Heart Block

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heart block

[′härt ‚bläk]
(medicine)
The cardiac condition resulting from defective transmission of impulses from atrium to ventricle.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Heart Block

 

disruption of the conductivity of the nerve impulse along the conductive system of the heart. Types of heart blocks—intra-auricular (sinoauricular) blocks, au-riculoventricular (atrioventricular) blocks, and blocks of the peduncles of the bundle of His and of the terminal branches—are distinguished depending on the site of the disruption. Heart block may be caused by organic diseases of the myocardium (rheumocarditis, coronary cardiosclerosis), more rarely by intoxications, and also by functional disturbances of the nervous system (neuroses). It may be temporary or permanent, complete or partial. Bradycardia (slowing of the pulse to 18–10 beats per minute) is noted in cases of complete heart block; this leads to severe anemia of the brain accompanied by dizziness, loss of consciousness, and sometimes convulsions. Treatment is directed at eliminating the causes of the heart block.

O. F. BORDIUG

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Conduction block that recovers without development of increased temporal dispersion or other demyelinating features.
When [Iso] is over 10-1 [micro]M/L, the SAN could drive the atrium continually (Figure 5(a), open circles, dashed line); however, conduction block in the atrial septum could not be avoided.
(161 These results together with the findings from the AMAN rabbits experiments (96) suggested that IgM-induced, complement-mediated injury occurs at the nodes of Ranvier in peripheral motor nerves, and generates conduction block and muscle weakness.
Also typical of GBS are normal CSF counts, increased CSF proteins, and electromyography data (peripheral neuropathy, conduction block).
"Creating multiple conduction blocks represents a return to the classic procedure that was developed approximately two decades ago, and it is the standard for AFib surgery at Cleveland Clinic," says Dr.
We also demonstrated that unidirectional (activation conduction sequence was from LA to PV-LAJ, and finally to LSPV by pacing at LA, from LSPV to PV-LAJ, and to LA by pacing at LSPVd) and bi-directional conduction (activation conduction sequence was from LSPVm to both PV-LAJ and LA as well as to LSPVd simultaneously by pacing at LSPVm), bi-directional decremented conduction as well as slowed retrograde conduction (from LSPV to LA) within LSPV and delayed conduction or conduction block from stimulation signal to local tissue potential before AF.
(5-10,16,40,41) Observations have also been made of prolonged wave I latencies of auditory brainstem responses attributable to nerve conduction block that occurred as a result of demyelination in patients with Guillain-Barre syndrome.
The loss of myelin results in a conduction block at the site of a lesion, slower conduction time along an affected nerve and increased fatigue due to compensation for neurologic deficits.[2]
It's common in MMD, especially after many years, to develop a conduction block, a block in the electricity-like signal that keeps the heart beating at a safe rate.
There are some nondemyelinating elements that contribute to the pathophysiological basis of MS, including edema, inflammation, gliosis, and axonal loss.[28] However, loss of myelin is the cardinal histopathological feature of MS.[11] Demyelinated fibers do not conduct rapid trains of stimuli as well as myelinated fibers and go into conduction block after repeated use.[28] In MS, this factor may be responsible for a "myasthenic phenomenon," which causes weakness and muscle fatigue in distal muscles after repeated contractions.
Other clinical differential diagnoses include the distal form of spinal muscular atrophy, post-polio syndrome, multifocal motor neuropathy with conduction block, toxic neuropathy, and structural lesions of the cervical cord (like syringomyelia or tumors).
If the nerve fibre is hyperpolarized, it is more difficult to achieve the threshold level, and it results in the nerve conduction block. Another possible mechanism for the analgesic action of magnesium is the voltage-dependent antagonism of NMDA receptors, leading to the prevention of central sensitization from the peripheral nociceptive stimulation and a decrease in the acute pain after tissue injury.