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Definitions beginning with the letter A


Abnormal coagulation

Can lead to either excessive bleeding or excessive clotting, both of which can be dangerous, causing heart attack, stroke, and peripheral arterial disease (PAD) or pulmonary embolism (PE).

Activated clotting time (ACT)

A bedside clotting test used to monitor coagulation levels during heparin administration, especially used during interventional percutaneous coronary intervention (PCI).

Acute coronary syndromes (ACS)

An umbrella term used to describe a group of conditions caused by narrowing of the arteries to the heart (see coronary arteries). ACS also covers any group of clinical symptoms indicative of acute myocardial ischemia, which is caused by abruptly decreased blood flow to the heart as a result of coronary artery disease (CAD). During myocardial ischaemia, the blockage of coronary arteries (occlusion) causes a reduction in oxygen supply to the heart, which leads to varying degrees of chest pain (angina pectoris) that can occur at rest or with mild exertion. Heart attack (myocardial infarction [MI]) is the most severe form of ACS. Patients who are admitted to hospital with cardiac chest pain of recent origin are usually diagnosed with one of three distinct conditions within ACS:

  • Unstable angina (UA) (without heart muscle damage)
  • or two forms of myocardial infarction (with heart muscle damage) according to their signs on electrocardiogram (ECG/EKG):
    • ST-segment elevation myocardial infarction with (STEMI)
    • Non-ST-segment elevation myocardial infarction (NSTEMI)

All of these conditions are potentially life-threatening, so prompt diagnosis and treatment are essential. The reason for such urgent evaluation is to identify patients with heart attack for whom immediate treatment to restore blood flow to ischaemic tissue (reperfusion) is imperative.

Acute myocardial infarction (AMI)

Acute heart attack (see Myocardial infarction).

Acute myocardial ischemia

Abrupt insufficient blood supply to the heart as a result of coronary artery disease (CAD).


Stage of clot formation when platelets clump together.

Angina pectoris

Angina pectoris is chest pain or discomfort that occurs while the heart muscle is not receiving enough oxygen (cardiac ischemia). Angina pectoris is a symptom of coronary artery disease (CAD), the most common form of heart disease in the US and Europe.


Blood-thinning medications that inhibit some of the blood clotting factors, therefore increasing the time it takes for a blood clot to form, preventing the risk of venous thromboembolism (see VTE) or arterial thrombosis.

Antiplatelet agents

Drugs that decrease platelet aggregation, helping to block the clot formation (mainly used for prevention of arterial blood clots, e.g. aspirin, thienopyridines,, glycoprotein IIb/IIIa [GP IIb/IIIA]).

Antithrombin III

A plasma glycoprotein which is an important inhibitor of blood clot formation; also called ATIII.

Arterial embolism

Sudden blockage of an artery by an atherosclerotic plaque, a blood clot or an air bubble, which was carried in the blood from another location.

Arterial thrombosis

The formation of unwanted blood clot(s) in arteries, blocking an artery. Arterial thrombosis is a leading cause of myocardial infarction (also known as heart attack) when a blood clot occurs in the coronary artery (artery of the heart), a cerebro-vascular accident (also known as stroke) when a blood clot occurs in the brain arteries, or a peripheral arterial disease (PAD) when a blood clot develops in leg arteries. Arterial thrombosis usually affects individuals who already have atherosclerosis.


A primary cause of cardiovascular disease (CVD), atherosclerosis is a process of progressive thickening and hardening of medium-sized and large arteries walls as a result of fat deposits on their inner lining (progressive build-up of plaque under the arterial wall lining). It may chronically restrict blood flow and oxygenation to the target organ and be acutely complicated by a clot if the plaque disrupts (see thrombus, atherothrombosis).


Characterized by sudden, unpredictable, atherosclerotic plaque disruption, leading to an abrupt platelet activation and clot formation. It can partially or totally block arterial blood flow in the artery and cause an abrupt local decrease in oxygen supply to the target organ. Depending on the artery, atherothrombosis can result in serious damages to the organ involved, such as: heart muscle lesions (myocardial infarction), brain lesions (stroke), leg lesions (peripheral artery disease [PAD]).

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