Ch. 15 Part 1 Flashcards
Indications for Temporary Pacing
Pacemaker System
Pacing Routes
Five-Letter Pacemaker Codes
Pacemaker Settings
Pacing Artifacts
Pacemaker Malfunctions
Medical Management
Nursing Management
Permanent Pacemakers
Permanent & Temporary Pacemakers
clinical indications for instituting temporary pacemaker therapy are similar regardless of the cause of the rhythm disturbance that necessitates the placement of a pacemaker
Therapeutic Indications
Diagnostic Indications
Indications for Temporary Pacing
Dysrhythmias that are unresponsive to medications and result in compromised hemodynamic status are a definite indication for pacemaker therapy.
Temporary pacing may be used in the treatment of symptomatic bradycardia or progressive heart block that occurs as a result of myocardial ischemia, medication overdose, or illegal drug toxicity. After cardiac surgery, temporary pacing may be used to improve a transiently depressed, rate-dependent cardiac output. Conduction disturbances that occur after valvular surgery can be managed effectively with temporary pacing.
Therapeutic Indications
Electrophysiology studies (EPS) are performed in cardiac catheterization laboratories equipped with specialized pacing equipment.
Catheter ablation may also be used as a therapeutic strategy for selected patients with atrial fibrillation.
Intracardiac electrograms, recordings of cardiac electrical activity obtained from pacing electrodes, may provide useful diagnostic information.
Stored intracardiac electrograms from permanently implanted cardiac electrical devices can be used to identify undetected episodes of atrial fibrillation that may increase a patient’s risk for ischemic stroke.
Diagnostic Indications
a simple electrical circuit consisting of a pulse generator and a pacing lead (an insulated electrical wire) with one, two, or three electrodes.
Pacing Pulse Generator
Pacing Lead Systems
Pacemaker System
designed to generate an electrical current that travels through the pacing lead and exits through an electrode (exposed portion of the wire) that is in direct contact with the heart.
This electrical current initiates a myocardial depolarization. The current then seeks to return by one of several pathways to the pulse generator to complete the circuit.
The power source for a temporary external pulse generator is a standard alkaline battery inserted into the generator. Implanted permanent pacemaker batteries are usually long-lived lithium cells.
Pacing Pulse Generator
pacing may be bipolar or unipolar. In a bipolar system, two electrodes (positive and negative) are located within the heart, whereas in a unipolar system, only one electrode (negative) is in direct contact with the myocardium. In both systems, the current flows from the negative terminal of the pulse generator, down the pacing lead to the negative electrode, and into the heart. The current is then picked up by the positive electrode (ground) and flows back up the lead to the positive terminal of the pulse generator.
An epicardial lead system is often used for temporary pacing after cardiac surgery.
A unipolar pacing system (epicardial or transvenous) has only one electrode (the negative electrode) making contact with the heart.
Because the unipolar pacing system has a wide sensing area as a result of the relatively long distance between the negative and positive electrodes, it has better sensing capabilities than a bipolar system.
Pacing Lead Systems
Permanent pacing usually is accomplished transvenously, although when a thoracotomy is otherwise indicated, as in cardiac surgery, the physician may elect to insert permanent epicardial pacing wires.
It is a rapid, noninvasive procedure that nurses can perform in the emergency setting and is recommended in the advanced cardiac life support algorithm for the treatment of symptomatic bradycardia that does not respond to atropine.
Discomfort may still be an issue for some patients, particularly when higher energy levels are required to achieve capture. This route is typically used as a short-term therapy until the situation resolves or another route of pacing can be established.
The insertion of temporary epicardial pacing wires has become a routine procedure during many cardiac surgical cases.
These wires can be removed several days after surgery by gentle traction at the skin surface with minimal risk of bleeding.
Temporary transvenous endocardial pacing is accomplished by advancing a pacing electrode wire through a vein, often the subclavian or internal jugular vein, and into the right atrium or right ventricle.
the pacing wire is inserted through a special pulmonary artery catheter by means of a port that exits in the right atrium or right ventricle.
Pacing Routes
programming characteristics and multisite pacing functions, to accommodate the development of newer devices that are rate responsive or that pace from more than one site within the atria and the ventricles.
The first letter refers to the cardiac chamber that is paced. The second letter designates which chamber is sensed, and the third letter indicates the pacemaker’s response to the sensed event. These three letters are used to describe the mode of pacing.
Five-Letter Pacemaker Codes
Their functions must be thoroughly understood so that pacing can be initiated quickly in an emergency situation and troubleshooting can be facilitated if problems with the pacemaker arise.
rate control regulates the number of impulses that can be delivered to the heart per minute.
If the pacemaker is operating in a dual-chamber mode, the ventricular rate control also regulates the atrial rate.
The output dial regulates the amount of electrical current, measured in milliamperes (mA), that is delivered to the heart to initiate depolarization. The point at which depolarization occurs, called threshold, is indicated by a myocardial response to the pacing stimulus (i.e., capture).
Separate output controls for atrium and ventricle are used with a dual-chamber pulse generator.
The sensitivity control regulates the ability of the pacemaker to detect the heart’s intrinsic electrical activity. Sensitivity is measured in millivolts (mV) and determines the size of the intracardiac signal that the generator will recognize.
The sensing ability of the pacemaker can be quickly evaluated by observing for a change in pacing rhythm in response to spontaneous depolarizations.
The AV interval control (available only on dual-chamber generators) regulates the time interval between the atrial and ventricular pacing stimuli.
Because the AV interval is limited by the length of the cardiac cycle, modern temporary generators automatically adjust the AV delay based on the programmed heart rate.
The lower rate, or base rate, determines the rate at which the generator will pace when intrinsic activity falls below the set rate of the pacemaker. The upper rate determines the fastest ventricular rate the pacemaker will deliver in response to sensed atrial activity.
There also is an atrial refractory period, programmable from 150 to 500 ms, which regulates the length of time, after a sensed or paced ventricular event, during which the pacemaker cannot respond to another atrial stimulus.
Pacemaker Settings
All patients with temporary pacemakers require continuous ECG monitoring. The pacing artifact is the spike that is seen on the ECG tracing as the pacing stimulus is delivered to the heart. A P wave is visible after the pacing artifact if the atrium is being paced
With dual-chamber pacing, a pacing artifact precedes both the P wave and the QRS complex
Not all paced beats look alike.
Pacing Artifacts
Most pacemaker malfunctions can be categorized as abnormalities of pacing or of sensing. Problems with pacing can involve failure of the pacemaker to deliver the pacing stimulus, a pacing stimulus that fails to depolarize the heart, or an incorrect number of pacing stimuli per minute.
Pacing Abnormalities
Sensing Abnormalities
Pacemaker Malfunctions
Failure of the pacemaker to deliver the pacing stimulus results in disappearance of the pacing artifact even if the patient’s intrinsic rate is less than the set rate on the pacer. This can occur intermittently or continuously and can be attributed to failure of the pulse generator or its battery, a loose connection between the various components of the pacemaker system, broken lead wires, or stimulus inhibition as a result of EMI.
Tightening connections, replacing the batteries or the pulse generator itself, or removing the source of EMI may restore pacemaker function.
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
This loss of capture can be attributed most often to displacement of the pacing electrode or to an increase in threshold (electrical stimulus necessary to elicit a myocardial depolarization) as a result of medications, metabolic disorders, electrolyte imbalances, or fibrosis or myocardial ischemia at the site of electrode placement.
Pacing can occur at inappropriate rates.
Inappropriate stimuli from a pacemaker may result in pacemaker-mediated tachycardia; this usually is caused by sensing of inappropriate signals in a dual-chamber pacemaker that is in a trigger mode
Pacing Abnormalities
Undersensing
Oversensing.
Sensing Abnormalities
inability of the pacemaker to sense spontaneous myocardial depolarizations.
results in competition between paced complexes and the heart’s intrinsic rhythm.
Undersensing can result in the delivery of pacing stimuli into a relative refractory period of the cardiac depolarization cycle
A ventricular pacing stimulus delivered into the downslope of the T wave (R-on-T phenomenon) is a real danger with this type of pacer aberration because it may precipitate a lethal dysrhythmia.
The cause often can be attributed to inadequate wave amplitude (height of the P or R wave).
Other possible causes include inappropriate (asynchronous) mode selection, lead displacement or fracture, loose cable connections, and pulse generator failure.
Undersensing
occurs as a result of inappropriate sensing of extraneous electrical signals that leads to unnecessary triggering or inhibition of stimulus output, depending on the pacer mode.
Because most temporary pulse generators are programmed in demand modes, oversensing results in unexplained pauses in the ECG tracing as the extraneous signals are sensed and inhibit pacing. Moving the sensitivity dial toward 20 mV (less sensitive) often stops the pauses.
With permanent pacemakers, a magnet may be placed over the generator to restore pacing in an asynchronous mode until appropriate changes in the generator settings can be programmed.
Oversensing.
The physician determines the pacing route based on the patient’s clinical situation.
The physician places the transvenous or epicardial pacing lead or leads, repositioning them as needed to obtain adequate pacing and sensing thresholds. Decisions regarding lead placement may later limit the pacing modes available to the clinician.
After lead placement, the initial settings for output and sensitivity are determined, the pacing rate and mode are selected, and the patient’s response to pacing is evaluated.
Medical Management
in the care of a patient with a temporary pacemaker are associated with several patient problems and can be combined into four primary areas: assessment and prevention of pacemaker malfunction, protection against microshock, surveillance for complications such as infection, and patient education.
Prevention of Pacemaker Malfunction
Microshock Protection
Infection risk
Educate the patient and family
Nursing Management
Continuous ECG monitoring is essential to facilitate prompt recognition of and appropriate intervention for pacemaker malfunction.
If the patient is on a regimen of bed rest, the pulse generator can be suspended with twill tape from an intravenous pole mounted overhead on the ceiling. This positioning prevents tension on the lead while the patient is moved (given adequate length of bridging cable) and alleviates the possibility of accidental dropping of the pulse generator.
The nurse inspects for loose connections between the leads and pulse generator on a regular basis. Replacement batteries and pulse generators must always be available on the unit.
The pulse generator must always be labeled with the date on which the battery was replaced.
It is important to be aware of all sources of EMI within the critical care environment that may interfere with the pace-maker’s function. Sources of EMI in the clinical area include electrocautery, defibrillation current, radiation therapy, magnetic resonance imaging (MRI) scanners, and transcutaneous electrical nerve stimulation units.
Prevention of Pacemaker Malfunction
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.
The possibility of microshock can be minimized by wearing gloves when handling the pacing wires and by proper insulation of terminal pins of pacing wires when they are not in use
The wires are taped securely to the patient’s chest to prevent accidental electrode displacement.
Microshock Protection
the lead insertion site is a rare but serious complication associated with temporary pacemakers. The site is carefully inspected for purulent drainage, erythema, and edema, and the patient is observed for signs of systemic infection.
endocarditis can occur in patients with endocardial pacing leads. A less common complication associated with transvenous pacing is myocardial perforation, which can result in rhythmic hiccoughs or cardiac tamponade.
Infection risk
instructed not to handle any exposed portion of the lead wire and to notify the nurse if the dressing over the insertion site becomes soiled, wet, or dislodged. The patient also is advised not to use any electrical devices brought in from home that could interfere with pacemaker functioning. Patients with temporary transvenous pacemakers need to be taught to restrict movement of the affected extremity to prevent lead displacement.
Educate the patient and family
A patient who undergoes implantation of a permanent pacemaker is usually in the hospital for less than 24 hours. Longer lengths of stay are expected for patients with serious comorbidities such as MI or cardiogenic shock.
Microprocessors have allowed for the development of increasingly smaller generators despite the incorporation of more complex features. Current generators are smaller, more energy efficient, and more reliable than previous models.
Newer enhancements include leadless pacemakers, which consist of a self-contained unit that is placed in the RV via the femoral vein. These devices eliminate the need for a subcutaneous pocket and transvenous leads that account for the majority of complications associated with permanent pacemakers.
New also compatible with MRI.
rapidly expanding role for permanent pacemakers has been the use of these devices as a type of nonpharmacologic therapy for treatment of heart failure.
Permanent Pacemakers
consists of leads and a generator and is similar to a pacemaker but with some key differences. The leads contain not only electrodes for sensing and pacing but also integrated defibrillator coils capable of delivering a shock. The generator is larger, to accommodate a more powerful battery and a highvoltage capacitor along with the microprocessor. It is surgically placed in the subcutaneous tissue of the pectoral region in the upper chest
Occasionally, the electrical rhythm may deteriorate to asystole or a slow idioventricular rhythm; in such cases, the bradycardia backup pacing function is activated.
Many patients with ICDs have structural heart disease and may require continuous pacing or benefit from CRT. ICD product development has resulted in dual-chamber devices with leads in both atria and ventricles to provide these additional therapies.
Other developments in ICD technology include improved diagnostic and telemetry functions, such as the ability to provide real-time electrograms obtained from the ICD electrodes or the ability to perform remote device interrogation using cellular or wireless technology.
Insertion of Implantable Cardioverter Defibrillator
Medical Management
Nursing Management
Implantable cardioverter-defibrillators (ICD)
The ICD has progressed in both programmable functions and insertion technique. Initially, all ICDs were implanted surgically during open-heart surgery or via thoracotomy, with electrode patches attached directly to the heart.
Procedural complications are infrequent but may include hematoma, pneumothorax, cardiac tamponade, or lead dislodgment. A fully subcutaneous ICD has been introduced more recently that consists of a generator implanted in the left axillary area and a single subcutaneous lead for detection of ventricular dysrhythmias and delivery of therapy. Although this device is unable to provide pacing therapies, it may provide an alternative for patients who lack vascular access and avoid complications related to transvenous lead placement.
Insertion of Implantable Cardioverter Defibrillator
ICD begins before implantation with a thorough evaluation of the patient’s risk for dysrhythmia and underlying cardiac function. Some patients may undergo EPS to determine the origin of the dysrhythmia and the effect of antidysrhythmic agents in suppressing or altering the rate of the dysrhythmia.
In these patients an external wearable cardioverter defibrillator may be used to address the risk of sudden cardiac death during the waiting period.
An electrophysiologist performs the initial programming of the device at the time of implantation. Defibrillation efficacy of the ICD may be assessed by inducing the dysrhythmia and then evaluating the ability of the device to terminate it.
Defibrillation testing is still considered a standard of care for subcutaneous ICD implants.
Other adjustments in programming may be performed to decrease unnecessary shocks, including aggressive use of antitachycardia pacing and withholding shocks for SVT or nonsustained ventricular rhythms.
After it has been determined that the ICD functions appropriately, further follow-up can be conducted on an outpatient basis, with remote monitoring options to monitor the number of discharges and the battery life of the device.
Medical Management
implanted during open-heart surgery, postoperative nursing management is similar to that for any patient undergoing cardiac surgery.
includes assessing for dysrhythmias and monitoring for complications related to insertion. In the case of a ventricular dysrhythmia, it is important to know the type of ICD implanted, how the device functions, and whether it is activated (i.e., “on”). If the patient experiences a shockable rhythm, the nurse should be prepared to defibrillate in the event that the device fails.
Most patients continue to take some antidysrhythmic medications to decrease the number of shocks required and to slow the rate of the tachycardia. Complications associated with a permanent ICD include infection from the implanted system, broken leads, and sensing of supraventricular tachydysrhythmias resulting in unneeded discharges.
Educate the Patient and Family
Nursing Management
