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Biomedical subjects

R O Bonow

Publications and source records attributed to R O Bonow.

At least 91 records · Page 5Linked to original sources
PubMed1993

Myocardial ischemia detected by thallium scintigraphy is frequently related to cardiac arrest and syncope in young patients with hypertrophic cardiomyopathy.

OBJECTIVES: The purpose of this study was to determine the frequency of myocardial ischemia as a potential mechanism for cardiac arrest and syncope in young patients with hypertrophic cardiomyopathy who experienced such complications. BACKGROUND: Sudden cardiac death and syncope occur frequently in patients with hypertrophic cardiomyopathy. Although ventricular arrhythmias account for most of these events in adult patients, the mechanism responsible for cardiac arrest and syncope in young patients has not been established. METHODS: Twenty-three patients with hypertrophic cardiomyopathy, aged 6 to 23 years, with previous cardiac arrest (n = 8), syncope (n = 7) or a family history of sudden cardiac death (n = 8) were evaluated to determine the prevalence of spontaneous ambulatory ventricular tachycardia (24- to 72-h electrocardiographic [ECG] monitoring), exercise-induced myocardial ischemia (thallium scintigraphy) and inducibility of ventricular tachycardia (electrophysiologic studies). RESULTS: Three of 15 patients with a history of cardiac arrest or syncope had ventricular tachycardia on ambulatory ECG monitoring. However, all 15 patients, had inducible ischemia by thallium scintigraphy compared with only 3 (37%) of 8 patients with no such history (p < 0.01). In contrast, ventricular tachycardia induction was uncommon in all of the young patients (27% in those with cardiac arrest or syncope; 0% in the others). During therapy for ischemia with verapamil alone or in combination with beta-adrenergic blocking agents, only 4 of the 15 patients with cardiac arrest or syncope had further episodes. In three of the four patients, these events were temporally related to discontinuation of verapamil. Among eight patients who had a repeat exercise thallium study while receiving anti-ischemic therapy, seven (88%) had improved regional thallium uptake, of whom three had normal thallium studies. CONCLUSIONS: These data suggest that in young patients with hypertrophic cardiomyopathy, sudden cardiac arrest or syncope is frequently related to ischemia rather than to a primary arrhythmogenic ventricular substrate.

Adolescent↗
PubMed1993

Concordance and discordance between stress-redistribution-reinjection and rest-redistribution thallium imaging for assessing viable myocardium. Comparison with metabolic activity by positron emission tomography.

BACKGROUND: Stress thallium scintigraphy provides important diagnostic and prognostic information in patients with coronary artery disease by demonstrating regional myocardial ischemia. However, if the clinical question being addressed is whether a region is viable and not whether there is inducible ischemia, then it may be more reasonable to perform rest-redistribution imaging rather than stress-redistribution imaging followed by either reinjection or late redistribution. Therefore, we determined whether stress-redistribution-reinjection and rest-redistribution imaging provide the same information regarding myocardial viability. METHODS AND RESULTS: Both stress-redistribution-reinjection and rest-redistribution thallium single photon emission computed tomographic imaging was performed in 41 patients with chronic stable coronary artery disease, with quantitative analysis of regional thallium activity. Thallium reinjection was performed immediately after the 3- to 4-hour redistribution images were completed. Of the 155 myocardial regions with perfusion defects on the stress images, 91 (59%) were irreversible on conventional 3- to 4-hour redistribution images. When the outcomes of these irreversible regions were assessed after reinjection and compared with rest-redistribution images, there was concordance of data regarding myocardial viability (normal/reversible or irreversible) in 72 of the 91 (79%) irreversible defects. Twenty of the 41 patients also underwent positron emission tomography at rest with [18F]fluorodeoxyglucose and [15O]water. In these patients, stress-redistribution-reinjection and rest-redistribution imaging provided concordant information regarding myocardial viability in 427 (72%) of 594 myocardial regions and discordance in 167 regions. However, when irreversible thallium defects were further analyzed according to the severity of the thallium defect in these discordant regions, 149 of 167 (89%) demonstrated only mild-to-moderate reduction in thallium activity (51% to 85% of normal activity), and positron emission tomography verified 98% of these regions to be metabolically active and viable. Thus, when the severity of thallium activity was considered within irreversible thallium defects, the concordance between stress-redistribution-reinjection and rest-redistribution imaging regarding myocardial viability increased to 94%. CONCLUSIONS: These data indicate that one of two imaging modalities, either stress-redistribution-reinjection or rest-redistribution imaging, may be used for identifying viable myocardium. However, if there are no contraindications to stress testing, stress-redistribution-reinjection imaging provides a more comprehensive assessment of the extent and severity of coronary artery disease by demonstrating regional myocardial ischemia without jeopardizing information on myocardial viability.

Coronary Angiography↗
PubMed1993

Thallium reinjection demonstrates viable myocardium in regions with reverse redistribution.

BACKGROUND: The clinical significance and pathophysiological mechanisms of reverse redistribution on stress-redistribution thallium-201 myocardial scintigraphy in patients with chronic coronary artery disease are unclear. Recent studies have shown that thallium-201 reinjection is a useful technique for the detection of myocardial viability in chronic coronary artery disease. In this investigation we determined whether thallium reinjection distinguishes viable from nonviable myocardium in regions with reverse redistribution. METHODS AND RESULTS: We studied 39 patients with chronic stable coronary artery disease (age, 60 +/- 10 years), all of whom demonstrated reverse redistribution on standard exercise-redistribution thallium single-photon emission computed tomography (SPECT). Reverse redistribution was defined as > or = 10% decrease in relative thallium-201 activity between stress and redistribution images and included either the worsening of a perfusion defect apparent on post-stress images or the appearance of a new defect on the redistribution images. Thallium reinjection was performed immediately after the 3- to 4-hour redistribution study. Of 39 regions with reverse redistribution, 32 (82%) showed enhanced thallium-201 activity (> or = 10% increase) after reinjection. In the other 7 regions (18%), the scintigraphic defect persisted after reinjection. Abnormal Q waves were present in only 8 of 32 (25%) regions with enhanced thallium-201 uptake after reinjection compared with 5 of 7 (71%) regions not responding to reinjection (P < .05). Akinetic or dyskinetic wall motion was present in 3 of 32 (9%) regions showing enhanced uptake after reinjection, in contrast with 5 of 7 (71%) regions not responding to reinjection (P < .01). Critically stenosed or totally occluded coronary arteries supplied 24 of 29 (83%) regions with enhanced thallium-201 uptake after reinjection but only 2 of 7 (28%) regions not showing a positive response to reinjection (P < .05). Collateral circulation was detected in 23 of 29 (79%) regions with a positive thallium reinjection effect but in only 1 of the other 7 regions (P < .01). Sixteen of the 39 patients also underwent positron emission tomography using 18F-fluorodeoxyglucose (FDG) to assess glucose utilization and H2(15)O to assess regional blood flow. The 14 regions with reverse redistribution that responded to reinjection with enhanced thallium uptake all showed either normal patterns of FDG uptake and flow or an ischemic pattern with increased FDG uptake relative to flow. Reduced FDG uptake and reduced flow values were seen in the two regions not responding to thallium reinjection. CONCLUSIONS: These observations indicate that reverse redistribution in chronic coronary artery disease usually reflects viable myocardium, critically dependent upon collateral circulation.

Cardiac Catheterization↗
PubMed1993

Three-dimensional registration of cardiac positron emission tomography attenuation scans.

A method is described and tested which allows three-dimensional registration of two cardiac PET attenuation scans of the same subject acquired at different times. The alignment method is based on maximizing the correlation coefficient between the stacks of slices obtained during each of the two imaging sessions. The method appears accurate to better than 1 mm in x, y and z, and better than 1.5 degrees in the three angles of rotation. The method has been tested by using it to realign deliberately misaligned attenuation scans, and also by using realigned attenuation scans to correct fluorodeoxyglucose (FDG) emission scan data. The FDG emission data reconstructed with the realigned attenuation scans do not differ appreciably from the FDG data obtained using the original attenuation data. The method should be useful in realigning emission data (using the alignment coordinates predicted by realigning the attenuation scans), correcting for subject motion between scans (especially multiple intervention scans) and may allow a subject to leave the scanning table between scans during long imaging sessions.

Deoxyglucose↗
PubMed1992

Assessing viable myocardium with thallium-201.

Patients with chronic coronary artery disease and potentially reversible left ventricular dysfunction can often be successfully identified by one or more clinical indicators of myocardial viability, including regional wall motion, systolic wall thickening, regional myocardial perfusion as determined by perfusion tracers, and redistribution of thallium-201. In some patients, however, viable but "hibernating" myocardium will exist even when none of the above are evident. Myocardial viability in this situation can be detected with a high degree of accuracy by the demonstration of preserved metabolic activity by positron emission tomography (PET) scanning. Additionally, modifications of the standard exercise-redistribution thallium protocol may also produce accurate results. These modifications include late thallium-201 redistribution imaging, performed 8-72 hours following initial thallium injection, and thallium reinjection at rest after early (3-4 hours) or late (8-72 hours) redistribution imaging. These methods can identify viable myocardium in many thallium defects that appear to be irreversible on a standard 3-4 hour redistribution image. In addition, serial imaging after administration of thallium-201 at rest may also provide valuable insights into myocardial viability. These imaging modalities have important practical applications in the evaluation and management of patients with coronary artery disease and left ventricular dysfunction.

Chronic Disease↗
PubMed1992

Left ventricular diastolic dysfunction as a cause of congestive heart failure. Mechanisms and management.

OBJECTIVE: To define the mechanisms underlying left ventricular diastolic dysfunction in patients with congestive heart failure and normal systolic function and to identify the patients at risk for this syndrome. STUDY SELECTION: Studies were selected that describe the clinical observations of congestive heart failure with normal systolic function and that provide experimental and clinical insights into the mechanisms responsible for ventricular diastolic dysfunction. DATA SYNTHESIS: Recent studies indicate that a large number of patients (up to 40% in some series) presenting with congestive heart failure have preserved left ventricular systolic function. The factors contributing to altered left ventricular diastolic function include fibrosis, hypertrophy, ischemia, and increased afterload. The latter three factors, alone or in combination, predispose to impaired left ventricular relaxation, an active energy-requiring process. Thus, decreased left ventricular diastolic distensibility (increased diastolic pressure at any level of diastolic volume) may arise not only from altered passive elastic properties stemming from fibrosis or increased muscle mass but also from derangements in the dynamics of ventricular relaxation. RESULTS: In patients with essential hypertension, all four of the above mechanisms may be operative. Considering the prevalence of hypertension in the general population, hypertension appears to be an important underlying factor in many patients with heart failure on the basis of diastolic mechanisms. In the patient presenting with dyspnea and elevated filling pressures, but with a nondilated, normally contracting ventricle, treatment with standard heart failure medications (such as digitalis, diuretics, and vasodilators) is often ineffective and may be deleterious. Such patients may respond more favorably to beta-blockers and calcium-channel blockers. CONCLUSIONS: Diastolic dysfunction should be considered in the patient presenting with heart failure symptoms but with normal systolic function, particularly in hypertensive patients with left ventricular hypertrophy.

Diastole↗
PubMed1992

Effects of regional systolic asynchrony on left ventricular global diastolic function in patients with coronary artery disease.

Patients with coronary artery disease often have impaired left ventricular diastolic filling despite normal global systolic function. The influence of regional systolic asynchrony on diastolic function was assessed by radionuclide angiography in 60 patients with coronary artery disease and normal ejection fraction at rest: group 1 (n = 30) with normal wall motion at rest and group 2 (n = 30) with abnormal wall motion. Data were compared with those obtained from 19 normal volunteers. Age, heart rate, ejection fraction and echocardiographic end-diastolic dimension did not differ among the three groups. Peak filling rate in group 1 and group 2 was similar (2.5 +/- 0.5 and 2.3 +/- 0.6 end-diastolic counts/s, respectively) and significantly lower than that in the normal subjects (2.8 +/- 0.7 end-diastolic counts/s; p less than 0.01 vs. group 2, p less than 0.05 vs group 1). Time to peak filling rate was prolonged in group 2 (184 +/- 27 ms) compared with that in normal subjects (162 +/- 19 ms; p less than 0.01) and group 1 (172 +/- 15 ms; p less than 0.05). Left ventricular end-diastolic pressure was significantly higher in group 2 than in group 1 (14 +/- 7 vs. 10 +/- 5 mm Hg, respectively; p less than 0.05). Asynchrony was assessed by sector analysis of the radionuclide left ventricular region of interest. Diastolic asynchrony was similar in the two patient groups (30 +/- 23 ms in group 2, 26 +/- 16 ms in group 1) and was higher in both groups than in the normal subjects (16 +/- 8 ms; p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1992

Long-term variation in myocardial ischemia during daily life in patients with stable coronary artery disease: its relation to changes in the ischemic threshold.

Long-term variation in the frequency of myocardial ischemia during daily activity in patients with coronary artery disease who do not experience symptomatic changes has not been documented. Because at one point in time, the magnitude of such ischemia is strongly related to the ischemic threshold measured during exercise testing, this study was undertaken to determine whether patients with stable coronary artery disease show long-term variations in the frequency and duration of myocardial ischemia and to establish whether such variability is related to parallel changes in the ischemic threshold during exercise testing. Forty consecutive patients (mean age 61 +/- 8 years) who showed a stable clinical course over greater than or equal to 12 months were studied with a repeat exercise treadmill test and ambulatory electrocardiographic (ECG) monitoring after withdrawal of antianginal medications. The ischemic threshold was determined as the exercise time at 1 mm of ST segment depression. The mean interval to both follow-up evaluations was 15 +/- 3 months. Among the 23 patients with myocardial ischemia on ambulatory ECG monitoring at initial evaluation, the number and duration of ischemic episodes at follow-up were increased in 5 patients (mean increase 3.6 +/- 2 episodes and 123 +/- 98 min), unchanged in 1 patient and decreased in 17 patients (mean decrease 2.6 +/- 2 episodes and 98 +/- 72 min). Of the 17 patients without ischemic episodes at initial evaluation, 3 had evidence of ischemia on follow-up ambulatory ECG monitoring.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Metabolic evidence of viable myocardium in regions with reduced wall thickness and absent wall thickening in patients with chronic ischemic left ventricular dysfunction.

Reduced end-diastolic wall thickness with absent systolic wall thickening has been reported to represent nonviable myocardium in patients with chronic coronary artery disease. To assess whether reduced regional end-diastolic wall thickness and absent wall thickening accurately identify nonviable myocardium, 25 patients with ischemic left ventricular dysfunction (ejection fraction at rest 27 +/- 10%) underwent positron emission tomography with oxygen-15-labeled water and 18fluorodeoxyglucose to assess metabolic activity and spin-echo gated nuclear magnetic resonance imaging to measure regional end-diastolic wall thickness and wall thickening. The presence of metabolic activity was defined as 18fluorodeoxyglucose uptake (corrected for partial volume) greater than 50% of that in normal regions. Of 355 myocardial regions evaluated, 266 were hypokinetic or normokinetic at rest and 89 were akinetic (that is, absent wall thickening). 18Fluorodeoxyglucose uptake was observed in 97% of the hypokinetic and normokinetic regions and in 74% of the akinetic regions. End-diastolic wall thickness was greater in akinetic regions with than in those without 18fluorodeoxyglucose uptake (11 +/- 4 vs. 7 +/- 3 mm, p less than 0.01). The highest values for sensitivity and specificity of end-diastolic wall thickness in predicting the absence of metabolic activity in akinetic regions were 74% and 79%, respectively, and corresponded to an end-diastolic threshold of 8 mm. However, the positive predictive accuracy was only 55% and did not improve for other end-diastolic wall thickness values. In all myocardial regions, there was only a weak correlation between 18fluorodeoxyglucose activity and either end-diastolic wall thickness (r = 0.17) or wall thickening (r = 0.32). Thus, metabolic activity is present in many regions with reduced end-diastolic wall thickness and absent wall thickening. These data indicate that assessment of regional anatomy and function may be inaccurate in distinguishing asynergic but viable myocardium from nonviable myocardium.

Adult↗
PubMed1992

Relation between left ventricular function at rest and with exercise and silent myocardial ischemia.

The prognostic value of radionuclide measures of left ventricular function at rest and exercise is well established. Some studies have suggested that the frequency and duration of silent ischemia during ambulatory monitoring provide similar prognostic information; however, studies comparing these two techniques have not been performed. This study examines the relation between left ventricular function at rest and exercise-induced ischemia assessed by radionuclide ventriculography with myocardial ischemia during ambulatory electrocardiographic (ECG) monitoring. Of the 155 patients with coronary artery disease studied, 88% had left ventricular dysfunction with exercise, defined as failure of the ejection fraction to increase by greater than 4% with exercise, and 33% of patients had left ventricular dysfunction at rest (ejection fraction less than 45%); 52% had transient episodes of ST segment depression during 48-h ambulatory ECG monitoring. Exercise-induced left ventricular dysfunction during radionuclide ventriculography was extremely sensitive (94%) in detecting patients with ischemic episodes during ambulatory ECG monitoring; however, only 55% of patients with exercise-induced left ventricular dysfunction had ST segment depression during ambulatory monitoring. Moreover, patients with left ventricular dysfunction at rest had a lower prevalence of transient episodes of ST segment depression (31%) than did patients with normal left ventricular function at rest (62%) (p = 0.008). The relation between prognostically important variables during exercise radionuclide ventriculography and the number and duration of transient episodes of ST depression was examined.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Regional thallium uptake in irreversible defects. Magnitude of change in thallium activity after reinjection distinguishes viable from nonviable myocardium.

BACKGROUND: Thallium reinjection immediately after stress-redistribution imaging identifies ischemic but viable myocardium in as many as 50% of the regions characterized by conventional redistribution imaging as irreversibly injured. However, we have previously shown that some regions in which irreversible defects persist despite reinjection are metabolically active, and hence viable, by positron emission tomography. In the current study, we determined whether the severity of reduction in thallium activity within irreversible defects on redistribution images and the magnitude of change in regional thallium activity after reinjection can further discriminate viable from nonviable myocardium in such defects. METHODS AND RESULTS: We studied 150 patients with coronary artery disease by exercise thallium tomography using the rest-reinjection protocol. The three sets of images (stress, redistribution, and reinjection) were then analyzed quantitatively. The increase in regional thallium activity from redistribution to reinjection was computed, normalized to the increase observed in a normal region, and termed "differential uptake." Of the 175 myocardial regions designated to have irreversible thallium defects on conventional 3-4 hour redistribution images, 132 had only mild-to-moderate reduction in thallium activity (51-85% of normal activity), and 43 had severe reduction in thallium activity (less than or equal to 50% of normal activity). Thallium reinjection resulted in enhanced relative activity in 60 of 132 (45%) of the mild-to-moderate irreversible defects and 22 of 43 (51%) of the severe irreversible defects, leaving roughly half of these defects remaining irreversible after reinjection. However, in regions that appeared to remain irreversible despite reinjection, the magnitude of differential uptake differed between mild-to-moderate (74 +/- 14%) and severe (35 +/- 16%) irreversible defects (p less than 0.001). All regions with mild-to-moderate defects demonstrated greater than 50% differential uptake after reinjection. In contrast, all except two of the regions with severe irreversible defects demonstrated differential uptake of less than 50%. Fifteen patients also underwent positron emission tomography at rest with 18F-fluorodeoxyglucose (FDG) and 15O-water. FDG uptake was present in 91% of regions with mild-to-moderate reduction in thallium activity, and the results of differential uptake and FDG data were concordant in 81% of these regions. CONCLUSIONS: These data indicate that the magnitude of thallium uptake after reinjection differs between mild-to-moderate and severe irreversible defects on standard 3-4 hour redistribution images. The substantial differential uptake of thallium (greater than 50%) after reinjection in mild-to-moderate defects, even when relative thallium activity does not increase appreciably (and the defect appears to remain irreversible), coupled with preserved metabolic activity by positron emission tomography, supports the concept that such mild-to-moderate irreversible defects represent viable myocardium.

Adult↗
PubMed1992

Differential uptake and apparent 201Tl washout after thallium reinjection. Options regarding early redistribution imaging before reinjection or late redistribution imaging after reinjection.

BACKGROUND: Because thallium reinjection enhances the identification of viable myocardium, many laboratories have adopted the routine practice of performing reinjection imaging instead of 3-4-hour redistribution imaging. This approach assumes that the stress-reinjection protocol provides the necessary information regarding both exercise-induced ischemia and myocardial viability. Because apparent "washout" of thallium may occur between redistribution and reinjection studies, we examined the limitations created by eliminating 3-4-hour redistribution images. METHODS AND RESULTS: We studied 50 patients with chronic stable coronary artery disease by exercise thallium tomography, radionuclide angiography, and coronary arteriography. Immediately after the 3-4-hour redistribution images, 1 mCi thallium was injected at rest, and images were reacquired both 10 minutes and 24 hours after reinjection. The stress, redistribution, reinjection, and 24-hour images were then analyzed quantitatively, and the magnitude of change in regional thallium activity after reinjection was termed "differential uptake." Of the 127 abnormal myocardial regions on the stress images, 55 (43%) demonstrated either complete or partial reversibility on 3-4-hour redistribution images. After reinjection, 14 of these regions (25%) demonstrated apparent thallium washout due to low differential uptake of thallium, which was only 46 +/- 20% of that observed in normal regions. As a result, the relative thallium activity, which was 55 +/- 13% during stress (relative to normal regions) and increased significantly to 75 +/- 13% on 3-4-hour redistribution studies (p less than 0.001), decreased to only 58 +/- 13% after thallium reinjection. At 24 hours, redistribution again developed in all 14 regions, resulting in a relative thallium activity of 71 +/- 16% (p less than 0.03), which was similar to that achieved on 3-4-hour redistribution images. Twelve of the 14 regions (86%) exhibiting apparent washout after reinjection were supplied by a totally occluded coronary artery, of which eight (67%) had normal wall motion at rest. In contrast, only 41% of the regions with either improved or unchanged thallium uptake after reinjection were supplied by a totally occluded coronary artery (p less than 0.05). CONCLUSIONS: These data indicate that regions with thallium defects that are reversible on 3-4-hour redistribution images may demonstrate apparent washout of thallium after reinjection due to low differential uptake. Although this occurs in only a small fraction of regions (8%) identified as abnormal on exercise images, these regions represent approximately 25% of regions showing redistribution. Such defects would appear irreversible if redistribution imaging is not performed before reinjection. However, these same myocardial regions also redistribute further after reinjection and are identified as reversible on 24-hour images. Thus, one of two imaging options, either stress-redistribution-reinjection imaging or stress-reinjection-24-hour imaging, may be used for a comprehensive assessment of myocardial ischemia and viability.

Coronary Angiography↗
PubMed1992

Impact of surgical relief of outflow obstruction on thallium perfusion abnormalities in hypertrophic cardiomyopathy.

BACKGROUND: To assess the impact of surgical relief of left ventricular outflow obstruction on myocardial perfusion abnormalities in patients with obstructive hypertrophic cardiomyopathy, 20 symptomatic patients who underwent a septal myectomy or mitral valve replacement were studied with assessment of myocardial perfusion during exercise by 201Tl emission computed tomography before and 6 months after surgery. METHODS AND RESULTS: Before surgery, 15 patients had myocardial perfusion defects during exercise that completely normalized at rest, one patient had both reversible and fixed perfusion defects, two patients had fixed defects only, and two patients had normal exercise and rest thallium scans. After surgical relief of left ventricular outflow obstruction (basal gradient reduced from 62 +/- 40 to 7 +/- 12 mm Hg, p less than 0.001; peak provokable gradient reduced from 131 +/- 27 to 49 +/- 36 mm Hg, p less than 0.001), repeat exercise thallium studies showed complete normalization of perfusion defects in 11 patients, including the two patients with fixed defects alone before surgery, and improvement in the magnitude and distribution of perfusion defects in five additional patients. This was associated with a significant reduction in the number of patients with reversible regional defects (five patients compared with 13 patients before surgery, p = 0.026) and of patients with endocardial hypoperfusion (four patients compared with 12 patients before surgery, p = 0.024). Furthermore, increased lung uptake of thallium was noted in five patients after surgery, compared with 12 patients before surgery (p = 0.055). Only two patients with reversible perfusion defects before surgery had unchanged postoperative studies. However, four patients acquired new fixed defects as a consequence of surgery, and two of these four had the greatest severity and distribution of left ventricular hypertrophy by echocardiography. These four patients experienced a substantially greater decrease in ejection fraction (-26 +/- 15%) after surgery than the remaining patients (-3 +/- 14%, p less than 0.01). CONCLUSIONS: Surgical relief of left ventricular outflow obstruction results in normalization or improvement of myocardial perfusion in the majority of patients with reversible and fixed perfusion defects by 201Tl scintigraphy. However, surgery may result in myocardial injury and scarring, with consequent decreased left ventricular ejection fraction in some patients.

Cardiac Catheterization↗
PubMed1992

Regional left ventricular wall thickening. Relation to regional uptake of 18fluorodeoxyglucose and 201Tl in patients with chronic coronary artery disease and left ventricular dysfunction.

BACKGROUND: In previous studies comparing regional 201Tl (201Tl) and 18fluorodeoxyglucose (FDG) activity in patients with chronic coronary artery disease and left ventricular dysfunction, we hypothesized that regions with mild-to-moderate reduction in FDG activity and regions with mild-to-moderate irreversible 201Tl defects after 3- to 4-hour redistribution represent viable myocardium. In the present study, regional FDG and 201Tl activities were compared with regional systolic wall thickening by gated magnetic resonance imaging (MRI) to confirm the presence of viable myocardium in these territories. METHODS AND RESULTS: Twenty-five patients with chronic stable coronary artery disease and left ventricular dysfunction (ejection fraction, 28 +/- 10) underwent exercise 201Tl tomographic imaging (SPECT), using a reinjection protocol, positron emission tomography (PET) with FDG and H2(15)O, and gated MRI. Matched SPECT, PET, and MRI tomograms were analyzed. From the PET data, 105 regions had matched reduction in FDG and blood flow, of which 69 regions had moderately reduced FDG uptake (50-79% uptake relative to a normal reference region) and 36 had severely reduced FDG uptake (less than 50% of normal activity). Regions with moderately reduced as compared with severely reduced FDG activity had greater end-diastolic wall thickness (9.4 +/- 2.6 versus 8.0 +/- 3.7 mm; p less than 0.05) and regional systolic wall thickening (1.7 +/- 2.7 versus -0.7 +/- 2.1 mm; p less than 0.01). From the SPECT data, 169 irreversible 201Tl defects after 3-4 hour redistribution were identified, of which 70 were mild (greater than 65 to less than 85% of maximal 201Tl activity), 52 were moderate (50-65% of maximal activity), and 47 were severe (less than 50% of maximal activity). Regional systolic wall thickening was greater in regions with normal 201Tl uptake (3.3 +/- 2.3 mm) as compared with all other regions. Regions showing only mild or moderate irreversible defects at redistribution, however, showed wall thickening (2.4 +/- 2.4 and 2.2 +/- 2.5 mm, respectively), which was similar to that observed in regions with reversible 201Tl defects (2.1 +/- 2.2 mm). Only regions with severe irreversible defects at redistribution showed absence of thickening (-0.1 +/- 2.9 mm, p less than 0.01 versus all other groups). After 201Tl reinjection, 12 of 47 (26%) regions with severe irreversible defects showed enhanced 201Tl uptake. The impairment in regional systolic wall thickening was not significantly different between 201Tl defects with and without enhanced 201Tl uptake after reinjection. FDG activity, however, was present in all 12 regions (100%) with enhanced 201Tl uptake after reinjection as compared with only five of 35 (14%) that were unchanged after reinjection (p less than 0.01). CONCLUSIONS: Therefore, preserved wall thickness and systolic wall thickening in regions with moderate reduction in blood flow and FDG activity, and in irreversible 201Tl defects that are only mild-to-moderate, provide additional evidence that such regions represent viable myocardium. Moreover, the finding of metabolic activity and 201Tl uptake in regions with reduced blood flow and absent wall thickening provides clinical evidence of hibernating myocardium in humans.

Adult↗
PubMed1992

Spatially dependent deadtime losses in high count rate cardiac PET.

Cardiac PET scans result in nonhomogeneous distributions of activity within the body, which might lead to great variations in singles rates around the detector ring. Conventional deadtime correction algorithms assume that the singles rates are uniform. This paper investigates singles nonuniformities during several typical cardiac scanning protocols (bolus injections of 15O-water and 82Rb, slow infusion of 18F-FDG and static imaging with FDG) and estimates how such nonuniformities might affect quantitative data. Nonuniformity was observed in all studies and was described by an asymmetry index which increased to 58% during bolus water injection, the most inhomogeneous study. These results are valid for any scanner with a ring diameter of approximately 78 cm and are independent of the amount of activity injected. Deadtime losses depend on the amount of activity and on the scanner type. Nonhomogeneities in singles can be shown to produce spatially dependent deadtime correction factors; for our scanner, these were seen to differ by up to 16% from the mean deadtime correction during bolus water injection. To demonstrate the distortions generated by average deadtime correction, the activity distribution during a clinical cardiac study was simulated using a phantom. A simple local deadtime correction and its implementation on our system are described, and the resulting improvements in both absolute and relative quantitation of the phantom study are shown.

Deoxyglucose↗