Myocardial metabolic changes in hypertrophic cardiomyopathy

We evaluated myocardial blood flow, glucose and oxygen metabolism using PET in hypertrophic cardiomyopathy (HCM).

METHODS

PET studies using 18F-fluorodeoxyglucose (FDG) and 11C-acetate were performed at rest in patients with HCM and normal subjects as a control group. The metabolic rate of glucose (MRGlu), K mono value as a marker of oxidative metabolism, and myocardial blood flow were estimated from serial dynamic FDG and 11C-acetate PET studies.

RESULTS

Myocardial blood flow (%) did not differ significantly in hypertrophic and nonhypertrophic myocardium (90.3 +/- 3.1 versus 91.7 +/- 3.4). The MRGlu in hypertrophic myocardium, however, was lower than that of hypertrophic and normal myocardium (0.44 +/- 0.10 versus 0.52 +/- 0.15 and 0.53 +/- 0.15 mumole/min/g, respectively, p < 0.05). The K mono values were also lower in hypertrophic myocardium than in nonhypertrophic and normal myocardium (0.05 +/- 0.010 versus 0.066 +/- 0.0011 and 0.065 +/- 0.017 per min, respectively, p < 0.05). The %FDG/%perfusion values in hypertrophic myocardium did not differ significantly from those in nonhypertrophic myocardium (0.96 +/- 0.10 versus 1.02 +/- 0.07).

CONCLUSION

Myocardial ischemia at rest is observed less frequently in patients with HCM. Impairment of oxidative and glucose metabolism may precede decreased blood flow. Primary metabolic impairment is considered to be dominant in hypertrophic myocardium.

Patency of infarct-related artery. Effect of restoration of anterograde flow on vagal reflexes. ATRAMI (Automatic Tone and Reflexes After Myocardial Infarction) Investigators

BACKGROUND

In post-myocardial infarction (MI) patients, the restoration of anterograde flow in the infarct-related artery (IRA) significantly improves survival. Limitation of infarct size and increased electrical stability of the myocardium are likely operating mechanisms for this beneficial effect. We tested the hypothesis that patency of the IRA may enhance vagal reflexes, a factor known to affect electrical stability of the infarcted myocardium.

METHODS AND RESULTS

Analysis of angiographic data was performed in 359 of 1284 post-MI patients enrolled in a multicenter prospective study within 8 weeks after the index MI. All the patients underwent baroreflex sensitivity (BRS) assessment by the phenylephrine method. The BRS of the entire population averaged 8.2+/-5.5 ms/mm Hg and was significantly related to age but not to ejection fraction (EF). One-, two-, and three-vessel disease was present in 138, 96, and 99 patients, respectively, while no coronary stenosis was observed in 26. IRA patency was documented in 234 patients (65%), while in the remaining 125 (35%), the artery remained occluded. Patients with occluded IRAs had more extensive coronary disease (2 to 3 vessels, 71% versus 46%, P<.01) and more depressed left ventricular (LV) function (LVEF, 48+/-13% versus 53+/-12%, P<.001). Patency of the IRA was associated with higher BRS values (BRS, 8.9+/-5.8 versus 7.1+/-4.7 ms/mm Hg, P<.005) and with a lower incidence (9% versus 18% P<.02) of markedly depressed BRS (<3 ms/mm Hg), a condition suggested by preliminary studies to be associated with an increased risk of post-MI mortality. The association between IRA patency and BRS was more evident in anterior than in inferior MI. Multivariate regression analysis showed that age of the patient and patency of the IRA were the major independent determinants of BRS, while LVEF was weakly related to BRS and only when analyzed as a categorized variable.

CONCLUSIONS

The presence of an open IRA is associated with higher baroreflex sensitivity, and this effect is largely independent of limitation of infarct size by IRA patency. These data offer new insights into the mechanisms by which coronary artery patency may affect cardiac electrical stability and survival.

Prognostic value of iodine-123 labelled BMIPP fatty acid analogue imaging in patients with myocardial infarction

This study was undertaken to evaluate the prognostic value of iodine-123 labelled 15-iodophenyl-3-R,S-methyl pentadecanoic acid (BMIPP) imaging in patients with myocardial infarction. BMIPP is an iodinated methyl branched fatty acid analogue which is trapped in the myocardium with little washout, thereby reflecting fatty acid utilization in the myocardium. We previously reported that in patients with myocardial infarction, regions are often observed where reduced BMIPP uptake is seen relative to thallium-201 perfusion at rest. However, the clinical significance of such discordant BMIPP uptake remains unknown. Fifty consecutive patients with chronic myocardial infarction referred for stress thallium scan and coronary arteriography underwent BMIPP imaging at rest. Each patient was in a stable condition at the time of the radionuclide study. Follow-up was performed at a mean interval of 23 months to investigate the prognostic implications of the radionuclide studies. Nine patients had cardiac events during the follow-up period. Univariate analysis showed that the number of discordant BMIPP versus 201TL uptake segments was the best predictor of future cardiac events (P=0.0245), followed by the presence of discordant BMIPP uptake (P=0.0388) and the number of 201TL redistribution segments (P=0.0444). When all the clinical and radionuclide variables were analysed by Cox regression analysis, the presence of discordant BMIPP uptake was the best, and an independent, predictor of future cardiac events (chi 2=8.5) followed by the number of coronary stenoses on angiography (chi 2=3.9). These preliminary data suggest that decreased BMIPP uptake relative to 201TL is a valuable predictor of future cardiac events in patients with myocardial infarction. Areas with such discordant BMIPP uptake may contain jeopardized myocardium where fatty acid utilization has been severely suppressed relative to myocardial perfusion.

Improvement of myocardial ischemic dysfunction with dichloroacetic acid: experimental study by repeated ischemia in dogs

We investigated metabolic factors related to the recovery of myocardial function during ischemia and after reperfusion using dichloroacetic acid (DCA) in canine models with repeated 10-min regional ischemia and reperfusion. Administration of 100 mg/kg DCA, which activates pyruvate dehydrogenase, improved regional wall motion significantly as compared with the nontreated controls (p < 0.05). The mechanism was studied by determining changes in myocardial levels of pH, glucose, lactate, and nonesterified fatty acids (NEFA). Glucose extraction was increased significantly during ischemia and reperfusion by the pretreatment of DCA (p < 0.01). the calculated contribution of glucose to myocardial oxidative metabolism during ischemia and reperfusion was greater than that of NEFA and lactate in case of DCA treatment. The uptake of [99mTc]pyrophosphate (PYP), which reflects myocardial injury, was also significantly suppressed by DCA (p < 0.01). pH was not affected by an infusion of DCA. These findings suggest that the activation of glucose metabolism by DCA, which is impaired and reduced during ischemia and reperfusion, may be responsible for the improved myocardial function after reperfusion.

Decreased uptake of iodinated branched fatty acid analog indicates metabolic alterations in ischemic myocardium

We previously reported that uptake of 123I-labeled 15-iodophenyl 3-methyl pentadecanoic acid (BMIPP) was lower than that of thallium in ischemic myocardium. Such discordant findings between BMIPP and thallium were compared with those of PET using 18F-deoxyglucose (FDG) and 11C-acetate to assess metabolic alterations in such segment.

METHODS

Sixteen patients with coronary artery disease underwent both BMIPP SPECT and PET. Relative FDG uptake (% FDG uptake) and the clearance rate constant (% Kmono) of 11C-acetate from the myocardium were calculated as markers of glucose and oxidative metabolism, respectively.

RESULTS

Relative FDG uptake of the myocardial segments with reduced BMIPP uptake and normal thallium uptake (discordant segments) was similar (85.3 +/- 10.3) to that of the normal segments (86.5 +/- 11.7) but higher than that of segments with reduced uptake of both BMIPP and thallium (67.5 +/- 19.9). Similarly, the discordant segments showed a higher % Kmono value (77.8 +/- 13.1 versus 70.0 +/- 19.1) and FDG-to-perfusion ratio (1.15 +/- 0.08 versus 1.01 +/- 0.22) than in the concordantly reduced segments.

CONCLUSION

BMIPP uptake appears to provide metabolic information independent of thallium uptake. Combined imaging of BMIPP and thallium may potentially identify ischemic but viable myocardium.

Assessment of coronary vasodilator reserve by N-13 ammonia PET using the microsphere method and Patlak plot analysis

Noninvasive quantification of regional myocardial blood flow (MBF) has been successfully achieved with N-13 ammonia. The microsphere method as a simple method for quantifying regional myocardial blood flow was reevaluated in comparison with Patlak graphical analysis. In addition coronary vasodilator reserve (CVR) was estimated by both methods.

METHODS

Dynamic N-13 ammonia PET studies were performed in 10 healthy volunteers and 10 patients with coronary artery disease at baseline and after dipyridamole infusion (0.56 mg/kg). MBF was estimated by the microsphere method at various times and by Patlak graphical analysis. In order to reduce the noise level in the microsphere method, MBF estimates were also performed after data in 10-40 seconds were averaged.

RESULTS

In the studies on normal subjects MBF (ml/min/g) determined by the microsphere method significantly differs from time to time. However, MBF determined by the modified microsphere method [with average (Extraction fraction) x MBF values obtained between 100 and 120 sec] linearly correlated well with MBF by Patlak graphical analysis (r = 0.97, slope = 0.98, intercept = 0.20). In the studies on patients with coronary artery disease a good agreement of the MBF estimates was also observed (r = 0.97, slope = 0.98, intercept = 0.22). In the studies on the normal subjects and patients with coronary artery disease, CVR obtained by the modified microsphere method after correcting the overestimated MBF values also correlated well with that by Patlak graphical analysis (r = 0.90, slope = 1.14, intercept = -0.15, and r = 0.92, slope = 0.82, intercept = 0.25, respectively).

CONCLUSION

The modified microsphere method is a very simple and reliable approach for quantifying MBF with N-13 ammonia PET which is comparable to Patlak graphical analysis. It also makes possible CVR assessment as accurate as Patlak graphical analysis.

[Myocardial uptake ratio of iodine-123 labeled beta-methyl iodophenylpentadecanoic acid (123I-BMIPP) in relation to the concentration of the substrates of energy]

Iodine-123 beta-methyl iodophenylpentadecanoic acid (BMIPP) has been used for evaluating myocardial fatty acid metabolism in vivo. The whole body BMIPP imaging was acquired in 26 patients (11 with HCM, 11 with CAD and 4 with DCM) to calculate % uptake in the myocardium and to correlate its uptake with biochemical data, including blood sugar (BS), nonesterified fatty acid (NEFA) and insulin in the blood. BMIPP was administered at rest with overnight fasting state, and the anterior and posterior whole body imaging was performed one hour later. The background corrected whole myocardial counts were calculated to obtain %BMIPP uptake. In addition, the heart to mediastinum count ratio (H/M ratio) was calculated from the mean counts in the heart and the upper mediastinum in the anterior view. The %BMIPP uptake was 3.70 +/- 1.22% and H/M ratio was 2.30 +/- 0.23. The patients with DCM showed higher %BMIPP uptake values (DCM = 5.58 +/- 0.67% vs. CAD = 3.09 +/- 0.97% and HCM = 3.63 +/- 0.86%, both p < 0.01), but similar values of H/M ratio with other patients (DCM = 2.43 +/- 0.20, CAD = 2.22 +/- 0.25 and HCM = 2.32 +/- 0.20). Although the biochemical data varied at the time of the tracer administration, they were not significantly correlated with the %BMIPP uptake or H/M ratio. However, there was a significant correlation between %BMIPP uptake and H/M ratio with the correlation coefficient of 0.80 (p < 0.001). We conclude that the myocardial uptake of BMIPP is not influenced by the plasma substrate level under the fasting state.

Effects of nisoldipine in silent myocardial ischemia after healing of acute myocardial infarction

Silent myocardial ischemia occurring after acute myocardial infarction is classified as Cohn type II and has a frequency of 20-30% in all patients with acute myocardial infarction. Follow-up data of patients with either silent or anginal ischemia show a poor prognosis. Thus, all ischemic episodes occurring after myocardial infarction should be treated aggressively. Many multicenter studies have evaluated whether drug treatment can improve prognosis or protect from a nonfatal second attack. Calcium antagonists, especially those that increase heart rate, have not been considered as drugs of choice for this purpose, despite the many beneficial effects shown on myocardial tissue in experimental studies. In the study reported here, the effect of nisoldipine on postinfarction silent myocardial ischemia was evaluated by ambulatory left ventricular function monitoring. Ten patients were selected for study who showed silent myocardial ischemia after their first acute infarction. Blood pressure fell significantly (p < 0.05) after 4 weeks of treatment with nisoldipine (5-10 mg/day), but heart rate showed no change at rest. Exercise time improved (p < 0.05), with increased peak double products. During exercise, there was no significant change in end-diastolic volume but there was a marked improvement in end-systolic volume, and at the submaximal point the ejection fraction was significantly (p < 0.05) increased. Ejection fraction at rest also improved. The deterioration in ejection fraction due to dipyridamole was ameliorated by nisoldipine. Ejection fraction and blood pressure improved during the calculation test, and work performance also improved.(ABSTRACT TRUNCATED AT 250 WORDS)

Prediction of reversible ischemia after revascularization. Perfusion and metabolic studies with positron emission tomography

BACKGROUND

Accurate noninvasive determination of myocardial viability is of paramount importance for the clinical identification of patients who will benefit most from revascularization. The preserved metabolic activity in the myocardium, as studied with positron emission tomography (PET), has been considered a gold standard for this purpose. However, recent reports show that moderate hypoperfusion or stress-induced ischemia may represent reversible ischemia. The present study was undertaken to compare the value of perfusion and metabolic studies with PET for predicting improvement in wall motion after revascularization.

METHODS AND RESULTS

Of 61 patients who had regional asynergy and underwent PET before revascularization, 43 patients who had successful revascularization were included in the study. Each patient underwent rest-stress 13N-ammonia perfusion scans and 18F-fluorodeoxyglucose (FDG) scan at rest while in a fasting state. Reversible ischemia was considered to be present when the resting perfusion was > or = 50% of the peak value, stress-induced hypoperfusion was present, or an increase in FDG uptake was observed. Of 130 asynergy segments, 51 segments had improved wall motion after revascularization. The positive and negative predictive values for improvement in asynergy were 48% and 87% by the rest perfusion study, 63% (P = .05 versus the rest value) and 87% by the rest-stress perfusion study, and 76% (P < .01 versus the rest value) and 92% by the FDG study.

CONCLUSIONS

FDG PET provided the best predictive value for improvement in wall motion after revascularization. On the other hand, 13N-ammonia PET is useful for predicting nonreversible myocardial scarring when it shows severe hypoperfusion at rest or hypoperfusion without stress-induced ischemia.

Modification of the circadian variation of symptom onset of acute myocardial infarction in diabetes mellitus

BACKGROUND

The effects of diabetes mellitus and its treatment on the circadian variation of symptom onset in acute myocardial infarction were examined.

METHODS

We obtained the time of symptom onset in 336 patients who had suffered acute myocardial infarction.

RESULTS

As in earlier studies, the peak of symptom onset occurred in the late morning, between 6:01 a.m. and 12:00 noon. Although a similar circadian variation was observed in non-diabetic patients, the late-morning peak was less prominent in diabetic patients. In diabetic patients receiving treatment, however, the circadian pattern was well preserved, whereas in untreated diabetic patients there were no peaks in the distribution of symptom onset of acute myocardial infarction.

CONCLUSION

These findings suggest that autonomic disturbances in diabetes mellitus may blunt the late-morning peak in the frequency of onset of acute myocardial infarction.

[Quantitative analysis of myocardial tracer distribution in patients with ischemic heart disease: comparison of 201T1 and 123I-15-(p-iodophenyl)-3-methylpentadecanoic acid (BMIPP)]

Quantitative assessment of myocardial tracer uptake in stress-delayed thallium and resting BMIPP imagings were performed in 24 patients with coronary artery disease. Each distribution was displayed on the bull's eye polar map and % uptake of each distribution was calculated as a mean value in 9 myocardial segments on the polar map. Redistribution index (% delayed uptake minus % stress uptake on thallium images) and discordance index (% delayed thallium uptake minus % BMIPP uptake) were also calculated. Each parameter was compared to the visual uptake score and wall motion score on contract left ventriculography. Excellent correlations were obtained between % uptake and the uptake score in each tracer. The % thallium and BMIPP uptake also correlated with regional wall motion score. Furthermore, a significant correlation was observed between redistribution and discordance indexes in the mildly hypoperfused segments. These data indicate that the quantitative analysis of thallium and BMIPP distributions seems to be valuable to understand relationship between perfusion and regional wall motion. The discordant BMIPP uptake may represent asynergic but viable segments. However, several important factors, such as attenuation factor should be also taken into consideration for such quantitative analysis.

Significance of myocardial uptake of iodine 123-labeled beta-methyl iodophenyl pentadecanoic acid: comparison with kinetics of carbon 11-labeled palmitate in positron emission tomography

BACKGROUND

A radioactively labeled beta-methyl branched fatty acid analog, 123I-15-(p-iodophenyl)-3-methyl pentadecanoic acid (BMIPP), has been developed to probe regional myocardial fatty acid metabolism. However, the significance of BMIPP uptake in the myocardium remains unclear.

METHODS AND RESULTS

To evaluate the significance of BMIPP uptake, single-photon emission computed tomography was performed 30 minutes after injection of BMIPP, and 201Tl-labeled single-photon emission computed tomography was taken on a separate day in 10 patients. Findings of BMIPP and 201Tl-labeled imaging were compared with the data obtained from positron emission tomography with 11C-labeled palmitate. The BMIPP uptake (percent of maximum) was significantly correlated with the early uptake (percent) and delayed uptake (percent) of 11C-labeled palmitate (r = 0.659 and r = 0.687, respectively) (p < 0.01 each), whereas it was not significantly correlated with the residual fraction (r = 0.205) or the clearance half-time of the early component (r = 0.138) of 11C-labeled palmitate as a marker of beta-oxidation of the fatty acid.

CONCLUSIONS

These data indicate that, although the myocardial uptake of BMIPP may not directly reflect beta-oxidation of fatty acids, its uptake may reflect both regional myocardial blood flow and fatty acid extraction.

Clinical and angiographic determinants of ventricular remodeling after acute myocardial infarction

BACKGROUND

Ventricular remodeling after acute myocardial infarction is a precursor of the development of overt heart failure and is an important indicator of mortality. However, clinical and angiographic determinants of ventricular remodeling have not been fully elucidated. The purpose of the present study was to evaluate the effects of long-standing preinfarction angina and the late reperfusion of the infarct-related coronary artery on ventricular remodeling and function.

METHODS

Coronary angiography and left ventricular cineangiography were performed 35 +/- 16 days after the onset of acute myocardial infarction in 80 patients with a relatively recent anterior Q-wave myocardial infarction who had received conventional therapy.

RESULTS

In patients with preinfarction angina that occurred more than 1 week before the onset of myocardial infarction, the left ventricular size and ejection fraction were better preserved than in those without preinfarction angina. On the other hand, the late reperfusion of the infarct-related coronary artery did not affect ventricular remodeling.

CONCLUSION

Our results indicate that the presence of residual flow to the infarct area through the collateral circulation, presumably developed by repetitive ischemic stimuli, appears to be a crucial determinant of subsequent left ventricular size and function in patients with acute myocardial infarction who have had conventional therapy.

Detection of exercise-induced silent ischemia and the sequence of ischemic events in coronary artery disease by radionuclide ambulatory ventricular function monitoring

Twenty-seven patients with stable coronary artery disease were continuously monitored with an ambulatory radionuclide ventricular function monitor (VEST) during exercise to determine the prevalence of silent ischemia and the temporal sequence of events during ischemic episodes. Exercise-induced ejection fraction abnormality was considered a < 6% increase in the control value lasting for more than 60 sec. Patients performed exercise for 424 +/- 111 sec during VEST recording. Seventeen exercise-induced ejection fraction abnormalities were observed in 17 patients, of which eight (47%) were silent electrocardiographically and 12 (71%) were silent symptomatically. In all of the patients, exercise-induced ischemia occurred in a temporal sequence of ejection fraction abnormalities, ST depressions and then symptoms. In nine patients with ejection fraction and ST abnormalities, ejection fraction abnormalities occurred earlier (199 +/- 87 sec) than ST depressions (321 +/- 117 sec; p < 0.01). In five patients with symptoms (399 +/- 151 sec), the sequence was ejection fraction abnormalities (205 +/- 64 sec; P < 0.05) followed by ST depressions (266 +/- 101 sec; P < 0.05) and symptoms (399 +/- 151 sec; P < 0.01). After termination of exercise, ejection fraction (49 +/- 12 sec) recovered sooner than symptoms (102 +/- 27 sec; p < 0.01) or ST abnormalities (191 +/- 96 sec; p < 0.01). Thus, hemodynamic monitoring by VEST may be helpful in detecting ischemic episodes in coronary artery disease which remain electrocardiographically or symptomatically silent. Furthermore, exercise-stress induces a cascade of temporal changes in ischemic events which may be helpful in understanding the pathophysiology of ischemia.

Technetium-99m-pyrophosphate uptake as an indicator of myocardial injury without infarct

Technetium-99m-pyrophosphate (PYP) is bound to calcium in necrotic myocardium and has been used clinically to evaluate myocardial infarction. Technetium-99m-PYP is also reported to accumulate in myocardium with unstable angina pectoris and it is speculated that severe ischemia with noninfarcted tissue may also increase uptake of 99mTc-PYP. In this paper, 99mTc-PYP uptake was determined in various models of myocardial ischemia of short duration to examine its applicability to the assessment of myocardial viability.

METHODS

In 23 open-chest dogs under anesthesia, models of ischemia-reperfusion of the left anterior descending artery (LAD) subjected to ischemia for 10, 30 or 60 min were produced. Wall motion was examined by echocardiography and myocardial blood flow was calculated using colored microspheres. Technetium-99m-PYP was injected after each ischemic intervention and reperfusion.

RESULTS

Technetium-99m-PYP showed 1.18 +/- 0.009 in the uptake ratio (ischemic area/normal area) following 10-min ischemia (11 dogs). The uptake ratio following 30-min ischemia (8 dogs) showed a significantly higher increase than that following 10-min ischemia (4.09 +/- 1.75; p < 0.05), permitting in vivo and ex vivo imaging. After 60-min ischemia resulting in infarction (4 dogs), 99mTc-PYP uptake of the ischemic area showed an uptake ten times that of the normal area (transmural: 12.2 +/- 2.9, epicardium: 7.5 +/- 1.9, endocardium: 16.8 +/- 4.1).

CONCLUSIONS

These findings indicate that since 99mTc-PYP accumulates in injured myocardium, its concurrent use with blood flow imaging is useful for the assessment of severity of ischemia, injured area and myocardial viability.

[Noninvasive and simple method for the estimation of myocardial metabolic rate of glucose by PET and 18F-FDG]

To estimate regional myocardial metabolic rate of glucose (rMRGlu) with positron emission tomography (PET) and 2-[18F]fluoro-2-deoxy-D-glucose (FDG), non invasive simple method has been investigated using dynamic PET imaging in 14 patients with ischemic heart disease. This imaging approach uses a blood time-activity curve (TAC) derived from a region of interest (ROI) drawn over dynamic PET images of the left ventricle (LV), left atrium (LA) and aorta. Patlak graphic analysis was used to estimate k1k3/(k2+k3) from serial plasma and myocardial radioactivities. FDG counts ratio between whole blood and plasma was relatively constant (0.91 +/- 0.02) both throughout the time and among different patients. Although TACs derived from dynamic PET images gradually increased at later phase due to spill over from the myocardium into the cavity, there were good agreements between the estimated K complex values obtained from arterial blood sampling and dynamic PET imaging (LV r = 0.95, LA r = 0.96, aorta r = 0.98). These results demonstrate the practical usefulness of a simplified and noninvasive method for the estimation of rMRGlu in humans by PET.

Glucose metabolism in relation to perfusion in patients with ischaemic heart disease

In order to correlate myocardial perfusion and residual metabolism in patients with coronary artery disease, the regional metabolic rate of glucose (rMRGlu) was compared with regional perfusion under glucose loading state (GL) and fasting state (FA). Fluorine-18 deoxyglucose dynamic scan was obtained in ten patients after oral GL and in 16 patients under FA. rMRGlu in seven segments was calculated using Patlak graphic analysis for comparison with normalized percent uptake of nitrogen-13 ammonia at rest in each segment. When perfusion was less than 45%, no segment showed an increase in rMRGlu (> or = 0.3 mumol/min/g) under either FA (0/6 segments) or GL (0/8 segments), indicating a certain threshold of perfusion for maintenance of glucose metabolism. When perfusion exceeded 45%, rMRGlu was higher in GL (0.37 +/- 0.18 mumol/min/g) than FA (0.15 +/- 0.12 mumol/min/g, P < 0.001) but there was very wide scatter of rMRGlu values under both states. Thus, both myocardium with preserved and myocardium with reduced glucose metabolism may exist when the perfusion exceeds 45%. In conclusion, a minimum threshold of perfusion for the maintenance of glucose metabolism may exist under both FA and GL. Below the threshold, irreversible damage may occur in the myocardium. Above the threshold, quantitative analysis of glucose metabolism should play an important role in differentiating reversibly injured myocardium from necrotic myocardium.

Myocardial tomography using technetium-99m-tetrofosmin to evaluate coronary artery disease

To assess the clinical value of the 99mTc-labeled myocardial perfusion agent, 99mTc-tetrofosmin, the findings of stress and rest myocardial tomography were compared with those of stress and 3-hr delayed 201Tl tomography and coronary arteriography.

METHODS

Twenty-five patients who had coronary arteriography were studied with both stress tetrofosmin and 201Tl tomography.

RESULTS

The image quality of tetrofosmin was superior to that of 201Tl despite a shorter acquisition time. Both the tetrofosmin and 201Tl studies were quite sensitive to detect coronary artery disease (100% and 95%, respectively) (p = ns). The two studies showed similar sensitivity (75% and 73%) and specificity (80% and 77%, respectively) for the detection of significant (> or = 75% diameter) coronary artery stenosis. Stress distribution of tetrofosmin tended to be slightly higher than that of 201Tl (% uptake: 63.3% +/- 13.5% versus 60.4% +/- 12.2%, p = 0.0006; uptake score: 2.33 +/- 1.03 versus 2.22 +/- 1.07, p = 0.007), indicating less defect contrast in the former. A high concordant rate (89%) of the stress perfusion score was observed between the two radiopharmaceuticals. Reversible perfusion abnormalities were observed to be similar between stress-rest tetrofosmin and stress-delayed 201Tl studies.

CONCLUSIONS

Stress tetrofosmin perfusion tomography is a valuable method to detect coronary artery disease and to assess tissue viability with accuracy similar to that of stress 201Tl tomography.

[Comparative study of 201Tl-scintigraphic image and endomyocardial biopsy findings in patients with dilated cardiomyopathy]

201Tl-SPECT image was compared with the findings of endomyocardial biopsy in patients with dilated cardiomyopathies (DCM), and diagnostic value of 201Tl patchy pattern image for fibrosis with DCM was evaluated. Serial 22 patients diagnosed as DCM with endomyocardial biopsy findings were selected for this study (age: 50 +/- 17 y.o., Male/Female = 17/5). Patchy pattern of 201Tl-SPECT image was visually classified to 4 stage according to the severity of inhomogeneous defect, and pathologic findings of fibrosis was also classified into 4 according to the severity of fibrosis (0: none, 1: mild, 2: moderate, 3: severe). Ejection fraction calculated from left ventriculography and end-diastolic dimension by echocardiography were also compared with 201Tl-SPECT image. Out of 22 patients, 21 patients (95%) showed fibrosis, and 18 patients (82%) showed patchy pattern with 201Tl-SPECT. Severity of patchy pattern was not in good relation to that of fibrosis (r = 0.374). 201Tl image was not related to the function nor dimension. Four autopsy studies revealed a good relation of macroscopic severity, spatial distribution of fibrosis and inhomogeneous 201Tl-defect pattern before death. Patchy pattern of 201Tl-SPECT image will show the myocardial fibrosis in patients with DCM, and is independent of the function. 201Tl-SPECT may show more clinically useful findings of spatial distribution and severity of fibrosis with focal myocardial biopsy.

[Evaluation of myocardial distribution of iodine-123 labeled metaiodobenzylguanidine (123I-MIBG) in normal subjects]

The normal pattern of the myocardial sympathetic innervation was studied in 15 subjects using gamma camera scintigraphy with iodine-123 labeled metaiodobenzylguanidine (123I-MIBG). Seven younger subjects (mean age 24.6 +/- 3.6) and eight older patients (mean age 60.9 +/- 8.4) with normal cardiac function were studied. Planar imaging was obtained at 15 minute and 3 hours, and SPECT was also performed 3 hours after injection of 111 MBq (3 mCi) of MIBG. The younger subjects showed higher the heart to mediastinum count ratio (2.91 +/- 0.25 vs. 2.67 +/- 0.34; p < 0.05) and higher inferior to anterior count ratio (1.19 +/- 0.15 vs. 0.97 +/- 0.13; p < 0.05) on the late scan. The bull's-eye polar map also differences in counts in the mid-inferior (p < 0.005), basal-inferior (p < 0.05) and mid-lateral sectors (p < 0.01). But there was no significant difference in MIBG washout rate from myocardium between two groups. These data suggest that there is a difference of the cardiac sympathetic innervation, with older subjects having fewer sympathetic nerve terminals, especially in inferior than younger subjects. We conclude that the age difference in sympathetic nerve function should be considered in the interpretation of MIBG scan.

Combined study with I-123 fatty acid and thallium-201 to assess ischemic myocardium: comparison with thallium redistribution and glucose metabolism

To assess the clinical value of combined SPECT imaging with I-123-15-(p-iodophenyl)-3-methyl pentadecanoic acid (BMIPP) and thallium-201 (Tl), the findings were compared with those obtained in a stress Tl study and positron emission tomography (PET) with fluorine-18-fluorodeoxyglucose (FDG) in 22 patients with myocardial infarction. In 20 patients who underwent a stress Tl study, among 75 hypoperfused segments, 27 segments exhibited less BMIPP uptake than Tl (discordant segments), and the remaining 48 segments showed a similar decrease in BMIPP uptake (concordant segments). Twenty-two of 27 discordant segments (81%) exhibited redistribution on stress Tl study. On the other hand, only one of the 48 concordant segments had redistribution (p < 0.001). In 10 patients who underwent a FDG PET study, among 33 hypoperfused segments, seven segments were discordant segments, and the remaining 25 segments were concordant segments. Seven of the eight discordant segments (88%) demonstrated an increase in FDG uptake. In contrast, only five of 25 concordant segments (20%) showed increase in FDG uptake (p < 0.01). Thus, the segments showing discordant BMIPP uptake are considered to be ischemic but viable myocardium. We conclude that combined imaging with BMIPP and Tl is a useful mean for evaluating tissue viability in patients with coronary artery disease, but it may underestimate the extent of tissue viability, compared with FDG PET imaging.