Prognostic value of submaximal exercise radionuclide ventriculography after myocardial infarction

Submaximal exercise testing with radionuclide ventriculography (RVG) was performed in 117 patients before hospital discharge 17 +/- 7 days (+/- standard deviation) after an acute myocardial infarction (MI). The hypothesis tested in these studies was that submaximal exercise testing coupled to RVG allows the identification of patients at risk for future ischemic events in the subsequent 6 months, irrespective of MI location and type. The sites of MI were characterized as anterior transmural in 33, inferior transmural in 39, limited nontransmural in 18, extensive nontransmural in 24 and indeterminant in 3. During 6 months of follow-up, 9 patients died, 14 had recurrent MI, 18 had refractory angina pectoris, 16 had limiting angina and 17 had congestive heart failure. Discriminant function analysis ranked exercise changes in left ventricular (LV) ejection fraction and end-systolic volume the most important of all clinical, exercise and scintigraphic variables for predicting future cardiac events. The predictive accuracy of changes in LV ejection fraction and end-systolic volume were 93 and 91%, respectively, for the entire group, and were significantly more sensitive than any degree of ST-segment depression or elevation (p less than 0.001). These findings were generally independent of MI location and type. Thus, submaximal exercise RVG after MI is an accurate means of identifying patients at risk for major cardiac events in the 6 months after hospital discharge.     

Alterations in left ventricular volumes and ejection fraction at rest and during exercise in patients with aortic regurgitation

This study was performed (1) to determine the changes in left ventricular volumes during exercise in patients with aortic regurgitation, and (2) to evaluate the importance of these alterations in characterizing left ventricular function in these patients. In 15 normal subjects (Group I) and in 17 patients with aortic regurgitation (Group II), left ventricular end-diastolic volume index, end-systolic volume index, ejection fraction and the ratio of peak systolic blood pressure to end-systolic volume index were measured at rest and during supine exercise. The patients with aortic regurgitation were classified into two groups on the basis of symptoms and chest radiographs: Group IIA, minimal or no symptoms, no cardiomegaly or pulmonary venous congestion; Group IIB, definite symptoms, with cardiomegaly and pulmonary venous congestion. Patients with aortic regurgitation had greater left ventricular end-diastolic and end-systolic volume indexes at rest and during exercise (p <0.05) than did normal subjects. During exercise, left ventricular end-diastolic volume index increased in normal subjects (53 ± 13 ml/m² [mean ± standard deviation] at rest, 67 ± 18 ml/m² during exercise, p <0.01), demonstrated a heterogeneous response in patients in Group IIA and increased in patients in Group IIB (180 ± 96 ml/m² at rest, 209 ± 102 ml/m² during exercise, p <0.05). During exercise, left ventricular end-systolic volume index decreased in normal subjects (18 ± 5 ml/m² at rest, $\text{15}\text{\$}\text{?}\text{6}$ ml/m² with exercise, p <0.01), increased in patients in Group IIB (82 ± 60 ml/m² at rest, 118 ± 93 ml/m² during exercise, p <0.05), and showed a variable response in those in Group IIA. At rest, left ventricular ejection fraction was similar in the three groups, but during exercise it increased in Group I (0.71 ± 0.07 at rest, 0.82 ± 0.07 with exercise, p <0.001), was unchanged in Group IIA and decreased in Group IIB (0.59 ± 0.15 at rest, 0.50 ± 0.16 during exercise, p <0.05). During exercise, there was an inverse relation between changes in left ventricular ejection fraction and endsystolic volume, but no relation between changes in end-diastolic volume and ejection fraction. Changes in the systolic pressure-volume ratio provided no more information than changes in end-systolic volume alone. Thus, abnormal alterations in left ventricular volumes occur during exercise in patients with aortic regurgitation and may be helpful in the further characterization of left ventricular performance in these patients.     

Myocardial rupture after myocardial infarction: Detection by multi-gated image-acquisition scintigraphy

Myocardial rupture following infarction usually is an acute and dramatic event. Rarely, it may take a subacute course, allowing surgical treatment. We report herein a case of subacute rupture of the heart in a 54 year old patient with acute myocardial infarction. The rupture was diagnosed by the appearance of a radiopaque halo around the heart during radionuclide ventriculography. The patient subsequently underwent surgical resection of a large anterolateral aneurysm and a 2 inch long rupture of the myocardium and survived. Clinical suspicion, prompt diagnosis, and surgical intervention are important in the management of this relatively unusual complication of infarction.     

Thallium-201 myocardial perfusion studies in patients with the mitral valve prolapse syndrome

To determine whether regional myocardial ischemia plays a role in patients with the mitral valve prolapse syndrome, we examined myocardial perfusion with exercise stress testing and thallium-201 myocardial scintigraphy. Twelve patients were studied, 11 women and one man aged 18 to 56 years, mean age 30 years. In all patients, mitral valve prolapse was documented by echocardiography or phonocardiography. Patients over 35 years of age underwent cardiac catheterization. Electrocardograms disclosed abnormalities during maximal exercise in eight of the 12 patients. In two patients, angina developed during exercise. Thallium-201 (²⁰¹TI) scintigrams were normal in the 11 patients with presumed or documented normal coronary arteries. One patient, in whom an apical defect was demonstrated on scintigraphy, had significant disease of the left main and left anterior descending coronary artery. Repeat testing after successful aortocoronary bypass grafting revealed improved exercise capacity and a normal ²⁰¹TI myocardial scintigram. The data indicate that patients with mitral valve prolapse alone do not have regional myocardial ischemia and that the presence of a defect on ²⁰¹TI myocardial scintigraphy following maximal stress testing would suggest the existence of concomitant coronary artery disease.     

Effect of chronic oral digoxin therapy on ventricular function at rest and peak exercise in patients with ischemic heart disease: Assessment with equilibrium gated blood pool imaging

The effect of chronic digoxin therapy on left ventricular ejection fraction, left ventricular volumes and cardiac output was assessed using multigated blood pool imaging both at rest and during supine exercise in 14 patients with known ischemic heart disease. Digoxin had no significant effect on ejection fraction at rest or at peak exercise. Neither exercise nor digoxin therapy had a significant influence on stroke volume index. Cardiac index was also not significantly influenced by digoxin either at rest (3.1 ± 1.15 without digoxin versus 2.9 ± 1.03 liters/min per m² during digoxin therapy) or at peak exercise (5.1 ± 2.08 versus 5.1 ± 2.04 liters/min per m², respectively), although the increase in heart rate resulted in a significant increase in cardiac index with exercise in each state (p <0.01).End-diastolic and end-systolic volume indexes both tended to be smaller at rest after digoxin therapy than before, but this difference was not significant. In the eight patients with an ejection fraction at rest of less than 0.50 (range 0.15 to 0.47), both end-diastolic and end-systolic volume indexes increased significantly with exercise (p <0.05) irrespective of therapy with digoxin. Conversely, in the six patients with a well preserved (greater than 0.50) ejection fraction at rest, digoxin prevented the exerciseinduced increase in end-diastolic and end-systolic volume indexes, and at peak exercise end-systolic volume index was significantly smaller during digoxin therapy than before it (p <0.05).It is concluded that chronic digoxin therapy in patients with stable ischemic heart disease (1) does not have a significant deleterious functional effect on the nonfailing heart, and (2) does not result in a significant change in left ventricular function at rest, but that it (3) does provide improved ventricular function at peak exercise in patients with well preserved left ventricular function at rest.     

Radioimmunoassay of serum creatine kinase B isoenzyme in the diagnosis of acute myocardial infarction. Correlation with technetium-99m stannous pyrophosphate myocardial scintigraphy

In 80 patients admitted to a coronary care unit within 24 hours of chest pain thought to be due to acute myocardial infarction, routine diagnostic tests (electrocardiograms, total serum creatine kinase) as well as ^99mtechnetium stannous pyrophosphate, TcPYP myocardial scintigraphy and serial serum radioimmunoassay determinations of the B subunit of creatine kinase (CK-B), were performed. None of these patients had clinical evidence of acute cerebral injury. A definite decision regarding the presence of acute myocardial infarction could be made in 77 patients on the basis of the results of routine diagnostic tests. The calculated sensitivity, specificity and predictive value of an elevated serum CK-B level in the recognition of acute myocardial infarction were each 100 per cent. Serial TcPYP scintigraphy was 97 per cent sensitive and 70 per cent specific, and had a predictive value of 96 per cent for the recognition of acute myocardial infarction. Both serum CK-B analysis and TcPYP myocardial scintigraphy were helpful in the recognition of infarct extension, and serial studies with both techniques suggested the presence of asymptomatic extension of infarction in several patients.The predictive value of each of these techniques for the recognition of a myocardial infarct suggests that both may be of diagnostic assistance to the physician in clinical settings in which the history, electrocardiogram or total serum creatine kinase are for some reason not interpretable. These techniques may also prove complementary in furthering the ability to assess the extent of acute myocardial damage and the course of its progression.     

Serum glucagon and insulin levels and their relationship to blood glucose values in patients with acute myocardial infarction and acute coronary insufficiency

Fasting serum glucagon, insulin and glucose levels were determined in 25 patients with acute myocardial infarction 1 day after their admission to the hospital and, in most instances, once again at a later date. Two control groups were used, one with coronary insufficiency but without myocardial infarction (10 patients) and the other without clinically recognizable coronary artery disease (12 patients). Serum glucagon levels were significantly higher in the patients with acute myocardial infarction on admission (121.6 ± 15.3 pg/ml) than in the other two groups and highest in patients with acute myocardial infarction and cardiogenic shock (239.3 ± 31 pg/ml, p < 0.001). Glucagon levels were elevated even in the three patients with cardiogenic shock who were not receiving catecholamines. Serum glucose values were also significantly higher in patients with acute myocardial infarction (155 ± 13.9 mg/100 ml), but serum insulin levels were not significantly different from those in patients with coronary insufficiency. These data suggest that the hyperglycemia of patients with acute myocardial infarction may be in part due to hyperglucagonemia.     

Prognostic value of resting and submaximal exercise radionuclide ventriculography after acute myocardial infarction in high-risk patients with single and multivessel disease

In patients who survive the acute phase of myocardial infarction, those with multivessel coronary artery disease generally have a worse prognosis than those with single-vessel disease. However, some patients with significant multivessel stenoses have a good prognosis, whereas some with a significant single-vessel stenosis have a poor prognosis. Thus, although definition of coronary anatomy may be helpful, it is a not a fail-safe prognosticator. In this retrospective analysis, the association of abnormalities at rest and during submaximal exercise testing with radionuclide ventriculography after acute myocardial infarction with major cardiac complications (death, recurrent infarction, severe angina or congestive heart failure) in the ensuing 6 months was assessed in patients with single and multivessel disease. Coronary angiography and submaximal exercise testing with radionuclide ventriculography were performed within 3 months of each other in 42 patients. Eleven of the 16 patients with single-vessel coronary stenosis had major cardiac complications. The subsequent course of these 16 patients was correctly predicted by left ventricular ejection fraction (LVEF) ≤ 0.40 in 8 patients, by LVEF < 0.55 in 7 patients, by failure of LVEF to increase by 0.05 units in 13 patients, and by an increase in left ventricular end-systolic volume index (LVESVI) during exercise >5% above baseline in 11 patients. Of the 26 patients with multivessel coronary artery disease, 24 had major cardiac complications. The subsequent course of these 26 patients was correctly predicted in 13 by LVEF ≤ 0.40, in 20 by LVEF < 0.55, in 25 by a failure of LVEF to increase by 0.05 units during exercise, and in 20 by an increase in LVESVI by > 5% during exercise. Thus, submaximal exercise testing with radionuclide ventriculography may provide valuable prognostic information concerning the occurrence of major cardiac events after myocardial infarction not only in patients with multivessel disease, but also in those with single-vessel disease. Exercise-induced abnormalities of left ventricular function may have greater prognostic importance than the delineation of coronary arterial anatomy or the assessment of residual left ventricular function at rest.     

Iodine-123 phenylpentadecanoic acid: Detection of acute myocardial infarction and injury in dogs using an iodinated fatty acid and single-photon emission tomography

The ability of an iodinated fatty acid, iodine-123 Phenylpentadecanoic acid (1–123 PPA), and single-photon emission computed tomography (SPECT) to detect myocardium injured by temporary or permanent coronary arterial occlusion was evaluated. In 5 control dogs, 11 dogs that underwent 90 to 120 minutes of fixed left anterior descending coronary artery (LAD) occlusion, and 8 dogs that underwent 90 minutes of temporary LAD occlusion and up to 90 minutes of reflow, 2 to 6 mCi of 1–123 PPA were injected and the dogs were imaged with SPECT. Control dogs showed relatively uniform uptake and clearance of 1–123 PPA in similar left ventricular (LV) regions. Dogs with permanent LAD occlusion were identified by computer algorithm as having regions of decreased 1–123 PPA uptake in the infarct-related area and a reduced rate of 1–123 PPA clearance (−9.4% in infarct sectors [washin], +3.7% in sectors adjacent to the area of infarction, and +15.4% in control LV sectors [p <0.01]). Dogs with temporary LAD occlusion and reperfusion had decreased clearance of 1–123 PPA from the regions with infarction; 1–123 PPA clearance was −5.2 ± 16.4% in infarct sectors, 12.7 ± 7.4% in periinfarct zones, and 30.4 ± 12% in control LV regions. These data demonstrate that tomographic analysis of 1–123 PPA uptake and clearance permits the relatively noninvasive detection of LV myocardium injured by permanent or temporary LAD occlusion and reperfusion.     

Submaximal exercise testing after acute myocardial infarction: myocardial scintigraphic and electrocardiographic observations.

The relation between global and regional left ventricular function and electrocardiographic signs of ischemia at rest and during submaximal supine exercise was studied in 27 patients 2 to 3 weeks after acute myocardial infarction. Dynamic myocardial scintigraphy was performed at rest and during submaximal exercise utilizing an in vivo method of labeling red blood cells with technetium-99m pertechnetate. Gated radionuclide blood pool scintigrams were obtained in a modified left anterior oblique, and in some patients also in the right anterior oblique projection, to measure left ventricular ejection fraction and segmental wall motion. Electrocardiographic monitoring of heart rate and rhythm was provided during the exercise. The submaximal exercise test was terminated when the patient's heart rate reached 125 beats/min or if angina, malignant ventricular ectopy or electrocardiographic evidence of myocardial ischemia developed before this rate was reached. The data demonstrate that patients with a recent anterior myocardial infarct, in contrast to patients with a recent inferior or nontransmural infarct, manifest a significant reduction in left ventricular ejection fraction with submaximal exercise. Of the eight patients with an anterior infarct, seven had segmental wall motion abnormalities at rest. Four of these eight manifested more severe abnormalities with submaximal exercise; three had abnormalities at rest that did not change with exercise. Four of the eight had a positive electrocardiographic response during exercise (two were taking digoxin). Of these four, only two had more marked wall motion abnormalities with effort. Of the 13 patients with an inferior infarct, 11 had apparently normal wall motion in the modified left anterior oblique projection at rest, including 2 who manifested segmental wall motion abnormalities with submaximal exercise; the 2 remaining patients had wall motion abnormalities at rest that, on exercise, became more marked in one and were unchanged in one. Four of the 13 had a positive electrocardiographic response with exercise (one was taking digoxin); only one of these had a detectably more severe wall motion abnormality with exercise. Of the six patients with a nontransmural infarct, four had no identifiable wall motion abnormalities at rest; in one of these, an abnormality developed with exercise. The remaining two patients had wall motion abnormalities at rest; in one, a positive electrocardiographic ischemic response developed with exercise. Patients with an anterior infarct appear to have a different functional ventricular response to submaximal exercise at the time of hospital discharge than patients with an inferior or nontransmural infarct. To identify ischemic responses with submaximal exercise in these patients one should ideally use both electrocardiographic monitoring and dynamic myocardial scintigraphy.     

Intraaortic balloon counterpulsation in patients in cardiogenic shock,medically refractory left ventricular failure and/or recurrent ventricular tachycardia

Of the 27 patients described, 23 were in cardiogenic shock, 2 had severe left ventricular failure, and 2 had medically refractory ventricular tachycardia. Utilizing intraaortic counterpulsation, adequate systemic blood pressure was initially restored in 19 patients. Nine of these were subsequently weaned from circulatory assistance, but only three were discharged from the hospital and are currently alive. The remaining 10 patients who derived initial benefit from circulatory assistance were balloon-dependent in that they could not be weaned from circulatory assistance. Eight of these patients subsequently underwent cardiac catheterization; four had inoperable disease. The remaining four patients underwent surgery for either resection of the area of infarction and/ or for myocardial revascularization; only one survived to subsequently leave the hospital. Ventricular volumes were abnormal and ejection fractions were below 30 per cent in all the patients in cardiogenic shock except one who underwent cardiac catheterization and ultimately died. Ejection fractions were greater than 30 per cent in the two patients with cardiogenic shock who were weaned from balloon support and survived to leave the hospital without surgery. Both of these patients had inferior myocardial infarction. The data obtained from this experience suggest that intraaortic counterpulsation is a very useful adjunct to currently existing medical measures to treat both cardiogenic shock and medically refractory left ventricular failure but that most patients have such extensive disease that they can neither be weaned from balloon support nor undergo successful infarctectomy or myocardial revascularization.     

Effect of verapamil and nifedipine on left ventricular function at rest and during exercise in patients with Prinzmetal''s variant angina pectoris

To assess the effects of verapamil and nifedipine on left ventricular function at rest and during exercise in patients with Prinzmetal's variant angina pectoris, 10 patients (6 men and 4 women with a mean age of 52 years) with variant angina were each treated for 2 month periods with placebo, verapamil (400 ± 80 mg/day, mean ± standard deviation [SD]) and nifedipine (82 ± 31 mg/day). During the final week of each 2 month treatment period equilibrium gated blood pool scintigraphy was performed at rest and during exercise. At rest, heart rate during verapamil therapy was lower than during treatment with nifedipine; systolic blood pressure and left ventricular volumes and ejection fraction were similar for the three interventions. The maximal work load achieved was similar during placebo, verapamil and nifedipine therapy. At the maximal work load common to all three exercise studies, heart rate and systolic blood pressure were lower with verapamil than with placebo and nifedipine; ventricular volumes and ejection fraction were similar with the three agents. Thus, in patients with variant angina and a wide range of left ventricular function at rest, neither verapamil nor nifedipine significantly alters left ventricular volumes or ejection fraction at rest or during exercise.     

Measurement of myocardial infarct size by technetium pyrophosphate single-photon tomography

The primary determinant of prognosis after acute myocardial infarction (AMI) is the size of the acute infarct. The present study evaluates 46 patients with different infarct distributions and sizes to test the hypothesis that single photon emission computed tomography with technetium-99m pyrophosphate (Tc-99m-PPi) and blood pool overlay allows measurements of AMI size that provide insight into prognosis irrespective of infarct location. Identical Tc-99m-PPi and ungated blood pool projections were acquired over 180 degrees with a rotating gamma camera. Reconstructed sections were color-coded and superimposed for purposes of infarct localization. Areas of increased pyrophosphate uptake within myocardial infarcts were thresholded at 65% of peak activity. The blood pool was thresholded at 50% and subtracted so as to determine an endocardial border for the left ventricle. Using this method, myocardial infarcts weighed 2.5 to 81.2 g. The correlation of infarct mass with prognosis showed that patients without previous AMI and with acute infarcts that weighed more than 40 g had an increased frequency of death and congestive heart failure (p less than 0.001). The correlation of measured infarct mass with peak serum creatine kinase level was significant (r = 0.83, p less than 0.001; y = 0.015x + 13.20). The correlation coefficients for anterior, inferior and nontransmural AMI were not significantly different from those for the entire group. In conclusion, tomographically determined infarct mass data correlate with subsequent clinical prognosis, and Tc-99m-PPi tomography with blood pool overlay is a safe and effective means of sizing infarcts in patients with AMI.     

Measurement of myocardial infarction fraction using single photon emission computed tomography

Although infarct size correlates generally with prognosis after acute myocardial infarction, an absolute measure of infarct size may have differing prognostic significance depending on absolute left ventricular mass. To test the hypothesis that single photon emission computed tomography can accurately measure myocardial infarct size as a percent of total left ventricular mass ("infarction fraction"), thallium-201 and technetium-99m pyrophosphate tomograms were acquired in 21 dogs 24 to 48 hours after fixed occlusion of the left anterior descending or circumflex coronary artery. Pathologic infarct weight was measured as the myocardial mass that showed no staining with triphenyltetrazolium chloride. Scintigraphic infarct mass by technetium-99m pyrophosphate was calculated from the total number of left ventricular volume elements (voxels) demonstrating technetium-99m pyrophosphate uptake X voxel dimension [( 0.476 cm]3) X specific gravity of myocardium (1.05 g/cm3). Scintigraphic left ventricular mass was calculated in a similar fashion using an overlay of the thallium-201 and technetium-99m pyrophosphate scans. The "infarction fraction" was calculated as: infarction fraction = infarct mass/left ventricular mass. There was good correlation between single photon emission computed tomography and pathologic measurements of infarct mass (technetium-99m pyrophosphate mass = 1.01 X pathologic infarct mass + 0.96; r = 0.98), left ventricular mass (single photon emission computed tomographic left ventricular mass = 0.60 X pathologic left ventricular mass + 37.4; r = 0.86) and "infarction fraction" (single photon emission computed tomographic infarction fraction = 1.09 X pathologic infarction fraction - 1.7; r = 0.94).(ABSTRACT TRUNCATED AT 250 WORDS)     

Measurement of infarct size in acute canine myocardial infarction by single-photon emission computed tomography with technetium-99m pyrophosphate

The location and extent of myocardial infarction (MI) are important predictors of patient course. The current study tests the hypothesis that MI size could be measured accurately using rotating gamma camera single-photon emission computed tomography ( SPECT ) and technetium-99m pyrophosphate (PPi) and that the accuracy of these measurements was independent of MI location and transmural or nontransmural distribution. SPECT was performed in 38 dogs 48 hours after ligation of the left anterior descending coronary artery (14 dogs) or left circumflex coronary artery (LC) (24 dogs) at the mid-level or below. Projection images were corrected for center-of-rotation and field nonuniformity and processed with a 1-dimensional low-pass filter to diminish rib activity. Sixteen 0.5-cm-thick transverse sections, including the entire left ventricle, were reconstructed by filtered backprojection , low-pass filtered, contrast enhanced and processed with a 3-dimensional boundary enhancement operator. The boundary of PPi uptake in each slice was marked automatically using an algorithm that combined a directional derivative and a threshold, and required continuity of the boundary in 3 dimensions. The total number of volume elements that showed abnormal tracer uptake were summed, corrected to absolute volume, and multiplied by the specific weight of cardiac muscle. Scintigraphic MI weight was compared with pathologic MI weight. There was an excellent correlation between scintigraphic and pathologic MI weight. The poorer correlation for nontransmural compared with transmural MIs is most likely a function of size alone, since MIs that weighed less than 10 g (n = 12, range 1.3 to 9.5 g), both transmural and nontransmural, showed a similar correlation: S = 1.07 X P + 0.56 (r = 0.81, standard error of the slope = 0.245).(ABSTRACT TRUNCATED AT 250 WORDS)     

Tomographic gated blood pool radionuclide ventriculography: analysis of wall motion and left ventricular volumes in patients with coronary artery disease

The use of planar radionuclide ventriculography to evaluate global and segmental ventricular function is limited by the superimposition of structures in some projections and the gross segmental resolution of the planar technique. Preliminary reports have suggested the feasibility of tomographic gated radionuclide ventriculography with rotating detector systems. This study tested the hypotheses that 1) tomographic radionuclide ventriculography detects segmental dysfunction at rest not identified with multiview planar studies and single plane contrast ventriculography, and 2) ventricular volumes and ejection fraction calculated from these studies provide data similar to those obtained with angiography and planar radionuclide ventriculography. Gated blood pool tomograms were acquired over 180 degrees at 15 frames per cardiac cycle during the initial 90% of the cardiac cycle. Compared with the multiview planar technique tomographic ventriculography showed an increased sensitivity for detecting left ventricular segments with significant coronary artery stenosis (97 versus 74%, p less than 0.025) without any loss in specificity. Compared with both planar radionuclide and contrast ventriculography, tomographic radionuclide ventriculography also detected more noninfarcted left ventricular segments supplied by stenosed coronary arteries (81 versus 39 and 32%, respectively, p less than 0.01). Tomographic radionuclide ventriculographic measurements of left ventricular volumes and ejection fraction showed close correlations with angiographic and planar radionuclide determinations. Gated blood pool tomography is a sensitive method for the evaluation of segmental wall motion and an accurate method for the measurement of global left ventricular volumes and ejection fraction.     

Value of radionuclide ventriculography in the immediate characterization of patients with acute myocardial infarction

The ability of admission radionuclide ventriculography to discriminate among various clinical subsets was evaluated in patients with acute myocardial infarction. One hundred patients with acute myocardial infarction were evaluated within 8 ± 3.1 hours (mean ± standard deviation) after the onset of chest pain. Forty-one patients were in Killip functional class I, 52 in class II and 7 in class III. The mean radionuclide left ventricular ejection fraction was significantly lower in patients with higher Killip classification because of significant elevation of mean left ventricular end-systolic volume rather than significantly altered mean end-diastolic volume. Killip classification frequently failed to correlate with ejection fraction in individual cases. Admission chest X-ray findings were categorized according to the presence of findings suggestive of impaired left ventricular function. Mean left ventricular ejection fraction was significantly lower in patients with abnormal than in patients with normal chest X-ray findings because of significant elevations in both mean end-diastolic and end-systolic volumes. The chest X-ray findings frequently failed to correlate with ejection fraction in individual cases.Stepwise linear regression analysis was employed to analyze the ability of historical, physical, electrocardiographic and chest X-ray findings to predict radionuclide left ventricular ejection fraction. The most predictive variables in order of decreasing significance were anterior myocardial infarction, abnormal chest X-ray findings, rales to two thirds of the posterior thorax, previous myocardial infarction, transmural myocardial infarction and heart rate greater than 100 beats/min. However, even these six optimal predictive variables could explain only 42 percent of the observed variability in left ventricular ejection fraction. Thus, early radionuclide ventriculography adds significantly to the discriminant power of clinical and radiographic characterization of ventricular function in patients with acute myocardial infarction.     

Short- and long-term influence of beta-adrenergic antagonists after acute myocardial infarction

After coronary arterial occlusion, catecholamines are released from storage depots in the left ventricle and injured myocardial cells are exposed to relatively high concentrations of catecholamines during the evolutionary period in which cell injury is becoming progressively more severe. In addition, in experimental animal models, there is a substantial increase in beta-adrenergic receptor density without any alteration in affinity within 1 hour of permanent coronary arterial occlusion. Recent data suggest that alpha-adrenergic receptor density increases within 30 to 60 minutes after coronary arterial occlusion in experimental animal models. The administration of catecholamines during the early phases of evolving myocardial injury can result in heightened adrenergic biochemical responses in severely injured compared with normally perfused tissue in the hearts of experimental animals. Thus, there is adequate rationale for anticipating that beta-adrenergic antagonists would protect ischemic myocardium and potentially reduce the incidence of life-threatening arrhythmias in individuals with evolving acute myocardial infarction (AMI). Studies in animal models demonstrate that the administration of beta-adrenergic antagonists in the first few minutes after coronary artery occlusion may reduce the ultimate extent of myocardial necrosis. Clinical data from several different trials in which beta-adrenergic antagonists were administered to (1) protect ischemic myocardium and preserve ventricular function and (2) reduce the severity of serious ventricular arrhythmias in patients with AMI are reviewed. The effects of longer-term administration of beta-adrenergic antagonists in patients after AMI in prolonging life and reducing risk of reinfarction are presented.     

Determination of left ventricular mass by single-photon emission computed tomography with thallium-201

To test the hypothesis that single-photon emission computed tomography (SPECT) might permit accurate, noninvasive measurement of LV mass, SPECT measurements of LV mass to LV weight were compared in 20 mongrel dogs. Projection images of the left ventricle were acquired after intravenous injection of thallium-201 (TI-201). Transverse sections were reconstructed using filtered backprojection. Coronal sections were extracted from the reconstructed volume. The boundary of LV uptake of TI-201 in each coronal section was defined automatically using a threshold detector. Scintigraphic LV mass [total number of volume elements (voxels) showing TI-201 uptake X voxel volume X specific gravity of myocardium] was compared to actual LV weight. There was good correlation between scintigraphic LV mass and LV weight. Mean LV weight was 68 +/- 20 g (+/- standard deviation) (range 27 to 94). Mean SPECT LV mass was 66 +/- 19 g (range 28 to 100). Linear regression analysis yielded the following relation: SPECT LV mass = 0.87 X LV weight + 6.79 (r = 0.91, root-mean-square deviation from regression = 7.5). SPECT measurements were reproducible, with a coefficient of variation of 0.24%. Thus, SPECT of LV TI-201 distribution can be used to measure LV mass in canine myocardium.