CRT and pacing

Question 1

What is CRT

Answer 1

pacemaker therapy to improve symptoms and mortality of HF

Question 2

What percentage of HF patients have impaired systolic function and how many of these have severely impaired LVEF (<50%)

Answer 2

50%

1/4 of these

Question 3

Who benefits from CRT

Answer 3

HFrEF
have severely impaired LVEF (<50%)
benefit the post

Question 4

CRT in HFpeF?

Answer 4

No real evidence for HFpEF

Question 5

Why CRT?

Answer 5

Pt with cardiac dyssynchrony appear to do worse

Question 6

Medical therapy for HF

Answer 6

ACEi
Beta blockers
Spironalactone

Question 7

Terminology:

CRT-P

Answer 7

Purely ability of a pacemaker to make walls contract at the same time.
Without defibrillator

Question 8

Terminology

CRT-D

Answer 8

CRT with defibrillator function

- Replace RV lead with defibrillator

Question 9

Leads of CRT

Answer 9

Atrial lead, RV lead (defibrillator or normal pacemaker lead), LV lead (important lead

Question 10

Important lead in CRT

Answer 10

LV lead

Question 11

Path of LV lead

Answer 11

across the heart, through the coronary sinus to lateral surface of the LV
- Stimulation of left ventricle via a vein, whole wire is in contact with the heart

Question 12

Layer of heart that the CRT leads are attached to

Answer 12

LV - Epicardium

Atrial and RV - Endocardium

Question 13

Another current name for CRT

Answer 13

Biventricular pacing

Question 14

What is dual chamber pacing?

Answer 14

Not CRT
- Refers to atrium and RV
NOT CRT

Question 15

What is cardiac dyssynchrony?

Answer 15

Uncoordinated activity of the heart

Question 16

Normal activation of heart in layers

Answer 16

Endocardial to epicardial

Question 17

Ways to think of dyssynchrony

Answer 17

1. Electrical

2. Mechanical

Question 18

What is mechanical dyssynchrony?

Answer 18

Can occur without significant electrical dyssynchrony
Normal QRS measures but echo measures of dyssynchrony
Not entirely understood:
- Latency in diseased hearts? leading to a delay between
the two (even through activation has occurred it takes
time for contraction to follow
- Or conduction disease is not visible to use in the
surface ECG? Electrical dyssynchrony is there we just cannot see it

Question 19

What is electrical dyssynchrony?

Answer 19

Conduction problem that is resulting in the walls not contracting at the same time. Contribute to and/or cause mechanical dyssynchrony

Long PR: (AVB)
Long QRS: (LBBB, RBBB, IVCD)

Question 20

Significants of LV lead in LBBB

Answer 20

Allows activation of lateral LV wall earlier than would have occurred in LBBB

Question 21

Impact of CRT on mechanical/electrical dyssynchrony

Answer 21

removes mechanical dyssynchrony as it ensures everything contracts as and when it should
Electrical dyssynchrony is also shown to disappear

Question 22

Impact of CRT on CO?

Does it really work

Answer 22

Pulmonary capillary wedge pressure reduced (heart lesss overloaded)
CO has significantly increased, improved contraction.
BUT same is seen for many inotropes (dopamine, dobutamine, milrinone).
Long term, survival probability is reduced with inotropic agents

Question 23

CRT vs Inotropes survival and hospital admission

Answer 23

CRT much better - CARE-HF

Question 24

Meta-analyses of >20 RCTs

Answer 24

Odds ratio favouring CRT over medical therapy

- Decreased mortality by almost 30%

Question 25

Optimization of CRT

Answer 25

- Epi to endo is non-physiological - RV apical pacing has shown to be harmful in HF pts. Thought of moving it to a more physiological position But caution due to knock-on effects - LV lead could be paced from a number of different points Quadripolar leads can pace from four different sites along the LV lead – creates a huge array of different vectors (64) that can be paced from Doesn't yet really improve CRT responsiveness but helps void diaphragmatic capture: As phrenic nerve runs over lateral border of pericardium If captured then pt experiences ‘hiccups’ with every paced heart beat - PATIENT SELECTION probably best way to optimize CRT

Question 26

What is E wave

Answer 26

passive’ ventricular filling. Relaxation of the ventricle as it fills with blood Note: this is not actually a passive process (sucking blood in)

Question 27

What is the A wave

Answer 27

atrial contraction, adding a little more blood

Question 28

Timing of A wave and E wave

Answer 28

These must be timed carefully to maximise efficiency Note the dead time between e and a wave We don’t want an overlap between the two at all as this will create an inefficiency BUT If the time increases then there is more backflow and also more inefficiency

Question 29

Impact of a prolonged A wave

Answer 29

encroaches on systole (can take a variable amount of time), causes systole to be pushed along then encroaches on E wave Passive filling overlapping with active filling Increased PR interval when longer time for atrial to contract

Question 30

CRT in pts with narrow QRS

Answer 30

When CRT used in pt with narrow QRS I.e. mechanical dyssynchrony without electrical dyssynchrony → DEATH rate increased CONTRAINDICATED