Left Circumflex Coronary Artery Territory Research Articles

Coronary Flow Velocity Reserve Measurement in Three Major Coronary Arteries Using Transthoracic Doppler Echocardiography

Measurement of the coronary flow velocity reserve (CFVR) by transthoracic Doppler echocardiography (TTDE) has been reported to be useful for the noninvasive assessment of significant coronary artery stenosis or myocardial ischemia. The purpose of this study was to evaluate the value of this method in three major coronary arteries for detecting myocardial ischemia in the clinical setting. We studied 89 consecutive patients who were referred to our outpatient clinic because of chest pain. We measured CFVR using TTDE in three major coronary arteries. We defined CFVR<2.0 in at least one vessel as being positive for myocardial ischemia. The accuracy of CFVR measurements for detecting myocardial ischemia was determined in comparison with exercise thallium-201 (Tl-201) single photon emission computed tomography (SPECT) as a reference standard. CFVR in at least one vessel was successfully measured in 87 of 89 patients (98%). The sensitivity and specificity of CFVR<2.0 in at least one coronary vessel, in any of the coronary territories, was 86% and 89%, respectively. In terms of assessing myocardial ischemia in each coronary artery territory, the agreement between CFVR<2.0 and Tl-201 SPECT for the left anterior descending coronary artery, the posterior descending coronary artery, and the left circumflex coronary artery territories was 95%, 81%, and 73%, respectively. Noninvasive CFVR measurement by TTDE may be useful for detecting myocardial ischemia, as well as for identifying ischemic territories in the clinical setting.

Comparison of Contrast-enhanced Real-time Live 3-Dimensional Dobutamine Stress Echocardiography with Contrast 2-Dimensional Echocardiography for Detecting Stress-induced Wall-motion Abnormalities

Two-dimensional (2D) contrast-enhanced dobutamine stress echocardiography (DSE) is used clinically to diagnose stress-induced wall-motion abnormality (WMA). We hypothesized that contrast-enhanced real-time 3-dimensional (3D) DSE could improve the detection rate of WMA, because from a single full-volume acquisition, multiple segments can be visualized. We acquired both 2D and 3D DSE in 78 patients with known or suggested coronary artery disease (mean age: 65 years; 44 men). Dobutamine was infused using a standard protocol, and atropine added, if required. For 2D DSE, the intravenous contrast agent was injected at each stage and images displayed in a quadscreen format. For 3D DSE, contrast harmonic 3D data sets (full volumes) were acquired at baseline and peak stress. Using custom software, 3 short-axis views (from apex to base) were created, and wall motion scored using a wall-motion score index using a 16-segment model. A positive stress test was defined as new or worsened WMA or fixed abnormality during stress. Heart rate increased from 72 +/- 13 to 133 +/- 15/min (86 +/- 11% of age-predicted). A total of 1248 segments were analyzed at each stage for both modalities. A single segment at baseline and 5 segments at peak stress could not be assessed with contrast 2D DSE. In contrast, 88 segments at baseline and 39 segments at peak stress could not be assessed with contrast 3D DSE. With 3D DSE, the majority of uninterpretable segments were in the anterior and lateral walls. Significant correlations were noted between wall-motion score index by 2D and 3D DSE at baseline (r = 0.78) and peak stress (r = 0.83). The concordance rate (positive/negative findings) between modalities was 69% (54/78) on a patient basis and 88% (206/234) on a perfusion territory basis. When using 2D DSE results as the gold standard, sensitivity and specificity for detecting WMA by 3D DSE was 58% and 75%, respectively. Sensitivity and specificity values were 67% and 94% for the right coronary artery, 53% and 81% for the left anterior descending coronary artery, and 88% and 100% for the left circumflex coronary artery territory, respectively. Contrast-enhanced 3D DSE was feasible in the majority of patients. However, the moderate concordance between both modalities was a result of: (1) difficulties in visualizing the anterolateral segments because of the relatively large imprint of the transducer; and (2) lower frame rates with 3D DSE resulting in the erroneous diagnosis of dyssynchrony.

Noninvasive quantification of the contractile reserve of stunned myocardium by ultrasonic strain rate and strain.

We sought to investigate ultrasonic strain rate and strain as new indices to quantify the contractile reserve of stunned myocardium during dobutamine infusion. Stunning of the left ventricular posterior wall was induced in 9 closed-chest pigs after 30 minutes of severe hypoperfusion followed by 60 minutes of reperfusion of the left circumflex coronary artery territory. A second group of 7 animals had no coronary occlusion and served as normal controls. An incremental dobutamine infusion protocol was used in both groups. Changes in regional radial function were monitored by use of ultrasound-derived maximal systolic radial strain rate (SR) and systolic strain (epsilon). In the control group, dobutamine induced an increase in both SR and maximal dP/dt, which correlated linearly (r=0.85). Conversely, epsilon values increased at low doses of dobutamine (2.5 to 5 microg. kg(-1). min(-1)) but decreased during higher infusion rates (10 to 20 microg. kg(-1). min(-1)). During circumflex hypoperfusion, SR and epsilon of the posterior wall decreased from 5.0+/-0.3 s(-1) and 63+/-6% to 2.9+/-0.3 s(-1) and 27+/-4%, respectively (P<0.01). After 60 minutes of reperfusion, SR and epsilon failed to fully resume because of stunning, averaging 3.6+/-0.2 s(-1) and 35+/-3%, respectively (P=0.12 versus ischemia, P<0.05 versus baseline). During dobutamine infusion, SR increased at 5 microg. kg(-1). min(-1) and exceeded baseline values at 20 microg. kg(-1). min(-1) (P<0.05), whereas epsilon increased only at high doses and remained below baseline levels (P<0.05). The changes in regional function of stunned myocardium during inotropic stimulation could be characterized by use of ultrasonic deformation parameters. During dobutamine infusion, strain-rate values quantified the contractile reserve better than strain values.

Myocardial Flow Reserve in Long-Term Survivors of Repair of Anomalous Left Coronary Artery From Pulmonary Artery

Objectives. This study sought to evaluate regional myocardial flow reserve in long-term survivors of repair of anomalous left coronary artery from pulmonary artery (ALCAPA) and to relate the flow abnormalities to the patients’ exercise performance.Background. Patients with ALCAPA usually present during infancy with severe ischemic cardiomyopathy. The left ventricular function recovers after surgical repair. However, the extent of recovery of myocardial blood flow (MBF) and its potential physiologic significance in long-term survivors are unknown.Methods. We evaluated MBF (ml/g per min) at baseline and during maximal coronary vasodilation by adenosine in 11 patients after ALCAPA repair (median age 17 years, range 7 to 22) using nitrogen-13 ammonia and dynamic positron emission tomographic imaging. Patients also underwent an incremental exercise test with metabolic monitoring. In each patient, MBF was quantified in the three major vascular territories: the left anterior descending and left circumflex coronary artery territories and the right coronary artery (control region) territory.Results. Basal MBF was mildly reduced in the left coronary territories versus the control region (0.79 ± 0.14 vs. 0.85 ± 0.19, p = 0.05). During hyperemia, flow in the left coronary territories was significantly lower than that in the control region (2.1 ± 0.5 vs. 2.6 ± 0.5, p < 0.001). As a result, myocardial flow reserve was lower in the left coronary territories than in the control region (2.6 ± 0.7 vs. 3.2 ± 0.7, p < 0.001). Exercise performance was impaired in patients when compared with age-matched control subjects. Maximal oxygen consumption correlated linearly with maximal hyperemic flows in the left coronary artery territories (r = 0.73, p = 0.03).Conclusions. Long-term survivors of ALCAPA repair demonstrate regional impairment of myocardial flow reserve. This may contribute to impaired exercise performance by limiting cardiac output reserve.

The value of dobutamine stress echocardiography for the detection of coronary artery disease in women

To determine whether there were any gender-based differences in the detection of coronary artery disease by dobutamine stress echocardiography, we examined 288 patients (187 men and 101 women) who underwent coronary angiography within 8 weeks of dobutamine stress testing. Abnormal test results were indicated by left ventricular wall motion abnormalities at rest, which did not improve or worsen, or inducible wall motion abnormalities in two or more segments with dobutamine. Overall, dobutamine stress echocardiography showed a high sensitivity, specificity, and accuracy in both men and women: 85%, 96%, and 88% and 90%, 79%, and 86%, respectively. The sensitivity in detecting significant coronary artery disease in our population was not influenced by gender. However, the sensitivity of the test was influenced by the extent and location of coronary disease and the pattern of left ventricular hypertrophy. The sensitivity was 80% in patients with single-vessel disease, whereas the sensitivity was 91% in patients with multivessel disease. In addition, patients with single-vessel disease had lower sensitivity when the abnormality was located in the left circumflex coronary artery territory (59% versus 86% in the left anterior descending and right coronary territories). Our data indicated that there is no gender-based difference in the sensitivity and specificity of dobutamine stress echocardiography in detecting coronary artery disease and that the limitations of the test should be attributed to the extent and location of coronary disease. (J Am Soc Echocardiogr 1997;10:811-17.)

Quantification of technetium 99m-labeled sestamibi single-photon emission computed tomography based on mean counts improves accuracy for assessment of relative regional myocardial blood flow: Experimental validation in a canine model

Background. Quantification of single-photon emission computed tomographic (SPECT) images is generally based on determination of maximal counts on radial sectors of short-axis slices. We hypothesized that analysis of mean counts may reduce estimation error. Methods and Results. We compared quantitative 99mTc-labeled sestamibi (MIBI) SPECT based on maximal myocardial counts with that based on mean myocardial counts for accuracy of quantifying relative regional myocardial perfusion in a canine model of permanent left anterior descending coronary artery occlusion. MIBI and radiolabeled microspheres were injected during left anterior descending coronary artery occlusion. Relative microsphere myocardial blood flow was expressed as a percentage of normal (left circumflex coronary artery territory) blood flow. SPECT imaging was performed in vivo and ex vivo. Relative MIBI uptake on SPECT short-axis slices was quantified with normalized circumferential profiles based on maximal and mean counts. In vivo and ex vivo SPECT relative myocardial count density was compared to relative myocardial blood flow in six dogs. In the comparisons, percent errors in estimating the relative blood flow and relative flow deficit with MIBI SPECT imaging were calculated. There was an excellent correlation between absolute myocardial tissue MIBI activity and regional myocardial blood flow for each of the six dogs ( r = 0.90 to 0.98). The correlations between relative myocardial count density on SPECT and relative blood flow for individual sectors were similar for maximal and mean count profiles (maximal, 0.79 to 0.83; mean, 0.77 to 0.82). Comparing the nadirs of in vivo and ex vivo circumferential count profiles, the correlations were slightly better (maximal, 0.82 to 0.91; mean, 0.87 to 0.91). Average percent errors in assessing relative blood flow and relative flow deficit were decreased significantly by use of mean count profiles ( p < 0.05). Conclusions. Relative SPECT count density with either maximal or mean count profiles correlated well with relative myocardial blood flow. Compared with maximal count profiles, quantification with mean count profiles improved estimation of relative flow.

Reproducibility of quantitative myocardial contrast echocardiography

To determine whether myocardial contrast echocardiography is quantitatively reproducible, repeated intracoronary injections of sonicated albumin (5%) were performed in eight open chest dogs. Paired injections were performed at baseline, during ischemia produced by ligation of a coronary artery, and during hyperemia induced by intravenous infusion of 0.75 mg/kg body weight of dipyridamole. Contrast washout curves were generated for the left anterior descending coronary artery territory (ischemic area) and left circumflex coronary artery territory (nonischemic area) by beat per beat analysis of frozen end-diastolic frames of left ventricular short-axis views. Peak contrast intensity, contrast washout half-time and area under the curve were derived from these curves. A total of 75 contrast washout curves were analyzed for the study of interinjection, intraobserver and interobserver reproducibility.The correlation coefficients between measurements obtained from paired injections of the echocardiographic contrast agent (interinjection reproducibility) ranged from 0.78 for peak contrast intensity to 0.87 for area under the curve. Percent error varied between 14.7% and 24.7%. The intraobserver variability in measurements was less than the interinjection variability, with a cumulative mean percent error of 17.8% and correlation coefficients of 0.72 (peak contrast intensity), 0.95 (area under the curve) and 0.96 (washout half-time). Interobserver correlation for all indexes was high (r = 0.92 to 0.96).It is concluded that peak contrast intensity, contrast washout half-time and the area under the curve derived from myocardial contrast washout curves can be measured reproducibly from videotapes. In addition, the variability between two injections attempted under identical conditions is greater than reader variability from videotapes.