Presentation
The symptoms of the congenital heart block can vary due to the underlying problems that associate / lead to the CHB, and the features of CHB reflects the other manifestations of these diseases.Bradycardia is usually the first symptom of CHB to be detected in utero. Due to the block in the atrioventricular node, less electric signals move from the sinoatrial node to the bundle of his and its right and left branches, leading to a lower heart rate. The atrioventricular block can be first degree or much more severe like a complete atrioventricular block (third degree). In addition, several changes in the ECG can be detected.Other manifestations of the congenital heart block can be related to the impact of the maternal autoantibodies in the autoimmune-mediated CHB. Fibrosis of the myocardium (Endocardial fibroelastosis) (EFE) is the obvious one and it occurs due to the damage caused by the maternal autoantibodies to the cardiac tissue of the fetus, and can lead to death in some cases. However, it is not a common feature of CHB.Another rare symptom that might accompany the autoimmune CHB is the disorder in the valvular function, and this happens due to the damage in the papillary muscles as a result of the maternal autoantibodies. Causes
In some cases the reason behind CHB remains unknown but in the great majority of affected kids, this disease is associated with the transference of autoantibodies from the mother during gestation or with major cardiac structural abnormalities that lead to a disturbance in the conducting signals in the atrioventricular node.
Physical therapy and other rehabilitative measures may also be used to help muscle function. Genetic counseling is available. Epidemiology
In northern Scandinavia, the prevalence of myotonia congenita has been estimated at 1:10,000.Myotonia congenita is estimated to affect 1 in 100,000 people worldwide. Research
The name Thomsen’s disease refers to the Danish physician Julius Thomsen (1815–1896) who described the condition in himself and his family.Myotonia can be achieved in preparations of intact isolated muscle by the administration of 9-Anthracenecarboxylic acid, a blocker of chloride channels. It is also possible to achieve myotonia in preparations of intact isolated muscle by greatly lowering or removing the extracellular content of chloride in the bathing medium.During the 1970s several murine models of myotonia appeared. One in particular has been used widely, the adr mouse or "arrested development of righting response". This model is often used in scientific work with muscular dystrophy, and displays myotonia due to lack of functional chloride channels. See also
Fainting goat
Tonic immobility
New Forest pony

References
External links
GeneReview/NCBI/NIH/UW entry on myotonia congenita
NINDS: Myotonia congenita
National Library of Medicine: Myotonia congenita