The pulse generator is designed to generate an electrical current that travels through pacing lead and exits through electrode that is in direct contact with the heart. This electrical current initiates a myocardial depolarization.
The power source for a temporary external pulse generator is standard 9-volt alkaline battery inserted into the generator
An epicardial lead system is often used for temporary pacing after cardiac surgery
The bipolar epicardial lead system has two separate insulated wires (one negative and one positive) that are loosely secured with sutures to the cardiac chambers to be paced. Both electrodes are in contact with myocardial tissues, so either wire may be use as the negative, or ground electrode
Delivers a pacing stimulus at a set (fixed) rate regardless of the occurrence of spontaneous myocardial depolarization; occurs in non-sensing modes. It delivers an electrical impulse at a present fixed rate to the heart and functions independently of cardiac activity.
Delivers a pacing stimulus only when the heart’s intrinsic pacemaker fails to function at a predetermined rate; the pacing stimulus is either inhibited or triggered by the sensing of intrinsic activity.
The pulse generator delivers artificial stimulus only when needed or on demand and therefore does not compete with patient’s rhythm
Failure of the pacemaker deliver the pacing stimulus results in the disappearance of the pacing artifact, even though the patient’s intrinsic rate is less than the set rate on the pacer. This can occur either intermittently or continuously and can be attributed to failure of the pulse generator or its battery
If the pacing stimulus fires but fails to initiate a myocardial depolarization, a pacing artifact will be present but will not be followed by the expected P wave or QRS complex, depending on the chamber being paced.
If the patient is undergoing heart surgery, epicardial leads may be electively placed at the end of the operation. The physician places the transvenous or epicardial pacing lead(s), repositioning as needed to obtain adequate pacing and sensing thresholds.
For the patient on a regimen of bed rest, the pulse generator can be suspended with twill tape from an intravenous (IV) pole mounted overhead on the ceiling.
This not only will prevent tension on the lead while the patient is moved (given adequate length of bridging cable) but will also alleviate the possibility of accidental dropping of the pulse generator.
Pulse generators (new generation) provide a low-battery signal 24 hours before complete loss of battery function to prevent inadvertent interruptions in pacing. The pulse generator must always be labeled with the date that the battery was replaced.
It is important to be aware of all sources of EMI within the critical care environment that could interfere with the pacemaker’s function. Sources of EMI in the clinical area include electrocautery, defibrillation current, radiation therapy, magnetic resonance imaging devices, and transcutaneous electrical nerve stimulation (TENS) units.
In most cases, if EMI is suspected of precipitating pacemaker malfunction, converting to asynchronous mode (fixed rate) will maintain pacing until the cause of the EMI is removed.
The pacing electrode provides a direct, low resistance path to the heart, the nurse takes special care while handling the external components of the pacing system to avoid conducting stray electrical current from other equipment.