Stroke and Atrial Fibrillation

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Stroke may be ischemic or haemorrhagic.

Stroke – classification
Type of stroke	Proportion of cases (%)
Ischemic	80 %
Haemorrhagic – intracranial	15 %
Haemorrhagic – subarachnoid	5 %

The overall prevalence of ischemic stroke is 2–3% (> 7% in the population > 65 years).

According to CT or MR imaging, ischemic stroke can be classified as:

• Lacunar
• Non-lacunar

Lacunar stroke

• Represents a “small cerebral infarction”.
• The Latin word “lacuna” means “small cavity” or “small lake”.
• In medicine, the term “lacuna” denotes a small round defect.
• Defined as a subcortical lesion < 15 mm (on CT) or < 20 mm (on MR).
• Results from disease of small intracerebral arterioles, mainly due to arterial hypertension and diabetes mellitus.

Non-lacunar stroke

• Represents a “large cerebral infarction”.
• Defined as a subcortical and cortical lesion > 15 mm (on CT) or > 20 mm (on MR).
• Caused by occlusion of large cerebral arteries supplying the cortex and subcortex:
• Basilar artery, vertebral artery.
• Middle, anterior, and posterior cerebral arteries.
• Internal carotid artery.
• Mainly results from embolization in atrial fibrillation (AF) and rupture of an atherosclerotic plaque.

Silent ischemic stroke

• Refers to small asymptomatic lacunar (30%) or non-lacunar (70%) infarctions
• Caused by arterial hypertension or diabetes mellitus.
• In AF, caused by embolization.
• Prevalence in the general population is 10–20%
• Prevalence in patients with AF is 15–50%
• Leads to cognitive dysfunction
• Is a risk factor for cardioembolic stroke in AF
• The effect of anticoagulation therapy is uncertain (insufficient data).

Histological examination can differentiate between cardioembolic and non-cardioembolic emboli.

• A cardioembolic embolus contains a higher proportion of fibrin.
• However, this is not a standard or recommended diagnostic method.

Atrial fibrillation (AF) may cause cardioembolic or cryptogenic ischemic stroke.

• Cardioembolic stroke in AF is diagnosed when a patient with previously diagnosed AF develops an ischemic stroke.
• Cryptogenic stroke in AF occurs when a patient has silent AF (asymptomatic and undiagnosed) and develops a stroke,
• if AF is later diagnosed by ECG monitoring (ECG Holter, implantable loop recorder),
• the stroke is reclassified from cryptogenic to cardioembolic.

In some cases, the cause of stroke cannot be clearly determined, e.g. if the patient has AF, significant carotid atherosclerosis, and a patent foramen ovale.

Atrial fibrillation (AF) causes cardioembolic ischemic stroke.

• In patients with diagnosed AF,
• the risk of ischemic stroke can be calculated using the CHA₂DS₂-VA score.

Cryptogenic ischemic stroke

• Accounts for 35% of all ischemic strokes
• Accounts for 40% of ischemic strokes in individuals < 55 years
• 30% of cryptogenic strokes are due to silent AF (undiagnosed, asymptomatic)
• Refers to any ischemic stroke without a known cause.
• Cryptogenic stroke means that standard imaging and laboratory investigations do not identify the cause or source of embolism:
• thrombus, embolus, > 50% atherosclerotic involvement of large arteries, small-vessel disease, other causes...
• May be lacunar or non-lacunar
• Cryptogenic stroke may result from:
• ESUS (Embolic Stroke of Undetermined Source) – accounts for 50% of all cryptogenic strokes
• Silent AF (asymptomatic, undiagnosed AF)
• Atrial cardiomyopathy
• Patent foramen ovale without documented thrombosis/embolus in the venous system or right heart

Cryptogenic stroke is a diagnosis per exclusionem, meaning that the cause of stroke is investigated step by step. Until the cause is clarified, the stroke remains classified as cryptogenic. If the cause of cryptogenic stroke is later diagnosed, e.g. silent AF, the cryptogenic stroke is reclassified as cardioembolic stroke in AF. In cryptogenic stroke, investigations are performed to diagnose:

• Atrial fibrillation
• Patent foramen ovale (PFO) and deep vein thrombosis
• Intracardiac thrombus
• Large-artery atherosclerosis (carotids, aorta)
• Hypercoagulable state
• Vasculitis

Patent foramen ovale (PFO)

• PFO is present in 25% of the population
• 37% of patients with cryptogenic stroke have PFO
• 9% of patients with cryptogenic stroke have an atrial septal defect
• If a patient has PFO (present in 25% of the population) and develops ischemic stroke, the most likely clinical scenarios are:
• if no thrombus/embolus is found in the venous system or heart, it is cryptogenic stroke associated with PFO,
• if a thrombus/embolus is found in the venous system or heart, it is paradoxical thromboembolism associated with PFO,
• however, a situation may also occur where the patient has PFO and left lower-leg thrombosis,
• and develops ischemic stroke due to silent atrial fibrillation.
• For example, a patient may develop paradoxical embolization during a long-haul flight.

Economy Class Syndrome

• Refers to deep vein thrombosis of the lower limbs occurring during an airplane flight.
• During prolonged sitting on a flight, a hypercoagulable state develops (even in healthy individuals):
• The patient moves minimally, the calves are inactive (do not function as a muscle pump), and knee flexion is present.

Economy Class Syndrome
Flight duration	Risk of venous thrombosis (lower limbs, pelvis)
< 4 hours	almost 0 %
4–8 hours	1 / 5 000
> 8 hours	1 / 1 500

Venous thrombosis does not embolize automatically; the risk of embolization depends on the location of the thrombus.

• The following table shows the risk of embolization in venous thrombosis according to localization.

Risk of embolization in venous thrombosis
Type of venous thrombosis (VT)	Risk of embolization
Proximal VT (femoral, iliac veins)	25–50 %
Distal VT (below the knee – v. tibialis, fibularis)	< 5 % (if it does not extend proximally)
Pelvic VT (v. iliaca interna/externa, v. cava inferior)	50–70 %

These guidelines are unofficial and do not represent formal guidelines issued by any professional cardiology society. They are intended for educational and informational purposes only.