CRM7: DDI/ Algorithms and introduction to ICD and CRT Flashcards
DDI vs DDD
-In DDI, after a sensed P wave, there is no sensed AV delay
-DDD has tracking, DDI does not
Uses of DDI
-Same functioning as VVI
-Used for patients with AV block and atrial disease (rapid AF episodes and sinus dysfunction)
What does this strip show?
Red = Paced P wave
Orange = Sensed P wave
-Sensed P wave has no V delay
-QRS generated by LRL
-Sensed QRS interrupts LRL
What does tracking mean?
-P wave sensing followed by V pacing
What is mode switching?
-Switching from DDD to DDI in AF
-If back into sinus, back into DDD
-Stops device tracking AF
What is an algorithm?
-Turned on to prevent future problems for patients
Examples of algorithms
Mode switch - Avoids ventricular tracking of fast pathological atrial arrhythmias
Ventricular pacing minimisation - encourages intrinsic rhythm and reduction of ventricular pacing
Rate drop - A methodology to try and prevent syncope in vaso-vagal patients
How do you stop tracking of atrial fibrillation?
-Use a non-tracking mode
When would you turn mode switch algorithm off?
-Persistent AF
-Programme to DDIR or VDIR instead
How does mode switching work?
-DDD/DDDR to DDIR/VDIR
-Change back to DDD/DDDR once normal sinus rhythm detected
Why do we want to minimise ventricular pacing?
-Chronic right ventricular pacing causes cardiac remodelling, AF and heart failure
-Caused by electrical and mechanical dysynchrony and disruption of sympathetic/parasympathetic balance
What are 3 algorithms to reduce ventricular pacing?
-Search AV
-MVP
-SafeR
Explain SafeR algorithm
-Provides AAI pacing while continuously monitoring AV conduction (ADI mode)
-Switch temporarily to DDD:
-after 2 consecutive blocked atrial events (paced or sensed)
-if device detects ventricular pause greater than programmable setting 2-4 seconds
Explain MVP - Managed Ventricular Pacing
-Starts in AAIR
-Goes into DDIR if AT-AF episode
-Goes into DDDR if loss of conduction
Explain AV search and hysteresis
-Prolongs AV delay
-Until there is intrinsic conduction
-If it gets too long, it will pace to avoid dropped beat
Issues with ventricular pacing minimisation alogorithms
Counting number of non-conducted atrial events/pauses:
-Produce symptoms in patients
-Persistence of complete AV block during intrinsic conduction may cause symptomatic ventricular pauses
-Pauses can cause brady-associated ventricular arrhythmia
AV search and hysteresis:
-Long AV intervals (>250ms) can cause haemodynamic compromise (e.g. pacemaker syndrome/ diastolic mitral regurgitation)
Example 1 of AAI switching to DDD
-A paced, V sensed
-A paced, not followed by V sense
-Switch to DDD
Example 2 of AAI switching to DDD
-3 non-conducted P waves out of so many
-Switch to DDD
-Works for A sensed and A paced
Example 3 of AAI switching to DDD
-AV search hysteresis
-Too many long AV delays
-Switches back to DDD
Example 4 of AAI switching to DDD
-Device didn’t sense p wave because it was in refractory period
-Therefore, it thinks long pause
-Switches to DDD
When do you use rate drop response?
-Vasovagal syncope
-Carotid sinus syndrome
Rationale behind using rate drop response?
-Pacing has proven useful in some forms of reflex syncope
-Provides backup pacing
-Prevents symptoms
How does rate drop response work?
-Detects a drop in heart rate that is classified as pathological
-Intervenes at a higher programmed intervention rate for a programmed duration
-Rate slowly flywheels down to a sinus or lower rate
When would you turn mode switch on?
-Paroxysmal AF
Why would you not use ventricular pacing minimisation in a patient in permanent 2:1 Mobitz type 2 AV block?
-You wouldn’t programme them AAI
-You’d programme them DDD
Single coil vs Dual coil leads
-Use single coil in RV
-Not dual coil in RV and SVC
-SVC coil has complications
What therapy can ICD give?
-Shock
-Anti-tachy pacing
How does ATP terminate VT?
-Paces the ventricle faster than intrinsic rate, suppresses the VT and then stops
Difference between cardioversion and defibrillation
-Cardioversion shocks on an R wave
-Defibrillation shocks wherever
Why do we give patients with heart failure CRTs
-HF patients have discoordinate contraction due to electrical activation delay
-This dyssynchrony further depresses systolic function and chamber efficiency
-This worsens morbidity and mortality
