ECGs/arrithmiyas

Question 1

Explain the mechanism of the direct Xa inhibitors

Answer 1

commonly used - rivaroxaban and apixiban
of note only ONE enzyme is blocked

Question 2

Explain the mechanism of dabigitran

Answer 2

oral direct thrombin inhibitor
of note only ONE enzyme is blocked

Question 3

When might a measured creatinine clearance become relevant?

Answer 3

patients with extremes of body size or composition. In these settings, a Cockcroft-Gault formula can also be used

Question 4

What is the creatinine clearance a marker of ?

Answer 4

reduced eGFR as it is hard to meausure eGFR directly

Question 5

Explain the approach to enoxaparin dosing in relation to the creatinine clearance

Answer 5

• CrCL >30 = enoxaparin 40mg SC
• CrCL <30 = enoxaparin 20mg SC

Question 6

If a patient has a CrCl <30 and requires long-term anticoagulation, what is the preferred medication?

Answer 6

warfarin

Question 7

Provide 2 clinical scenarios where warfarin would be the preferred option over a DOAC

Answer 7

• pregnancy (limited evidence)
• mechanical heart valve (DOACs have a higher risk of valve thrombosis)

Question 8

A patient with AF has impaired kidney function, but a CrCL>30. Which would be the best DOAC to prescribe and why?

Answer 8

The approximate degrees of excretion by the kidney are as follows:
- Dabigatran – 80 to 85 percent
- Rivaroxaban – 35 percent
- Apixaban – 25 percent

Therefore apixiban, as it is least dependent on the kidney for excretion

Question 9

As per the AMH guidelines, what are the contraindications for DOACs in the setting of kidney disease?

Answer 9

• if CrCl<30
• reduced dose for CrCl between 30-50

Question 10

A 90 year old man, weighing 55kg has AF and his GP would like to commence apixiban. What is the appropriate dose

Answer 10

3 criteria. If 2 or more are met, a lower dose of apixiban should be prescribed (i.e. 2.5mg BD)
- age >80
- body weight <60
- serum Creat >1.5 (133)

Question 11

In a patient with a normal weight, what would be the rough CrCl if Creat was 100 or 200

Answer 11

100 - CrCL 20
200 - CrCL - 10

Question 12

A 80y male with a CrCl of 20 would like to have dabigitran. It should be prescribed. True or False?

Answer 12

False
> for patients with CrCl >30 - give
> CrCl 15-30 usually avoided

Question 13

List 3 relative contraindications to anticoagulation*

Answer 13

• cancer- these patients have a higher risk of anticoagulation related bleeding
• poorly controlled or untreated hypertension
• Previous history of intracranial hemorrhage
• Recent history of a major extracranial bleed without known cause
• History of peptic ulceration within the past three months.
• Recent history of repeated falling episodes with a patient at a higher risk for bleeds > ikelihood of poor patient compliance due to dementia or cognitive impairment, particularly in cases when there is no available caretaker.
• Alcoholism, especially binge drinking
  Poorly controlled or untreated hypertension

Question 14

Describe a scenario where the serum creatinine could be underestimated?

Answer 14

• possible in children, women, elderly and malnourished
• this is because creatinine generation from the muscles is proportional to the total muscle mass and catbolism

For example, the GFR may be reduced as low as 20-30 mL/min in a small elderly woman, while her serum creatinine remains in the upper range of normal.

Question 15

Describe three examples that would cause the creatinine to be overstimated

Answer 15

• eating cooked meat
• ketosis
• hyperbilirubinaemia
• cephlasporins
• trimethoprim
• body building
• renal disease

Question 16

what is the calculated creatinine clearance and why is it useful?

Answer 16

• serum creatinine is so highly dependent on age, sex and body size, a number of corrections and formulae have been developed to estimate the muscle mass and assumed creatinine production The most well-known formula is the Cockcroft-Gault formula
  > good estimate of GFR
  > inaccurate if larger body mass OR renal function is very impaired (i.e. GFR <20 mL/min). In these circumstances an isotopic method can be used if the GFR needs to be accurately measured.

Question 17

what is the method used if an extremely accurate eGFR is required?

Answer 17

Isotopic methods can be used if a very accurate measurement of the GFR is required.