| genetic block | <biochemistry, molecular biology> An obstruction in a biochemical pathway caused by a mutation that has crippled production of an enzyme critical to the pathway. (07 May 1998) |
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| partial heart block | Impulses penetrate the atrioventricular junction in some relation to the ventricular rate. Synonym: incomplete atrioventricular block. (05 Mar 2000) |
| retrograde block | Impaired conduction backward from the ventricles or A-V node into the atria. (05 Mar 2000) |
| peri-infarction block | An electrocardiographic abnormality associated with an old myocardial infarct and caused by delayed activation of the myocardium in the region of the infarct; characterised by an initial vector directed away from the infarcted region with the terminal vector directed toward it. (05 Mar 2000) |
| phase I block | Inhibition of nerve impulse transmission across the myoneural junction associated with depolarisation of the motor endplate, as in the muscle paralysis produced by succinylcholine. (05 Mar 2000) |
| phase II block | Inhibition of nerve impulse transmission across the myoneural junction unaccompanied by depolarisation of the motor endplate, as in the muscle paralysis produced by tubocurarine. (05 Mar 2000) |
| Mobitz block | Second degree atrioventricular block in which there is a ratio of two or more atrial deflections (P waves) to ventricular responses. Mobitz types of atrioventricular block, type I, the dropped beat of the Wenckebach phenomenon; type II, a dropped cardiac cycle that occurs without alteration in the conduction of the preceding intervals. (05 Mar 2000) |
| Wenckebach block | A form of block in any cardiac tissue (most often the atrioventricular junction) in which there is progressive lengthening of conduction until the beat is dropped. (05 Mar 2000) |
| complete A-V block | complete atrioventricular dissociation, complete A-V dissociation |
| Wilson block | The commonest form of right bundle-branch block, characterised in lead I by a tall slender R wave followed by a wider S wave of lower voltage. (05 Mar 2000) |
| Wolff-Chaikoff block | Blocking of the organic binding of iodine and its incorporation into hormone caused by large doses of iodine; usually a transient effect, but in large doses in susceptible individuals it can be prolonged and cause iodine myxoedema. Synonym: Wolff-Chaikoff effect. (05 Mar 2000) |
| conduction block | Failure of impulse transmission at some point along a nerve, although conduction along the segments proximal and distal to it are unaffected. Clinically, most often caused by an area of focal demyelination; when caused by focal trauma, called neurapraxia. (05 Mar 2000) |
| congenital heart block | Atrioventricular block present in utero or at birth and usually of advanced or complete degree. (05 Mar 2000) |
| hanging-block culture | The propagation of microorganisms on a cube of solidified agar medium which is inoculated, attached to a cover glass, and inverted over a moist chamber or hollowed slide. (05 Mar 2000) |
| saddle block anaesthesia | A form of spinal anaesthesia limited in area to the buttocks, perineum, and inner surfaces of the thighs. Synonym: saddle anaesthesia. (05 Mar 2000) |