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Atopic prurigo
Atopic prurigo (ICD-11 EC91.1) is a clinical variant of atopic eczema with multiple discrete itchy, excoriated papules on the limbs, bridging atopic dermatitis and chronic prurigo; about half of prurigo patients are atopic, and systemic steroids are not recommended.
Atopy
Atopy: a genetic tendency to produce IgE antibodies against environmental allergens, causing allergic rhinitis, asthma, atopic dermatitis, and food allergy; term coined by Coca and Cooke in 1923.
Atorvastatin
Atorvastatin, sold originally as Lipitor, is a statin medicine that blocks cholesterol synthesis, lowering LDL cholesterol by up to about 50% and preventing heart attacks and strokes.
Atosiban
Atosiban (Tractocile) is a synthetic oxytocin receptor antagonist peptide used as a tocolytic to delay preterm birth at 24 to 33 weeks gestation; given by IV bolus plus 48-hour infusion, it matches beta-agonists and nifedipine in efficacy with fewer maternal side effects.
Atovaquone
Atovaquone (Mepron, 566C80) is a hydroxynaphthoquinone antiprotozoal drug inhibiting the mitochondrial cytochrome bc1 complex; used for Pneumocystis pneumonia and, with proguanil, malaria treatment and prophylaxis.
ATP study
ATP study (ATP Project, Asthma afTer Polypectomy), NCT02427503: a completed Spanish observational cohort study of 106 adults with persistent asthma and grade II-III nasal polyposis, measuring eosinophils, FEV1, FeNO, and asthma control for 12 months after endoscopic sinus surgery.
ATP6AP1-CDG
ATP6AP1-CDG (CDG-IIs, Immunodeficiency 47, OMIM 300972) is a rare X-linked recessive congenital disorder of glycosylation causing hepatopathy, immunodeficiency, cutis laxa, and type II transferrin glycosylation defects, first described in 2016.
Atrasentan
Atrasentan, sold as Vanrafia and formerly Xinlay, is an oral endothelin A receptor antagonist approved in 2025 to reduce proteinuria in adults with primary IgA nephropathy.
Atraumatic restorative treatment
Atraumatic restorative treatment (ART) is a minimally invasive dental procedure that removes decayed tissue with hand instruments only and fills the cavity with glass ionomer cement, usable outside dental clinics without electricity or anesthesia.
Atresia of urethra
Atresia of urethra (urethral atresia, ORPHA:105, ICD-10 Q64.3) is a rare fetal lower urinary tract obstruction from closure of the urethra, causing megacystis, oligohydramnios, Potter sequence, and high fetal mortality without shunting.
Atrial fibrillation
Atrial fibrillation (AF, AFib) is the most common treated heart arrhythmia, an irregular atrial rhythm raising stroke and heart failure risk; treated with anticoagulation, rate or rhythm control, and ablation.
Atrial flutter
Atrial flutter (AFL): rapid regular atrial rhythm at 250-350 bpm from a macroreentrant circuit dependent on the cavotricuspid isthmus; sawtooth ECG waves, curable by isthmus ablation, lower stroke risk than atrial fibrillation.
Atrial flutter ablation
Atrial flutter ablation is a catheter procedure that destroys a small strip of right atrial tissue to interrupt the electrical circuit driving atrial flutter, with about 91% acute success.
Atrial natriuretic peptide
Atrial natriuretic peptide (ANP, atrial natriuretic factor), a 28-amino-acid cardiac hormone discovered by de Bold in 1981, released on atrial stretch, acting via NPR-A and cGMP to drive natriuresis, vasodilation, and RAAS inhibition.
Atrial septal aneurysm
Atrial septal aneurysm (interatrial septal aneurysm): congenital bulging of the heart's atrial septum over 10 mm into an atrium. Found in about 2.4% of adults by echocardiography; with patent foramen ovale it raises cryptogenic stroke and recurrence risk.
Atrial septal defect
An atrial septal defect (ASD) is a hole in the wall between the heart's two upper chambers, present at birth, allowing oxygen-rich blood to shunt into the right atrium.
Atrial septostomy
Atrial septostomy (Rashkind septostomy, balloon atrial septostomy) is a catheter procedure creating an opening between the heart's atria, used to palliate neonatal transposition of the great arteries and to decompress the right ventricle in severe pulmonary hypertension as a bridge to lung transplantation.
Atrial tachycardia
Atrial tachycardia (AT) is a supraventricular arrhythmia with regular atrial rates above 100 bpm and P waves originating outside the sinus node, caused by automaticity, triggered activity, or microreentry; classified as focal or macroreentrant, treated with drugs and catheter ablation.
Atrichia with papular lesions
Atrichia with papular lesions (papular atrichia, OMIM 209500) is a rare autosomal recessive alopecia caused by hairless (HR) gene mutations on chromosome 8p, with irreversible hair loss soon after birth and keratin papules years later.
Atrioventricular block
Atrioventricular block (AV block, heart block) is partial or complete interruption of electrical impulse transmission from the atria to the ventricles, classified as first-, second- (Mobitz I/II), or third-degree; diagnosed by ECG and treated with pacemakers when needed.
Atrioventricular nodal reentrant tachycardia
Atrioventricular nodal reentrant tachycardia (AVNRT) is a rapid heart rhythm caused by an electrical impulse circling two pathways at the AV node, causing sudden palpitations.
Atrioventricular node
The atrioventricular node, or AV node, is a mass of cardiac muscle at the base of the atrial septum that conducts electrical impulses from the atria to the ventricles.
Atrioventricular node ablation
Atrioventricular node ablation is a catheter procedure that destroys the AV node to permanently control rapid ventricular rates in atrial fibrillation, requiring lifelong pacemaker dependence.
Atrioventricular reentrant tachycardia
Atrioventricular reentrant tachycardia (AVRT), the reentrant arrhythmia of Wolff-Parkinson-White syndrome, uses an accessory pathway plus the AV node as a macroreentrant circuit; orthodromic forms are narrow-complex, antidromic wide-complex, and radiofrequency ablation is curative.
Atrioventricular septal defect
Atrioventricular septal defect (AVSD), also called AV canal or endocardial cushion defect, is a congenital heart defect with holes between heart chambers and a common five-leaflet AV valve, common in Down syndrome, repaired surgically in infancy.
Atrioventricular septum
Atrioventricular septum: septal heart structure between right atrium and left ventricle at the crux, partly membranous and partly muscular. Defects (AVSD) cause 0.24–0.31/1000 live-birth congenital heart disease, strongly linked to Down syndrome; repair mortality about 3%.
Atrium (heart)
Atrium (heart): the two upper heart chambers (right and left atrium) that collect incoming blood. Distinct right pectinate muscles versus smooth left walls, three-phase reservoir-conduit-booster function, and the left atrial appendage as the main AF thrombus site.
Atrophia bulbi
Atrophia bulbi (eyeball atrophy, ICD-11 9C22.0) is atrophy of intraocular structures with low eye pressure from end-stage ocular disease; with shrinkage and disorganization it becomes phthisis bulbi (9C22.1).
Atrophic gastritis
Atrophic gastritis: chronic gastric inflammation causing thinning of the stomach lining; type A autoimmune (corpus, pernicious anemia) or type B H. pylori-associated; staged by OLGA/OLGIM, a gastric cancer risk factor.
Atrophic lichen planus
Atrophic lichen planus (atrophic LP, lichen planus atrophicans) is a rare variant of cutaneous lichen planus with pale, atrophic-centered papules or plaques on previously affected skin; prevalence and etiology unknown, ICD-10 L43.8.