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Biomedical subjects

A S Iskandrian

Publications and source records attributed to A S Iskandrian.

At least 37 records · Page 2Linked to original sources
PubMed1995

Results of adenosine single photon emission computed tomography thallium-201 imaging in hemodynamic nonresponders.

Systolic blood pressure typically decreases during adenosine infusion because of stimulation of A2b receptors, resulting in systemic vasodilation. This study examined the results of adenosine single photon emission computed tomography (SPECT) thallium-201 imaging in patients who did not show such a decrease in blood pressure during peak adenosine effect (nonresponders). The 102 nonresponders and 341 responders had no significant differences in age, gender, history of diabetes mellitus, hypertension, or previous myocardial infarction. The extent of coronary artery disease (CAD) by angiography was also similar. The sensitivity of SPECT thallium-201 imaging in patients with one-vessel disease was 82% in nonresponders and 84% in responders (p value not significant [NS]); in patients with multivessel disease, it was 90% in nonresponders and 94% in responders (p = NS) and for all CAD, it was 87% in non-responders and 91% in responders (p = NS). Thus lack of hemodynamic systemic response during adenosine infusion does not affect sensitivity for detecting CAD.

Adenosine↗
PubMed1995

Relation between diastolic left ventricular function and myocardial blood volume during adenosine-induced coronary hyperemia.

Adenosine infusion is accompanied by increases in coronary blood flow and myocardial blood volume. Myocardial blood volume may produce changes in diastolic left ventricular (LV) performance by increasing myocardial turgor. Diastolic dysfunction may also be the result of myocardial ischemia. The relation between changes in LV mass and diastolic function has not been previously investigated. This study examined the relation between changes in LV mass during adenosine-induced coronary hyperemia and LV diastolic function. Serial two-dimensional and Doppler echocardiographic measurements were made before, during, and after adenosine infusion (140 micrograms/min for 6 min) in 21 patients with (group 1) and 10 patients without (group 2) coronary artery disease (CAD). The LV mass and transmitral diastolic filling indexes were determined from digitized images from apical four-chamber view. Adenosine infusion produced a greater increase in LV mass in group 2 than in group 1 (29% +/- 11% vs 9% +/- 6%, p < 0.0002). The ratio of transmitral early (E) to atrial (A) filling velocity (E/A) increased 10% +/- 16% in group 2 and decreased 8% +/- 20% in group 1 (p < 0.02), and the velocity time integral of early filling increased 11% +/- 52% in group 2 and decreased 20% +/- 31% in group 1 (p < 0.04). There was a correlation between the change in E/A ratio and the LV mass (r = 0.53, p < 0.003). Thus adenosine infusion caused a greater increase in LV mass in normal subjects than in patients with CAD. There were also changes in Doppler-derived indexes of diastolic LV function.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1995

Implications of increased lung thallium uptake during exercise single photon emission computed tomography imaging.

Increased lung thallium uptake during exercise is an important marker of patients who are at high risk and have CAD; however, most previous studies were done with planar imaging, and therefore it is unclear whether this conclusion is also true with SPECT imaging. This study examined the lung thallium uptake during exercise SPECT imaging in 1031 patients who also underwent coronary angiography. The lung thallium uptake was increased in 309 patients (group 1) and normal in 722 patients (group 2). Compared with patients in group 2, those in group 1 had more ST segment depression (44% vs 28%, p = 0.01), previous Q-wave myocardial infarction (28% vs 17%, p = 0.0001), larger perfusion defects (24% +/- 11% vs 10% +/- 11%, p = 0.0001), and multivessel CAD by angiography (75% vs 47%, p = 0.0001). Multivariate discriminant analysis identified left ventricular dilation, reversible defects, the size of perfusion abnormality, and the extent of CAD as independent predictors of increased lung thallium uptake. Increased lung thallium uptake was more common in men than women regardless of the extent of CAD: 26% versus 11% in patients with one-vessel, 38% versus 18% in patients with two-vessel, and 51% versus 31% in patients with three-vessel disease (p < 0.001 each). Thus increased lung thallium uptake by SPECT identifies patients with more severe anatomic and functional evidence of CAD. The sex-related difference suggests the need for a sex-specific normal file for quantitative analysis.

Aged↗
PubMed1995

Prediction of improvement in left ventricular function with iodine-123-IPPA after coronary revascularization.

UNLABELLED: Iodine-123-phenylpentadecanoic acid (IPPA) is a synthetic fatty acid suitable for myocardial imaging. This study is the result of a Phase I/II trial to evaluate IPPA's ability to predict functional recovery in patients undergoing coronary revascularization. METHODS: Twenty-three patients with documented coronary disease underwent sequential SPECT imaging with IPPA before and radionuclide ventriculography both before and 8 wk after revascularization. Software was developed to evaluate myocardial IPPA metabolism and to determine the fraction of the left ventricle with intermediate metabolism. RESULTS: There was a significant correlation between initial IPPA uptake and final LVEF. The fractional area of the left ventricle demonstrating IPPA metabolism in the intermediate metabolic range was significantly higher in patients who demonstrated a 5% or greater increase in EF after revascularization (0.90 +/- 0.08 versus 0.78 +/- 0.17, p = 0.04). When only the patients who received complete revascularization were evaluated, there was a more significant difference (improved 0.92 +/- 0.05 versus 0.74 +/- 0.17, p = 0.011). Taking a lower limit of 1 s.d. from the mean, (87%) the six patients who had > or = 5% increase in LVEF after revascularization had more than 87% of the left ventricle in the intermediate metabolic range, whereas seven of ten patients whose change in LVEF was < 5% had less than 87% in the intermediate metabolic range (p = 0.011). CONCLUSION: In this initial experience, the amount of myocardium in the intermediate metabolic range is associated with improvement in LVEF after revascularization, especially in patients receiving complete revascularization.

Coronary Disease↗
PubMed1994

Prognostic implications of normal exercise tomographic thallium images in patients with angiographic evidence of significant coronary artery disease.

This study examines the prognostic implications of normal exercise tomographic thallium images in medically treated patients with angiographic evidence of coronary artery disease (CAD). There were 97 patients aged 60 +/- 10 years; 52 had 1-, 30 had 2-, and 15 had 3-vessel CAD (> or = 50% diameter stenosis). The exercise test was submaximal in 51 patients (53%); ST-segment depression during exercise occurred in 20 patients (21%), and angina during exercise occurred in 23 patients (24%). Most patients (71%) were receiving antianginal therapy. During a mean follow-up of 32 months, only 3 patients had cardiac events: 2 died of cardiac causes and 1 had nonfatal myocardial infarction (event rate 1.1%/year). None of those 3 patients had positive ST response during exercise. Thus, medically treated patients with CAD (including those with multivessel CAD) have a benign prognosis in the presence of normal exercise thallium images. These results have important implications in patient management and cost of health delivery.

Coronary Angiography↗
PubMed1994

Sudden cardiac death from coronary artery spasm in a healthy subject.

The true incidence of sudden cardiac death (SCD) from coronary artery spasm is unknown. The following case involves SCD in a previously asymptomatic young man with reasonable evidence to implicate coronary artery spasm as a potential cause for his clinical event. Ergonovine provocation may be warranted in patients who present with SCD and no discernable cause.

Adult↗
PubMed1994

Doppler echocardiographic evaluation of the spectrum of left ventricular diastolic dysfunction in essential hypertension.

Left ventricular topography and diastolic and systolic functions were studied in 41 patients with essential hypertension (group 1) and 33 age-matched normal adults (group 2) by Doppler echocardiography. In group 1 54% had LV concentric hypertrophy, 19% had combined concentric hypertrophy and eccentric remodeling, and 27% had concentric remodeling. LV systolic function was within the normal range. In concentric LV remodeling, the EDV was significantly decreased (compared with group 2) (84 +/- 15 vs 130 +/- 38 ml, p < 0.05), whereas the NPFR was normal (2.89 +/- 0.65 vs 3.22 +/- 0.83 sec-1, p = NS). In concentric hypertrophy, LV end-diastolic and end-systolic volumes were normal, but the NPFR was decreased (2.04 +/- 0.59 sec-1). Patients with concentric hypertrophy and eccentric remodeling had the largest end-diastolic (140 +/- 48 ml) and end-systolic (62 +/- 32 ml) volumes and the lowest NPFR (1.67 +/- 0.69 sec-1). The LVMI inversely correlated with the NPFR (r = -0.89, p < 0.0001). Thus LV concentric hypertrophy with or without concentric or eccentric remodeling is seen in patients with systemic hypertension. A decrease in peak filling occurs early in the evolution of hypertensive heart disease and is observed even when systolic performance is still normal.

Diastole↗
PubMed1994

Safety profile of adenosine stress perfusion imaging: results from the Adenoscan Multicenter Trial Registry.

OBJECTIVES: The purpose of this study was to determine the safety of adenosine infusion at 140 micrograms/kg per min in conjunction with radionuclide imaging in 9,256 consecutive patients. BACKGROUND: Adenosine produces maximal myocardial hyperemia directly with a rapid onset of action. In addition, when used in conjunction with radionuclide perfusion imaging, it has proven efficacy for the diagnosis of coronary artery disease in patients unable to exercise. Because the ultrashort half-life (< 10s) allows dose titration and rapid reversal of side effects, it may be safer than other available pharmacologic agents. METHODS: Patients were prospectively entered at 21 clinical sites. Information on safety and adverse events during and immediately after adenosine infusion was maintained in the Adenoscan Multicenter Trial Registry. RESULTS: The infusion protocol was completed in 80% of patients, required dose reduction in 13% and was terminated early in 7%. Interpretable imaging studies were obtained in 98.7% of patients, and 0.8% of patients received aminophylline. Minor and well tolerated side effects were reported in 81.1% of patients. There were no deaths, one myocardial infarction, seven episodes of severe bronchospasm and one episode of pulmonary edema. Transient atrioventricular (AV) node block occurred in 706 patients (first-degree in 256, second-degree in 378 and third-degree in 72) and resolved spontaneously in most patients (n = 508) without alteration in the adenosine infusion. There were no sustained episodes of AV block. Patients > 70 years of age had an increased risk of developing AV block (age < 70, 7.05% vs. > or = 70, 9.44%, p = 0.001, relative risk 1.37). CONCLUSIONS: Adenosine infusion is safe. Vasodilator and negative dromotropic side effects are generally well tolerated. Serious side effects are relatively rare, and they reverse with termination of adenosine infusion. Interpretable radionuclide studies were obtained in 98.7% of patients and aminophylline reversal was seldom required.

Adenosine↗
PubMed1994

Technetium-labeled myocardial perfusion agents.

Since its approval for clinical use in 1975, thallium-201 has been the mainstay for myocardial perfusion imaging to diagnose and manage patients with coronary artery disease. In 1992, 80% of 2.6 million myocardial perfusion imaging studies were done with thallium-201. Thallium-201 has important limitations, however, related to photon energy, half life, and availability. In December 1990, two Tc-99m-labeled agents (sestamibi and teboroxime) were approved for clinical use. There are ongoing clinical trials with other classes of Tc-99m agents. This article describes kinetics and imaging experience with Tc-99m-labeled perfusion agents.

Animals↗
PubMed1994

Biokinetics of thallium-201 in normal subjects: comparison between adenosine, dipyridamole, dobutamine and exercise.

UNLABELLED: There are currently four common types of stress used with thallium-201 imaging in the diagnosis of coronary artery disease and risk assessment. The objective of this study was to examine the thallium biokinetics during exercise, adenosine, dipyridamole and dobutamine stress testing in 15 healthy volunteers. METHODS: Each subject underwent planar 201Tl imaging during maximal treadmill exercise testing, adenosine infusion (140 micrograms/kg/min for 6 min), dipyridamole infusion (142 micrograms/kg/min for 4 min) and dobutamine infusion (40 micrograms/kg/min). RESULTS: Absolute myocardial thallium activity was greater after pharmacologic testing than exercise, (p < 0.001 each). Thus, the activity was 505 counts/pixel with adenosine, 491 counts/pixel with dipyridamole, 517 counts/pixel with dobutamine and 409 counts/pixel with exercise. The myocardial thallium clearance was lower with pharmacologic testing than exercise; 9.7%/hr with adenosine, 9.9%/hr with dipyridamole, 11.3%/hr with dobutamine and 13%/hr with exercise (p < 0.01 each). The thallium uptake and clearance in the lung and liver were also greater with pharmacologic stress testing than exercise (p < 0.05). CONCLUSIONS: Thus, thallium biokinetics are different during pharmacologic stress testing with adenosine, dipyridamole and dobutamine than during exercise. Diagnostic criteria for quantitative analysis of myocardial perfusion imaging must therefore be specific for the type of stress used.

Adenosine↗
PubMed1994

Sequential dual-isotope SPECT imaging with thallium-201 and technetium-99m-sestamibi.

UNLABELLED: This study examined the results of sequential SPECT dual-isotope imaging with 201Tl and 99mTc-sestamibi in 148 patients, 114 of whom also had coronary angiography and 34 had < 5% pretest probability for coronary artery disease (CAD). METHODS: Stress thallium/rest sestamibi was used in 82 patients and rest thallium/stress sestamibi in 66 patients. Coronary angiography showed that 17 patients had no CAD, 27 patients had one-vessel CAD, 41 patients had two-vessel CAD and 29 patients had three-vessel CAD. The thallium study (3 mCi) was always done before the sestamibi study (20-25 mCi). The stress was either symptom-limited treadmill exercise testing or adenosine infusion at a rate of 140 micrograms/kg/min for 6 min. RESULTS: The study was completed within 2 hr. The stress and rest images were normal in 11 of 17 patients (65%) with no CAD by angiography and in 33 of 34 patients with a low pretest probability of CAD (normalcy rate = 97%). The images were abnormal in 75 patients with CAD (77%). The perfusion pattern was compared to wall motion in 485 segments (97 patients) assessed by contrast ventriculography. There were no or reversible perfusion defects in 357 of 386 segments (92%) with no wall motion abnormality. CONCLUSION: Sequential dual-isotope imaging is feasible and can be completed in a short period of time and may therefore enhance laboratory throughput and patient convenience.

Aged↗
PubMed1994

Adenosine myocardial perfusion imaging.

Adenosine myocardial perfusion imaging is useful in diagnosis of coronary artery disease (CAD) and risk assessment in patients who have exercise limitations. As a pharmacologic stressor, adenosine acts on two cell-surface purine receptors, A1 and A2. Activation of A2 receptors cause coronary vasodilation. Unlike other pharmacologic stressors, such as dipyridamole and dobutamine, adenosine is an endogenous biochemical. Adenosine perfusion studies have a relatively high sensitivity and specificity (80%-90%) for identifying CAD. Images from adenosine studies are comparable to, or better than, images from exercise myocardial perfusion studies. The side effects are common, but not serious; they are short-lived and rarely require the administration of aminophylline.

Adenosine↗
PubMed1994

When is myocardial viability an important clinical issue?

Myocardial viability is a clinically important issue in patients after acute myocardial infarction and in patients with left ventricular dysfunction in the presence or absence of symptoms. With these broad criteria, roughly 10% to 20% of patients with coronary artery disease will be suitable candidates for myocardial viability studies. Techniques that predict improvement in regional or global left ventricular function must be able to detect hibernating myocardium. The improvement observed following coronary revascularization represents a complex interaction between compensatory mechanisms, coronary anatomy, surgical outcome and patient selection.

Coronary Disease↗
PubMed1993

Study of myocardial infarct remodeling by single-photon emission computed tomographic imaging.

Left ventricular (LV) remodeling after Q-wave anterior acute myocardial infarction (AMI) was examined with single-photon emission computed tomographic thallium imaging. Initial (after adenosine infusion) and 4-hour delayed reinjection images were obtained in 34 patients aged 65 +/- 12 years. Short-axis slices from the delayed images were quantitatively analyzed by measuring the outer and inner diameters, and wall thickness. The results were compared with those in a group of normal subjects. The outer diameter was greater in patients than in normal subjects at the apical, mid- and basal levels (all p < 0.01); the average outer diameter was 16.9 +/- 1.9 mm in patients, and 12.2 +/- 1.3 mm in normal subjects (p < 0.001). Similarly, the inner diameter was greater in patients than in normal subjects at the 3 levels (all p < 0.05); the average inner diameter was 6.5 +/- 1.8 mm in patients, and 4.7 +/- 1.3 mm in normal subjects (p < 0.01). Wall thickness was greater in patients than in normal subjects (5.2 +/- 0.5 vs 3.8 +/- 0.5 mm; p < 0.0001). There were significant correlations between LV dilation and time elapsed (in weeks) since AMI (r = 0.57; p < 0.005), and the size of the perfusion abnormality (r = 0.44; p < 0.03). Thus, LV dilation occurs after Q-wave anterior AMI, and is related to infarct size and duration. These changes can be studied by single-photon emission computed tomographic thallium imaging.

Adenosine↗
PubMed1993

Simplified method for calculating aortic valve resistance: correlation with valve area and standard formula.

Aortic valve resistance (AVR) is a useful index to assess the severity of aortic stenosis. This study compared the standard method to calculate AVR with a simplified method based on the conventional approach for measuring vascular resistance: AVR = (peak-to-peak transaortic pressure gradient/(cardiac output*2.5))*80, where 80 is a conversion factor and 2.5 assumes that the systolic ejection period comprises 40% of the R-R cycle. We compared the standard AVR, the simplified AVR, and the Gorlin-derived value area in 118 patients with pure or dominant aortic stenosis. There was a strong linear correlation between the standard and simplified AVR (r = 0.96, p < .0001). There was a curvilinear relation between the aortic valve area and AVR (r = 0.92, p < .001). In 48 patients with aortic valve area > or = 0.7 cm2, the AVR was < 300 dynes-sec-cm-5 in 45 patients (94%) by the standard method and in 42 patients (88%) by the simplified method (p = NS). In conclusion, our method for measuring AVR is accurate and simpler than the standard method.

Aged↗
PubMed1993

Variations in the size of the ischemic myocardium due to differences in the normal file.

The myocardial thallium concentration is different during pharmacologic than exercise stress testing due to differences in coronary blood flow and cardiac output. These differences may affect the quantitative measurement of the size of ischemic myocardium if a stress-specific normal file is not used. This study examined this concept in 34 patients with isolated left anterior descending coronary artery disease. All patients underwent tomographic thallium imaging during adenosine infusion (140 micrograms/kg/min for 6 minutes). The size of the ischemic myocardium was measured from the polar map using two different normal files; one derived from normal subjects undergoing treadmill exercise testing, and the second from normal subjects undergoing adenosine stress testing. The extent perfusion abnormality was 19 +/- 13% using the exercise file, and 11 +/- 10% using adenosine file (difference; 8.1 +/- 1.6%, P = 0.0001), the severity score was 580 +/- 480 using exercise file, and 310 +/- 310 using the adenosine file (P < 0.001). The differences were present in the 20 patients with moderate stenosis (50 to 70% diameter stenosis); 17 +/- 10% versus 7 +/- 7% (P = 0.001), and in the 14 patients with severe stenosis (> 70% diameter stenosis); 24 +/- 16% versus 18 +/- 10% (P = 0.03). Thus, stress-specific normal file should be used for sizing the perfusion abnormality. The use of exercise file overestimates defect size in patients undergoing pharmacologic stress testing.

Adenosine↗