Atrial Fibrillation Flashcards
1
Q
Heparins and fondaparinux
MOA (NOT used in AF)
A
- Thrombin and factor Xa are key components of the final coagulation pathway that leads to the formation of fibrin clots
- By inhibiting these factors, prevents coagulation and propagation of blood clots
- Unfractionated heparin (UFH) activates antithrombin that in tern inactivates clotting factor Xa and thrombin
- LMWH (enoxaparin) only inhibit Xa
- Fandaparinux is a synthetic compound that is similar to heparin
- It inhibits factor Xa
2
Q
Warfarin- MOA
A
- Warfarin inhibits hepatic production of vitamin K-dependent coagulation factors and co-factors
- Vitamin K must be in its reduced form for the synthesis of coagulation factors
- It is then oxidised during the synthetic process
- An enzyme called Vit K epoxide reductase reactivates oxidised Vit K
- Warfarin inhibits Vit K epoxide reductase, preventing reactivation of vit K and coagulation factor synthesis
3
Q
Warfarin
Adverse effects
A
-
Bleeding
- A slight excess of warfarin increases the risk of bleeding from existing abnormalities such as peptic ulcers or minor trauma
- A large excess of warfarin can trigger spontaneous haemorrhage such epistaxis (nose bleed) or retroperitoneal haemorrhage
4
Q
Warfarin
warnings
A
- Immediate risk of haemorrhage- trauma, requires surgery
- Liver disease- who are less able to metabolise the drug are at risk of over-anticoagulation/bleeding
- Pregnancy- warfarin should not be used in the first trimester as it causes fetal malformations including cardiac and cranial abnormalities
5
Q
Warfarin
Important interactions
A
- Low therapeutic index
- Cytochrome P450 metabolites- e.g. fluconazole, macrolides, decrease warfarin metabolism and increase bleeding risk
- Inducers- e.g. phenytoin, carbamazepine, rifampicin) increase warfarin metabolism and risk of clots.
- Many antibiotics can increase anticoagulation in patients on warfarin by killing gut flora which synthesise vit k
6
Q
Warfarin
Administration + Communication
A
- Traditionally, warfarin is taken each day at around 6 for consistent effects on the INR taken the following morning. This may also help patients remember when to take it
- Advise patients that warfarin treatment is a balance between benefits and risks
- It is important for patients to understand how food, alcohol and other drugs can affect warfarin treatment
- `Patient receives an anticoagulation book which acts as an alert to their warfarin therapy and is used to record doses, blood tests, indication and duration
7
Q
Warfarin
Monitoring
A
- The INR is the prothrombin time of a person on warfarin divided by that of a non-warfarin control. INR target values vary by indication for warfarin
- In atrial fibrillation the target range is 2-3, INR is measure daily in hospital inpatients and every few days in outpatients commencing warfarin
- Once a stable dose of warfarin has been established, INR becomes less frequent
8
Q
dabigatran
Dose
A
- 150mg BD
9
Q
BB- MOA
Atenolol
A
- Beta1-adrenoreceptors are located mainly in the heart, whereas B2-adrenoreceptors are found mostly in the smooth muscle of blood vessels and the airways
- Via B1-receptors, BB reduces the force of contraction and speed of conduction in the heart
- This relieves myocardial ischaemia by reducing cardiac work and oxygen demand, and increasing myocardial perfusion
- Improves prognosis in HF by protecting the heart from teffects of chronic sympathetic stimulation
- They slow the ventricular rate in AF mainly by prolonging the refractory period of the AV node
- Reduce renin secretion (B1 mediated) which lowers BP
10
Q
BB
Important adverse effects
A
- Fatigue
- Cold extremities
- Headache
- GI disturbance
- Sleep disturbance and nightmares
- Impotence in men
11
Q
BB warnings
A
- Asthma- cause life-threatening bronchospasm and should be avoided
- This effect is mediated by blockade of B2-adrenoreceptors in the airways
- BB is usually safe in COPD (best to use B1 selective (atenolol)) rather than non-selective
- HF- BB should be started at a low dose and increased slowly, as they may initially impair cardiac function
- They should be avoided in haemodynamic instability
- Contraindicated in heart block
- significant hepatic failure
12
Q
BB
Interactions
A
- BB must not be used with Non-dihydropyridine CCB (E.g. Verapamil, Diltiazem), this combination can cause HF, bradycardia and asystole
13
Q
BB
Monitoring
A
- The best guide to dosage adjustment is the patient’s symptoms (e.g. chest pain) and heart rate (in ischaemic heart disease)
- Aim for Resting heart rate of 55-60 BPM
14
Q
CCB
A
- We can use verapamil instead of BB- look at HTN (amlodipine) for info
15
Q
Amiodarone
Common indications
A
- Wide range of tachyarrhythmias
- AF
- Atrial flutter
- SVT
- VT
- VF
