1.1.3 Chrontropy Flashcards
What 3 things does tachycardia cause?
Increases myocardial oxygen consumption
Reduces time for ventricular filling
Reduces time available for coronary blood flow
What does bradycardia cause?
Decreased cardiac output and tissue perfusion
What is heart rate dependent on?
Autonomic nervous system
What does Na, Ca and K do to allow a current?
Na moves into the cell to depolarise it
Ca moves into the cell to depolarise it
K moves out of the cell to repolarise it
Explain what occurs in a pacemaker potential
Slow increase in depolarisation until threshold reached, action potential trigered, channels close and K+ exits cell, repolarise
What is the order of conduction in the heart?
SAN generates pacemaker potential
Depolarisation passed over both atria
reaches AVN = small pause
Cascade down purkinje system to ventricles for contraction
What does the vagus nerve innervate?
SAN
AVN
Small amount of atria
What do adrenergic fibres innervate?
SAN
AVN
Atria
Ventricles
How does sympathetic stimulation increase heart rate?
Sympathetic fibres release noradrenaline which opens more Na channels so depolarisation is faster
How does parasympathetic stimulation slow heart rate?
Parasympathetic fibres release acetylcholine opens fewer Na channels so depolarisation is slower
What receptor do muscle cells use to detect noradrenaline?
B1 adrenergic receptors
What receptors detect acetylcholine in the SAN and AVN?
M2 Muscarinic
Arrhythmias
Abnormalities of cardiac rhythm affecting heart rate, filling of the heart and can therefore compromise cardiac output
Sinus Rhythm
SA node is acting as pacemaker; a QRS complex follows each P wave, PR and QT intervals normal, RR interval regular
Sinus Arrhythmia
Normal QRS complex, PR and QT intervals but RR interval varies in a set pattern
