Force-Frequency Relationship in the Echocardiography Laboratory: A Noninvasive Assessment of Bowditch Treppe?

Background: Estimation of contractility of the left ventricle is an important, and as yet elusive, goal with noninvasive techniques. Objective: We sought to assess the feasibility of a totally noninvasive estimation of force-frequency relation (FFR) during exercise stress in the echocardiography laboratory. Methods: We enrolled 13 healthy control patients (12 men, age 38 ± 15 years) as group I, and 50 patients (38 men, age 64 ± 11 years) referred for exercise echocardiography as group II. To build the FFR, the force was determined at each step as the ratio of the systolic pressure (cuff sphygmomanometer)/end-systolic volume index (biplane Simpson's rule/body surface area). The slope of the relationship was calculated with the linear best fit of the FFR. Results: Noninvasive systolic pressure/end-systolic volume ratio was obtained in all patients. The slope of the linear best fit of the force-frequency curve was lower in group II compared with group I (group II = 10.1 ± 9.3 × 10^-2 vs group I = 14.9 ± 9.9 × 10^-2 group I, P = .04). By regional wall-motion analysis, 2 subgroups were identified in group II: group IIA (n = 8) had a positive echocardiogram; and group IIB (n = 42) had a negative echocardiogram. The slope of the force-frequency curve was lower in patients with ischemia compared with those without (group IIA = 3.5 ± 4.2 × 10^-2 vs group IIB = 11.4 ± 9.5 × 10^-2; P = .012). Heart rate-systolic pressure/end-systolic volume index relation was biphasic, with an initial positive slope and a subsequent negative slope in 1 patient of group I, 4 patients of group IIA, and 15 patients of group IIB (P <.05 vs group I). Conclusiom A noninvasive estimation of FFR can be easily determined during exercise echocardiography. This index of global contractility is theoretically appealing for identification of limited contractile reserve and latent global left ventricular dysfunction.