Assessment of myocardial ischemic memory using persistence of post-systolic thickening after recovery from ischemia.

OBJECTIVES: We sought to investigate the time course of post-systolic thickening (PST) and systolic abnormality after recovery from brief myocardial ischemia. BACKGROUND: Myocardial ischemic memory imaging, denoting the visualization of abnormalities provoked by ischemia and sustained even after restoration of perfusion, is desirable and allows after-the-fact recognition of ischemic insult. PST offers a sensitive marker of myocardial ischemia, but whether this abnormal thickening remains after relief from brief ischemia is unclear. METHODS: Tissue strain echocardiographic data were acquired from 27 dogs under 2 different conditions of myocardial ischemia induced by either brief coronary occlusion (15 or 5 min) followed by reperfusion (Protocol 1) or by dobutamine stress during nonflow-limiting stenosis (Protocol 2). Peak systolic strain and post-systolic strain index (PSI), a parameter of PST, were analyzed. RESULTS: In Protocol 1, peak systolic strain was significantly decreased in the risk area during occlusion. This decrease in peak systolic strain in the 15-min group did not completely recover to baseline levels even 120 min after reperfusion, whereas the decrease in the 5-min group recovered immediately after reperfusion. We found that PSI was significantly increased during occlusion, but increased PSI in the 5-min group remained until 30 min after reperfusion (-0.19 +/- 0.18 [baseline] vs. 0.19 +/- 0.14 [30 min], p < 0.05) despite the rapid recovery of peak systolic strain. In Protocol 2, increased PSI was sustained until 20 min after the end of dobutamine infusion (-0.26 +/- 0.11 [baseline] vs. -0.16 +/- 0.10 [20 min], p < 0.05), although peak systolic strain recovered by 5 min after the end of dobutamine infusion. CONCLUSIONS: PST remained longer than abnormal peak systolic strain after recovery from ischemia. Assessment of PST may be valuable for detecting myocardial ischemic memory.

Quantitative assessment of microcollateral recruitment during coronary occlusion using real-time intravenous myocardial contrast echocardiography.

BACKGROUND: Residual collateral-derived myocardial blood flow (MBF) (A x beta) is important to protect against myocardial ischemia after acute coronary occlusion. METHODS: Recruitment of microcollateral was assessed in 22 dogs with left circumflex coronary artery occlusion by analysis of MBF and regional wall thickening (WT) using real-time myocardial contrast echocardiography. RESULTS: Video intensity and WT at the center of risk area were significantly lower than those at the border of risk area. The video intensity, A value, beta value, and MBF correlated well with WT after left circumflex coronary artery occlusion. The WT of the area with above 25% of normal MBF was preserved and was higher than that at below 25%. However, the deterioration of WT was not distinguished according to A value. CONCLUSION: Real-time myocardial contrast echocardiography is a useful noninvasive method to evaluate collateral-derived MBF, which can be a reliable index of protection against myocardial ischemia.

Assessment of dyssynchronous wall motion during acute myocardial ischemia using velocity vector imaging.

OBJECTIVES: The purpose of this study was to investigate the diagnostic value of velocity vector imaging (VVI) for detecting acute myocardial ischemia and whether VVI can accurately demonstrate the spatial extent of ischemic risk area. BACKGROUND: Using a tracking algorithm, VVI can display velocity vectors of regional wall motion overlaid onto the B-mode image and allows the quantitative assessment of myocardial mechanics. However, its efficacy for diagnosing myocardial ischemia has not been evaluated. METHODS: In 18 dogs with flow-limiting stenosis and/or total occlusion of the coronary artery, peak systolic radial velocity (V(SYS)), radial velocity at mitral valve opening (V(MVO)), peak systolic radial strain, and the percent change in wall thickening (%WT) were measured in the normal and risk areas and compared to those at baseline. Sensitivity and specificity for detecting the stenosis and occlusion were analyzed in each parameter. The area of inward velocity vectors at mitral valve opening (MVO) detected by VVI was compared to the risk area derived from real-time myocardial contrast echocardiography (MCE). Twelve image clips were randomly selected from the baseline, stenosis, and occlusions to determine the intra- and inter-observer agreement for the VVI parameters. RESULTS: The left circumflex coronary flow was reduced by 44.3 +/- 9.0% during stenosis and completely interrupted during occlusion. During coronary artery occlusion, inward motion at MVO was observed in the risk area. Percent WT, peak systolic radial strain, V(SYS), and V(MVO) changed significantly from values at baseline. During stenosis, %WT, peak systolic radial strain, and V(SYS) did not differ from those at baseline; however, V(MVO) was significantly increased (-0.12 +/- 0.60 cm/s vs. -0.96 +/- 0.55 cm/s, p = 0.015). Sensitivity and specificity of V(MVO) for detecting ischemia were superior to those of other parameters. The spatial extent of inward velocity vectors at MVO correlated well with that of the risk area derived from MCE (r = 0.74, p < 0.001 with a linear regression). CONCLUSIONS: The assessment of VVI at MVO permits easy detection of dyssynchronous wall motion during acute myocardial ischemia that cannot be diagnosed by conventional measurement of systolic wall thickness. The spatial extent of inward motion at MVO suggests the size of the risk area.

Validation of transthoracic tissue Doppler assessment of left atrial appendage function.

This study aimed to validate left atrial (LA) wall contraction velocity during atrial contraction (LAWV) in assessing LA function in 22 patients with paroxysmal atrial fibrillation. LAWV at the posterobasal LA wall was measured by transthoracic tissue Doppler echocardiography. LAWV was lower in patients with paroxysmal atrial fibrillation than in control subjects. It was more correlated with LA appendage velocity (r = 0.81) and fractional shortening (r = 0.85) than with parameters related to mitral inflow velocity or ring motion. With a LAWV cut-off value of 1.0 cm/s, receiver operator characteristic analysis curve showed a diagnostic sensitivity of 92% and a specificity of 80% in the identification of patients with spontaneous echocontrast. Among 8 patients with LAWV < or = 1.0 cm/s, cerebral embolism was evident in 3 and LA thrombus in 2, whereas the patients with LAWV greater than 1.0 cm/s had neither. LAWV may be useful to evaluate LA function and risk of embolism.

Noninvasive quantification of regional ventricular function in rats: assessment of serial change and spatial distribution using ultrasound strain analysis.

BACKGROUND: The optimal method for quantitative assessment of regional ventricular function in rats remains unclear. The goal of this study was to investigate the use of ultrasonic strain rate (SR) and strain analysis in evaluating the serial change and spatial distribution of regional contractile function in rats. METHODS: In all, 22 anesthetized rats underwent incremental dobutamine infusion (protocol 1) for assessment of serial change or underwent coronary ligation (protocol 2) for assessment of spatial distribution. For protocol 1, the serial change of systolic SR and strain during dobutamine was measured in the posterior myocardium on the short-axis view, and the systolic strain was compared with the percent change in wall thickening. For protocol 2, the spatial distribution of strain profile was analyzed in normal, peripheral ischemic, and central ischemic regions that were identified by myocardial contrast echocardiography. RESULTS: In protocol 1, the incremental dobutamine infusion resulted in a gradual increase in peak systolic SR. In contrast, peak systolic strain increased with low-dose dobutamine but tended to decrease for higher doses of dobutamine. Further, the serial change of peak systolic strain corresponded to changes in percent change in wall thickening, but the strain values were always lower than percent change in wall thickening. In protocol 2, the strain profile indicated postsystolic thickening in the peripheral ischemic region and indicated systolic wall thinning in the central ischemic region. CONCLUSIONS: Ultrasonic determination of SR and strain is an accurate and noninvasive method of quantitation of the serial change and spatial distribution of regional contractile function in rats.

Myocardial contrast echocardiography assessment of acute changes in collateral perfusion of contralateral coronary artery with coronary flow reserve after coronary angioplasty.

BACKGROUND: Coronary flow velocity reserve (CFVR) is used to evaluate the severity of epicardial and intramyocardial coronary artery disease. Collateral flow to an adjacent compromised myocardial territory may influence the CFVR of a specific artery. METHODS: To assess the impact of collateral flow on CFVR, we measured CFVR and assessed perfusion area (PA) with myocardial contrast echocardiography in the right coronary arteries of 18 patients with total/subtotal occlusion of the left anterior descending coronary artery before and after angioplasty. A total of 10 patients had well-developed collaterals emerging from the right coronary artery (group I) and 8 patients did not (group II). Using a Doppler-tipped guidewire, we measured CFVR, which is defined as the ratio of papaverine-induced hyperemic average peak velocity of coronary flow to baseline. RESULTS: Before angioplasty of the left anterior descending coronary artery, CFVR was significantly reduced in group I compared with group II (2.35 +/- 0.47 vs 3.26 +/- 0.54, P < .01). Baseline average peak velocity in group I before angioplasty was significantly greater than that after angioplasty (23.7 +/- 11.6 vs 19.2 +/- 9.7 cm/s, P < .05). After angioplasty, CFVR immediately increased in group I to 3.46 +/- 0.54 ( P < .001). The increase in CFVR was well correlated with the decrement in PA after angioplasty (r = 0.883, P < .001). CONCLUSION: The CFVR of an artery that supplies extensive collaterals is limited because of an elevation in the baseline resting flow velocity. This restriction in CFVR improves proportionally with decreases in PA that occurs after angioplasty of the ipsilateral coronary artery. These data suggest that PA, in addition to coronary artery structure, influences CFVR.

[Efficacy of intravenous myocardial contrast echocardiography for assessment of perfusion area of the heart in mice].

BACKGROUND AND OBJECTIVES: Intravenous myocardial contrast echocardiography is used clinically, but use in small animals has not been evaluated. The conditions for myocardial opacification and the feasibility of myocardial contrast echocardiography were examined in mice. METHODS: Closed chest mice were examined. The left ventricular short-axis view at the mid papillary muscle level was recorded before and after NC100100 injection using a SONOS 5500 (PHILIPS). Real time and intermittent triggering (every 5 beats) myocardial contrast echocardiography was performed with a mechanical index of low (0.3), middle (0.7), and high (1.5). Open chest mice were examined after left anterior descending coronary artery ligation. Myocardial contrast echocardiography was performed using intermittent triggering imaging (every 5 beats) with high mechanical index (1.5). The ratio of the non-perfused area to the whole left ventricular wall area was compared with that of the non-stained area by Evans Blue. RESULTS: The left ventricular myocardium was opacified in any setting. Good opacification was acquired at middle mechanical index (0.7) in real time myocardial contrast echocardiography and at high mechanical index (1.5) in intermittent myocardial contrast echocardiography. The opacified and non-opacified myocardium were clearly identified in all mice with coronary ligation. The non-opacified area ratio showed a good correlation with the non-stained area ratio (y = 0.93x + 0.51, r = 0.94, p < 0.05). CONCLUSIONS: Myocardial contrast echocardiography can be used to assess myocardial perfusion and determine the ischemic area accurately in situ in the mouse.

Echocardiographic assessment of LV hypertrophy and function in aortic-banded mice: necropsy validation.

We characterized the time course of the left ventricular (LV) geometric and functional changes after aortic banding, validated them by necropsy, and investigated the sensitivity of echocardiographic findings on LV hypertrophy. C57BL/6 mice were subjected to transverse aortic constriction (TAC) or sham operation; echocardiographic assessments were performed before or at 2, 4, 6, and 11 wk after surgery; and some of the mice were euthanized at the corresponding time points. There was a progressive increase in diastolic posterior wall thickness and LV systolic dimension; the percentage of LV fractional shortening (LV%FS) decreased progressively at 4 wk, whereas these parameters remained stable in sham-operated mice. Echo LV mass and LV%FS correlated well with actual whole heart mass and ratio of lung weight to body weight, respectively (r = 0.765 and -0.749, respectively; P < 0.0001). These results suggest that the development of myocardial hypertrophy and systolic dysfunction is a time-dependent process. Echocardiographic assessment of myocardial hypertrophy and functional changes correlate well with the actual heart mass and lung mass. Echocardiography is sensitive enough to assess myocardial hypertrophy and heart functional changes induced by pressure overload in mice.