[show abstract][hide abstract] ABSTRACT: Rats and genetically manipulated mouse models have played an important role in the exploration of molecular causes of cardiovascular diseases. However, it has not been fully investigated whether mice or rats and humans manifest similar patterns of ventricular wall motion. Although similarities in anatomy and myofiber architecture suggest that fundamental patterns of ventricular wall motion may be similar, the considerable differences in heart size, heart rate, and sarcomeric protein isoforms may yield quantitative differences in ventricular wall mechanics. To further our understanding of the basic mechanisms of myofiber contractile performance, we quantified regional and global indexes of ventricular wall motion in mice, rats, and men using magnetic resonance (MR) imaging. Both regular cine and tagged MR images at apical, midventricular, and basal levels were acquired from six male volunteers, six Fischer 344 rats, and seven C57BL/6 mice. Morphological parameters and ejection fraction were computed directly from cine images. Myocardial twist (rotation angle), torsion (net twist per unit length), circumferential strain, and normalized radial shortening were calculated by homogeneous strain analysis from tagged images. Our data show that ventricular twist was conserved among the three species, leading to a significantly smaller torsion, measured as net twist per unit length, in men. However, both circumferential strain and normalized radial shortening were the largest in male subjects. Although other parameters, such as circumferential-longitudinal shear strain, need to be evaluated, and the causes of these differences in contractile mechanics remain to be elucidated, the preservation of twist appears fundamental to cardiac function and should be considered in studies that extrapolate data from animals to humans.
[show abstract][hide abstract] ABSTRACT: The purpose of this study was to evaluate the reliability of the pressure half-time (PHT) method for estimating mitral valve areas (MVAs) by velocity-encoded cardiovascular magnetic resonance (VE-CMR) and to compare the method with paired Doppler ultrasound.
The pressure half-time Doppler echocardiography method is a practical technique for clinical evaluation of mitral stenosis. As CMR continues evolving as a routine clinical tool, its use for estimating MVA requires thorough evaluation.
Seventeen patients with mitral stenosis underwent echocardiography and CMR. Using VE-CMR, MVA was estimated by PHT method. Additionally, peak E and peak A velocities were defined. Interobserver repeatability of VE-CMR was evaluated.
By Doppler, MVAs ranged from 0.87 to 4.49 cm2; by CMR, 0.91 to 2.70 cm2, correlating well between modalities (r = 0.86). The correlation coefficient for peak E and peak A between modalities was 0.81 and 0.89, respectively. Velocity-encoded CMR data analysis provided robust, repeatable estimates of peak E, peak A, and MVA (r = 0.99, 0.99, and 0.96, respectively).
Velocity-encoded cardiovascular magnetic resonance can be used routinely as a robust tool to quantify MVA via mitral flow velocity analysis with PHT method.
Journal of the American College of Cardiology 08/2004; 44(1):133-7. · 14.09 Impact Factor
[show abstract][hide abstract] ABSTRACT: Valvular pathology can be analyzed quickly and accurately through the use of Doppler ultrasound. For aortic stenosis, the continuity equation approach with Doppler velocity-time integral (VTI) data is by far the most commonly used clinical method of quantification. In view of the emerging popularity of cardiac magnetic resonance (CMR) as a routine clinical imaging tool, the purposes of this study were to define the reliability of velocity-encoded CMR as a routine method for quantifying stenotic aortic valve area, to compare this method with the accepted standard, and to evaluate its reproducibility.
Patients (n=24) with aortic stenosis (ranging from 0.5 to 1.8 cm2) were imaged with CMR and echocardiography. Velocity-encoded CMR was used to obtain velocity information in the aorta and left ventricular outflow tract. From this flow data, pressure gradients were estimated by means of the modified Bernoulli equation, and VTIs were calculated to estimate aortic valve orifice dimensions by means of the continuity equation. The correlation coefficients between modalities for pressure gradients were r=0.83 for peak and r=0.87 for mean. The measurements of VTI correlated well, leading to an overall strong correlation between modalities for the estimation of valve dimension (r=0.83, by means of the identified best approach). For 5 patients, the CMR examination was repeated using the best approach. The repeat calculations of valve size correlated well (r=0.94).
Velocity-encoded CMR can be used as a reliable, user-friendly tool to evaluate stenotic aortic valves. The measurements of pressure gradients, VTIs, and the valve dimension correlate well with the accepted standard of Doppler ultrasound.