Ultrasound assessment of the force-frequency relationship from the law of conservation of momentum in patients with left ventricular dysfunction

Measurement of force-frequency relationship (FFR) is useful in the evaluation of heart rate-dependent contractile dysfunction. The purpose of this study was to evaluate a new Doppler-derived method for assessing FFR. Doppler velocity spectra at the left ventricular (LV) outflow tract was used to estimate mean blood flow velocity (mBFV), ejection time (ET) and velocity-time integral. LV ejection force (LVF) was then calculated ac- cording to the law of conservation of momentum: 1060 kg/m 3 3 (mBFV(m/sec)/ET (s)) 3 Stroke volume (mL). A symptom-limited, graded, bicycle semi-supine exercise test was performed in 56 patients with LV dysfunction (LVejection fraction 527 ± 6%). Measurements were obtained at baseline and serially during the test. The change in FFR was defined as up-sloping when the peak LVF was higher than the baseline value. The change was biphasic when the trendwas initially up-sloping, then down-sloping; it wasflat or negative when peak LVF was less than the baseline value. LVF was 30 ± 12 mN in patients with up-sloping FFR (n 5 39) and 15 ± 6 mN in those with biphasic or flat FFR (n 5 17; p , 0.0001). The ultrasound assessment of the FFR was highly concordant with a previously validated method based on pressure-end-systolic volume index ratio (k 5 0.75; 95% confidence interval, 0.55-94.0). The evaluation of the LVF using Doppler is an alternative method for the assessment of FFR during stress echocardiography in patients with LV dysfunction. (E-mail: f.dini@ao-pisa.toscana.it) � 2013 World Federation for Ultrasound in Medicine & Biology.