Thrombosis, embolism, ischaemia & infarction

Question 1

What are 3 things which predispose to thrombosis? Virchow’s Triad

Answer 1

1. Change in vessel wall (trauma, hypertension, invasive procedures eg. cannulation)
2. Change in blood flow (immobility, AF, varicose veins, venous obstruction eg. pregnancy, ventricular insufficiency)
3. Change in blood constituents (sepsis, smoking, coagulation disorders, malignancy)

Question 2

What are the causes & consequences of arterial thromboembolism?

Answer 2

Usually occurs due to erosion or rupture of an atherosclerotic plaque. Platelet mediated thrombi can cause ischaemic injuries (particularly in tissues with end vascular bed)

Increased risk of artherosclerosis:

• getting older
• smoking
• unhealthy diet
• lack of exercise
• being overweight or obese
• excessive alcohol drinking regularly
• HTN, cholesterol, DM
• AF or anti-phospholipid syndrome
• Family hx of artherosclerosis

Complications:

• Myocardial infarction ** (not caused by VTE)
• Stroke ** (not caused by VTE)
• TIA
• Critical limb ischaemia (complication of PVD when blood supple to the limb is blocked causing it to become painful, discoloured and cold)

Question 3

What are the 2 main types of VTE?

What are the risk factors, signs/symptoms, complications, prevention and treatment of DVT?

Answer 3

VTE is the most common vascular disease after acute MI and stroke, pathology not well known.

1. Pulmonary embolism
2. Deep vein thrombosis

Risk factors:

• Age
• Pregnancy
• Increased oestrogen (HTR, COC)
• Trauma
• Surgery
• Past DVT
• Cancer
• Obesity
• Immobility
• Thrombophilia

Signs:

• calf warmth
• tenderness
• swelling
• erythema
• mild fever
• pitting oedema

Complications:

• Most serious is PE
• If small clot people can recover from PE, if large it is fatal
• 1/3 of people will have long term problems from DVT clot = post thrombotic syndrome (PTS)
• PTS causes swelling, pain, discolouration and sometimes scaling and ulcers in the affected part of the body
• 30% are at risk of having another DVT or PE

Prevention of DVT:

• Stop OCP 4 weeks pre op
• Mobilise early
• LMWH (enoxaparin) for high risk patients
• Graduated compression stockings and intermittent pneumatic compression devices
• Fondaparinux (a factor Xa inhibitor) in major orthopaedic surgery

Treatment:

• LMWH (enoxaparin) or fondaparinux
• Cancer patients receive LMWH for 6 months and review
• In other patients, start warfarin simultaneously with LMWH. Stop heparin when INR 2-3.
• Treat for 3 months in most (longer if patients are high risk)
• Direct oral anticoagulants are licensed for use in DVT with less monitoring required, less risk of bleeding and simpler dosing (Dabigatan, apixaban, rivaroxaban).

Question 4

What scoring system do we use for DVT? What do results mean?

Answer 4

Wells score

• *0 score = DVT unlikely with prevalence of 5% DVT**
• positive D-dimer should warrant USS investigation.
• USS positive = strong recommendation for anticoagulation
• *1-2 = moderate risk (pretest probability 17%)**
• perform high sensitivity D-dimer and if neg = DVT unlikely.
• If D-dimer positive, proceed to USS.
• If USS negative = exclude DVT.
• If USS positive = concerning for DVT, strongly recommend anticoagulation
• *>3 = DVT likely (pretest probability 17-53%)**
• Perform d-dimer and ultrasound scan.
• Negative USS + negative d dimer = exclude DVT
• Positive USS + negative d dimer = concerning for DVT, anticoagulate.
• Positive D dimer + positive USS = treat as DVT & anticoagulate
• Positive D dimer and negative USS = repeat USS in 1 week.

Question 5

What is an embolus?

Answer 5

Mass of material in vascular system that lodges in a system and blocks it
Doesn’t need to be blood clot, can be air bubble, foreign material (IV drug users for eg.)

Question 6

Name some drugs which affect blood coagulation

antiplatelet drugs, oral anticoagulants, fibrinolytic drugs

Answer 6

Antiplatelet drugs:

• Low dose aspirin
• Clopidogrel
• Tirofiban
• Eptifibatide

Oral anticoagulants:

• Warfarin - vit K antagonist
• Dabigatrin - thrombin inhibitor
• Rivaroxaban, apixaban, edoxaban - Factor Xa inhibitors
• LMWH, Fondaparinux, Unfractionated heparin (parenteral anticoagulants)

Fibrinolytic drugs:

• Streptokinase
• Altepase
• Reteplase

Question 7

What is ischaemia?

Answer 7

Reduction in blood flow

Question 8

What is a pulmonary embolism?

What is the most common cause/risk factors, symptoms, tests used to investigate, treatment & prevention for PE?

Answer 8

Blocked blood vessel in the lungs
Most common cause is underlying DVT in the legs or pelvis.

Risk factors: same as DVT

Signs and symptoms:

• You can have a small PE without any symptoms of a DVT.
• Pleuritic chest pain
• Coughing up blood (haemoptysis)
• Dizziness & syncope
• Acute breathlessness
• Tachycardia
• Hypotension
• Pyrexia
• Cyanosis
• Raised JVP
• Pleural rub
• Pleural effusion

Tests for PE:

• FBC, U&E, baseline clotting, D-Dimers
• ABG may show reduced PaO2 and reduced PaCO2
• CXR may be normal or show oligaemia (hypovolaemia), dilated pulmonary artery, small pleural effusion
• ECG may be normal or show tachycardia, RBBB, right ventricular strain (inverted T wave in V1-V4)

Treatment:

1. Immediate medical attention is necessary to treat PE - if happy with diagnosis, start treatment before official diagnosis as most deaths occur within 1 hr of PE.
   
   • Commence LMWH or fondaparinux
   • Oxygen therapy may be required in early stages to help with breathlessness
2. Consider thombolysis if haemodynamic instability (alteplase 10mg IV over 1 min then 90mg IVI over 2 hr)
3. Long term anticoagulants may be prescribed to prevent more clots from forming (either DOAC or warfarin)
   
   • Aim for INR of 2-3 or 3.5 if recurrent PE or DVT while anticoagulated.
4. Prevention = heparin to all immobile patients, stop HRT and combined pill pre-op if reliable with another form of contraception.