient’s heart rate drops, and be prepared to initiate CPR if needed.

A pacemaker spike should appear here but doesn’t.

Failure to sense intrinsic beats

•If the pacemaker is undersensing (it fires but at the wrong times or for the wrong reasons), turn the sensitivity control to a smaller number.

•Change the battery or pulse generator.

•Remove items in the room that might cause electromechanical interference. Check if the bed is grounded. Unplug each piece of equipment, and then check to see if the interference stops.

•If the pacemaker still fires on the

T wave, turn off the pacemaker (per facility policy or practitioner’s order). Make sure atropine is available in case the patient’s heart rate drops, and be prepared to initiate CPR if needed.

There is a pacemaker spike but no response from the heart.

The pacemaker fires anywhere in the cycle.

Causes include hypoxia, acidosis, an electrolyte imbalance, fibrosis, an incorrect lead position, a low milliampere setting, depletion of the battery, a broken or cracked leadwire, or perforation of the leadwire through the myocardium.

Failure to pace

Failure to pace is indicated by no pacemaker activity on an ECG. The problem is caused by battery or circuit failure, cracked or broken leads, loose connections, oversensing, or the millivolts set too low. It can lead to asystole.

Failure to sense

Undersensing is indicated by a pacemaker spike when intrinsic cardiac activity is already present. Think of it as help being given when none is needed. When undersensing occurs in synchronous pacemakers, spikes occur on the ECG where they shouldn’t. Although they may appear in any part of the cardiac cycle, the spikes are especially dangerous if they fall on the T wave, where they can cause ventricular tachycardia or fibrillation.

In synchronous pacemakers, the problem is caused by millivoltage set too high, electrolyte imbalances, disconnection or dislodgment of a lead, improper lead placement, increased sensing threshold from edema or fibrosis at the electrode tip, drug interactions, or a depleted or dead pacemaker battery.

Memory jogger

Malfunction of a

pacemaker can lead to arrhythmias, hypotension, and syncope. To help you remember common pacemaker problems think “failure times two, under, over”:

failure to capture— spike without a complex

failure to pace—no ECG activity

undersensing—spike when intrinsic activity already present

oversensing—no pacing when patient needs it.

Oversensing

If the pacemaker is too sensitive, it can misinterpret muscle movement or events in a chamber other than the one that it should be sensing as depolarization. Then it won’t pace when the patient actually needs it, and heart rate and AV synchrony won’t be maintained.

How you intervene

Make sure you’re familiar with different types of pacemakers and how they function. This will save you time and worry during an emergency. When caring for a patient with a pacemaker, follow these guidelines.

Checks and balances

Familiarize yourself with the various types of pacemakers and how they work.