Regulation of heart and QT interval Flashcards
How many layers does cardiac muscle have?
3
Which layer of the cardiac muscle lines the entire circulatory system?
Endothelium
What is the middle layer of the cardiac muscle called?
Myocardium
What is the outer layer of the cardiac muscle called?
Epicardium
What properties of skeletal and smooth muscle does heart muscle share?
Striated
What structures join heart muscle cells together?
Intercalated disks
What structural feature is unique to heart muscle cells compared to skeletal muscle cells?
Branches
What type of junction provides mechanical strength in intercalated disks?
Desmosomes
What type of junction provides electrical coupling in intercalated disks?
Gap junctions
What percentage of heart muscle cells primarily contract?
99%
What is the functional significance of the syncytium in heart muscle?
Allows for coordinated contraction
What percentage of cells comprise the conducting system of the heart?
1%
What part of the nervous system innervates the heart muscle?
Autonomic NS
What blood vessels supply blood to the heart muscle? What kind of pump system is the heart?
Coronary arteries
Simultaneous dual pump
What electrical event triggers the heartbeat?
Depolarisation via action potential
What are the regions of the heart that exhibit auto-rhythmicity?
SA node
AV node
Bundle of His
Purkinje fibres
What is the primary function of autorhythmic cells in the heart?
Initiate and conduct action potentials
What electrical behavior is characteristic of autorhythmic cells as they approach threshold?
Slowly drift to threshold
What term describes the gradual depolarization of autorhythmic cells?
Pacemaker potential
Which node is normally the heart’s pacemaker?
SA node
Following membrane depolarization in cardiac contractile cells, what type of channels open?
Voltage gated Ca2+ channels
What type of calcium channels are activated during the plateau phase of the cardiac action potential?
L type (long lasting)
What role do L-type calcium channels play in the cardiac action potential?
Balances K+ removal
What happens to calcium channels during repolarization? Which ion channels open during repolarization?
Ca2+ channels inactivate
K+ channels
What triggers cross-bridge formation in cardiac muscle? Where are calcium sensitive receptors located? What are calcium sensitive receptors also known as?
Calcium combines with troponin
Sarcoplasmic reticulum
Ryanodine receptors
How is calcium actively transported back into the sarcoplasmic reticulum? How do abnormal levels of extracellular potassium affect the resting potential of cardiac cells? How does a rise in extracellular potassium affect cardiac contractility?
Ca2+ ATPase pumps
Change resting potential
Decreased
Why does increased extracellular potassium reduce cardiac contractility? What effect can high levels of extracellular potassium have on the heart? How does a decrease in extracellular potassium affect resting potential?
Inactivates Na+ channels
Arrythmias and fatalities
Hyperpolarisation
What effect does elevated extracellular calcium have on cardiac contractions? What is the effect of calcium channel blockers on the force of cardiac contraction? What term describes the force of cardiac contraction?
Longer contractions
Reduces force of contraction
Ionotropy
What effect does Digoxin have on intracellular calcium and contractility?
Increases Ca2+ and contractility
What does ECG stand for? What abnormalities can be detected using an ECG? What are the abnormalities that can be detected by ECG?
Electrocardiogram
Abnormalities in rate and rhythm
Atrial flutter, atrial fibrillation, ventricular fibrillation and heart block
What can be diagnosed via ECG?
Cardiomyopathies, ischaemia, infarction
What are the two main phases of the cardiac cycle? What occurs during isovolumetric ventricular contraction? What occurs during ventricular ejection? What volume is present in the ventricle at the end of systole?
Systole (contraction) and diastole (relaxation)
Valves closed
Valves open
End systolic volume
What occurs during isovolumetric ventricular relaxation? How much ventricular filling occurs before atrial contraction? What volume is present in the ventricle at the end of diastole?
Valves closed
80%
End-diastolic volume
What is the formula for stroke volume?
End diastolic volume - end systolic volume
What are possible targets for drugs in the heart?
Receptors, enzymes, ion channels and carrier proteins
According to the Vaughan Williams classification, what do Class I antiarrhythmic drugs block? Examples of class Ia antiarrhythmic drugs? Examples of Ib antiarrhythmic drugs? Examples of Ic antiarrhythmic drugs?
Sodium channels
Quinidine, procainamide, disopyramide
Lignocaine
Flecainide
According to the Vaughan Williams classification, what do Class II antiarrhythmic drugs block? Examples of Class II antiarrhythmic drugs?
ß-adrenoceptor
Atenolol and sotalol
According to the Vaughan Williams classification, what is the action of Class III antiarrhythmic drugs? According to the Vaughan Williams classification, what is the action of Class III antiarrhythmic drugs? What is the therapeutic effect of Class III antiarrhythmic drugs? Examples of Class III antiarrhythmic drugs?
Prolong action potential
Prolong refractory period
Suppress re-entrant rhythms
Amiodarone and sotalol
According to the Vaughan Williams classification, what do Class IV antiarrhythmic drugs block? What is the mechanism of action of Class IV antiarrhythmic drugs? Example of a Class IV antiarrhythmic drug? Examples of other antiarrhythmic drugs?
Calcium channels
Impair impulse propagation
Verapamil
Digoxin and adenosine
How many states do Na+ channels have?
3 (closed, open and refractory)
What condition is Torsades de Pointes?
A type of ventricular tachycardia (outline on ECG looks like a party streamer)
How does Class Ia antiarrhythmic drugs affect the duration of the action potential? How does Class Ib antiarrhythmic drugs affect the duration of the action potential? How does Class Ic antiarrhythmic drugs affect the duration of the action potential?
Prolong AP
Shorten AP
No change to AP
