CRM7: DDI/ Algorithms and introduction to ICD and CRT

Question 1

DDI vs DDD

Answer 1

-In DDI, after a sensed P wave, there is no sensed AV delay
-DDD has tracking, DDI does not

Question 2

Uses of DDI

Answer 2

-Same functioning as VVI
-Used for patients with AV block and atrial disease (rapid AF episodes and sinus dysfunction)

Question 3

What does this strip show?

Answer 3

Red = Paced P wave
Orange = Sensed P wave
-Sensed P wave has no V delay
-QRS generated by LRL
-Sensed QRS interrupts LRL

Question 4

What does tracking mean?

Answer 4

-P wave sensing followed by V pacing

Question 5

What is mode switching?

Answer 5

-Switching from DDD to DDI in AF
-If back into sinus, back into DDD
-Stops device tracking AF

Question 6

What is an algorithm?

Answer 6

-Turned on to prevent future problems for patients

Question 7

Examples of algorithms

Answer 7

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

Question 8

How do you stop tracking of atrial fibrillation?

Answer 8

-Use a non-tracking mode

Question 9

When would you turn mode switch algorithm off?

Answer 9

-Persistent AF
-Programme to DDIR or VDIR instead

Question 10

How does mode switching work?

Answer 10

-DDD/DDDR to DDIR/VDIR
-Change back to DDD/DDDR once normal sinus rhythm detected

Question 11

Why do we want to minimise ventricular pacing?

Answer 11

-Chronic right ventricular pacing causes cardiac remodelling, AF and heart failure
-Caused by electrical and mechanical dysynchrony and disruption of sympathetic/parasympathetic balance

Question 12

What are 3 algorithms to reduce ventricular pacing?

Answer 12

-Search AV
-MVP
-SafeR

Question 13

Explain SafeR algorithm

Answer 13

-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

Question 14

Explain MVP - Managed Ventricular Pacing

Answer 14

-Starts in AAIR
-Goes into DDIR if AT-AF episode
-Goes into DDDR if loss of conduction

Question 15

Explain AV search and hysteresis

Answer 15

-Prolongs AV delay
-Until there is intrinsic conduction
-If it gets too long, it will pace to avoid dropped beat

Question 16

Issues with ventricular pacing minimisation alogorithms

Answer 16

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)

Question 17

Example 1 of AAI switching to DDD

Answer 17

-A paced, V sensed
-A paced, not followed by V sense
-Switch to DDD

Question 18

Example 2 of AAI switching to DDD

Answer 18

-3 non-conducted P waves out of so many
-Switch to DDD
-Works for A sensed and A paced

Question 19

Example 3 of AAI switching to DDD

Answer 19

-AV search hysteresis
-Too many long AV delays
-Switches back to DDD

Question 20

Example 4 of AAI switching to DDD

Answer 20

-Device didn’t sense p wave because it was in refractory period
-Therefore, it thinks long pause
-Switches to DDD

Question 21

When do you use rate drop response?

Answer 21

-Vasovagal syncope
-Carotid sinus syndrome

Question 22

Rationale behind using rate drop response?

Answer 22

-Pacing has proven useful in some forms of reflex syncope
-Provides backup pacing
-Prevents symptoms

Question 23

How does rate drop response work?

Answer 23

-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

Question 24

When would you turn mode switch on?

Answer 24

-Paroxysmal AF

Question 25

Why would you not use ventricular pacing minimisation in a patient in permanent 2:1 Mobitz type 2 AV block?

Answer 25

-You wouldn’t programme them AAI
-You’d programme them DDD

Question 26

Single coil vs Dual coil leads

Answer 26

-Use single coil in RV
-Not dual coil in RV and SVC
-SVC coil has complications

Question 27

What therapy can ICD give?

Answer 27

-Shock
-Anti-tachy pacing

Question 28

How does ATP terminate VT?

Answer 28

-Paces the ventricle faster than intrinsic rate, suppresses the VT and then stops

Question 29

Difference between cardioversion and defibrillation

Answer 29

-Cardioversion shocks on an R wave
-Defibrillation shocks wherever

Question 30

Why do we give patients with heart failure CRTs

Answer 30

-HF patients have discoordinate contraction due to electrical activation delay
-This dyssynchrony further depresses systolic function and chamber efficiency
-This worsens morbidity and mortality