Some of the best illustrations in basic cardiac electrophysiology
Posted Dec 17 2009 10:00am
Here is the link to one of the best illustration for cardiac action potential which I have stumbled upon !
Spend some time on the following illustration depicting the normal cardiac action potential that explain the ionic movements . Understand why a cardiac muscle has two refractory periods , why there is a sustained dome for myocardial action potential and this is missing in SA and AV nodal potential ?
Red curve indicates electrical action potential .Blue depicts the mechanical contraction . Both red and blue curves together from the electromechanical systole. Realise , it is the QT interval that represents electro mechanical systole . It includes both cardiac deplarisation and repolarsation .
Identify the gap between the Red and blue curves that represen 50% of ARP .This is the time the myocytes can not be stimulated whatever be the power of stimuli because the Na channels are closed .
Understand ,the above action potential represents only half of the cardiac cycle as diastole is not fully illustrated here .Recognise the fact , diastole begins at the end of phase 3 and goes into pahse 4as diastolic depolarisation by a slow Na current.
After learning the basics of action potenial read about the antiarrhythmic drugs . You will get to understand it better .
Know which drug acts on which receptors or channels and what does it do the various intervals .For example realise any drug that is prolonging an action potential duration is fraught with risk of ventricular arrhythmia as it is synonymous with prolonging QT interval (Eg Class 1 A /1B/Class 3) .
Understand the paradox of QT interval getting shortens with Class 1 B (ligocaine /Mexilitine ) while 1 A does the opposite !
Class 1 Drugs blocks sodium channels .The blockage occurs in a complex rate dependent fashion . It blunts the slope the phase 0 and hence prolongs the action potential .
Class 2 . Beta blockers
Class 3 . Blocks K + Channels and hence prolongs the AP
Class 4 .Calcium blockers
Finally don’t forget to say thanks to Copenhagen medical publishers for this excellent illustration .
Here is the link to one of the best illustration for cardiac action potential which I have stumbled upon !
Spend some time on the following illustration depicting the normal cardiac action potential that explain the ionic movements . Understand why a cardiac muscle has two refractory periods , why there is a sustained dome for myocardial action potential and this is missing in SA and AV nodal potential ?
Click below to reach the online book
Textbook in Medical Physiology And Pathophysiology
Essentials and clinical problems Copenhagen Medical Publisher
Note :
Red curve indicates electrical action potential .Blue depicts the mechanical contraction . Both red and blue curves together from the electromechanical systole. Realise , it is the QT interval that represents electro mechanical systole . It includes both cardiac deplarisation and repolarsation .
Identify the gap between the Red and blue curves that represen 50% of ARP .This is the time the myocytes can not be stimulated whatever be the power of stimuli because the Na channels are closed .
Understand ,the above action potential represents only half of the cardiac cycle as diastole is not fully illustrated here .Recognise the fact , diastole begins at the end of phase 3 and goes into pahse 4as diastolic depolarisation by a slow Na current.
Know which drug acts on which receptors or channels and what does it do the various intervals .For example realise any drug that is prolonging an action potential duration is fraught with risk of ventricular arrhythmia as it is synonymous with prolonging QT interval (Eg Class 1 A /1B/Class 3) .
Sicilian gambit is the receptor & channel based classification for anti arrhythmic drugs . (Sicilian gambit 2 )
Class 1 Drugs blocks sodium channels .The blockage occurs in a complex rate dependent fashion . It blunts the slope the phase 0 and hence prolongs the action potential .
Class 2 . Beta blockers
Class 3 . Blocks K + Channels and hence prolongs the AP
Class 4 .Calcium blockers
Finally don’t forget to say thanks to Copenhagen medical publishers for this excellent illustration .