F. C. Visser

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 (T1/2 oral load=16.2±5.7 min) as compared with clamping (T1/2 clamp=8.1±3.1 min) and acipimox (T1/2 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.

Comparison of the haemodynamics of different pacing sites in patients undergoing resynchronisation treatment: need for individualisation of lead localisation

Background: Biventricular pacing is a new therapy for the treatment of heart failure. However, a substantial number of patients do not respond to this therapy. Hypothesis: Individually determined maximal pacing sites will improve the haemodynamic response and increase the number of responders. Methods: In 48 patients with heart failure, the acute haemodynamic effects of nine different pacing configurations were studied, using two right and left ventricular pacing sites and their combinations. Cardiac index was measured using Doppler echocardiography. For further analysis, the combination with the highest cardiac index improvement was compared with baseline. Moreover, the number of responders was calculated using a cut-off value of 10% increase in cardiac index. Results: The mean (SD) increase in cardiac index ranged between 3.8% (6.0%) and 11.1% (8.6%). The pacing site with maximal cardiac index was highly variable between patients, and here the cardiac index increased to 14.8% (7.6%; (p<0.001). The number of responders varied between 15% and 64%, increasing to 75% at the site with maximal increase in cardiac index. In a subset of patients, the haemodynamic improvement after pacemaker implantation correlated well with the acute haemodynamics. Conclusion: Individualisation of pacing configuration for biventricular pacing leads to further haemodynamic improvement in patients with heart failure and reduces the number of patients not responding to this therapy.

Magnetic resonance imaging of the heart for determination of ejection fraction

In 28 patients with various cardiac diseases we compared ejection fractions obtained by magnetic resonance imaging in a single oblique slice with monoplane ventriculography in the right anterior oblique projection, the latter serving as the standard. Also, results were evaluated for clinical relevance and relation to image quality. The correlation between the two techniques was moderate (r = 0.65). According to our standardized limits for clinical relevance, insufficiently correlating ejection fractions were obtained in 14 patients. In 8 of these patients this was attributed to poor endocardial edge detection. Edge detection problems were more frequently encountered by imaging with echo-time 20 msec than with echo-time 32 msec. Other causes for mismatching of the obtained ejection fractions are discussed. It is concluded that determination of ejection fraction by single slice magnetic resonance imaging should not be used for clinical application. Improvement can be expected by using a contiguous slicing technique, a longer echo-time in the spin-echo pulse sequence, or in due course by application of newly developed fast-imaging pulse sequences.

Oblique Views in Magnetic Resonance Imaging of the Heart by Combined Axial Rotations

Magnetic resonance imaging of the heart, and more specifically of the left ventricle (LV), is optimized by using oblique imaging planes adapted to the long and short axes of the LV, comparable to other imaging modalities in cardiology. We report a procedure to perform two chamber views, four chamber views and true short axis views by combinations of electronic axial rotations. The technique of selecting appropriate gradient angles is explained. Thus, there is no requirement for altering patient position in the imager, while individual anatomic variations are taken into account.

Radioiodinated free fatty acids; can we measure myocardial metabolism?

To investigate the feasibility of radioiodinated free fatty acids for ‘metabolic imaging’, the kinetics and distribution pattern of metabolites of 131I-heptadecanoic acid were studied in canine myocardium throughout metabolic interventions. In control dogs and in dogs during glucose/insulin and sodium lactate infusion, biopsy specimens were taken during a 90-min period after 131I-HDA administration and analyzed. Clearly distinct patterns of distribution and elimination were seen during the metabolic interventions, indicating the usefulness of iodinated fatty acids for metabolic studies.

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.

Variables of myocardial backdiffusion, determined with 17-IODO-131 heptadecanoic acid in the normal dog heart

Under normal and ischemic conditions backdiffusion of radiolabeled non-esterified fatty acids (NEFA) has been demonstrated. In the fasted normal canine heart the extraction fraction (EF) during interventions with glucose or lactate loading, vasodilation, and metabolic level augmentation was determined, and compared with the control EF. Backdiffusion alterations were deduced from the EF changes. After iv injection of 17-iodo-131 heptadecanoic acid (IHDA), 11 blood samples were drawn from aorta and coronary sinus in a time period of 60 minutes. In the control and vasodilation group the EF slowly decreased from 40 to 10%. In contrast, the EF in the noradrenaline group was constant. During glucose and lactate infusion the EF became negative within 10 min and remained negative. These results suggest that during physiological circumstances backdiffusion is determined by the metabolic level of the heart and its substrate availability.

Prediction of spontaneous coronary reperfusion in myocardial infarction.

To investigate the possibility of predicting the occurrence of spontaneous coronary reperfusion in acute myocardial infarction we studied 91 patients in a randomized trial on the clinical efficacy of intracoronary streptokinase compared to conventional treatment. Of the 46 patients treated conventionally 40 had catheterization 6 weeks after the infarction. Spontaneous coronary reperfusion was found in 19 patients (48%). The time to peak CK-MB in these patients was considerably longer than in patients with streptokinase-induced coronary reperfusion and similar to the time in patients without spontaneous coronary reperfusion. Spontaneous coronary reperfusion was associated with a relative improvement of radionuclide ejection fraction from day 1 to day 14 after admission. There was no difference in the occurrence of ventricular arrhythmia or recurrent ischaemic events between the patients with and those without spontaneous coronary reperfusion. Thus, spontaneous coronary reperfusion is not uncommon in traditionally treated myocardial infarction, but its occurrence cannot be predicted by enzymatic or clinical parameters.

The elimination rate of 123I-heptadecanoic acid after intracoronary and intravenous administration

When calculating the elimination rate of radioactivity after the administration of radioiodinated heptadecanoic acid (123I-HDA), background correction is necessary due to the high level of background activity. In the present study, the subtraction method of Freundlieb et al. was investigated on validity. This was done by comparing the half-time values of the elimination rate after intravenous (i.v.) and intracoronary (i.c.) injection. In the latter case, no background correction was necessary. Six patients underoging cardiac catheterization were studied. Scintigraphy was performed after the injection of 123I-HDA into the left coronary artery and after i.v. injection. Half-time values were calculated from regions of interest drawn over myocardium perfused by the left-anterior descending branch (LAD) and the left circumflex artery (LCX). In the LAD region, the mean half-time value in the i.c. study was 22 min, while in the corrected i.v. study, the mean value was 27 min. In the LCX region, the half-time values were 24 and 33 min, respectively. The background-subtraction procedure proposed by Freundlieb et al. for i.v.-injected 123I-HDA ss incomplete, as it resulted in half-time values that were higher than those of the i.c. study.

The Effect of Rate Responsive Pacing in Patients with Angina Pectoris on the Extent of Ischemia on 201-Thallium Exercise Scintigraphy

VAN CAMPEN, L.C.M.C., et al.: The Effect of Rate Responsive Pacing in Patients with Angina Pectoris on the Extent of Ischemia on 201‐Thallium Exercise Scintigraphy. In patients with coronary artery disease (CAD), rate responsive pacing is considered to be contraindicated because an increase in heart rate may increase oxygen demand. Although previous studies have shown no subjective increase in ischemia during rate responsive pacing, data from objective assessment have not been documented. The goal of this study was to determine if there was an increase in ischemia on 201‐Thallium (201TI) exercise scintigraphy in this mode of pacing in patients with CAD and angina. Eighteen consecutive patients with chronic atrial fibrillation and symptomatic bradyarrhythmias with a pacemaker for more than 6 months participated in the study. In VVI and VVIR modes a symptom‐limited exercise 201TI scintigram was performed in a single blind randomized crossover fashion. Exercise duration, anginal attacks, use of nitroglycerine (NTG) tablets, blood pressure, and analysis of the scintigrams were assessed during each pacing mode. Fifteen men and three women were included (age 65.9 ± 4.9 years, LVEF 0.44 ± 0.07). Four were in Class III angina pectoris, and 14 in class II. The mean exercise duration increased 28% in the VVIR group without an increase in anginal attacks per week or the use of NTG tablets. On scintigrams, no differences were seen between the two groups. One patient was withdrawn from the study because of an increase in angina pectoris (AP) attacks during VVIR pacing. Rate responsive pacing is safe and effective in patients with CAD without an increase in subjective and objective signs of ischemia.