Tissue Doppler Echocardiography

Tissue Doppler Imaging

Tissue Doppler Imaging (TDI) is a robust and highly reproducible echocardiographic modality that was first described by Isaaz et al in 1989. This modality uses Doppler principles to measure velocity, displacement, event timing or deformation of the myocardium by recording the low Doppler shift frequencies of high energy by the ventricular wall motion that are usually filtered out (high pass filter) in spectral Doppler studies. TDI provides real-time quantification of the myocardial motion throughout the cardiac cycle. TDI can measure circumferential and longitudinal intrinsic myocardial motion velocity in various short-axis and long-axis views. Therefore, it can be used for evaluating both systolic and diastolic function in dogs and cats. Myocardial structures move in the velocity range of a few cm/s to > 20 cm /s. A major disadvantage of TDI is the angle dependency. Furthermore, we recommend high frame rates (>150 fps) for image acquisition with excellent temporal resolution.

TDI can be performed in pulsed-wave and color modes TDI.

Pulsed-wave TDI provides information on circumferential and longitudinal myocardial movements with high temporal resolution. PW TDI measures peak longitudinal myocardial velocity ”real-time” from a single segment (placement of the sample volume). This method allows for precise velocity quantification.

An apical 4CH view showing spectral tissue velocity curves from the mitral annulus in the septum from a young Siberian forest cat. The curves show multiple heartbeats

Color TDI (C-TDI) allows superimposing wall motion velocity on two-dimensional echocardiographic imaging by velocity color coding with excellent spatial resolution. C-TDI shows all velocity data at once and gives the best overall picture. Furthermore, C-TDI allows off-line analysis of the transverse and longitudinal myocardial motions. This method can interrogate velocities from multiple sites simultaneously (mean peak velocities approximately 25% lower than pulsed TDI).

Color TDI derived tissue velocity curves from the mitral annulus (septum and lateral). The curves show velocities towards the probe (positive velocity) in systole, and away from the probe (negative velocities) in diastole. The cardiac cycle is presented by three main waveforms - one positive systolic wave (S´, as the heart base, moves towards the apex in systole) and 2 negative diastolic peaks (E´ represent a passive filling curve and A´ represent the atrial contraction curve, as heart base ascends away from the apex).

Different cTDI methods

  • TVI, Strain, Strain rate, displacement, m-mode
    • Tissue Velocity Imaging analyzes myocardial velocities within a color sector. Myocardium moving towards the transducer is colored red and myocardium moving away from the transducer is colored blue. From heart base to apex a velocity gradient can be demonstrated by placing multiple sample volumes. The apex of the heart is almost stationary.
    • Displacement or tissue tracking is an easy and robust parameter that can be used in the assessment of the longitudinal function. This TDI technique quantifies only the axial components of velocity, along the direction of the ultrasound wave.
    • Strain is a measure of myocardial deformation. Strain is an index of contractile capacity intrinsic to the myocardium which is derived from the myocardial velocity gradient. This signal is strongly subjected noise problems which make interpretation difficult and hardly reproducible.
    • Strain rate is the difference in velocity measured between 2 points along the myocardial wall normalized to the distance between the 2 points.
    • Color M-mode affords a much higher temporal resolution compared to 2D TDI imaging. In this mode, myocardial velocities are analyzed along a single scan line.
A left apical 4 CH view showing a TDI strain rate curve from a healthy Cavalier King Charles Spaniels. Strain implies regional myocardial deformation and the rate at which this change occurs is called strain rate. The first report of echocardiographic strain (strain rate) was derived from TDI velocity data using the Doppler equation to convert ultrasound frequency shifts to velocity information along the scan lines. This TDI technique is highly sensitive to noise and has a low reproducibility.

TDI indications

  • Assessment of the myocardial function in various heart diseases in dogs and cats
    • Systolic dysfunction
    • Diastolic dysfunction
      • E´/A´< 1
Color tissue Doppler imaging from the apical 4CH view sampling from the septal mitral annulus. Note the E´/A´ratio < 1 indicating a mild impaired diastolic dysfunction. The reduced E’ velocity is a measure of LV relaxation in early diastole and is relatively load independent. A´ velocity is a marker of global atrial function.

  • Longitudinal displacement (systolic parameter)
    • Tissue tracking (TT) is an offline robust color TDI technique that can be used for a rapid assessment of the myocardial longitudinal displacement. TT displays the integral of tissue velocity as the distance of motion along the axis
An apical 4CH view displaying longitudinal displacement curves of the mitral annular plane from a young Siberian forrest cat. Note that the maximal systolic displacement of +4 mm happens after the closure of the aortic valve. Normal displacement in cats is +4 mm to + 6 mm.

  •  Dyssynchrony
    • Tissue Synchronisation Imaging is a new technique to assess left ventricular dyssynchrony. TSI uses a signal‐processing algorithm of tissue Doppler data to automatically detect peak positive velocities.
TSI color-codes for areas of maximal delay in myocardial velocities. This figure from a healthy Ragdoll cat shows no delay between septal and lateral peak velocities in the left ventricle (Septal Lat delay = 0 ms).

Tissue tracking image from a young Persian cat with LV dyssynchrony. A delay in mitral annulussept (yellow) displacement to mitral annuluslat (indigo) displacement of > 60 ms is seen. In healthy cat a delay < 15 ms is expected.

  • Post systolic shortening
    •  Definition of PSS is a late systolic myocardial shortening appearing after aortic valve closure may be associated with myocardial ischemia.
A color TVI image obtained from an apical 4CH view sampling the septal and lateral mitral annulus. Note the positive curve after closure of the aortic valve representing a post systolic shortening (PSS = myocardial shortening after end-systole) of the left ventricle. PSS can be caused by delayed electrical activation of the myocardium often associated with ischemia.

  • E/E´- correlates with the left ventricular filling pressure
    • A ratio of mitral peak velocity of early filling (E) to early diastolic mitral annular velocity (E´) – (E/E`)

  • Event timing
    • Tissue Doppler imaging supplemented by anatomical M-mode images can be used to evaluate the mitral- and aortic valve movements. This allows a reliable analysis of the rapid isovolumic myocardial movements because IVCT, IVRT and LVET can be measured from a single cardiac cycle with the use of a single line through the anterior mitral leaflets (figure)
Myocardial performance index can be derived using curved anatomical m-mode modality on the mitral valve movement. A perpendicular line is drawn through the anterior mitral leaflet. The positions of mitral valve opening and closure together with aortic valve opening can be identified on the above figure. Aorta valve opening is the beginning of the red area just after the QRS-complex and aorta valve closure is identified as the end of the thin blue line after ejection (end systole). Myocardial performance index (TEI) is the sum of isovolumic contraction time (IVCT) and isovolumic relaxation time (IVRT), divided by ejection time (ET). TDI-MPI was derived as (a-b)/b, where ‘a’ is the measured duration from mitral-closure-to-opening and ‘b’ is the aortic flow ejection time.

How to perform tissue velocity imaging (TVI)

  • Optimize images/loops (sample rate > 160/min, improve lateral resolution (narrow image width), parallel with ultrasound beam (< 20 degree), velocity scale adjusted to avoid aliasing 8-15 cm/s)
  • To measure myocardial and annular velocities
    • Transducer position left apical 4CH & 2 CH view
    • A small sample volume – 3x1 mm (cats) is placed in the ventricular myocardium adjacent to the mitral annulus (septum and posterior wall (LV)
    • Low gain and filter settings

The cardiac cycle is presented by three main waveforms - one positive systolic wave (S´, as heart base, moves towards the apex in systole) and 2 negative diastolic peaks (E´ and A´, as heart base ascends away from the apex).

The cardiac cycle is presented by three main waveforms - one positive systolic wave (S´, as heart base, moves towards the apex in systole) and 2 negative diastolic peaks (E´ and A´, as heart base ascends away from the apex).

Limitations

TDI measurements are affected by translation of the heart, tethering and surrounding myocardial motions. Furthermore, TDI is dependent on the angle between the transducer and the direction of myocardial movement. Strain and Strain rate techniques are very dependent on observer experience and excellent data acquisition.

Authors:

Maiken Thode Bach, DVM, Jakob Willesen, DVM, PhD, Jørgen Koch, DVM, PhD

 

 References

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