M-mode magnetic resonance imaging: a new modality for assessing cardiac function

Mitral annular excursion during exercise in endurance athletes

The aim of the present study was to quantify the left ventricular (LV) longitudinal motion during exercise at rest and during upright exercise in 24 healthy male endurance athletes. By using M-mode and two-dimensional echocardiography, the relative mitral annular motion and the absolute LV longitudinal axis was measured at end-diastole and end-systole at rest and during exercise. From rest to peak exercise at a heart rate of 160 beats per minute (bpm) the mitral annular motion increased in the septal and lateral annular borders by 68% and 49% respectively. At rest, mitral annular excursion was significantly (13%) higher in the lateral than in the septal wall but at peak exercise at a heart rate of 160 bpm there was no difference between the septal and lateral annular motion. The total end-diastolic LV axial length did not increase from rest to peak exercise. In conclusion, during upright exercise, mitral annular motion increased significantly with no difference between the septal and lateral annular excursion at peak exercise. The absolute increase in mitral annular motion during exercise was explained by a decrease in axial end-systolic length.

Three-dimensional assessment of two-dimensional technique for evaluation of right ventricular function by tricuspid annulus motion

BACKGROUND

Measurement of tricuspid annulus motion (TAM) is an easy way to estimate right ventricular ejection fraction (RVEF). However the accuracy of two-dimensional (2-D) methods for analyzing the three-dimensional (3-D) structure of the tricuspid annulus has not been evaluated.

OBJECTIVE

This study evaluated the accuracy with which 2-D measurements of TAM reflect RVEF using 3-D reconstructions of the heart at end diastole (ED) and end systole (ES).

METHODS

2-D echocardiographic studies were performed on 12 subjects and used to reconstruct the RV and tricuspid annulus in 3-D at ED and ES. Measurements of TAM from medial and lateral positions on the annulus were selected from the standard echocardiographic apical four-chamber view. The minimum and maximum possible TAM values, RV volumes, and movement of the apex of the heart along the trajectory of TAM were calculated from the 3-D reconstructions.

RESULTS

TAM correlated highly with RVEF (r > or = 0.90). Values found by 2-D and 3-D techniques were not significantly different. Correcting TAM for apex motion did not improve correlation. Summation of medial and lateral TAM data increased correlation values slightly relative to lateral TAM alone. Regional aberrant contractility degraded the predictive value of TAM.

CONCLUSION

Estimation of RVEF from 2-D echo measurement of TAM is accurate, especially when medial and lateral TAM are summed, except in patients with severe apical RV dysfunction.

Influence of posture on left ventricular long- and short-axis shortening

End-diastolic volume and left ventricular stroke volume are increased in the supine compared with upright position, but the contribution of long-axis (LAS) and short-axis shortening (SAS) to these changes with change in posture has not been established. We examined long- and short-axis motion and dimensions with echocardiography in 10 healthy subjects in the upright and supine position. Long-axis length at end diastole was almost identical, whereas the diastolic short-axis diameter was increased in the supine position. At end systole, there was a decreased long-axis length and increased short-axis length in the supine vs. upright position. Both LAS and SAS were enhanced in supine vs. upright positions [LAS: 9.3 +/- 2.2 vs. 15.1 +/- 3.1 mm (P < 0.001); SAS: 12.7 +/- 3.2 vs. 16.3 +/- 2.8 mm (P < 0.001)], presumably via Starling mechanisms. LAS increased more in the lateral part of the mitral annulus than in the septal part [7.7 +/- 2.6 vs. 4.0 +/- 2.8 mm (P < 0.006)], which implies that the more spherical form, in the supine position, induces more stretch at the lateral free wall than in the ventricular septum. These findings support the notion that Starling mechanisms affect systolic LAS.

Echocardiographic assessment of ejection fraction in left ventricular hypertrophy

OBJECTIVE

To investigate the value of Simpson's rule, Teichholz's formula, and recording of mitral ring motion in assessing left ventricular ejection fraction (EF) in patients with left ventricular hypertrophy.

DESIGN

Left ventricular ejection fraction calculated by Simpson's rule and by Techholz's formula and estimated by mitral ring motion was compared with values obtained by radionuclide angiography.

SETTING

Secondary referral centre.

PATIENTS

16 patients with left ventricular hypertrophy and a clinical diagnosis of hypertrophic cardiomyopathy or hypertension.

RESULTS

Calculation by Teichholz's formula overestimated left ventricular ejection fraction by 10% (p = 0.002) and estimation based on mitral ring motion-that is, long axis measurements-underestimated ejection fraction by 19% (p = 0.002), without significant correlation between ring motion and ejection fraction. There was no significant difference between mean values of ejection fraction calculated by Simpson's rule and measured by the reference method, but a considerable scatter about the regression line with a standard error of the estimate of 9.3 EF%.

CONCLUSIONS

In patients with left ventricular hypertrophy the ejection fraction, calculated by Teichholz's formula or Simpson's rule, is a poor measure of left ventricular function. When mitral ring motion is used for the assessment in these patients the function should be expressed in ways other than by the ejection fraction.

Long and short axis dimensions of the left ventricle change in opposite ways during respiration

Cardiac output and stroke volume are known to vary with respiration. While right ventricular stroke volume increases on inspiration, left ventricular stroke volume decreases. This is an echocardiographic study of the changes in left ventricular dimensions in 20 healthy subjects. Our results show that the decrease in left ventricular stroke volume on inspiration is a net effect of a decrease in short axis shortening due to a decrease in diastolic diameter by 4.8% (P < 0.001) and an increased motion in the long axis direction expressed as an increase in mitral ring motion by 5.5% (P < 0.001). The findings point to the importance of the interventricular septum for the regulation of stroke volume.