Assessment of left ventricular function in horses with aortic regurgitation by 2D speckle tracking.

BACKGROUND: Aortic regurgitation (AR) may lead to left ventricular (LV) dilatation, cardiac arrhythmias and heart failure. Close follow-up of horses with AR is therefore paramount to detect onset of cardiac decompensation. The aim of this study was to examine whether two-dimensional speckle tracking (2DST) can be used to detect altered myocardial function in horses with chronic AR compared to control horses. Speckle tracking was performed on short axis and long axis images of the LV in 29 healthy Warmblood horses and 57 Warmblood horses with AR. Radial, circumferential and longitudinal strain, strain rate and displacement were measured for each segment separately and the average was calculated over all segments. Data generated from the apical segments were not included in the analysis. RESULTS: Radial (SR) and circumferential (SC) strain were significantly higher in horses with moderate AR (average SR 75.5 ± 24.3%, SC 19.3 ± 3.2%) but not in horses with severe AR (SR 65.5 ± 26.2%, SC 16.3 ± 3.5%), compared to control horses (SR 54.5 ± 18.0%, SC 16.8 ± 3.0%). Longitudinal strain did not show significant differences, but longitudinal displacement (DL) was larger in horses with moderate (average DL 29.5 ± 4.1 cm) and severe AR (DL 32.4 ± 6.1 cm) compared to control horses (DL 25.7 ± 4.0 cm), especially in the interventricular septum. Diastolic longitudinal strain rate was lower in early diastole in horses with severe AR (0.93 ± 0.18/s) compared to controls (1.13 ± 0.13/s). CONCLUSIONS: 2DST is able to detect altered myocardial motion in horses with AR, which showed significantly higher radial and circumferential strain. Further research is needed to determine whether these findings contribute to a more accurate diagnosis and prognosis in clinical cases.

How GDPR Enhances Transparency and Fosters Pseudonymisation in Academic Medical Research.

The European General Data Protection Regulation (GDPR) has dotted the i's and crossed the t's in the context of academic medical research. One year into GDPR, it is clear that a change of mind and the uptake of new procedures is required. Research organisations have been looking at the possibility to establish a code-of-conduct, good practices and/or guidelines for researchers that translate GDPR's abstract principles to concrete measures suitable for implementation. We introduce a proposal for the implementation of GDPR in the context of academic research which involves the processing of health related data, as developed by a multidisciplinary team at the University Hospitals Leuven. The proposal is based on three elements, three stages and six specific safeguards. Transparency and pseudonymisation are considered key to find a balance between the need for researchers to collect and analyse personal data and the increasing wish of data subjects for informational control.

Detection of subclinical left ventricular dysfunction by tissue Doppler imaging in horses with aortic regurgitation.

BACKGROUND: Aortic regurgitation (AR) can have an important clinical impact and in some cases leads to left ventricular (LV) failure. Tissue Doppler imaging (TDI) is an echocardiographic technique that has been used in horses to detect LV dysfunction. OBJECTIVES: To examine whether TDI detects changes in radial myocardial wall motion in horses with AR compared with control horses. STUDY DESIGN: Case-control study. METHODS: Echocardiography was performed in 30 healthy Warmblood horses and 34 Warmblood horses with AR, subdivided in groups with mild, moderate or severe AR. TDI measurements were performed on six segments of the short-axis images of the LV myocardial wall. Myocardial wall motion was evaluated by measuring velocity and deformation during isovolumetric contraction, systole, early and late diastole. Timing of different events was also measured. RESULTS: In most segments, a significantly higher systolic myocardial velocity was found in horses with AR compared with controls. Horses with AR also had higher late diastolic velocity, although the difference was not significant in all segments. TDI measurement of timing intervals demonstrated less difference between groups. MAIN LIMITATIONS: There was a significant difference in age between the control group and horses with AR, which may confound the results. The assessment of AR severity was based on subjective criteria as there is no gold standard. CONCLUSIONS: TDI showed significant differences in radial systolic and late diastolic myocardial velocity in horses with AR. This could indicate an altered LV function in these horses, but further research is needed to investigate the prognostic value of these measurements.

Assessment of strain and strain rate by two-dimensional speckle tracking in mice: comparison with tissue Doppler echocardiography and conductance catheter measurements.

AIMS: This study was designed in order to compare the strain and strain rate deformation parameters assessed by speckle tracking imaging (STI) with those of tissue Doppler imaging (TDI) and conductance catheter measurements in chronic murine models of left ventricular (LV) dysfunction. METHODS AND RESULTS: Twenty-four male C57BL/6J mice were assigned to wild-type (n = 8), myocardial infarction (n = 8) and transaortic constriction (n = 8) groups. Echocardiographic and conductance measurements were simultaneously performed at rest and during dobutamine infusion (5 µg/kg/min) in all animals 10 weeks post-surgery. The LV circumferential strain (Scirc) and the strain rate (SRcirc) were derived from grey scale and tissue Doppler data at frame rates of 224 and 375 Hz, respectively. Scirc and SRcirc by TDI/STI correlated well with the preload recruitable stroke work (PRSW) (r = -0.64 and -0.71 for TDI; r = -0.46 and -0.50 for STI, P < 0.05). Both modalities showed a good agreement with respect to Scirc and SRcirc (r = 0.60 and r = 0.63, P < 0.05). During stress, however, TDI-estimated Scirc and SRcirc values were predominantly higher than those measured by STI (P < 0.05). The similarity of Scirc and SRcirc measurements with respect to the STI/TDI data was examined by the Bland-Altman analysis. CONCLUSION: In mice, the STI- and TDI-derived strain and strain rate deformation parameters relate closely to intrinsic myocardial function. At low heart rate-to-frame rate ratios (HR/FR), both STI and TDI are equally acceptable for assessing the LV function non-invasively in these animals. At HR/FR (e.g. dobutamine challenge), however, these methods cannot be used interchangeably as STI underestimates S and SR at high values.

The relative value of strain and strain rate for defining intrinsic myocardial function.

It is well accepted that strain and strain rate deformation parameters are not only a measure of intrinsic myocardial contractility but are also influenced by changes in cardiac load and structure. To date, no information is available on the relative importance of these confounders. This study was designed to investigate how strain and strain rate, measured by Doppler echocardiography, relate to the individual factors that determine cardiac performance. Echocardiographic and conductance measurements were simultaneously performed in mice in which individual determinants of cardiac performance were mechanically and/or pharmacologically modulated. A multivariable analysis was performed with radial and circumferential strains and peak systolic radial and circumferential strain rates as dependent parameters and preload recruitable stroke work (PRSW), arterial elastance (E(a)), end-diastolic pressure, and left ventricular myocardial volume (LVMV) as independent factors representing myocardial contractility, afterload, preload, and myocardial volume, respectively. Radial strain was most influenced by E(a) (ß = -0.58, R(2) = 0.34), whereas circumferential strain was strongly associated with E(a) and moderately with LVMV (ß = 0.79 and -0.52, respectively, R(2) = 0.54). Radial strain rate was related to both PRSW and LVMV (ß = 0.79 and -0.62, respectively, R(2) = 0.50), whereas circumferential strain rate showed a prominent correlation only with PRSW (ß = -0.61, R(2) = 0.51). In conclusion, strain (both radial and circumferential) is not a good surrogate measure of intrinsic myocardial contractility unless the strong confounding influence of afterload is considered. Strain rate is a more robust measure of contractility that is less influenced by changes in cardiac load and structure. Thus, peak systolic strain rate is the more relevant parameter to assess myocardial contractile function noninvasively.

Effect of endurance training on blood pressure regulation, biomarkers and the heart in subjects at a higher age.

We reported previously that two otherwise identical training programs at lower (LI) and higher intensity (HI) similarly reduced resting systolic blood pressure (BP) by approximately 4-6 mmHg. Here, we determined the effects of both programs on BP-regulating mechanisms, on biomarkers of systemic inflammation and prothrombotic state and on the heart. In this cross-over study (3 × 10 weeks), healthy participants exercised three times 1 h/week at, respectively, 33% and 66% of the heart rate (HR) reserve, in a random order, with a sedentary period in between. Measurements, performed at baseline and at the end of each period, involved blood sampling, HR variability, systolic BP variability (SBPV) and cardiac magnetic resonance imaging. Thirty-nine participants (18 men; mean age 59 years) completed the study. Responses were not different between both programs (P>0.05). Pooled data from LI and HI showed a reduction in HR (-4.3 ± 8.1%) and an increase in stroke volume (+11 ± 23.1%). No significant effect was seen on SBPV, plasma renin activity, basal nitric oxide and left ventricular mass. Our results suggest that the BP reduction observed appears to be due to a decrease in systemic vascular resistance; training intensity does not significantly affect the results on mechanisms, biomarkers and the heart.

Influence of left-ventricular shape on passive filling properties and end-diastolic fiber stress and strain.

Passive filling is a major determinant for the pump performance of the left ventricle and is determined by the filling pressure and the ventricular compliance. In the quantification of the passive mechanical behaviour of the left ventricle and its compliance, focus has been mainly on fiber orientation and constitutive parameters. Although it has been shown that the left-ventricular shape plays an important role in cardiac (patho-)physiology, the dependency on left-ventricular shape has never been studied in detail. Therefore, we have quantified the influence of left-ventricular shape on the overall compliance and the intramyocardial distribution of passive fiber stress and strain during the passive filling period. Hereto, fiber stress and strain were calculated in a finite element analysis of passive inflation of left ventricles with different shapes, ranging from an elongated ellipsoid to a sphere, but keeping the initial cavity volume constant. For each shape, the wall volume was varied to obtain ventricles with different wall thickness. The passive myocardium was described by an incompressible hyperelastic material law with transverse isotropic symmetry along the muscle fiber directions. A realistic transmural distribution in fiber orientation was assumed. We found that compliance was not altered substantially, but the transmural distribution of both passive fiber stress and strain was highly dependent on regional wall curvature and thickness. A low curvature wall was characterized by a maximum in the transmural fiber stress and strain in the mid-wall region, while a steep subendocardial transmural gradient was present in a high curvature wall. The transmural fiber stress and strain gradients in a low and high curvature wall were, respectively, flattened and steepened by an increase in wall thickness.

Deformation imaging describes right ventricular function better than longitudinal displacement of the tricuspid ring.

AIMS: To quantify right ventricular (RV) function in patients with chronic thromboembolic pulmonary hypertension (CTEPH) before and after pulmonary endarterectomy (PEA). METHODS: Out of 33 patients, 16 were evaluated clinically and with echocardiography (conventional and myocardial deformation parameters) before PEA (preop) and at 1 week, 1 month, 3 months and 6 months after PEA. RV fractional area change (RVFAC), tricuspid annular plane systolic excursion (TAPSE) as well as mid-apical and basal peak ejection strain (S) and strain rate (SR) of the RV free wall were measured. Left ventricular (LV) apical lateral wall motion was regarded as indicating changes in overall heart rocking motion (RM). Heart catheterisation was performed before, within 1 week and at 6 months after PEA. RESULTS: Clinical and haemodynamic parameters improved significantly after PEA. This correlated with the improvement in RVFAC, S and SR. TAPSE, on the other hand, showed a biphasic response (14.5 (4) mm preop, 8.5 (2.7) mm at 1 week and 11 (1.5) mm at 6 months). Changes in LV apical motion explain this finding. At baseline, TAPSE was enhanced by rocking motion of the heart as a result of the failing RV. Unloading the RV by PEA normalised the rocking motion and TAPSE decreased. CONCLUSIONS: RV function of CTEPH patients improves steadily after PEA. Unlike S, SR and RVFAC, this is not reflected by TAPSE because of postoperative changes in overall heart motion. Motion independent deformation parameters (S, SR) appear superior in the accurate description of regional RV function.

Echocardiographic assessment of left ventricular untwist rate: comparison of tissue Doppler and speckle tracking methodologies.

AIMS: The study was designed to test the influence of the temporal resolution, at which tissue Doppler imaging (TDI) and speckle tracking imaging (STI) operate, on the accurate assessment of left ventricular (LV) untwist rate (UR). METHODS AND RESULTS: Echo imaging and invasive LV pressure measurements were performed during right atrial (RA) pacing and dobutamine challenge in eight pigs. LV torsion and torsional rate profiles were analysed from grey scale and tissue Doppler data (apical and basal short axis) at frame rates of 82 +/- 17 and 183 +/- 14 Hz, respectively. Temporal subsampling of TDI data sets was performed at 82 +/- 6 Hz in order to mimic the mean temporal resolution of STI and the LV torsional curves were again extracted. At rest, LV UR values were comparable for both imaging techniques. However, during dobutamine stimulation, TDI estimated peak UR was predominantly higher than UR measured by STI (-112.1 +/- 64.5 degrees /s vs. -75.5 +/- 31.4 degrees /s, P < 0.05). The similarity of LV UR measurements with respect to the STI/TDI data was examined by a Bland-Altman analysis. CONCLUSION: Although both methods regarding LV UR correlated well, these methods cannot be interchanged. STI showed a bias to underestimate UR at high values.

Quantitative dobutamine stress echocardiography for the early detection of cardiac allograft vasculopathy in heart transplant recipients.

BACKGROUND: A non-invasive method to detect the presence of cardiac allograft vasculopathy (CAV) remains an important goal in clinical cardiology. OBJECTIVE: To assess the value of quantitative dobutamine stress echocardiography (DSE) for the early detection of CAV. METHODS: 42 heart transplant recipients underwent DSE with acquisition of both conventional two-dimensional and colour tissue Doppler data. All studies were analysed conventionally and quantitatively using regional deformation parameters-that is, peak systolic longitudinal strain (in(peak sys)), strain rate (SR(peak sys)) and post-systolic strain index. Myocardial segments were classified as normal, mildly abnormal or severely abnormal based on correlative angiographic findings. RESULTS: At baseline, in(peak sys) was significantly lower in severely abnormal segments than in normal ones. However, at peak stress, in(peak sys) was able to separate three groups of segments. Receiver operating characteristic analysis showed an SR(peak sys) response of <0.5/s to identify patients with CAV with a sensitivity of 88%, specificity of 85% and a negative predictive value of 92%. CONCLUSION: Regional myocardial function is impaired in heart transplant recipients with CAV even when the disease is considered to be non-significant on conventional angiography. Systolic deformation parameters tended to detect the existence of CAV more accurately than conventional visual DSE assessment. Strain rate imaging during stress can therefore safely be used as a non-invasive screening test for detecting CAV in heart transplant recipients.

Feasibility of strain and strain rate imaging for the assessment of regional left atrial deformation: a study in normal subjects.

AIMS: There are no data on the use of Myocardial Velocity Imaging (MVI) to study the left atrium (LA) wall deformation. The aims of this study were to assess the feasibility of measuring regional longitudinal strain/strain rate (epsilon/SR) profiles in the LA wall, to define the normal values and to validate these measurements. METHODS AND RESULTS: MVI data were recorded in 40 healthy young individuals using a GE Vivid7 for the lateral, anterior and inferior LA walls. The peak epsilon/SR values and total epsilon values during the contractile, reservoir and conduit LA phases were measured. For the LA lateral wall, the total epsilon values were correlated with the LA volumetric indicators (LA active emptying fraction: LA AEF; LA expansion index: LA EI; and LA passive emptying fraction: LA PEF). The correlations were significant for all three periods: contractile (total epsilon vs. LA AEF, r=-0.78, P<0.001), reservoir (total epsilon vs. LA EI, r=0.43, P<0.01) and conduit (total epsilon vs. LA PEF, r=-0.46, P<0.005). CONCLUSION: SR/epsilon imaging for the quantification of longitudinal myocardial LA deformation was shown to be feasible and the normal values were reported and validated. These data may improve the understanding of the LA pathophysiology.

Quantifying myocardial deformation throughout the cardiac cycle: a comparison of ultrasound strain rate, grey-scale M-mode and magnetic resonance imaging.

Strain rate imaging (SRI) is a new ultrasound (US) approach to the quantification of regional myocardial deformation. It previously has been validated in vitro and in vivo against other imaging techniques. However, in all such studies, only peak strain values were compared, and the temporal evolution of the strain curve was not studied. Yet, it is the temporal evolution of the strain curves that contains the more important clinical information (e.g., asynchrony, viability, etc). Thus, the aim of this study was to compare the evolution of strain during the complete cardiac cycle as measured by US SRI, US grey-scale M-mode and magnetic resonance imaging (MRI). In 10 healthy volunteers and 20 patients with chronic ischaemic heart disease, radial deformation of the inferolateral segment of the left ventricle was measured by US SRI, US M-mode and MRI. The correspondence of the temporal characteristics of these strain curves were compared by defining an intraclass correlation coefficient (ICC). In healthy volunteers, an overall good agreement (mean ICC: 0.75 and 0.63 for systole and diastole) was found between the different methods. However, in patients with abnormal segmental deformation and low peak strain values, the agreement was less (mean ICC: 0.42 and 0.32), but remained within acceptable limits for clinical decision making. Myocardial deformation measurements using SRI correlated well with MRI and US M-mode measurements throughout the complete cardiac cycle.

Role of magnetic resonance imaging in coronary heart disease.

Coronary heart disease (CHD) is the number one cause of morbidity and mortality in the developed countries. CHD involves a very broad clinical spectrum, ranging from stable angina pectoris to sudden cardiac death. Despite a huge improvement in treatment in the last 3 decades, significantly reducing the death rate, the prevalence of CHD will increase in the coming years due to an improved survival after a first acute myocardial infarction and due to an overall increased longevity, fueled by an epidemic of type-2 diabetes and obesity. This increased prevalence of cardiovascular disease will greatly impact the cost of health care. Moreover, new but often expensive imaging technologies are appealing for more accurate clinical and preclinical detection of CHD. Among these techniques, magnetic resonance imaging (MRI) is certainly one of the most promising. In this review we would like to highlight its potential in diagnosing CHD, against the background of a steadily increasing cost in health care and the need to choose the most cost-effective technique.

Quantification of the spectrum of changes in regional myocardial function during acute ischemia in closed chest pigs: an ultrasonic strain rate and strain study.

The objectives of this study were to define the spectrum of regional myocardial function changes during acute ischemia in closed chest animals by using newly developed ultrasonic strain rate and strain indexes derived from regional color Doppler myocardial imaging (CDMI) velocity data. Myocardial ischemia was induced in 18 pigs either with acute total 20-second occlusions (group 1, n = 12) or graded hypoperfusion (40 to 0 mL/min, group 2, n = 6) of the circumflex coronary artery. In addition, a dobutamine challenge (5 to 10 microg/kg per minute) was performed during sustained subtotal ischemia (10 mL/min) in group 2. CDMI acquisitions with parasternal views monitored the myocardial posterior wall function. Regional radial strain rate and strain (epsilon(r)) were measured for systole, isovolumic relaxation, early diastole, and atrial filling, respectively. During total and graded ischemia, epsilon(r) profiles were consistently modified, showing a delayed onset and a decrease in regional systolic thickening as well as increased postsystolic thickening. Radial strain rate and epsilon(r) indexes decreased consistently during systole and early diastole and increased during isovolumic relaxation. End-systolic epsilon(r) could differentiate total ischemia from severe hypoperfusion (10 mL/min), decreasing from 32% +/- 8% to 16% +/- 5% (versus 60% +/- 10% at baseline). During dobutamine infusion (10 microg/kg per minute), end-systolic epsilon(r) tended to decrease from 27% +/- 5% to 18% +/- 11%, whereas postsystolic thickening increased by 2-fold (P <.05). The combined analysis of regional deformation characteristics and global cardiac event timing derived from CDMI data can identify and quantify regional function changes induced by experimental acute ischemia in closed chest pigs. This would appear to be a potentially promising new noninvasive approach to the clinical evaluation of ischemia-induced changes in segmental myocardial function.

Can natural strain and strain rate quantify regional myocardial deformation? A study in healthy subjects.

Strain rate (SR) and strain (epsilon) have been proposed as new ultrasound (US) indices for quantifying regional wall deformation, and can be measured from color Doppler myocardial data by determining the local spatial velocity gradient. The aim of this study was to define normal regional SR/epsilon values for both radial and longitudinal myocardial deformation. SR/epsilon profiles were obtained from 40 healthy volunteers. For radial deformation, posterior left ventricular (LV) wall SR/epsilon were calculated. For longitudinal, they were determined for basal, mid- and apical segments of the 1. septum; 2. lateral, 3. posterior and 4. anterior LV walls and for the 5. right ventricular (RV) lateral wall. SR/epsilon values describing radial deformation were higher than the corresponding SR/epsilon values obtained for longitudinal deformation. Longitudinal SR/epsilon were homogeneous throughout the septum and all LV walls. This was in contrast to the normal base-apex velocity gradient. The RV segmental SR/epsilon values were higher than those obtained from the corresponding LV wall and inhomogeneous (higher in the apical segments). SR/epsilon imaging appears to be a robust technique for quantifying regional myocardial deformation.

Changes in systolic and postsystolic wall thickening during acute coronary occlusion and reperfusion in closed-chest pigs: Implications for the assessment of regional myocardial function.

The aim of the study was to characterize the impact of short-lived total coronary occlusions in closed-chest pigs on radial wall thickening within the "at-risk" myocardial segment by using gray-scale M-mode echocardiography. Twelve pigs underwent a series of 20-second total circumflex coronary artery occlusions with an angioplasty balloon. Myocardial thickening/thinning indexes were continuously monitored before ischemia, during ischemia, and on reperfusion by high-resolution M-mode recordings of the posterior wall obtained from parasternal views. The timing of regional events was compared with global systolic time intervals derived from the color Doppler myocardial imaging velocity data. Each occlusion induced a rapid decrease in end-systolic thickening (epsilon(ES)), closely paralleled by an increase in postsystolic thickening in the ischemic segment. After 20 seconds of ischemia, epsilon(ES) decreased by -86% and postsystolic thickening increased by +100%, whereas maximal thickening decreased only by -34% in comparison with preocclusion values. All wall thickening parameters returned to baseline after 15 seconds of reperfusion. During acute total ischemia in a closed-chest animal model, the changes in regional myocardial function were best characterized by the combined analysis of systolic and postsystolic thickening abnormalities and by their respective timings relative to global cardiac events markers.

Regional nonuniformity of normal adult human left ventricle.

Regional nonuniformity is a feature of both diseased and normal left ventricles (LV). With the use of magnetic resonance (MR) myocardial tagging, we performed three-dimensional strain analysis on 87 healthy adults in local cardiac and fiber coordinate systems (radial, circumferential, longitudinal, and fiber strains) to characterize normal nonuniformities and to test the validity of wall thickening as a parameter of regional function. Regional morphology included wall thickness and radii of curvature measurements. With respect to transmural nonuniformity, subendocardial strains exceeded subepicardial strains. Going from base to apex, wall thickness and circumferential radii of curvature decreased, whereas longitudinal radii of curvature increased. All of the strains increased from LV base to apex, resulting in a higher ejection fraction (EF) at the apex than at the base (70.9 +/- 0.4 vs. 62.4 +/- 0.4%; means +/- SE, P < 0.0001). When we looked around the circumference of the ventricle, the anterior part of the LV was the flattest and thinnest and showed the largest wall thickening (46.6 +/- 1.2%) but the lowest EF (64.7 +/- 0.5%). The posterior LV wall was thicker, more curved, and showed a lower wall thickening (32.8 +/- 1.0%) but a higher EF (71.3 +/- 0.5%). The regional contribution of the LV wall to the ejection of blood is thus highly variable and is not fully characterized by wall thickening alone. Differences in regional LV architecture and probably local stress are possible explanations for this marked functional nonuniformity.

Remote myocardial dysfunction after acute anterior myocardial infarction: impact of left ventricular shape on regional function: a magnetic resonance myocardial tagging study.

OBJECTIVES: We sought to evaluate regional morphology and function in patients in their first week after having a reperfused anterior myocardial infarction (MI) using magnetic resonance (MR) myocardial tagging. BACKGROUND: The mechanism of myocardial dysfunction in the remote, noninfarct-related regions is an unresolved issue to date. METHODS: Sixteen patients with a first reperfused transmural anterior MI were studied with MR tagging at 5 +/- 2 days after the event, and the results were compared with those of an age-matched control group regions. The left ventricle (LV) was divided into infarct, adjacent and remote regions. Magnetic resonance tagging provided information on the regional ventricular morphology and function. RESULTS: Morphologically, an increase of the circumferential radius of curvature was found in the remote myocardium, whereas the longitudinal radius of curvature was increased in all regions of the LV. A significant increase in apical sphericity was also found. A significant reduction in strain and function was found not only in the infarct region, but also in the adjacent and remote myocardium. The loss in regional ejection fraction in the remote myocardium (61.4 +/- 11.7% in patients vs. 68.7 +/- 10.0% in control subjects, p < 0.0001) was related to a significant reduction of the longitudinal and circumferential strain, whereas systolic wall thickening was preserved. CONCLUSIONS: Remote myocardial dysfunction contributes significantly to the loss in global ventricular function. This could be secondary to morphologic changes in the infarct region, leading to an increased systolic longitudinal wall stress without loss of intrinsic contractility in the remote regions.

High frame rate myocardial integrated backscatter. Does this change our understanding of this acoustic parameter?

AIMS: Integrated backscatter (IB) and its cyclic variation (CV) derived from radio-frequency (RF) data have been used as parameters to attempt myocardial tissue characterization. Prior imaging systems used to measure IB and its CV typically acquired data at frame rates of 20-30 Hz and at a resolution of 6-8 bits. If changes in IB levels are in part related to specific short-lived events, occurring within the cardiac cycle, this frame rate and resolution could have been too low to resolve adequately what might be a more complex data set. METHODS AND RESULTS: To investigate this possibility, we acquired real time two-dimensional (2D) myocardial IQ data (the 'in-phase quadrature' sampled RF data) at high frame rate (> 100 Hz), high dynamic resolution (theoretical 19-bit) and a sector angle of 20 degrees. Several consecutive heart cycles of myocardial data were acquired from individual cardiac walls in five closed chest dogs and 10 healthy, young volunteers at normal heart rates. On the reconstructed RF data regions of interest were indicated, and IB and its CV were calculated. The extracted high frame rate curves showed that the CV of IB is not a smooth sinusoidal-like curve, but is made up of multiple reproducible peaks and troughs with local minima and maxima which are temporally related to active or passive mechanical events, i.e. systolic contraction, early ventricular relaxation and ventricular filling due to atrial contraction. CONCLUSIONS: This study shows that increasing the rate of real-time RF data acquisition results in a more complex, reproducible IB curve. The resolved maxima and minima in IB levels are related to specific phases of the myocardial contraction. Furthermore, spectral analysis showed that IB curves acquired at normal heart rates contain information up to 40 Hz. Hence, cardiac imaging data sets used to analyse regional myocardial function obtained at frequencies lower than 80 frames per second can contain aliased information.

Regional strain and strain rate measurements by cardiac ultrasound: principles, implementation and limitations.

The non-invasive quantification of regional myocardial function is an important goal in clinical cardiology. Myocardial thickening/thinning indices is one method of attempting to define regional myocardial function. A new ultrasonic method of quantifying regional deformation has been introduced based on the principles of 'strain' and 'strain rate' imaging. These new imaging modes introduce concepts derived from mechanical engineering which most echocardiographers are not familiar with. In order to maximally exploit these new techniques, an understanding of what they measure is indispensable. This paper will define each of these modalities in terms of physical principles and will give an introduction to the principles of data acquisition and processing required to implement ultrasonic strain and strain rate imaging. In addition, the current status of development of the technique and its limitations will be discussed, together with examples of potential clinical applications.