Electrical activity of the heart Flashcards
Which channels are responsible for the entry of extracellular Ca into the cell following depolarisation through the t-tubules?
L-type voltage gated calcium channels
What detects an increase in intracellular calcium to initiate the release of calcium from the sarcoplasmic reticulum?
Ryanodine receptors
How does calcium allow contraction of muscles?
Binds to troponin C, which removes tropomyosin from the actin binding site on myosin, allowing the head to bind actin
How do intracellular calcium levels return to normal?
ATPase pump on SR/ER
Ejected from cell via Na-Ca exchanger
Plasma membrane calcium ATPase
Taken up by mitochondria
What enzyme acts as a “brake” for the ATPase?
Phospholamban
What structures are vital for the cardiac muscles to act as a “functional syncytium”?
Intercalated discs, made up of gap junctions and desmosomes so cardiac muscle cells are linked electrically and physically
How long is a cardiac muscle action potential?
250msec
How long is a skeletal muscle action potential?
2msec
What is another name for the pacemaker potential?
Diastolic depolarisation, as the pacemaker potential represents the non-contracting time between heart beats during diastole
What do cardiac glycosides do to electrical activity?
Increase calcium release, increasing the force of muscle contraction
Give an example of an cardiac glycoside
Digoxin
What affect does temperature have on electrical activity of the heart?
Increases ~10 beats per min per degree difference
What is responsible for the early increase in Na in the pacemaker potential?
PF, funny current, opens Na upon repolarisation to allow pacemaking
What affect does hyperkalaemia have on electrical activity?
Fibrillation and heart block
What affect does hypokalaemia have on electrical activity?
Fibrillation and heart block (anomalous)
What affect does hypercalcaemia have on electrical activity?
Increased HR and force of contraction
What affect does hypocalcaemia have on electrical activity?
Descreased HR and force of contraction
What speed are the electrical impulses in the SA node?
0.5m/sec
What is the function of the annulus fibrosus?
Non-conducting, prevent the exit of electrical currents except at the AV nodes
What speed are the electrical impulses in the AV node?
0.05m/sec (delayed to allow complete emptying of the atria before ventricle contracts)
What speed are the electrical impulses in the bundle of His?
5m/sec (rapid for ventricular depolarisation)
What does the P wave correspond to in the cardiac cycle?
Atrial depolarisation
What does the QRS complex correspond to in the cardiac cycle?
Ventricular depolarisation
What does the T wave correspond to in the cardiac cycle?
Ventricular repolarisation
What are some common causes of heart block?
Coronary heart disease
Cardiomyopathy
Fibrosis of conducting system (particularly in elderly)
Whats the most common type of arrhythmia?
Atrial fibrillation (no P waves, only f waves, fine oscillations)
What % of those over 65yo have atrial fibrillation?
5-10%
Which arrhythmia has the characteristic “sawtooth” appearance on ECGs?
Atrial flutter, F waves
What causes atrial flutter?
IHD
Cardiomyopathy
Atrial septal defects
Describe ventricular tachyarrhythmia
Ectopic electrical activity is not conducted to ventricles through normal conducting system, thus the QRS complexes are widened with a bizarre configuration
