10 Arrhythmia and Drugs Flashcards
What is the normal resting heart rate?
60 to 100bpm
What are the different causes of tachycardic arrhythmias?
Ectopic pacemaker
Afterdepolriations
Atrial fibrillation
When are do delayed afterdepolrization arise?
When intracellular calcium is high?
When do early afterrepolarization arise?
During repolarization
More likely in a prolonged action potential
In what conditions does atrial fibrillation arise?
Conditions that put extra stretch and pressure on the atria
What is the most common arrhytmia mechanism?
Re-entry
What is re-entry?
The wave of depolarization travels back to re-excite the area of muscle that has already contracted
What does re-entry often happen as a conseqeunce of?
Myocardial infarction
What 3 things are required for reentry?
the Presence of a unidirectional block
Critical timing
the Length of the effective refractory period of normal tissue
What diseases underlying mechanism involves the accessory conduction pathway?
Wolff-Parkinson-White syndrome
What different drugs are used to target rhythm and rate?
Voltage sensitive sodium channel blockers
Beta-adrenoreceptor antagonists
Potassium channel blockers
Drugs that block calcium channels
How do sodium channel blockers work?
Use dependent, only blocks voltage gated sodium channels that are open, therefore preferentially blocks damaged depolarised tissue
Name a sodium channel blocker?
Lidocaine
What do beta blockers do?
Block increase in pacemaker activity
Slow conduction
When are beta blockers used?
When catecholamine levels are, following a myocadial infarction
List some beta blockers
Atenolol
Propranolol
Why are potassium channel blockers used?
Prolong the action potential by blocking potassium channels
What is the problem with Potassium channel blockers?
Not used as in relality cause EADs
What one potassium channel blocker is used?
Amiodarone
Blocking calcium channels has what effect?
Decreases the slope of the action potential in the SA node
Decreases AV nodal conduction
Decrease force of contraction
What does adenosine do?
Used to terminate supravetricular tachycardias
Enhances potassium conductance
How do cardiac glycosides work?
Inhibit sodium/potassium pump ATPase, leading to an intracellular rise in sodium ions, leading to a decrease in acitivty of sodium calcium exchanger, causing an increase in, intracellular calcium concentration
What are the actions of cardiac glycosides?
Increases the force of contraction
Slows heart rate
reduces the hearts oxygen consumption
What nerve to cardiac glycosides have an effect on?
Cause an increase in vagal activity
