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Biomedical subjects

F C Visser

Publications and source records attributed to F C Visser.

At least 19 recordsLinked to original sources

Predictive value of planar 18F-fluorodeoxyglucose imaging for cardiac events in patients after acute myocardial infarction.

This long-term study examines the predictive value of planar myocardial 18F-fluorodeoxyglucose (FDG) imaging for cardiac events after acute myocardial infarction (AMI). From December 1989 to April 1991, 59 consecutive patients with AMI had undergone planar rest thallium-201 (Tl-201)/FDG imaging for viability assessment; 53 (42 men) were included in this study. Mean follow-up was 47 +/- 15 months. Cardiac events were defined as cardiac-related death, reinfarction, late revascularization, and unstable angina pectoris. A mismatch pattern was defined as a FDG uptake exceeding Tl-201 uptake by > or = 20%. A concordant reduction in flow and metabolism was defined as a match. In the mismatch group (n = 39) were 19 events versus 1 event in the match group (n = 14) (p <0.009). In the mismatch group were 5 cardiac deaths, 3 reinfarctions, 7 late revascularizations, and 4 patients had unstable angina pectoris. There was 1 cardiac death in the match group. The event-free rate estimated using Kaplan Meier curves for patients with and without a mismatch was significantly different (p = 0.018). The relative risk for patients with a mismatch for developing a future cardiac event was estimated at 7.8 versus patients with a match. Thus, planar myocardial FDG imaging shortly after AMI has important prognostic significance for prediction of future cardiac events. Patients with a mismatch shortly after AMI have a high risk for future cardiac events on medical therapy.

Aged

Increased uptake of iodine-123-BMIPP in chronic ischemic heart disease: comparison with fluorine-18-FDG SPECT.

UNLABELLED: To evaluate the potential role of 15-p-[123I]iodophenyl-3-(R,S)-methylpentadecanoic acid (BMIPP) for the assessment of myocardial viability, the patterns of BMIPP versus 18F-fluorodeoxyglucose (FDG) uptake were evaluated in patients with chronic ischemic heart disease. METHODS: Twenty-one patients with stable chronic coronary artery disease underwent resting TI SPECT to delineate myocardial perfusion followed by FDG SPECT to detect residual viability in regions showing perfusion defects. Resting BMIPP SPECT was obtained on a separate day. SPECT images were displayed as polar maps (13 segments) and analyzed semiquantitatively. A total of 273 segments were analyzed. RESULTS: In 87 (32%) of the segments, a perfusion defect was observed. In perfusion defects, the distributions of BMIPP/TI (mis)matches were significantly different (p < 0.0001) between the FDG viable (n = 42) and nonviable (n = 45) segments. A BMIPP/TI mismatch (BMIPP uptake higher than perfusion) was found in 74% of FDG viable segments, whereas a BMIPP/TI match (BMIPP uptake equal or lower than perfusion) was found in 69% of FDG nonviable segments. Agreement between matching or mismatching of segments was assessed to be 71%. Agreement was 81% when the data were analyzed on a patient basis. The observed frequency of BMIPP/TI mismatches was significantly higher (p < 0.05) in segments with an old myocardial infarction (20 of 36; 55%) than it was in subacute infarcted myocardium (5 of 21; 24%). CONCLUSION: In chronically hypoperfused myocardium, an increased BMIPP uptake relative to perfusion was detected, which is different from the decreased BMIPP uptake often reported in (sub)acute myocardial ischemia. Therefore, the interval from infarction may be an important factor in the interpretation of BMIPP scintigraphic data. Increased BMIPP uptake was associated with FDG/TI mismatches and may, therefore, confirm myocardial viability. Some segments with a FDG/TI mismatch, however, revealed a BMIPP/TI match. These segments may contain viable but more severely damaged tissue. Further studies on functional recovery are warranted to assess the significance of a BMIPP/perfusion (mis)match for tissue viability.

Aged

Accuracy of currently available techniques for prediction of functional recovery after revascularization in patients with left ventricular dysfunction due to chronic coronary artery disease: comparison of pooled data.

OBJECTIVES: This study evaluated the relative merits of the most frequently used techniques for predicting improvement in regional contractile function after coronary revascularization in patients with left ventricular dysfunction due to chronic coronary artery disease. BACKGROUND: Several techniques have been proposed for predicting improvement in regional contractile function after revascularization, including thallium-201 (Tl-201) stress-redistribution-reinjection, Tl-201 rest-redistribution, fluorine-18 fluorodeoxyglucose with positron emission tomography, technetium-99m sestamibi imaging and low dose dobutamine echocardiography (LDDE). METHODS: A systematic review of all reports on prediction of functional recovery after revascularization in patients with chronic coronary artery disease (published between 1980 and March 1997) revealed 37 with sufficient details for calculating the sensitivity and specificity of each imaging modality. From the pooled data, 95% and 99% confidence intervals were also calculated. RESULTS: Sensitivity for predicting regional functional recovery after revascularization was high for all techniques. The specificity of both Tl-201 protocols was significantly lower (p < 0.05) and LDDE significantly higher (p < 0.01) than that of the other techniques. CONCLUSIONS: Pooled analysis of 37 studies showed that although all techniques accurately identify segments with improved contractile function after revascularization, the Tl-201 protocols may overestimate functional recovery. The evidence available thus far indicates that LDDE appears to have the highest predictive accuracy.

Chronic Disease

[Angiotensin-converting enzyme inhibitors following a myocardial infarct: clinical abd echographic indications].

-Angiotensin converting enzyme (ACE) inhibitors can limit mortality and the occurrence of cardiac failure after myocardial infarction because they interfere with the ventricular remodelling process. ACE inhibitors also have anti-arrhythmic and possibly anti-ischaemic potency and therefore a primary cardioprotective effect. It is not advised to treat all patients with a myocardial infarction with an ACE inhibitor, but patients with a large anterior wall infarct, with heart failure or who had a previous infarct should be treated. After three months, the remodelling process can be reevaluated. The ACE inhibitor can be discontinued if the left ventricular function has strongly improved. There is no preference for a particular ACE inhibitor.

Angiotensin-Converting Enzyme Inhibitors

Comparison between 360 degrees and 180 degrees data sampling in thallium-201 rest-redistribution single-photon emission tomography to predict functional recovery after revascularization.

Whether 360 degrees or 180 degrees imaging should be used in cardiac thallium-201 single-photon emission tomography (SPET) studies to detect coronary artery disease remains controversial. Moreover, the relative diagnostic accuracy of 360 degrees and 180 degrees 201Tl SPET for the assessment of myocardial viability has never previously been studied. The aim of this study was to perform a direct comparison between 180 degrees and 360 degrees data sampling to detect viable myocardium in patients undergoing revascularization; in order to allow optimal detection of viability a rest-redistribution protocol was used. The 201Tl results were compared with improvement of regional wall motion abnormalities after the revascularization, which was considered as the "gold standard" for myocardial viability. Thirty-two patients, scheduled for revascularization, underwent rest-redistribution 201Tl SPET, using a 360 degrees arc. Raw data along a 180 degrees arc (45 degrees RAO to LPO) were selected from the original 360 degrees data sets (both early an late 201Tl images). All SPET data were analysed semiquantitatively using circumferential profiles of the short-axis images; the data were displayed in polar maps. Criteria for viability included percentage 201Tl redistribution and percentage 201Tl activity on the late image. Regional wall motion was assessed with two-dimensional echocardiography before and 3 months after revascularization. The sensitivities of 360 degrees and 180 degrees imaging for the prediction of functional recovery were 82% and 89%, respectively, whereas the specificities were 51% and 55%, respectively. The diagnostic accuracy of 360 degrees imaging was 62% and that of 180 degrees imaging 67%. This study shows that 360 degrees and 180 degrees imaging have comparable diagnostic accuracy in the prediction of functional recovery after revascularization. With the newer dual-head gamma camera systems with each detector opposing each other, 360 degrees imaging may be preferred.

Angioplasty, Balloon, Coronary

Optimal metabolic conditions during fluorine-18 fluorodeoxyglucose imaging; a comparative study using different protocols.

Positron emission tomography (PET) with fluorine-18 fluorodeoxyglucose (FDG) can identify viable myocardium in patients with coronary artery disease. Recently, FDG imaging with single-photon emission tomography (SPET) and 511-keV collimators has been described. To obtain optimal image quality in all patients, cardiac FDG studies should be performed during hyperinsulinaemic glucose clamping. It has been suggested that FDG imaging after the administration of a nicotinic acid derivative may yield comparable image quality to clamping. We studied eight patients and compared the image quality of cardiac FDG SPET studies after oral glucose loading, after administration of a nicotinic acid derivative (acipimox, 250 mg orally) and during hyperinsulinaemic glucose clamping. The image quality was expressed as the myocardial to blood pool (M/B) activity ratio, which is used as a measure of the target-to-background ratio The M/B ratios were comparable after clamping and acipimox (2.8+/-0.8 vs 2.9+/-0.7), whereas the M/B ratio was lower after oral glucose loading (2.2+/-0.3, P<0.05 vs clamp and acipimox). To determine the clearance of FDG from the plasma, blood samples were drawn at fixed time intervals and the FDG activity was measured in a gamma well counter. The FDG clearance was significantly lower after oral glucose loading (T(1/2) oral load=16. 2+/-5.7 min) as compared with clamping (T(1/2) clamp=8.1+/-3.1 min) and acipimox (T(1/2) acipimox=10.7+/-4.0 min, NS vs clamp, P<0.05 vs oral load). It may be concluded that FDG SPET imaging after acipimox administration yields image quality and clearance rates comparable to those obtained during clamping. FDG SPET in combination with acipimox may useful in clinical routine for the assessment of myocardial viability.

Aged

Prediction of improvement of contractile function in patients with ischemic ventricular dysfunction after revascularization by fluorine-18 fluorodeoxyglucose single-photon emission computed tomography.

OBJECTIVES: We evaluated the use of fluorine-18 fluorodeoxyglucose (FDG) and single-photon emission computed tomography (SPECT) to predict improvement of left ventricular ejection fraction (LVEF) after revascularization. BACKGROUND: FDG SPECT has recently been proposed for assessment of myocardial viability. However, FDG SPECT still awaits validation in terms of predicting improvement of contractile function after revascularization in patients with poor left ventricular (LV) function. METHODS: Fifty-five patients with contractile dysfunction (including 22 with LVEF < 30%) underwent FDG SPECT during hyperinsulinemic glucose clamping and early thallium-201 SPECT (to assess perfusion). Improvement of LV function was evaluated 3 months after revascularization with echocardiography and radionuclide ventriculography. RESULTS: The 55 patients were arbitrarily classified into two groups: 19 with three or more viable, dysfunctional segments on FDG SPECT and 36 with less than three viable, dysfunctional segments. LVEF increased significantly in the first group, from 28 +/- 8% (mean +/- SD) before to 35 +/- 9% (p < 0.01) after revascularization. In the second group, LVEF remained unchanged after revascularization (45 +/- 14% vs. 44 +/- 14%, p = NS). The 22 patients with severely depressed LV function were similarly classified into two groups: 14 with three or more viable segments on FDG SPECT in whom LVEF improved significantly (25 +/- 6% vs. 32 +/- 6%) and 8 with less than three viable segments in whom LVEF remained unchanged (24 +/- 6% vs. 25 +/- 6%). CONCLUSIONS: This study shows that FDG SPECT can identify patients in whom LV function improves after revascularization. Because SPECT is widely available, this technique may contribute to more routine use of FDG for determination of viability.

Echocardiography

Myocardial perfusion imaging: clinical experience and recent progress in radionuclide scintigraphy and magnetic resonance imaging.

In the past 20 years, radionuclide scintigraphy has proven to be a sensitive clinical tool in the assessment of myocardial perfusion abnormalities. Magnetic resonance imaging may also be used to study myocardial perfusion, but its potential value still has to emerge in the clinical setting. This review addresses the potential and achievements of both methods in clinical cardiology.

Animals

Metabolic imaging using F18-fluorodeoxyglucose to assess myocardial viability.

Over the past 10 years, F18-fluorodeoxyglucose (FDG) imaging with positron emission tomography (PET) has emerged as an important technique in the delineation of myocardial viability. Using this technique it has become possible to predict recovery of ventricular function after revascularization in patients with chronic coronary artery disease. Data from long-term (although retrospective) follow-up studies have demonstrated that patients with viable myocardium on FDG PET who do not undergo revascularization are prone to cardiac events, including cardiac death and non-fatal infarction. The same studies have pointed out that patients with viable tissue on FDG PET, who do undergo revascularization, improve substantially in symptoms related to congestive heart failure. To allow FDG imaging in centers without PET equipment, recent studies have evaluated the use of FDG imaging with single photon emission computed tomography (SPECT) and 511 keV collimators. Preliminary data using this alternative approach are promising, but need further confirmation. In this review the experience with FDG imaging (using either PET or SPECT) in the assessment of tissue viability in patients with coronary artery disease will be discussed.

Coronary Disease

FDG SPECT in the assessment of myocardial viability. Comparison with dobutamine echo.

The use of 18F-fluorodeoxyglucose (FDG) imaging with single photon emission computed tomography (SPECT) has been introduced recently to assess myocardial viability. Several centres have now gained experience with cardiac FDG SPECT imaging, and this report is a summary of the currently available FDG SPECT data. Three studies have compared FDG SPECT with FDG positron emission tomography and demonstrated good agreement between them. Initial results in patients undergoing revascularization suggest that FDG SPECT can predict improvement in contractile function after revascularization. Although the initial results are promising, larger studies are needed to determine the precise role of FDG SPECT in the assessment of myocardial viability.

Cardiotonic Agents

Prediction of improvement of ventricular function after revascularization. 18F-fluorodeoxyglucose single-photon emission computed tomography vs low-dose dobutamine echocardiography.

AIMS: To compare assessment of myocardial flow and glucose metabolism by single-photon emission computed tomography (SPECT) with low-dose dobutamine echocardiography in predicting improvement in regional and global left ventricular function after coronary artery bypass grafting. METHODS AND RESULTS: Thirty patients with regional wall motion abnormalities (mean ejection fraction 32 +/- 19%) were studied with low-dose dobutamine echocardiography (5 and 10 micrograms. kg-1 min-1) and thallium-201/ 18F-fluorodeoxyglucose(FDG) SPECT prior to surgery. For comparative analysis, a 13-segment model was used. Postoperative improvement was predicted if the echocardiogram showed that wall motion abnormalities were reversible during the dobutamine infusion and there was normal perfusion or relatively increased FDG uptake in perfusion defects (mismatch) in dyssynergic segments on SPECT. After surgery, ventricular function was reassessed. An echocardiogram was taken at the 3 month follow-up with the patient at rest. Regional wall motion had improved in 62/168 (37%) revascularized segments. In predicting functional outcome, low-dose dobutamine echocardiography reached a sensitivity of 89% and a specificity of 82%, with a positive predictive value of 74% and a negative predictive value of 93%, whereas for thallium-201/FDG SPECT these values were 84%, 86%, 78% and 90%, respectively. In patients with more than two viable segments on either technique, the wall motion score index, a surrogate of global ventricular function, improved significantly. CONCLUSION: For the optimal prediction of functional outcome, combined assessment of flow and FDG imaging is needed. Both thallium-201/FDG SPECT and low-dose dobutamine echocardiography appear comparable and similarly accurate in predicting improvement of left ventricular function after surgical revascularization.

Analysis of Variance

Cardiac 18F-FDG-SPET studies in patients with non-insulin-dependent diabetes mellitus during hyperinsulinaemic euglycaemic clamping.

Identification of viable myocardium is possible with 18F-fluorodeoxyglucose (FDG) and positron emission tomography (PET). More recently, the feasibility of cardiac FDG imaging with single photon emission tomography (SPET) has been reported. In patients with diabetes mellitus, poor image quality is frequently obtained with FDG-PET, due to relative or absolute insulin deficiency and peripheral insulin resistance. To improve image quality of the FDG-PET studies, the hyperinsulinaemic glucose clamp has been proposed. We assessed the image quality of cardiac FDG-SPET studies in 10 patients with non-insulin-dependent diabetes mellitus (NIDDM) and compared the results with those obtained in 10 patients without NIDDM. All FDG studies were performed during hyperinsulinaemic glucose clamping. Image quality was expressed as myocardial to blood pool activity (M/B) ratios. Residual viability was assessed in dysfunctional myocardium. The M/B ratios were comparable between patients with and without NIDDM (2.67 +/- 0.8 vs 2.50 +/- 0.7, N.S.). Residual viability was detected in 51% of the dysfunctional segments of the patients with NIDDM and in 49% of the segments of the patients without NIDDM. In the small subset of patients (n = 10) undergoing revascularization, 19 of 20 (95%) segments that had improved wall motion were viable on FDG-SPET. In contrast, 27 of 36 (75%) segments that did not improve were necrotic on FDG-SPET. Thus FDG-SPET during hyperinsulinaemic glucose clamping provides adequate image quality in patients with NIDDM compared with patients without NIDDM, and can be used in the detection of viable myocardium.

Aged

Evaluation of heart-to-organ ratios of 123I-BMIPP and the dimethyl-substituted 123I-DMIPP fatty acid analogue in humans.

Radioiodinated fatty acid analogues modified by methyl-substitution are used for single photon emission tomography (SPET) imaging of the heart. The effect of mono- and dimethyl-substitution on heart-to-organ ratios was investigated in humans to evaluate their relative merits for SPET image quality. Planar total body scans were performed in fasting patients with coronary artery disease, but without heart failure, 1 h after administration of 111 MBq 15-(p-[I-123]-iodophenyl)-3-(R,S)-methylpentadecanoic acid (BMIPP, n = 7) or 111 MBq 15-(p-[I-123]-iodophenyl)-3,3-dimethylpentadecanoic acid (DMIPP, n = 4). Because these branched fatty acids are used for cardiac imaging, we focused on heart-to-organ (heart/organ) ratios by comparing small regions of interest in heart, liver, lung, muscle and bladder. Both tracers showed good visualization of the heart. DMIPP showed a relatively high liver uptake: the heart/liver ratios for DMIPP and BMIPP were 0.39 +/- 0.05 and 1.00 +/- 0.12, respectively (P < 0.0001). Increased lung activity was found for BMIPP, with a heart/lung ratio of 1.63 +/- 0.17 versus 2.32 +/- 0.28 for DMIPP (P < 0.001). In contrast to DMIPP, BMIPP also showed increased activity in the bladder. In conclusion, BMIPP and DMIPP show different distribution patterns. Despite the more favourable heart/lung ratios for DMIPP, the high liver uptake affects cardiac SPET image quality and therefore BMIPP appears to provide superior cardiac SPET image quality in humans.

Blood Glucose

High prevalence of hyperhomocysteinemia and asymptomatic vascular disease in siblings of young patients with vascular disease and hyperhomocysteinemia.

Hyperhomocysteinemia (HHC) is associated with an increased risk of atherosclerotic vascular disease and may be inherited. Fasting and postmethionine HHC are independent risk factors that overlap to a limited extent. To study the familial occurrence of HHC, we investigated the prevalence of HHC (both fasting and after methionine) among 450 siblings of 167 consecutive young patients with vascular disease and postmethionine HHC. Furthermore, all subjects with postmethionine HHC (n = 125) were invited for noninvasive vascular testing; 101 (80.8%) agreed. Of those with a normal postmethionine plasma level (n = 325), we randomly selected 73 subjects for further studies; 53 agreed (72.6%). Thus, a total of 154 siblings underwent ultrasonography of the carotid arteries, measurement of ankle-brachial pressure indices at rest and after a treadmill exercise test, and exercise electrocardiographic stress testing. We observed HHC after methionine, fasting, or both, in 27.8% (95% CI, 23.7 to 31.9), 11.1% (CI, 8.2 to 14.0) and 8.7% (CI, 6.1 to 11.3) of the siblings. Abnormal peripheral, coronary, or carotid artery tests were observed in 35.7% (CI, 28.1 to 43.3), 7.1% (CI, 3.0 to 11.2), and 7.1% (CI, 3.0 to 11.2). Univariate and multivariate analyses revealed weak evidence of a relationship with homocysteine levels. In conclusion, we found a high prevalence of HHC and asymptomatic vascular disease in siblings of young patients with vascular (mainly peripheral arterial) disease and HHC. Our data raise the possibility that homocysteine does not play a major role in the early, asymptomatic phases of vascular disease, at least among siblings of young patients with vascular disease.

Adult

Heterogeneity of DMIPP uptake and its relationship with heterogeneous myocardial blood flow.

UNLABELLED: To assess its potential role as a new metabolic probe, the relationship between regional uptake of the 15-(p-[125I]-iodophenyl)-3,3-dimethylpentadecanoic acid (DMIPP) fatty acid analog and myocardial blood flow was studied. METHODS: In 14 open-chest dogs, the left anterior descending coronary artery was cannulated and extracorporal bypass-perfused at normal (control group; n = 4) and reduced flow (intervention group; n = 10). Myocardial blood flow (MBF) was assessed with 46Sc-labeled microspheres. Forty minutes after intravenous injection of DMIPP, the heart was excised and cut into 120 samples. In each sample, MBF ml x g(-1) x min(-1) and DMIPP uptake (percentage of the injected dose per gram, %ID/g) were assessed. RESULTS: In normal myocardium, MBF and DMIPP uptake were 1.10 +/- 0.18 ml x g(-1) x min(-1) and 1.18 +/- 0.42 x 10(-2) %ID/g, respectively. In the extracorporal bypass area, flow was reduced to 0.49 +/- 0.20 ml x g(-1) x min(-1) (p < 0.0001 compared to normal), and DMIPP uptake was decreased to 0.75 +/- 0.26 x 10(-2) %ID/g (p < 0.0001 compared to normal). DMIPP uptake and MBF positively correlated in normal (DMIPP uptake = 0.77 +/- 0.23 x MBF; r = 0.41; p < 0.0001) and hypoperfused (DMIPP uptake = 0.35 +/- 0.70 x MBF; r = 0.63; p < 0.0001) myocardium. The heterogeneity, indicated by the coefficient of variation, in normal myocardium was 0.23 +/- 0.05 for MBF and was lower (p < 0.0001) for DMIPP uptake: 0.13 +/- 0.05. During flow reduction, heterogeneity increased significantly (p < 0.0001) for both MBF (0.59 +/- 0.22) and DMIPP uptake (0.37 +/- 0.23). Also heterogeneity of the DMIPP uptake to MBF ratio, as an indicator of agreement, increased from 0.23 +/- 0.07 in normal to 0.46 +/- 0.19 in hypoperfused myocardium (p < 0.0001). CONCLUSION: DMIPP detects regionally hypoperfused myocardium, in which agreement between MBF and fatty acid uptake deteriorates. DMIPP uptake shows a different relationship with MBF in hypoperfused compared to normal myocardium. These observations suggest that DMIPP uptake may provide additional, unique information on regional myocardial ischemia.

Animals

Detection of myocardial viability with F-18-fluorodeoxyglucose and single photon emission computed tomography.

The application of 18-F-fluorodeoxyglucose (FDG) imaging with single photon emission computed tomography (SPECT) to detect tissue viability has been introduced recently in several centers, both in Europe and the USA. This paper summarizes the available data on FDG SPECT. Three studies have performed a direct comparison between FDG SPECT and FDG PET, showing good agreement between these techniques. Preliminary data in patients with poor left ventricular function undergoing revascularization suggest that FDG SPECT can predict improvement of ventricular function after revascularization. Comparative studies between FDG SPECT and low-dose dobutamine echocardiography also showed close agreement. Although the initial results are promising, larger studies are needed to determine the precise role of FDG SPECT in the assessment of myocardial viability.

Cardiotonic Agents

Course of impaired left ventricular function after acute myocardial infarction predicted with planar thallium-201 chloride and F18-fluorodeoxyglucose imaging.

UNLABELLED: Planar reset myocardial thallium-201 chloride (201Tl)/F18-fluorodeoxyglucose (FDG) imaging has been shown to distinguish between viable and non-viable tissue. Twenty-five patients (60 +/- 9 years) with acute myocardial infarction were studied using this technique within 6 +/- 2 days (T1) after infarction and again after 42 +/- 4 days (T6). Serial assessment of wall motion with 2D-echocardiography was performed to determine the predictive value of radionuclide indices for the course of impaired regional left ventricular function. No revascularization procedure was performed. Segmental 201Tl and FDG uptake was evaluated using circumferential profiles. Echocardiographic wall motion was scored as normal, hypokinetic or akinetic. Myocardial segments were considered non-viable if a match between 201Tl and FDG uptake was present, which is a concordant reduction in 201 Tl and FDG uptake (Group A). Myocardial segments were considered viable if: a mismatch was present between 201Tl and FDG uptake which was defined as a segmental FDG uptake exceeding 201Tl uptake by > or = 20% in a segment with reduced 201Tl uptake (Group B); a normal FDG uptake (> or = 75%) was present without a mismatch pattern in a segment with reduced 201Tl uptake (201Tl < 75% of peak activity) (Group C); a normal 201Tl uptake was present in the area of wall motion abnormality (Group D). Corresponding scintigraphic images obtained at T1 and T6 were compared. RESULTS: 51 segments were normokinetic, 37 were hypokinetic and 6 were akinetic at T1. Of the 63 segments with wall motion abnormalities at T1, 18 regions showed a match (FDG-201Tl < 20%) (Group A). Regional function improved in only one (6%) of these segments. In 19 regions a mismatch was present (FDG-201Tl > 20%) (Group B) of which three (16%) showed spontaneous improvement in function (p = NS vs. matched segments), although recovery varied considerably among patients. Regional function in two segments deteriorated. In 14 regions with reduced 201Tl uptake, FDG uptake was normal (Group C) of which five (36%) were improved after 6 weeks (p < 0.05 vs. match; p = NS vs. mismatched segments). Of the 12 segments with normal 201Tl uptake (Group D), seven (58%) showed improvement in function, whereas five (42%) did not show improvement (p < 0.05 vs. match). In addition, all scintigraphically selected viable segments were grouped (Group B + C + D) and compared with the non-viable segments (Group A). The predictive value of a positive viability test for spontaneous functional improvement was 33%. The predictive value of a negative viability test for lack of functional improvement was 94%. CONCLUSIONS: absence of residual FDG uptake shortly after infarction is associated with irreversible injury, while preservation of metabolic activity identifies segments with variable outcome. Wall motion alone is not a good indicator for the presence of viable tissue. Planar 201Tl/FDG imaging allows early identification of viable but jeopardized tissue and may help select patients who will benefit from aggressive therapy to salvage endangered myocardium.

Deoxyglucose

Transesophageal cardiac pacing during magnetic resonance imaging: feasibility and safety considerations.

The feasibility and safety of transesophageal cardiac pacing during clinical MRI at 1.5 Tesla is considered. An MRI compatible pace catheter was developed. In vitro testing showed a normal performance of the pulse generator, image artifacts that extended less than 11 mm from the catheter, and a less than 5% increase in noise. Cardiac stimulation induced by MRI was not observed and, theoretically, is not expected. Potentially, tissue around the catheter tip may become heated. This heating (delta tau) was monitored. Eight dogs were exposed to MRI during pacing. For low RF radiation exposure, a time-averaged squared B1 field below 0.08 p tau 2 (SAR < 0.03 W/kg), delta tau was below 1 degree C. For high RF radiation exposure, but at normal RF radiation specific absorption rate (0.4 W/kg) delta tau was 5 degrees C. Thus, transesophageal atrial pacing during MRI at low RF exposure seems to be possible to perform cardiac stress studies or to correct unstable heart rates.

Animals