P465A new force sensor for imaging-independent assessment of force-frequency relationship in the stress echo lab: clinical validation

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Background: The force-frequency relation (FFR) can be obtained in the stress echo lab, where the force is computed as the systolic pressure/end-systolic volume index ratio, and measured for increasing heart rates during stress. Ideally, the noninvasive, imaging independent, objective assessment of FFR would greatly enhance its practical appeal.Aims: To evaluate the feasibility of the FFR measurement by a precordial cutaneous sensor and to compare the standard stress echo results vs. this sensor operator-independent FFR.Methods: The transcutaneous force sensor was positioned in the precordial region in 147 consecutive patients referred for exercise (n=100), dipyridamole (n=41), or pacing (n=6) stress. The force was measured as the myocardial vibration amplitude in the isovolumic contraction period. FFR was computed as the curve of force variation as a function of heart rate. Standard echocardiographic FFR measurements were simultaneously performed.Results: A consistent FFR was obtained in all patients. The sensor (see figure, left panel) FFR slope and shape mirrored the more technically demanding and time-consuming echo (see figure, right panel). The best cut-off value of the sensor built FFR was 15.5 g x 10-3 (Sensitivity = 0.85, Specificity = 0.77). Sensor mirror pressure/volume relation during stress (R = 0.6).Conclusions: Force-frequency relation assessment with this new non-invasive, operator-independent force sensor is extendable to daily physiological exercise and could be potentially attractive for quantitative, non-imaging assessment of left ventricular contractile reserve, of potential interest in the stress lab and for home monitoring systems in cardiac heart failure.

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