| 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) |
| second degree A-V block | See: atrioventricular block. (05 Mar 2000) |
| pupillary block glaucoma | Glaucoma secondary to failure of the aqueous humor to pass through the pupil to the anterior chamber. (05 Mar 2000) |
| sinoatrial block | <cardiology, physiology> Disturbance of heart conduction in which the atrial response is delayed or omitted because of partial or complete interference with the propagation of impulses from the sinoatrial node to the atria. (12 Dec 1998) |
| sinoauricular block | <cardiology, physiology> Disturbance of heart conduction in which the atrial response is delayed or omitted because of partial or complete interference with the propagation of impulses from the sinoatrial node to the atria. (12 Dec 1998) |
| spinal block | An obstruction to the flow of cerebrospinal fluid in the spinal subarachnoid space; used inaccurately to refer to spinal anaesthesia. (05 Mar 2000) |
| stellate block | Injection of local anaesthetic solution in the vicinity of the stellate ganglion. (05 Mar 2000) |
| neurolytic block | <procedure> The injection of a chemical agent to cause destruction and consequent prolonged interruption of peripheral somatic or sympathetic nerves or in some cases, the neuraxis. (16 Dec 1997) |
| nondepolarising block | Skeletal mucle paralysis unaccompanied by changes in polarity of the motor endplate, as occurs following administration of tubocurarine. (05 Mar 2000) |
| suprahisian block | Atrioventricular conduction delay occurring above, or cephalad to, the bundle of His. (05 Mar 2000) |
| depolarising block | <physiology> Skeletal muscle paralysis associated with loss of polarity of the motor endplate, as occurs following administration of succinylcholine. (05 Mar 2000) |
| double thymidine block | <cell culture, procedure> A lab technique used to synchronise the cell cycles of all the cells in a culture. This is done by adding excessive amounts of thymidine (a deoxynucleoside) to the culture so that DNA replication is blocked. Eventually, all of the cells will reach the same point in the cell cycle and stop. (09 Oct 1997) |
| incomplete atrioventricular block | Impulses penetrate the atrioventricular junction in some relation to the ventricular rate. Synonym: incomplete atrioventricular block. (05 Mar 2000) |
| intra-atrial block | Impaired conduction through the atria, manifested by widened and often notched P waves in the electrocardiogram. (05 Mar 2000) |