Pacemakers Flashcards
Indications for temporary pacemakers
- Symptomatic bradycardia unresponsive to medical therapy
– 2nd Degree Type II and 3rd Degree Heart Block
– Permanent pacemaker failure
– Support cardiac output after cardiac surgery
– Tachy dysrhythmias (overdrive pacing)
– Diagnostic studies: Electrophysiology studies (EPS)
Permanent pacemaker indications
– Sick Sinus Node Syndrome
– Symptomatic AV block
– Pan-conduction disease (often age related conduction tissue changes)
– Hereditary, idiopathic, or drug-related QT interval prolongation
Permanent ventricular lead placement
The ventricular lead is usually placed in the apex of the right ventricle and held in
with tines at the end to lead.
Permanent Atrial Lead Placement
The atrial lead is harder to keep in place due to the smooth surface, therefore often a lead is used with a screw on the end to fix it within the atria
Some leads emit steroids to reduce inflammation and scarring
Pacemaker function: Pace
Electrical stimulus to the ventricle or atria
– Capture is the effective depolarization of the heart by the artificial pacemaker
– Capture threshold is the minimum pacemaker output setting required to pace the heart
Pacemaker function: Sense
The pacemaker wire senses electrical activity in the chamber in which it is placed
Pacemaker function: Pacing triggered
The pacemaker fires an electrical stimulus if it senses no electrical activity
Pacemaker function: Pacing inhibited
The pacemaker inhibits electrical stimulus due to sensed intrinsic rhythm
Pacemakers deliver a pacing stimulus only when…?
The hearts intrinsic pacemaker fails to function
VVI
- The ventricular lead paces the ventricle and inhibits itself if it senses an intrinsic rhythm
- The patient loses atrial filling and atrial kick (loss of CO)
DDD
– 1st D = both chambers are paced
– 2nd D = both chambers are sensed
– 3rd D = inhibits both atrial and ventricular pacing when sensing intrinsic rhythm; and triggers response to sensed atrial activity to allow for rate responsive pacing
DDD: Atrial sensed with ventricular paced rhythm
– The SA node is intact and pacing normally
– AV synchrony remains intact
DDD: Atrial Paced with intrinsic ventricular rhythm
- This strip shows loss of intrinsic SA node activity, the atrial lead then paces the atria
- The impulse travels normally through the AV node
- There is intrinsic BBB
Limitations for DDD pacing
Atrial pacing cannot be achieved with chronic atrial fib
If a patient with a DDD pacer goes into Afib there are rate limitations set for the atrial and ventricular responses
Pacemaker Codes
- Chamber Paced
- Chamber Sensed
- Response to Sensing
- Rate ResponsiveP
Common occurrence: Fusion Beats
Causes
– A paced and an intrinsic ventricular beat occur simultaneously
– Resulting QRS a mix between intrinsic and paced
Intervention : none
Common occurrences: PVC
Causes
– electrode causing irritable ventricular focus
– Note: PVC’s normally occur in the first 24h after lead placement
Intervention
– May need to administer antiarrhythmic drugs – May need reposition of lead wire
Complication: Battery Failure
Applying a magnet over the pacer will illicit fixed (asynchronous) pacing
If the battery is failing, the pacer will pace at a different rate than what’s programmed
If the battery of a DDD pacer begins to fail it will convert to VVI to conserve battery time
Complication: Loss of output
Possible Causes – Battery depletion – Pacemakeroff
– Oversensing
– Faulty cable connection
– Dislodged/fracturedlead
Complication: Failure to capture
The pacemaker spikes fail to initiate the depolarization of the ventricle
– EKG pacemaker spikes not followed by QRS complexes
S/S Failure to capture
Signs and Symptoms – bradycardia
– hypotension
– fatigue
Failure to capture: Potential causes
– Displacement of the pacing lead wire (most common) – mA set too low – fracture of the lead – battery failure – perforation of the myocardium by the lead wire – edema or scar tissue formation at electrode tip – fibrin formation at the lead tip
Failure to capture interventions
Intervention:
– Notify physician immediately
– The physician may need to reprogram the pacer, replace or reposition the pacing wire
– May reposition patient onto left side
Less Common Causes of Noncapture May Include:
Twiddler’s syndrome Electrolyte abnormalities – e.g.,
hyperkalemia Myocardial infarction Drug therapy Battery depletion Exit block
Accurate Sensing
The pacer needs to be able to “see”
If the pacer can’t see the patient’s intrinsic it will fire indiscriminately
DANGER: R ON T Phenomenon
Rare in today’s sophisticated pacers
Complication: Failure to sense
Pacemaker cannot see the patient’s intrinsic rhythm
– EKG pacemaker spikes that fall where they shouldn’t; spikes
may fall on T waves
Failure to sense potential causes:
– misplacement of ventricular lead placement (most common) – inflammation or swelling around the electrode
– battery failure
– fracture of pacing lead wire
Interventions for under-sensing
Interventions: Notify physician
– Reposition the patient to the left side
– The physician may need to reprogram the generator or replace or reposition lead wire
– Prepare for code situation
Complications: Oversensing
Lack of pacemaker activity
– pacemaker does not pace or paces at a rate slower than the set rate
Symptoms depend on underlying rhythm and rate
Probably causes of oversensing
– the pacemaker may sense or be inhibited by skeletal muscle contractions (more frequent with a unipolar lead)
– electromagnetic interference
– sensing of T waves or atrial activity
– pacemaker sensitivity set too high
Complication: Diaphragm pacing
Signs and Symptoms – hiccups – EKG artifact Possible causes – stimulation of phrenic nerve by the electrode tip – myocardial perforation by lead wire – excessive pacemaker voltage Interventions – position patient on left side – surgery (reposition lead wire) – reduce mA
Complications: : Chest or Abd. Muscle Stimulation
Signs and Symptoms – muscle twitching – pacemaker identification letters appear backward on chest x-ray Possible causes – high pacemaker output – lead fracture or insulation break – flipped pulse generator Intervention – reduce pacemaker output – replace lead – reposition generator
Founded Sources of EMI (Electrical magnetic interference)
- Use of arc welding machinery
- High-tension electrical wires
- Carrying cellular phone in pocket near pacemaker generator
- Magnetic resonance imaging (MRI)
- Radiation therapy to the chest (pacemaker generator should be shielded)
- Electrical cardioversion
- Electrocautery use during surgical procedures (biggest
problem in the hospital in regards to EMI) - Lithotripsy treatment
- Transthoracic defibrillation 10. TENS Units
Pacemaker Syndrome
Defined as:
Loss of AV synchrony
Retrograde ventriculoatrial (VA)
conduction
Absence of rate response to physiological need
S & S related to lower cardiac output.
Treatment focuses on use of dual-chamber pacing as well as reprogramming timing.
Transcutaneous Pacemaker
External pacemakers are built into portable cardiac monitor/defibrillators
The impulse is conducted across the intact chest wall to activate the myocardium
Used for emergent situations
Energy and current for transcutaneous pacemaker
The mean current required for electrical capture is usually 50 - 100 mA
IV analgesia and sedation is required for currents of 50 mA or more
Transcutaneous pacing technique
Place the pads on the patient
Set desired heart rate
Slowly increase mA until capture is obtained
– Electrical capture is characterized by a pacer spike followed by a QRS
– The QRS will change morphology
– Cardiac capture is assessed by pulse
– Assess hemodynamic response (BP, UO, skin)
Transcutaneous pacing precautions
Precautions
– Failure to capture may occur due to electrode placement or
patient size and body habitus (barrel-shaped chest)
– Transcutaneous pacing contracts the chest muscle therefore:
The rhythm strip could look like capture is occurring but just the chest wall is contracting
– must check pulse for cardiac capture
Failure to recognize the presence of treatable VF Failure to recognize that pacemaker is not capturing
– Third degree burns can occur with prolonged use
Antitachycardia overdrive pacing
– accomplished by pacing the heart for a few seconds at a rate faster than the tachycardia rate, then returning to the regularly paced or intrinsic rhythm
– This is usually incorporated in implantable defibrillator devices
Three lead pacing for BBB and CHF
– Pacing the atria and both ventricles to improve CO (cardiac resynchronization or CRT)
Pacemaker mediated tachycardia
Can be stopped by placing a magnet over the generator
If SVT is in progress, the magnet will have little effect
Pacemaker and magnet application
Magnet will result in asynchronous (DOO or VOO) pacing at either 65 or 85 BPM (for a Medtronic device) depending on battery status
Application will not permanently affect the device (most devices)
Analyzing pacemaker function
Identify the intrinsic rate and rhythm – are P waves present - what rate
– are QRS complexes present - what rate
Note evidence of paced activity: atrial, ventricular, both
– measure the distance between two consecutive paced beats
– determine the rate and regularity of the paced interval
– measure the hysteresis - the period between an intrinsic beat and the next paced beat
Evaluate the escape interval
Evaluate the strip for failure to capture, failure to sense, oversensing, and failure to pace
