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Function and mechanics of the left ventricle: Patel, 3 Natesa G. Received on May 13, ; Accepted on February 13, One of the most common indications in echocardiography is the evaluation of left ventricular function. The traditional measurement of ejection fraction is based upon tracing the left ventricular borders and calculating left ventricular volumes using geometric assumptions. However, regional myocardial function is more difficult to evaluate because it guadalajaea on visual assessment of endocardial motion and wall thickening.
Three dimensional speckle tracking 3DST has potential to be an ideal tool to assess not only global myocardial function but regional function through deformation, rotation, twist and untwisting parameters.
Besides, the inadvertent use of foreshortened views can raise its inaccuracy and low reproducibility. Alternatively, LV function can be assessed by Doppler techniques through the measurements of stroke volume using the continuity equation.
However, calculations of stroke volume by Doppler are dependent on the accuracy of left ventricle outflow tract measurement LVOT ; errors in the measurement, which cqrdiologia squared in the calculation of the LVOT area, limit the reliability of this parameter. Never the less, segmental wall motion has been more difficult to evaluate. Visual assessment has limited ability to detect more subtle changes in function and in timing of myocardial motion throughout systole and diastole.
Recently, echocardiographic modalities for objective quantification of global and regional function have been developed such as tissue Doppler and speckle tracking imaging. In this article, we review in a concise manner the methodology behind the development, usefulness, and shortcomings of these echocardiographic techniques. In cardiac muscle physiology, strain is a measurement of deformation representing shortening or stretching of the tissue or myocardial fibers. The strain value is dimensionless and can be represented as a fractional number or as a percentage change from an object’s original dimension Figure cardiologiz.
Cardiologia: Jose Fernando Guadalajara Boo: : Books
As the ventricle contracts, muscle shortens in the circumferential and longitudinal dimensions a negative strain and thickens in the radial and transversal direction a positive strain. Theoretically, strain values are not affected by the uniform translational motion of the heart and, as a consequence, they offer a clear advantage over velocity and displacement to assess the local functionality of the myocardium.
Completely passive segments can show motion relative to the transducer due to tethering, but without any deformation, making velocity fernand displacement information completely unreliable guadalajra the characterization of such regions. Strain rate SR is the rate at which deformation occurs, i.
By definition it is the temporal derivative of strain and expresses the rate of shortening or lengthening of a part of the heart. Currently, the principal strain vectors and their velocity derivatives Strain Rate can be assessed by tissue Doppler and speckle tracking echocardiography. Rather than assessing the rapid velocity blood pool as with conventional Doppler, uses filters to remove these signals to concentrate solely on the lower velocity myocardial motion.
Tissue Doppler imaging allows a quantitative analysis of the motion pattern of the cardiac walls. Several guadalajraa of investigators have demonstrated that strain analysis of a broader area is probably superior to tissue velocity data at one site and wall motion score for tracking local systolic function.
One of the most important clinical applications of TDI is the quantification of global LV systolic function; this can be done by measuring the myocardial peak systolic velocities of the mitral valve annulus at several locations and to derive an average of them. Gulati et al, reported an excellent correlation between systolic mitral annulus velocity Sm averaged from the apical views and LV ejection fraction.
Limitations of tissue doppler imaging: This implies that strain measurements from myocardial segments close to the left ventricle apical curvature cannot be reliably assessed by tissue Doppler imaging. Speckles are natural acoustic markers that occur as small and bright elements in conventional gray scale ultrasound images.
Understanding Heart Failure
The speckles are backscattered from structures smaller than a wavelength of ultrasound. These speckles are distributed all through the myocardium on the ultrasound image. In the speckle tracking methodology, a small area of the myocardium with its unique speckle pattern can be defined it is called “kernel” and tracked, following a search algorithm based on optical flow method, trying to recognize the feernando similar speckle pattern from one frame to another.
The algorithm searches for an area with the smallest difference in the total sum of pixel values, which is the smallest sum of absolute differences 39 Figure 6. For accurate speckle tracking, a high frame rate is important.
A high frame rate decreases the speckle change between frames, allowing better tracking.
The distance between selected speckles is measured within a predefined myocardial area as a function of time, and parameters of myocardial deformation can be calculated. Another important advantage by using the new technique is independence from insonation angle and cardiac translation. These values are not independent, one is positive wall thickening when the other is negative segment shortening in a normal heart.
The potential of 2D speckle tracking echocardiography has been investigated in numerous experimental and clinical studies for exploration of systolic and diastolic ventricular function, assessing ischemia, dyssynchrony, and other cardiac conditions, 46 some of which will be cited representatively in this review.
In initial studies, Becker et al, used 2D speckle tracking imaging huadalajara assess regional LV function. They compared a healthy group with a group of patients with previous myocardial infarction.
All subjects underwent guadlaajara magnetic resonance imaging CMRI. They found excellent correlation between the values obtained for peak radial and circumferential strains and the visual assessment of the MRI images. The sensitivity and specificity of this technique in the detection of dyssynergy were The results of these studies demonstrated concordance in the estimation of LV torsion between speckle tracking and tagged MRI and made the assessment of LV rotation and torsion available in clinical cardiology.
Left ventricular torsion is a critical component of cardiac biomechanics because it is important for normal ejection and suction and is a feature of the normal spread of excitation and connections among fibers.
The difference guuadalajara apex and base in the rotation angle is called twist and contributes significantly to LV ejection, in addition to myocardial shortening and thickening. It also has an important role in diastole since it contributes to diastolic suction in the early phases of ventricular filling in a process called untwist. Left ventricular torsion can be quantified by speckle tracking echocardiography. The interpretation of echocardiographic images requires a complex mental integration of different planes to understand anatomic structures and physiologic functions.
Three dimensional speckle tracking is a recent modality and its clinical application is currently being evaluated. Guaddalajara concluded that 3D speckle tracking “is a simple, feasible, and reproducible method to measure strain”.
They also reported differences in strain measurements and time to perform a complete 3DSTE analysis compared with 2D speckle tracking results. Currently 3D STE is being applied in the clinical field by several groups around the world.
Current limitations of speckle tracking echocardiography.
Further improvement of guadwlajara and temporal resolution of 3D STE is likely to overcome these drawbacks. As speckle tracking echocardiography evolves and becomes familiar, it will be mandatory to ensure standardization of terminology, steps in data acquisition, and optimal training to increase data accuracy and reproducibility.
A developing body of evidence suggests that guadalaajara of LV mechanics by tissue Doppler imaging and speckle tracking echocardiography offers valuable information in several clinical scenarios. Understanding such events could provide novel insight into the mechanisms of LV dysfunction, and may have the potential to identify subtle changes in LV mechanics in patients with subclinical myocardial dysfunction. With the advent of 3D echocardiography, three dimensional speckle tracking is emerging as a new tool that combines the usefulness of myocardial motion tracking with a better guadalzjara of the anatomic structures and physiologic function of the heart.
The evidence for the utility of this tool is growing and offers valuable fernaneo over TDI and two dimensional speckle tracking echocardiography, holding the promise for a better understanding of the mechanisms of LV dysfunction and tracking the impact of current and future therapies.
Recommendations for Chamber Quantification: J Am Soc Echocardiogr ; Recommendations for quantification of Doppler echocardiography: Eur Heart J ; J Am Coll Cardiol ; Pavlopoulos H, Nihoyannopoulos P. Strain and strain rate deformation parameters: Int J Cardiovasc Imaging ; Quantitative assessment of intrinsic regional myocardial deformation by Doppler strain fernanco echocardiography in humans: Myocardial strain by Doppler echocardiography.
Validation of a new method to quantify regional myocardial function. Regional myocardial systolic function during acute myocardial ischemia assessed by strain Doppler echocardiography.
J Am Coll Cardiol Strain rate imaging by ultrasonography in the diagnosis of coronary artery disease. J Am Soc Echocardiogr ; Strain rate imaging during dobutamine stress echocardiography provides objective evidence of inducible ischemia. Use of peak systolic strain as an index of regional left ventricular function: Am J Bok ; Mitral annular descent velocity by tissue Doppler echocardiography as an index guxdalajara global left ventricular function.
Assessment of left ventricular systolic wall motion velocity with pulsed tissue Doppler imaging: Prognostic value of systolic mitral annular velocity measured with Doppler tissue imaging in patients with chronic heart failure caused by left ventricular systolic dysfunction.
Assessment of mitral annulus velocity by Doppler tissue imaging in the evaluation of left ventricular diastolic function.
Clinical utility of Doppler echocardiography and tissue Doppler imaging in the estimation of left ventricular filling pressures: Differentiation of constrictive pericarditis from restrictive cardiomyopathy: Differentiation of constrictive pericarditis from restrictive cardiomyopathy using mitral annular velocities by tissue Doppler echocardiography.
The use of TDI for the assessment of changes in myocardial structure and function in inherited cardiomyopathies. Eur J Echocardiogr ;6: Tissue Doppler imaging consistently detects myocardial abnormalities in patients with hypertrophic cardiomyopathy and provides a novel means for an early diagnosis before and independently of hypertrophy.
Assessment of diastolic function with Doppler tissue imaging to predict genotype in preclinical hypertrophic cardiomyopathy. Echocardiographic characterization of cardiomyopathy in Friedreich’s ataxia with tissue Doppler echocardiographically derived myocardial velocity gradients. Doppler tissue imaging quantitates regional wall motion during myocardial ischemia and reperfusion. Detection of early abnormalities of left ventricular function by hemodynamic, echotissue Doppler imaging, and mitral Doppler flow techniques in patients with coronary artery disease and normal ejection fraction.
Quantitaive evaluation of the segmental left ventricular response to dobutamine stress by tissue Doppler echocardiography. Regonal diastolic function by pulsed Doppler myocardial mapping cardiologla the detection of left ventricular ischemia during pharmacologic stress testing.
Am Heart J ; A novel tool to assess systolic asynchrony and identify responders of cardiac resynchronization therapy by tissue synchronization imaging. Tissue synchronization imaging accurately measures left ventricular dyssynchrony and predicts response to cardiac resynchronization therapy.