| retrograde block | Impaired conduction backward from the ventricles or A-V node into the atria. (05 Mar 2000) |
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| 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) |
| heart block | <cardiology, physiology> A conduction disturbance that results in the inappropriate delay (or complete inability) of a electrical impulse, generated in the atria, to reach the ventricles (via the atrioventricular node). Clinical types are divided into first (nonserious), second and third degree (most serious) AV blocks. Some drugs may precipitate an AV block (for example clonidine, methyldopa, verapamil). A permanent pacemaker may be required for a third degree (complete) heart block. (07 Apr 1998) |
| protective block | An incompletely understood mechanism whereby a pacemaker is protected from being discharged by the impulse from another centre; the mechanism, usually conceived as an encircling zone of unidirectionally refractory tissue permitting egress of impulses from the centre but preventing access to the centre, is seen in operation in ventricular parasystole where the parasystolic centre is protected from discharge by the sinus pacemaker and so is able to maintain its intrinsic rhythm undisturbed. Synonym: entrance block, protection. (05 Mar 2000) |