Incremental Value of Two Dimensional Speckle Tracking Echocardiography in the Functional Assessment and Characterization of Subclinical Left Ventricular Dysfunction.

Subclinical left ventricular (LV) dysfunction refers to subtle abnormalities in LV function which typically precede a reduction in the left ventricular ejection fraction (LVEF). The assessment of myocardial function using LVEF, a radial metric of systolic function, is subject to load dependence, intra-observer and inter-observer variability. Reductions in LVEF typically manifest late in the disease process thus compromising the ability to intervene before irreversible impairment of systolic performance sets in. 2-Dimensional speckle tracking echocardiography (2D-STE), a novel strain imaging modality has shown promise as a sensitive indicator of myocardial contractility. It arms the clinician with a powerful and practical tool to rapidly quantify cardiac mechanics, circumventing several inherent limitations of conventional echocardiography. This article highlights the incremental utility of 2D-STE in the detection of subclinical LV dysfunction.

INTRODUCTION

Strain refers to the change in the length of a segment of the myocardium relative to its original length and strain rate refers to the net change in strain per unit time. 2-Dimensional speckle tracking echocardiography (2D-STE), an angle-independent technique, employs automated algorithms to analyze temporal variations (frame to frame) in the mobility of acoustic speckle markers of 20-40 pixels size along different spatial orientations such as longitudinal, circumferential and radial planes to then quantitatively derive respective strain or deformational parameters. The endocardium contributes maximally to longitudinal strain (LS). Location of the endocardium farthest away from the epicardial coronary arteries and its exquisite sensitivity to ischemia makes it vulnerable to a variety of insults thereby making LS a highly sensitive indicator of LV dysfunction. In contrast, radial strain (RS), circumferential strain (CS) and torsional strains (TS) are affected later in the disease and are widely acknowledged to have lower inter- and intra-observer reproducibility [1].

One of the utilities of myocardial strain might be timely identification of subclinical left ventricular (LV) dysfunction, which could provide the clinician with a wider therapeutic window to potentially arrest or delay progression to clinically evident cardiovascular disease or impairment of myocardial performance. In this article, subclinical LV dysfunction refers to a compromise in LV function prior to reduction in LVEF ≤ 50%. The focus of this article is to highlight: 1. The clinical entities where subclinical LV dysfunction has been described by 2D-STE and 2. The potential incremental value of 2D-STE over conventional 2D-echocardiography in the management of these patients.

APPLICATIONS OF STRAIN

Valvular Heart Disease

A clear consensus on the timing of valve repair or replacement in asymptomatic patients with preserved LVEF is currently lacking [2]. In addition to the detection of subclinical LV dysfunction, strain parameters have shown promise for the prediction of post-surgical LV dysfunction. Myocardial strain could plausibly assist in the identification of high-risk patients who might benefit from early surgical intervention prior to a decline in the LVEF below guideline recommended threshold levels for surgical intervention (Table 1). Adaptive remodeling in early aortic regurgitation (AR) preserves LVEF by a compensatory rise in RS and CS for the

Table 1

Studies evaluating strain in valvular heart disease with speckle tracking echocardiography.

Study		Sample size with description		Imaging modality (vendor name)		Objective		Outcomes
Aortic Regurgitation
Mizariene et al. [41]		Chronic AR:NT-proBNP<400 (n=44) vs. >400 vs. controls (n=64)		2D-STE (EchoPac-GE)		Effect of LV strain on NT-proBNP		GLS>-16% predicts levels>400
Olsen et al. [5]		Chronic AR: Surgical (n=29) vs. conservative (n=35)		2D-STE (EchoPAC-GE)		Strain indices in AR progression		Progression correlates with reduced systolic (-1.04 vs. -1.19s-1), early diastolic (1.2 vs. 1.6s-1) and myocardial SR (-16.3 vs. -19%)
Smedsrud et al. [6]		Chronic AR (n=47) vs. controls (n=31)		2D-STE (EchoPAC-GE)		GLS impairment and early LV dysfunction		Reduced GLS (-17.5 vs.-22.1%) identifies subclinical LV dysfunction; GLS and not LVEF correlates with post-operative LV function
Kaneko et al. [37]		Chronic AR (n=36) vs. controls (n=15)		2D-STE (Toshiba)		GRS decline-marker of myocardial dysfunction?		Endocardial GRS loss (28.9 vs. 37.1%) predicts myocardial dysfunction
Di Salvo et al. [4]		Stable (n=17) vs. progressive AR (n=9)		2D-STE (EchoPAC)		Strain parameters and AR progression		LV LS (cut-off >-19.5%) - only predictor for AR Progression
Aortic Stenosis
Van Dalen et al. [11]		AS (n=60) vs. controls (n=30)		2D-STE (QLAB-Philips)		Twist indices and severity of AS, subendocardial ischemia		Elevated peak systolic LV twist (13.6 vs. 11.4) and endocardial twist-shortening ratio (0.6vs.0.4) correlates with ischemia and AS severity
Ng et al. [9]		Aortic sclerosis (n=118) vs. Mild (n=81) vs. moderate (n=109) vs. severe (n=112) AS		2D-STE (EchoPAC-GE)		Strain and severity of AS		Sequential deterioration in LS, CS, RS and SR correlates with progressive reduction in valve area
Levy et al. [42]		Severe symptomatic AS		2D-STE (EchoPAC-GE)		GLS on post-surgical atrial fibrillation rates		GLS>-15% predicts post-surgical atrial fibrillation
Delgado et al. [10]		Severe AS (n=73) vs. controls (n=40)		2D-STE (EchoPAC-GE)		Changes in LV strain pre and post-surgery		GLS (-14.6 vs. -20.3%) and SR-impaired despite pEF. LS, CS and RS improved following valve replacement
Mitral Stenosis
Ozdemir et al. [12]		Mild-moderate MS (n=60) vs. controls (n=52)		2D-ECHO, STE (EchoPAC-GE)		LV dysfunction in MS with pEF		GLS (-17 vs.-19%) and GLS rate compromised in MS
Mitral Regurgitation
Isla et al. [7]		Chronic severe MR (n=38)		2D, 3D-ECHO, Doppler ECHO and 2D-STE (Q-Lab)		Preoperative strain on post-operative LV dysfunction		Longitudinal SR at mid interventricular septal level <-0.8s-1 -best predictors of LVEF reduction > 10%
Kim et al. [43]		Chronic severe MR (n=59) vs. controls (n=34)		2D-ECHO,angiography and 2D-STE (EchoPac-GE)		Strain assessment of latent LV dysfunction		Peak systolic radial SR of 2.0 s-1 best correlates with peak dP/dt; short axis function offers better prediction
Study	Sample size with description		Imaging modality (vendor name)		Objective		Outcomes
Florescu et al. [8]	Severe primary MR (n=28) vs. controls (n=10)		2D-ECHO, TVI and STE (EchoPac-GE)		Pre-op strain and post-valve replacement LV function		Systolic TVI and the combination of systolic TVI and LS are main independent predictors of post-operative LVEF drop >10%
Pandis et al. [44]	Degenerative MR (n=40)		2D, 3D-ECHO, and 2D-STE (TomTec)		Predictors of recurrent MR post-surgery		Mid-lateral RS≤-27 and apical lateral RS ≤-25-significant predictors
Mascle et al. [45]	Severe degenerative MR: post op LVEF≥50% (n=73) + LVEF<50% (n=15)		2D-ECHO, 2D-STE and TDI (EchoPAC-GE)		Pre-operative GLS on post-operative LV dysfunction		GLS >-18% predicts post-operative LVEF drop to <50%

2D, 2 dimensional; 3D, 3 dimensional; AS, aortic stenosis; AR, aortic regurgitation; CS, circumferential strain; ECHO, echocardiography; GLS, global longitudinal strain; GRS, global radial strain; LS, longitudinal strain; LV, left ventricle; LVEF, left ventricular ejection fraction; MS, mitral stenosis; MR, mitral regurgitation; NT-proBNP, N terminal-pro brain natriuretic peptide; pEF, preserved ejection fraction; RS, radial strain; SR, strain rate; TDI, tissue Doppler imaging; TVI, tissue velocity imaging.

early loss of LS with additional compensation provided by LV hypertrophy and increase in LV volume [3]. Reduction in LVEF to <50% in asymptomatic AR heralds an increase in the rate of progression to symptoms, a surgical indication, from 4.3% to 25% per year [2]. Amongst patients with preserved ejection fraction (pEF), LS attenuation >-19.5% is 77% sensitive and 94% specific for symptomatic progression of asymptomatic moderate-severe AR [4]. Pre-operative GLS attenuation, but not LVEF, has been associated with post-operative LV dysfunction [5, 6]. Likewise, in mitral regurgitation, pre-operative GLS impairment (GLS<-18%) has been shown to identify subclinical LV dysfunction in patients with LVEF>60% and also predict post-operative LV dysfunction [7, 8].

In aortic stenosis (AS), the degree of strain deterioration correlates significantly with lower aortic valve (AV) area and severity of AS [9] while strain recovery has been noted post AV replacement [10], even prior to recovery of LVEF. Furthermore, altered twist mechanics in AS offers a non-invasive means of predicting subendocardial ischemia [11]. Similarly, identification of subclinical LV dysfunction by attenuated GLS and GLS rate in asymptomatic or minimally symptomatic mitral stenosis (MS) [12] might aid in optimal timing of mitral valve (MV) interventions prior to permanent myocardial remodeling [13, 14].

Coronary Artery Disease

2D-STE is robust in terms of its prognostic utility and reproducibility in the assessment of subclinical CAD (Table 2) [15]. Various strain parameters such as early myocardial systolic lengthening (15), ratio of peak systolic LS difference to peak systolic GLS [16] and a combination of early systolic and early diastolic SR [17] provide incremental value over GLS for obstructive CAD. Strain assessment during dobutamine stress echocardiography (DSE) could enhance the sensitivity of conventional 2D-echo by minimizing inter-observer variability in delineating endocardial borders and interpreting wall motion abnormalities as demonstrated by using software such as automated functional imaging (AFI). Strain rate imaging offers incremental value over DSE derived wall motion scores in the prediction of mortality [18]. Additionally, a remarkable coronary territorial correlation between AFI derived strain and angiography with a sensitivity >90% in the anterior and >79% in the posterior circulations has been demonstrated [16, 18].

Table 2

Studies highlighting utility of speckle tracking echocardiography in subclinical coronary artery disease.

Study	Sample size with description	Imaging modality with vendor name	Objective	Outcomes
Nucifora et al. [46]	Non-obstructive (n=60) vs. obstructive (n=63) vs. no CAD (n=59)	CT angiography and 2D-STE (EchoPAC-GE)	GLS prediction of obstructive CAD	GLS≥-17.4% predicts obstructive CAD better than diastolic dysfunction or Duke clinical scores
Hanekom et al. [47]	Significant CAD (150)	2D-STE, TVI, DSE and coronary angiography (EchoPAC-GE)	Strain from STE vs. TVI during DSE in predicting obstructive CAD	STE-equally efficacious to TVI in anterior but not in posterior circulation
Liang et al. [17]	Obstructive (n=39) vs. non-obstructive or no CAD (n=15)	2D-STE, coronary angiography (EchoPAC-GE)	Diastolic strain in obstructive CAD	Early diastolic SR impairment is superior to systolic strain: 77% sensitive, 93% specific
Tsai et al. [16]	CAD (n=75) vs. no CAD (n=77)	STE, coronary angiography (EchoPAC-GE)	LS in prediction of obstructive CAD	Sensitivity, specificity of GLS>-19%: 75%, 81%; peak segmental LS difference/peak systolic GLS ratio>1: 77%, 79%
Smedsrud et al. [15]	Significant (n=43) vs. non-significant CAD (n=43)	2D-STE, coronary angiography (EchoPac-GE)	Does duration of early systolic lengthening predict significant CAD?	Early systolic lengthening (cutoff 58 milliseconds) predicts significant CAD better than peak systolic LS attenuation

2D-STE, 2 dimensional-speckle tracking echocardiography; CAD, coronary artery disease; CT, computerized tomography; DSE, dobutamine stress echocardiography; GLS, global longitudinal strain; LS, longitudinal strain; pEF, preserved ejection fraction; SR, strain rate; TVI, tissue velocity imaging.

Hypertension and Diabetes Mellitus

Attenuation of 2D-STE derived GLS presents a vital differentiating parameter between hypertensive heart disease and an athlete’s heart while providing excellent correlation with the magnitude of diastolic dysfunction in hypertensives [19]. Detection of LS impairment by 2D-STE precedes detection by tissue Doppler imaging (TDI) in hypertensives with preserved LVEF even prior to the development of left ventricular hypertrophy (LVH) [20] thus providing an early opportunity to arrest progression to LVH. Indeed, preserved CS and consequential wall thickening despite reduction in LS has been posited to explain preservation of LVEF in patients with systemic hypertension [21].

2D-STE derived GLS attenuation might be useful for risk stratification in asymptomatic diabetics via prediction of subclinical systolic LV dysfunction with the decrease in LS being proportional to diabetes duration [22]. Furthermore, impairment of GLS has been associated with higher coronary artery calcium scores in diabetics, a surrogate for subclinical coronary atherosclerosis [23].

Heart Failure with Preserved Ejection Fraction (HFpEF)

Although diastolic dysfunction is believed to be the underlying pathophysiology in HFpEF, recent studies have indicated abnormalities of systolic function in these patients [24]. Indeed, traditional diastolic dysfunction parameters were absent in approximately one-third of the HFpEF trial cohorts [25, 26]. Systolic impairment of strain parameters (LS, CS) has been demonstrated in HFpEF patients, with LS attenuation being associated with higher NT-pro BNP levels [27]. 2D-STE derived increases in LS delay index and time to achieve peak longitudinal velocity unveil the dysfunctional systolic component of HFpEF indicating dyssynchronous and ineffective ventricular contraction [28] (Table 3). Previous studies have hypothesized that reduction of dyssynchrony by cardiac resynchronization therapy could translate into energy efficient contractility and mitigate progression to systolic failure [28].

Table 3

Evaluation of heart failure with preserved ejection fraction with speckle tracking echocardiography.

Study	Sample size with description	Imaging modality with vendor name	Objective	Outcomes
Phan et al. [48]	HfPEF (n=47) vs. young (n=27) vs. old controls (n=26)	2D-ECHO, 2D-STE (EchoPAC-GE)	Comparing strain profiles: HfPEF vs. age related changes	Increased TS seen with ageing. CS increase (-24.7% vs. -20%) differentiates HfPEF from old controls
Phan et al. [28]	HfPEF (n=38) vs. controls (n=33)	2D-ECHO and 2D-STE (EchoPAC-GE)	Dyssynchrony assessment in HfPEF	Systolic and diastolic dyssynchrony observed. LS impairment (-17.6% vs. -19.9%) and higher LV dyssynchrony (LS delay index-14.4% vs.-10.7%) noted
Donal et al. [39]	HfPEF (n=21) vs. controls (n=15)	2D-ECHO, exercise stress testing and 2D-STE (EchoPAC-GE)	To characterize resting and exercise induced strain changes	GLS impaired at rest [Rest: (-16% vs. -20%) and aggravated by stress: (-17% vs. -23%); similar trend with global CS
Kraigher-Krainer et al. [27]	HfPEF (n=219) vs. controls (n=50) and Hypertensive Heart Disease (n=44)	Vendor independent STE Software	Strain parameters in HfPEF	Lower LS and CS in HfPEF (-14.6±3.3 vs.. 20.0±2.1 in controls); Lower LS values co-related with higher NT-ProBNP

2D, 2 dimensional; CS, circumferential strain; ECHO, echocardiography; GLS, global longitudinal strain; HfPEF, heart failure with preserved ejection fraction; LS, longitudinal strain; RS, radial strain; STE, speckle tracking echocardiography; TS: torsional strain; BNP: Brain Natiuretic Peptide.

Perimyocarditis

Incipient myocardial dysfunction has been demonstrated in acute perimyocarditis with compromise in GLS and twist angle preceding reduction of LVEF [29] (Fig. ). Impairment of CS and TS with intact LS in constrictive pericarditis as opposed to impaired LS and intact CS in restrictive cardiomyopathy effectively differentiates these conditions [30].

Cancer Chemotherapy

Routine serial assessment of LV strain parameters could aid in earlier identification of chemotherapy-induced cardiotoxicity prior to conventional changes in LVEF (Table 4). Attenuation of 2D-STE derived LV apical cap peak systolic strain [31], GLS, torsion, twisting and untwisting rates occur as early as 1 month after anthracycline (AT) therapy, preceding impairment in LVEF and Doppler parameters and also offers excellent correlation with cumulative AT dose [32]. AT therapy has been associated with a 16% prevalence of higher LV systolic dyssynchrony index reflective of energy inefficient contraction, positing a role for cardiac resynchronization therapy in these patients. Likewise, strain imaging has been shown to recognize pre-clinical changes in systolic function in prospectively followed breast cancer patients on adjuvant trastuzumab therapy [31].

Table 4

Strain imaging in the assessment of chemotherapy associated cardio toxicity.

Study	Sample size with description	Imaging modality with vendor name	Objective	Outcomes
Tsai et al. [40]	Hodgkin's lymphoma and radiotherapy (n=47) [AT (n=27), No AT (n=20)] vs. controls (n=20)	2D-ECHO and 2D-STE (EchoPAC-GE)	LV dysfunction with anthracycline (AT) and radiotherapy (RT)	Higher GLS impairment in RT+AT (-16.1%) than RT and no AT (-17.5%); CS-similar trend; pEF-all groups
Poterucha et al. [31]	AT (n=19) vs. controls (n=19)	2D-ECHO and 2D-STE (EchoPAC-GE)	Temporal changes in strain and LVEF	Longitudinal PSS reduction started at 4 months (8.7%) and worsened by 8 months (9.2%) with AT. LVEF decreased by 4.3% only at 8 months.
Motoki et al. [32]	AT therapy (n=25)	2D-ECHO, TDI and 2D-STE (EchoPAC-GE)	Torsional strain and subclinical LV dysfunction	Impairment in GLS, TS, twisting and untwisting rates occur as early as 1 month; LVEF, TDI indices-preserved
Ho et al. [49]	AT (n=19) vs. AT+TZ (n=51) vs. controls (n=50)	2D-ECHO, Doppler ECHO and 2D-STE (EchoPAC-GE)	Subclinical LV dysfunction in combination therapy (AT+TZ)	Reduced GLS in AT (-17.7) vs. AT+TZ (-19.2) vs. controls (-19.6). No additive cardiotoxicity with TZ
Fallah-Rad et al. [50]	No toxicity (n=10) vs. TZ toxicity (n=32)	TVI, CMR and 2D-STE (EchoPac-GE)	Detection of TZ cardiotoxicity with various techniques	2D-STE impairment in GLS (-19.9 ± 1.8% to. -16.4 ± 1.1%) and GRS (42.4 ± 10.5% to. 32.5 ± 15.2%) occur earliest (3 months). LVEF preserved until 6 months

2D-ECHO, 2 dimensional echocardiography; 2D-STE, 2 dimensional speckle tracking echocardiography; AT, anthracycline; CMR, cardiac magnetic resonance; CS, circumferential strain; GLS, global longitudinal strain; GRS, global radial strain; LV, left ventricle; LVEF, left ventricular ejection fraction; pEF, preserved ejection fraction; PSS, peak systolic strain; RS, radial strain; RT, radiotherapy; TS, torsional strain; TDI, tissue Doppler imaging; TZ, trastuzumab.

Miscellaneous Conditions

Apical sparing, evidenced by relative apical LS>1 (mean apical LS/mean basal LS+ mean mid-LS) discriminates cardiac amyloidosis from AS or hypertrophic cardiomyopathy induced LVH with a sensitivity>90% and specificity>80% [32] (Fig. ). LS impairment is associated with elevated NT-proBNP in Behcet’s disease (Table 5). In Fabry’s disease, systolic strain attenuation in the basal postero-lateral segments offers a sensitivity and specificity of 90% and 97% respectively, for the identification of MRI confirmed fibrotic arrhythmogenic foci [33]. Systemic Sclerosis is characterized by impairment of global and LV longitudinal peak systolic strain (PSS) with higher attenuation in the basal segments and sparing of the apical and medial segments [34]. Moreover, reduced GLS and global CS were independently predictive of ventricular arrhythmias in systemic sclerosis patients [35].

Table 5

Miscellaneous conditions underscoring the clinical applicability of speckle tracking echocardiography.

Study	Sample size with description	Imaging modality with vendor name	Objective	Outcomes
Yagmur et al.	Behcets disease (n=32) vs. controls (n=27)	2D-ECHO and 2D-STE (QLab-Philips)	Detection of subclinical LV dysfunction	Reduced LS (-17.8 ± 2.7%) in disease vs. controls (-20.5 ± 1.8%); NT-proBNP independent corelate of mean LS
Liu et al. [51]	Hemodialysis patients (n=102)	2D-ECHO, TDI and 2D-STE (EchoPac-GE)	Predictors of significant CAD despite pEF in hemodialysis patients	Reduction in LS ≥-15% in ≥6 myocardial segments predicts CAD
Dedobbeleer et al. [52]	Friedreich’s ataxia (n=20) vs. controls (n=20)	2D-ECHO and 2D-STE (Qlab-Philips)	Stain profiling, detection of subclinical LV dysfunction	Reduced GLS (-15.3 vs. -17.5%), peak LV twist and untwisting rates
Caputo et al. [53]	At least 1 cardiovascular risk factor (n=70)	2D-ECHO, TDI and 2D-STE (EchoPAC-GE)	Abnormal LV strain in overweight (BMI) despite pEF	Peak LS of LV-reduced in overweight vs. normal BMI (-17.2% vs. -18.7%)
Takamura et al. [54]	Acute PE (n=25) vs. controls (n=25)	2D-ECHO and 2D-STE (EchoPAC-GE)	Impact of acute RV pressure overload on LV strain	Global LS (-16 vs. -20), CS (-17 vs. -24) and RS (44 vs. 59) reduced in acute PE, recover with the resolution of pressure overload
Shahul et al. [55]	Preeclampsia (n=11) vs. non-proteinuric hypertension (n=11) vs. normotensives (n=17)	2D-ECHO and 2D-STE (TomTec)	Is subclinical LV dysfunction inherent to preeclampsia?	Impaired GLS (-13.7 vs. -15.9 vs. -20.1), GRS (22.4 vs. 40.7 vs. 39.8) and GCS (-17.9 vs. -28.2 vs. -21.6) in preeclampsia. pEF in all groups
Inoue et al. [56]	RV apical pacing (n=51)+ RV septal pacing (n=52) vs. controls (n=50)	2D-ECHO and 2D-STE (EchoPAC-GE)	Subclinical LV dysfunction with RV apical pacing	Maximal impairment of GLS with RV apical pacing [-14.3 vs. -16.8 vs. -18.2]
Miszalski-Jamka et al. [57-59]	Wegener's granulomatosis (n=22) vs. controls (n=22)	2D-ECHO and 2D-STE (EchoPAC-GE)	Subclinical LV dysfunction identification	Global LS (-17.9 vs.-19.7), CS (-18.4 vs. -21.6) and RS (38.8 vs. 50.1) impairment noted, correlate with disease severity.

2D-ECHO, 2 dimensional echocardiography; 2D-STE, 2 dimensional speckle tracking echocardiography; BMI, body mass index; CAD, coronary artery disease; CS, circumferential strain; GCS, global circumferential strain, GRS, global radial strain; LS, longitudinal strain; LV, left ventricle; PE, pulmonary embolism; pEF, preserved ejection fraction; RS, radial strain; RV, right ventricle; TDI, tissue Doppler imaging.

Strain derived radial LV wall motion discoordination was shown to be an independent predictor of decline in cardiac output in acute pulmonary embolism [54]. Subclinical LV dysfunction inherent to preeclampsia has been identified by a higher decline in global LS, RS and CS than in non-proteinuric hypertension [55]. Sickle cell crisis results in transient LV dysfunction with reversal of regional LS impairment on crisis resolution [38].

Obligatory Need for Standardization in Speckle Tracking Echocardiography

Marwick et al. have described discordant strain values from different vendors to result from three components: 1) Image procurement and storage resolution; 2) Processing of image data for strain quantification and 3) Hemodynamic status [35]. Image acquisition with vendor specific ultrasound machines, heterogeneity in frame rates used for compression (30 frames/sec for vendor neutral software), differences in the methodology of algorithms used to derive strain, types of strain used (natural or Lagrangian strain), anatomical regions studied to derive strain (endocardial, epicardial or both), phase of the cardiac cycle in which images are acquired and blood pressure variations during image procurement are all sources of discrepancies [35]. Head-to-head comparisons between different combinations of ultrasound machines and vendor specific versus vendor neutral post-processing software has depicted higher variations from post-processing and not image acquisition [36]. When vendor neutral software is used, standardization of methods to derive strain has been shown to minimize GLS variations even at frame rates as low as 30 frames/second [39, 40].

A concerted effort to standardize strain software between a conglomerate of vendors supported by the American Society of Echocardiography and the European Society of Echocardiography is afoot. It is hoped that this endeavor will eventually culminate into standardization of postprocessing software to minimize variability between vendor offerings.

Future Directions

Barriers to use of strain imaging in routine practice include physician reluctance to adopt innovative technology with perceived complexity, lack of standardization and reimbursement limitations. Whether interventions following identification of subclinical LV dysfunction could translate into reduced cardiovascular morbidity and mortality needs further appraisal in prospective randomized controlled trials. Further technologic refinements targeting these limitations could transform 2D-STE into a robust modality for the routine detection of subclinical myocardial dysfunction, given its increasing ease of use and wide applicability.