PubMed · 11132431
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M Nürnberg. 2000. [Pacemaker therapy].. https://pubmed.ncbi.nlm.nih.gov/11132431/
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Using an apexcardiogram, Galabin was the first person to document atrioventricular (AV) block in humans. He performed his studies while working as a house officer at Guy's Hospital, London, United Kingdom. His patient was 34 years old, experienced attacks of near syncope, and had a pulse rate that varied between 25 and 30 beats/min. A laddergram of the patient's apexcardiogram suggests advanced AV block with 3 to 1 and 2 to 1 AV conduction with Wenckebach periodicity. We review the history of AV block beginning with the introduction of graphic recordings in 1847 by Ludwig, and include the contributions of Stannius, Luciani, Gaskell, Wenckebach, Hay, and Mobitz. Although he is little known today among cardiovascular physicians, we recognize Galabin as the first person to demonstrate AV block in humans.
Defects of the SCN5A gene encoding the cardiac sodium channel alpha-subunit are associated with both the long QT-3 (LQT-3) subtype of long-QT syndrome and Brugada syndrome (BrS). One previously described SCN5A mutation (1795insD) in the C terminus results in a clinical phenotype combining QT prolongation and ST segment elevation, indicating a close interrelationship between the two disorders. Here we provide additional evidence that these two disorders are closely related. We report the analysis of two novel mutations on the same codon, Y1795C (LQT-3) and Y1795H (BrS), expressed in HEK 293 cells and characterized using whole-cell patch clamp procedures. We find marked and opposing effects on channel gating consistent with activity associated with the cellular basis of each clinical disorder. Y1795H speeds and Y1795C slows the onset of inactivation. The Y1795H, but not the Y1795C, mutation causes a marked negative shift in the voltage dependence of inactivation, and neither mutation affects the kinetics of the recovery from inactivation. Interestingly, both mutations increase the expression of sustained Na+ channel activity compared with wild type (WT) channels, although this effect is most pronounced for the Y1795C mutation, and both mutations promote entrance into an intermediate or a slowly developing inactivated state. These data confirm the key role of the C-terminal tail of the cardiac Na+ channel in the control of channel gating, illustrate how subtle changes in channel biophysics can have significant and distinct effects in human disease, and, additionally, provide further evidence of the close interrelationship between BrS and LQT-3 at the molecular level.
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