Keeping pace with permanent pacemakers, part II

Nursing, Jul 1999 by Shaffer, Rose B

LEARN TROUBLESHOOTING AND TEACHING TIPS FOR PATIENTS WITH PACE,ALERS.

In the first part of this series (June 1999), I described how permanent pacemakers work and their modes of operation. In this article, I'll discuss indications for permanent pacemakers, the use of the electrocardiogram (ECG) to help determine the pacemaker's mode, troubleshooting tips, and what to teach a patient with a permanent pacemaker.

WHO NEEDS A PACEMAKER?

Many patients who receive pacemakers have symptomatic bradycardia. Their dizziness, lightheadedness, syncope, hypotension, or fatigue may be caused by sinus node dysfunction (sick sinus syndrome), second-degree (type II) atrioventricular (AV) block, complete heart block, atrial fibrillation (AF) with a slow ventricular response, or hypersensitive carotid sinus syndrome.

Patients with chronic AF and a slow ventricular response and patients with enlarged atria (which could trigger AF) are candidates for a VVI or VVIR pacemaker. (For a key to the letters used to designate pacemaker operations, see Decoding the Pacemaker Code.) Because a fibrillating atrium can't be paced, these patients wouldn't benefit from a pacemaker with an atrial lead.

Patients with an intact sinus node with a conduction block in the AV node or lower in the conduction pathway are candidates for a DDD or DDDR pacemaker. Although a WI pacemaker could be used for these patients, the loss of AV synchrony means the patient wouldn't obtain maximum hemodynamic benefit and would lose atrial kick, which accounts for up to 20% of cardiac output. A DDD pacemaker, which preserves AV synchrony, is a better choice.

The DDD pacemaker is contraindicated in patients with known paroxysmal supraventricular tachycardia (PSVT) and chronic AF; however, a new DDD pacemaker with a mode-switching device automatically switches to the VVI mode if the patient develops PSVT or AF.

CLUES TO PACEMAKER TYPE

In most cases, if you're caring for a patient with a permanent pacemaker, information about the pacemaker type and mode will come from the patient, family, or old medical records. But in cases where information isn't available or is incomplete and you suspect that the patient has a permanent pacemaker, you'll need to do a little detective work.

First, check for a subclavian scar and palpate for a generator. Next, look for the presence of an underlying rhythm and determine the rate and rhythm if possible. Then, look closely on the ECG for pacemaker spikes, remembering that bipolar electrodes often produce small spikes. Remember that wide QRS complexes in a row can be mistaken for an accelerated idioventricular rhythm instead of a paced rhythm.

Next, look for the presence of P waves (intrinsic or paced) and their relationship to the QRS complexes. If you see ventricular pacing, take note whether each ventricular paced beat is preceded by a paced or intrinsic P wave. Note if the AV interval is constant before each ventricular paced beat. If it is, you've probably determined that the patient has a DDD pacemaker because it's sensing P waves. VVI pacemakers can't sense P waves. The ECG is a tool to help you determine the type of pacemaker if you can't get any other information. You should never guess from the ECG alone.

TROUBLEESHOOTING TIPS

Pacemaker malfunctions can lead to arrhythmias, hypotension, and syncope. Problems fall into three basic categories:

failure to capture. If the pacemaker can't stimulate the cardiac chamber to contract, you'll see a pacemaker spike on the ECG at the appropriate time but no atrial or ventricular response following it. Possible causes of failure to capture include a dislodged or malpositioned lead, battery failure, faulty connections, lead fracture, ventricular perforation, and electrolyte imbalances.

In a patient who has no intrinsic ventricular electrical activity, failure to capture can be fatal: The patient will be pulseless (in asystole).

failure to pace. When the pacemaker isn't working, no pacemaker activity appears on the ECG. This can be caused by battery failure, lead dislodgment, wire fracture, a disconnected wire or cable, generator failure, or oversensing, in which the pacemaker misinterprets skeletal muscle activity as a QRS complex and fails to fire.

failure to sense. If the pacemaker fires anywhere in the cardiac cycle instead of at the appropriate times, the sensitivity may need to be adjusted. Possible causes of failure to sense are battery failure, lead malposition or fracture, pulse generator failure, or a break in the lead's insulation.

Report episodes of failure to capture, pace, or sense to the physician or nurse practitioner.

GOING INTO OVERDRIVE

Suppose the patient develops persistent tachycardia-atrial or ventricular. You can use overdrive pacing to catch the runaway heart and bring it back under control. Although overdrive pacing typically is used with temporary pacemakers, some permanent pacemakers also have this capability.

For example, suppose your patient's pacemaker is set at a rate of 70 beats/minute, but he develops atrial tachycardia with a rate of 160 beats/minute. Set the pacemaker for a higher rate-for example, 170 beats/minute-so that it takes over pacing the patient's heart. Once the pacemaker is calling the shots, slowly reduce its rate back to the original preset rate-in this case, 70 beats/minute.