Critical care - Pacemakers: Nursing

Pacemakers are electronic devices that deliver electrical impulses to help the heart maintain a cardiac rate or rhythm that can produce effective cardiac output.

These electrical impulses initiate depolarization. The process where the impulse moves through the conduction system and causes cardiac contraction.

Pacemakers can be used as a temporary supportive or preventative measure until the underlying cause of a conduction problem is resolved or they can be implanted permanently.

Common indications for a pacemaker include treatment of brady arrhythmias such as symptomatic bradycardia related to heart block or sick sinus syndrome or tachyarrhythmias like from supraventricular tachycardia.

They're also used for cardiac support during or after heart surgery or during diagnostic studies and procedures like atrial electrograms or catheter ablations.

Temporary pacemakers can be categorized as transcutaneous transvenous or epicardial starting with transcutaneous pacing.

This is where electrical stimulation is applied through the skin using two noninvasive electrode pads connected to an external pacemaker.

Typically one pad is attached anteriorly on the chest and the other pad is placed posteriorly on the back. This type of pacing is typically done in emergency situations and sometimes they can also act as a defibrillator.

Next is transvenous pacing or a pacing electrode catheter is inserted through a large vein such as the subclavian, internal jugular or femoral vein in into the right atrium or right ventricle.

When there's a lead in both chambers, then it's called a dual chamber pacemaker. From there, the external ends of the electrode wires are connected to a pulse generator.

Then there's epicardial pacing which is established during cardiac surgery where ventricular and sometimes atrial pacing wires are loosely sewn onto the epicardium, they're either removed before the chest wall is surgically closed or they remain inside temporarily while the other ends of the wires are tunneled through the chest wall and connected to an external pulse generator.

Now, there are a few settings that are used to tell the pacemaker what to do. First, the pacemaker rate controls the number of impulses sent to the heart per minute.

The rate is typically set between 6080 BPM but can be adjusted based on patient need to assure effective cardiac output.

Next, the pacemaker mode can be sent to either a demand or synchronous mode or to a fixed rate or asynchronous mode. In demand mode.

The pacemaker senses the patient's own natural or intrinsic heartbeats and will only send an impulse if the heart rate drops below a certain threshold.

Conversely in fixed rate mode, the pacemaker paces the heart at a set rate regardless of the patient's own intrinsic heartbeats.

This mode is not typically the mode of choice because the pacemaker can compete with the patient's intrinsic heart rate and might deliver a pacing impulse on the T wave which is a critical time during ventricular repolarization.

This is referred to as the R on T phenomenon. And it has the potential to destabilize the heart rhythm and cause life threatening arrhythmias like ventricular fibrillation.

Another setting is the pacemaker's output, which is an adjustable setting that regulates the amount of electrical current delivered to the heart, which is measured in milli amperes.

The lowest level of output needed to consistently initiate depolarization is called the threshold. When the energy level results in depolarization and a heartbeat, that's called capture.

The output is usually set 2 to 3 times higher than the threshold to account for variations in the threshold needed over time.

Additionally, output can be individualized depending on the pacing device. For instance, patients with a transcutaneous pacing device will need more milli amperes than those with transvenous or epicardial pacing.

Since the electrical energy has to penetrate the chest wall. Lastly, sensitivity refers to the pacemaker's ability to detect the heart's intrinsic electrical activity which is measured in millivolts.

A higher setting decreases the pacemaker sensitivity while a lower setting increases its sensitivity. So the ideal setting is one that detects even the smallest intrinsic cardiac activity but not so sensitive that it detects noncardiac activity like the electrical activity from strong noncardiac muscle contractions.

Now, there are three common malfunctions of pacemakers including failure to pace capture or sense failure to pace, also called failure to fire occurs when the pacemaker doesn't deliver a pacing stimulus.

When it should. Normally, when a pacing stimulus occurs, there's a visible mark on the ECG called a pacer spike.

So this problem can be noted by an absence of these spikes on the rhythm strip failure to pace can occur due to a malfunctioning pulse generator, low battery loose or broken lead wires or electromagnetic interference from electrical equipment like heavy machinery to restore pacemaker function troubleshooting may involve tightening connections, replacing the battery or the pulse generator or eliminating the source of interference.

Next up is failure to capture. This occurs when the pacemaker produces an electrical impulse that doesn't cause depolarization on an ecg.

This can be visualized as a pacer spike without a subsequent P wave for atrial pacemakers or QR S complex. For ventricular pacemakers failure to capture can happen if the output is set too low or if pacing wires are displaced, failure to capture can also occur when the heart needs a higher threshold to stimulate contraction, which could be due to electrolyte, imbalances, myocardial ischemia or fibrosis or due to certain medications like beta blockers.

Strategies to mitigate this malfunction include adjusting the output by increasing the mieres and positioning the patient on their left side which encourages increased contact between the transvenous pacing wire with the myocardium.

So it can detect the heart's intrinsic electrical signals. Lastly, failure to sense.

Also known as undersensing is when the pacemaker is unable to detect the patient's intrinsic heart rhythm. So it sends an electrical impulse without regard to the patient's own rhythm.

On ecg this manifests as pacer spikes occurring too close to the patient's own heartbeats leading to asynchronous pacing, which can cause ventricular tachycardia or R NT phenomenon.

Typically failure to sense is caused by electrode wires being misplaced or when the pacemaker sensitivity setting is too high strategies to resolve.

This include adjusting the sensitivity level on the pacemaker. The patient can also be positioned on their left side to facilitate contact between the lead and the myocardium.

Keep in mind if any of these malfunctions can't be resolved through troubleshooting measures, emergency transcutaneous pacing should be initiated to maintain cardiac output until a solution is found.

All right. As a quick recap, pacemakers are temporary or permanent electronic devices that send electrical impulses to the heart to regulate rate and rhythm and promote adequate cardiac output.

Pacemaker function is regulated through settings that include rate mode output and sensitivity. Common malfunctions of pacemakers include failure to pace capture or sense.