Comparison of quantitative wall-motion analysis and strain for detection of coronary stenosis with three-dimensional dobutamine stress echocardiography.

BACKGROUND: Quantitative analysis of wall motion from three-dimensional (3D) dobutamine stress echocardiography (DSE) could provide additional diagnostic information not available from qualitative analysis. In this study, we compare the effectiveness of 3D fractional shortening (3DFS), a measure of wall motion computed from 3D echocardiography (3DE), to strain and strain rate measured with sonomicrometry for detecting critical stenoses during DSE. METHODS: Eleven open-chest dogs underwent DSE both with and without a critical stenosis. 3DFS was measured from 3DE images acquired at peak stress. 3DFS was normalized by subtracting average 3DFS during control peak stress (∆3DFS). Strains in the perfusion defect (PD) were measured from sonomicrometry, and PD size and location were measured with microspheres. RESULTS: A ∆3DFS abnormality indicated the presence of a critical stenosis with high sensitivity and specificity (88% and 100%, respectively), and ∆3DFS abnormality size correlated with PD size (R(2) = 0.54). The sensitivity and specificity for ∆3DFS were similar to that for area strain (88%, 100%) and circumferential strain and strain rate (88%, 92% and 88%, 86%, respectively), while longitudinal strain and strain rate were less specific. ∆3DFS correlated significantly with both coronary flow reserve (R(2) = 0.71) and PD size (R(2) = 0.97), while area strain correlated with PD size only (R(2) = 0.67), and other measures were not significantly correlated with flow reserve or PD size. CONCLUSION: Quantitative wall-motion analysis using ∆3DFS is effective for detecting critical stenoses during DSE, performing similar to 3D strain, and provides potentially useful information on the size and location of a perfusion defect.

Postprocedure mapping of cardiac resynchronization lead position using standard fluoroscopy systems: implications for the nonresponder with scar.

BACKGROUND: The relationship between cardiac resynchronization therapy (CRT), left ventricular (LV) lead position, scar, and regional mechanical function influences CRT response. OBJECTIVE: To determine LV lead position relative to LV structural characteristics in standard clinical practice, we developed and validated a practical yet mathematically rigorous method to register procedural fluoroscopic LV lead position with pre-CRT cardiac magnetic resonance (CMR). METHODS: After one-time calibration of the standard fluoroscopic suite, we identified the projected CMR LV lead position using three reference landmarks on both CMR and fluoroscopy. This predicted lead position was validated in a canine model by histology and in eight "validation group" patients based on postoperative computed tomography scans (n = 7) or CMR coronary sinus venography (n = 1). The methodology was applied in an additional eight patients with CRT nonresponse and infarction-related myocardial scar. RESULTS: The projected and actual lead positions were within 1.2 mm in the canine model. The median distance between projected and actual lead positions for the validation group (n = 8) and animal validation case was 11.3 mm (interquartile range 9.2-14.6 mm). In the application (nonresponder) group (n = 8), the lead mapped to the scar periphery in three patients, the core of the scar in one patient, and more than 3 cm from scar in four patients. CONCLUSIONS: This methodology projects procedural fluoroscopic LV lead position onto pre-CRT CMR using standard fluoroscopic equipment and a one-time calibration, enabling assessment of LV lead position with sufficient accuracy to identify the lead position relative to regional function and infarction-related scar in CRT nonresponders.

Impact of mechanical activation, scar, and electrical timing on cardiac resynchronization therapy response and clinical outcomes.

OBJECTIVES: Using cardiac magnetic resonance (CMR), we sought to evaluate the relative influences of mechanical, electrical, and scar properties at the left ventricular lead position (LVLP) on cardiac resynchronization therapy (CRT) response and clinical events. BACKGROUND: CMR cine displacement encoding with stimulated echoes (DENSE) provides high-quality strain for overall dyssynchrony (circumferential uniformity ratio estimate [CURE] 0 to 1) and timing of onset of circumferential contraction at the LVLP. CMR DENSE, late gadolinium enhancement, and electrical timing together could improve upon other imaging modalities for evaluating the optimal LVLP. METHODS: Patients had complete CMR studies and echocardiography before CRT. CRT response was defined as a 15% reduction in left ventricular end-systolic volume. Electrical activation was assessed as the time from QRS onset to LVLP electrogram (QLV). Patients were then followed for clinical events. RESULTS: In 75 patients, multivariable logistic modeling accurately identified the 40 patients (53%) with CRT response (area under the curve: 0.95 [p < 0.0001]) based on CURE (odds ratio [OR]: 2.59/0.1 decrease), delayed circumferential contraction onset at LVLP (OR: 6.55), absent LVLP scar (OR: 14.9), and QLV (OR: 1.31/10 ms increase). The 33% of patients with CURE <0.70, absence of LVLP scar, and delayed LVLP contraction onset had a 100% response rate, whereas those with CURE ≥0.70 had a 0% CRT response rate and a 12-fold increased risk of death; the remaining patients had a mixed response profile. CONCLUSIONS: Mechanical, electrical, and scar properties at the LVLP together with CMR mechanical dyssynchrony are strongly associated with echocardiographic CRT response and clinical events after CRT. Modeling these findings holds promise for improving CRT outcomes.

Anisotropic reinforcement of acute anteroapical infarcts improves pump function.

BACKGROUND: We hypothesize that a therapy that improves left ventricular (LV) pump function early after infarction should decrease the need for compensation through sympathetic activation and dilation, thereby reducing the risk of developing heart failure. The mechanical properties of healing myocardial infarcts are an important determinant of LV function, yet improving function by altering infarct properties has proven unexpectedly difficult. Using a computational model, we recently predicted that stiffening a large anterior infarct anisotropically (in only one direction) would improve LV function, whereas isotropic stiffening, the focus of previous studies and therapies, would not. The goal of this study was to test the novel strategy of anisotropic infarct reinforcement. METHODS AND RESULTS: We tested the effects of anisotropic infarct reinforcement in 10 open-chest dogs with large anteroapical infarcts that depressed LV pump function. We measured regional mechanics, LV volumes, and cardiac output at a range of preloads at baseline, 45 minutes after coronary ligation (ischemia), and 30 minutes later, after surgical reinforcement in the longitudinal direction (anisotropic). Ischemia shifted the end-systolic pressure-volume relationship and cardiac output curves rightward, decreasing cardiac output at matched end-diastolic pressure by 44%. Anisotropic reinforcement significantly improved systolic function without impairing diastolic function, recovering half the deficit in overall LV function. CONCLUSIONS: We conclude that anisotropic reinforcement is a promising new approach to improving LV function after a large myocardial infarction.

Quantitative three-dimensional wall motion analysis predicts ischemic region size and location.

Stress echocardiography is an important screening test for coronary artery disease. Currently, cardiologists rely on visual analysis of left ventricular (LV) wall motion abnormalities, which is subjective and qualitative. We previously used finite-element models of the regionally ischemic left ventricle to develop a wall motion measure, 3DFS, for predicting ischemic region size and location from real-time 3D echocardiography (RT3DE). The purpose of this study was to validate these methods against regional blood flow measurements during regional ischemia and to compare the accuracy of our methods to the current state of the art, visual scoring by trained cardiologists. We acquired RT3DE images during 20 brief (<2 min) coronary occlusions in dogs and determined ischemic region size and location by microsphere-based measurement of regional perfusion. We identified regions of abnormal wall motion using 3DFS and by blinded visual scoring. 3DFS predicted ischemic region size well (correlation r (2) = 0.64 against microspheres, p < 0.0001), reducing error by more than half compared to visual scoring (8 +/- 9% vs. 19 +/- 14%, p < 0.05), while localizing the ischemic region with equal accuracy. We conclude that 3DFS is an objective, quantitative measure of wall motion that localizes acutely ischemic regions as accurately as wall motion scoring while providing superior quantification of ischemic region size.

QUANTITATIVE VALIDATION OF OPTICAL FLOW BASED MYOCARDIAL STRAIN MEASURES USING SONOMICROMETRY.

Dynamic cardiac metrics, including myocardial strains and displacements, provide a quantitative approach to evaluate cardiac function. However, in current clinical diagnosis, largely 2D strain measures are used despite the fact that cardiac motions are complex 3D volumes over time. Recent advances in 4D ultrasound enable the capability to capture such complex motion in a single image data set. In our previous work, a 4D optical flow based motion tracking algorithm was developed to extract fully 4D dynamic cardiac metrics from such 4D ultrasound data. In order to quantitatively evaluate our tracking method, in-vivo coronary artery occlusion experiments at various locations were performed on three canine hearts. Each dog was screened with 4D ultrasound and sonomicrometry data was acquired during each occlusion study. The 4D ultrasound data from these experiments was then analyzed with our tracking method and estimated principal strain measures were directly compared to those recorded by sonomicrometry, and showed strong agreement. This is the first validation study of optical flow based strain estimation for 4D ultrasound with direct comparison with sonomicrometry using in-vivo data.