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Biomedical subjects

R O Bonow

Publications and source records attributed to R O Bonow.

At least 109 records · Page 6Linked to original sources
PubMed1992

Misalignment between PET transmission and emission scans: its effect on myocardial imaging.

Patient movement between PET scanning sequences can produce misalignment between attenuation and emission scans. Such misalignment introduces errors in the emission image. This study evaluates the severity of these errors and their effect upon quantitation of regional myocardial activity. Myocardial FDG scans from 14 patients were reconstructed with simulated translational, rotational and out-of-plane patient movement. Eight myocardial regions from each patient were examined to determine the effect such misalignment might have on regional myocardial activity. A 2-cm shift between attenuation and emission scans produced up to a 30% change in regional activity. Some regions of the myocardium increased while others decreased for a given magnitude and direction of shift, producing anomalous regional myocardial inhomogeneities in the image. Such changes could easily cause qualitative and quantitative misinterpretations. We present data permitting the reader to assess the magnitude of this effect in his/her own clinical setting.

Cardiomyopathy, Hypertrophic↗
PubMed1991

Systemic and left ventricular responses to exercise stress in asymptomatic patients with valvular aortic stenosis.

Patients with heart disease may have myocardial ischemia or left ventricular (LV) dysfunction without symptoms. The exercise responses of 14 asymptomatic patients with valvular aortic stenosis (AS) were studied using treadmill testing, thallium-201 scintigraphy and radionuclide angiography. Compared with age- and gender-matched control subjects, patients with AS demonstrated reduced exercise tolerance (10.7 +/- 2.5 vs 13.3 +/- 4.2 min; p = 0.06) and maximal oxygen consumption (26.7 +/- 6.3 vs 36.3 +/- 9.5 ml O2/min/kg; p = 0.004) associated with decreased peak systolic blood pressure response to exercise (177 +/- 18 vs 214 +/- 42 mm Hg; p less than 0.004). Ten of 14 patients developed ST-segment depression during exercise, only 3 of whom had reversible thallium defects. Patients with AS tended to have greater LV ejection fractions at rest (65 +/- 11 vs 58 +/- 7; p = 0.08) and significantly decreased early peak filling rates (4.8 +/- 1.3 vs 6.1 +/- 0.6 stroke volume/s; p = 0.003) compared with those of control subjects. During maximal supine exercise, patients with AS had less of an increase in ejection fraction (2 +/- 9 vs 15 +/- 7%; p less than 0.001) associated with a decrease in end-diastolic (-7 +/- 15 vs +5 +/- 16%; p = 0.06) and stroke (-6 +/- 17 vs +30 +/- 13%; p less than 0.001) volumes from baseline measurements.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Comparison of exercise radionuclide angiography with thallium SPECT imaging for detection of significant narrowing of the left circumflex coronary artery.

Although quantitation of exercise thallium tomograms has enhanced the noninvasive diagnosis and localization of coronary artery disease, the detection of stenosis of the left circumflex coronary artery remains suboptimal. Because posterolateral regional wall motion during exercise is well assessed by radionuclide angiography, this study determined whether regional dysfunction of the posterolateral wall during exercise radionuclide angiography is more sensitive in identifying left circumflex disease than thallium perfusion abnormalities assessed by single-photon emission computed tomography (SPECT). One hundred ten consecutive patients with CAD were studied, of whom 70 had a significant stenosis of the left circumflex coronary artery or a major obtuse marginal branch. Both regional function and segmental thallium activity of the posterolateral wall were assessed using visual and quantitative analysis. Left ventricular regional function was assessed objectively by dividing the left ventricular region of interest into 20 sectors; the 8 sectors corresponding to the posterolateral free wall were used to assess function in the left circumflex artery distribution. Similarly, using circumferential profile analysis of short-axis thallium tomograms, left ventricular myocardial activity was subdivided into 64 sectors; the 16 sectors corresponding to the posterolateral region were used to assess thallium perfusion abnormalities in the left circumflex artery territory. Qualitative posterolateral wall motion analysis detected 76% of patients with left circumflex coronary artery stenosis, with a specificity of 83%, compared with only 44% by qualitative thallium tomography (p less than 0.001) and a specificity of 92%. Whereas quantitation of thallium activity increased the sensitivity for detecting left circumflex coronary artery stenosis to 80% with a specificity of 55%, it did not achieve statistical significance when compared with qualitative wall motion analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Impaired left ventricular filling and regional diastolic asynchrony at rest in coronary artery disease and relation to exercise-induced myocardial ischemia.

Impaired left ventricular (LV) diastolic filling at rest is frequently observed in patients with coronary artery disease (CAD) who have normal LV systolic function and no previous infarction. To test the hypothesis that abnormal diastolic function at rest might reflect the functional severity of CAD, as estimated by exercise-induced ischemia, the relation between regional and global LV diastolic function at rest and during exercise-induced ischemia was evaluated in 49 patients with radionuclide angiography. All patients had normal systolic function at rest. Group 1 (n = 26) patients manifested a normal ejection fraction response to exercise and group 2 (n = 23) patients an abnormal response. Data obtained from 22 age-comparable normal volunteers were used for comparison. Although regional and global diastolic function were not different between normal subjects and group 1 patients, peak filling rate was lower in group 2 patients than in normal subjects (2.5 +/- 0.8 vs 3.2 +/- 0.6 end-diastolic counts/s; p less than 0.01). Moreover, regional diastolic asynchrony, as assessed from the radionuclide data by using a regional sector analysis of the LV region of interest, was greater in group 2 patients (46 +/- 44 ms) than in both normal subjects (25 +/- 16 ms; p less than 0.05) and group 1 patients (23 +/- 16 ms; p less than 0.05). Thus, among patients with CAD and with normal LV systolic function at rest, impaired LV filling and regional asynchrony predict a greater degree of exercise-induced ischemia, suggesting a greater extent of jeopardized myocardium.

Coronary Circulation↗
PubMed1991

Sudden death during empiric amiodarone therapy in symptomatic hypertrophic cardiomyopathy.

Amiodarone is reported to improve symptoms and to prevent sudden death in patients with hypertrophic cardiomyopathy (HC). Amiodarone treatment (loading dose 30 g given over 6 weeks; maintenance dose 400 mg/day) was prospectively evaluated in 50 patients with HC in whom the drug was initiated because of symptoms refractory to conventional drug therapy (calcium antagonists and beta blockers). Twenty-one (42%) patients had ventricular tachycardia (VT) during Holter monitoring. Amiodarone significantly and often markedly improved the patients' New York Heart Association functional class status (from 3.3 to 2.7 at 2 months, p less than 0.001) and treadmill exercise duration (p less than 0.001). Eight patients, however, died (7 suddenly) during a mean follow-up period of 2.2 +/- 1.8 years. Of the 7 sudden deaths, 6 occurred within 5 months of initiation of treatment. The 6-month and 1- and 2-year survival rates were 87, 85 and 80%, respectively. The survival rate of patients with VT was significantly worse than that of patients without VT (61 vs 97% at 2 years; p less than 0.01). Sudden death occurred despite abolition of VT on Holter monitoring. Amiodarone increased left ventricular peak filling rate by radionuclide angiography in 20 of 33 patients (61%) (p less than 0.01). Decrease in peak left ventricular filling rate within 10 days of amiodarone therapy (8 of 33 patients) was associated with subsequent sudden death (p less than 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Thallium 201 for assessment of myocardial viability.

Left ventricular (LV) performance is reduced in a large subset of patients with chronic coronary artery disease (CAD) and LV dysfunction on the basis of regionally ischemic or hibernating myocardium rather than irreversibly infarcted tissue. The detection of dysfunctional but viable myocardium is clinically relevant since regional and global LV function in such patients will improve after revascularization procedures; however, the identification of patients with such potentially reversible LV dysfunction is difficult. Although thallium 201 imaging may be of value in detecting viable myocardium if regions with perfusion defects during exercise demonstrate redistribution of thallium on a 3- to 4-hour resting image, thallium defects often appear persistently "fixed" within regions of severely ischemic or hibernating myocardium. It has been shown that up to 50% of regions with apparently irreversible thallium defects will improve in function after revascularization. Thus, standard exercise-redistribution thallium scintigraphy may not differentiate LV dysfunction arising from infarcted versus hibernating myocardium. The precision with which thallium imaging identifies viable myocardium can be improved greatly by additional studies once 4-hour redistribution imaging demonstrates an irreversible thallium defect. These additional studies include late (24-hour) redistribution imaging, repeat imaging after thallium reinjection, or a combination of thallium reinjection followed by late imaging. Several recent studies suggest that thallium reinjection techniques, by demonstrating thallium uptake in dysfunctional regions with apparently irreversible defects, predict improvement after revascularization with similar predictive accuracy as that achieved using metabolic imaging with positron emission tomography (PET). Studies directly comparing such thallium methods and PET, which thus far involve only small numbers of patients, suggest that the assessment of regional metabolic activity using PET and the assessment of regional thallium activity using single photon emission computed tomography provide concordant results. These findings, if confirmed by larger ongoing studies, suggest that thallium reinjection imaging is a convenient, clinically accurate, and relatively inexpensive method with which to identify viable myocardium in patients with chronic CAD and LV dysfunction.

Coronary Disease↗
PubMed1991

Identification of viable myocardium in patients with chronic coronary artery disease and left ventricular dysfunction. Comparison of thallium scintigraphy with reinjection and PET imaging with 18F-fluorodeoxyglucose.

In patients with chronic coronary artery disease and left ventricular dysfunction, the distinction between ventricular dysfunction arising from myocardial fibrosis and ischemic, but viable, myocardium has important clinical implications. By positron emission tomography (PET), enhanced fluorine-18-labeled fluorodeoxyglucose (FDG) uptake in myocardial segments with impaired function and reduced blood flow is evidence of myocardial viability. Reinjection of thallium-201 at rest immediately after stress-redistribution imaging may also provide evidence of myocardial viability by demonstrating thallium uptake in regions with apparently "irreversible" defects. To compare these two methods, we studied 16 patients with chronic coronary artery disease and left ventricular dysfunction (ejection fraction, 27 +/- 9%), all of whom had irreversible defects on standard exercise-redistribution thallium single-photon emission computed tomography (SPECT) imaging. Thallium was reinjected immediately after the redistribution study, and SPECT images were reacquired. The patients also underwent PET imaging with FDG and oxygen-15-labeled water. A total of 432 myocardial segments were analyzed from comparable transaxial tomograms, of which 166 (38%) had irreversible thallium defects on redistribution images before reinjection. FDG uptake was demonstrated in 121 (73%) of these irreversible defects. Irreversible defects were then subgrouped according to the degree of thallium activity, relative to peak activity in normal regions. Irreversible defects with only mild (60-85% of peak activity) or moderate (50-59% of peak) reduction in thallium activity were considered viable on the basis of FDG uptake in 91% and 84% of these segments, respectively. In contrast, in irreversible defects with severe reduction in thallium activity (less than 50% of peak), FDG uptake was present in 51% of segments. In such severe defects, an identical number of segments (51%) demonstrated enhanced uptake of thallium after reinjection. In these severe "irreversible" defects, data on myocardial viability were concordant by the two techniques in 88% of segments, with 45% identified as viable and 43% identified as scar on both PET and thallium reinjection studies. These observations suggest that thallium imaging can be used to identify viable myocardium in patients with chronic coronary artery disease and left ventricular dysfunction. Most irreversible defects with only mild or moderate reduction in thallium activity represent viable myocardium as confirmed by FDG uptake.(ABSTRACT TRUNCATED AT 400 WORDS)

Coronary Disease↗
PubMed1991

Thallium reinjection after stress-redistribution imaging. Does 24-hour delayed imaging after reinjection enhance detection of viable myocardium?

BACKGROUND: Thallium reinjection immediately after conventional stress-redistribution imaging improves the detection of viable myocardium, as many myocardial regions with apparently "irreversible" thallium defects on standard 3-4-hour redistribution images manifest enhanced thallium uptake after reinjection. Because the 10-minute period between reinjection and imaging may be too short, the present study was designed to determine whether 24-hour imaging after thallium reinjection provides additional information regarding myocardial viability beyond that obtained by imaging shortly after reinjection. METHODS AND RESULTS: We studied 50 patients with chronic stable coronary artery disease undergoing exercise thallium tomography, radionuclide angiography, and coronary arteriography. Immediately after the 3-4-hour redistribution images were obtained, 1 mCi thallium was injected at rest, and images were reacquired at 10 minutes and 24 hours after reinjection. The stress, redistribution, reinjection, and 24-hour images were then analyzed qualitatively and quantitatively. Of the 127 abnormal myocardial regions on the stress images, 55 had persistent defects on redistribution images by qualitative analysis, of which 25 (45%) demonstrated improved thallium uptake after reinjection. At the 24-hour study, 23 of the 25 regions (92%) with previously improved thallium uptake by reinjection showed no further improvement. Similarly, of the 30 regions determined to have irreversible defects after reinjection, 29 (97%) remained irreversible on 24-hour images. These findings were confirmed by the quantitative analysis. The mean normalized thallium activity in regions with enhanced thallium activity after reinjection increased from 57 +/- 13% on redistribution studies to 70 +/- 14% after reinjection but did not change at 24 hours (71 +/- 14%). In regions with irreversible defects that were unaltered by reinjection, mean regional thallium activity did not differ from the reinjection to the 24-hour studies (57 +/- 17% and 58 +/- 17%, respectively). Twenty-four-hour imaging after reinjection showed improvement in only four of 35 irreversible regions (involving three of the 50 patients). CONCLUSIONS: These data indicate that thallium reinjection at rest after 3-4 hours of redistribution provides most of the clinically relevant information pertaining to myocardial viability in regions with apparently irreversible thallium defects. Hence, thallium reinjection may be used instead of 24-hour imaging in most patients in whom a persistent thallium defect is observed on conventional redistribution images.

Coronary Angiography↗
PubMed1991

Myocardial metabolic, hemodynamic, and electrocardiographic significance of reversible thallium-201 abnormalities in hypertrophic cardiomyopathy.

BACKGROUND: Exercise-induced abnormalities during thallium-201 scintigraphy that normalize at rest frequently occur in patients with hypertrophic cardiomyopathy. However, it is not known whether these abnormalities are indicative of myocardial ischemia. METHODS AND RESULTS: Fifty patients with hypertrophic cardiomyopathy underwent exercise 201Tl scintigraphy and, during the same week, measurement of myocardial lactate metabolism and hemodynamics during pacing stress. Thirty-seven patients (74%) had one or more 201Tl abnormalities that completely normalized after 3 hours of rest; 26 had regional myocardial 201Tl defects, and 26 had apparent left ventricular cavity dilatation with exercise, with 15 having coexistence of these abnormal findings. Of the 37 patients with reversible 201Tl abnormalities, 27 (73%) had metabolic evidence of myocardial ischemia during rapid atrial pacing (myocardial lactate extraction of 0 mmol/l or less) compared with four of 13 patients (31%) with normal 201Tl scans (p less than 0.01). Eleven patients had apparent cavity dilatation as their only 201Tl abnormality; their mean postpacing left ventricular end-diastolic pressure was significantly higher than that of the 13 patients with normal 201Tl studies (33 +/- 5 versus 21 +/- 10 mm Hg, p less than 0.001). There was no correlation between the angiographic presence of systolic septal or epicardial coronary arterial compression and the presence or distribution of 201Tl abnormalities. Patients with ischemic ST segment responses to exercise had an 80% prevalence rate of reversible 201Tl abnormalities and a 70% prevalence rate of pacing-induced ischemia. However, 69% of patients with nonischemic ST segment responses had reversible 201Tl abnormalities, and 55% had pacing-induced ischemia. CONCLUSIONS: Reversible 201Tl abnormalities during exercise stress are markers of myocardial ischemia in hypertrophic cardiomyopathy and most likely identify relatively underperfused myocardium. In contrast, ST segment changes with exercise and systolic compression of coronary arteries on angiography are unreliable markers of inducible myocardial ischemia in hypertrophic cardiomyopathy. Apparent cavity dilatation during 201Tl scintigraphy may indicate ischemia-related changes in left ventricular filling, with elevation in diastolic pressures and endocardial compression.

Adolescent↗
PubMed1991

Serial long-term assessment of the natural history of asymptomatic patients with chronic aortic regurgitation and normal left ventricular systolic function.

BACKGROUND: Many asymptomatic patients with aorta regurgitation and normal left ventricular systolic function remain clinically stable for many years, but others ultimately develop symptoms or left ventricular dysfunction and require operation. To identify indexes of left ventricular function predictive of symptomatic and functional deterioration during the long-term course of asymptomatic patients, we studied 104 asymptomatic patients with chronic severe aortic regurgitation and normal left ventricular ejection fraction at rest. METHODS AND RESULTS: Serial echocardiographic (average, 7.8 per patient) and radionuclide angiographic (average, 5.0 per patient) studies were obtained over a mean follow-up period of 8 years (range, 2-16 years). By Kaplan-Meier life table analysis, 58 +/- 9% of patients remained asymptomatic with normal ejection fraction at 11 years, an average attrition rate of less than 5% per year; two patients died suddenly, four developed asymptomatic left ventricular dysfunction, and 19 underwent operation because symptoms developed. By univariate Cox regression analysis, many variables on initial study were associated with death, ventricular dysfunction, or symptoms, including age, left ventricular end-systolic dimension and end-diastolic dimension, fractional shortening, and both rest and exercise ejection fraction (all p less than 0.001). The average rates of change of rest ejection fraction, fractional shortening, and end-systolic dimension were also associated with death or symptoms by univariate Cox analysis (all p less than 0.01). However, when all variables were included in a multivariate Cox analysis, only age (p less than 0.05), initial end-systolic dimension (p less than 0.001), and rate of change in end-systolic dimension and rest ejection fraction during serial studies (both p less than 0.05) predicted outcome. CONCLUSIONS: Thus, in addition to indexes of left ventricular function determined on initial evaluation, serial long-term changes in systolic function identify patients likely to develop symptoms and require operation. Patients have a higher risk of symptomatic deterioration if there is progressive change in end-systolic dimension or resting ejection fraction during the course of serial studies.

Adult↗
PubMed1991

A theoretical comparison of first-pass and gated equilibrium methods in the measurement of systolic left ventricular function.

First-pass and gated equilibrium radionuclide studies of left ventricular function have proven extremely useful in the detection and management of patients with heart disease. Despite this practical experience, however, comparison of these methods generally has been confined to procedural differences that do not reflect the intrinsic properties of the methods. Here, we describe the results of a simple theoretical calculation from first principles that compares the methods based on their relative statistical precision. This analysis assumes that each procedure is carried out with the same tracer dose in the same hypothetical patient under identical conditions and with the same ideal imaging equipment. Results obtained with this model suggest that the imaging time required for a gated equilibrium study to achieve the same statistical precision as a first-pass study is typically less than 2 min in resting subjects and less than 1 min during stress. The analysis also indicates that gated equilibrium studies will tend to possess the greater statistical precision when cardiac output is elevated, such as when the heart is imaged during exercise. On the other hand, this analysis indicates that the first-pass method will tend to possess the greater precision when cardiac output is low and when imaging time is highly constrained.

Gated Blood-Pool Imaging↗
PubMed1991

Radionuclide angiographic evaluation of left ventricular diastolic function.

Left ventricular diastolic function is altered in the majority of patients with cardiac diseases, especially those characterized by myocardial ischemia or hypertrophy. In many circumstances, such abnormalities related to impaired relaxation or reduced distensibility may precede evidence of left ventricular systolic dysfunction. Radionuclide angiography may be adapted to study the rapid filling phase of diastole, the duration of the isovolumic relaxation phase, the relative contributions of rapid filling and atrial systole to left ventricular stroke volume, and the relation between regional nonuniformity of left ventricular function and global filling properties. Technical aspects of data acquisition that must be considered for such studies include the effects of cardiac cycle length fluctuations, temporal resolution, temporal smoothing, and normalization parameters. As noninvasive radionuclide methods (and any other analyses using purely noninvasive techniques) do not permit assessment of the left atrial-left ventricular pressure gradient or the simultaneous evaluation of changes in left ventricular pressure and volume during relaxation and filling, complete clinical interpretation of "abnormal" left ventricular filling indexes, or changes in these indexes after interventions, is not possible. Despite the inherent limitations of noninvasive assessment of left ventricular diastolic function, radionuclide evaluation of left ventricular filling may provide clinically useful insights, especially in patients with congestive heart failure symptoms and normal left ventricular systolic function.

Aging↗
PubMed1991

Radionuclide angiography in the management of asymptomatic aortic regurgitation.

Left ventricular systolic function is an important determinant of long-term prognosis in patients with chronic aortic regurgitation. In patients undergoing aortic valve replacement, those with preoperative left ventricular dysfunction have a greater risk of postoperative congestive heart failure and death than do those in whom preoperative left ventricular systolic function is normal. However, patients with preoperative left ventricular dysfunction are not a homogeneous group but may be further stratified according to risk on the basis of the severity of symptoms, exercise intolerance, and temporal duration of left ventricular dysfunction. Therefore, asymptomatic patients with reproducible and definite evidence of impaired left ventricular function should undergo operation without waiting for the development of symptoms or more severe left ventricular dysfunction. In addition, among asymptomatic patients with normal systolic function, indexes of left ventricular function are also helpful, especially when measured serially, in predicting the development of symptoms and the need for valve replacement surgery over the course of the next 5 to 10 years. Noninvasive imaging techniques should play a major role in this evaluation, and radionuclide angiography is ideally suited for the quantitative evaluation of systolic function in the volume-overloaded left ventricle. Although the prognostic value of left ventricular ejection fraction at rest is well established, ejection fraction during exercise has little value once age and left ventricular function at rest are accounted for and is of minor importance in formulating patient management decisions.

Aortic Valve↗