CRM 4,5 - Introduction to Pacemaker Timing and the NBG Pacing Code Flashcards
Describe the complex
-A paced, V sensed
Describe the complex
-A sensed, V sensed
-A paced, V paced
Describe the complex
-A sensed, V paced
What is capture?
-Depolarisation following the pacing impulse
What is sensing?
-When intrinsic complex is seen
How do you convert interval to rate?
60bpm = 1000ms
How do you convert rate to interval?
60bpm = 1000ms
What is pacing interval?
-Time period between an event (paced or sensed) and the next event in the same chamber
What is an active pacing interval?
-Active pacing intervals can be interrupted and restarted by a paced or sensed event
What are refractory/blanking intervals?
-Refractory interval starts after paced/sensed beat
-Refractory interval categorises signals picked up
-Blanking period ignores signals picked up
Lower rate interval/limit
How does pacemaker create intracardiac electrogram (EGM)?
-Measured from tip/ring of pacing lead
-Only a few discrete cells at the point of contact create the sharp bipolar signal
-Pacemaker can only see this sharp signal, not surface ECG
What are farfield signals?
-Signals from another cardiac chamber seen on electrogram
What is atrial refractory?
-Notices the complex
-But does nothing
What is retrograde
-Signals that fall into refractory periods can be termed retrograde
Pacemaker code
Pace
Sense
Trigger/Inhibit
E.g. DOO - Dual pace, nothing, nothing
What is this?
-AOO
-Atrial pacing spikes
-Exact interval between spikes
What is this?
-VOO
-Ventricular pacing spikes
-Exact interval between spikes
Issue with non-sensing modes
-VOO can cause VF (R on T)
-AOO can cause AF
-Uses up battery
What is the interval that matters in AAO/VOO?
-Lower rate interval
What is this?
DOO
-AV interval (PR interval)
Features of DOO
-Atrial and ventricular spikes
-Lower rate limit and AV interval
-Intrinsic A and V not sensed
-Intrinsic signals do not trigger/inhibit
What do refractory periods prevent?
-Double counting the same event
-Sensing the pacing stimulus, it’s after potential, and the evoked response
-In dual chamber devices, prevent PMT and cross-talk
What is this?
AAI(R)
-Lower rate interval shortens at the end
What is this?
VVI(R)
What is this?
DDD
-Paced QRS if there is no intrinsic beat during AV interval
Other modes to consider
AAT - sees intrinsic atrial beat, triggers atrial paced beat
VVT - sees intrinsic ventricular beat, triggers ventricular paced beat
VDD - Only paces ventricle, senses both to set up AV interval
DDI- A-sensed events inhibit atrial spike
Pacemaker timing (could be in exam)
What are the 2 types of refractory period?
Absolute/blanking - no signals ‘seen’
Relative/noise sampling - ‘sees’ and categorises signals but does not reset lower rate/refractory period
Absolute refractory period
Relative/noise sampling period
Alert period
Normal sinus node, complete AV block
-Let sinus node control atria
-Dual chamber pacemaker
-To sense P waves and create AV delay
Or
-Single chamber pacemaker with rate response
How does VVIR work?
-Upper rate interval
-Lower rate interval
-If it doesn’t see anything, it will pace
-Makes interval shorter with activity
Symptoms in VVI pacemaker
-Dizziness
-Fatigue
-SOB
-Oedema
-Hypotension
-Due to loss of AV synchrony
-V pace while atria is contracting
Which devices have AV delay?
-Only dual chamber devices (AV synchronous pacing)
What are the 2 types of AV delay?
pAV - paced AV interval
sAV - sensed AV interval
-Allows ventricular filling
Why is pAV longer than sAV?
-Sensing starts in the middle of the P wave
What is the VA interval?
-Interval from paced/sensed ventricular event to next atrial event
What type of pacing does MTR apply to?
As Vp
When does MTR start?
-After AV delay
-When p/s V wave starts
-Along with lower rate limit
What is the MTR?
Maximum Tracking Rate
-Fastest rate at which dual chamber pacemaker can pace ventricle after a sensed p wave
If patient’s sinus node is working (p waves), what type of pacemaker should you give?
-Dual chamber pacemaker
