Hayes Chapter 2 Flashcards
What are attempts to restore or mimic normal cardiac conduction physiology? (4)
- DDD pacing
- Algorithms to reduce RV pacing
- Ventricular rate regularisation
- CRT
What factors make up cardiac output? (2)
Heart rate x strike volume = cardiac output
What is strike volume? (2)
Amount of blood ejected with each ventricular contraction
Ie. end diastolic volume minus end systolic volume
Emotion & exercise increase cardiac output. The contribution of each is determined by what factors? (4)
- Age
- Type/intensity of activity
- Baseline cardiac fitness
- Presence of cardiac disease
In a normal heart, what affects end-diastolic volume? (4)
- Diastolic filling pressure
- Total blood volume
- Distribution of blood volume
- Atrial systole (preload)
In a healthy heart, what determined end-systolic volume? (2)
- Myocardial contractility
2. Afterload
What factors can influence myocardial contractility and afterload? (4)
- Metabolic changes
- Autonomic tone
- Drugs (work either on SA node or affect ANS)
- Cardiac rhythm
What are the two factors that heart conditions will affect? (2)
- Heart rate
- Stroke volume
Or both
What is chronotopic incompetence? (1)
Inability to increase heart rate during exercise or stress
Why will patients with poor LV function be less tolerant of chronotopic incompetence? (1)
Because their stroke volume is already lower (their heart is weak) and so they are more dependent on heart rate for cardiac output.
What cardiac diseases can impair myocardial contractility? (5)
- Coronary artery disease
- MI
- Non-ischaemic cardiomyopathy
- Valvular disease
- Pericardial disease
What is preload? (1)
End-diastolic volume that stretches the right or left ventricle of the heart TO ITS GREATEST DIMENSION
What is interventricular dyssynchrony? (1)
A mechanical delay in contraction of the right and left ventricles (usually >40ms)
What is intraventricular dyssynchrony? (1)
Difference in max strain time of different segments within ONE ventricle
What is pre-ejection time? (1)
Delay in time from QRS onset to onset of pulmonary or aortic flow
What are some metabolic problems that impact cardiac function? (3)
- Chronic acidosis
- Hypoxia
- Hypercarbia
At low, moderate and extreme exercise, what are the biggest factors in increasing cardiac output? (2)
- Moderate/extreme exercise = increased heart rate
2. Low levels activity/rest = AV synchrony is most important
Why are many paced patients more dependant on preload? (2)
- Because they have reduced ventricular compliance
2. This is why AV synchrony is SUPER important for them (just as important as RR)
What is pacemaker syndrome? (1)
Ventriculoatrial conduction or atrial conduction against closed valves
How does pacemaker syndrome affect haemodynamics? (4)
- Activates mechanical stretch receptors in walls of atria and pulmonary veins
- leads to vagal affects
- peripheral vasodilation
- hypotension
What causes pacemaker syndrome?
Any loss of AV synchrony (including really long AV delays)
Describe the MOST trial (mode selection trial)
Severe pacemaker syndrome occurred in 20% of subjects
By how much can AV synchrony increase stroke volume?
By up to 50%
Describe what happens of A.V. delays are too long?
Ventricular contraction doesn’t follow straight after atrial emptying, and AV valves float up towards atria (soft lub 1st heart sound = diastolic AV regurgitation)
What is the downside of a really short AV delay?
Ventricular systole occurs before atrial emptying (loose atrial kick)
Why can programming AV delays be tricky for heart failure patients?
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
How is right intra-atrial conduction delay measured?
From beginning of p wave (or signal recorded in RA) to onset of atrial depolarisation in the para-Hisian bundle region
Normal = 30-60ms
How is interatrial conduction time measured?
Beginning of p-wave/signal recorded in RA to onset of left atrial depolarisation, measured at distal coronary sinus.
Normal = 60-85ms
What are signs that AV optimisation might be helpful? (2)
- P wave duration >120ms
2. Absent or negative PR segment
Describe the relationship between HR and AV delay
Linear relationship/inversely proportional. AV slickens up as HR increases
Describe when AV delays may not shorten with increased heart rate (2)
- Conduction disease
2. Autonomic dysfunction
Describe how lead position and inter/intra-atrial conduction delays affect AV timing
Lead site affects point of activation/when signal is sensed by lead.
