title: Alternation of atrial cycle length in supraventricular tachycardia.
abstract: Nine cases of alternation of the atrial cycles during supraventricular tachycardia are presented, three of which were manifestly due to digitalis toxicity. They presented the following features: absence of 1/1 conduction, upright P waves in Lead II, atrial rates of 156-218. When alternation disappeared, the atrium adopted the longest of the previously inscribed cycles. A ventriculophasic cause was excluded. The possible mechanisms are discussed in terms of the known functional anatomy of the various forms of SVT.
mesh_terms: D000328:Adult; D004071:Digitalis Glycosides / Q000009:adverse effects; D004562:Electrocardiography; D005260:Female; D006325:Heart Atria / Q000503:physiopathology; D006329:Heart Conduction System / Q000503:physiopathology; D006801:Humans; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D013268:Stimulation, Chemical; D013614:Tachycardia, Paroxysmal / Q000139:chemically induced / Q000175:diagnosis* / Q000209:etiology
chemical_list: D004071:Digitalis Glycosides