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 preventive 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 bradyarrhythmias, 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 non-invasive 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, where a pacing electrode catheter is inserted through a large vein such as the subclavian, internal jugular, or femoral vein and 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 though 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 60 and 80 beats per minute but can be adjusted based on patient need to ensure effective cardiac output.

Next, the pacemaker mode can be set 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 arrythmias like ventricular fibrillation.