Kiran B. Sagar

Dobutamine Stress Echocardiography for Risk Stratification After Myocardial Infarction

BACKGROUND Because dobutamine stress echocardiography (DSE) provides assessment of left ventricular function and ischemia at a distance, the major determinants of adverse outcome after acute myocardial infarction (AMI), we undertook this study to determine the role of DSE in risk stratification after AMI. METHODS AND RESULTS A graded DSE in 5-minute stages was performed in 214 patients (age, 57 +/- 13 years [mean +/- SD]) at 2 to 7 days after AMI. Coronary angiography was performed in 193 patients. Follow-up data regarding major cardiac events were obtained through telephone interviews and chart reviews. All patients were followed for > or = 500 days or until a hard cardiac event occurred. The mean follow-up interval was 494 +/- 182 days after AMI. Peak heart rate and systolic blood pressure were 115 +/- 21 bpm and 135 +/- 29 mm Hg, respectively. An adverse outcome occurred in 80 of 214 patients; cardiac death occurred in 15, nonfatal AMI occurred in 15, sustained or symptomatic ventricular arrhythmia occurred in 5, congestive heart failure occurred in 14, and unstable angina occurred in 31. Significant predictors of adverse outcome by univariate analysis were prior myocardial infarction (P = .005), anterior infarction (P = .006), multivessel coronary artery disease (P < .0001), global resting left ventricular wall motion score index (P < .0001), infarction zone nonviability based on akinesis unresponsive to low-dose dobutamine (P < .0001), and ischemia/infarction at a distance (P < .0001). Furthermore, the extent of infarct zone and nonviability correlated with the severity of the cardiac event. Multivariate analysis of clinical, angiographic, and DSE variables revealed that the only independent predictors of adverse outcome were ischemia/infarction at a distance (P < .0001) and infarction zone nonviability (P < .0001). Multivessel disease identified through DSE was more predictive of adverse outcome than was angiographically determined multivessel disease. CONCLUSIONS DSE can be used to predict adverse outcomes after AMI.

The influence of preload and heart rate on Doppler echocardiographic indexes of left ventricular performance: comparison with invasive indexes in an experimental preparation.

We evaluated the ability of Doppler echocardiography to assess left ventricular performance in six open-chest dogs studied under various conditions. Intravenous infusions of nitroglycerin were used to vary preload, atrial pacing was used to control heart rate, and changes in inotropic state were induced by two different doses of dobutamine (5 and 10 micrograms/kg/min iv) and by administration of propranolol (1 mg/kg iv). Left ventricular anterior wall myocardial segment length was used as an index of preload. Maximum aortic blood flow, peak acceleration of aortic blood flow, and dP/dt were measured with an electromagnetic flow probe around the ascending aorta and a high-fidelity pressure transducer in the left ventricle. A continuous-wave Doppler transducer applied to the aortic arch was used to measure peak aortic blood velocity, mean acceleration, time to peak velocity, and the systolic velocity integral. The differences between mean values obtained under different inotropic conditions were significant at the p less than .01 level for peak velocity and at the p less than .05 level for mean acceleration. Within a given animal, Doppler measurements of peak velocity correlated very closely with maximum aortic flow (r = .96), maximum acceleration of aortic flow (r = .95), and with maximum dP/dt (r = .92). Mean acceleration measured by Doppler echocardiography also correlated very closely with conventional indexes, but was subject to greater interobserver variability. Doppler measurements of time to peak and the systolic velocity integral correlated less well with conventional hemodynamic indexes.(ABSTRACT TRUNCATED AT 250 WORDS)

Intramyocardial variability in integrated backscatter: effects of coronary occlusion and reperfusion.

The present study was undertaken to characterize regional myocardial alterations of reflected ultrasound during the cardiac cycle in normal, ischemic, and postischemic reperfused myocardium. Time-averaged integrated backscatter (IB) and cardiac cycle-dependent amplitude modulation were measured from subepicardial, midmyocardial, and subendocardial regions of the left ventricular apex and the midportion of the right ventricular free wall under normal conditions (n = 5), after 1 hr of 100% acute left anterior descending (LAD) occlusion (n = 8), and after 15 min LAD occlusion plus 120 min reperfusion (n = 5) in anesthetized, ventilated open-chest dogs. A significant increase in time-averaged IB was observed in the subepicardium, the midmyocardium, and the subendocardium during ischemia and reperfusion, but there was no intramyocardial variability. Cardiac cycle-dependent amplitude modulation of IB was significantly higher in the normal subendocardium than in the subepicardium (4.3 +/- 0.6 vs 2.9 +/- 0.8 dB, p less than .01) and midmyocardium (2.8 +/- .05 dB, p less than .01). This transmural gradient in amplitude modulation was abolished during ischemia and reperfusion. We conclude that cardiac cycle-dependent amplitude modulation in IB has a transmural dependence in the normal myocardium and this is abolished during acute myocardial ischemia.

Doppler echocardiographic evaluation of Hancock and Björk-Shiley prosthetic valves

Doppler echocardiographic characteristics of normally functioning Hancock and Björk-Shiley prostheses in the mitral and aortic positions were studied in 50 patients whose valvular function was considered normal by clinical evaluation. Doppler studies were also performed in 46 patients with suspected malfunction of Hancock and Björk-Shiley valves and who subsequently underwent cardiac catheterization. Mean gradients were estimated for both mitral and aortic valve prostheses and valve area was calculated for the mitral prostheses. Doppler prosthetic mitral valve gradient and valve area showed good correlation with values obtained with cardiac catheterization (r = 0.93 and 0.97, respectively) for both types of prosthetic valves. The correlation coefficient (r = 0.93) for mean prosthetic aortic valve gradient was also good, although Doppler echocardiography overestimated the mean gradient at lower degrees of obstruction. Regurgitation of Hancock and Björk-Shiley prostheses in the mitral and aortic positions was correctly diagnosed. These results suggest that Doppler echocardiography is a reliable method for the characterization of normal and abnormal prosthetic valve function.

Safety and Accuracy of Dobutamine-Atropine Stress Echocardiography for the Detection of Residual Stenosis of the Infarct-Related Artery and Multivessel Disease During the First Week After Acute Myocardial Infarction

BACKGROUND The safety of dobutamine-atropine echocardiography early after acute myocardial infarction is unknown. Its accuracy for the early detection of infarct artery stenosis and multivessel coronary artery disease is also unclear. The objective of the present study was to document its safety and accuracy during the first week after acute myocardial infarction. METHODS AND RESULTS Multistage dobutamine-atropine stress echocardiography was performed in 232 patients (age, 58 +/- 13 years; 58 women) at 5 +/- 2 days after acute myocardial infarction. The peak heart rate was 116 +/- 20 bpm. There were no episodes of sustained ventricular tachycardia, myocardial infarction, or death. Atropine with dobutamine was tolerated well. Coronary angiography was performed in 206 patients (89%). There were 171 patients (83%) with infarct artery stenosis of > or = 50% and 114 patients (55%) with multivessel disease. Ischemic or biphasic responses in the infarction zone were 82% (140 of 171) sensitive and 80% (28 of 35) specific for residual stenosis. Sensitivity was similar for occluded arteries (77%, 36 of 47) and patent but stenotic arteries (84%, 104 of 124). Wall motion abnormalities outside the infarction zone were specific (97%, 89 of 92) and moderately sensitive (68%, 77 of 114) for multivessel disease. The only determinant of sensitivity for residual infarct artery stenosis was improved wall motion at low dose (P < .01). The determinants of sensitivity for multivessel disease were peak heart rate and infarct size (P < .01). CONCLUSIONS Dobutamine-atropine stress echocardiography was safely used to detect residual infarct artery stenosis and multivessel disease during the first week after acute myocardial infarction. The test may be very effective for evaluating patients with acute myocardial infarction because sensitivity for residual stenosis and multivessel disease was maximal in the high-risk subsets of patients with viable, jeopardized myocardium and large infarct size.

Dobutamine-Atropine Stress Echocardiography for the Detection of Coronary Artery Disease in Patients With Left Ventricular Hypertrophy Importance of Chamber Size and Systolic Wall Stress

BACKGROUND Left ventricular hypertrophy is a heterogeneous disorder with distinct morphologies. Changes in wall thickness, left ventricular chamber diameter, and mass alter systolic wall stress of the left ventricle and may influence ischemic threshold. Thus, the goal of this study was to investigate the effect of the different patterns of left ventricular hypertrophy on the accuracy of dobutamine-atropine stress echocardiography. METHODS AND RESULTS Three-hundred eighty-six patients underwent multistage dobutamine-atropine stress echocardiography and diagnostic angiography. Echocardiograms were measured for mean and relative wall thicknesses, chamber size, left ventricular mass, and end-systolic wall stress. The patterns of ventricular hypertrophy were concentric hypertrophy (increased wall thickness and mass), eccentric hypertrophy (normal wall thickness and increased mass), and concentric remodeling (increased wall thickness and normal mass). The overall sensitivity, specificity, and accuracy of dobutamine-atropine stress echocardiography for the detection of coronary artery disease were 85%, 87%, and 86%, respectively. Increased left ventricular mass index alone did not affect accuracy. Sensitivity was markedly reduced (36%) only in those with concentric remodeling. The univariate predictors of false-negative studies were single-vessel left circumflex disease, increased wall thickness, small chamber size, hyperdynamic ejection fraction, and left ventricular concentric remodeling. Multivariate predictors were concentric remodeling (P<0.0001; odds ratio, 13.5), left ventricular ejection fraction >2 SD above normal (P<0.0001), and single-vessel left circumflex disease (P<0.0007; odds ratio, 7.6). Sensitivity was excellent in patients with small ventricles and normal wall thickness and in those with normal or large chambers regardless of wall thickness. CONCLUSIONS Dobutamine-atropine stress echocardiography is an accurate test in most patients with left ventricular hypertrophy, but it is insensitive in the small subset with concentric remodeling.

Relation of Ultrasonic Backscatter and Acoustic Propagation Properties to Myofibrillar Length and Myocardial Thickness

BACKGROUND Ultrasonic backscatter demonstrates a cardiac cycle-dependent modulation. The exact mechanism of the modulation is under debate. The objective of the present study was to test the hypothesis that a change in size and configuration of myofilaments from systole to diastole alters acoustic propagation properties and backscatter. METHODS AND RESULTS In vivo measurements were made of integrated backscatter at 5 MHz (IBR5), followed by in vitro measurements of ultrasonic attenuation, speed, and heterogeneity index using a scanning laser acoustic microscope at 100 MHz. Studies were performed in canine hearts (16) arrested in systole (8) with calcium chloride or arrested in diastole (8) with potassium chloride. Sarcomere length was measured with a calibrated eyepiece on a Ziess microscope. Wall thickness was measured with calipers. The attenuation coefficient of 220 +/- 34 dB/cm during systole was significantly higher than the coefficient of 189 +/- 24 dB/cm during diastole (P < .01); the IBR5 of -44.7 +/- 1.2 dB during systole was significantly greater than the IBR5 of -47.0 +/- 1.0 dB during diastole (P < .01); the ultrasonic speed of 1591 +/- 11 m/s during systole was higher than the speed of 1575 +/- 4.2 m/s during diastole (P < .01); and the heterogeneity index of 7.4 +/- 1.8 m/s during systole was significantly lower than the index of 9.0 +/- 2.0 m/s during diastole (P < .02). The sarcomere length of 1.804 +/- 0.142 microns during diastole was significantly higher than the length of 1.075 +/- 0.177 micron during systole (P < .01). Wall thickness was significantly greater during systole than during diastole (20 +/- 3 versus 9 +/- 3 mm, P < .01). CONCLUSIONS Ultrasonic backscatter and propagation properties are directly related to sarcomere length and myocardial thickness and may be responsible for cardiac cycle-dependent variation in backscatter.

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 let 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% anx 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.

Dobutamine-atropine stress echocardiography and dipyridamole sestamibi scintigraphy for the detection of coronary artery disease : Limitations and concordance

OBJECTIVES We sought to compare dobutamine-atropine stress echocardiography (DASE) and dipyridamole Technetium 99-m (Tc-99m) sestamibi single photon emission computed tomography (SPECT) scintigraphy (DMIBI) for detecting coronary artery disease (CAD). BACKGROUND Both DASE and DMIBI are effective for evaluating patients for CAD, but their concordance and limitations have not been directly compared. METHODS To investigate these aims, patients underwent multistage DASE, DMIBI and coronary angiography within three months. Dobutamine-atropine stress echocardiography and stress-rest DMIBI were performed according to standard techniques and analyzed for their accuracy in predicting the extent of CAD. Segments were assigned to vascular territories according to standard models. Angiography was performed using the Judkins technique. RESULTS The 183 patients (mean age: 60 +/- 11 years, including 50 women) consisted of 64 patients with no coronary disease and 61 with single-, 40 with two- and 18 with three-vessel coronary disease. Dobutamine-atropine stress echocardiography and DMIBI were similarly sensitive (87%, 104/119 and 80%, 95/119, respectively) for the detection of CAD, but DASE was more specific (91%, 58/64 vs. 73%, 47/64, p < 0.01). Sensitivity was similar for the detection of CAD in patients with single-vessel disease (84%, 51/61 vs. 74%, 45/61, respectively) and multivessel disease (91%, 53/58 vs. 86%, 50/58, respectively). Multiple wall motion abnormalities and perfusion defects were similarly sensitive for multivessel disease (72%, 42/58 vs. 66%, 38/53, respectively), but, again, DASE was more specific than DMIBI (95%, 119/125 vs. 76%, 95/125, respectively, p < 0.01). Dobutamine-atropine stress echocardiography and DMIBI were moderately concordant for the detection and extent of CAD (Kappa 0.47, p < 0.0001) but were only fairly (Kappa 0.35, p < 0.001) concordant for the type of abnormalities (normal, fixed, ischemia or mixed). CONCLUSIONS Dobutamine-atropine stress echocardiography and DMIBI were comparable tests for the detection of CAD. Both were very sensitive for the detection of CAD and moderately sensitive for the extent of disease. The only advantage of DASE was greater specificity, especially for multivessel disease. Dobutamine-atropine stress echocardiography may be advantageous in patients with lower probabilities of CAD.

Relationship of left ventricular mass to defibrillation threshold for the implantable defibrillator: A combined clinical and animal study

Defibrillation results when a critical mass of myocardium is depolarized. The relationship between echocardiographic determinations of left ventricular mass, volume, and cavity radius to wall thickness ratio and defibrillation threshold for the implantable defibrillator was examined. Ten patients with two large patch defibrillating lead systems were studied. Defibrillation threshold was determined intraoperatively as the lowest energy terminating ventricular fibrillation. Left ventricular mass, volume, and radius/posterior wall thickness ratio were calculated from two-dimensional echocardiograms. A significant correlation was found between left ventricular mass and defibrillation threshold (r = 0.78, p less than 0.01). The correlations between defibrillation threshold and left ventricular volume (r = 0.59) and radius/wall thickness ratio (r = 0.55) were not significant. Subsequently, 11 dogs undergoing defibrillation trials with a transvenous catheter and a chest wall patch were studied. Defibrillation threshold was defined as the lowest energy-terminating ventricular fibrillation (four separate attempts). Subsequently, the heart was dissected, and the left ventricle (including the septum) was weighed. The correlation between left ventricular weight and defibrillation threshold (r = 0.76) was significant (p less than 0.01). We conclude that noninvasive assessment of left ventricular mass and direct measurement of left ventricular weight are significantly correlated with defibrillation threshold and consistent with the critical mass hypothesis.