WEEK 3: Cardiac Electrophysiology & Cardiac Cycle Flashcards
What is the conduction system of the heart?
- sinoatrial node (SA node)
- atrioventricular node (AV node)
- Bundle of His
- left and right branches of bundle of his
-Purkinje fibres
What are the cells that create action potentials in the heart?
modified heart muscle cells
The nodes and fibres are?
cardiac tissue
The function of the conduction system can be modified by what nervous system?
the autonomic nervous system
Where is the SA node located?
localised in the right atrium near the entry of the superior vena cava
SA node has specialised __ fibres?
myocardial
Why is the SA node known as the pacemaker of the heart?
because it generates impules about 70/minute & initiates the contraction of cardiac muscle, producing a heartbeat
Where is the AV node located?
it is localised in the right atrium above the fibrous tissue ring (cardiac skeleton), near the tricuspid valve that separates and isolates atria from ventricles
How does it conduct the cardiac impulse to the ventricle?
via the atrioventricular bundle
The AV node is capable of generating impulses at a rate of about __ per minute
60
Where is the bundle of His located?
it is normally found distal to the AV node next to the tricuspid valve, still in the atria
the bundle of his is the only means of conducting impulses between which two structures?
atria & ventricles
Where are the bundle branches located?
under the endocard of the interventricular septum, towards the apex of the heart
Where are purkinje fibres located?
subendocardial and ‘deliver’ the excitation to the cardiomyocytes
What is the location of the sinoatrial node?
Sinus node
What is the conducting system of the heart made up of?
specialised cardiac muscle fibres
What is the conducting system responsible for?
the initiation and conduction of cardiac impulse
summarise the contraction of cardiac muscle
- SA node initiates an impulse which rapidly spreads to the muscles of the atria, making them contract
- AV nodes picks up the cardiac impulse from the atria and conducts it through the atrioventricular bundle and its branches to the papillary muscles and the walls of the ventricles
- the papillary muscles contract first to tighten the chordae tendinae and then the contraction of the ventricular muscle occurs
what does the defect/damage of the conducting system cause?
cardiac arrhythmia
what occurs if the AV bundle fails to conduct normal impulses?
an alteration in the rhythmic contraction of the ventricles - arrhythmia
what happens if complete bundle block occurs?
there is complete dissociation in the rate of contraction of atria and ventricles
what is the most common cause of defective conduction through AV bundles?
atherosclerosis of the coronary arteries
what two broad phases make up the cardiac cycle?
systole and diastole
what phases are observed in diastole?
isovolumetric relaxation
rapid inflow into ventricles
diastasis
atrial contraction
what phases are involved in systole?
isovolumetric contraction
rapid ventricular ejection
reduced ventricular ejection
overall how many phases are in the cardiac cycle?
7
cardiac output =
stroke volume * heart rate
what is cardiac output?
blood ejected from the left ventricle each minute
what is stroke volume?
blood ejected from the left ventricle with each cardiac cycle
the stroke volume of the left ventricle is influenced by _ and _?
preload
afterload
what is preload?
end-diastolic pressure when the ventricle is filled
what is afterload?
the pressure in the aorta (resistance in the circulation)
intrinsic cardiac regulation of output is acheived primarily via the ___?
Frank-starling Mechanism
the greater the return of venous blood to the heart the greater the ____?
subsequent output that can be achieved
to what capacity do individuals have in being able to increase their cardiac output?
4-6 fold
