Changes in the transthoracic impedance signal predict the outcome of a 70 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.

Cardiovascular variables do not predict head-up tilt test outcome better than body composition

“…Body surface area (BSA = 0.024265 AE weight(kg) 0.5378 AE height (m) 0.3964 ) [12]; hematocrit, hemoglobin, and osmolality (Roebling osmometer, Berlin, Germany); estimates of total body water, fat and fat-free mass (body impedance analyzer, BIA-101/S, Akern, RJL system, Detroit, MI, USA) after 30 min in supine position; plasma volume (indocyanine green dilution) after 45 min of supine rest [11]; heart rate (MAC-vu, Marquette, Milwaukee, WI, USA), systolic, diastolic, mean, and pulse blood pressures (Finapres 2300, Ohmeda, Englewood, NJ, USA), amplitude of the first derivative impedance (an index of stroke volume), contractility index, left ventricular ejection time, and slow ejection time (transthoracic impedance, Physioflow, Manatech Biomedical, Macheren, France) [1] during the last 5 min of supine rest.…”

“…j Key words blood volume AE energy metabolism AE tilt table test AE orthostatic hypotension AE vasovagal syncope AE autonomic nervous system demonstrated that combinations of variables that included variables obtained before the head-up position may help to statistically predict the difference between patients with a negative and a positive outcome [1]. It then could be hypothesized that patients with a positive outcome are in a ''not-yet defined'' abnormal state even before the head-up position.…”

Increased hydration alone does not improve orthostatic tolerance in patients with neurocardiogenic syncope

“…The signal was then normalized to mean RRinterval to discard the specific effect of heart rate [22], and amplitude of dZ/dt max (in Ohm s )1 ) was used as an index of stroke volume [3,18]. This technique has been described in detail elsewhere [2].…”

“…Our aim was to (1) determine whether plasma volume was low in patients with recurrent neurocardiogenic syncope, and (2) determine how recommendation about increased daily fluid intake, without an accompanying high dose of sodium, effects plasma volume and if this potential therapy improves orthostatic tolerance. Eighty-six patients with neurocardiogenic syncope were recruited in a prospective randomized open study.…”

Early prediction of unexplained syncope by support vector machines

“…For medical costs, recent works tried to reduce again the duration of the time interval which could predict the issue of the test. Bellard et al (2003) tried to use only the supine position to predict the outcome of the HUTT. In addition, because the systematic use of invasive techniques (i.e.…”