L16- Anti-dysrhythmic drugs 1 Flashcards
In the ECG wave what do each of these correspond to?
P wave
QRS complex
T wave
P wave- atrial depolarization
QRS- ventricular depolarization and atrial repolarization
T wave- Ventricular repolarization
What is likely to happen when bloods pumped back and forth between atria and ventricles?
Blood will clot
What’s the difference between arrhythmia and dysrhythmia?
Arhythmia means absence of rhythm. (a subclass of dysrhythmia)
Dysrythmia is a disturbance of rhythm
How are dyrhythmias classified?
According to their site of origin, effect and frequency of occurance. eg. supraventricular tachycardia, paroxysmal. In the AV node, too fast, occuring in attacks.
What does true arrhythmia mean?
A very disogranized rhythm
What are 5 main mechanisms that lead to dysrhythmia?
- Ectopic pacemakers- heart develops extra pacemakers
- Delayed after depolarization
- Re-entry circuits- damage causes AP to travel in circles
- Congenital abnormalities- additional conducting pathways between atria and ventricles
- Heart block- damage to conducting pathway, disrupts A to V signalling, leads to bradycardia
Where do re-entry dysrhuthmias arise?
At rings of cardiac tissue. Normally the wave branches around non-conducting region and mutual annihalation occurs where they meet. If there’s damage on one side, signal spreads back up th side.
What is Wollf Parkinson White syndrome?
An inherited abnormality wher there are additional conducting pathways between the atria and the ventricles known as Kent bundles.
What 2 problems does WPW syndrome cause?
- The signal from the atria to ventricles go via Kent bundles too. Kent bundles can’t limit rate (like AVN) so causes atrial flutter and tachycardia
- Can set up a giant re-entry circuit between atria and ventricles.
Why are dysrhythmias often experienced by people who already have CVS problems?
Reduced O2 to cardiac muscle will depolarize cells slightly, making them more likely to fir innapropraite APs. Can also be due to damage and scarring to heart.
How can drugs cause dysrhythmias?
Drugs to change the heart alter cardiac rhythm. If you give some to a healthy person, or too much drug is prescribed, can alter th heart rate too much.
What effect would an ectopic pacemaker have?
If its rate exceeds that of the SAN then heart rate will increase. The P wave will have an odd shape too.
How will the ECG change for someone with heart block?
As the ventricles can’t keep us with the atria, the P wave is probably normal. But the ventricles ar not depolarized and can’t contract so there’s no QRS complex. omg
What is treated with shock paddles?
Ventricular fibrillation. (which is true arrhythmia- no real pattern in ECG)
What does the Vaughan-Williams classificastion system do?
Divides anti dysrhythmia drugs into their mechanism, which channel they work at. 4 classes with class 1 subdivided into a, b and c
What does each class target in the VW classification system?
1 = sodium channels
2 = Beta adrenoceptors
3 = potassium channels
4 = calcium channels
Name one drug for each 4 classes of VW?
- Lidocaine
- Atenolol
- Amiodarone
- Verapamil
In the cardiac AP what happens step by step?
Sodium channels cause depolarisation
Membrane brought to threshold
More sodium rushes in. Sodium closes
Calcium causes plateau phase
Calcium channels inactivated
Potassium channels open
Repolarization
Which class is Amiodarone?
It’s formally class 3 blocks K channels.
However also blocks Na and Ca channels.
By blocking K channels, it prolongs the refractory period so slows down HR.
WHat;’s a problem with Amiodarone?
It’s very lipophilic so gets into fats easily, forms microcrystals which can cause problems.
Takes a long time to get to steady plasma levels.
Then lasts a long time in the body.
How is Amiodarone administered and what is its advantage?
Orally or by IV injection.
Although it slows the heart, does not alter the force of contraction.
What does AMioderone do to the skin?
Builds up in skin and eyes and is photoreactive. Causes grey skin discolouration.
What does sotalol do?
Blocks K channels. L isomers also work as class 2 (beta adrenoceptors). Prolongs AP.
If you block K then you prevent repolarization.
What does adenosine do?
It activates K channels and slows pacemaker potential, slowing heart rate. Not in the VW class system.
What does digoxin do? Which class?
Digoxin is unclassified in VW.
It can slow AV node conduction and improve ventricular filling during atrial fibrillation.
Has a very narrow therapeutic window.
When is adenosine used for?
Suppressing tachycardias.
PSVT (paroxysmal supraventricular tachycardia) occure in attacks. General anaesthetics can provoke dysrhythmias in surgery, adenosine can treat this is emergencies.
Why can adenosine only be used in emergencies?
Has a half life of 10 seconds. Given in a big dose by injection. Effects only last 20-30 seconds.
suppresses tachycardias
What are the side effects of adenosine?
Dramatic slowing of heart can cause problems if patient has heart block.
Can cause bronchospasm in patients with asthma
WHen should you not use adenosine?
asthma or heart block patients
