Flashcards in Pacemakers Deck (31)
Indications for pacemakers
-Sinus node dysfunction, sick sinus, tachy-brady, sinus arrest
-Post cardiac transplantation
-Hypersensitive carotid syndrome
-LV dysfunction, dilated cardiomyopathy
-Overdrive pacing to suppress fast rhythms
What do pacing circuits consist of?
1) Pulse generator
1) Unipolar circuit
2) Bipolar circuit
What is a pulse generator?
Electrical source which initiates the impulse causing depolarization. Contains controls and settings and a sensing mechanism detecting and interpreting info about pt's intrinsic activity
What are leads (wires)?
Conduct electrical stimuli from the pulse generator to the myocardium. Also transmit sensing info from heart to the pulse generator
What are electrodes?
Exposed metal ends of the lead wires that conduct the impulse to the heart.
1) Negative = Cathode
2) Positive = Anode
What are the two types of pacing circuits?
---> Only one electrode in direct contact with the heart (cathode). The other electrode (anode) is located outside of heart. Impulse travels from pulse generator to the myocardium then through body tissue to the positive electrode.
---> Both positive and negative electrodes in contact with heart
What are the modes of pacing?
1) Transvenous pacing
---> Pacing electrode advanced via catheter or wire through a vein and into the endocardium of right atrium or ventricle
---> Thin stainless steel wires coated in insulation that are attached through surgery to epicardial surface
---> Large pads placed on pt chest wall, temporary pacing used in emergency situations. Much higher output necessary, pt may require analgesia
What are the three pacemaker functions?
1) Firing (pacing)
What is pacemaker firing?
Pulse generator fires an impulse which produces pacer spike on ECG.
Nursing responsibility to ensure:
-Firing occurred when it should
-Pacemaker is not firing when the heart is working properly
What is pacemaker capture?
Depolarization occurs when myocardium responds appropriately to a pacing stimulus. Atrium, ventricle, or both can be paced. Capturing occurs every time a pacer spike is followed immediately by electrical activity.
If the ventricle is paced, what will the QRS look like?
Will look wide and bizarre because conduction occurs through an abnormal ventricular route
What is pacemaker sensing?
Ability to "see" when intrinsic depolarization occurs. We then do not want the pacemaker to fire and capture the heart. Once pulse generator senses intrinsic activity, it will either:
1) Inhibition --> Prevent firing
2) Triggering --> If an intrinsic beat is NOT sensed, pulse generator will fire
What is demand pacing?
Most common mode, pulse generator sees all intrinsic activity and fires IF THERE IS NO INTRINSIC BEAT.
What is asynchronous pacing?
Pulse generator fires regardless of pt's own intrinsic beats. Sensitivity is either turned off or set to highest level so pacemaker does not see anything.
**If pacemaker fires on a T wave the pt may go into fatal arrythmia
How does magnetic activation work with permanent pacemakers?
MD may deactivate permanent pacemaker by placing a magnet over the pacemaker, changing the pacemaker to ASYNCHRONOUS MODE. Pre-set values are restored upon removal of magnet
What is the automatic interval?
Interval between two consecutive pacemaker spikes
What is an escape interval?
Interval between an intrinsic beat and the next paced beat
What is a fusion beat?
Intrinsic stimulus and paced stimulus arrive at the heart at the same time and simultaneously depolarize. Has characteristics of both paced and intrinsic beat
What is a capture threshold?
Established by MD when pacemaker is initiated, is the minimum stimulus (mA) required to cause depolarization
What is the breakdown of pacemaker identification codes?
1) Chamber to be paced
2) Chamber to be sensed
3) Response to sensing (inhibit or trigger)
4) Rate modulation (permanent pacemaker)
5) Multisite pacing (permanent pacemaker)
What are pros / cons of VVI?
-Rate responsiveness allows pacemaker to adjust rate to meet pt metabolic needs
-Loss of atrial kick (only sensing the ventricle)
What are ECG characteristics of VVI?
-Spike followed by wide QRS
-P waves may be seen on ECG but no association with paced beats since PM cannot see them
What are the pros / cons of AAI?
-May restore AV synchrony and restore atrial kick
-Used in sick sinus syndrome
-Does not provide ventricular pacing (ineffective in AV block)
What are ECG characteristics of AAI?
Pacemaker spike followed by P wave, then normal QRS
What are the pros of DDD and what are ECG characteristics?
Maintains AV synchrony at all times.
Will appear as intrinsic or paced P wave followed by intrinsic (narrow) or paced (wide) QRS
What must a nurse troubleshoot for with pacemakers?
1) Failure to fire
2) Failure to capture
3) Inappropriate sensing (under / over)
What happens with failure to fire?
Pulse generator fails to initiate impulse or problem with getting the impulse to the heart.
-Lack of pacemaker spikes
-HR is low and pacemaker does not fire
Causes: Generator failure / battery depletion, loose connections, lead malposition or wire fracture, over sensing
Fix: Check connections, ensure turned on, change battery, decrease sensitivity
What happens with failure to capture?
Pacer impulse is delivered but fails to depolarize or capture the heart.
-Pacer spike is not followed by the desired depolarization
Causes: Output setting low, loose connections, lead or wire issues, catheter dislodgement, edema/fibrosis at catheter tip
Fix: Increase mA, reposition catheter, change battery / generator
What happens with under sensing?
Inability of pacemaker to recognize pt intrinsic activity
-Pacer spike follows too closely behind intrinsic QRS
-Danger that firing occurs on the T wave
Causes: Sensitivity too high, pacemaker set in asynchronous mode, loose connections, lead and wire issues
Fix: Increase sensitivity by decreasing mV, reposition catheter, replace leads / generator