Doppler echocardiography and myocardial dyssynchrony: a practical update of old and new ultrasound technologies
© Galderisi et al; licensee BioMed Central Ltd. 2007
Received: 09 August 2007
Accepted: 06 September 2007
Published: 06 September 2007
Morbidity and mortality rates are higher in patients with severe left ventricular (LV) systolic dysfunction and ECG-derived prolonged QRS interval than in those with normal QRS duration. QRS duration is currently used on the grounds that it reflects the presence of ventricular dyssynchrony. However, 30–40% of patients selected on the basis of a prolonged QRS do not receive benefit by cardiac resynchronization therapy (CRT) since they do not show any significant inverse LV remodeling and QRS duration does not accurately distinguish responders to CRT. Consequently, mechanical dyssynchrony (particularly intra-ventricular dyssynchrony) seems to be much more important than electrical dyssinchrony. Pre- and post-echocardiographic assessment should require the combination of conventional and specific applications ranging from M-mode and pulsed/continuous Doppler, to pulsed Tissue Doppler, the off-line analysis of colour Tissue Velocity Imaging, Strain Rate Imaging, and real time three-dimensional reconstruction However, there is not no consensus about the best approach and the best ultrasound parameter for selecting candidates to CRT and ECG representation of abnormal cardiac conduction still remains as the main criterion in guidelines. This review is a practical update of ultrasound methods and measurements of atrio-ventricular, inter-ventricular and intra-ventricular dyssynchrony and describes experiences which used either conventional Doppler echocardiography and more advanced techniques. By these experiences, the global amount of LV dyssynchrony seems to be critical: the greater intra-ventricular dyssynchrony, the higher the possibility of significant LV inverse remodeling. After CRT, it is necessary also to evaluate the optimal atrio-ventricular delay and ventricular-ventricular delay setting that maximizes LV systolic function.
Morbidity and mortality rates are higher in patients with severe left ventricular (LV) systolic dysfunction and ECG-derived prolonged QRS interval than in those with normal QRS duration . Bi-Ventricular Pacing (BIVP) and Cardiac Resynchronization Therapy (CRT) have become additional treatment aimed to synchronizing biventricular activation and contraction in patients with severe chronic heart failure (CHF) associated with interventricular conduction delay. CRT is effective in improving functional capacity and degree of secondary mitral regurgitation [2–4] and, above all, in reducing the mortality in cases of refractory CHF. NYHA classes III-IV, a LV ejection fraction (EF) of ≤ 35%, a LV end-diastolic diameter > 30 mm/m2 and a surface ECG derived QRS duration > 120 ms, together with a need for maximal pharmacological therapy, are considered from guidelines to select patients for CRT .
QRS duration is currently used on the grounds that it reflects the presence of ventricular dyssynchrony. However, 30–40% of patients selected on the basis of a prolonged QRS do not receive benefit by CRT since they do not show any significant inverse LV remodeling (a ≥ 15% reduction of LV end-systolic volume six months after device implantation) [6, 7]. Furthermore, QRS duration does not accurately distinguish responders to CRT . Although factors responsible for the absence of favourable response may be lead dislodgement or inappropriate location of LV lead, mechanical dyssynchrony (particularly intra-ventricular dyssynchrony) seems to be much more important than electrical dyssinchrony, and Doppler echocardiography should be widely used before and after implantation of a CRT device [9, 10].
Pre- and post-echocardiographic assessment includes conventional and/or specific applications ranging from M-mode and pulsed/continuous Doppler, to pulsed Tissue Doppler, the off-line analysis of colour Tissue Doppler, Strain Rate Imaging (SRI), and real time 3-D reconstruction [9–13]. The different modalities of the transthoracic ultrasound approach are able to identify the 3 different kinds of mechanical dyssynchrony: 1. Atrio-ventricular dyssinchrony, 2. Inter-ventricular dyssynchrony, 3. Intra-ventricular dyssynchrony.
1. Atrio-ventricular dyssynchrony
2. Inter-ventricular dyssynchrony
Alternatively, pulsed Tissue Doppler can be used to determine IVMD by measuring the time from QRS onset to the peak myocardial systolic velocities (Sm) of the RV free wall (tricuspid annulus) versus the same time of LV lateral mitral annulus (apical 4-chamber view) .
It is important to state that intraventricular dyssynchrony does not correlate with reverse LV remodeling after CRT, even when data from patients with and without coronary artery disease are evaluated separately [17–19].
3. Intra-ventricular mechanical dyssynchrony
Intra-ventricular dyssynchrony is characterized by either premature or late contraction of LV wall segments due to delayed electrical conduction . It can be identified by means of simple M-mode, pulsed Tissue Doppler, or, better, by colour Tissue Velocity Imaging (TVI), SRI and 3-D echocardiography.
Pulsed (PW) Tissue Doppler
Extensions of these method have been proposed by recording 2D imaging in the 4- 2- and 5-chamber apical views, in order to place PW Tissue Doppler sample volume in a specific myocardial segment and to measure Q to peak Sm and/or Q to Sm onset in various LV segments. The number of LV segments to be evaluated include mainly a 12-segment model (LV basal and middle segments in 4-, 2- and 5-chamber views) whereas LV apical segments are not considered reliable because of the basal-apical myocardial gradient own of Tissue Doppler. Technical refinements include the need to set the velocity scale of PW Tissue Doppler to display spectral velocities of 20 cm/s above and below the zero baseline because myocardial motion is characterized by low velocities. Spectral Doppler gain must be usually reduced, wall filters adjusted and spectral velocities recorded at sweep speed of 100 mm/s (during held respiratory expiration), in order to obtain the clearest delineation of Sm onset and peak. Electromechanical delay has to be averaged over at least 3 cardiac cycles. The main limitation of PW Tissue Doppler corresponds to the impossibility of measuring the time intervals of different segments during the same cardiac cycle. It is also necessary to take into account that the Sm recorded in apical views reflects LV longitudinal shortening and not circumferential contraction.
Colour Tissue Doppler
TSI is an implementation of Ts method. It displays Ts in multiple LV segments by colour coding wall motion green (corresponding to early systolic contraction) or red, which corresponds to delayed contraction (sensitivity = 87%, specificity = 81% and accuracy = 84% at a cut-off value of 34.4 ms in 56 patients with severe heart failure) .
It is important to point out that all colour Tissue Doppler derived techniques require high 2-D frames rates (>90 frames/s)  and that 2-D image should be optimized with a narrow sector width that includes the basal and middle segments of opposite LV walls and depth setting that include left ventricle, mitral annulus and the base of the left atrium . Colour Tissue Doppler gain has to be adjusted in order to display myocardial motion clearly. At least 3 cardiac cycles should be recorded during held respiration. Before performing measurements, aortic valve opening (= AVO) and AVC must be marked by means of a previous recorded PW Doppler of LV outflow tract, in order to avoid confusion between systolic (normal) and post-systolic (abnormal) contraction .
The 2-D strain (speckle tracking) technique has very recently been used to assess radial dyssynchrony before/after CRT. Speckle tracking has been applied to routine mid-ventricular short-axis images to calculate radial strain from multiple circumferential points averaged to six standard segments and dyssynchrony from timing of peak radial strain has been demonstrated to be correlated with Tissue Doppler measures in 47 subjects . A time difference ≥ 130 ms between the radial strain peak of LV posterior wall and anterior septum has shown to be highly predictive of an improved EF during follow-up, with 89% sensitivity and 83% specificity .
What to measure before and after CRT
Main ultrasound techniques, parameters and reference values for detection of intra-ventricular dyssynchrony and prediction of LV reverse remodeling.
Pitzalis et al, J Am Coll Cardiol 2002
> 130 ms
M-mode and PW Doppler
Sassone et al, Am J Cardiol 2007
PW Tissue Doppler
Diff. of Ts between LV segments
Bax JJ et al, J Am Coll Cardiol 2004
> 65 ms
Yu et al, Am J Cardiol 2003
> 32.6 ms
Yu et al, J Am Coll Cardiol 2005
> 34.4 ms
Mele et al, Eur Heart J 2006
> 60 ms
Porciani MC et al, Eur Heart J 2006
> 760 ms
2D radial strain
Time diff. in peak septal wall-to-posterior wall strain
Suffoletto et al, Circulation 2006
≥ 130 ms
Van der Veire NR et al, Am J Cardiol 2007
≥ 35.8 *
Sensitivity, specificity and accuracy, and confirmatory or conflicting data of the main ultrasound techniques presented in Table 1.
M-mode and PW Doppler
Diff. of Ts between LV segments
2D radial strain
Time diff. peak septal-to-posterior wall strain
Although several studies have demonstrated the superiority of ultrasound over QRS duration to assess LV dyssynchrony, there are no conclusive data on prediction of CRT response either using conventional or more advanced echocardiographic technologies. The Cardiac Resynchronization-Heart Failure (CARE-HF) study is the only large randomized and controlled trial that required direct, ultrasound measurement of cardiac dyssynchrony in a subset of patients with mild to moderate QRS enlargement (= 120–149 ms) (5). However, in the CARE-HF study only 92 patients (11%) underwent CRT based on Doppler echocardiographic indexes of myocardial dyssynchrony. Of consequence, the results cannot be considered exhaustive. It is not unexpected, therefore, that the ECG representation of abnormal cardiac conduction still remains as the main criterion to identify patients with dyssynchronous ventricular contraction. Accordingly, no consensus definition of cardiac dyssynchrony exists as yet from the main cardiologic associations [44–47], although several of the mentioned echocardiographic measures appear very promising
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