title: Echocardiographic demonstration of decreased left ventricular dimensions and vigorous myocardial contraction during syncope induced by head-up tilt.
abstract: Two-dimensional echocardiography was performed during a head-up tilt test in 11 control subjects (group I) and 18 patients with recurrent unexplained syncope. In four patients (group II), the head-up tilt test was negative at baseline and after isoproterenol infusion. Syncope was induced during baseline head-up tilt in nine patients (group III) and after isoproterenol challenge in five (group IV). The echocardiographic variables assessed were left ventricular end-systolic and end-diastolic areas and percent fractional shortening. At the end of head-up tilt, end-systolic area decreased by 4.5 +/- 1.3 and 3.0 +/- 1.2 cm2 in groups III and IV, respectively, compared with 0.5 +/- 0.7 and 0.2 +/- 0.1 cm2 in groups I and II, respectively (p less than 0.04). Similarly, end-diastolic area decreased by 5.5 +/- 2.6 cm2 in group III compared with 2.7 +/- 1.9 and 1.75 +/- 0.4 cm2 in group I and II, respectively (p less than 0.04). Additionally, at the end of the baseline study, fractional shortening was significantly greater in group III and group IV (43 +/- 5%) than in groups I and II (p less than 0.01). In conclusion, syncope induced by head-up tilt is associated with vigorous myocardial contraction and a significant decrease in left ventricular end-systolic dimensions. This left ventricular hypercontractility may play an important role in the pathogenesis of syncope induced by head-up tilt.
authors.affiliation: Natalie and Norman Soref and Family Electrophysiology Laboratory, University of Wisconsin Medical School, Milwaukee.
authors.forename: Y
authors.initials: Y
authors.lastname: Shalev
authors.forename: R
authors.initials: R
authors.lastname: Gal
authors.forename: P J
authors.initials: PJ
authors.lastname: Tchou
authors.forename: A J
authors.initials: AJ
authors.lastname: Anderson
authors.forename: B
authors.initials: B
authors.lastname: Avitall
authors.forename: M
authors.initials: M
authors.lastname: Akhtar
authors.forename: M R
authors.initials: MR
authors.lastname: Jazayeri
mesh_terms: D000328:Adult; D004452:Echocardiography; D005260:Female; D006801:Humans; D007545:Isoproterenol; D008297:Male; D008790:Metoprolol; D009200:Myocardial Contraction / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D013575:Syncope / Q000209:etiology* / Q000503:physiopathology; D016277:Ventricular Function, Left / Q000502:physiology*
chemical_list: D008790:Metoprolol; D007545:Isoproterenol