Time to therapy and salvage in myocardial infarction

OBJECTIVES

This study sought to examine the influence of time to reperfusion on myocardial salvage.

BACKGROUND

Major trials of reperfusion therapy for myocardial infarction (MI) have demonstrated improved outcome for patients achieving earlier reperfusion. However, some patients experience significant benefit despite delayed reperfusion.

METHODS

Fifty-five patients with a first anterior MI underwent successful reperfusion therapy (angioplasty or thrombolysis). Technetium-99m (Tc-99m) sestamibi was injected before reperfusion therapy and again at hospital discharge to determine the myocardial salvage index for each patient. Residual flow to the infarct territory was assessed by the nadir of the Tc-99m sestamibi count-profile curve.

RESULTS

The salvage index showed wide variability (range -0.04 to 1.0), and extreme values were seen in 34.5% of the group (<0.10 in 9%, >0.90 in 25%). A high salvage index was associated with reperfusion therapy before 2 h (p=0.02) or good residual blood flow (p < 0.01). For the 10 patients who received reperfusion therapy within 2 h, residual blood flow was not correlated with salvage (p=0.12). For the 45 patients treated after 2 h, residual blood flow correlated significantly with salvage (r=0.57, p < 0.0001). There was a significant interaction (p < 0.05) between residual blood flow and time to therapy, indicating that the effect of each variable on salvage depended on the value of the other. Multiple historic and hemodynamic variables were examined, but none demonstrated any association with residual flow or myocardial salvage.

CONCLUSIONS

In patients with acute MI, successful reperfusion therapy within 2 h is associated with the greatest degree of myocardial salvage. For patients treated after 2 h, residual blood flow to the infarct-related territory appears to be the most important determinant of myocardial salvage.

Influence of patient height and weight and type of stress on myocardial count density during SPECT imaging with thallium-201 and technetium 99m-sestamibi

BACKGROUND

The aim of this study was to determine the variability in myocardial activity with 99mTc-labeled sestamibi and 201Tl tomographic imaging, and to correlate this variability with patient anthropometric data and type of stress.

METHODS AND RESULTS

Conventional tomographic acquisition (all-purpose collimator, 30 views, 40 sec/view) was performed in 249 patients (155 with 99mTc-sestamibi, 84 with 201Tl). Normal myocardium was identified in three short-axis tomographic slices between the base and mid-ventricle. To exclude abnormal myocardium, all myocardial activity below an 85% threshold of peak counts was excluded. The average counts per pixel in the remaining myocardium was determined. All data were normalized to a collimator sensitivity of 8.1 counts/min/kBq and corrected for decay. Myocardial count densities in both 201Tl and 99mTc-sestamibi studies exhibited a high degree of variability and varied by factors of 3 to 4 and 2.5 to 3 respectively, between the 10th and 90th percentile of count densities. All 99mTc-sestamibi studies showed an inverse correlation (R approximately 0.7) between myocardial count density and patient weight. For stress 201Tl studies in male patients, a similar inverse correlation (R = 0.63) was found between patient weight and myocardial count density. No correlation was found for female patients. For rest 99mTc-sestamibi studies, the average myocardial count density was 1245 +/- 297 counts/pixel for a 1.11 GBq (30 mCi) injection. This was similar with pharmacologic stress (1224 +/- 297 counts/pixel per 1.11 GBq (30 mCi), but significantly higher with exercise (1569 +/- 363 counts/pixel per 1.11 GBq (30 mCi) (p < 0.005). 201Tl studies averaged 327 +/- 97 counts/pixel (111 MBq [3 mCi] injection) with exercise and 374 +/- 145 counts/pixel/111 MBq (3 mCi) with pharmacologic stress (p = NS). Redistribution studies after exercise/pharmacologic stress (with a 37 MBq [1 mCi] reinjection) averaged 267 +/- 83 counts/pixel (148 MBq [3+1 mCi]).

CONCLUSIONS

Measured count densities in the myocardium demonstrate a high degree of variability that is only weakly correlated with patient anthropometric data. Nevertheless, knowledge of the mean values of myocardial activity as a function of administered dose may be useful in the optimization of rapid imaging procedures for 99mTc-based perfusion agents.

Prognostic value of vasodilator myocardial perfusion imaging in patients with left bundle-branch block

BACKGROUND

The prognostic value of tomographic myocardial perfusion imaging with dipyridamole or adenosine in patients with left bundle-branch block has not been established.

METHODS AND RESULTS

The study group consisted of 245 patients with left bundle-branch block who underwent tomographic (single photon emission tomography) myocardial perfusion imaging with thallium-201 (n=173) or technetium-99m sestamibi (n=72) and either dipyridamole (n=153) or adenosine (n=92) stress. Patients were prospectively classified into two groups. Patients were classified as "high risk" if they had (1) a large severe fixed defect (n=28), (2) a large reversible defect (n=36), or (3) cardiac enlargement and either increased pulmonary uptake (thallium) or a decreased resting ejection fraction (sestamibi) (n=20). The remaining 161 patients (66% of the study group) were at "low risk." Follow-up was 99% complete at 3+/-1.4 years. Three-year overall survival was 57% in the high-risk group compared with 87% in the low-risk group (P<.0001). Survival free of cardiac death/nonfatal myocardial infarction/cardiac transplantation was 55% in the high-risk group and 93% in the low-risk group (P<.0001). The presence of a high-risk scan had significant incremental prognostic value after adjustment for age, sex, diabetes, and previous myocardial infarction (P<.0001). Patients with a low-risk scan had an overall survival that was not significantly different from that of a US age-matched population (P=.86).

CONCLUSIONS

Tomographic myocardial perfusion imaging with adenosine or dipyridamole stress provides important prognostic information in patients with left bundle-branch block, which is incremental to clinical assessment.

Prognostic value of exercise thallium-201 imaging in a community population

BACKGROUND

The prognostic value of exercise thallium-201 imaging has been well established in referral patient populations at tertiary care centers, but these results may be influenced by referral bias.

METHODS

This study was performed to evaluate the prognostic value of thallium imaging in a community-based population of 446 residents of Olmsted County, Minn. Eleven variables were prospectively selected and tested for their associations with outcome end points.

RESULTS

Four variables (age, history of myocardial infarction, number of abnormal thallium segments on the postexercise images, and increased thallium lung uptake) contained the most independent prognostic information. For the end point overall mortality rate, the multivariate chi-square values were 17.2 (p < 0.0001) for age and 20.9 (p < 0.0001) for the number of abnormal thallium segments on the postexercise images. Five-year survival rate for patients older than the median age of 59 years with an abnormal scan was 84% versus 97% for patients < or = 59 years of age with a normal scan.

CONCLUSION

Exercise thallium imaging was useful for prognostic purposes in this relatively low-risk community population, confirming the findings of referral population studies.

Clinical determinants of hemodynamic and symptomatic responses in 2,000 patients during adenosine scintigraphy

OBJECTIVE

To determine whether subsets of patients referred for a clinically indicated radionuclide adenosine stress study respond differently to a standard infusion of adenosine.

MATERIAL AND METHODS

We assessed multiple clinical and hemodynamic variables in the first 2,000 patients who underwent adenosine perfusion studies in our laboratory. A relevant clinical variable was defined as one that was significantly associated with changes in heart rate and blood pressure during adenosine infusion. Relevant clinical variables that were most significantly related to hemodynamic variables included age, gender, rhythm (atrial fibrillation), diabetes, and left ventricular function. These variables were then related to symptomatic responses (adverse effects) to adenosine infusion. To determine whether the different peripheral responses to adenosine reflected clinically important differences in coronary vasodilatation, we compared perfusion imaging with coronary angiographic findings in the 408 patients who underwent both studies within 6 months of each other.

RESULTS

The decrease in systolic blood pressure was greater and the reflex tachycardia was less in patients 70 years of age or older and in those with insulin-dependent diabetes in comparison with younger patients and those without type 1 diabetes. Men had smaller decreases in blood pressure and smaller increases in heart rate than did women. Patients with atrial fibrillation and those with left ventricular ejection fraction less than 40% had smaller decreases in blood pressure and smaller increases in heart rate than did those in sinus rhythm or those with an ejection fraction of 40% or more. Age 70 years or older, male gender, atrial fibrillation, and left ventricular ejection fraction less than 40% were associated with fewer symptoms and less severe chest pain in comparison with patients without these variables. For patients with coronary angiograms, the relationship between coronary artery disease evident on angiography and perfusion abnormalities noted on scintigraphy was not different for any of the relevant clinical variables.

CONCLUSION

Common clinical patient subsets are associated with different peripheral hemodynamic and symptomatic responses to infusion of adenosine. Despite these observations, however, the ability to detect coronary artery disease with perfusion imaging is not obviously altered.

Prognostic value of exercise thallium-201 imaging performed within 2 years of coronary artery bypass graft surgery

OBJECTIVES

We sought to determine the prognostic capabilities of exercise thallium (Tl)-201 tomographic imaging performed relatively early (within 2 years) after coronary artery bypass graft surgery (CABG).

BACKGROUND

Exercise testing is commonly performed after CABG, but few data exist demonstrating its prognostic value in this setting.

METHODS

Four hundred eleven patients were followed up for a median duration of 5.8 years. Eleven prospectively chosen clinical, exercise and Tl-201 variables were tested for their associations with outcome end points by means of proportional hazards regression models.

RESULTS

During follow-up there were 60 deaths from any cause, 53 initial cardiac deaths or nonfatal myocardial infarctions (MIs) and 22 late (>3 months after the Tl-201 study) revascularization procedures. The number of abnormal Tl-201 segments on the postexercise image was the only variable in the multivariate analyses to show a significant association with all three outcome end points: chi-square 7.3, p = 0.007 for overall mortality; chi-square 8.1, p = 0.004 for cardiac death or MI; chi-square 7.8, p = 0.005 for any cardiac event. Other independent predictors of outcome were exercise duration (chi-square 10.7, p = 0.001) and age (chi-square 3.9, p = 0.049) for overall mortality and exercise angina score (chi-square 8.7, p = 0.003) for cardiac death or MI. The 5-year survival rate free of cardiac death or MI was 93% for patients without angina and a normal image or small postexercise perfusion defect versus 71% for patients with angina and a medium or large defect.

CONCLUSIONS

Exercise Tl-201 imaging performed within 2 years of CABG can stratify patients into low and high risk subgroups.

An optimal dual-size vial system for the cost-effective usage of Adenoscan

BACKGROUND

Adenoscan (Fujisawa USA, Inc., Deerfield, Ill.) has been initially packaged in a 30 ml glass vial for single use only because it contains no preservative. This restricted usage has generated considerable waste and high cost for the patient. Although the new 20 ml vial of Adenoscan provides some reduction in waste, the savings offered by the 20 ml and 30 ml vial system is still not optimal. The purpose of this study was to investigate an optimal dual-size vial system that would provide limited amounts of waste while maintaining its practicality to satisfy different patient populations.

MATERIALS AND RESULTS

The least waste for each potential combination (n = 344) of two vials was calculated by assuming that patient weights (30 to 200 kg) follow a normal distribution. The 6 ml and 15 ml vial combination had the least expected waste for lighter patient populations, and the 9 ml and 15 ml vial system had the least expected waste for heavier populations. The calculated wastes for 4207 patients (83 +/- 19 kg) undergoing adenosine stress myocardial perfusion studies at the Mayo Clinic were 10.5 +/- 9.3 ml (30 ml vial), 5.1 +/- 2.9 ml (20 ml and 30 ml vial system), 1.6 +/- 1.0 ml (6 ml and 15 ml vial system), and 1.8 +/- 1.2 ml (9 ml and 15 ml vial system).

CONCLUSIONS

In general, both the 6 ml and 15 ml and 9 ml and 15 ml vial systems perform better than either the single 30 ml vial or the 20 ml and 30 ml vial system. Furthermore, the 6 ml and 15 ml vial combination offers the lowest expected waste for the actual patient population that underwent the adenosine stress myocardial perfusion imaging studies at our institution.

Prevalence of spontaneous reperfusion and associated myocardial salvage in patients with acute myocardial infarction

This study sought to determine the prevalence of spontaneous reperfusion of an infarct-related artery (IRA) and associated myocardial salvage in the absence of thrombolysis or angioplasty. Twenty-one patients with acute myocardial infarction received only heparin and aspirin. At a median of 18 hours after presentation, 12 patients (57%) had angiographic patency of the IRA. Technetium-99m sestamibi was injected acutely on presentation and again at hospital discharge. Acute and final perfusion defect sizes were measured. Their difference, myocardial salvage, was calculated along with salvage index (myocardial salvage/acute defect). Comparing patients with a patent versus occluded IRA, myocardium at risk was similar (16% +/- 12% vs 12% +/- 9% left ventricle, p = NS); however, myocardial salvage (9% +/- 9% vs -2% +/- 7% left ventricle, p = 0.01), and salvage index (0.62 +/- 0.37 vs 0.19 +/- 0.33, p = 0.01) were greater in patients with spontaneous reperfusion. Resolution of chest pain was greater in patients with a patent IRA (100% vs 55%, p = 0.003). Spontaneous reperfusion of the IRA occurs frequently in patients with acute myocardial infarction and is associated with significant myocardial salvage.

Intercenter variability in outcome for patients treated with direct coronary angioplasty during acute myocardial infarction

BACKGROUND

Direct coronary angioplasty is an effective therapy for acute myocardial infarction, but its success may be dependent on both ready availability and operator skill. The purpose of this study was to investigate the impact of the center performing direct coronary angioplasty for acute myocardial infarction while controlling for parameters known to affect outcome.

METHODS AND RESULTS

The study group consisted of 99 patients with ST elevation who were treated with direct angioplasty in four high-volume centers. Patients were injected with technetium-99m sestamibi intravenously and then taken to the cardiac catheterization laboratory. Antegrade flow was graded before and after direct coronary angioplasty. Single photon emission computed tomography was performed 1 to 6 hours after injection to measure myocardium at risk and residual blood flow to the jeopardized zone using previously published quantitative methods. A repeat sestamibi injection and tomographic acquisition were performed at hospital discharge to measure actual infarct size. There were no significant differences by center for baseline clinical characteristics, mean myocardium at risk (29% to 37% left ventricle [LV]), time to reperfusion (3.1 to 4.1 hours), residual blood flow, infarct location, or antegrade flow. Despite these similarities, there were differences in outcome measures by center. Mean infarct size was as follows: center 1, 15%; center 2, 12%; center 3, 10%, center 4, 23% (all LV; p = 0.11 ). Mean left ventricular ejection fraction at discharge also demonstrated significant differences: center 1, 0.57; center 2, 0.47; center 3, 0.53; center 4, 0.47 (p = 0.002). The prevalence of Thrombolysis in Myocardial Infarction grade 3 flow after angioplasty significantly differed by center: center 1, 92%; center 2, 94%; center 3, 87%; center 4, 71 %; (p = 0.01). There was a low mortality rate for all four centers ranging from 0% to 6%. After adjustment for myocardium at risk, residual blood flow, and time to reperfusion, the primary outcome of the center where the angioplasty was performed was an independent determinant of both infarct size and left ventricular ejection fraction.

CONCLUSION

The success of direct coronary angioplasty in reducing infarct size and preserving left ventricular function depends on the center performing the procedure. Direct measurement of the effectiveness of this reperfusion modality in community practice is required to assess the impact of this effect.

Coronary endothelial dysfunction in humans is associated with myocardial perfusion defects

BACKGROUND

Coronary endothelial dysfunction may occur in patients with minimally obstructive coronary artery disease and angina, and potentially may cause myocardial ischemia.

METHODS AND RESULTS

Coronary endothelium-dependent vasodilation was examined in patients with angina and <50% coronary artery diameter (CAD) stenosis by selectively infusing acetylcholine (10(-6) mol/L to 10(-4) mol/L) into the left anterior descending coronary artery (LAD). Percent change in CAD (%deltaCAD) was measured by quantitative coronary angiography, and percent change in coronary blood flow (%deltaCBF) was calculated using intracoronary flow Doppler. Coronary endothelium-independent vasodilation was examined using intracoronary adenosine and nitroglycerin. 99mTc sestamibi was injected intravenously just prior to the infusion of the highest dose of acetylcholine. Patients were divided blindly into three groups: Perfusion defects in non-LAD territory (group 1, n=6), no perfusion defects (group 2, n=7), and perfusion defects in the LAD territory (group 3, n=7). All patients had intact endothelium-independent vasodilation. In group 1, perfusion defects outside the LAD territory reflected an increase in %deltaCAD and %deltaCBF by 24+/-5% and 241+/-46% in the LAD. In group 2, %deltaCAD decreased by 26+/-5%, but %deltaCBF increased by 54+/-17%. In group 3, perfusion defects were within the LAD territory, reflecting a decrease in %deltaCAD and %deltaCBF by 35+/-5% and 51+/-14%, respectively.

CONCLUSIONS

This study demonstrates that coronary endothelial dysfunction in humans may be temporally associated with myocardial perfusion defects and supports a role for the coronary epicardial and microcirculation endothelium in regulating myocardial perfusion. Myocardial ischemia may occur in humans with impaired endothelium-dependent coronary flow reserve of the coronary epicardial and microcirculation.

Predictive power of the relative lymphocyte concentration in patients with advanced heart failure

BACKGROUND

The physiological stress suffered by patients with heart failure results in an increased production of cortisol and a shift in the leukocyte differential toward a decreased percentage of lymphocytes (%L). The purpose of this study was to determine the prognostic significance of a low %L in advanced heart failure.

METHODS AND RESULTS

Patients evaluated in our cardiac transplantation clinic between April 1988 and July 1995 were retrospectively reviewed (n=263). Fifty-two patients were excluded because they had recent trauma, infection, surgery, myocardial infarction, corticosteroid use, or history of malignancy. In the remaining 211 patients, we used Cox proportional hazards analysis to examine the association between survival and transplant-free survival with baseline variables. Univariate analysis showed a significant association between time to death and %L (P=.004), New York Heart Association (NYHA) class (P=.002), and maximal oxygen uptake (P=.05). Univariate analysis of the end point of survival free from transplantation yielded similar results. One- and 4-year survival rates for patients with a low %L (<20.3%) were 78% and 34% compared with 90% and 73% for those with a normal %L. Multivariate analysis showed NYHA class (P<.008) and %L (P<.01) were independent predictors of survival and survival free from cardiac transplantation.

CONCLUSIONS

The relative lymphocyte concentration is an inexpensive, readily available, simple prognostic marker in patients with symptomatic heart failure who do not have recent trauma, infection, surgery, myocardial infarction, corticosteroid use, or history of malignancy. It could be incorporated into clinical models to predict patient outcome and to aid in the selection of patients for cardiac transplantation.

Association between anterior ST depression and increased myocardial salvage following reperfusion therapy in patients with inferior myocardial infarction

PURPOSE

To determine electrocardiographic features associated with myocardial salvage following reperfusion therapy in patients with inferior myocardial infarction.

PATIENTS AND METHODS

Ninety-two consecutive patients with acute inferior myocardial infarction were treated with reperfusion therapy in a tertiary care center. Several features were measured on the presenting electrocardiogram, including the presence or absence of ST depression in the chest leads and the total magnitudes of ST elevation or depression, and were then evaluated for their association with myocardial salvage. Myocardial salvage (% of left ventricle) was the difference between myocardium at risk and final infarct size. Tomographic myocardial perfusion imaging with technetium-99m sestamibi was performed acutely to measure myocardium at risk and repeated prior to hospital discharge to measure final infarct size.

RESULTS

The amount of myocardium at risk of infarction in the 92 patients was 19.1%+/-11.3% (range 1% to 68%), and the final infarct size was 10.6%+/-10.0% (range 0% to 45%). Thus, myocardial salvage in the 92 patients was 8.5%+/-8.4% (range -11% to 35%) of the left ventricle, or 0.51+/-0.38 (range 0.0 to 1.0) when expressed as a fraction of the myocardium at risk (salvage index). The presence or absence of anterior ST depression was the only one of seven electrocardiographic variables that was associated with myocardial salvage. Myocardial salvage was significantly greater in patients with anterior ST depression compared with those without it (10.6%+/-9.0% versus 5.9%+/-6.7%, P=0.025). Myocardium at risk was significantly greater in patients with anterior ST depression compared with those without the depression (22.8%+/-12.2% versus 14.6%+/-8.3%, P=0.0006), and infarct size tended to be larger (12.1%+/-10.4% versus 8.7%+/-9.4%, P=0.10). Myocardial salvage as a fraction of the myocardium at risk (salvage index) was similar between the two patient groups (0.52+/-0.37 versus 0.50+/-0.39, P=NS).

CONCLUSION

The presence of anterior ST depression during inferior myocardial infarction identifies a group of patients with the potential for greater myocardial salvage with reperfusion therapy. Such patients derive greater absolute benefit from reperfusion therapy because they have a larger amount of myocardium at risk, although their response to therapy (salvage index) is not intrinsically different.

Prognosis in patients with spontaneous chest pain, a nondiagnostic electrocardiogram, normal cardiac enzymes, and no evidence of severe resting ischemia by quantitative technetium 99m sestamibi tomographic imaging

BACKGROUND

There are limited data addressing the outcome of patients with normal or near normal myocardial perfusion during chest pain at rest. The purpose of this study was to determine the prognosis of patients with spontaneous chest pain, a normal or nondiagnostic electrocardiogram, no enzymatic evidence of myocardial infarction, and no evidence of severe resting ischemia by quantitative technetium 99m (99mTc) sestamibi imaging.

METHODS

In the study, 111 patients who fulfilled the above criteria were injected with 99mTc sestamibi during resting chest pain and were followed for a median 2.7 years. Of the patients in the study group, 58% had coronary artery disease that was documented by clinical history or coronary angiography. Tomographic 99mTc perfusion images were interpreted with a quantitative threshold technique initially developed to detect severely hypoperfused myocardium. The images were also interpreted qualitatively to detect patients with milder degrees of hypoperfused myocardium.

RESULTS

During follow-up 3 patients had cardiac deaths, 5 had nonfatal myocardial infarctions, and 21 underwent revascularization procedures (13 within 3 months and 8 more than 3 months after the sestamibi study). At 3 years, survival free of cardiac death was 97%, survival free of cardiac death or myocardial infarction was 91%, and survival of cardiac death, myocardial infarction, or late revascularization was 82%. Quantitative analysis of the scans revealed that 100% of patients without fixed defects had 3-year survival free of cardiac death versus 76% of patients who had fixed defects (p < 0.001). Mild to moderate resting ischemia by qualitative interpretation of the scans was present in 20% of patients, but this did not predict outcome.

CONCLUSIONS

Patients with spontaneous chest pain and nonischemic quantitative 99mTc sestamibi images were at reasonably low risk for hard cardiac events although some patients (18%) required revascularization.

Comparison of primary coronary angioplasty and intravenous thrombolytic therapy for acute myocardial infarction: a quantitative review

OBJECTIVE

To provide a quantitative review of the treatment effects of primary coronary angioplasty vs intravenous thrombolysis for acute myocardial infarction.

DATA SOURCES

Ten randomized trials were identified through computerized bibliographic search of MEDLINE from January 1985 through March 1996 and by queries of principal investigators.

STUDY SELECTION

Single-center and multicenter randomized trials comparing primary angioplasty with intravenous thrombolytic therapy among 2606 patients were included. Four trials compared angioplasty with streptokinase, 3 compared angioplasty with a 3- to 4-hour infusion of tissue-type plasminogen activator, and 3 compared angioplasty with "accelerated" administration of tissue-type plasminogen activator over 90 minutes.

DATA EXTRACTION

Each investigator provided definitions and exact data for outcome events. Odds ratios (ORs), 95% confidence intervals (CIs), and P values were calculated using exact tests for categorical data.

DATA SYNTHESIS

Mortality at 30 days or less was 4.4% for the 1290 patients treated with primary angioplasty compared with 6.5% for the 1316 patients treated with thrombolysis (34% reduction; OR, 0.66; 95% CI, 0.46-0.94; P=.02). The effect was similar among thrombolytic regimens, and no subgroup demonstrated a significant reduction in death. The rates of death or nonfatal reinfarction were 7.2% for angioplasty and 11.9% for thrombolytic therapy (OR, 0.58; 95% CI, 0.44-0.76; P<.001). Angioplasty was associated with a significant reduction in total stroke (0.7% vs 2.0%; P=.007) and hemorrhagic stroke (0.1% vs 1.1%; P<.001).

CONCLUSIONS

Based on outcomes at hospital discharge or 30 days, primary angioplasty appears to be superior to thrombolytic therapy for treatment of patients with acute myocardial infarction, with the proviso that success rates for angioplasty are as good as those achieved in these trials. Data evaluating longer-term outcomes, operator experience, and time delay before treatment are needed before primary angioplasty can be universally recommended as the preferred treatment.

Prospective identification of myocardial stunning using technetium-99m sestamibi-based measurements of infarct size

OBJECTIVES

We sought to prospectively identify patients with stunning and hyperkinesia at hospital discharge on the basis of mismatches between left ventricular (LV) function and infarct size as assessed by technetium-99m (Tc-99m) sestamibi perfusion tomographic imaging.

BACKGROUND

Mechanical indexes of LV function may not accurately reflect myocardial damage after acute myocardial infarction (MI) because of myocardial stunning and compensatory hyperkinesia in noninfarct-related territories. Myocardial perfusion techniques are unaffected by these variables.

METHODS

Eighty-four patients with acute MI underwent hospital admission and discharge Tc-99m-sestamibi tomographic imaging. Global LV ejection fraction (LVEF) was measured at hospital discharge and 6 weeks later. The perfusion defect size was quantified and expressed as a percentage of the LV. The discharge perfusion defect, which is a measure of infarct size, was used to predict the 6-week LVEF for each patient based on a previously reported regression equation. Patients were classified into one of three groups depending on whether their LVEF at hospital discharge fell within, above or below one standard error (6.8 LVEF points) of the predicted 6-week LVEF.

RESULTS

There were 48 patients classified as having a "match" between function and infarct size; these patients demonstrated no significant change in LVEF at 6 weeks. There were 21 patients (25%) classified as "mismatch stunned" who had discharge LVEFs lower than those predicted by infarct size. These patients demonstrated a significant improvement in mean LVEF at 6 weeks (mean [+/-SD] discharge LVEF 0.41 +/- 0.08, 6-week LVEF 0.47 +/- 0.10; p = 0.003). Fifteen patients (18%) were classified as "mismatch-hyperkinetic." The mean LVEF for these patients significantly declined at 6 weeks (discharge LVEF 0.64 +/- 0.06, 6-week LVEF 0.58 +/- 0.09; p = 0.002). There was a marked increase in LVEF within the infarct zone (8 +/- 15 LVEF points; p = 0.03) for patients predicted to have stunning and a marked decline in LVEF outside the infarct zone (9 +/- 15 LVEF points; p = 0.06) in patients predicted to have hyperkinesia. Both discharge LVEF (p < 0.0001) and group classification (p = 0.005) were independent predictors of LVEF 6 weeks later.

CONCLUSIONS

Perfusion imaging with Tc-99m-sestamibi can identify post-MI patients at hospital discharge in whom LV function is discordant with the measured infarct size. Patients with stunning have late increases in LVEF; patients with hyperkinesia have late decreases. This methodology, performed at discharge, is predictive of late changes in LV function.

Acute myocardial infarction followed by technetium-99m-sestamibi SPECT imaging and pathologic correlation

A 79-yr-old man received thrombolytic therapy for acute myocardial infarction after injection with 99mTc-sestamibi and died shortly thereafter. Postmortem in situ SPECT imaging of the heart was performed. The heart was then removed and sectioned into short-axis slices, which were placed directly on the SPECT camera face for imaging, and examined by routine gross and microscopic pathologic methods. Pathologic findings were consistent with a small acute inferoseptal myocardial infarction, as demonstrated on both SPECT imaging of the intact heart and imaging of the heart slices. This case report provides further evidence of the validity of SPECT sestamibi imaging for the determination of myocardium at risk during acute myocardial infarction.

Technetium-99m MIBI to assess coronary collateral flow during acute myocardial infarction in two closed-chest animal models

Collateral flow is an independent determinant of infarct size in both animal and clinical studies of myocardial infarction. The purpose of this study was to quantitatively evaluate, in a closed-chest animal model, a noninvasive method of measuring coronary collateral flow over a wide spectrum of collateral flow rates from a tracer that can be injected during occlusion but measured after reperfusion.

METHODS

Fourteen animals underwent 40 min of coronary occlusion using a closed-chest technique. Two closed-chest models representing different rates of collateral flow were used: canine and porcine. Coronary blood flow was measured by radiolabeled microspheres. Collateral blood within the risk zone was estimated from the severity of 99mTc-sestamibi tomographic perfusion defect.

RESULTS

Collateral blood flow was significantly higher in the canine model than it was in the porcine model. There was close agreement (r = 0.90) between absolute collateral flow by microspheres and the severity of the tomographic perfusion defect.

CONCLUSION

These results suggest that an accurate noninvasive estimate of collateral blood flow can be provided by an intravenous injection of 99mTc-sestamibi.

Coronary endothelial dysfunction in humans is associated with myocardial perfusion defects

BACKGROUND

Coronary endothelial dysfunction may occur in patients with minimally obstructive coronary artery disease and angina, and potentially may cause myocardial ischemia.

METHODS AND RESULTS

Coronary endothelium-dependent vasodilation was examined in patients with angina and <50% coronary artery diameter (CAD) stenosis by selectively infusing acetylcholine (10(-6) mol/L to 10(-4) mol/L) into the left anterior descending coronary artery (LAD). Percent change in CAD (%deltaCAD) was measured by quantitative coronary angiography, and percent change in coronary blood flow (%deltaCBF) was calculated using intracoronary flow Doppler. Coronary endothelium-independent vasodilation was examined using intracoronary adenosine and nitroglycerin. 99mTc sestamibi was injected intravenously just prior to the infusion of the highest dose of acetylcholine. Patients were divided blindly into three groups: Perfusion defects in non-LAD territory (group 1, n=6), no perfusion defects (group 2, n=7), and perfusion defects in the LAD territory (group 3, n=7). All patients had intact endothelium-independent vasodilation. In group 1, perfusion defects outside the LAD territory reflected an increase in %deltaCAD and %deltaCBF by 24+/-5% and 241+/-46% in the LAD. In group 2, %deltaCAD decreased by 26+/-5%, but %deltaCBF increased by 54+/-17%. In group 3, perfusion defects were within the LAD territory, reflecting a decrease in %deltaCAD and %deltaCBF by 35+/-5% and 51+/-14%, respectively.

CONCLUSIONS

This study demonstrates that coronary endothelial dysfunction in humans may be temporally associated with myocardial perfusion defects and supports a role for the coronary epicardial and microcirculation endothelium in regulating myocardial perfusion. Myocardial ischemia may occur in humans with impaired endothelium-dependent coronary flow reserve of the coronary epicardial and microcirculation.

Noninvasive prediction of residual blood flow within the risk area during acute myocardial infarction: a multicenter validation study of patients undergoing direct coronary angioplasty

BACKGROUND

In a previous study from a single center, radionuclide measures of collateral flow with technetium 99m sestamibi have been shown to be significantly associated with angiographic residual (antegrade and collateral) flow and independent predictors of final infarct size in acute myocardial infarction. This study examined whether the previously described radionuclide measures of blood flow to the infarct zone were reproducible with different laboratories and imaging systems.

METHODS AND RESULTS

Residual flow to the infarct zone was assessed by both invasive and noninvasive methods in 77 patients with first-time myocardial infarction (32 anterior, 45 nonanterior). All patients underwent acute coronary angiography before any intervention within 8 hours of the onset of chest pain (4.0 +/- 1.5 hours; range 1.2 to 7.9 hours). 99mTc sestamibi was injected intravenously before reperfusion therapy, and tomographic imaging was performed 1 to 6 hours after injection. A central core laboratory processed the acquired images from three centers, each with a unique camera and computer system. Three previously published methods based on the severity of the acute perfusion defect were used to measure residual flow to the infarct zone (nadir, severity index, area). Antegrade (Thrombolysis in Myocardial Infarction flow) and collateral flow before direct angioplasty were blindly graded on a four-point scale (0 to 3) from the acute angiogram. The simple sum of the two grades was defined as the angiographic flow index, representing residual flow to the jeopardized zone. All three noninvasive measures of residual flow were highly associated with the angiographic flow index in a linear fashion: severity index (p = 0.0006), area (p = 0.003), and nadir (minimum/maximum counts; p = 0.004). This association was independent of the laboratory where the data were acquired.

CONCLUSIONS

Despite different laboratories and camera systems, radionuclide measures of residual flow were highly associated with the angiographic flow index before reperfusion therapy. These results suggest that these measures are applicable on a broader scale for the noninvasive determination of collateral and antegrade flow in acute myocardial infarction.

Worsening left ventricular performance on serial exercise radionuclide angiography does not identify high-risk patients

OBJECTIVE

To determine whether worsening exercise performance on serial exercise radionuclide angiography identifies patients at increased risk of future cardiac events.

MATERIAL AND METHODS

One hundred nine medically treated patients with previous Q-wave myocardial infarction underwent two exercise radionuclide angiographic studies at least 6 months apart (median, 16 months) without an intervening clinical event. Worsening exercise performance between the two studies was defined by five criteria: (1) lower (5% or more) peak exercise ejection fraction; (2) worsening peak exercise wall motion score; (3) combination of criteria 1 and 2; (4) worsening serial delta (exercise - rest) ejection fraction; or (5) increasing exercise ST-segment depression of 1 mm or more. Patients were followed up for a median duration of 3.9 years after the second exercise study.

RESULTS

Five cardiac deaths and 10 nonfatal myocardial infarctions occurred during follow-up. A Cox proportional hazards analysis failed to show an association between any of the aforementioned variables and cardiac events. Of the 15 patients with cardiac events, 4 (27%) had a lower (5% or more) exercise ejection fraction and 2 (13%) had a worsening exercise wall motion score. Of the 94 patients without cardiac events, 37 (39%) had a lower (5% or more) exercise ejection fraction and 28 (30%) had a worsening serial exercise wall motion score (not a statistically significant difference).

CONCLUSION

Worsening exercise performance on serial exercise radionuclide angiography does not identify patients at increased risk of future cardiac events.