Use of electron beam tomography to quantify cardiac diastolic function.

Early diastolic relaxation of the left ventricle, which incorporates the isovolumetric relaxation period and the rapid filling phase, is an energy dependent process that is highly dependent on cytosolic calcium sequestration. 4 Investigations into the early phase of ventricular filling have demonstrated clinical situations in which there is a dissociation between diastolic functional abnormalities and discrete systolic functional abnormalities. 10,18,27 Additionally, there is evidence that a significant number of patients who present with clinical signs and symptoms of congestive heart failure, classically considered to be the hallmark of systolic dysfunction, have in fact a normal ejection fraction but distinct abnormalities in early left ventricular filling. 3,26 Currently available methods to evaluate left ventricular diastolic function in humans include assessment of ventricular pressure and volume during contrast angiography, 8,15 two-dimensional echocardiography/Doppler velocimetry, 2,23,30 and radionuclide angiography. 1,16,19 Direct angiography provides an excellent method to evaluate left ventricular function with simultaneous definition of time-dependent changes in cavity volume and pressure through the cardiac cycle. This facilitates assessment of diastolic function through analysis of pressure/volume loops; however, the invasive nature of this technique makes it unacceptable for serial determinations and is of limited practical value in a given patient with suspected diastolic dysfunction. Cardiac ultrasonography, and in particular transthoracic assessment of mitral inflow velocities by Doppler techniques, is commonly used to evaluate left ventricular diastolic function; however, the limited ability to obtain multiple tomographic images of the left ventricle in routine clinical practice using two-dimensional echocardiography and the necessity of using geometric assumptions regarding calculations of time-dependent volumes lead to errors and inconsistencies regarding quantitation of filling dynamics. Mitral valve inflow characteristics can be determined in most patients using routine Doppler methods; however, these velocities are only indirect measurements of ventricular volumes and depend on the instantaneous pressure gradient between the left atrium and the left ventricle in addition to the compliance characteristics of the ventricular chamber. Radionuclide angiography (RNA) is a widely described technique used to evaluate details of global left ventricular filling. This method allows for an accurate evaluation of relative changes in ventricular volume through time without resorting to assumptions regarding left ventricular geometry. Although qualitative analysis of regional function can be performed at the same time as analysis of diastolic filling, the low spatial resolution, despite the recent application of gated single photon emission computed tomography (SPECT) using technetium sestamibi imaging, limits additional information as to details of ventricular anatomy. Electron beam tomography (EBT; also called "ultrafast" or "cine CT") can provide quantitative information of ventricular size and shape 7,20,21 and of global and regional systolic function at rest 6,11 and during exercise. 22 Analyses however have been primarily directed towards determination of absolute differences between end-systolic and end-diastolic ventricular shapes and dimensions and have ignored the character of the time-dependent volumetric changes that occur between these two standard measurement cardiac cycle end-points. This article describes the application of EBT imaging in quantitative analysis of the time-dependent changes in global early left ventricular filling and provides examples of this application in normals and in patients with cardiac pathology.