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Aortic valve area calculation
Aortic valve area calculation estimates aortic valve opening (cm²) via the invasive Gorlin formula (1951), the Doppler continuity equation, or planimetry by TEE, CMR, or CT; AVA <1.0 cm² defines severe aortic stenosis.
Aortic valve repair
Aortic valve repair: surgical restoration or preservation of the native aortic valve without a prosthesis, using cusp repair, remodeling (Yacoub), or reimplantation (David); low early mortality, ~10% bicuspid reoperation risk.
Aortic valve replacement
Aortic valve replacement (AVR) replaces a diseased aortic valve, via open-heart SAVR or catheter-based TAVR/TAVI, using mechanical valves needing lifelong warfarin or tissue valves; ESC 2025 prefers SAVR under 70, TAVI at 70+.
Aortoenteric fistula
Aortoenteric fistula (AEF): abnormal communication between the aorta and GI tract, usually the duodenum; primary (aneurysm erosion) or secondary (graft erosion after aortic surgery). Causes massive GI bleeding or sepsis; treated by open or endovascular repair with high mortality.
Aortoiliac occlusive disease
Aortoiliac occlusive disease (AIOD, Leriche syndrome) is atherosclerotic narrowing or blockage of the distal aorta and iliac arteries, causing claudication, erectile dysfunction, and absent femoral pulses; treated endovascular-first with stenting or aortobifemoral bypass.
Aortopulmonary space
Aortopulmonary space (aortopulmonary window): a mediastinal compartment between aortic arch and left pulmonary artery, and a rare congenital hole between aorta and pulmonary artery requiring patch repair.
APACE study
APACE study (Advantageous Predictors of Acute Coronary Syndromes Evaluation, NCT00470587): prospective multicenter cohort by University Hospital Basel testing history, ECG, and biomarkers for rapid AMI diagnosis in chest pain.
Apadenoson
Apadenoson (BMS068645, ATL146e, Stedivaze) is a selective adenosine A2A receptor agonist developed as a pharmacologic stress agent for myocardial perfusion imaging; its Phase 3 program was terminated for business reasons and it was never approved.
Apex beat
Apex beat (apical impulse, point of maximal impulse): the palpable left ventricular impulse, normally in the fifth left intercostal space at the midclavicular line; palpable in about 50% of adults and used to assess cardiomegaly and ventricular character.
Aphakia
Aphakia is the absence of the crystalline lens in the eye. This condition severely blurs vision and loses accommodation, requiring correction with an IOL or spectacles.
Apocrine sweat gland
Apocrine sweat gland: large skin gland opening into hair follicles in the axilla, anogenital region, ear canal, and areola; inactive until puberty; its milky secretion is broken down by skin bacteria to produce body odor.
Appendicular skeleton
The appendicular skeleton is the portion of the human skeleton formed by the upper and lower limb bones and the girdles attaching them to the axial skeleton, totaling 126 bones.
Appendix (anatomy)
Vermiform appendix (appendix vermiformis): narrow blind-ended tube from the cecum, about 10 cm long, rich in lymphoid tissue, a reservoir for gut bacteria, and the site of appendicitis, the most common abdominal surgical emergency.
Apraclonidine
Apraclonidine (Iopidine) is a selective alpha-2 adrenergic agonist eye drop, a para-amino clonidine derivative approved in 1987 to prevent post-laser IOP spikes and in 1993 for short-term glaucoma therapy; tachyphylaxis limits chronic use.
Aqueous humour
Aqueous humour is the clear fluid filling the eye's anterior and posterior chambers, produced by ciliary processes at 2–3 µL/min, nourishing the avascular cornea and lens, and drained via trabecular and uveoscleral pathways to set intraocular pressure.
Aquiline nose
Aquiline nose (Roman nose): a human nose with a convex, eagle-beak-like curved profile, from Latin aquilinus. Literary term; anatomically a bony-cartilaginous dorsal hump; historically noble in Europe, criminalized in physiognomy.
Arachnoid cyst
An arachnoid cyst is a benign, fluid-filled sac within the arachnoid layer of the membranes around the brain and spinal cord, filled with cerebrospinal fluid and usually found by accident on imaging.
Arbutamine
Arbutamine is a synthetic catecholamine developed as a pharmacologic stress agent for diagnosing coronary artery disease in patients unable to exercise, approved by the FDA in 1997.
Arctic Sun medical device
Arctic Sun (Arctic Sun 5000, Medivance/Bard/BD) is a non-invasive temperature management system using circulating-water hydrogel pads for targeted temperature management after cardiac arrest, cooling at about 1.1°C/h.
Arcus senilis
Arcus senilis (corneal arcus, gerontoxon): gray-white lipid ring in the peripheral cornea, common after 50, harmless to vision; premature arcus (arcus juvenilis) flags dyslipidemia and cardiovascular risk.
Areola
Areola (areola mammae): circular pigmented breast skin surrounding the nipple, bearing Montgomery glands and areolar tubercles; 3-6 cm wide, darkens in pregnancy, site of duct convergence and NAC reconstruction.
Arm
Arm (brachium): the upper limb region between shoulder and elbow, built on the single humerus bone. Covers the glenohumeral and elbow joints, brachial artery and brachial plexus, carrying angle, and common fractures.
Arousal
Arousal: physiological and psychological responsiveness state spanning sleep to vigilance, driven by brainstem ascending systems (locus coeruleus, basal forebrain, orexin); distinct from attention and valence, and prerequisite for assessing consciousness.
Arrhythmogenic cardiomyopathy
Arrhythmogenic cardiomyopathy (ACM), formerly ARVC, is an inherited heart muscle disease with fibro-fatty myocardial replacement, ventricular arrhythmias, and sudden death risk; diagnosed by 1994/2010 Task Force and 2020 Padua criteria.
Arterial system
The arterial system is the branching network of arteries and arterioles that carries blood from the aorta to the capillaries, distributing flow and smoothing the heart's pulse.
Arteriole
An arteriole is a very small artery delivering blood into capillary beds, with 1 to 4 layers of smooth muscle and diameters of 7 to 100 μm.
Arteriosclerosis
Arteriosclerosis, or hardening of the arteries, is the thickening and stiffening of artery walls from several causes; atherosclerosis, plaque buildup, is its most common type, underlying coronary, cerebrovascular, and peripheral artery disease.
Arteriovenous fistula
An arteriovenous fistula, also known as an arteriovenous shunt or AV fistula, is an abnormal artery-vein connection; surgically created ones are the most common, mainly for hemodialysis access.
Arteriovenous oxygen difference
Arteriovenous oxygen difference (a-v O2 diff, C(a-v)O2): difference between arterial and venous blood oxygen content, about 5 mL/100 mL at rest and 15-20 during exercise; basis of the Fick cardiac output method.
Artificial cardiac pacemaker
Artificial cardiac pacemaker: implantable device delivering electrical impulses to correct slow or irregular heartbeats. Invented as an implant in 1958 (Elmqvist/Senning) and 1960 (Chardack/Greatbatch); now includes leadless catheter-delivered capsules like Medtronic Micra and Abbott Aveir.