New options in noninvasive assessment of left ventricular torsion

5110.2217/14796678.5.1.51 © 2009 Future Medicine ISSN 1479-6678Future Cardiol. (2009) 5(1), 51–61

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Congestive heart failure (CHF) is a major cause of morbidity and mortality worldwide. Approximately 5.2 million Americans have the diagnosis of heart failure, with 550,000 cases diagnosed each year [101]. In 2001, CHF had an overall death rate of 19.7 people per 1000, and cost an estimated $29.6 billion in direct and indi-rect costs in 2006 [1]. The disease occurs when myocardial performance is insufficient to meet the metabolic demands of vital tissues and organs, resulting in hypertrophy, dilation, diminished performance and, subsequently, heart failure. This complex state represents the final common pathway after prolonged stress from a variety of conditions, including hypertension, coronary artery disease, valvular disease, cardiomyopa-thy and congenital heart disease [2]. Torsion, the twisting motion of the left ventricle (LV) about its long axis, has been demonstrated to be sig-nificantly altered in CHF, as well as in a variety of other disease states known to predispose risk for developing heart failure [3–7]. Torsion has also been investigated as a potential marker for pre-dicting favorable LV systolic response to cardiac resynchronization therapy [8–10]. Understanding torsion is critical for enhancing further under-standing of CHF and other diseases of myocar-dial function. While the complicated 3D twisting and untwisting motions are difficult to quantify, several noninvasive techniques have been shown to be effective in the noninvasive assessment of LV torsion. The purpose of this paper is to

p rovide a succinct but comprehensive review of the mechanics of LV torsion, as well as new n oninvasive options.

Mechanics of left ventricular torsionCardiac myocytes are arranged in axial tracts. Since the length of the myocyte far exceeds the width, each myocyte branches and intercon-nects with its neighbors in longitudinal strands supported within a matrix of fibrous tissue, thus forming a ‘grain’. These myocardial grains spiral about the LV in a helical arrangement from apex to base. In 1628, Sir William Harvey hypothesized that this helical orientation might have functional implications on cardiac function [11]. As elegantly demonstrated by Pettigrew, careful dissection of the myocardium reveals that the left-handed helix of the subepicardial grain gradually changes heli-cal angle to become circumferential to the long axis of the LV in the midwall to form an ‘equator’, before changing into a right-handed helix in the subendocardium [12–14]. As a result of the counter-directional geometries of the subendo cardial and subepicardial helices, the vectors of contraction occur at approximately the same angle but with opposite directions relative to the LV long axis, an arrangement believed to be both energetically optimal and important for equal redistribution of LV stresses and strain (Figure 1) [15]. Careful histo-logic study reveals that, by and large, the orienta-tion of the individual myocytes aligns with the long axis of the removed grain [16].

New options in noninvasive assessment of left ventricular torsion

Andrew J Yoon & Jonathan N Bella†

†Author for correspondence: Albert Einstein College of Medicine, The Bronx, NY, USA and Bronx-Lebanon Hospital Center, Division of Cardiology, 1650 Grand Concourse, 12th Floor, The Bronx, NY 10467, USA n Tel.: +1 718 518 5222 n Fax: +1 718 518 5545 n [email protected]

The complex, intricate 3D pattern of ventricular torsion has both fascinated and perplexed scientists for centuries. The identity of the underlying anatomic myocardial unit responsible for this pattern of contraction continues to be an arena of debate. While the complicated wringing motions involved in torsion are difficult to quantify, several techniques have been demonstrated to be effective in the noninvasive assessment of left ventricular (LV) torsion. Magnetic resonance tissue-tagging with dynamic MRI is the gold standard for the noninvasive quantitative evaluation of torsion with high spatial and temporal resolution. However, this is a technically involved and potentially time-consuming process. Echocardiography is another alternative noninvasive method. Both tissue Doppler imaging and speckle-tracking imaging have been shown to be sufficiently accurate and reliable alternatives to MRI in the noninvasive assessment of LV torsion. While the potential applications of these techniques to assess LV torsion appears boundless, further studies are needed to validate measures of LV torsion by the additional, but most important, test of demonstrating its clinical utility as a predictor of prognosis.

Keywords

cardiac imaging n left ventricle n torsion

k.rowland

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Future Cardiol. (2009) 5(1)52 future science group

Review Yoon & Bella

Numerous attempts have been made to arrange and organize the individual myocytes into higher order superstructures in an effort to better understand myocardial function. Torrent-Guasp et al. demonstrated that care-ful blunt dissection of the LV could unravel the myocardium into a single, continuous ‘unique myocardial band’ [17]. In a competing theory, Nielson and colleagues postulated that myo-cytes are packaged and structured in lamellar layers interspersed between uniform fibrous sheets extending radially from the endocar-dium to the epicardium [18,19]. Critics have argued that there is no anatomic or histologic basis for these models [20,21]. Alternatively, they propose a model of the myocardium and its sup-porting fibrous structure as a spatially netted mesh consisting of a continuous 3D syncytium of interlacing myocytes, the design of which cannot be reconciled with radially organized sheets or a ‘unique myocardial band’ [22,23]. In a series of detailed histologic and MRI studies, Anderson et al. have demonstrated that there are two distinct populations of myocytes in

the myocardial wall: the predominant group of myocytes aligned tangential to the LV wall, and a smaller group of myocytes with their long axis oriented obliquely at various angles of intrusion from the epicardium to the endocardium [24–26]. The predominant population of tangentially ori-ented myocytes generate the unloading forces responsible for systolic ventricular emptying, while the second population of obliquely ori-ented myocytes produce smaller auxotonic, or augmenting, forces that act to support both ventricular constriction while also promoting ventricular dilation. During contraction, the individual myocytes realign themselves within the 3D mesh, thus demonstrating how a mean 5% increase in individual sarcomere thickness during systole results in a substantially greater increase in LV wall thickening [27,28]. It is likely that the twisting of the myocardial mass is part and parcel of the myocyte rearrangement that occurs during mural systolic thickening.

In LV torsion, the motion of the apex and base are conventionally described from an apex-to-base view down the longitudinal axis of the LV, with clockwise rotations measured in nega-tive degrees, and counterclockwise rotations measured in positive degrees (Figure 2). When isovolumic contraction (IVC) begins, the apex transiently rotates clockwise as the right-handed subendocardial myofibers shorten. As systole continues, the left-handed subepicardial myofib-ers begin to predominate, and apical rotation reverses and becomes counterclockwise for the duration of systole. This counterclockwise api-cal rotation is the primary contributor to global systolic LV torsion. The LV base rotates in the opposite direction with significantly decreased magnitude, in comparison. When IVC begins, the base undergoes an initial, brief counterclock-wise rotation due to the subendocardial fibers, which is then followed by a longer clockwise

rotation as the subepicardal myofiber forces

predominate. LV torsion is the combined sum of the counterdirectional twisting motions of the apex and base during systole and is expressed in degrees or radians. By adding this twisting motion to the traditional paradigm of the heart as a balloon-like pump, a model of the LV as a 3D ‘wringing’ pump (best visualized as wringing a wet towel) is obtained.

Apical rotation also plays the dominant role during diastole when the LV apex begins to ‘untwist’ and recoil in the clockwise direc-tion [29]. It is hypothesized that the deformation of the subendocardial matrix by LV torsion stores potential energy during systole, and that the rapid

Figure 1. Schematic illustration of the orientation of the subepicardial and subendocardial helices. The subepicardial and subendocardial myocyte tracts are arranged in counterdirectional helices with different ‘handedness’ or chirality. During ventricular systole, subepicardial tracts predominate at the apex while subendocardial tracts predominate at the base. The counterdirectional rotations of the apex and base result in a twisting motion of the ventricle during contraction (arrows indicate direction of rotation). Untwisting, which occurs during diastole, is the same process in reverse.

www.futuremedicine.com 53future science group

New options in noninvasive assessment of left ventricular torsion Review

untwisting motion of the LV during early diastole is the kinetic manifestation of that energy release [30–32]. This untwisting motion begins just before aortic valve closure and continues throughout the isovolumic relaxation (IVR) phase. Approximately 40% of untwisting occurs before the mitral valve opens, with an additional 40% occurring by the time of peak early-mitral filling.

Untwisting velocity is believed to be a signifi-cant contributor to diastolic LV filling [33]. The untwisting motion, especially at the apex, forms an intraventricular pressure gradient (IVPG). The apical intracavitary pressure is only 2 mmHg lower in comparison to the base. However, this 2 mmHg IVPG may help suction blood into the ventricle during diastole, thus allowing the ventricle to fill at very low left atrial pressures. Most noninvasive measures of diastolic function are made during LV filling and are, therefore, subject to ‘pseudonor-malization’, since variations in left atrial pressure

may confound the estimation of relaxation rate. Dong et al. have demonstrated that the rate of untwisting remains constant with volume loading, is independent of left atrial pressure, and is there-fore more closely correlated to τ (the time con-stant of relaxation) than the IVR time [29]. Rovner et al. demonstrated that the ability to augment diastolic suction was the best predictor of how far heart failure patients could run on a treadmill [34]. As a result, it has been suggested that the rate of untwisting might be a more direct measure of diastolic function than conventional echo Doppler

measures of filling-related parameters.

Noninvasive assessment of LV TorsionThe complicated 3D wringing motions involved in torsion are difficult to measure. Previous invasive strategies used to quantify LV torsion included tracking coronary artery bifurcations in 3D [35] and tracking the motion of metal mark-ers implanted near the midwall in transplanted human hearts by biplane cine radiography [36,37]. However, recent studies have demonstrated that the noninvasive measurement of LV torsion is feasible, accurate and reliable.

Magnetic resonance imagingMagnetic resonance tissue tagging with dynamic

MRI is the gold standard for the noninvasive quantitative evaluation of cardiac mechanical function with high spatial and temporal resol-ution. Tags are noninvasive, transient mark-ers that are imprinted on the myocardium by special MR radiofrequency pulses on 2D tissue planes (Figure 3) [38]. These pulses change the

magnetization of the protons compared with the

neighboring nontagged regions [39]. Differences in signal intensity between tagged and untagged regions serve as a means of accurately tracking

the motion of the underlying myocardium [40]. Mathematical equations have been derived to calculate LV t orsion from tag positions on cine

MR images [41].By convention, LV torsion in MRI is measured

in total base-to-apex deformation. In MRI, the base is assigned a reference value of 0°, with the clockwise rotation of the apex reported as positive values. In normal adults, Young et al. demon-strated mean apical torsion of 12–14°, with torsion at the apical endocardium (16.5°) exceeding that at the apical epicardium (10.3°) using grid-tagged MRI [42]. Similarly, Azhari et al. reported that apical endocardial torsion exceeded epicardial torsion (14.5 vs 9.2°) [43]. Buchalter et al. also reported a mean a pical torsion of 12.2° ± 1.3 e ndocardially and 11.2° ± 3 epicardially [44].

Magnetic resonance tissue tagging has r elatively poor spatial resolution and does not account for the 3D motion of the heart owing to its reliance on 2D tissue planes. In addition, tissue-tagging typically requires time-consuming manual involvement to delineate tag lines for analysis. The harmonic phase (HARP) method was develop ed to automatically extract and analyze harmonic images from each tagged MR image and rapidly

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Figure 2. Schematic illustration of torsion (α + β) and circumferential–longitudinal shear (γ) for one point. h is the distance between basal and apical image planes. The arrows indicate the direction of rotation.


Review Yoon & Bella

provide data on regional myocardial function (Figure 3) [38,45]. However, since the HARP method significantly filters the raw MRI data to obtain harmonic images, the spatial resolution of the resultant data is s ignificantly decreased [46].

Phase contrast velocity mapping is another MRI method of measuring regional m yocardial function. In phase contrast velocity mapping, instantaneous myocardial tissue velocities can be measured in successive cardiac phases throughout the cardiac cycle by detecting phase shifts that are linearly proportional to velocity [47]. The succes-sive instantaneous velocities can be used to esti-mate strain, strain rates and torsion [48–50]. One limitation of phase c ontrast velocity mapping is that errors in velocity measurement are propagated cumulatively as each volume of tissue is tracked through time [45]. Another disadvantage is the inability to measure large movements because the tracking algorithms are based on the assumption that there is little spatial variation in the velocity field from one position to the next [51].

Given the poor spatial resolution of tissue-tagged MR and the inability of phase contrast velocity mapping to track tissues inherently, displacement encoding with stimulated ech-oes (DENSE) was developed in 1999 to com-bine the advantages of both of the HARP and phase contrast velocity mapping techniques. In contrast to phase contrast velocity mapping, DENSE modulates each phase according to its position rather than its velocity. Since the phase

measures displacement and not velocity, inherent tissue tracking and pixel-wise spatial resolution is achieved, thus allowing for the measurement of large tissue displacements over long time per iods while maintaining high spatial resolution [52]. The DENSE technique allows for the immediate 2D or 3D encoding of displacement with rapid postprocessing methods [53], and has been used to measure torsion in a murine model [54].

While MRI remains the gold standard in the noninvasive quantitative evaluation of LV tor-sion, it is a technically-involved and time-con-suming process. Furthermore, the high cost of immobile MRI laboratories and patient aversion to claustrophobic milieus limit its widespread use. Thus, other noninvasive strategies have been evaluated as potential alternatives to MRI in the assessment of LV torsion.

Myocardial perfusion imaging & multislice computed tomography In single photon emission computed tomogra-phy (SPECT), myocardial perfusion maps do not account for the counterclockwise apical rotation and clockwise basal rotation of the LV. However, Nichols et al. demonstrated that measurement of LV torsion is possible using gated cardiac SPECT by tracking count minimums in gated perfusion maps to quantify the degree of rotation in 52 patients who had both Tc-99m sestamibi SPECT and cardiac catheterization [55]. However, the relatively poor pixel and time resolution

Figure 3. MRI assessment of left ventricular torsion. (A) Horizontally and vertically tagged MRI in a normal adult. Left: end-diastole; right: end-systole. The tag lines appear slightly sinusoidal, which is optimal for the HARP-tracking procedure. (B) Visualization of tracked points using the extended HARP tracking method. The red lines represent the myocardial contours and the yellow lines mark the tracked points. Taken with permission from [38].



of gated cardiac SPECT significantly limits the acquisition of reliable and precise torsion m easurements using this imaging modality.

Multislice computed tomography (MSCT) is an emerging imaging modality that has the abil-ity to measure ventricular volumes and systolic function [56]. Unfortunately, the limited tempo-ral resol ution is a critical limitation preventing the measure ment of torsion by this modality at this time.

EchocardiographyEchocardiography is a safe, accurate and r eliable noninvasive method to assess cardiac anatomy and function. An index of LV torsion was d eveloped using short-axis Echo scans to track the motion

of anatomic landmarks, such as the papillary muscles or mitral valve (Figure 6) [57,58]. However, this method of measuring torsion is limited to the mid-LV myocardial region and is, therefore, insufficient to assess torsion in nonsymmetrically contracting ventricles as seen in patients with coronary artery disease. Recent advances have provided novel 2D and Doppler techniques to assess LV torsion by echocardiography.

Tissue Doppler imaging: a velocity-based approachThe measurement of LV rotational velocity (LV rot-v) by tissue Doppler imaging (TDI) has recently been validated and established (Figure 4) [59]. Notomi et al. demonstrated that TDI accurately reflects myocardial velocity with better temporal resolution than MRI [60]. TDI is intrinsically a

unidimensional approach, with torsion calculated from the rotation of 2D apical and basal LV short-axis planes obtained by standard 2D echocardiog-raphy. Briefly, LV rotational velocity is estimated

from tissue velocity data taken from four regions of interest (ROI) at both the apical and basal lev-els. The four ROI include septal and lateral sites to measure tangential velocity and anterior and posterior sites to measure radial velocity (Figure 4). Doppler velocity data sets from the ROI are then used to calculate LV rotational velocity. LV rota-tion can be determined by calculating the integral

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Figure 4. Tissue Doppler imaging in the parasternal short-axis view from sample sites in the septal, lateral, anterior and inferior walls in a normal adult.

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Figure 5. Speckle tracking imaging measuring apical rotation in (A) a normal adult and (B) a patient with dilated cardiomyopathy. Peak apical rotation is approximately 12o in the normal patient, and is markedly decreased to approximately 6° in the patient with dilated cardiomyopathy.


Review Yoon & Bella

of LV rotational velocity from end diastole to end systole, which is semi-automatically derived by echocardiography software. LV rotation for the apex and base are then calculated separately:

LV torsion = Apical LV – Basal LV rotation rotation

As with any Doppler technique, the angle-dependency of myocardial tissue velocity data is a limiting factor. This is partially offset by extract-ing tangential velocity from two points rather than one point. In addition, the high-frame rates necessary for TDI also require complex and time-involved processes to accurately and reli-ably estimate LV torsion. Another factor affect-ing TDI-obtained LV torsion measurements is through-plane motion. TDI-obtained rotation underestimates MRI measurements more at the base than at the apex, where through-plane

motion is minimal.

Speckle-tracking imaging: an angle-independent approachWhile TDI is able to characterize global and regional myocardial motion with high temporal resolution, the angle-dependency of Doppler-dependent techniques is an inherent limitation [61]. 2D speckle-tracking imaging (STI), a non-Doppler approach, is independent of both cardiac

translation and angle-dependency (Figure 5) [62]. One of the characteristics of static B-mode

ultrasound imaging is the appearance of speckle patterns within the tissue. These speckles are the result of constructive and destructive ultrasound interference back-scattered from structures smaller than the wavelength of ultrasound [63]. The motion of these speckle patterns closely

correlates with underlying tissue motion when small displacements are involved [64]. When speckle patterns are tracked frame-by-frame through the cardiac cycle, the angular displace-ment of the corresponding tissue can be meas-ured. Images obtained by standard 2D echocar-diography are planar by definition, making it difficult to track the 3D movement of speckle patterns through 2D planes. However, the STI

method is able to use block-matching and auto-correlation search algorithms that require only a statistically meaningful proportion of speck-les to be present on successive frames. Thus, STI provides a 2D approach to measuring tor-sion in contrast to TDI. The potential use of 3D echocardio graphy to track speckle motions more accurately remains a p romising area of investigation.

An advantage of using STI to calculate torsion is the semiautomatic analytical process. Once the appropriate 2D images are selected and myo-cardial borders are delineated, the STI software automatically selects suitable ROIs for tracking, and then computes LV rotation and LV rotation velocity. Averaged (global) LV rotation and LV rotational velocity data are then used to calcu-late LV torsion and LV torsion velocity (Figure 7). The time required to analyze LV torsion for one patient is typically less than 15 min, making this

a tool for both research and potential clinical assessment. In a validation study comparing STI with sonomicrometer measurements in canines,

Helle-Valle et al. found an excellent correlation between both methods for measuring torsion (r = 0.94; p < 0.0001) [65]. Correlation between the two methods was better for apical rotation

than for basal rotation (r = 0.98 vs r = 0.76). They also compared STI to MRI in 29 normal human

θD θS

Figure 6. Twist angle, an index of left ventricular torsion, developed using 2D Echo tracking of the mid-papillary muscles in both (A) diastole and (B) systole. In the parasternal mid-LV short-axis view, a line is drawn from the center of the sector screen to the center of the LV in end-diastole. Another line is drawn through the midpoint of the anterolateral papillary muscle. The angle between the two lines is θD (diastolic angle). The steps are repeated in end-systole to determine θS (systolic angle). Twist angle (θAngle) is the difference between θD and θS. LV: Left ventricle.



subjects and found that the correlation for peak apical rotation was again better than for basal rotation (r = 0.91 vs r = 0.67).

The automated process of ROI selection, although an advantage time-wise, could be a potential source of error in STI. The ROIs encompass all layers of the myocardial wall, preventing the calculation of separate torsion values for the endocardium and epicardium as is possible in MRI. In addition, in STI the speckle patterns in the subendocardium are preferentially tracked since they are more eas-ily identified than subepicardial speckles. As MRI data have demonstrated, subendocardial torsion has greater magnitude than torsion in the subepicardium, and subendocardial fibers untwist later than subepicardial fibers. As a result, the inadvertent preferential selection of subendocardial ROIs in STI may result in both increased LV torsion values as well as altered timing measurements.

Speckle-tracking imaging was developed by General Electric Medical Systems (UK). Velocity vector imaging (VVI), developed by Siemens Medical Solutions (Germany), is an alternative 2D Echo method utilizing similar principles of speckle and endocardial border tracking, and has been validated as an alternative noninvasive method to assess LV torsion [66].

Conclusion & future perspectiveIn summary, accumulating evidence lends support to the theory that the LV myocardium

is composed of an intricate 3D meshwork of myocytes set within a supporting matrix of fibrous tissue, with no structural unit of greater order than the individual myocyte. While the complicated 3D wringing motions

Table 1. Noninvasive methods to assess left ventricular torsion.

Imaging modality Advantage Limitation

MRI tissue tagging Excellent temporal resolution• Relatively poor spatial resolution•Reliance on 2D tissue planes•Time-consuming manual processing, •unless automated harmonic phase software is usedTechnically demanding•Patient claustrophobia•

MRI phase-contrast velocity mapping

Excellent temporal and spatial resolution• Errors in velocity measurement are cumulatively propagated•Inability to inherently track myocardial tissues•Technically demanding•Patient claustrophobia•

MRI displacement encoding with stimulated echoes technique

Inherent tissue tracking with pixel-wise •spatial resolutionAllows for 2D or 3D encoding •of displacementRapid postprocessing methods•

Technically demanding•Patient claustrophobia•

Tissue Doppler imaging echocardiography

Excellent temporal resolution•Rapid acquisition•

Limited ability to obtain 2D planes•Angle-dependency of velocity data•Susceptible to translational motion•

Speckle tracking echocardiography

Excellent temporal resolution•Rapid semiautomated acquisition •and processing

Limited ability to obtain 2D planes•Subendocardial speckles preferentially tracked•Limited ability to measure regional variations within left •ventricular wall (i.e., subendocardium vs subepicardium)

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Figure 7. Schematic illustration of LV torsion velocity measured by speckle-tracking echocardiography in a normal adult. (1) During torsion, there is an initial positive torsion velocity peak in early systole. (2) This is followed by the peak systolic torsional velocity, a second positive velocity peak that occurs in late systole. (3) Peak untwisting velocity occurs at the time of mitral valve opening. The two other smaller negative velocity peaks correspond to the early (4) and late (5) filling phases of diastole. AVC: Aortic valve closing; AVO: Aortic valve opening; MVC: Mitral valve closing; MVO: Mitral valve opening.


Review Yoon & Bella

involved in torsion are difficult to quantify, new noninvasive techniques have been evalu-ated as p otential options in the noninvasive assessment of LV t orsion. Magnetic resonance tissue tagging with dynamic MRI remains the gold standard for the noninvasive quantitative evaluation of cardiac mechanical function with high spatial and temporal resolution. However, TDI and STI have recently been shown to be

sufficiently accurate and reliable alternatives. Awareness of the a dvantages and disadvan-tages of these new options in the noninvasive evaluation of LV t orsion will allow its further use (Table 1). While the p otential applications of these t echniques to assess LV torsion appear boundless, much further work is needed for the validation of LV torsion as a possible p redictor of clinical prognosis.

Executive summary

IntroductionUnderstanding torsion mechanics and the ability to measure torsion are critical for enhancing our understanding of congestive heart n

failure and other diseases of myocardial function.

Mechanics of left ventricular torsionLeft ventricular (LV) torsion occurs because myocardial fibers are structured in a helical orientation across the LV wall. n

The myocardium and its supporting fibrous structure are a spatially netted mesh consisting of a continuous 3D syncytium of n

interlacing myocytes.

When isovolumic contraction (IVC) begins, the apex transiently rotates clockwise as the right-handed subendocardial myofibers shorten.n

As systole continues, the left-handed subepicardial myofibers begin to predominate, and apical rotation reverses and becomesn

counterclockwise for the duration of systole, which is the primary contributor to global systolic LV torsion.

The LV base rotates in the opposite direction with significantly decreased magnitude in comparison. n

When IVC begins, the base undergoesn an initial, brief, counterclockwise rotation due to the subendocardial fibers that is then followed by a longer clockwise rotation as the subepicardal myofiber forces predominate.

Magnetic resonance imagingMagnetic resonance tissue tagging with dynamicn MRI is the gold standard for the noninvasive quantitative evaluation of cardiac mechanical function.

Phase contrast velocity mapping measures instantaneous myocardial tissue velocities by detecting phase shifts that are linearly n

proportional to velocity.

Displacement encoding with stimulated echoes was developed to combine the advantages of both tissue tagging and phase contrast n

velocity mapping.

MRI is a technically involving, time-consuming and costly process, and patient aversion to claustrophobic milieus limits its widespread use.n

Myocardial perfusion imagingMeasurement of LV torsion is possible using ECG-gated single photon emission computed tomography (SPECT).n

The relatively poor pixel and time resolution of gated cardiac SPECT significantly limits the acquisition of reliable and precise LV torsion n

measurements using this imaging modality.

Multislice computed tomographyMultislice computed tomography (MSCT) is an emerging imaging modality that has the ability to measure ventricular volumes and n

systolic function.

However, the temporal resolution is not sufficiently advanced to allow the measurement of torsion at this time.n

2D echocardiographyEchocardiography is a safe, accurate and reliable noninvasive method to assess cardiac anatomy and function. n

An index of LV torsion was developed using short-axis Echo scans to track the motionn of anatomic landmarks, such as the papillary muscles or mitral valve.

This method of measuring torsion is limited to the mid-LV myocardial region and is, therefore, insufficient to assess torsion in n

nonsymmetrically contracting ventricles as seen in patients with coronary artery disease.

Tissue Doppler imagingThe measurement of LV rotational velocity by tissue Doppler imagingn (TDI) has recently been validated and established.

TDI accurately reflects myocardial velocityn with better temporal resolution than MRI and is obtained by standard 2D echocardiography.

Limitations of TDI for the assessment of LV torsion include angle-dependency of myocardial tissue velocity, high-frame rate image n

acquisition and through-plane LV motion.

Speckle-tracking echocardiographyOne of the characteristics of static B-mode ultrasoundn imaging is the appearance of speckle patterns within the tissue, which, when tracked frame-by-frame through the cardiac cycle, can measure the angular displacement of the corresponding tissue.

The speckle-tracking imagingn method calculated LV torsion through a semiautomatic analytical process that uses block-matching and autocorrelation search algorithms that require only a statistically meaningful proportion of speckles to be present on successive frames.



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Financial & competing interests disclosureThe authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials dis-cussed in the m anuscript. This includes employ-ment, consultancies, honoraria, stock ownership or options, expert t estimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the p roduction of this manuscript.


Review Yoon & Bella

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Validates velocity vector imaging as an n

echocardiographic modality to measure torsion.

WebsiteMorbidity & Mortality Report: 2007 Chart 101.

Book on Cardiovascular, Lung, and Blood Diseases, June 2007. www:nhlbi.nih.gov/resources/docs/07-chtbk.pdf

AffiliationsAndrew J Yoon n

Albert Einstein College of Medicine, The Bronx, NY, USA and, Bronx-Lebanon Hospital Center, Division of Cardiology, The Bronx, NY 10467, USA Tel.: +1 718 518 5222 Fax: +1 718 518 5545 [email protected]

Jonathan N Bella n

Albert Einstein College of Medicine, The Bronx, NY, USA and, Bronx-Lebanon Hospital Center, Division of Cardiology, 1650 Grand Concourse, 12th Floor, The Bronx, NY 10467, USA Tel: +1 718 518 5222 Fax: +1 718 518 5545 [email protected]

New options in noninvasive assessment of left ventricular torsion

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