title: A cellular basis for the primary long Q-T syndromes.
abstract: In several syndromes sudden death is associated with a long Q-T interval on the electrocardiogram. Current treatment is aimed at correcting a notional imbalance of cardiac sympathetic drive. Although this approach can be effective, the primary disorder may be a defect in the cellular mechanism that alters the length of the ventricular action potential, and hence the Q-T interval, in response to a change of heart rate. Such defects may be underdiagnosed because the long Q-T syndromes are defined simply in terms of a prolonged Q-T interval, without consideration of the fact that susceptibility to arrhythmias is likely to be due, not to a lengthened Q-T per se, but to an absence or alteration of the normal Q-T shortening in response to an increase of heart rate. People susceptible to R-on-T related arrhythmias could be identified by measurement of the dependence of the Q-T interval on heart rate and how quickly the Q-T interval adapts to a change in rate.
mesh_terms: D000200:Action Potentials; D000319:Adrenergic beta-Antagonists / Q000627:therapeutic use; D001145:Arrhythmias, Cardiac / Q000503:physiopathology*; D004562:Electrocardiography; D006321:Heart / Q000294:innervation; D006339:Heart Rate; D006801:Humans; D008133:Long QT Syndrome / Q000175:diagnosis / Q000188:drug therapy / Q000503:physiopathology*; D013564:Sympathetic Nervous System / Q000503:physiopathology
chemical_list: D000319:Adrenergic beta-Antagonists