Aortofemoral transfer function: a method to determine the instantaneous aortic valve gradient in aortic valve stenosis
DH Fitchett
Division of Cardiology, Royal Victoria Hospital, McGill University, Montreal, Quebec, Canada.
OBJECTIVES. This study was performed to evaluate the use of synthesized ascending aorta pressure, calculated from femoral artery pressure using an aortofemoral transfer function, in the assessment of aortic valve stenosis. BACKGROUND. Measurement of an accurate aortic valve gradient in patients with aortic stenosis often requires simultaneous recordings of ascending aorta and left ventricular pressures. The use of femoral artery pressure is considered to be a poor substitute for ascending aorta pressure. However, the aortic pressure wave can be calculated from the femoral artery pressure if the aortofemoral transfer function has been determined. METHOD. Femoral artery pressure from the side arm of an introducer sheath and ascending aorta pressure are recorded simultaneously and the data stored in a personal computer. An aortofemoral transfer function is determined from the ratio of the Fourier components of aortic and femoral pressures. Left ventricular and femoral artery pressures are then recorded. Using the previously determined transfer function, the simultaneous ascending aorta pressure is calculated from the femoral pressure. RESULTS. Ascending aorta pressure waveforms estimated from femoral artery pressure closely resembled the simultaneously recorded ascending aorta pressure. Mean aortic valve gradients calculated from the synthesized aortic pressure correlated well with the gradient measured from direct recordings of aortic pressure (r = 0.98). There was also a good relation between valve areas (r = 0.93) and valve resistances (r = 0.98) calculated using the two methods. CONCLUSIONS. Using current computer technology, accurate aortic valve gradients can be rapidly calculated using femoral artery pressure as a substitute for ascending aorta pressure. This technique will reduce the need and risks of multiple catheters to determine aortic valve gradients.
