Hayes Chapter 2

Question 1

What are attempts to restore or mimic normal cardiac conduction physiology? (4)

Answer 1

1. DDD pacing
2. Algorithms to reduce RV pacing
3. Ventricular rate regularisation
4. CRT

Question 2

What factors make up cardiac output? (2)

Answer 2

Heart rate x strike volume = cardiac output

Question 3

What is strike volume? (2)

Answer 3

Amount of blood ejected with each ventricular contraction

Ie. end diastolic volume minus end systolic volume

Question 4

Emotion & exercise increase cardiac output. The contribution of each is determined by what factors? (4)

Answer 4

1. Age
2. Type/intensity of activity
3. Baseline cardiac fitness
4. Presence of cardiac disease

Question 5

In a normal heart, what affects end-diastolic volume? (4)

Answer 5

1. Diastolic filling pressure
2. Total blood volume
3. Distribution of blood volume
4. Atrial systole (preload)

Question 6

In a healthy heart, what determined end-systolic volume? (2)

Answer 6

1. Myocardial contractility

2. Afterload

Question 7

What factors can influence myocardial contractility and afterload? (4)

Answer 7

1. Metabolic changes
2. Autonomic tone
3. Drugs (work either on SA node or affect ANS)
4. Cardiac rhythm

Question 8

What are the two factors that heart conditions will affect? (2)

Answer 8

1. Heart rate
2. Stroke volume

Or both

Question 9

What is chronotopic incompetence? (1)

Answer 9

Inability to increase heart rate during exercise or stress

Question 10

Why will patients with poor LV function be less tolerant of chronotopic incompetence? (1)

Answer 10

Because their stroke volume is already lower (their heart is weak) and so they are more dependent on heart rate for cardiac output.

Question 11

What cardiac diseases can impair myocardial contractility? (5)

Answer 11

1. Coronary artery disease
2. MI
3. Non-ischaemic cardiomyopathy
4. Valvular disease
5. Pericardial disease

Question 12

What is preload? (1)

Answer 12

End-diastolic volume that stretches the right or left ventricle of the heart TO ITS GREATEST DIMENSION

Question 13

What is interventricular dyssynchrony? (1)

Answer 13

A mechanical delay in contraction of the right and left ventricles (usually >40ms)

Question 14

What is intraventricular dyssynchrony? (1)

Answer 14

Difference in max strain time of different segments within ONE ventricle

Question 15

What is pre-ejection time? (1)

Answer 15

Delay in time from QRS onset to onset of pulmonary or aortic flow

Question 16

What are some metabolic problems that impact cardiac function? (3)

Answer 16

1. Chronic acidosis
2. Hypoxia
3. Hypercarbia

Question 17

At low, moderate and extreme exercise, what are the biggest factors in increasing cardiac output? (2)

Answer 17

1. Moderate/extreme exercise = increased heart rate

2. Low levels activity/rest = AV synchrony is most important

Question 18

Why are many paced patients more dependant on preload? (2)

Answer 18

1. Because they have reduced ventricular compliance

2. This is why AV synchrony is SUPER important for them (just as important as RR)

Question 19

What is pacemaker syndrome? (1)

Answer 19

Ventriculoatrial conduction or atrial conduction against closed valves

Question 20

How does pacemaker syndrome affect haemodynamics? (4)

Answer 20

1. Activates mechanical stretch receptors in walls of atria and pulmonary veins
2. leads to vagal affects
3. peripheral vasodilation
4. hypotension

Question 21

What causes pacemaker syndrome?

Answer 21

Any loss of AV synchrony (including really long AV delays)

Question 22

Describe the MOST trial (mode selection trial)

Answer 22

Severe pacemaker syndrome occurred in 20% of subjects

Question 23

By how much can AV synchrony increase stroke volume?

Answer 23

By up to 50%

Question 24

Describe what happens of A.V. delays are too long?

Answer 24

Ventricular contraction doesn’t follow straight after atrial emptying, and AV valves float up towards atria (soft lub 1st heart sound = diastolic AV regurgitation)

Question 25

What is the downside of a really short AV delay?

Answer 25

Ventricular systole occurs before atrial emptying (loose atrial kick)

Question 26

Why can programming AV delays be tricky for heart failure patients?

Answer 26

Because they can have a big difference in RV and LV contraction time, so optimal AV timing may be different for each side of circulation

Question 27

How is right intra-atrial conduction delay measured?

Answer 27

From beginning of p wave (or signal recorded in RA) to onset of atrial depolarisation in the para-Hisian bundle region Normal = 30-60ms

Question 28

How is interatrial conduction time measured?

Answer 28

Beginning of p-wave/signal recorded in RA to onset of left atrial depolarisation, measured at distal coronary sinus. Normal = 60-85ms

Question 29

What are signs that AV optimisation might be helpful? (2)

Answer 29

1. P wave duration >120ms | 2. Absent or negative PR segment

Question 30

Describe the relationship between HR and AV delay

Answer 30

Linear relationship/inversely proportional. AV slickens up as HR increases

Question 31

Describe when AV delays may not shorten with increased heart rate (2)

Answer 31

1. Conduction disease | 2. Autonomic dysfunction

Question 32

Describe how lead position and inter/intra-atrial conduction delays affect AV timing

Answer 32

Lead site affects point of activation/when signal is sensed by lead.