title: Changes in the transthoracic impedance signal predict the outcome of a 70 degrees head-up tilt test.
abstract: We determined whether early changes in central haemodynamics, as determined by transthoracic impedance, induced by a 70 degrees head-up tilt (HUT) test could predict syncope. Heart rate, arterial blood pressure and central haemodynamics [pre-ejection period and rapid left ventricular ejection time ( T (1)), slow ejection time ( T (2)) and d Z /d t (max) (where Z is thoracic impedance), assessed by the transthoracic impedance technique], were recorded during supine rest and during a 45 min 70 degrees HUT test in 68 patients (40+/-2 years) with a history of unexplained recurrent syncope. We found that 38 patients (42+/-3 years) had a symptomatic outcome to 70 degrees HUT (fainters) and 30 (39+/-2 years) had a negative outcome (non-fainters). When measured between 5 and 10 min of 70 degrees HUT, T (2) had increased significantly only in the fainters, and a change in T (2) of >40 ms from baseline predicted a positive outcome with a sensitivity of 68% and a specificity of 70%. During supine rest prior to 70 degrees HUT, the fainters exhibited a shorter T (2) than non-fainters (183+/-10 compared with 233+/-14 ms; P <0.01), and a T (2) of <199 ms predicted a positive outcome to 70 degrees HUT with a sensitivity of 68% and a specificity of 63%. Incorporation of the changes that occurred from rest to 70 degrees HUT in other haemodynamic variables (heart rate >11 beats/min, systolic pressure <2 mmHg, diastolic pressure <7 mmHg and pulse pressure <-3 mmHg) increased the specificity to 97% and the positive predictive value to 93%. Thus transthoracic impedance could detect differences in central haemodynamics between fainters and non-fainters during supine rest and during the initial period of 70 degrees HUT with a consistent sensitivity and specificity when combined with peripheral haemodynamic variables.
authors.affiliation: Laboratoire de Physiologie - UPRES EA 2170, Faculté de Médecine, rue haute de Reculée, 49035 Angers cedex, France.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Bellard
authors.forename: Jacques-Olivier
authors.initials: JO
authors.lastname: Fortrat
authors.forename: Daniel
authors.initials: D
authors.lastname: Schang
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Dupuis
authors.forename: Jacques
authors.initials: J
authors.lastname: Victor
authors.forename: Georges
authors.initials: G
authors.lastname: Lefthériotis
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002307:Cardiography, Impedance; D005260:Female; D006439:Hemodynamics; D006801:Humans; D008297:Male; D008875:Middle Aged; D011187:Posture; D011237:Predictive Value of Tests; D012008:Recurrence; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016683:Supine Position; D019462:Syncope, Vasovagal / Q000503:physiopathology*; D018667:Tilt-Table Test