Pacers can be _________ or ___________
temporary or permanent
Asynchronous
generate impulses at fixed rate
Synchronous
generate a response to demand
Pacing can be
atrial, ventricular, atrio-ventricular or biventricular
Indications for pacing
conditions that interfere with heart intrinsic ability to initiate or conduct electrical impulses-- sinus node dysfunction, symptomatic bradyarrhythmias, tachyarrhythmias
Indications fro pacing 2
prophilaxis with post-cardiac surgery, biventricular pacing in HF to optimize CO-- EF </= 35%, IVCD >0.12 NYHA class III/IV
Temporary pacers
post open heart-- epicardial pacing
Transcutaneous or external pacing
temporary, use in emergent situations, stimuli delivered through defib system
Transvenous pacing
electrical stimuli delivered to endocardium surface of heart, delivered from external pulse generator or SC implanted generated
QRS deflection
impulses originate from endocardial surface look like LBBB; impulses originate from epicardial surgace look like RBBB
Firing
electrical impulse generated by pacer; a pacer spike
Capture
myocardial cells respond to electrical impulse
Sensing
detection of presence or absence of patient intrinisic electrical activity; capable in demand mode only
Rate control - fixed
asynchronous-- stimulus provided at preset rate, incapable of sensing intrinsic activity
Rate control- demand
synchronous-- stimulus provided when patient's rate falls below preset rate; must be able to adequately sense
Milliamps (mA)
amouont of current to elicit capture, mA
Pacing threshold
minimum current or mA needed for 100% capture
Sensitivity
allows pacer to detect intrinsic activity in demand mode; measured in millivolts mV-- lower number = greater sensitivity
Sense indictor
light flashes when inherent complex is detected
Threshold
minimum amplitude needed for detection by pulse generator; set sensitivity per policy; 1/2 of threshold
Failure to pace
generator off or faulty, battery dead
failure to capture
impulse from pacer, but not followed by appropriate wave form-- inadequate mA, electrode displaced, electrolyte imbalances--- pacer spike with no QRS
failure to sense (BAD BAD BAD)
pacer does not sense rhythm, sends sporadic spikes, can cause R on T--> v.fib. sensitivity TOO low (NUMBER IS HIGH), electrode dislodged, loose connections, depleted battery
Demand mode-- AAI
atrial paced and sensed, inhibited when P waves sensed
Demand mode-- VVI
ventricles paced and sensed, inhibited when QRS sensed, cannot restore atrial synchronicity
Demand mode-- DDD
designed to inhibit atrial and/or pacing if normal event is sensed
Undersensing
pacer fails to register depolarization of a chamber--
Oversensing
pacer detects signals other than depolarization of relevant chamber-- pacer can withhold pacing-- e.g artifact-- change sensitivity