Figure 6
Exercise stress echo. Lower panels. The ventricular force is expressed as SP/ESV assessed by echocardiography in the stress echo lab. Left, force-frequency curve with stress echo in a normal subject. An increased heart rate is accompanied by an increased systolic pressure with smaller end-systolic volumes (normal up sloping force-frequency relation). The Δ rest-peak SP/ESV index is >4 mmHg/ml/m2 (normal contractile reserve). Middle, force-frequency curve with stress echo in a subject with systemic hypertension with BB therapy on. The force-frequency relation is up sloping with a biphasic pattern at higher heart rates. Right, force-frequency curve with stress echo in a subject with coronary artery disease, and stress induced ischemia (abnormal force-frequency relation). The Δ rest-peak SP/ESV index is = 3, lower than 4 mmHg/ml/m2 (normal cut-off for positive contractile reserve). Upper panels. Sensor built force-frequency relation simultaneously recorded in the same patients in which standard echo force-frequency relation was built. Blue curve = exercise in progress; red curve = recovery. Left, normal up sloping force-frequency relation: the Δ rest-peak force is >15.5 g * 10-3 (cut-off value for normal contractile reserve). Middle, normal force-frequency relation: (Δ rest-peak force is >15.5 g * 10-3) but less up sloping than the control subject. Right, abnormal flat force-frequency relation: the Δ rest-peak force is 5 g * 10-3, much less than 15.5 g * 10-3 (cut-off value for normal contractile reserve).