Stroke is a leading cause of death and disability in developed countries.
Worldwide,
brain infarction is the second most common cause of mortality and the third most common cause of disability.
While the overall rate of stroke-related mortality is decreasing,
the absolute number of people with stroke and the global burden of stroke-related disability is high and increasing.
Cardiogenic strokes account for approximately 25% of all ischemic strokes,
with an increasing risk in elderly population.
Overall,
it has a similar frequency throughout the world if adjusted for mean population age.
There are three main subtypes of brain ischemia:
- Intravascular thrombosis: refers to obstruction of an artery due to the formation of a thrombus generally after arterial wall disease,
such as arteriosclerosis,
dissection or fibromuscular dysplasia.
- Embolism: refers to occlusion of cerebral vessels with debris from extra-cerebral origin,
most commonly cardiac.
An embolus may consist of platelet aggregates,
thrombus,
platelet-thrombi,
cholesterol,
calcium,
bacteria,
etc.
Further events may occur if the embolic source is not identified.
- Systemic hypoperfusion: refers to a diminished vascular supply due to several causes,
most related to cardiac dysfunction (myocardial ischemia,
cardiac arrest,
arrhythmias).
It may affect the brain and also other organs.
Cardiogenic strokes are characterized by affecting proximal arteries with larger infarct areas,
greater recurrence chance and higher disability and mortality rates (Fig. 2).
Fig. 2: Cardioembolic stroke.
References: Department of Radiology, Hospital del Mar. Barcelona
The underlying mechanism of cardioembolic stroke is obstruction of cerebral vessels with embolic debris from a cardiac origin,
commonly from left chambers (Fig. 3).
Fig. 3: Mechanism of cardioembolic stroke.
References: Department of Radiology, Hospital del Mar. Barcelona
However,
abnormal intracardiac communication between the right and left circulation together with a pressure gradient that promotes a right-to-left shunt,
may lead to unnatural passage from the venous to the arterial circulation; what is known as a paradoxical embolism.
Emboli from the heart are distributed evenly throughout the body,
yet more than 80% of symptomatic emboli affect the brain.
The vascular territory affected is equivalent to the distribution of cerebral blood flow,
as much as 80% involve the anterior circulation (ie,
carotid artery region),
and approximately 20% have a vertebrobasilar distribution (Fig. 4).
Fig. 4: Clinical features of cardioembolic stroke.
References: Department of Radiology, Hospital del Mar. Barcelona
In brain CT an MRI studies embolic infarctions appear as extensive or multiple lesions,
simultaneously or sequentially affecting different arterial territories,
corresponding to different emboli.
Hemorrhagic transformation usually occurs in established ischemic lesions (Fig. 5).
Fig. 5: Imaging features of cardioembolic stroke.
References: Department of Radiology, Hospital del Mar. Barcelona
Cardioembolic stroke is largely preventable with an optimal primary prevention.
When this is not achieved and stroke occurs,
diagnosis of the potential cardiac source is fundamental to avoid further events.
Echocardiography is usually the initial cardiac imaging technique of choice,
since it has several advantages; it is easily accessible,
has a relatively low cost and does not imply radiation exposure.
Both transthoracic echocardiography (TTE) and transesophageal echocardiography (TEE) can be used.
Despite the indisputable advantages,
echocardiography has also some limitations: it is operator-dependent and some potential cardiac findings responsible for stroke,
may remain unnoticed.
In most patients with stroke of undetermined etiology or infarction with a suspected cardiac origin,
no further cardiac evaluation is performed.
Actually,
only few patients are assessed with CT or MR,
so subtle fundamental diagnostic findings may remain undetected.
However,
revision of both thoracic CT and cardiac MRI studies (whether prior or coincident with the ischemic episode) can provide much information regarding a cardiac or large artery origin of stroke (Fig. 6).
In recent years,
cardiac CT is increasingly being used as a complementary imaging technique for cardiac assessment after echocardiography.
Fig. 6: Patient with chronic heart failure and atrial fibrillation with symptoms suggesting stroke in the right middle cerebral artery (MCA). Brain CT (A) and CT angiography (B) confirm occlusion of right MCA (arrow) and absence of distal collateral circulation. The patient is an adequate candidate for thrombectomy. 2 hours later presents a new stroke episode. A new brain CT and CT angiography (C,D) is performed, confirming left MCA occlusion (arrow) with poor distal collateral circulation (circle) and reperfusion of previously occluded vessel. Thoracic CT (E) shows an hypodense lesion in the left ventricle suggestive of ventricular thrombus (arrow) probably responsible of a cardiac origin of stroke.
References: Department of Radiology, Hospital del Mar. Barcelona
Some authors,
even recommend early cardiac and extracranial vascular CT angiography (CTA) additional to brain CT angiography during the evaluation of patients with acute ischemic stroke.
They advocate that an earlier risk factor management may potentially reduce recurrence and improve the outcome,
while adding only few minutes to the protocol and making radiation dose increase feasible with adjusted protocols.