[Idiopathic orthostatic tachycardia. Etiology, diagnosis and treatment]

For nearly a century, physicians have been aware of a syndrome consisting of a relatively stereotyped presentation, usually in young patients, who complain of fatigue, malaise and effort intolerance, sometimes of trembling and weakness of the lower limbs. This is associated with an excessive tachycardia in the orthostatic position. This syndrome has recently been called idiopathic orthostatic tachycardia. The tilt test has enabled "quantification" of normal responses. Patients complaining of the symptoms described above and which, during the first minutes of orthostatism, increase their heart rates by more than 30 beats per minute or attain a rate of at least 110/min, are considered to be suffering from this syndrome. The physiopathology is not clear but, globally, there seems to be two sub-groups, the first considered to be a partial dysautonomic disorder and the second, the result of hypersensitivity of the beta-receptors. Besides the tilt test, the diagnosis can also be presumed after an excessive tachycardia response to an intravenous infusion of 1 microgram/min of isoprenaline. The treatment of these patients is uncertain as there is no single approach which is always effective. In addition to "simple" but essential advice, a number of drugs may be used although there is no means of predicting the efficacy of the result in a given patient. A major principle should be emphasised: ablation of the sinus node for inappropriate tachycardia may eliminate the only compensatory mechanism of autonomic dystonia and make the patients even more symptomatic than they were.