Relation of ultrasonic tissue characterization with integrated backscatter to contractile reserve in chronic left ventricular ischemic dysfunction

Multimodality imaging of myocardial viability: an expert consensus document from the European Association of Cardiovascular Imaging (EACVI)

In clinical decision making, myocardial viability is defined as myocardium in acute or chronic coronary artery disease and other conditions with contractile dysfunction but maintained metabolic and electrical function, having the potential to improve dysfunction upon revascularization or other therapy. Several pathophysiological conditions may coexist to explain this phenomenon. Cardiac imaging may allow identification of myocardial viability through different principles, with the purpose of prediction of therapeutic response and selection for treatment. This expert consensus document reviews current insight into the underlying pathophysiology and available methods for assessing viability. In particular the document reviews contemporary viability imaging techniques, including stress echocardiography, single photon emission computed tomography, positron emission tomography, cardiovascular magnetic resonance, and computed tomography and provides clinical recommendations for how to standardize these methods in terms of acquisition and interpretation. Finally, it presents clinical scenarios where viability assessment is clinically useful.

Myocardial viability: what we knew and what is new

Some patients with chronic ischemic left ventricular dysfunction have shown significant improvements of contractility with favorable long-term prognosis after revascularization. Several imaging techniques are available for the assessment of viable myocardium, based on the detection of preserved perfusion, preserved glucose metabolism, intact cell membrane and mitochondria, and presence of contractile reserve. Nuclear cardiology techniques, dobutamine echocardiography and positron emission tomography are used to assess myocardial viability. In recent years, new advances have improved methods of detecting myocardial viability. This paper summarizes the pathophysiology, methods, and impact of detection of myocardial viability, concentrating on recent advances in such methods. We reviewed the literature using search engines MIDLINE, SCOUPS, and EMBASE from 1988 to February 2012. We used key words: myocardial viability, hibernation, stunning, and ischemic cardiomyopathy. Recent studies showed that the presence of viable myocardium was associated with a greater likelihood of survival in patients with coronary artery disease and LV dysfunction, but the assessment of myocardial viability did not identify patients with survival benefit from revascularization, as compared with medical therapy alone. This topic is still debatable and needs more evidence.

Application of paramagnetically tagged molecules for magnetic resonance imaging of biofilm mass transport processes

Molecules become readily visible by magnetic resonance imaging (MRI) when labeled with a paramagnetic tag. Consequently, MRI can be used to image their transport through porous media. In this study, we demonstrated that this method could be applied to image mass transport processes in biofilms. The transport of a complex of gadolinium and diethylenetriamine pentaacetic acid (Gd-DTPA), a commercially available paramagnetic molecule, was imaged both in agar (as a homogeneous test system) and in a phototrophic biofilm. The images collected were T(1) weighted, where T(1) is an MRI property of the biofilm and is dependent on Gd-DTPA concentration. A calibration protocol was applied to convert T(1) parameter maps into concentration maps, thus revealing the spatially resolved concentrations of this tracer at different time intervals. Comparing the data obtained from the agar experiment with data from a one-dimensional diffusion model revealed that transport of Gd-DTPA in agar was purely via diffusion, with a diffusion coefficient of 7.2 x 10(-10) m(2) s(-1). In contrast, comparison of data from the phototrophic biofilm experiment with data from a two-dimensional diffusion model revealed that transport of Gd-DTPA inside the biofilm was by both diffusion and advection, equivalent to a diffusion coefficient of 1.04 x 10(-9) m(2) s(-1). This technology can be used to further explore mass transport processes in biofilms, either by using the wide range of commercially available paramagnetically tagged molecules and nanoparticles or by using bespoke tagged molecules.

Integrated backscatter for the assessment of myocardial viability

PURPOSE OF REVIEW

Ultrasonic tissue characterization is a non-invasive diagnostic method that uses myocardial integrated backscatter analysis to determine contractile performance and myocardial viability independent of wall motion. This review discusses recent clinical findings regarding the application of ultrasonic tissue characterization for the assessment of myocardial viability.

RECENT FINDINGS

As this technique is non-invasive, ultrasonic tissue characterization can be used to predict the patency of infarct-related arteries in patients in the early stage of acute myocardial infarction. Several recent studies have shown that this technique is useful in identifying myocardial contractile reserve. The accuracy of ultrasonic tissue characterization for predicting functional recovery after coronary reperfusion is comparable to dobutamine echocardiography and radionuclide methods. Several studies have suggested that the cyclic variation of myocardial integrated backscatter reflects myocardial viability rather than contractile reserve. The cyclic variation of integrated backscatter is associated with myocardial viability confirmed by the integrity of the microvasculature identified by contrast echocardiography. In addition, the cyclic variation of integrated backscatter better reflects myocardial viability confirmed by the integrity of cellar metabolism than contractile reserve.

SUMMARY

Ultrasonic tissue characterization with integrated backscatter is a useful non-invasive method that can provide unique information for the assessment of myocardial viability.

Measurements of the anisotropy of ultrasonic attenuation in freshly excised myocardium

Echocardiography requires imaging of the heart with sound propagating at varying angles relative to the predominant direction of the myofibers. The degree of anisotropy of attenuation can significantly influence ultrasonic imaging and tissue characterization measurements in vivo. This study quantifies the anisotropy of attenuation of freshly excised myocardium at frequencies typical of echocardiographic imaging. Results show a significantly larger anisotropy than previously reported in specimens of locally unidirectional myofibers. Through-transmission radio frequency-based measurements were performed on specimens from 12 ovine and 12 bovine hearts. Although ovine hearts are closer in size to human, the larger size of bovine hearts offers the potential for specimens in which myofibers are more nearly unidirectionally aligned. The attenuation coefficient increased approximately linearly with frequency. The mean slope of attenuation with frequency was 3-4 times larger for propagation parallel than for perpendicular to the myofibers. At perpendicular insonification, slopes between ovine and bovine myocardium were approximately equal. However, attenuation in bovine specimens was larger for angles approaching parallel. The difference in results for parallel appears consistent with what might be expected from increased myofiber curvature associated with smaller lamb hearts. Quantitative knowledge of anisotropy of attenuation may be useful in understanding mechanisms underlying the interaction of ultrasound with myocardium.

Evaluation of the effect of nifedipine upon myocardial perfusion and contractility using cardiac magnetic resonance imaging and tissue Doppler echocardiography in systemic sclerosis

BACKGROUND

Primary myocardial involvement due to microcirculation impairment is common in systemic sclerosis (SSc). Cardiovascular magnetic resonance imaging (MRI) and tissue Doppler echocardiography (TDE) were recently shown to be more sensitive than conventional methods for the respective assessment of myocardial perfusion and contractility. Previous studies have suggested that dihydropyridine-type calcium channel blockers mitigate both myocardial perfusion and function abnormalities.

OBJECTIVE

To investigate the effects of nifedipine on myocardial perfusion by MRI and on contractility by TDE, in patients with SSc.

PATIENTS AND METHODS

18 patients with SSc without clinical heart failure and with normal pulmonary arterial pressure (14 women, 4 men; mean (SD) age 59 (9) years; mean (SD) disease duration 7 (4) years, 10 with diffuse and 8 with limited cutaneous forms) were prospectively evaluated. The MRI perfusion index, determined from time-intensity curves, and systolic and diastolic strain rate determined by TDE were assessed at baseline, after a 72 hour vasodilator washout period, and after 14 days of oral treatment with nifedipine 60 mg/day.

RESULTS

Nifedipine treatment led to a significant increase in the MRI perfusion index (mean (SD) 0.26 (0.07) v 0.19 (0.05) at baseline, p = 0.0003) and in systolic and diastolic strain rate (2.3 (0.6) v 1.5 (0.4) s(-1) at baseline, p = 0.0002, and 4.2 (1.6) v 3.0 (1.2) at baseline, p = 0.0003, respectively).

CONCLUSION

Fourteen days of treatment with nifedipine simultaneously improves myocardial perfusion and function, as evaluated by highly sensitive and quantitative methods.

Comparison of Acoustic Densitometry and Dobutamine Echocardiography for an Assessment of Myocardial Viability

AIM

The aim of this study has been to compare acoustic densitometry and dobutamine echocardiography for an assessment of myocardial viability.

METHODS AND RESULTS

Thirty-four patients with coronary artery disease and dysfunctional myocardial segments, who were referred for myocardial revascularization, underwent a viability assessment using low-dose dobutamine echocardiography and acoustic densitometry. Results of the two techniques were compared to follow-up resting echocardiography. This follow-up examination was performed at a mean of 3 months after successful revascularization in order to assess the recovery of function in revascularized, initially dysfunctional segments. Echocardiography was performed in standard views using 16-segment model of the left ventricle. Viable myocardium was identified by the augmentation of systolic thickening of an abnormal segment by at least one grade during dobutamine infusion and by the value of the maximal amplitude of cyclic variation of integrated backscatter. Acoustic densitometry had the sensitivity and specificity to predict functional recovery 90% and 77%, respectively. Dobutamine echocardiography had the sensitivity and specificity to predict contractile reserve 83% and 81%, respectively. The results were statistically comparable. Concordance between these methods was 80%.

CONCLUSION

Acoustic densitometry and dobutamine echocardiography did not statistically differ in the prediction of functional recovery dysfunctional myocardial segments after revascularization.

Serial assessment of myocardial properties using cyclic variation of integrated backscatter in an adriamycin-induced cardiomyopathy rat model

Although adriamycin (Doxorubicin) is one of the most effective and useful antineoplastic agents for the treatment of a variety of malignancies, its repeated administration can induce irreversible myocardial damage and resultant heart failure. Currently, no marker to detect early cardiac damage is available. The purpose of this study was to investigate whether an assessment of the acoustic properties of the myocardium could enable the earlier detection of myocardial damage after adriamycin chemotherapy. Forty Wistar rats were treated with adriamycin (2 mg/kg, i.v.) once a week for 2, 4, 6 or 8 weeks consecutively. Left ventricular ejection fraction (LVEF) was calculated using M-mode echocardiography data. The magnitude of cardiac cycle dependent variation of integrated backscatter (CVIB) of the myocardium was measured in the mid segment of the septum and in the posterior wall of the left ventricle, using a real time two dimensional integrated backscatter imaging system. LVEF was significantly lower in the adriamycin-treated 8-week group than in the controls (75+/-9 vs 57+/-8%, p<0.05). Myocyte damage was only seen in the 8-week adriamycin-treated group. However, no significant changes of CVIB were observed between baseline or during follow-up in the ADR or control group. In conclusion, serial assessment of the acoustic properties of the myocardium may not be an optimal tool for the early detection of myocardial damage after doxorubicin chemotherapy in a rat model.

Relation of ultrasonic tissue characterization with integrated backscatter to contractile reserve in patients with chronic coronary artery disease

BACKGROUND

Previous studies have shown that viable but stunned myocardium displays contractile reserve and exhibits cardiac cycle-dependent variations of integrated backscatter (CVIB), whereas infarcted myocardium does not.

HYPOTHESIS

This study was designed to clarify whether assessment of the acoustic properties of the myocardium can predict contractile reserve in patients with chronic coronary artery disease (CAD).

METHODS

In all, 21 patients with chronic CAD and 19 normal control subjects were studied. The magnitude of CVIB of the myocardium was measured in the basal and mid segment of the anterior septum and posterior wall of the left ventricle, using a real-time, two-dimensional integrated backscatter imaging system. The results were compared with the percent systolic wall thickening and the wall motion before and after revascularization. The wall motion was graded as normal, hypokinetic, or akinetic, and contractile reserve was considered present when an akinetic or hypokinetic segment improved after revascularization.

RESULTS

The average magnitude of CVIB was lower among dysfunctional segments of CAD than among normal segments of controls (3.73 +/- 1.71 vs. 6.35 +/- 0.69, p < 0.001). Of the 77 segments examined, 38 showed reversible dysfunction. Before revascularization, percent systolic wall thickening was similar among segments showing contractile reserve compared with those with persistent dysfunction myocardium (17.97 +/- 8.41 vs. 16.83 +/- 6.37%, p = 0.19), and the mean CVIB was significantly greater in segments with than in those without contractile reserve (4.73 +/- 1.47 vs. 2.75 +/- 1.31, p < 0.001). The CVIB above 3 dB before percutaneous transluminal coronary angioplasty predicted segments with contractile reserve with a sensitivity and specificity of 84.2 and 79.5%, respectively.

CONCLUSIONS

Cardiac cycle-dependent variations of integrated backscatter reflected myocardial contractility and functional capacity of the myocardium. They predicted segmental contractile reserve in patients with CAD.

Prediction of functional recovery of the left ventricle after coronary revascularization in patients with prior anterior myocardial infarction: a myocardial integrated backscatter study

Cyclic variation (CV) of myocardial integrated backscatter (IBS), which reflects intrinsic contractile performance, can predict myocardial viability in patients with a reperfused acute myocardial infarction (MI), but the use of this method has not been validated for chronic left ventricular (LV) dysfunction. The aim of this study was to examine whether myocardial IBS was useful for predicting LV functional recovery after coronary revascularization in 17 patients with prior anterior MI and LV dysfunction (ejection fraction <50%). Within 24 h of the revascularization procedure (percutaneous transluminal coronary angioplasty or coronary stenting), IBS curves were obtained by placing the region of interest on the anterior wall on the short-axis IBS image. The patients had repeat left heart catheterization at 3 or 6 months after the revascularization procedure, and were grouped according to the patterns of the IBS curve within the anterior wall. In 8 patients (group A), the IBS curve had a synchronized pattern with the magnitude of CV > or = 3.5, and in the remaining 9 patients (group B), the curve had either an asynchronized pattern or the magnitude of CV was less than 3.5 dB even in the case of synchronized pattern, or both. At baseline, there were no significant differences in LV functional indices between the 2 groups. After the follow-up period, the LV end-systolic volume decreased (75 +/- 21 ml to 56 +/- 20ml, p = 0.05), LV ejection fraction increased (35 +/- 12% to 50 +/- 14%, p = 0.014), and LV end-diastolic pressure decreased (19 +/- 10 mmHg to 13 +/- 6 mmHg, p = 0.02) in group A, whereas only the LV ejection fraction increased (34 +/- 9% to 40 +/- 11%, p = 0.03) in group B; LV end-systolic volume (72 +/- 19 ml to 66 +/- 16 ml, p = 0.126) and LV end-diastolic pressure (18 +/- 12 mmHg to 14 +/- 8 mmHg, p = 0.184) showed no significant changes. In conclusion, IBS is valuable for predicting LV functional recovery after coronary revascularization in patients with LV dysfunction caused by a remote anterior MI. A large-scale study is be needed to establish these data.

Coronary microvascular functional reserve: quantification of long-term changes with electron-beam CT preliminary results in a porcine model

PURPOSE

To evaluate the ability of electron-beam computed tomography (CT) to help quantify long-term changes in coronary microvascular functional reserve in a porcine model.

MATERIALS AND METHODS

Electron-beam CT-based intramyocardial blood volume and perfusion and Doppler ultrasonography (US)-based intracoronary blood flow were obtained in 13 pigs at baseline and again 3 months later. Measurements were obtained at rest and after the administration of adenosine. The short-term variation during 30 minutes of electron-beam CT measurements was assessed in nine additional pigs.

RESULTS

Short-term variation of blood volume and perfusion averaged 8% and 9%, respectively, and was similar for both weight groups at rest and after adenosine administration. At rest, intracoronary blood flow, blood volume, and perfusion remained unchanged from baseline to follow-up. Long-term increases (percentage change with adenosine relative to that at rest) in blood volume and perfusion reserves were consistent with increasing intracoronary blood flow reserves. Despite these long-term changes in intracoronary blood flow, blood volume, and perfusion, the blood volume-to-perfusion relationship suggests a similar blood volume distribution among different microvascular functional components in normal porcine myocardium at both weight groups.

CONCLUSION

Electron-beam CT may be of value for quantifying long-term changes in intramyocardial microvascular function.

Alterations of myocardial ultrasonic tissue characterization by coronary angioplasty in patients with chronic stable coronary artery disease

We conducted a study to delineate the alterations in the cyclic changes of myocardial ultrasonic integrated backscatter (IBS) in patients receiving angioplasty for chronic coronary artery disease. Ultrasonic tissue characterization (UTC) and dobutamine stress echocardiography were performed in 43 patients before and 24 h after angioplasty, as well as before the follow-up angiography 3 months later. For segments being normokinetic with ischemic burden, the blunted amplitude and increased nadir deviation of IBS cyclic modulation recovered soon after angioplasty. For dyssynergic segments with contractile reserve, the angioplasty rebuilt the amplitude before the wall motion recovered, but corrected the nadir deviation tardily. In both circumstances, the coronary restenosis abolished the initial restoration. Those nonviable segments persistently revealed large deviations and small weighted amplitudes irrelevant to coronary lesions. The progress of myocardial ischemia, the development of wall motion dyssynergy and, then, the loss of viability, show different patterns of alterations in UTC after alleviating coronary obstructions.

Prediction of contractile reserve by cyclic variation of integrated backscatter of the myocardium in patients with chronic left ventricular dysfunction

OBJECTIVE

To clarify whether assessment of the acoustic properties of the myocardium at rest can predict contractile reserve in patients with chronic left ventricular dysfunction.

METHODS

23 patients (mean (SD) age 63 (12) years) with chronic left ventricular dysfunction were studied. The magnitude of cardiac cycle dependent variation of integrated backscatter (CVIB) of the myocardium was measured at rest in the basal and mid segment of the septum and posterior wall of the left ventricle, using a real time two dimensional integrated backscatter imaging system. The results were compared with the percentage wall thickening and the wall motion at rest and during low dose dobutamine infusion. The wall motion was graded as normal, hypokinetic, or akinetic and contractile reserve was considered present when an akinetic or hypokinetic segment improved during dobutamine infusion.

RESULTS

The CVIB at rest correlated with per cent wall thickening at rest and during dobutamine infusion (at rest, r = 0.61, p < 0.0001, during dobutamine, r = 0.76, p < 0.0001). Of the 76 segments examined, 27 showed contractile reserve. The mean CVIB at rest was significantly greater in segments with contractile reserve than in those without (p < 0.0001). CVIB above 3 dB at rest predicted segments with contractile reserve with a sensitivity and specificity of 81% and 60%, respectively (p < 0.0001).

CONCLUSIONS

CVIB reflected not only myocardial contractility but also the functional capacity of the myocardium. It predicted segmental contractile reserve in patients with chronic left ventricular dysfunction.

Resting Ultrasonic Tissue Characterization and Dobutamine Stress Echocardiography for Prediction of Functional Recovery in Chronic Left Ventricular Ischemic Dysfunction

This study was designed to assess the diagnostic accuracy of the percentage of resting systolic wall thickening (WT), dobutamine stress echocardiography (DSE), resting cyclic variation of integrated backscatter (IBS-CV), and low-dose dobutamine stress IBS-CV (DSE-IB) for the prediction of regional function recovery (RFR) in patients with chronic left ventricular (LV) ischemic dysfunction. The study also evaluated whether or not global LV function affected the diagnostic accuracy. All studies were conducted before percutaneous transluminal coronary angioplasty (PTCA) and RFR was assessed after PTCA (mean interval, 10 months) in 30 patients with chronic LV ischemic dysfunction. Patients were divided into 2 groups according to the LV ejection fraction (LVEF): group A, LVEF<40%, n=14; group B, LVEF> or =40%, n=16. Of a total of 480 segments, 37 initially demonstrating akinetic wall motion before PTCA were analyzed. The wall motion of 24 of the 37 segments improved on visual analysis after PTCA. In the prediction of RFR, resting WT, DSE, resting IBS-CV and DSE-IB had sensitivities of 79%, 79%, 92% and 62%, and specificities of 54%, 84%, 83% and 69%, respectively. In particular, the resting IBS-CV in group A, as well as DSE, was an excellent predictor of RFR (sensitivity, 100%; specificity, 86%; vs sensitivity, 82%; specificity, 78%; respectively). Therefore, both resting IBS-CV and DSE are useful predictors for RFR in patients with chronic LV ischemic dysfunction.

Minimally invasive evaluation of coronary microvascular function by electron beam computed tomography

BACKGROUND

We previously demonstrated that in vivo electron-beam computed tomography (EBCT)-based indicator-dilution methods provide an estimate of intramyocardial blood volume (BV) and perfusion (F), which relate as BV=aF+b radicalF, where a characterizes the recruitable (exchange) and b the nonrecruitable (conduit) component of the myocardial microcirculation. In the present study, we compared BV and F with intracoronary Doppler ultrasound-based coronary blood flow (CBF) as a method for detecting and quantifying differential responses of these microvascular components to vasoactive drugs in normal (control) and hypercholesterolemic (HC) pigs.

METHODS AND RESULTS

BV and F values were obtained from contrast-enhanced EBCT studies in 14 HC and 14 control pigs. BV, F, and CBF values were obtained at baseline (intracoronary infusion of saline) and after 5 minutes each of intracoronary infusion of adenosine (100 microgram. kg(-1). min(-1)) and nitroglycerin (40 microgram/min). BV and CBF reserves in response to adenosine were attenuated in HC pigs compared with controls (90+/-36% versus 127+/-42%, P<0.03, and 485+/-182% versus 688+/-160%, P<0.01, respectively). The relationship between BV and F showed consistently lower recruitable BV in HC versus control pigs. Nonrecruitable BV reserve in response to adenosine was attenuated in HC compared with controls (77+/-20% versus 135+/-28%, P<0.001). Our findings are consistent with HC-induced impairment of intramyocardial resistance vessel function.

CONCLUSIONS

EBCT technology allows minimally invasive evaluation of intramyocardial microcirculatory function and permits assessment of microvascular BV distribution in different functional components. This method may be of value in evaluating the coronary microcirculation in pathophysiological states such as hypercholesterolemia.

Ultrasonic tissue characterization with integrated backscatter during inotropic stimulation

Ultrasonic tissue characterization with integrated backscatter is an objective method to quantitatively define the physical state of the myocardium. To determine if backscatter imaging during inotropic stimulation could be used objectively to determine the myocardial viability and ischemia in patients with ischemic heart disease, the backscatter changes were examined in 23 patients with myocardial infarction during dobutamine stress two-dimensional (2-D) echocardiography. Coronary angiography was performed within 1 to 2 days after the stress test. The results of this study demonstrated that changes in backscatter variability correlated significantly with the wall motion changes in stress echocardiography during dobutamine infusion (p < 0.0001). In addition, it was shown that the backscatter changes were significantly different in various types of myocardial tissue. In 23 healthy control segments, the ultrasonic backscatter variability was preserved and unchanged during inotropic stimulation (p = NS). In 15 viable infarct zones, restoration or an increase in backscatter variability during low-dose dobutamine infusion was noted, this being lost when ischemia developing during high-dose dobutamine infusion (p < 0.01). In 9 nonviable infarct zones, the phase-weighted variation was usually < or = 0 and did not change significantly during inotropic stimulation, regardless of the patency of the infarct-related arteries. In 15 remote ischemic myocardial zones, the backscatter variability was preserved at the baseline level, did not change during low-dose dobutamine infusion, but decreased significantly during high-dose dobutamine stress (p < 0.01). In conclusion, dobutamine stress tissue characterization could offer an objective approach for the detection of myocardial viability and ischemia, and might be a useful adjunct to the conventional stress echocardiography.

Comparison of simultaneous dobutamine echocardiography and thallium-201 stress-reinjection single-photon emission computed tomography in predicting improvement of chronic myocardial dysfunction after revascularization

Previous studies have shown that ultrasonic integrated backscatter is valuable in characterizing stunned myocardium. Recent investigations have demonstrated that resting cardiac cycle-dependent variation of integrated backscatter closely paralleled the contractile reserve in patients with chronic left ventricular ischemic dysfunction. The purpose of this study was to validate whether ultrasonic tissue characterization (UTC) compared with dobutamine stress echocardiography (DSE) and thallium-201 stress-reinjection single-photon emission computed tomography (Tl-SPECT) could predict reversible myocardial dyssynergy in patients with chronic coronary artery disease. Forty-eight patients with stable coronary artery disease underwent UTC, DSE, and Tl-SPECT simultaneously before successful coronary revascularization and were followed up with echocardiograms at rest >3 months later. Among the 58 investigated segments, the weighted amplitude, a composite parameter derived from the integrated backscatter power curve, was larger for those groups with greater functional recovery (p <0.001). For the persistent akinetic segments, the weighted amplitudes were small with large deviations of the nadir ratios that represented the asynchrony between the intramural contractile events and the global systole. Using the cut-off value 2.0 of the weighted amplitude, the sensitivity and specificity for predicting functional improvement after revascularization were both 82.8% (kappa = 0.66) and comparable to the sensitivity and specificity of DSE and Tl-SPECT. UTC, delineating the myocardial physical state and intramural contraction, can be a novel approach in predicting functional improvement of chronic dyssynergy after revascularization.

Ultrasonic tissue characterization evaluates myocardial viability and ischemia in patients with coronary artery disease

To evaluate whether or not ultrasonic tissue characterization (UTC) can detect jeopardized or salvageable myocardium in patients having chronic coronary artery disease, we studied 103 patients with sequential UTC, dobutamine stress echocardiography (DSE) and (201)thallium stress-reinjection single-photon emission computed tomography (T1-SPECT). This revealed that the weighted amplitude of the cyclic modulation of integrated backscatter was larger for the myocardium with less ischemia burden or greater viability (p<0.001). The segments with larger ischemia burden or the nonviable myocardium demonstrated the contrary result. Using the receiver-operating characteristic curve analyses to determine the cutoff value of weighted amplitude for various predictions, UTC can detect ischemia in normokinetic myocardium (kappa = 0.34 compared to DSE or T1-SPECT) and viability in dyssynergic myocardium (kappa = 0.57 compared to DSE and 0.45, to T1-SPECT). These observations show that UTC may prove useful in the identification and pathophysiological understanding of myocardial ischemia and viability.

Myocardial integrated ultrasonic backscatter in patients with dilated cardiomyopathy: prediction of response to beta-blocker therapy

BACKGROUND

Myocardial integrated backscatter (IB) imaging has been reported to be useful for ultrasonic tissue characterization and delineation of myocardial viability or fibrosis. beta-Blocker therapy has beneficial effects for patients with dilated cardiomyopathy (DCM), but there are no clear findings that indicate which patients with DCM will respond to this therapy. This study was performed to evaluate whether myocardial IB analysis can predict the response to beta-blocker therapy.

METHODS AND RESULTS

We prospectively performed echocardiographic examination with IB analysis in 29 patients with DCM (20 men, 9 women) before starting bisoprolol therapy and in 15 normal subjects. Standard echocardiographic examination and IB analysis in the left ventricular wall in the 2-dimensional short-axis view were performed and the magnitude of cyclic variation (CV) of IB and calibrated myocardial IB intensity (subtracted pericardial) were obtained from the interventricular septum and the left ventricular posterior wall. Sixteen patients responded to bisoprolol therapy and 13 did not respond after 12 months of full-dose therapy. Calibrated myocardial IB intensity was lower in responders relative to nonresponders in both the interventricular septum (responders, -20.1 +/- 3.6 dB vs nonresponders, -9.8 +/- 5.1 dB, P <.0001; controls, -20.1 +/- 4.4 dB) and posterior wall (responders, -20.6 +/- 3.6 dB vs nonresponders, -14.6 +/- 4.2 dB, P =.0002; controls, -22.7 +/- 3.3 dB). Also, the lower the myocardial intensity in the interventricular septum or posterior wall, the better left ventricular systolic function improved after beta-blocker therapy. However, CV was lower in both DCM groups than in the controls, and CV in the interventricular septum was lower in nonresponders than in responders (responders, 4.0 +/- 4.1 dB vs nonresponders, -0.8 +/- 6. 1 dB, P <.02; controls, 8.3 +/- 2.4 dB). In addition, CV in the posterior wall showed no difference between the 2 DCM groups (responders, 5.6 +/- 1.3 dB vs nonresponders, 5.1 +/- 3.5 dB, P = not significant; controls, 9.6 +/- 2.5 dB). Also, the percent fibrosis on right ventricular endomyocardial biopsy specimens showed no distinctions between these 2 groups (responders, 25.1% +/- 16.1% vs nonresponders, 24.9% +/- 15.0%, P = not significant).

CONCLUSIONS

These findings suggest that left ventricular myocardial IB data, especially IB intensity, provide useful information for predicting the response to beta-blocker therapy in patients with DCM. However, right ventricular endomyocardial biopsy findings do not appear to contribute to discriminating between the 2 groups.

Are changes in myocardial integrated backscatter restricted to the ischemic zone in acute induced ischemia? An in vivo animal study

Integrated backscatter (IB) from a myocardial region, calculated from radiofrequency echocardiographic data, has been proposed as a useful parameter for investigating changes in myocardial tissue induced by ischemia. In 10 closed-chest dogs, 5 minutes of myocardial ischemia was induced by either a proximal occlusion of the circumflex coronary artery (CX) (5 dogs), resulting in extensive ischemia in the posterior wall, or by occluding the distal CX vessel (5 dogs) to produce a small localized ischemic zone in the posterior wall. High-resolution digital radiofrequency data from the whole left ventricular myocardium, in the imaging plane during one complete heart cycle, were acquired with a whole-image real-time acquisition approach. Regions in the septum and posterior wall (both ischemic tissue and, in the case of distal occlusions, tissue surrounding the ischemic zone) were chosen for analysis, and IB and cyclic variation (CV) of IB were calculated. Post occlusion, an increase in mean IB values was found in the ischemic segment. However, an increase in CV was also observed in the peri-ischemic zone for the distal CX occlusion and in the septum after proximal CX occlusion. These findings show that changes in CV are not restricted to the ischemic zone but may also occur in distal myocardium. This may be explained by changes in the regional contractile state and loading conditions of the "normal" myocardium, which are altered in response to the distal ischemia.

[Characterization of myocardial tissue by ultrasound: backscatter]

One of the most important goals in Cardiology is to identify, noninvasively, the normal as well as pathological changes in structure and function of myocardial tissue in order to recognize their etiology and severity. Ultrasonic Tissue Characterization is an approach to define the physical state of the heart by the analysis of the pathological changes that modify cardiac tissue physical properties, therefore generating an ultrasonic signal alteration. Among the most practical types of analysis of this data is the acoustic parameters measurement, and measurements based on integrated backscatter have been utilized the most. Backscatter is the ultrasonic quantification reflected back to the transducer, therefore emanating from myocardial structures or "scatterers". This method has been used to study many patients with hypertrophy, cardiomyopathies, cardiac allograft rejection. But is the investigation of myocardial ischemia-viability one of the most clinically relevant applications because of the importance of selecting, non-invasively, and at a relatively low cost those patients with coronary artery disease in whom myocardial asynergy is noted by conventional echocardiography and/or angiography. The magnitude of alterations in backscatter measurements such as the cyclic variation of integrated backscatter are markers of myocardial viability and could better identify patients who stand to benefit the most revascularization procedures.

Myocardial tissue characterization in heart failure by real-time integrated backscatter

OBJECTIVE

Differentiation between normal and abnormal physical state of the myocardium, not possible with conventional echocardiography, so far could be done with integrated backscatter (IBS) as a research tool only.

METHODS

This study investigates myocardial texture analysis with new commercially available real time IBS in 12 normal individuals and in 18 patients with severe left ventricular dysfunction due to coronary artery disease (CAD) in 8 and dilated cardiomyopathy (DCM) in 10 patients. Analysis of IBS amplitude and cyclic variation (dB) in the parasternal long and short axis view of the septum and the posterior wall were measured and corrected with IBS curve of the blood to get absolute values.

RESULTS

Compared to normal individuals patients with left ventricular dysfunction had a reduced myocardial cyclic variation (P<0.0001), which correlated to regional systolic wall thickening (r=0.64, P=0.001) and global shortening fraction (r=0.62, P<0.01). Although systolic wall thickening in the posterior wall was lower in CAD patients (% thickening, 11.9+/-10 vs. 21.9+/-8, P=0.004), absolute cyclic variation was reduced in both, CAD and DCM patients in the same order of magnitude. However, the higher maximal IBS amplitude in the posterior wall observed in CAD when compared to DCM patients (13.2+/-4.4 vs. 9.2+/-2.4 dB; P=0.002) indicate fibrosis or scar. The dissociation between cyclic variation and systolic wall thickening could implicate hybernating myocardium.

CONCLUSION

Real-time IBS has progressed from research to routine as a tool to obtain additional and valuable information to conventional echocardiography in daily practice.