Chapter 8 Flashcards
Pacemaker
Battery powered device that delivers an electrical current to the heart to stimulate depolarization
Consists of a pulse generator and pacing leads
Pacing lead
Insulated wire that is used to carry an electrical impulse from the pacemaker to the patients heart and information about the hearts electrical activity back to the pacemaker
Triggering - start
Inhibition - stop
Pulse generator (power source)
Houses a battery and electronic circuitry
Temporary pacing routes
An artificial pacemaker can be external (temporary intervention) or implanted
Pulse generator of temporary pacemaker is located externally
External pacemakers may be used to control transient disturbances in the heart rate or conduction
Can be accomplished through transvenous, epicardial, or transcutaneous means
Transvenous pacing
Transvenous pacemakers stimulate the endocardium of the right atrium of ventricle (or both)
Electrode is introduced into a central vein, such as the subclavian, femoral, bronchial, internal jugular, or external jugular vein
Epicardial pacing
Epicardial pacing is the placement of pacing leads directly onto or through the epicardium
May be used when a patient is undergoing cardiac surgery and the hearts outer surface is easy to reach
Transcutaneous pacing (TCP)
Uses electrical stimulation through two pacing pads positioned on a patients torso to stimulate contraction of the heart
Electrical stimulus exists from the negative terminal on the machine (and subsequently the negative electrode) and passes through the chest wall to the heart
Range of output current varies depending on the manufacturer
(Doesn’t work too well)
Transcutaneous pacing - complications
-coughing
-skin burns
-interference with sensing
-discomfort from electrical stimulation of the skin and muscles
-failure to recognize that the pacemaker is not capturing
-tissue damage, including third degree burns
-pacing threshold changes
Permanent pacemakers
Patients who have chronic dysrhythmias that are unresponsive to medication therapy and that result in decreased cardiac output may require the surgical implantation of a permanent pacemaker or an implantable cardioverterdefibrillator (ICD)
Pacemakers and ICDs are called cardiovascular implantable electronic devices (CIEDs)
Used to treat disorders of the Sinoatrial (SA) node, disorders of the AV conduction pathways, or both, that produce signs and symptoms as a result of inadequate cardiac output
Pacemakers pulse generator is usually implanted under the local anesthesia into the subcutaneous tissue of the anterior chest just below the right or left clavicle
Pacemaker leads
Pacemaker lead systems may consist of single, double, or multiple leads
-separate lead is used for each heart chamber paced
Electrode
- the exposed portion of the pacing lead that is placed in direct contact with the heart
Unipolar electrode
-has one pacing electrode located at its distal tip
-less commonly used than bipolar lead systems
Bipolar lead system
-contains a positive and negative electrode at the distal tip of the pacing lead wire
Leadless pacemakers
Consists of self contained generator and lead systems
Inserted through the femoral vein and into the right ventricle, eliminating the need for a chest incision and creating a pocket in the patients chest to house a pulse generator
First generation leadless pacemakers provide only single chamber ventricular pacing
Pacing principles
Pacing occurs when the pacemakers pulse generator delivers energy (milliamperes [mA]) through the pacing electrode to the myocardium
A pacemaker responds to the information received either by sending a pacing stimulus to the heart (triggering) or by not sending a pacing stimulus to the heart (inhibiting)
Fixed rate pacemakers
Continuously discharge at a preset rate (usually 70-80 impulses/min) regardless of patients heart rate or metabolic demands
Simple circuitry
Does not sense patients own cardiac rhythm
-may result in competition between the patients cardiac rhythm and that of the pacemaker
Not often used today
Demand pacemakers
Discharge when the patients heart rate drops below the pacemakers rate limit
Expressed in paced pulses per minute (PPM)
Set up depending on what your heart needs
Capture
Capture
-the successful conduction of an artificial pacemakers impulse through the myocardium, resulting in depolarization
Electrical capture
-can be seen as a pacemaker spike followed by an atrial or ventricular complex on the ECG depending on the chamber that is being paced
Mechanical capture
-assessed by palpating the patients pulse
Atrial pacing
Pacing electrode placed in the right atrium
Produces a carmaker spike followed by a P wave
May be used when SA node is diseased or damaged but conduction through AV junction and ventricles is normal
Ventricular pacing
Pacing electrode placed in right ventricle
Produces pacemaker spike followed by a wide QRS, resembling a ventricular ectopic beat
Pacemaker spike in front of QRS (wide)
Pacemaker syndrome
Because a ventricular demand pacemaker does not coordinate pacing with the patients intrinsic atrial rate, it can result in asynchronous contraction in the atrium and ventricle
Loss of AV synchrony can result in a loss of the atrial contribution to cardiac output, decreased stroke volume and decreased cardiac output
Dual chamber pacemaker
Two lead system placed in the heart
-one lead is placed in the right atrium
-a second lead is placed in the right ventricle
Venricular synchronous pacemaker (VDD)
Senses both atrial and ventricular activity but paces only the ventricle when a spontaneous ventricular depolarization does not occur
Used for patients who have impaired AV conduction but an intact SA node
Presence of SA node disease is a contraindication for a VDD pacemaker
AV sequential pacemaker (DVI)
First stimulates the right atrium and then the right ventricle but senses only the ventricle
May be used for patients with severe sinus bradycardia
Asynchronous atrial pacing and the potential for AV asynchrony (with possible pacemaker syndrome) can occur
Optimal sequential pacemaker (DDD)
Also called physiologic or universal pacemaker
Used when the SA node is intact but AV conduction is impaired
In DDD mode, both the atrium and ventricle are paced (D), both chambers are sensed (D), and the pacemaker has both a triggered and inhibited mode of response (D)
Programmed to wait between atrial and ventricular stimulation, stimulating the usual delay in conduction through the AV node
Failure to pace
Failure to fire
Pacemaker malfunction that occurs when the artificial pacemaker fails to deliver an electrical stimulus at its programmed time
Battery is dying
Lead got cut or disconnected
Recognizing on ECG as an absence of pacemaker spikes and a return of the underlying rhythm for which pacing was initiated
Causes of failure to pace
- Battery failure
- Broken or loose connection between the pacing lead and the pulse generator
- Displacement of the electrode tip
- Electromagnetic interference
- Fracture of the pacing lead wire
- Pulse generator failure
- Sensitivity set too high
Failure to pace - possible interventions
- Adjusting sensitivity setting
- Replacing pulse generator battery
- Replacing pacing lead
- Replacing pulse generator unit
- Tightening connections between pacing lead and pulse generator
- Removing source of electromagnetic interference
Failure to capture
Inability of the artificial pacemaker stimulus to depolarize the myocardium
Recognized on the ECG by visible pacemaker spikes not followed by P waves (if electrode in atrium) or QRS complexes (if electrode in right ventricle)
Pacemaker worked, but heart did not respond to stimuli — no electrical activity
Failure to capture — causes
- Battery life
- Displacement of pacing lead wire (common cause)
- Edema or scar tissue formation at the electrode tip
- Faulty connections
- Fracture of the pacing lead wire
- Increased stimulation threshold as a result of medications of electrolyte imbalance
- Output energy set too low
Ventricular perforation
Failure to capture - possible interventions
Slowly increasing the output setting until capture occurs
Repositioning the patient to the left side
Failure to sense
Sensitivity
Extent to which an artificial pacemaker recognizes inartistic electrical activity
Undersensing
Occurs when the artificial pacemaker fails to recognize spontaneous myocardial depolarization
Recognized on ECG by the following
Pacemaker spikes that occur within P waves
Pacemaker spikes that follow too closely behind the patients QRS complex
Pacemaker spikes that appear within T waves
In simple terms, heart works better than the pacemaker thinks — pacemaker gets reading heart rhythm is not pacing properly, but it is
Overprotected heart pacemaker
Oversensing
Pacemaker malfunction that results from inappropriate sensing of extraneous electrical signals
Recognized on ECG as pacemaker spikes at a rate slower than the pacemakers preset rate or no paced beats even though the pacemakers preset rate is greater than patients inartistic rate
Pacemaker thinks the heart is working properly, so no stimuli, but heart is not
Failure to sense — causes
- Battery life
- Circuitry dysfunction
- Decreased P wave or QRS voltage
- Displacement of the electrode tip (most common cause)
- Fracture of pacing lead wire
- Increased sensing threshold from antiarrhythmic medications
- Myocardial perforation
- Sensitivity setting too high
- Severe electrolyte disturbances
Failure to sense — possible interventions
Increasing sensitivity setting
Replacing pulse generator battery
Replacing or repositioning pacing lead
A vertical line on the ECG that indicates the pacemaker has discharged
Pacemaker spike
A pacemaker malfunction that occurs when the artificial pacemaker fails to recognize spontaneous myocardial depolarization
Undersensing
A pacemaker malfunction that occurs when the artificial pacemaker stimulus is unable to depolarize the myocardium
Failure to capture
The period between two consecutive paced events in the same cardiac chamber
Paced interval
This type of pacemaker uses an atrial and ventricular lead
Dual chamber
An artificial PR interval
AV interval
This type of pacemaker discharges only when the patients heart rate drops below the preset rate for the pacemaker
Demand
The ability of a pacemaker to increase the pacing rate in response to physical activity or metabolic demand
Rate modulation
This type of pacemaker continuously discharges at a preset rate regardless of the patients intrinsic activity
Fixed rate
A pacemaker malfunction that results from inappropriate sensing of extraneous electrical signals
Oversensing
The power source that houses the battery and circuitry for regulating a pacemaker
Pulse generator
The rate at which the pacemakers pulse generator initiates impulses when no intrinsic activity is detected; expressed in pulses per minute
Lower rate limit
The minimum amount of voltage needed to obtain consistent capture
Threshold
Pacemaker response in which the output pulse is suppressed when an intrinsic event is sensed
Inhibition
A pacemaker malfunction that occurs when the pacemaker fails to deliver an electrical stimulus at its programmed time
Failure to pace
