Reversibility of cardiac wall-motion abnormalities predicted by positron tomography

Positron emission tomography (PET) can be used with nitrogen-13-ammonia (13NH3) to estimate regional myocardial blood flow, and with fluorine-18-deoxyglucose (18FDG) to measure exogenous glucose uptake by the myocardium. We used PET to predict whether preoperative abnormalities in left ventricular wall motion in 17 patients who underwent coronary-artery bypass surgery were reversible. The abnormalities were quantified by radionuclide or contrast angiography or both, before and after grafting. PET images were obtained preoperatively. Abnormal wall motion in regions in which PET images showed preserved glucose uptake was predicted to be reversible, whereas abnormal motion in regions with depressed glucose uptake was predicted to be irreversible. According to these criteria, abnormal contraction in 35 of 41 segments was correctly predicted to be reversible (85 percent predictive accuracy), and abnormal contraction in 4 of 26 regions was correctly predicted to be irreversible (92 percent predictive accuracy). In contrast, electrocardiograms showing pathological Q waves in the region of asynergy predicted irreversibility in only 43 percent of regions. We conclude that PET imaging with 13NH3 to assess blood flow and 18FDG to assess the metabolic viability of the myocardium is an accurate method of predicting potential reversibility of wall-motion abnormalities after surgical revascularization.

Anatomic versus physiologic assessment of coronary artery disease. Role of coronary flow reserve, fractional flow reserve, and positron emission tomography imaging in revascularization decision-making

Angiographic severity of coronary artery stenosis has historically been the primary guide to revascularization or medical management of coronary artery disease. However, physiologic severity defined by coronary pressure and/or flow has resurged into clinical prominence as a potential, fundamental change from anatomically to physiologically guided management. This review addresses clinical coronary physiology-pressure and flow-as clinical tools for treating patients. We clarify the basic concepts that hold true for whatever technology measures coronary physiology directly and reliably, here focusing on positron emission tomography and its interplay with intracoronary measurements.

Noninvasive quantification of regional blood flow in the human heart using N-13 ammonia and dynamic positron emission tomographic imaging

Evaluation of regional myocardial blood flow by conventional scintigraphic techniques is limited to the qualitative assessment of regional tracer distribution. Dynamic imaging with positron emission tomography allows the quantitative delineation of myocardial tracer kinetics and, hence, the measurement of physiologic processes such as myocardial blood flow. To test this hypothesis, positron emission tomographic imaging in combination with N-13 ammonia was performed at rest and after pharmacologically induced vasodilation in seven healthy volunteers. Myocardial and blood time-activity curves derived from regions of interest over the heart and ventricular chamber were fitted using a three compartment model for N-13 ammonia, yielding rate constants for tracer uptake and retention. Myocardial blood flow (K1) averaged 88 +/- 17 ml/min per 100 g at rest and increased to 417 +/- 112 ml/min per 100 g after dipyridamole infusion (0.56 mg/kg) and handgrip exercise. The coronary reserve averaged 4.8 +/- 1.3 and was not significantly different in the septal, anterior and lateral walls of the left ventricle. Blood flow values showed only a minor dependence on the correction for blood metabolites of N-13 ammonia. These data demonstrate that quantification of regional myocardial blood flow is feasible by dynamic positron emission tomographic imaging. The observed coronary flow reserve after dipyridamole is in close agreement with the results obtained by invasive techniques, indicating accurate flow estimates over a wide range. Thus, positron emission tomography may provide accurate and noninvasive definition of the functional significance of coronary artery disease and may allow the improved selection of patients for revascularization.

Identification and differentiation of resting myocardial ischemia and infarction in man with positron computed tomography, 18F-labeled fluorodeoxyglucose and N-13 ammonia

Studies have shown that the extraction of glucose per unit flow is increased in moderately ischemic myocardium primarily due to anaerobic glucose metabolism manifested as lactate production, whereas myocardial infarction is characterized by the loss of metabolically active myocardium. To determine the feasibility of demonstrating these metabolic abnormalities reflecting both ischemia and infarction, we used positron computed tomography (PCT) to evaluate relative regional myocardial exogenous glucose utilization and perfusion in 15 patients with recent myocardial infarction. The positron-emitting tracers of glucose metabolism and perfusion, 18F-2-fluoro-2-deoxyglucose (FDG) and N-13 ammonia, respectively, were used. Fourteen of 19 documented infarctions were demonstrated by PCT to have concordantly decreased glucose utilization and perfusion. However, in an additional 11 regions, glucose utilization was disproportionately increased relative to perfusion, consistent with ischemic glucose consumption. These findings correlated with the presence of postinfarction angina, the site of ischemic electrocardiographic changes during chest pain, and the presence of regional left ventricular dysfunction and severe coronary artery disease. Because three ECG infarct zones not detected by PCT demonstrated ischemic glucose utilization, only two of 19 electrocardiographically defined infarctions had no detectable metabolic abnormality. We conclude that the changes in regional FDG and N-13 ammonia concentrations detected with PCT in patients who had had a recent myocardial infarction are consistent with regional exogenous glucose utilization and perfusion in moderately ischemic and irreversibly infarcted myocardium. This approach has the potential to identify and differentiate resting myocardial ischemia from infarction and to assess tissue viability after an ischemic event.

Influence of age and hemodynamics on myocardial blood flow and flow reserve

BACKGROUND

Aging is associated with changes of the systolic blood pressure that may increase cardiac work and myocardial blood flow at rest and reduce the myocardial flow reserve. This might be misinterpreted as age-related impairment of the coronary vasodilator capacity.

METHODS AND RESULTS

Myocardial blood flow was quantified at rest and after administration of intravenous dipyridamole in 40 healthy volunteers (12 women and 28 men) with 13N-ammonia and positron emission tomography. Eighteen of the normal subjects were less than and 22 were older than 50 years (31 +/- 9 versus 64 +/- 9 years). The resting rate-pressure product was lower in the younger than in the older subjects (6895 +/- 1070 versus 8634 +/- 1890; P < 0.01). Myocardial blood flow at rest averaged 0.76 +/- 0.17 mL.min-1.g-1 in the younger volunteers and 0.92 +/- 0.25 mL.min-1.g-1 in the older volunteers (P < 0.05). Hyperemic blood flows did not differ between younger and older subjects (3.0 +/- 0.8 versus 2.7 +/- 0.6 mL.min-1.g-1; P = NS); however, minimal coronary resistance was higher in the older subjects. Corrected for indexes of coronary driving pressure, hyperemic flow was lower in older than in younger normal subjects. The higher resting blood flows combined with similar hyperemic flows resulted in a lower myocardial flow reserve in the older than in the younger normal subjects (4.1 +/- 0.9 versus 3.0 +/- 0.70; P < 0.0001). The flow reserve was more closely correlated with resting than with hyperemic blood flows.

CONCLUSIONS

Aging does not alter significantly dipyridamole-induced hyperemic flows; although coronary vascular resistance after dipyridamole was somewhat increased in older subjects. The gradual decline of the myocardial blood flow reserve correlates with an age-related increase of baseline myocardial work and blood flow. These findings suggest that the reduced flow reserve with age is primarily due to increased cardiac work and blood flow at rest rather than to an abnormal vasodilator capacity.

Cardiac PET imaging for the detection and monitoring of coronary artery disease and microvascular health

Positron emission tomography (PET) myocardial perfusion imaging in concert with tracer-kinetic modeling affords the assessment of regional myocardial blood flow (MBF) of the left ventricle in absolute terms (milliliters per gram per minute). Assessment of MBF both at rest and during various forms of vasomotor stress provides insight into early and subclinical abnormalities in coronary arterial vascular function and/or structure, noninvasively. The noninvasive evaluation and quantification of MBF and myocardial flow reserve (MFR) extend the scope of conventional myocardial perfusion imaging from detection of end-stage, advanced, and flow-limiting, epicardial coronary artery disease (CAD) to early stages of atherosclerosis or microvascular dysfunction. Recent studies have shown that impaired hyperemic MBF or MFR with PET, with or without accompanying CAD, is predictive of increased relative risk of death or progression of heart failure. Quantitative approaches that measure MBF with PET identify multivessel CAD and offer the opportunity to monitor responses to lifestyle and/or risk factor modification and to therapeutic interventions. Whether improvement or normalization of hyperemic MBF and/or the MFR will translate to improvement in long-term cardiovascular outcome remains clinically untested. In the meantime, absolute measures of MBF with PET can be used as a surrogate marker for coronary vascular health, and to monitor therapeutic interventions. Although the assessment of myocardial perfusion with PET has become an indispensable tool in cardiac research, it remains underutilized in clinical practice. Individualized, image-guided cardiovascular therapy may likely change this paradigm in the near future.

Quantitative relation between myocardial viability and improvement in heart failure symptoms after revascularization in patients with ischemic cardiomyopathy

BACKGROUND

Studies of patients with coronary artery disease and left ventricular dysfunction have shown that preoperative quantification of myocardial viability may be clinically useful to identify those patients who will benefit most from revascularization both functionally and prognostically. However, the relation between preoperative extent of viability and change in heart failure symptoms has not been documented carefully. We assessed the relation between the magnitude of improvement in heart failure symptoms after coronary artery bypass surgery (CABG) and the extent of myocardial viability as assessed by use of quantitative analysis of preoperative positron emission tomography (PET) images.

METHODS AND RESULTS

We studied 36 patients with ischemic cardiomyopathy (mean left ventricular ejection fraction, 28 +/- 6%) undergoing CABG. Preoperative extent and severity of perfusion abnormalities and myocardial viability (flow-metabolism mismatch) were assessed by use of quantitative analysis of PET images with 13N ammonia and fluorine-18-deoxyglucose. Each patient's functional status was determined before and after CABG by use of a Specific Activity Scale. Mean perfusion defect size and severity were 63 +/- 13% and 33 +/- 12%, respectively. Total extent of a PET mismatch correlated linearly and significantly with percent improvement in functional status after CABG (r = .87, P < .0001). A blood flow-metabolism mismatch > or = 18% was associated with a sensitivity of 76% and a specificity of 78% for predicting a change in functional status after revascularization. Patients with large mismatches (> or = 18%) achieved a significantly higher functional status compared with those with minimal or no PET mismatch (< 5%) (5.7 +/- 0.8 versus 4.9 +/- 0.7 metabolic equivalents, P = .009). This resulted in an improvement of 107% in patients with large mismatches compared with only 34% in patients with minimal or no PET mismatch.

CONCLUSIONS

In patients with ischemic cardiomyopathy, the magnitude of improvement in heart failure symptoms after CABG is related to the preoperative extent and magnitude of myocardial viability as assessed by use of PET imaging. Patients with large perfusion-metabolism mismatches exhibit the greatest clinical benefit after CABG.

Positron emission tomography detects tissue metabolic activity in myocardial segments with persistent thallium perfusion defects

Positron emission tomography with 13N-ammonia and 18F-2-deoxyglucose was used to assess myocardial perfusion and glucose utilization in 51 myocardial segments with a stress thallium defect in 12 patients. Myocardial infarction was defined by a concordant reduction in segmental perfusion and glucose utilization, and myocardial ischemia was identified by preservation of glucose utilization in segments with rest hypoperfusion. Of the 51 segments studied, 36 had a fixed thallium defect, 11 had a partially reversible defect and 4 had a completely reversible defect. Only 15 (42%) of the 36 segments with a fixed defect and 4 (36%) of the 11 segments with a partially reversible defect exhibited myocardial infarction on study with positron tomography. In contrast, residual myocardial glucose utilization was identified in the majority of segments with a fixed (58%) or a partially reversible (64%) thallium defect. All of the segments with a completely reversible defect appeared normal on positron tomography. Apparent improvement in the thallium defect on delayed images did not distinguish segments with ischemia from infarction. Thus, positron emission tomography reveals evidence of persistent tissue metabolism in the majority of segments with a fixed or partially resolving stress thallium defect, implying that markers of perfusion alone may underestimate the extent of viable tissue in hypoperfused myocardial segments.

Relation among stenosis severity, myocardial blood flow, and flow reserve in patients with coronary artery disease

BACKGROUND

Coronary arteriography is considered the "gold standard" for evaluating the severity of a coronary stenosis. Because the resistance to blood flow through a stenotic lesion depends on a number of lesion characteristics, the physiological significance of coronary lesions of intermediate severity is often difficult to determine from angiography alone. This study of patients with coronary artery disease seeks to determine the relation between myocardial blood flow and flow reserve measured by positron emission tomography (PET) and the percent area stenosis on quantitative coronary arteriography.

METHODS AND RESULTS

We studied 28 subjects: 18 patients with coronary artery disease (66 +/- 8 years) and 10 age-matched healthy volunteers (64 +/- 13 years) with dynamic N-13 ammonia PET imaging at rest and after dipyridamole (0.56 mg/kg). The percent cross-sectional area stenosis was quantified on the coronary arteriograms as described by Brown et al. In the 18 patients, a total of 41 non-infarct-related coronary vessels were analyzed. Myocardial blood flows in normal regions of patients with coronary artery disease were not different than those in healthy volunteers, both at rest and after dipyridamole. As a result, the myocardial flow reserve was also similar in both groups (2.4 +/- 0.4 versus 2.6 +/- 0.7, respectively; P = NS). Quantitative PET estimates of hyperemic blood flow (r = .81, P < .00001), flow reserve (r = .78, P < .00001), and an index of the "minimal coronary resistance" (r = .78, P < .00001) were inversely and nonlinearly correlated with the percent area stenosis on angiography. Of note, PET estimates of myocardial flow reserve successfully differentiated coronary lesions of intermediate severity (50% to 70% and 70% to 90%; 2.4 +/- 0.4 versus 1.8 +/- 0.5, respectively; P = .04).

CONCLUSIONS

In patients with coronary artery disease, non-invasive measurements of myocardial blood flow and flow reserve by PET are inversely and nonlinearly related to stenosis severity as defined by quantitative angiography. Importantly, coronary lesions of intermediate severity have a differential flow reserve that decreases as stenosis increases that can be detected noninvasively by PET, thus allowing better definition of the functional importance of known coronary stenosis.

Sustained regional abnormalities in cardiac metabolism after transient ischemia in the chronic dog model

Positron emission tomography allows noninvasive assessment of myocardial blood flow and metabolism, and may aid in defining the extent and severity of an ischemic injury. This hypothesis was tested by studying, in chronically instrumented dogs, regional blood flow and metabolism during and after a 3 hour balloon occlusion of the left anterior descending coronary artery. The metabolic findings after ischemia were compared with the recovery of regional function over a 4 week period. N-13 ammonia was used as a blood flow tracer, and C-11 palmitic acid and F-18 deoxyglucose as tracers of fatty acid and glucose metabolism, respectively. Regional myocardial function was monitored with ultrasonic crystals implanted subendocardially. Regional function improved most between 24 hours and 1 week after reperfusion, but was still attenuated at 4 weeks. The slow functional recovery was paralleled by sustained metabolic abnormalities, reflected by segmentally delayed clearance of C-11 activity from myocardium and increased uptake of F-18 deoxyglucose. Absence of blood flow and C-11 palmitic acid uptake at 24 hours of reperfusion correlated with extensive necrosis as evidenced by histologic examination. Conversely, uptake of C-11 palmitic acid with delayed C-11 clearance and increased F-18 deoxyglucose accumulation identified reversibly injured tissue that subsequently recovered functionally and revealed little necrosis. Thus, recovery of metabolism after 3 hours of ischemia is slow in canine myocardium and paralleled by slow recovery of function. Metabolic indexes by positron tomography early after reperfusion can identify necrotic and reversibly injured tissue. Positron tomography may therefore aid in defining the extent and prognosis of an ischemic injury in patients undergoing reperfusion during evolving myocardial infarction.

Regional perfusion, glucose metabolism, and wall motion in patients with chronic electrocardiographic Q wave infarctions: evidence for persistence of viable tissue in some infarct regions by positron emission tomography

Positron-emission tomography with 13N-ammonia and 18F-2-deoxyglucose was used to assess regional perfusion and glucose utilization in 31 chronic electrocardiographic Q wave regions in 20 patients. With previously published criteria, regions of infarction were identified by a concordant reduction in regional perfusion and glucose utilization, and regions of ischemia were identified by preservation of glucose utilization in regions of diminished perfusion. Only 10 of the 31 regions (32%) exhibited myocardial infarction tomographically. In contrast, positron tomography revealed ischemia in six regions (20%) and was normal in 15 regions (48%). Even when Q wave regions were reassigned and consolidated to enhance the specificity of the electrocardiogram, uptake of 18F-2-deoxyglucose was noted in the majority (54%) of the regions. Neither electrocardiographic ST-T changes nor severity of associated wall motion abnormality reliably distinguished tomographically identified regions of ischemia from infarction. Thus positron tomography reveals evidence of persistent tissue metabolism in a high proportion of chronic electrocardiographic Q wave regions, and commonly used clinical tests do not reliably distinguish hypoperfused but viable regions from tomographically defined regions of myocardial infarction.

Coronary circulatory dysfunction in insulin resistance, impaired glucose tolerance, and type 2 diabetes mellitus

BACKGROUND

Abnormal coronary endothelial reactivity has been demonstrated in diabetes and is associated with an increased rate of cardiovascular events. Our objectives were to investigate the presence of functional coronary circulatory abnormalities over the full spectrum of insulin resistance and to determine whether these would differ in severity with more advanced states of insulin resistance.

METHODS AND RESULTS

Myocardial blood flow (MBF) was measured with positron emission tomography and 13N-ammonia to characterize coronary circulatory function in states of insulin resistance without carbohydrate intolerance (IR), impaired glucose tolerance (IGT), and normotensive and hypertensive type 2 diabetes mellitus (DM) compared with insulin-sensitive (IS) individuals. Indices of coronary function were total vasodilator capacity (mostly vascular smooth muscle-mediated) during pharmacological vasodilation and the nitric oxide-mediated, endothelium-dependent vasomotion in response to cold pressor testing. Total vasodilator capacity was similar in normoglycemic individuals (IS, IR, and IGT), whereas it was significantly decreased in normotensive (-17%) and hypertensive (-34%) DM patients. Compared with IS, endothelium-dependent coronary vasomotion was significantly diminished in IR (-56%), as well as in IGT and normotensive and hypertensive diabetic patients (-85%, -91%, and -120%, respectively).

CONCLUSIONS

Progressively worsening functional coronary circulatory abnormalities of nitric oxide-mediated, endothelium-dependent vasomotion occur with increasing severity of insulin-resistance and carbohydrate intolerance. Attenuated total vasodilator capacity accompanies the more clinically evident metabolic abnormalities in diabetes.

Long-term survival of patients with coronary artery disease and left ventricular dysfunction: implications for the role of myocardial viability assessment in management decisions

OBJECTIVES

Our purpose was to evaluate the long-term benefit of myocardial viability assessment for stratifying risk and selecting patients with low ejection fraction for coronary artery bypass grafting and to determine the relation between the severity of anginal symptoms, the amount of ischemic myocardium, and clinical outcome.

METHODS

We studied 93 consecutive patients with severe coronary artery disease and low ejection fraction (median, 25%) who underwent positron emission tomography to delineate the extent of perfusion-metabolism mismatch (reflecting hibernating myocardium) for potential myocardial revascularization. Median follow-up was 4 years (range, 0 to 6.2 years).

RESULTS

Fifty patients received medical therapy, and 43 patients underwent bypass grafting. In Cox survival models, heart failure class, prior myocardial infarction, and positron emission tomographic mismatch were the best predictors of survival. Patients with positron emission tomographic mismatch receiving bypass grafting had improved 4-year survival compared with those on medical therapy (75% versus 30%; P =.007) and a significant improvement in angina and heart failure symptoms. In patients without positron emission tomographic mismatch, bypass grafting tended to improve survival and symptoms only in those patients with severe angina (100% versus 60%; P =.085), whereas no survival advantage was apparent in patients with minimal or no anginal symptoms (63% versus 52%; P =.462).

CONCLUSIONS

Patients with low ejection fraction and evidence of viable myocardium by positron emission tomography have improved survival and symptoms with coronary bypass grafting compared with medical therapy. In patients without evidence of viability, survival and symptom improvement with bypass grafting are apparent only among those patients with severe angina.

Relationship between increasing body weight, insulin resistance, inflammation, adipocytokine leptin, and coronary circulatory function

OBJECTIVES

We sought to evaluate effects of obesity, insulin resistance, and inflammation on coronary circulatory function and its relationship to leptin plasma levels.

BACKGROUND

It is not known whether obesity, commonly paralleled by insulin resistance, inflammation, and leptin, is independently associated with coronary circulatory dysfunction.

METHODS

Myocardial blood flow (MBF) responses to cold pressor test (CPT) and pharmacologic vasodilation was measured with positron emission tomography and 13N-ammonia. Study participants were divided into three groups based on their body mass index (BMI, kg/m2): control, 20 < or = BMI <25 (n = 19); overweight, 25 < or = BMI <30 (n = 21); and obese, BMI >30 (n = 32).

RESULTS

Body mass index was significantly correlated to the Homeostasis Model Assessment Index of insulin resistance and C-reactive protein levels (r = 0.60 and r = 0.47, p < 0.0001). Compared with control subjects, endothelium-related change in MBF (DeltaMBF) to CPT progressively declined in overweight and obese groups (0.32 +/- 0.09 vs. 0.21 +/- 0.19 and 0.07 +/- 0.16 ml/g/min; p < 0.03 and p < 0.0001). The dipyridamole-induced total vasodilator capacity was significantly lower in obese than in control subjects (1.77 +/- 0.51 vs. 2.04 +/- 0.37 ml/g/min, p < 0.02). On multivariate analysis, BMI (p < 0.012) and age (p < 0.035) were significant independent predictors of DeltaMBF. Finally, only in the obese group leptin plasma levels significantly correlated with DeltaMBF (r = 0.37, p < 0.036).

CONCLUSIONS

Increased body weight is independently associated with abnormal coronary circulatory function that progresses from an impairment in endothelium-related coronary vasomotion in overweight individuals to an impairment of the total vasodilator capacity in obese individuals. The findings that elevated leptin plasma levels in patients that are obese might exert beneficial effects on the coronary endothelium to counterbalance the adverse effects of increases in body weight on coronary circulatory function should be tested.

Myocardial imaging with thallium-201: a multicenter study in patients with angina pectoris or acute myocardial infarction

A multicenter study of rest and exercise thallium-201 myocardial imaging in 190 patients from five centers was performed. Exercise images were obtained after graded treadmill or bicycle stress with use of five different gamma camera models and were interpreted by the originating investigator without knowledge of other clinical data. Of 42 patients with less than 50 percent coronary stenosis, 4 (10 percent) had a resting image defect, 1 (2 percent) a new exercise defect and 5 (12 percent) either a resting or an exercise image defect, or both. Of 148 patients with coronary stenosis of 50 percent or greater, 64, (45 percent) had an image defect in the study at rest, 90 (61 percent) had new or increased defects after exercise, and 115 (78 percent) had resting or exercise defects, or both. New exercise image defects were more common than exercise S-T depression (90 of 148 [61 percent] versus 62 of 148[42 percent]; P less than 0.01). In a second group of 111 patients with acute myocardial infarction studied at three centers, 90 patients (81 percent) had image defects compared with 71 (64 percent) two had new electrocardiographic Q waves (P less than 0.01). Smaller infractions, as assessed with serum enzyme values, and diaphragmatic infarctions were less commonly detected than larger or anterior infarctions. These findings suggest that myocardial imaging complements the electrocardiographic identification of acute myocardial infarction of exericse-induced myocardial ischemia.

Serial measurements of left ventricular ejection fraction by radionuclide angiography early and late after myocardial infarction

The left ventricular ejection fraction was determined serially with radioisotope angiography in 63 patients with acute myocardial infarction. After the peripheral injection of a bolus of technetium-99m, precordial radioactivity was recorded with a gamma scintillation camera and the ejection fraction calculated from the high frequency left ventricular time-activity curve. Since this technique requires no assumptions with respect to left ventricular geometry, it is particularly useful in patients with segmental left ventricular dysfunction. Serial measurements during the first 5 days after hospital admission were made in 50 patients, 30 of whom were studied during the subsequent 2 to 39 months (mean 19.9 months). Late follow-up serial studies were also performed in an additional 13 patients who had only one measurement of the left ventricular ejection fraction during the early postinfarction period. Early after infarction, the left ventricular ejection fraction was normal (more than 0.52) in only 15 of the 63 patients, and averaged 0.52 +/- 0.05 (standard deviation) in the 27 patients with an uncomplicated infarct. The ejection fraction was reduced in 24 patients with mild to moderate left ventricular failure (0.40 +/- 0.05, P less than 0.0001) and in the 12 patients with overt pulmonary edema (0.33 +/- 0.07, P less than 0.0001). In 35 patients the ejection fraction correlated with the mean pulmonary arterial wedge pressure (r = 0.72). In 15 patients with normal left ventricular wall motion by heart motion videotracking, the ejection fraction was significantly higher (0.53 +/- 0.08) than in the 26 patients with regional left ventricular dysfunction (0.41 +/- 0.10, P less than 0.0001). During the early postinfarction period, the left ventricular ejection fraction improved in 55 percent of patients and remained unchanged or decreased in 45 percent. A further increase in the ejection fraction was noted in 61 percent of patients during the late follow-up period. Patients with an initially low or decreasing ejection fraction had a significantly greater incidence of early mortality and left ventricular dysfunction (P less than 0.02) than those whose ejection fraction was normal or improved to normal early after infarction. These data indicate that the ejection fraction is a sensitive indicator of left ventricular function after acute myocardial infarction and that serial measurements are helpful in predicting early mortality and morbidity.

Right ventricular ejection fraction in patients with acute anterior and inferior myocardial infarction assessed by radionuclide angiography

We measured right and left ventricular ejection fracttion (EF) from high frequency time-activity curves obtained during the initial passage of an intravenous bolus of 99mTc (Sn) pyrophosphate. In 22 normal controls right ventricular EF averaged 0.52 +/- 0.04 (SD). In 24 acute anterior or lateral infarction patients right ventricular EF was normal (0.56 +/- 0.10), while left ventricular EF was reduced (0.45 +/- 0.10, P less than 0.001 vs controls). In 19 acute inferior infarction patients left ventricular EF also was depressed (0.51 +/- 0.09, P less than 0.001 vs controls). Among 7 of 19 inferior infarction patients with right ventricular by scintigraphy, right ventricular EF was reduced (0.39 +/- 0.05; P less than 0.001 vs normals; P less than 0.01 vs inferior infarction patients without right ventricular involvement). In the latter group right ventricular EF averaged 0.51 +/- 0.10 (NS vs normals). We conclude 1) a single injection of 99mTc (Sn) pyrophosphate can identify right and left ventricular dysfunction and infarct location in acute myocardial infarction, 2) right ventricular EF is well-preserved except when inferior infarction involves the right ventricle.

Noninvasive assessment of coronary stenoses by myocardial imaging during pharmacologic coronary vasodilation. VI. Detection of coronary artery disease in human beings with intravenous N-13 ammonia and positron computed tomography

The possibility of detecting mild coronary stenoses with positron computed tomography and nitrogen (N-13) ammonia administered during pharmacologic coronary vasodilation was previously demonstrated in chronically instrumented dogs. The feasibility of using this technique in human beings and its sensitivity in determining the degree and extent of coronary artery disease were examined in 13 young normal healthy volunteers and 32 patients with angiographically documented coronary artery disease. N-13 ammonia was administered intravenously and its distribution in the left ventricular myocardium recorded at rest and during dipyridamole-induced coronary hyperemia. In the 13 volunteers, N-13 activity was homogeneous at rest and during hyperemia, whereas 31 of the 32 patients had regional defects on the hyperemic images not present during rest. All six patients with double, all 10 with triple and 15 of 16 patients with single vessel disease (97 percent) were correctly identified with the technique. Two vessel involvement was correctly identified in five of the six patients with double vessel disease and three vessel disease in six of 10 patients. Of all 58 coronary stenoses, 52 (90 percent) were correctly identified. In a subgroup of 11 patients, the technique was compared with exercise thallium-201 planar images, which were abnormal in 10 (91 percent) whereas N-13 images were abnormal in all 11. Of the 19 stenosed coronary arteries in this subgroup, 11 (58 percent) were correctly identified with thallium-201 and 17 (89 percent) with tomography (p less than 0.01). It is concluded that cross-sectional imaging of the myocardial distribution of N-13 ammonia administered during pharmacologic coronary vasodilation is a highly sensitive and accurate means for noninvasive detection of coronary stenoses in human beings and for estimating the extent of coronary artery disease.

Regional myocardial metabolism in patients with acute myocardial infarction assessed by positron emission tomography

Positron emission tomography has been shown to distinguish between reversible and irreversible ischemic tissue injury. Using this technique, 13 patients with acute myocardial infarction were studied within 72 hours of onset of symptoms to evaluate regional blood flow and glucose metabolism with nitrogen (N)-13 ammonia and fluorine (F)-18 deoxyglucose, respectively. Serial noninvasive assessment of wall motion was performed to determine the prognostic value of metabolic indexes for functional tissue recovery. Segmental blood flow and glucose utilization were evaluated using a circumferential profile technique and compared with previously established semiquantitative criteria. Relative N-13 ammonia uptake was depressed in 32 left ventricular segments. Sixteen segments demonstrated a concordant decrease in flow and glucose metabolism. Regional function did not change over time in these segments. In contrast, 16 other segments with reduced blood flow revealed maintained F-18 deoxyglucose uptake consistent with remaining viable tissue. The average wall motion score improved significantly in these segments (p less than 0.01), yet the degree of recovery varied considerably among patients. Coronary anatomy was defined in 9 of 13 patients: patent infarct vessels supplied 8 of 10 segments with F-18 deoxyglucose uptake, while 10 of 13 segments in the territory of an occluded vessel showed concordant decreases in flow and metabolism (p less than 0.01). Thus, positron emission tomography reveals a high incidence of residual tissue viability in ventricular segments with reduced flow and impaired function during the subacute phase of myocardial infarction. Absence of residual tissue metabolism is associated with irreversible injury, while preservation of metabolic activity identifies segments with a variable outcome.(ABSTRACT TRUNCATED AT 250 WORDS)

13N ammonia myocardial imaging at rest and with exercise in normal volunteers. Quantification of absolute myocardial perfusion with dynamic positron emission tomography

Positron emission tomography (PET) was applied to the measurement of myocardial perfusion using the perfusion tracer 13N-labeled ammonia. 13N ammonia was delivered intravenously to 13 healthy volunteers both at rest and during supine bicycle exercise. Dynamic PET imaging was obtained in three cross-sectional planes for 10 minutes commencing with each injection. The left ventricle was divided into eight sectors, and a small region of interest was assigned to the left ventricular blood pool to obtain the arterial input function. The net extraction of 13N ammonia was obtained for each sector by dividing the tissue 13N concentration at 10 minutes by the integral of the input function from the time of injection to 10 minutes. With this approach for calculating net extractions, rest and exercise net extractions were not significantly different from each other. To obviate possible overestimation of the true 13N ammonia input function by contamination by 13N-labeled compounds other than 13N ammonia or by spillover from myocardium into blood pool, the net extractions were calculated using only the first 90 seconds of the blood and tissue time-activity curves. This approach for calculating net extractions yielded significant differences between rest and exercise, with an average ratio of exercise to rest of 1.38 +/- 0.34. Nonetheless, the increase was less than predicted from the average 2.7-2.8-fold increase in double product at peak exercise or the 1.7-fold increase in double product at 1 minute after exercise. However, when the first 90 seconds of dynamic data were fit with a two compartment tracer kinetic model, average perfusion rates of 0.75 +/- 0.43 ml/min/g at rest and 1.50 +/- 0.74 ml/min/g with exercise were obtained. This average increase in perfusion of 2.2-fold corresponded to similar average increases in double product. Thus, the noninvasive technique of PET imaging with 13N ammonia shows promise for future applications in determining absolute flows in patients with coronary artery disease.

Nontraumatic determination of left ventricular ejection fraction by radionuclide angiocardiography

Previous reports have suggested that left ventricular ejection fraction can be assessed by recording the passage of peripherally administered radioactive bolus through the heart. The accuracy and validity of this technique were examined in 20 patients undergoing diagnostic cardiac catheterization. 99m-Tc-human serum albumin was injected via a central venous catheter into the superior vena cava and precordial activity recorded with a gamma scintillation camera interfaced to a small digital computer. A computer program was designed to generate time-activity curves from the left ventricular blood pool and to calculate left ventricular ejection fractions from the cyclic fluctuations of the left ventricular time-activity curve which correspond to left ventricular volume changes during each cardiac cycle. The results correlated well with those obtained by biplane cineangiocardiography (r equals 0.94) and indicated that the technique should allow accurate and reproducible determination of left ventricular ejection fraction. The findings, however, demonstrated that the time-activity curve must be generated from a region-of-interest which fits the left ventricular blood pool precisely and must be corrected for contributions arising from noncardiac background structures. This nontraumatic and potentially noninvasive technique appears particularly useful for serial evaluation of the acutely ill patient and for follow-up studies in nonhospitalized patients.

Coronary vasomotor abnormalities in insulin-resistant individuals

BACKGROUND

Insulin resistance is a metabolic spectrum that progresses from hyperinsulinemia to the metabolic syndrome, impaired glucose tolerance, and finally type 2 diabetes mellitus. It is unclear when vascular abnormalities begin in this spectrum of metabolic effects.

OBJECTIVE

To evaluate the association of insulin resistance with the presence and reversibility of coronary vasomotor abnormalities in young adults at low cardiovascular risk.

DESIGN

Cross-sectional study followed by prospective, open-label treatment study.

SETTING

University hospital.

PATIENTS

50 insulin-resistant and 22 insulin-sensitive, age-matched Mexican-American participants without glucose intolerance or traditional risk factors for or evidence of coronary artery disease.

INTERVENTION

3 months of thiazolidinedione therapy for 25 insulin-resistant patients.

MEASUREMENTS

Glucose infusion rate in response to insulin infusion was used to define insulin resistance (glucose infusion rate < or = 4.00 mg/kg of body weight per minute [range, 0.90 to 3.96 mg/kg per minute]) and insulin sensitivity (glucose infusion rate > or = 7.50 mg/kg per minute [range, 7.52 to 13.92 mg/kg per minute]). Myocardial blood flow was measured by using positron emission tomography at rest, during cold pressor test (largely endothelium-dependent), and after dipyridamole administration (largely vascular smooth muscle-dependent).

RESULTS

Myocardial blood flow responses to dipyridamole were similar in the insulin-sensitive and insulin-resistant groups. However, myocardial blood flow response to cold pressor test increased by 47.6% from resting values in insulin-sensitive patients and by 14.4% in insulin-resistant patients. During thiazolidinedione therapy in a subgroup of insulin-resistant patients, insulin sensitivity improved, fasting plasma insulin levels decreased, and myocardial blood flow responses to cold pressor test normalized.

LIMITATIONS

The study was not randomized, and it included only 1 ethnic group.

CONCLUSIONS

Insulin-resistant patients who do not have hypercholesterolemia or hypertension and do not smoke manifest coronary vasomotor abnormalities. Insulin-sensitizing thiazolidinedione therapy normalized these abnormalities. These results suggest an association between insulin resistance and abnormal coronary vasomotor function, a relationship that requires confirmation in larger studies.