Emerging clinical role of strain imaging in echocardiography

Emerging role of echocardiographic strain/strain rate imaging and twist in systolic function evaluation and operative procedure in patients with aortic stenosis

Systolic function of the left ventricle is vital for patients with aortic stenosis. Unfortunately, the most widely used clinical parameter, the left ventricular ejection fraction, is not sensitive enough, especially for patients with left ventricular hypertrophy. Echocardiographic strain/strain rate and twist are emerging parameters for left ventricular systolic and diastolic function evaluation. Aortic stenosis could reduce strain/strain rate while magnifying twist. Furthermore, strain/strain rate correlates well with the prognosis of patients with aortic stenosis. Most importantly the circumferential strain, strain rate and twist also play a role in differentiating cardiac compensation or decompensation. In any case, these parameters could normalize after successful surgical aortic valve replacement or transcatheter aortic valve replacement. Regardless of these advantages, clinical evidence is needed to ensure their usefulness.

Peak systolic velocity using color-coded tissue Doppler imaging, a strong and independent predictor of outcome in acute coronary syndrome patients

Background

Traditional echocardiographic methods like left ventricular ejection fraction(EF) and wall motion scoring (WMS) and new methods like speckle tracking (ST) based 2D strain carry important prognostic information in acute coronary syndrome (ACS) patients. Parameters from tissue Doppler imaging (TDI), with its high time resolution, may further increase the prognostic value. Peak systolic velocity (PSV) of the basal segments of the left ventricle from TDI is a robust and user independent parameter. The aim was to investigate the prognostic value of PSV compared to EF, WMS, 2D strain and E/e'.

Methods

Echocardiographic images were collected and post processed in 227 ACS patients. Additional clinical data was prospectively gathered and patients were followed for 3-5 years regarding the combined endpoint of death or re-admission due to ACS or heart failure.

Results

The combined endpoint occurred in 85 (37%) patients. Those with an event had lower median PSV than those without (4,4 cm/s) vs. (5,3 cm/s), (p<0.001). In a ROC analysis, the AUC was larger for PSV (0.75) than for EF (0.68), WMS (0.63), 2D strain (0.67) and E/e'(0.70). The combined endpoint increased with decreasing PSV. When adjusting for differences in baseline characteristics in a COX-regression model, PSV remained independently associated with outcome where the others did not. PSV was also less sensitive to image quality with fewer values missing or unacceptable for analysis.

Conclusion

Peak systolic velocity (PSV) is a robust measurement that seems to have a strong and independent association with outcome compared to traditional echocardiographic measurements in ACS patients.

Left atrial and right atrial deformation in patients with coronary artery disease: a velocity vector imaging-based study

Background

Impaired left ventricular (LV) function has been shown by strain rate (SR) imaging in patients with coronary artery disease (CAD). Our aim was to investigate global and regional, systolic and diastolic left atrial (LA) and right atrial (RA) longitudinal deformation in CAD using velocity vector imaging.

Methods

Echocardiographic and velocity vector imaging studies were performed in 20 patients with mild CAD, 40 patients with severe CAD and 25 controls. Maximal atrial volume, peak atrial longitudinal strain (ε_s) and SR during LV systole (SRs), SR during early LV filling (SRe) and late LV filling (SRa) were measured. Longitudinal strain during atrial contraction (ε_a) was obtained at the onset of P-wave on electrocardiography, and ε_a/ε_s was calculated.

Results

Longitudinal peak ε_s and SRs of LA showed decreased trend among CAD patients. The global and lateral LA SRe were prominently lower, while RA ε_a, SRa and ε_a/ε_s were prominently higher in 2 CAD groups than control group (P value <0.05). As compared with controls and patients with other single-vessel disease, LA SRa and ε_a/ε_s ratio were significantly increased among patients with exclusively left anterior descending coronary artery (LAD) stenosis (SRa 1.14±0.38 s⁻¹, 1.10±0.41 s⁻¹, 1.45±0.46 s⁻¹, P value<0.05; ε_a/ε_s 0.44±0.11, 0.44±0.20, 0.57±0.12, P value<0.01).

Conclusions

Apparently decreased SRe of LA and increased ε_a, SRa and ε_a/ε_s of RA were found in CAD patients with preserved LVEF and E/E' in gray zone. SRa and ε_a/ε_s of LA were found to significantly increase in those with LAD stenosis.

Tissue Doppler imaging for diagnosis of coronary artery disease: a systematic review and meta-analysis

Global and regional left ventricular (LV) systolic dysfunction is a marker of coronary artery disease (CAD), which is conventionally assessed using two-dimensional echocardiography. Tissue Doppler imaging (TDI) has emerged as an adjunct tool in the diagnosis of regional wall motion abnormalities from CAD. We performed a systematic review and meta-analysis to assess the efficacy of TDI indices in the diagnosis of CAD. We searched MEDLINE and the Cochrane Library for controlled studies comparing TDI measurements in those with and without CAD as confirmed by coronary angiography. Meta-analyses of mean differences in TDI velocities between these populations were performed. Screening of titles and abstracts followed by full-text screening identified 8 studies. At rest, TDI was associated with a significant decrease in the pooled maximum systolic velocity among CAD patients compared to those without CAD [mean difference (MD): -0.66; 95% confidence interval (CI): -0.98 to −0.34]. There were no significant differences in maximum early and late diastolic velocities. Post-stress, TDI was associated with a significant decrease in maximum early diastolic velocity (MD: -1.91; 95% CI: -2.74 to −1.09) and maximum late diastolic velocity (MD: -1.57; 95% CI: -2.95 to −0.18) among CAD patients compared to those without CAD. There was no significant difference in maximum systolic velocity post-stress. Our results suggest that TDI may have a role in the evaluation of CAD. Future studies should evaluate the incremental value of TDI velocities over LV ejection fraction and two dimensional wall motion analysis in the detection of CAD and assessment of its severity. (Word Count: 249)

Murine ultrasound imaging for circumferential strain analyses in the angiotensin II abdominal aortic aneurysm model

OBJECTIVE

The underlying causes of abdominal aortic aneurysms (AAAs) remain obscure, although research tools such as the angiotensin II (Ang II) apolipoprotein E-deficient (apoE(-/-)) mouse model have aided investigations. Longitudinal imaging and determination of biomechanical forces in this small-scale model have been difficult. We hypothesized that high-frequency ultrasound biomicroscopy combined with speckle-tracking analytical strategies can be used to define the role of circumferential mechanical strain in AAA formation in the Ang II/apoE(-/-) mouse model of AAAs. We simultaneously examined dietary perturbations that might impact the biomechanical properties of the aortic wall, hypothesizing that the generalized inflammatory phenotype associated with diet-induced obesity would be associated with accelerated loss of circumferential strain and aneurysmal aortic degeneration.

METHODS

Receiving either a 60 kcal% fat Western diet or standard 10 kcal% fat normal chow, Ang II-treated apoE(-/-) mice (n = 34) underwent sequential aortic duplex ultrasound scan imaging (Vevo 2100 System; VisualSonics, Toronto, Ontario, Canada) of their entire aorta. Circumferential strains were calculated using speckle-tracking algorithms and a custom MatLab analysis.

RESULTS

Decreased strains in all aortic locations after just 3 days of Ang II treatment were observed, and this effect progressed during the 4-week observation period. Anatomic segments along the aorta impacted wall strain (baseline highest in ascending aorta; P < .05), whereas diet did not. At 2 and 4 weeks, there was the largest progressive decrease in strain in the paravisceral/supraceliac aorta (P < .05), which was the segment most likely to be involved in aneurysm formation in this model.

CONCLUSIONS

In the Ang II/apoE(-/-) aneurysm model, the aorta significantly stiffens (with decreased strain) shortly after Ang II infusion, and this progressively continues through the next 4 weeks. High-fat feeding did not have an impact on wall strain. Delineation of biomechanical factors and AAA morphology via duplex scan and speckle-tracking algorithms in mouse models should accelerate insights into human AAAs.

Tissue Doppler and strain rate imaging detect improvement of myocardial function in iron deficient patients with congestive heart failure after iron replacement therapy

BACKGROUND

Iron deficiency may contribute to diminished exercise tolerance in patients with congestive heart failure (CHF) even in absence of anemia. The aim of this study was to evaluate the effect of correction of iron deficiency on functional capacity and myocardial function in patients with CHF.

METHODS

We studied 40 patients with ejection fraction <40%, hemoglobin% >12 g/dL, serum ferritin <100 ug/L, and transferrin saturation <20%. Patients received 200 mg weekly doses of iron dextran complex until serum ferritin level was between 200 and 300 ug/L or transferrin saturation level was between 30% and 40%. Transthoracic echocardiogram, tissue Doppler imaging, peak systolic strain rate, and 6 minute walk test were performed before iron therapy and at 12-week follow up. Peak early diastolic myocardial tissue velocity (E'), peak late diastolic myocardial tissue velocity (A'), and peak systolic myocardial tissue velocity (S') were measured.

RESULTS

There was a significant improvement of New York Heart Association functional class (3.0 ± 0.4 vs. 2.1 ± 0.3, P < 0.05) and 6minutes walk distance (322 ± 104 vs. 377 ± 76, P < 0.01) from rest to follow up, respectively. Ejection fraction did not change significantly (32 ± 8% vs. 34 ± 9%, respectively). There was a significant improvement of S'-wave (3.0 ± 0.8 cm/sec vs. 6.0 ± 1.2 cm/sec, P < 0.05), E/E' ratio (22 ± 3 vs. 13 ± 3, P < 0.05), and peak systolic strain rate (-0.72 ± 0.11/s vs. -1.09 ± 0.37/s, P < 0.05) from baseline to follow-up, respectively.

CONCLUSION

Correction of iron deficiency improves functional class and walking distance in nonanemic iron deficient patients with systolic heart failure. Tissue Doppler and strain rate demonstrated a significant improvement of diastolic and systolic function after therapy despite lack of improvement of ejection fraction. (Echocardiography 2012;29:13-18).

Multimodality imaging in diabetic heart disease

Diabetic heart disease is currently defined as left ventricular dysfunction that occurs independently of coronary artery disease and hypertension. Its underlying etiology is likely to be multifactorial, acting synergistically together to cause myocardial dysfunction. Multimodality cardiac imaging, such as echocardiography, nuclear, computed tomography, and magnetic resonance imaging, can provide invaluable insight into different aspects of the disease process, from imaging at the cellular level for altered myocardial metabolism to microvascular and endothelial dysfunction, autonomic neuropathy, coronary atherosclerosis, and finally, interstitial fibrosis with scar formation. Furthermore, cardiac imaging is pivotal in diagnosing diabetic heart disease. Thus, the aim of the present review is to illustrate the role of multimodality cardiac imaging in elucidating the underlying pathophysiologic mechanisms of diabetic heart disease.

Echocardiographic speckle-tracking based strain imaging for rapid cardiovascular phenotyping in mice

RATIONALE

High-sensitivity in vivo phenotyping of cardiac function is essential for evaluating genes of interest and novel therapies in small animal models of cardiovascular disease. Transthoracic echocardiography is the principal method currently used for assessing cardiac structure and function; however, standard echocardiographic techniques are relatively insensitive to early or subtle changes in cardiac performance, particularly in mice.

OBJECTIVE

To develop and validate an echocardiographic strain imaging methodology for sensitive and rapid cardiac phenotyping in small animal models.

METHODS AND RESULTS

Herein, we describe a modified echocardiographic technique that uses speckle-tracking based strain analysis for the noninvasive evaluation of cardiac performance in adult mice. This method is found to be rapid, reproducible, and highly sensitive in assessing both regional and global left ventricular (LV) function. Compared with conventional echocardiographic measures of LV structure and function, peak longitudinal strain and strain rate were able to detect changes in adult mouse hearts at an earlier time point following myocardial infarction and predicted the later development of adverse LV remodeling. Moreover, speckle-tracking based strain analysis was able to clearly identify subtle improvement in LV function that occurred early in response to standard post-myocardial infarction cardiac therapy.

CONCLUSIONS

Our results highlight the utility of speckle-tracking based strain imaging for detecting discrete functional alterations in mouse models of cardiovascular disease in an efficient and comprehensive manner. Echocardiography speckle-tracking based strain analysis represents a method for relatively high-throughput and sensitive cardiac phenotyping, particularly in evaluating emerging cardiac agents and therapies in mice.

The potential role of echocardiographic strain imaging for evaluating cardiotoxicity due to cancer therapy

Refinements to conventional treatment and the development of new therapies have led to significant improvements in cancer survival. Yet, many frontline cancer treatments continue to be hindered by their significant side effects, amongst which cardiotoxicity is particularly important. Therefore, the focus of cancer management has changed; treatment is no longer aimed solely at overcoming malignancy, but emphasises early identification and treatment of potential side effects. In this regard, the cardiotoxic potential of certain anticancer agents mandate close monitoring of cardiac function, and the method of choice for monitoring is transthoracic echocardiography. Whilst this method has its limitations, a newer echocardiographic technique called myocardial strain imaging has the potential to detect early sub-clinical changes in cardiac function due to cardiotoxicity. Strain analysis has been the subject of several recent studies to evaluate its potential in monitoring cardiotoxicity, and this article reviews the recent literature and explores the potential role of myocardial strain imaging in cancer management and avenues for future research.

Exploring oligodendrocyte guidance: 'to boldly go where no cell has gone before'

Oligodendrocytes, the myelinating cells of the central nervous system (CNS), originate early in the formation of the brain in specific foci, and migrate throughout the parenchyma. The instructional cues guiding the migration of these progenitor cells must be encoded into their developing environment. Soluble factors as well as membrane-bound cues most likely synergize to create a complex thoroughfare needed to sculpt and organize the brain into a functional organ with white and gray matter. Classically, the focus of many guidance related studies in the CNS has been limited to neuron physiology. However, It is becoming increasingly clear that their lifelong partners, oligodendrocytes, express both ligands and receptors able to both present and respond to these classical cues. In this short review, some recent findings in the Semaphorin and Eph fields will be presented with respect to oligodendrocyte expression and function.