G. A. K. Heidendal

Biventricular performance during volume loading in patients with early septic shock, with emphasis on the right ventricle: A combined hemodynamic and radionuclide study

The cardiac response to a rapid volume infusion was studied in 18 patients with septic shock accompanied by pulmonary hypertension. Right and left ventricular ejection fractions were measured, and right and left ventricular volume indices were calculated from ejection fractions and stroke volumes before and 30 minutes after the start of the infusion. Responders (13 patients) showed an increase in stroke volume index (SVI) as a result of a mean 30% increase in right ventricular end-diastolic volume index (RVEDVI) and a mean 17% increase in left ventricular end-diastolic volume index (LVEDVI) during volume loading. In the nonresponders (five patients) fluid loading resulted in a decreased or unchanged SVI; this was accompanied by a 7% increase in RVEDVI but no change in LVEDVI, although both the central venous pressure and pulmonary capillary wedge pressure increased. At baseline, nonresponders differed from responders as evidenced by a high central venous pressure and RVEDVI but a lower mean arterial pressure: thus, right ventricular coronary perfusion pressure was lower and right ventricular wall stress may have been higher. Mean pulmonary artery pressure did not differ between the groups. Our data suggest that in some patients with septic shock volume loading does not result in increased forward flow because of right ventricular failure associated with pulmonary hypertension and coronary hypotension.

Dynamic myocardial scintigraphy with 123I-labeled free fatty acids in patients with myocardial infarction

We have already shown that myocardial imaging properties of radio-iodinated long-chain free fatty acids (123I-FFA) and thallium 201 (201Tl) are comparable in detecting areas of inadequate myocardial perfusion (van der Wall et al. 1980). Besides confirming our earlier observations, the present study tests the potential of 123I-FFA, hexadecenoic acid (123I-16-HA), and heptadecanoic acid (123I-17-HoA), in assessing regional myocardial metabolism in 30 patients within a week of proven myocardial infarction. The clearance rates (t1/2) of FFA were estimated from mono-exponential time-activity curves, obtained by external detection over infarcted and normally perfused areas during a 30-min period after IV administration of 3–5 mCi 123I-16-HA or 123I-17-HoA. Six normal subjects served as controls. The t1/2 values in the infarcted areas were found to be significantly lower (18.5±2.5 min; mean±SD, with 123I-16-HA and 16.8±3.5 min with 123I-17-HoA) than in noninfarcted areas (34.0±8.4 min with 123I-16-HA and 34.8±7.7 with 123I-17-HoA). The t1/2 values in the control group (27.5±3.0 min with 123I-17-HoA) were not significantly different from values found in noninfarcted areas in the patient group. Our findings of faster FFA turn-over rates in infarcted tissue are in contrast to previous studies, which have shown prolonged turn-over rates in reversibly ischaemic myocardium. We coclude that the study of turn-over rates of FFA provides a means to distinguish normally perfused, reversibly ischaemic and irreversibly ischaemic myocardium.

Metabolic myocardial imaging with 123I-labeled heptadecanoic acid in patients with angina pectoris

The potential value of 123I-heptadecanoic acid (123I-HoA) in myocardial scintigraphy has recently been assessed in patients with acute myocardial infarction (AMI) by studying regional myocardial metabolism (Van der Wall et al. 1981 a). To determine the metabolic behavior of 123I-HoA in patients with stable angina pectoris (AP) as well, 30 patients with AP were included in this study: 18 patients were exercised and 12 patients were studied at rest.Regional myocardial metabolism was evaluated by generating background subtracted time-activity curves, acquired by external detection over normally perfused and ischemic regions during a 30-min period after intravenous injection of 123I-HoA. Following monoexponential curve-fitting, clearance rates were measured representing turnover rate (T1/2) of 123I-HoA.The exercise group showed prolonged T1/2 values of 46.7±7.1 min (mean±SD) in ischemic regions and 28.7±3.6 min in normally perfused regions. The group at rest did not reveal any scintigraphic abnormalities and showed normal T1/2 values in all myocardial regions (29.1±4.7 min).Our observations of prolonged turnover rates in ischemic areas differ from the results of our recent study in patients with AMI, which demonstrated fast turnover rates in infarcted tissue. These data imply that 123I-HoA permits the study of myocardial metabolism in patients with AP and the discrimination of normally perfused, reversibly ischemic (AP) and irreversibly ischemic (AMI) myocardium.

I-123 labeled hexadecenoic acid in comparison with Thallium-201 for myocardial imaging in coronary heart disease

The imaging properties of 123I-16-iodo-9-hexadecenoic acid (123I-HA), a terminally iodinated 17-carbon atom fatty acid analogue, were compared with Thallium-201 (201Tl). Because of its shorter half-life, favourable photon-energy and rapid myocardial turnover rate, 123I-HA possesses potential advantages in the study of regional myocardial perfusion and metabolism. Twelve patients with documented coronary artery disease (CAD) were studied; eight patients sustained an acute myocardial infarction, four patients suffered from unstable angina. Visually assessed, a similar distribution pattern and comparable imaging quality was demonstrated with both radionuclides. The scintigraphic results were also correlated with coronary arteriographic findings. A good relationship was found between the perfusion defects and the location of the coronary artery lesions in the patients with acute myocardial infarction.We conclude that 123I-HA is comparable to 201Tl in detecting areas of reduced myocardial perfusion in patients with CAD with the advantage of studying myocardial metabolism.

Metabolic fate of radioiodinated heptadecanoic acid in the normal canine heart.

To clarify the metabolic fate of radioiodinated heptadecanoic acid in myocardium, the time course and distribution of the radioactivity over 131I-heptadecanoic acid, free radioiodide, and various lipids (with incorporated iodoheptadecanoic acid) were determined in normal canine myocardium. In 10 dogs seven biopsy specimens were taken over 30 min after injection of 131I-heptadecanoic acid. The radioactivity in the specimens increased until the fifth minute and decreased thereafter, with a half-time of 36 min. In the fifth minute, 61% of the radioactivity was free iodide, and its curve paralleled the curve of the total radioactivity. As early as the first minute 131I-heptadecanoic acid activity was reduced to 14% and decreased further. Activity of radioiodinated phospholipids, (mono, di, tri)-glycerides, and cholesterol-esters remained constant after an initial increase. These results indicate that immediately after uptake, 131I-heptadecanoic acid is either metabolized, liberating the radioiodide, or stored in lipids. Because the activity of radiolabeled lipids remained constant during the study period and because iodide activity paralleled the total activity in biopsy specimens, it is concluded that in normal myocardium, washout of free radioiodide determines the elimination rate as observed during a scintigraphic study. Thus the elimination rate cannot be related to the beta-oxidation rate as previously supposed.

Noninvasive assessment of regional albumin extravasation in porcine septic shock

In order to study noninvasively the regional distribution of changes in microvascular albumin flux in septic shock, 131I human serum albumin and 98mTc red blood cells were injected IV into anesthetized pigs randomized to receive saline (n = 4) or live E. coli bacteria 3 × 108 × kg−1 IV (n = 8). Images of thorax, abdomen, and left hindlimb were obtained using a gamma camera and a computer. Septic pigs developed pulmonary hypertension and low cardiac output circulatory shock. Hematocrit rose and plasma colloid osmotic pressure fell. Regions of interest were drawn in the 99mTc images. For each region we calculated an albumin leak index. The albumin leak index over the lungs was higher in sepsis than in controls (1.62 ± 0.42 × 10−3 v 0.45 ± 0.05 × 10-3 × min−1, P < .005), even when divided by the pulmonary intravascular filtration pressure, incorporating hydrostatic and colloid osmotic pressures (P < .01). The index was also higher in abdominal regions (for the peripheral abdomen, 6.07 ± 2.98 × 10−3 v 0.40 ± 0.72 × 10−3 × min−1, P < .005), but not in the hindlimb. In sepsis, the albumin leak index increased more in the abdomen than in the lungs (P < .05). We conclude that in porcine septic shock pulmonary microvascular permeability is increased, but the microvascular albumin flux and thus plasma extravasation increased more in the abdomen than in the lungs.

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.

Reproducibility of ejection fraction measurements by gated equilibrium blood pool scintigraphy

The reproducibility of ejection fraction measurements has been studied using gated equilibrium blood pool scintigraphy. The use of appropriate statistical tests is proposed and commented upon. The intra-observer variability for our group of patients has a standard deviation of 6.4%, the interobserver variability of 3.2% and sequential studies done on the same and different days give standard deviations (due to “time” alone) of 1.0% and 1.9%, respectively. Different factors and sources involved in variability are mentioned. Variability values reported in the literature are discussed.

A comparison between terminally radioiodinated hexadecenoic acid (125I-HA) and heptadecanoic acid (131I-H0A) in the dog heart

The regional myocardial distribution of 125I-16-iodo-9-hexadecenoic acid (125I-HA) and 131I-17-iodo-heptadecanoic acid (131I-H0A) was determined in one normal dog and in five dogs within 5 min after coronary artery occlusion. The total myocardial uptake of 125I-H A was about 40% lower than that of 131I-H0A. The ratio 125I:131I in the normally perfused parts of the myocardium was 0.38–0.81, but the ischemic tissue showed a higher 125I:131I-131I ratio (0.87–1.03), due to lower accumulation of 131I-H0A in ischemic myocardium. We conclude that both radioiodinated fatty acids are reliable indicators of myocardial perfusion and that iodo-heptadecanoic acid, when labeled with 123I, may be preferred to iodo-hexadecenoic acid as the labeled fatty acid for cardiac imaging agent in clinical practice.

The cold pressor test during radionuclide ventriculography: A feasibility study in cancer patients

To monitor the use of cardiotoxic drugs, adequate assessment of myocardial function is required. Although serial radionuclide left ventricular ejection fraction (EF) studies allow a simple and rapid assessment of the myocardial function without risk or discomfort to the patient, they appear not to be sensitive enough. Determination of the EF during cold application may be more sensitive. In this study we tested the feasibility of the cold pressor test (CPT) in relation to EF determination in 23 cancer patients. Only minor side effects were recorded. The response of heart rate to cold was similar to the response reported in healthy volunteers and patients with coronary artery disease. In selected cases EF determination during CPT appeared to be more sensitive than EF at rest. EFCPT may be an attractive alternative for EFexercise in cancer patients who cannot perform enough exercise to stress cardiac function adequately, but for a more definite conclusion a prospective comparative study is required.