The clinical relevance of myocardial viability in patient management

This study examined the importance of viability as a clinical issue in 532 patients with angiographically proven CAD who underwent exercise SPECT thallium imaging. Conventional 4-hour delayed images were used to differentiate scar tissue from ischemia (20 segments per patient). There were 90 patients (17%) with normal images, 274 patients (52%) with reversible defects only, and 168 patients (31%) with scar tissue either with or without associated ischemia. The patients with scar tissue were subdivided according to the number of segments with fixed defects and the number of additional reversible defects. There were 114 patients with scar tissue alone or more scar tissue than ischemia. Contrast ventriculography in these 114 patients revealed normal wall motion or ejection fraction in 50 patients. On the basis of results of thallium imaging alone, the issue of viability was probably significant in 114 patients (21%); however, when the ventriculographic data were also included, the issue was significant in only 64 patients (12%) (p < 0.001). Thus myocardial viability is an important issue in 21% of patients with CAD when conventional thallium imaging is used, but this percentage decreases to 12% when wall motion and ejection fraction data are also included. These data may be important in considerations for the need of metabolic imaging and emerging scintigraphic techniques.

Effect of intravenous adenosine infusion on myocardial perfusion and function. Hemodynamic/angiographic and scintigraphic study

BACKGROUND

Myocardial perfusion imaging during adenosine-induced hyperemia with dipyridamole or adenosine is an accepted method to diagnose coronary artery disease (CAD) and risk assessment. The mechanism of perfusion abnormality may be caused by disparate flow responses or coronary steal. This study examined the relation between 201Tl perfusion pattern and hemodynamic/angiographic changes during intravenous adenosine infusion.

METHODS AND RESULTS

Patients with suspected CAD underwent sequential hemodynamic, coronary arteriographic, and left ventriculographic studies simultaneously with 201Tl imaging during adenosine infusion (140 micrograms.kg-1.min-1 for 6 minutes). There were 33 patients with CAD and 12 patients without CAD. The 201Tl images (using single-photon emission computed tomography) were abnormal in 31 patients with CAD (sensitivity, 94%) and normal in the patients without CAD (specificity, 100%). In patients with and without CAD, there were significant increases in heart rate and cardiac output (p less than 0.0001) and decreases in systemic vascular resistance and blood pressure (p less than 0.0001). There was a 77 +/- 38% increase in pulmonary capillary wedge pressure in normal subjects and a 125 +/- 83% increase in patients with CAD (p = 0.02). ST segment depression was observed in 11 patients with CAD (33%). In CAD patients, there was no change in percent diameter or area stenosis measured quantitatively during adenosine infusion. In 15 patients, contrast left ventriculography was repeated during adenosine infusion. In these patients, 201Tl perfusion defects were seen in 31 of 75 segments (41%) whereas only six of 75 segments (8%) developed regional wall motion abnormality (p less than 0.001); the remaining segments showed either no change or improved function. The left ventricular ejection fraction did not change significantly (73% versus 75%).

CONCLUSIONS

There is a disparity between the effects of adenosine on left ventricular perfusion and function; most patients with CAD have perfusion defects whereas the global and regional systolic function remains unchanged or improves. Diastolic left ventricular dysfunction is a probable mechanism of the increase in pulmonary capillary wedge pressure.

Side effects during adenosine thallium imaging with single-port or double-port infusion protocols

The double-port infusion protocol during adenosine thallium imaging involves the use of two infusion systems, one for adenosine and one for thallium. The single-port infusion protocol, on the other hand, uses one infusion system; both adenosine and thallium are injected via a "Y" connection. This study examined the possibility that the single infusion system, by displacing a column of blood filled with adenosine, may be responsible for a greater incidence of side effects. In a parallel study, 140 patients underwent adenosine thallium imaging with the single-port system (group 1) and 140 patients underwent imaging with the double-port system (group 2). Both groups were comparable in age (67 +/- 10 years vs 64 +/- 11 years), gender (men comprised 56% of patients in group 1 and 64% in group 2), resting heart rate, and systolic blood pressure. More patients in group 1 had chest pains (57% vs 44%; p = 0.03), ST-segment depression (25% vs 9%; p = 0.005), nausea (11% vs 4%; p = 0.04), and second- or third-degree atrioventricular block (11% vs 5%; p less than 0.08) than did patients in group 2. The other side effects were similar, and peak heart rate and peak systolic blood pressure were also similar. The thallium images that used single-photon emission computed tomography were abnormal in 61% of patients in group 1 and in 65% of patients in group 2 (p = not significant).(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanism of exercise-induced hypotension in coronary artery disease

Hypotension during exercise testing has been considered a marker of extensive coronary artery disease (CAD) and poor prognosis. The mechanism of hypotension was examined in 25 CAD patients who developed hypotension during treadmill exercise testing (mean decrease in systolic blood pressure [BP] 33 +/- 13 mm Hg) (group 1) and was compared with the results of 25 CAD patients who had a normal systolic BP response to exercise (mean increase 53 +/- 15 mm Hg) (group 2). The 2 groups were comparable in age, sex, extent of CAD, previous myocardial infarction, left ventricular ejection fraction, history of hypertension and cardiac medications. Exercise heart rate (121 +/- 23 vs 133 +/- 25 beats/min; p = not significant [NS]) and duration (6 +/- 2 vs 7 +/- 3 minutes; p = NS) were comparable. ST-segment depression occurred in 44% of patients in group 1 and in 52% in group 2 (p = NS), and angina during exercise occurred in 60% of both groups. Single-photon emission computed tomographic thallium images were abnormal in 24 patients (96%) in group 1 and in 20 patients (80%) in group 2 (p = NS). Percent thallium abnormality was 19 +/- 12% in group 1, and 18 +/- 14% in group 2 (p = NS), and the severity of thallium abnormality was 710 +/- 510 in group 1, and 510 +/- 500 in group 2 (p = NS). Ischemia involving the inferior/posterior segments was seen in 68% of patients in group 1 and in 60% in group 2 (p = NS). Increased lung thallium uptake was seen in 48% of both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrioventricular block during adenosine thallium imaging

Transient atrioventricular (AV) block has been reported during adenosine thallium imaging. This study examined the predictors and hemodynamic implications in 55 patients who had second- or third-degree AV block (group 1) and compared the results with those in 803 patients who did not have AV block (group 2). There were no significant differences in age, sex, or heart rate at baseline between the two groups. ST segment depression was observed in 25% of patients in group 1 and 16% in group 2 (p = NS). Chest pain occurred in 56% in group 1 and 44% in group 2 (p = NS). Preexisting conduction abnormalities (17% vs 16%) and treatment with digitalis (15% vs 15%) and beta-blockers (31% vs 36%) were similar in the two groups. The results of thallium imaging were abnormal in 66% in group 1 and 67% in group 2 (p = NS). Reversible thallium defects were seen in 51% in group 1 and 52% in group 2 (p = NS). The AV block appeared during the first 2 minutes of infusion in 40 patients (73%) and disappeared despite continuation of infusion in 43 (78%). The heart rate during AV block was 79 +/- 18 beats/min, and the systolic blood pressure was 127 +/- 27 mm Hg. Premature termination of adenosine infusion was required in one patient (2%). Aminophylline was used in 5% in group 1 and 2% in group 2 (p = NS). Thus AV block is transient, occurs during the early minutes of infusion, is not aggravated by digitalis or beta-blocker therapy, can be seen in patients with normal perfusion images, and is often well tolerated.

Differentiation between primary dilated cardiomyopathy and ischemic cardiomyopathy based on right ventricular performance

The differentiation of primary dilated cardiomyopathy from ischemic cardiomyopathy, though important, is difficult clinically and may require coronary angiography or metabolic imaging. Both patient groups have severe left ventricular dysfunction and severe wall motion abnormality. This study examined the differences in right ventricular performance between the two groups. There were 90 patients with a left ventricular ejection fraction less than 30% who had coronary angiography and multigated radionuclide angiography (MUGA). Of these, 69 had ischemic cardiomyopathy and 21 had primary cardiomyopathy. The left ventricular ejection fraction was similar; 22 +/- 6% in ischemic cardiomyopathy and 21 +/- 6% in primary cardiomyopathy. However, the right ventricular ejection fraction was higher in ischemic cardiomyopathy (38 +/- 16% versus 29 +/- 12%, p less than 0.01). There were 59 patients with right ventricular ejection fraction greater than or equal to 30%, of whom 50 patients (85%) had ischemic cardiomyopathy. The left ventricular and right ventricular volumes were determined by a count-based method. The right ventricular end-diastolic volume/left ventricular end-diastolic volume ratio was 0.57 in ischemic cardiomyopathy and 1.07 in primary cardiomyopathy (p less than 0.05). Thus assessment of right ventricular function may help differentiate primary from ischemic cardiomyopathy; a preserved right ventricular performance is highly suggestive of ischemic cardiomyopathy.

Comparison of same-day protocols using technetium-99m-sestamibi myocardial imaging

Two same-day protocols (rest/exercise [Protocol 1] and exercise/rest [Protocol 2]) with sestamibi (hexakis 2-methoxy-2-isobutyl-isonitrile) were performed within 2 to 14 days of each other after randomization. The initial study in each protocol was done using a dose of 185-296 MBq of 99mTc-sestamibi. The second study in each protocol used a dose of 555-925 MBq. SPECT imaging was started 30 to 60 min after injection using a 180 degrees anterior arc. Segmental analysis was interpreted as normal, scar or ischemia (20 segments/patient). Among the protocols, there was concordance in 93% of the segments (593/640 segments). In the 11 patients with coronary artery disease and no prior myocardial infarction who had ischemic abnormality, count densities from abnormal and normal zones were compared between the two protocols. Protocol 1 showed greater count differences between abnormal and normal zones on exercise images with better normalization of abnormality on rest images than Protocol 2 (p less than 0.05). Technetium-99m-sestamibi provides high quality images using either of the two same-day protocols. However, the rest/exercise protocol provides better image contrast and ability to detect reversibility of perfusion defects, and is the preferred same-day protocol.

Tomographic myocardial perfusion imaging with technetium-99m teboroxime during adenosine-induced coronary hyperemia: correlation with thallium-201 imaging

Single-photon emission computed tomographic imaging with technetium-99m teboroxime during exercise has been found to be feasible and the results correlate with those obtained with thallium-201. This study examined the feasibility of this technique and compared tomographic imaging with technetium-99m teboroxime during adenosine-induced coronary hyperemia with thallium-201 imaging. With the patient positioned on the imaging table, adenosine was infused at a rate of 140 micrograms/kg per min for 6 min. At 4 min, 20 to 25 mCi (740 to 925 MBq) of technetium-99m teboroxime was injected intravenously and imaging was started as soon as the infusion was completed with use of a 180 degrees anterior arc and 32 stops at 10 s/stop (total imaging time 7.8 min). Rest images were obtained 60 to 90 min later with use of a similar dose of technetium-99m teboroxime. Exercise tomographic thallium images were obtained within 2 weeks of the teboroxime studies. In the 20 patients studied, the teboroxime images were normal in 2 (50%) of 4 normal subjects and abnormal in 15 (94%) of 16 patients with coronary artery disease; 4 of the 15 had a fixed defect and 11 a reversible defect. There was agreement between teboroxime and thallium studies in 16 patients (80%), in 319 (80%) of 400 segments and in 50 (83%) of 60 vascular segments (p less than 0.05). In two normal subjects, an apparent fixed defect involving the inferior wall was seen on the teboroxime but not the thallium images and was thought to be due to an attenuation artifact secondary to extracardiac activity in the left lobe of the liver.(ABSTRACT TRUNCATED AT 250 WORDS)

Nuclear cardiac imaging

Important developments in the field of nuclear cardiac imaging include increasing use of single-photon emission computed tomography; the availability of pharmacologic stress testing; the introduction of newer technetium-labeled perfusion imaging agents; and a number of other newer imaging agents and imaging techniques. Tomographic imaging improves image quality as well as sensitivity. This improvement is probably more noticeable with pharmacologic stress testing and with the newer technetium agents. A number of pharmacologic stress agents are now being used. These include dipyridamole, adenosine, and dobutamine. In our experience, thallium tomographic imaging during adenosine-induced coronary hyperemia has resulted in a high degree of accuracy in the diagnosis of coronary artery disease. Both 99mTc-sestaMIBI (hexakis-2-methoxyisobutyl-isonitrile) and 99mTc-teboroxime may be used for simultaneous assessment of perfusion and function. These agents, although similar to thallium in many aspects, differ in many other aspects as they differ from each other. For example, sestaMIBI has a long retention time, but teboroxime has a very rapid washout time. Therefore, the imaging protocols using these two agents are considerably different. Assessment of myocardial viability has been an area of interest; specifically, the use of the reinjection technique has improved the ability to differentiate between scar tissue and viable myocardium.

Remote fiber-optic chemical sensing using evanescent-wave interactions in chalcogenide glass fibers

An infrared-transmitting chalcogenide fiber was used as an optical probe to analyze qualitatively and quantitatively various chemical substances in aqueous solutions. An unclad fiber with 380-microm diameter was combined with a Fourier transform infrared spectrometer to monitor the concentration of the analytes in solutions by measuring the changes in the absorbance of their fundamental vibration peaks. A linear relationship was observed between the absorption by the vanescent field and concentrations of various analytes. For this study low concentrations of acetone, ethyl alcohol, and sulfuric acid were detected in aqueous solutions. The minimum detection limit for these three chemical substances was 5, 3, and 2 vol. %, respectively, with a sensor length of 15 cm. It was also demonstrated that the same sensor design is capable of monitoring gaseous species such as dichlorodifluoromethane.

Assessment of coronary artery disease using single-photon emission computed tomography with thallium-201 during adenosine-induced coronary hyperemia

Thallium-201 myocardial imaging during dipyridamole-induced coronary hyperemia has been an accepted method for diagnosing coronary artery disease (CAD) and risk stratification. Adenosine is a powerful short-acting coronary vasodilator. Initial results of thallium imaging during adenosine infusion have been encouraging. In 132 patients with CAD and in 16 patients with normal coronary angiograms, adenosine was given intravenously at a dose of 0.14 mg/kg/min for 6 minutes and thallium-201 was injected at 3 minutes. The thallium images using single-photon emission computed tomography were abnormal in 47 of the 54 patients (87%) with 1-vessel, in 34 of 37 patients (92%) with 2-vessel and in 40 of 41 patients (98%) with 3-vessel CAD. The sensitivity was 92% in the 132 patients with CAD (95% confidence intervals, 86 to 96%). In patients with normal coronary angiograms, 14 of 16 patients had normal thallium images (specificity, 88%; 95% confidence intervals, 59 to 100%). The results were very similar when subgroups of patients were analyzed: those without prior myocardial infarction, elderly patients and women. The nature of the perfusion defects (fixed or reversible) was assessed in relation to whether the 4-hour delayed images were obtained with or without the reinjection technique. In patients who underwent conventional delayed imaging, there were more fixed perfusion defects than in patients with reinjection delayed imaging (16 vs 0%, p less than 0.0001). The adverse effects were mild, transient and well tolerated. Thus, adenosine thallium tomographic imaging provides a high degree of accuracy in the diagnosis of CAD. The use of the reinjection technique enhances the ability to detect reversible defects.

Dipyridamole thallium imaging

Dipyridamole cardiac imaging is a useful alternative to exercise stress testing in the evaluation of patients with ischemic heart disease. Intravenous dipyridamole has been approved recently for clinical use. Oral dipyridamole is widely available. The hemodynamic effects of dipyridamole include an increase in coronary blood flow in excess of the increase in myocardial oxygen consumption and cardiac output. The quality of the thallium images is better or similar to that of exercise thallium images. The optimal dose of intravenous dipyridamole is 0.56 mg/kg and the optimal oral dose is 300-375 mg, although higher doses may be necessary in some patients. The sensitivity and specificity of dipyridamole-thallium imaging, whether intravenous or oral, have been shown in a number of studies to be quite adequate and comparable to that achieved during exercise thallium imaging. Dipyridamole-thallium imaging has also been useful in identifying high-risk patients undergoing major elective vascular surgery. The relative merits of dipyridamole imaging versus exercise testing after acute myocardial infarction require further studies.

Myocardial imaging with Tc-99m teboroxime: technique and initial results

This study examined the results of Tc-99m teboroxime imaging in 22 patients aged 59 +/- 9 years and compared the results with those of thallium-201. The exercise and rest teboroxime studies were obtained within 3 hours of each other using a dose of 15 mCi/study. Because of the very short wash-out half-life of teboroxime, imaging was begun within 1 to 2 minutes after injection. Both SPECT and planar images were obtained; the SPECT protocol was modified by changing the number of frames, the time per frame, or the filters used for reconstruction of images. The planar images were obtained in the supine or upright position. Shorter acquisition time for SPECT (10 sec/frame) and the use of a Butterworth filter with a frequency cutoff of 0.3 cycle/cm and a power of 10 yielded best image quality. There was a close agreement with thallium results in identifying an abnormal or normal perfusion pattern in 89% of vascular territories. The scans were abnormal by both techniques in 12 patients, normal in nine patients, and discordant in only one patient. Thus Tc-99m teboroxime myocardial imaging is feasible at rest and during exercise using either SPECT or planar imaging. Shorter acquisition time and appropriate filtering for SPECT imaging and the upright position in planar imaging improve image quality and are convenient for the patient.

Single photon emission computed tomography with thallium-201 during adenosine-induced coronary hyperemia: correlation with coronary arteriography, exercise thallium imaging and two-dimensional echocardiography

The feasibility, safety and diagnostic accuracy of single photon emission computed tomography (SPECT) with thallium-201 imaging during adenosine-induced coronary hyperemia were evaluated in 53 patients with and 7 without coronary artery disease proved by coronary angiography. Adenosine was infused intravenously at a dose of 0.14 mg/kg body weight per min for 6 min and thallium was injected at 3 min. Adenosine caused an increase in heart rate (68 +/- 12 at baseline versus 87 +/- 18 beats/min at peak effect, p less than 0.0001) but no change in blood pressure. The sensitivity and specificity were 92% (95% confidence intervals 81% to 98%) and 100% (95% confidence intervals 59% to 100%), respectively; 20 (61%) of 33 patients with multivessel coronary artery disease were also correctly identified. In 30 patients, the predictive accuracy of adenosine thallium imaging was slightly higher than that of exercise SPECT thallium imaging (90% versus 80%, p = NS) (95% confidence intervals 72% to 97% and 61% to 92%, respectively). In 25 patients, two-dimensional echocardiography during adenosine infusion disclosed a new wall motion abnormality in 2 (10%) of 20 patients with coronary artery disease; 80% of these patients had reversible thallium defects (p less than 0.001). Side effects were mild and transient; aminophylline was used in only three patients. Thus, adenosine SPECT thallium imaging provides a high degree of accuracy in the diagnosis of coronary artery disease. The results are comparable with those of exercise SPECT thallium imaging. Most reversible defects in the adenosine study are not associated with any transient wall motion abnormality.

Quantification of the reversibility of stress-induced thallium-201 myocardial perfusion defects: a multicenter trial using bull's-eye polar maps and standard normal limits

A multicenter trial was performed on 140 patients from four centers to determine the accuracy of quantitative analysis of stress/delayed thallium-201 myocardial tomograms using normal limits to assess the relative amount of reversibility of stress-induced defects. The patients were found to have 85 fixed and 124 reversible defects, as determined by visual interpretation. Reversibility bull's-eye polar maps were compared to gender-matched normal limits from 36 normals. Regions were identified as reversible if their normalized difference between stress and 4 hr greater than 1.5 s.d.s. from the mean normal limits. Overall agreement between experts at multicenter sites and reversibility maps was 73% for reversible defects and 80% of fixed defects. Sensitivity in detecting reversibility was highest for the left circumflex (88%) and lowest for the right coronary (60%). These results indicate that reversibility polar maps and normal limits offer an objective, accurate technique for determining the reversibility of stress-induced perfusion defects.

Left ventricular dilatation and pulmonary thallium uptake after single-photon emission computer tomography using thallium-201 during adenosine-induced coronary hyperemia

This study examined the implications of left ventricular (LV) dilatation and increased pulmonary thallium uptake during adenosine-induced coronary hyperemia. The lung-to-heart thallium ratio in the initial images was significantly higher in patients with coronary artery disease (CAD) than normal subjects; 0.48 +/- 0.16 in 3-vessel disease (n = 16), 0.43 +/- 0.10 in 2-vessel disease (n = 20), 0.43 +/- 0.08 in 1-vessel disease (n = 16) and 0.36 +/- 0.05 in normal subjects (n = 7) (p less than 0.001, 0.09 and 0.06, respectively). There was a significant correlation between the severity and the extent of the perfusion abnormality (determined from the polar maps) and the lung-to-heart thallium ratio (r = 0.51 and 0.52, respectively, p less than 0.0002). There was also a significant correlation between lung thallium washout and lung-to-heart thallium ratio (r = 0.42, p = 0.0009) and peak heart rate (r = -0.49, p less than 0.0001). The LV dilatation was mostly due to an increase in cavity dimension (30% increase) and to a lesser extent (6% increase) due to increase in LV size. (The cavity dimensions were measured from the short-axis slices at the midventricular level in the initial and delayed images). The dilation was seen in patients with CAD but not in the normal subjects. These changes correlated with the extent and severity of the thallium perfusion abnormality. Thus, adenosine-induced coronary hyperemia may cause LV dilation and increased lung thallium uptake on the basis of subendocardial ischemia.

Effect of exercise level on the ability of thallium-201 tomographic imaging in detecting coronary artery disease: analysis of 461 patients

This study examined the effect of the level of exercise on the ability of thallium-201 imaging with single photon emission computed tomography (SPECT) to detect coronary artery disease. Patients in group 1 (n = 164) achieved adequate exercise end points, defined as positive exercise electrocardiograms or greater than or equal to 85% of maximal predicted heart rate. Patients in group 2 (n = 108) had submaximal exercise. The SPECT thallium-201 images showed perfusion defects in 74%, 88%, and 98%, respectively, of patients with one, two and three vessel coronary artery disease in group 1, compared with 52%, 84% and 79%, respectively, of such patients in group 2 (p less than 0.05). Perfusion defects showed partial or complete redistribution consistent with ischemia in 56%, 80% and 88%, respectively, of patients with one, two and three vessel coronary artery disease in group 1 compared with 35%, 58% and 56%, respectively, of such patients in group 2 (p = 0.08, less than 0.03 and less than 0.001, respectively). Of 58 patients with normal coronary angiograms or less than 50% diameter stenosis, 36 (62%) had normal SPECT images. In a separate group of 131 patients with less than 5% pretest probability of coronary artery disease, the specificity was 93%. The sensitivity of exercise SPECT imaging in group 1 was higher than that of ST segment depression (p less than 0.001). Thus, the level of exercise affects the results of SPECT thallium imaging in the localization and evaluation of the extent of coronary artery disease and the detection of ischemia.

Use of oral dipyridamole SPECT thallium-201 imaging in detection of coronary artery disease

This study examined the merits of oral dipyridamole SPECT thallium-201 imaging in detecting CAD and multivessel CAD. The 65 patients included in this study (aged 62 +/- 11 years) were not candidates for exercise testing (for the usual reasons). Coronary arteriography revealed no significant CAD in 17 patients and greater than or equal to 50% narrowing of one or more vessels in 48 patients; 12 had one-vessel and 36 had multivessel CAD (high-risk group). Thallium-201 was injected intravenously 45 minutes after an oral dose of 375 mg of dipyridamole, and SPECT imaging was performed within 10 minutes and 4 hours after injection. There were no serious side effects; only six patients (8%) had ST segment depression and 18 patients (28%) had chest pain. The heart rate increased from 74 +/- 15 beats/min at rest to 84 +/- 14 beats/min at peak effect (p = 0.001); the systolic blood pressure did not change (130 +/- 18 and 128 +/- 20 mm Hg, respectively, p = NS). The thallium images were abnormal in 6 of 17 patients (35%) with no CAD, in 7 of 12 patients with one-vessel disease (58%), and in 34 of 36 patients with multivessel CAD (94%) (p = 0.001). Twenty-one of 25 patients (84%) with a perfusion abnormality in more than one vascular territory had multivessel CAD assessed by angiography. Thus oral dipyridamole SPECT thallium-201 imaging is a safe and inexpensive method for the detection of CAD in patients who are otherwise not candidates for exercise testing.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of technetium-99m isonitrile (RP-30A) in assessing left ventricular perfusion and function at rest and during exercise in coronary artery disease, and comparison with coronary arteriography and exercise thallium-201 SPECT imaging

This study compared the results of stress and rest single-photon emission computed tomography imaging of myocardial perfusion using technetium-99m isonitrile (RP-30A) with the results of stress and redistribution tomographic thallium imaging and the results of coronary arteriography in 39 patients, 11 without and 28 with coronary artery disease (CAD). Each patient underwent 2 exercise studies at identical workload, heart rate and double product. In a subset of 13 patients, concomitant evaluation of left ventricular (LV) function using first-pass radionuclide angiography with a multi-crystal camera also was performed with bolus injections of isonitrile. Isonitrile had similar sensitivity (82 vs 82%, difference not significant), a slightly--but not significantly--higher specificity (100 vs 82%) and similar predictive accuracy (87 vs 82%) to thallium-201. The tracer uptake was assessed in 20 segments/study. There was concordance between the isonitrile and thallium-201 images in 723 of the 780 segments (93%) (kappa = 0.83 +/- 0.02). In general, the isonitrile images were considered of better quality than the thallium-201 images. All 10 patients with CAD who underwent concomitant first-pass radionuclide angiography had either perfusion abnormalities or an abnormal ejection fraction response to exercise. Thus, technetium-99m isonitrile provides a reliable method of assessment of CAD with a sensitivity, specificity and predictive accuracy comparable to that of exercise thallium-201 imaging. Additional advantages include better image quality and the ability to obtain concomitant assessment of LV function with the use of first-pass radionuclide angiography.

Relation between myocardial thallium-201 kinetics during exercise and quantitative coronary angiography in patients with one vessel coronary artery disease

This study examined the relation between the kinetics of thallium-201 and coronary stenosis in 30 patients with one vessel coronary artery disease; 25 patients had no visible collateral vessels. The myocardial thallium concentration in the postexercise images and percent washout were determined in the distribution of the diseased vessel and a normal vessel, and each was expressed as a ratio. Coronary stenosis was assessed as minimal diameter stenosis, minimal area stenosis and percent diameter stenosis. The correlations between the myocardial concentration ratio or washout ratio and the descriptors of coronary stenosis improved when the patients with collateral vessels were excluded. There were significant correlations between the myocardial thallium concentration ratio and minimal diameter stenosis (r = 0.73, p less than 0.001), minimal area stenosis (r = 0.72, p less than 0.001) and, to a lesser degree, percent diameter stenosis (r = -0.51, p less than 0.01). Similarly, there were significant correlations between washout ratio and minimal diameter stenosis (r = 0.50, p less than 0.01) and minimal area stenosis (r = 0.45, p less than 0.02) but not percent diameter stenosis (r = 0.37, p = 0.06). Thus, variation in thallium kinetics in relation to the severity of coronary stenosis can be demonstrated with conventional imaging in patients with one vessel disease. The myocardial thallium concentration and washout are physiologic expressions of the severity of perfusion deficit and are dependent on collateral flow. The myocardial thallium concentration ratio and washout ratio correlate better with minimal diameter and area stenosis than with percent diameter stenosis.

Dipyridamole cardiac imaging

Dipyridamole cardiac imaging is a useful alternative technique to exercise stress testing in the evaluation of patients with ischemic heart disease. Intravenous dipyridamole is still in the investigational phase, while oral dipyridamole is widely available. The hemodynamic effects of dipyridamole include an increase in coronary blood flow (due to coronary vasodilation) which is in excess of the increase in myocardial oxygen consumption and cardiac output. The disparity in the increase in coronary blood flow relative to the cardiac output results in an increase in myocardial thallium activity and an increase in the myocardial/background activity ratio. The quality of the thallium images is better or similar to that of exercise thallium images. The optimal dose of intravenous dipyridamole is 0.56 mg/kg, and of the oral dose it is 300 to 400 mg, although higher doses may be necessary in some patients. Analysis of the thallium images has been to a large extent based on visual inspection of the planar images. Delayed images are helpful to establish the nature of the perfusion abnormalities (transient or fixed). The process of redistribution is based on disparate rates of washout from the normal and abnormal zones. The sensitivity and specificity of dipyridamole thallium imaging, whether intravenous or oral, have been shown in a number of studies to be quite adequate and comparable to that achieved during exercise thallium imaging. Dipyridamole two-dimensional echocardiography has also been used in the detection of coronary artery disease; transient (new or worsening of preexisting) wall motion abnormalities have been found to be a specific marker of coronary artery disease. Transmural as well as regional coronary steal phenomena have been postulated as the mechanism for dipyridamole-induced regional wall motion abnormalities. Compared to exercise two-dimensional echocardiography, dipyridamole echocardiography provides high-quality studies and in higher proportions of patients. The results of dipyridamole thallium imaging have also been extremely important in identifying high-risk patients after acute myocardial infarction or patients with peripheral vascular disease undergoing elective vascular surgery; the presence of a dipyridamole-induced perfusion abnormality identifies patients at high risk for future cardiac events. Thus, dipyridamole cardiac imaging is helpful in the diagnosis of coronary artery disease and in risk stratification.

Exaggerated systolic blood pressure response to exercise: a normal variant or a hyperdynamic phase of essential hypertension?

This study examines the left ventricular function (by first-pass radionuclide angiography with a multicrystal gamma camera) at rest and during symptom-limited upright exercise in 27 normal subjects (group 1), 25 normotensive subjects with exaggerated systolic blood pressure response to exercise (greater than 200 mm Hg) (group 2) and 25 patients with essential hypertension and no associated coronary artery disease (group 3). There were no significant differences between groups 1 and 2 in exercise tolerance, heart rate, total vascular resistance, left ventricular ejection fraction and end-systolic volume. However, the exercise cardiac index and systolic blood pressure were significantly higher in group 2 (P less than 0.02). Compared to group 3, the subjects in group 2 had higher exercise heart rate (P less than 0.0001), cardiac index (P less than 0.0001), systolic blood pressure (P less than 0.0001) and left ventricular ejection fraction (P less than 0.0001) and lower exercise total vascular resistance (P less than 0.0002) and end-systolic volume (P less than 0.01). Thus, the hemodynamic profile in subjects with exaggerated systolic blood pressure response to exercise differs from that of essential hypertension; it may represent a supernormal response.

Use of exercise thallium-201 imaging for risk stratification of elderly patients with coronary artery disease

Although coronary artery disease (CAD) may be asymptomatic, it is the most common cause of death in elderly patients in the U.S. This study examined the prognosis of 449 patients with a mean age of 65 years using exercise thallium-201 imaging. At a follow-up of 25 months, 45 patients underwent coronary artery revascularization, 8 died of cardiac causes and 10 had nonfatal acute myocardial infarctions (AMIs). Thus the total of patients with "hard" events was 18. The events included 12 of 276 patients with atypical or non-anginal symptoms versus 6 of 128 with typical angina (p = not significant); 7 of 51 patients (14%) with Q-wave AMI versus 11 of 353 (3%) without Q-wave AMI (p less than 0.001); 1 of 183 patients (1%) with normal versus 17 of 221 (8%) with abnormal exercise thallium-201 images (p less than 0.002); 10 of 76 patients (13%) with multi vessel thallium-201 abnormality vs 8 of 328 (2%) with no or 1-vessel thallium-201 abnormality (p less than 0.001) and 10 of 96 patients (10%) with greater than or equal to 3 abnormal segments by thallium-201 imaging (total segments = 9) versus 8 of 308 patients with no or less than 3 abnormal segments (p less than 0.001). The number of segments with thallium-201 defects was 1 +/- 2 patients without and 3 +/- 2 in patients with hard events (p less than 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)

Merits and limitations of quantitative treadmill exercise score

This study examined the ability of the treadmill exercise score (TES) in determining the presence and extent of coronary artery disease (CAD). The score was derived from the integrated area of ST segment depression and ST slope in two leads (V5 and a VF), corrected for R wave amplitude, exercise time, and percent of maximum predicted heart rate. The ST segment depression was measured at 80 msec after the J point. There were 34 patients with no significant CAD, 38 patients with one-vessel CAD (greater than or equal to 50% diameter stenosis), and 58 patients with multivessel CAD. The TES showed a considerable scatter in patients with and without CAD. A receiver operating characteristic curve showed different levels of sensitivity and specificity, depending on the cut-point. The TES was similar to ST segment depression in detecting CAD (predictive accuracy, 77% vs 78%, p = NS). A markedly abnormal score (less than -1.0) was seen in 41 patients, of whom 32 (78%) had multivessel CAD. On the other hand, a score greater than 0 was seen in 49 patients, of whom 40 (82%) had no or one-vessel CAD. In 40 patients with TES between -1.0 and 0, 17 (43%) had multivessel CAD and 23 (57%) had no or one-vessel CAD. In 51 patients with nondiagnostic ST changes, the TES correctly classified the extent of CAD in 20 patients (40%). Thus, the TES has a similar accuracy to the ST segment depression criteria in detecting CAD. The extent of CAD can, however, be ascertained in 80% of the patients with very high or very low TES.

Thallium imaging with single photon emission computed tomography

Evaluation of myocardial perfusion with thallium-201 SPECT has advantages over planar images. These advantages are related to better contrast of the images, lack of superimposition of normal and abnormal areas, and a three-dimensional representation of the site and extent of perfusion abnormalities (ischemia, scar, or both). For this reason, rotational tomography is superior to planar imaging in assessing the extent of coronary artery disease, in the detection of small infarcts, and for quantitative measurements. Several techniques have provided accurate quantitative data for infarct sizing both in animals and men. The ability to quantitate infarct size (or ischemia) will be extremely important in studies of myocardial salvage, risk stratification, and longitudinal studies to evaluate the effects of medical and surgical interventions.

Relative prognostic value of rest thallium-201 imaging, radionuclide ventriculography and 24 hour ambulatory electrocardiographic monitoring after acute myocardial infarction

Rest thallium-201 scintigraphy, radionuclide ventriculography and 24 hour Holter monitoring are acceptable methods to assess myocardial necrosis, performance and electrical instability. This study examined the relative value of the three tests, when obtained a mean of 7 days after acute myocardial infarction, in predicting 1 year mortality in 93 patients. Planar thallium-201 images were obtained in three projections and were scored on a scale of 0 to 4 in 15 segments (normal score = 60). Patients were classified as having high risk test results as follows: thallium score less than or equal to 45 (33 patients), left ventricular ejection fraction less than or equal to 40% (51 patients) and complex ventricular arrhythmias on Holter monitoring (36 patients). During the follow-up of 6.4 +/- 3.4 months (mean +/- SD), 15 patients died of cardiac causes. All three tests were important predictors of survival by univariate Cox survival analysis; the thallium score, however, was the only important predictor by multivariate analysis. The predictive power of the thallium score was comparable with that of combined ejection fraction and Holter monitoring (chi-square = 21 versus chi-square = 22). Thus, rest thallium-201 imaging performed before hospital discharge provides important prognostic information in survivors of acute myocardial infarction which is comparable with that provided by left ventricular ejection fraction and Holter monitoring. Patients with a lower thallium score (large perfusion defects) are at high risk of cardiac death during the first year after infarction.

Effects of beta blockade on systolic and diastolic left ventricular function at rest and during exercise in patients with chronic stable angina pectoris

This study examined the effects of beta blockade with betaxolol, a cardioselective, lipid-soluble, beta-adrenergic-blocking agent, on rest and exercise systolic and diastolic left ventricular function in 15 patients, aged 40 to 70 years (mean = 52), with chronic stable angina pectoris. Each patient underwent three upright exercise studies at identical workloads; the first was a baseline study, the second was done 3 hours after a single oral dose, and the third was obtained after chronic therapy for 2 weeks. Beta blockade was evident by significant decreases in heart rate, systolic blood pressure, and diastolic blood pressure at rest and during exercise (p less than 0.04). Although there were no significant changes (at rest or during exercise) in mean left ventricular ejection fraction and peak filling rate, individual variations were seen after 3 hours and 2 weeks of therapy. During chronic therapy, the peak filling rate increased in three patients, decreased in five, and remained unchanged in seven. Also, discordant changes in systolic and diastolic functions were seen at rest and during exercise during both acute and chronic therapy. Thus, although acute and chronic beta blockade produces no significant changes in mean measurements of diastolic and systolic left ventricular performance, individual variations and discordant results are seen in many patients. The acute effects are generally consistent with the chronic effects, but exceptions are present.

Exercise thallium imaging in patients with diabetes mellitus. Prognostic implications

We used exercise thallium 201 imaging in 123 patients with diabetes mellitus (77 men and 46 women, aged 56 +/- 8 years), 75% of whom had angina pectoris (typical or atypical). During exercise testing, 18 patients (15%) had angina pectoris, 28 (23%) had ischemic ST changes, and 69 (56%) had abnormal thallium images. During follow-up (up to 36 months), there were 12 cardiac events; four patients died of cardiac causes and eight had nonfatal acute myocardial infarction. Univariate and multivariate survival analysis identified two independent predictors of cardiac events: the event rate was significantly less in patients with normal images and exercise heart rate over 120 beats per minute than in patients with abnormal images and exercise heart rate of 120 beats per minute or less (0% vs 22%). The patients with abnormal images or exercise heart rate of 120 beats per minute or less had an intermediate event rate (11.5%). Furthermore, two of the 54 patients with normal images and ten of 69 patients with abnormal images had subsequent cardiac events. Thus, exercise thallium imaging is useful in risk stratification in patients with diabetes mellitus.

The role of radionuclide cardiac imaging in coronary artery bypass surgery

The main applications of cardiac nuclear imaging in coronary artery bypass surgery include: patient selection, prediction of improvement in resting LV function after revascularization, diagnosis of perioperative myocardial infarction, assessment of the results of revascularization, evaluation of new or recurrent symptoms, and in risk stratification. Proper understanding of which test to be used, when, and why may be important to optimize patient management.

Angina: DDx of atypical presentations in the elderly

Pretest probability of coronary heart disease should be considered in interpreting exercise test results. In general, 90% of patients with typical angina pectoris, 50% of patients with atypical angina pectoris, and only 10% of patients with nonanginal chest pains have CHD. Marked ST-segment depression in multiple leads is a good indication of extensive coronary artery disease, especially when it occurs early during exercise or at submaximal exercise, and if associated with a blunted or a hypotensive BP response.

Ventricular systolic and diastolic impairment during pacing-induced myocardial ischemia in coronary artery disease: simultaneous hemodynamic, electrocardiographic, and radionuclide angiographic evaluation

This study examined the impairment in systolic and diastolic performance of both ventricles during pacing-induced myocardial ischemia in 12 men with coronary artery disease. Simultaneous hemodynamic, ECG, and radionuclide angiographic assessments were made: pre pacing (pre-P); intermediate pacing (P-1); maximum pacing (P-2); and immediately after pacing (post pacing (P-P). The prepacing measurements were made with the patient in the supine position and during leg elevation. Pacing produced a leftward and upward shift in the diastolic pressure-volume relation, a progressive decrease in left ventricular (LV) end-diastolic volume (p less than 0.003) and right ventricular (RV) end-diastolic volume (p less than 0.01), concomitant with an increase in the pulmonary artery wedge pressure (p less than 0.004) and the right atrial pressure (p less than 0.04). The shift in the LV pressure-volume relation was associated with an initial increase (P-1), followed by a decrease (P-2) in the peak filling rate (p less than 0.001). Pacing also resulted in systolic dysfunction: abnormal LV ejection fraction responses in eight patients, LV regional wall motion abnormalities in eight patients, and abnormal RV ejection fraction responses in seven patients. Leg elevation resulted in a 7% increase in cardiac output, a 20% increase in RV end-diastolic volume, a 28% increase in right atrial pressure, a 29% increase in pulmonary artery wedge pressure, and a 10% increase in LV end-diastolic volume (p less than 0.05). Thus, the ischemic response to pacing results in systolic and diastolic LV and RV dysfunction, with the diastolic impairment being more frequent than the systolic impairment.

Left ventricular pressure/volume relationship in coronary artery disease

This study examined the changes during exercise in LV EF and P/V relationship (systolic blood pressure/end-systolic volume index ratio) in 287 patients. Normal range (mean +/- standard deviation) for exercise EF, exercise P/V, and the changes from rest to exercise (delta) in EF and P/V were established in 51 subjects with less than 1% probability of CAD. The results were compared to those obtained in 53 patients with normal coronary angiograms and 183 patients with angiographically proven CAD. Abnormality in either delta EF or percent delta P/V were observed in 76% of the patients with one-vessel disease and in 91% of patients with multivessel disease. Abnormalities in either delta EF or percent delta P/V were more common than delta EF alone in the total CAD group and in subgroups stratified according to the resting EF, extent of CAD, and adequacy of exercise end points. Similar results were obtained when absolute exercise EF or exercise P/V were used. Abnormalities in the percent delta P/V or delta EF were also seen in 26 of the 53 patients with normal coronary angiograms. Thus, abnormalities in the P/V relationship or EF during exercise are more common than abnormalities in the EF alone. Relative and absolute measurements provide similar results.

Implications of abnormal right ventricular thallium uptake in acute myocardial infarction

The correlates of abnormal right ventricular (RV) thallium uptake were examined in 116 patients with documented acute myocardial infarction (AMI) who underwent predischarge thallium-201 scintigraphy at rest, radionuclide angiography and 24-hour ambulatory electrocardiography. The patients were separated into 2 groups: patients group 1 (n = 31) had increased RV thallium uptake and those in group 2 (n = 85) had no such uptake. The 2 groups were comparable in age, type and site of AMI, peak creatine kinase level, systolic blood pressure and heart rate. However, compared with group 2, group 1 had a lower mean left ventricular (LV) ejection fraction (33 +/- 15% vs 39 +/- 14%, p less than 0.05), higher prevalence of increased lung thallium uptake (45% vs 22%, p less than 0.02), more extensive LV perfusion defects (4.4 +/- 2.9 vs 3.0 +/- 3.0 segments, p less than 0.03) and more complex ventricular arrhythmias (55% vs 35%, p less than 0.05). At a mean follow-up of 6 months, 17 patients (8 in group 1 and 9 in group 2) died from cardiac causes. Actuarial life-table analysis showed that the survival rate was better in group 2 than in group 1 (Mantel-Cox statistics = 4.62, p = 0.03). Thus, patients with AMI and abnormal RV thallium uptake have worse LV function, more complex ventricular arrhythmias and worse prognosis.

Effects of esmolol on patients with left ventricular dysfunction

This study examined the effect of esmolol, an ultrashort-acting beta-receptor blocker, in 10 patients with severe left ventricular dysfunction. Simultaneous hemodynamic and radionuclide angiographic measurements were obtained at incremental doses of esmolol (2, 4, 8, 12 and 16 mg/min). At a dose of 4 mg/min, esmolol produced beats blockade: a decrease in heart rate from 91 +/- 4 to 83 +/- 4 beats/min (p less than 0.05) (mean +/- SEM) and a decrease in systolic aortic pressure from 133 +/- 5 to 128 +/- 5 mm Hg (p less than 0.05). At the maximal dose, the heart rate decreased to 79 +/- 3 beats/min (p less than 0.05) and biventricular function was depressed; the left ventricular ejection fraction decreased from 27 +/- 2 to 21 +/- 2% (p less than 0.05) and the right ventricular ejection fraction decreased from 38 +/- 2 to 29 +/- 2% (p less than 0.05). These changes were accompanied by increases in left ventricular end-diastolic volume (p less than 0.05), left ventricular end-systolic volume (p less than 0.05) and pulmonary artery wedge pressure (p less than 0.05), as well as a decrease in cardiac output (p less than 0.05). The hemodynamic abnormalities (which showed considerable interindividual variability) returned to near baseline levels 10 to 30 minutes after infusion was stopped. Thus, esmolol can be administered to patients with severe left ventricular dysfunction. The beneficial effect (beta-adrenergic blockade) is usually achieved with small doses without clinically important hemodynamic changes. At larger doses, however, significant changes in biventricular function may be observed.

Age- and gender-related changes in exercise left ventricular function in mitral valve prolapse

The correlates of exercise left ventricular (LV) performance were examined in 45 patients with isolated mitral valve prolapse (no associated mitral regurgitation or coronary artery disease). There were 18 men and 27 women, aged 16 to 73 years; 20 patients were 40 years or younger and 25 were older than 40. The response of the LV ejection fraction (EF) to symptom-limited upright exercise was normal (at least a 5% increase) in 27 patients (60%) and abnormal in 18 (40%). There were no significant differences between patients with normal and abnormal EF response in clinical presentation, electrocardiographic findings (at rest or during exercise), medications, rest EF, heart rate (at rest or during exercise) and systemic arterial pressure (at rest and during exercise). A normal EF response was observed more frequently in patients 40 years or younger than in those older than 40 (80 vs 44%, p less than 0.01), and more often in men than in women (78 vs 48%, p less than 0.04). The change in EF from rest to exercise was 18 +/- 9% in men and 5 +/- 10% in women 40 years or younger (p less than 0.01), and 9 +/- 8% in men and 2 +/- 8% in women older than 40 (p less than 0.04). Thus, patients (especially women and those older than 40 years) with isolated mitral valve prolapse may have abnormal LV functional reserve. Genetic differences in the expression of the disease in both sexes and age-related irreversible myocardial changes may explain these observations.

Radionuclide angiographic evaluation of left ventricular performance at rest and during exercise in patients with aortic regurgitation

Radionuclide angiographic evaluation of LV performance at rest and during exercise in patients with AR have shown that an abnormal EF response to exercise may be observed in asymptomatic patients with normal resting LV function. The EF response to exercise has been correlated with a number of clinical and exercise measurements; important among these are the slope of the systolic pressure-to-end-systolic volume, end-systolic volume, cardiac index, pulmonary capillary wedge pressure, and wall stress. The changes in the regurgitant fraction, EF, and LV volume have shown considerable individual variability; they have also allowed a better understanding of the circulatory responses during exercise. Radionuclide angiography provides a reliable and reproducible method of measuring the rest LVEF that is important in the timing and the outcome of valve replacement. The value of the EF response to exercise in patient management is not yet clear; it is possible that other radionuclide-derived measurements at rest or during exercise, such as the systolic pressure-to-end-systolic volume relationship, and the end-systolic volume may provide complementary information to that provided by the EF.

Relation between left ventricular diastolic function and exercise tolerance in patients with left ventricular dysfunction

Previous studies show no correlation between resting systolic left ventricular performance assessed as the ejection fraction and exercise tolerance. This study examined the relation between left ventricular diastolic performance and exercise tolerance in 63 patients with left ventricular dysfunction (ejection fraction less than 50%) due to known or suspected coronary artery disease. The 51 men and 12 women, aged 54 +/- 8 years (mean +/- standard deviation), underwent symptom-limited upright exercise testing on a bicycle ergometer. The exercise end-points were angina (n:5), dyspnea (n:16), and fatigue (n:42). The patients were divided into three groups: group 1 (n:28) with normal exercise tolerance (9.5 +/- 2.4 minutes), group 2 (n:18) with mild exercise intolerance (5.8 +/- 0.5 minutes), and group 3 (n:17) had severe exercise intolerance (3.7 +/- 0.9 minutes). The three groups did not differ in age, ejection fraction, end-diastolic volume, exercise end-point, exercise heart rate, and left ventricular peak filling rate at rest. The exercise peak filling rate was, however, significantly higher in group 1 (p = 0.03). Stepwise multivariate discriminant analysis of important variables identified the exercise peak filling rate as the only predictor of exercise tolerance (F = 6.0). Thus, variation in exercise peak filling rate may in part explain the variability of exercise tolerance in patients with left ventricular dysfunction; patients with preserved exercise capacity have higher exercise peak filling rate than those with exercise intolerance.