Quantitative relation of myocardial infarct size and myocardial viability by positron emission tomography to left ventricular ejection fraction and 3-year mortality with and without revascularization

OBJECTIVES

The purpose of this study was to determine the clinical prognostic value, with and without revascularization, of the size of myocardial infarction and viability as measured by positron emission tomography (PET).

BACKGROUND

Poorly contracting but viable myocardium recovers contractile performance after revascularization. However, the quantitative relation among size of infarction and viability by PET, ejection fraction and long-term survival with and without revascularization in patients after myocardial infarction has not been previously reported.

METHODS

Infarct size and viability imaged by PET using generator-produced rubidium-82 were quantified objectively by automated software and related to coronary arteriography, left ventricular ejection fraction, revascularization and 3-year mortality.

RESULTS

Myocardial infarction or scar > or = 23% of the left ventricle was associated with a 3-year mortality rate of 43% versus that of 5% associated with scar < 23% of the left ventricle (p = 0.014). An ejection fraction < or = 43% correlated with a 3-year mortality rate of 38% compared with 6% for an ejection fraction > or = 43% (p = 0.029) because infarct size > or = 23% of the left ventricle was also associated with an ejection fraction < or = 43%. For patients with a low ejection fraction (< or = 43%) or large infarcts/scar (> or = 23% of the left ventricle), ejection fraction value or infarct size did not predict mortality. However, in patients with an ejection fraction < or = 43%, the absence of viable myocardium in arterial zones at risk was associated with a mortality rate of 63% versus 13% in subjects with viable myocardium, a difference with only a 5.9% probability of occurring by chance alone (p = 0.059). For all patients with viable myocardium in arterial zones at risk, the mortality rate was 8%, and 80% had revascularization over 3 years. For patients with only fixed scar in arterial zones at risk, the mortality rate was 50% versus 8% (p = 0.018), and 40% had revascularization, with no difference in mortality with or without revascularization, thereby suggesting no benefit in this subgroup.

CONCLUSIONS

Size of scar and viable myocardium by PET in arterial zones at risk in patients after myocardial infarction are highly predictive of 3-year mortality, particularly in patients with low ejection fraction, and identify patients who are suitable candidates for revascularization after myocardial infarction.

Analysis of 5' flanking sequences from the Schizosaccharomyces pombe cdc2 gene

Previously, the sequence of the Schizosaccaromyces pombe cdc2 gene was reported to begin at a HindIII site, 141 nucleotides (nt) upstream from the ATG start codon [Hindley and Phear, Gene 31 (1984) 129-134]. We have extended the sequence of the 5' untranslated region of the gene to a PsI site at -822 nt. We demonstrate by primer extension analysis that transcription of the gene initiates at one major point 180 nt upstream from the ATG start codon. Since the 822-nt fragment extending from the PstI site to the start codon has been used in many studies as the promoter for cdc2 [Booher and Beach, Mol. Cell. Biol. 6 (1986) 3523-3530; Carr et al., Mol. Gen. Genet 218 (1989) 41-49; Gould and Nurse, Nature 342 (1989) 39-45], we investigated the strength of this promoter element relative to the SV40 early promoter, a promoter known to work very well in S. pombe [Jones et al., Cell 53 (1988) 659-667]. We confirm that the cdc2 gene fragment has significant promoting activity, albeit 20- to 60-fold less than the SV40 early promoter, when assayed in S. pombe.

Experimental basis of determining maximum coronary, myocardial, and collateral blood flow by pressure measurements for assessing functional stenosis severity before and after percutaneous transluminal coronary angioplasty

BACKGROUND

Severity of coronary artery stenosis has been defined in terms of geometric dimensions, pressure gradient-flow relations, resistance to flow and coronary flow reserve, or maximum flow capacity after maximum arteriolar vasodilation. A direct relation between coronary pressure and flow, however, may only be presumed if the resistances in the coronary circulation are constant (and minimal) as theoretically is the case during maximum arteriolar vasodilation. In that case, pressure measurements theoretically can be used to predict maximum flow and assess functional stenosis severity.

METHODS AND RESULTS

A theoretical model was developed for the different components of the coronary circulation, and a set of equations was derived by which the relative maximum flow or fractional flow reserve in both the stenotic epicardial artery and the myocardial vascular bed and the proportional contribution of coronary arterial and collateral flow to myocardial blood flow are calculated from measurements of arterial, distal coronary, and central venous pressures during maximum arteriolar vasodilation. To test this model, five dogs were acutely instrumented with an epicardial, coronary Doppler flow velocity transducer. Distal coronary pressures were measured by an ultrathin pressure-monitoring guide wire (0.015 in.) with minimal influence on transstenotic pressure gradient. Fractional flow reserve was calculated from the pressure measurements and compared with relative maximum coronary artery flow measured directly by the Doppler flowmeter at three different levels of arterial pressure for each of 12 different severities of stenosis at each pressure level. Relative maximum blood flow through the stenotic artery (Qs) measured directly by the Doppler flowmeter showed an excellent correlation with the pressure-derived values of Qs (r = 0.98 +/- 0.01, intercept = 0.02 +/- 0.03, slope = 0.98 +/- 0.04), of the relative maximum myocardial flow (r = 0.98 +/- 0.02, intercept = 0.26 +/- 0.07, slope = 0.73 +/- 0.08), and of the collateral blood flow (r = 0.96 +/- 0.04, intercept = 0.24 +/- 0.07, slope = -0.24 +/- 0.06). Moreover, the theoretically predicted constant relation between mean arterial pressure and coronary wedge pressure, both corrected for venous pressure, was confirmed experimentally (r = 0.97 +/- 0.03, intercept = 9.5 +/- 13.3, slope = 4.4 +/- 1.2).

CONCLUSIONS

These results provide the experimental basis for determining relative maximum flow or fractional flow reserve of both the epicardial coronary artery and the myocardium, including collateral flow, from pressure measurements during maximum arteriolar vasodilation. With a suitable guide wire for reliably measuring distal coronary pressure clinically, this method may have potential applications during percutaneous transluminal coronary angioplasty for assessing changes in the functional severity of coronary artery stenoses and for estimating collateral flow achievable during occlusion of the coronary artery.

Measurement from arteriograms of regional myocardial bed size distal to any point in the coronary vascular tree for assessing anatomic area at risk

OBJECTIVES

To obtain the size of regional myocardial mass for individual coronary arteries in vivo.

BACKGROUND

The anatomic site of occlusion in a coronary artery does not predict the size of the risk area because location of the occlusion does not account for the size of the artery or of its dependent myocardial bed.

METHODS

Intracoronary radiolabeled microspheres were injected and coronary arteriograms were quantitatively analyzed by semiautomated methods. The coronary artery lumen areas and the sum of epicardial coronary artery branch lengths distal to the points where radiomicrospheres had been injected were determined from both in vivo and postmortem coronary arteriograms. Regional myocardial mass distal to the point of each microsphere injection was correlated with corresponding distal summed coronary branch lengths and with coronary artery lumen areas.

RESULTS

1) Regional myocardial mass was closely and linearly related to sum of coronary artery branch lengths distal to any point in the coronary artery tree and therefore could be determined for any location on a coronary arteriogram. 2) The fraction of total left ventricular mass at risk distal to a stenosis could be determined from the corresponding fraction of total coronary artery tree length independently of the scale or X-ray magnification used to measure absolute branch lengths. 3) Cross-sectional lumen area at any point in the left coronary artery tree was closely related to the size of the dependent vascular bed with a curvilinear relation similar to that observed in humans with normal coronary arteriograms.

CONCLUSIONS

On coronary arteriograms, the anatomic area at risk for myocardial infarction distal to any point in the coronary artery tree can be determined from the sum of distal coronary artery branch lengths. There is a curvilinear relation between coronary artery lumen area and dependent regional myocardial mass comparable to that in humans, reflecting fundamental physical principles underlying the structure of the coronary vascular tree.

Basic structure-function relations of the epicardial coronary vascular tree. Basis of quantitative coronary arteriography for diffuse coronary artery disease

BACKGROUND

Quantitative coronary arteriography has been validated for stenotic segments of coronary arteries. However, it does not currently account for diffuse coronary artery disease, because the normal size of the coronary artery for its distal myocardial bed size is not known and cannot be measured directly with diffuse involvement of the artery.

METHODS AND RESULTS

From clinical coronary arteriograms of 12 patients without coronary artery disease (group 1) and in 17 patients with coronary artery disease (group 2), we determined by quantitative coronary arteriography 1) the relations among measured coronary artery cross-sectional lumen area, summed distal branch lengths, and regional myocardial mass distal to each point in each coronary artery; 2) the ratio of coronary artery lumen area between parent and daughter vessels at 50 bifurcations; and 3) which of three different theoretical physical principles could underlie the tree structure of the human coronary artery system, by comparing the coronary artery size, branch lengths, regional mass, and relations between parent-to-daughter lumen area ratios with those for the different theoretical physical principles to test which principle best fit the observed data and therefore which principle most probably characterizes the human coronary artery tree structure. The results showed that 1) there is a close correlation between the lumen area of a coronary artery at each point along its length and the corresponding summed distal branch lengths and regional myocardial mass in patients without and with coronary artery disease; 2) measured coronary artery lumen area in patients with coronary artery disease is diffusely 30-50% too small for distal myocardial bed size compared with normal subjects; and 3) the observed relations among coronary artery size, distal summed lengths, myocardial bed size, and parent-to-daughter size ratios are not consistent with the theoretical principle of constant mean blood flow velocity in the coronary circulation but are consistent with the principles of minimum viscous energy loss and of limited/adaptive vascular wall shear stress characterized by a 2/3 power law relating coronary artery lumen area to distal summed branch lengths and regional mass or parent-to-daughter branching ratios.

CONCLUSIONS

These observations provide a basis for quantifying diffuse coronary artery disease on clinical arteriograms.

A dominant negative allele of p34cdc2 shows altered phosphoamino acid content and sequesters p56cdc13 cyclin

The cdc2 gene product, a 34-kDa phosphoprotein with serine/threonine protein kinase activity, has been implicated as the key component in the regulation of the eucaryotic cell cycle. Activation of the cdc2 protein kinase is regulated by its phosphorylation state and by interaction with other proteins. We have mutagenized the fission yeast cdc2 gene to obtain conditionally dominant negative alleles. One of these mutants, named DL2, is characterized in this report. Overexpression of the mutant protein in a wild-type cdc2 background is lethal and leads to arrest in the G2 phase of the cell cycle. The mutant phenotype is the result of a single amino acid change in the GDSEID motif of the protein, a region of identity in all cdc2 homologs, and results in a nonfunctional protein that shows an altered content of phosphothreonine. Multicopy suppressors of the dominant negative phenotype have been isolated, and one of these has been shown to encode the cdc13 cyclin B gene product.

Improved stenosis geometry by quantitative coronary arteriography after vigorous risk factor modification

This study is a randomized, controlled, blinded, arteriographic trial to determine the effects of a low-cholesterol, low-fat, vegetarian diet, stress management and moderate aerobic exercise on geometric dimensions, shape and fluid dynamic characteristics of coronary artery stenoses in humans. Complex changes of different primary stenosis dimensions in opposite directions or to different degrees cause stenosis shape change with profound effects on fluid dynamic severity, not accounted for by simple percent narrowing. Accordingly, all stenosis dimensions were analyzed, including proximal, minimal, distal diameter, integrated length, exit angles and exit effects, determining stenosis shape and a single integrated measure of stenosis severity, stenosis flow reserve reflecting functional severity. In the control group, complex shape change and a stenosis-molding characteristic of statistically significant progressing severity occurred with worsening of stenosis flow reserve. In the treated group, complex shape change and stenosis molding characteristic of significant regressing severity was observed with improved stenosis flow reserve, thereby documenting the multidimensional characteristics of regressing coronary artery disease in humans.

Phosphorylation at Thr167 is required for Schizosaccharomyces pombe p34cdc2 function

Eukaryotic cell cycle progression requires the periodic activation and inactivation of a protein-serine/threonine kinase which in fission yeast is encoded by the cdc2+ gene. The activity of this gene product, p34cdc2, is controlled by numerous interactions with other proteins and by its phosphorylation state. In fission yeast, p34cdc2 is phosphorylated on two sites, one of which has been identified as Tyr15. Dephosphorylation of Tyr15 regulates the initiation of mitosis. To understand more completely the regulation of p34cdc2 kinase activity, we have identified the second site of phosphorylation as Thr167, a residue conserved amongst all p34cdc2 homologues. By analysing the phenotypes of cells expressing various position 167 mutations and performing in vitro experiments, we establish that Thr167 phosphorylation is required for p34cdc2 kinase activity at mitosis and is involved in the association of p34cdc2 with cyclin B. Dephosphorylation of Thr167 might also play a role in the exit from mitosis.

Patterns in visual interpretation of coronary arteriograms as detected by quantitative coronary arteriography

In part 1 of a three-part study, 14 novice readers and 6 experienced cardiologists interpreted phantom images of known stenosis severity. No difference between the interpretations of experienced and novice readers was detectable. Visual estimates of "moderately" severe stenosis were 30% higher than actual percent diameter stenosis. In part 2 of the study, visual interpretation of percent diameter stenosis from 212 stenoses on 241 arteriograms was compared with quantitative coronary arteriographic assessment. The visual analysis overestimated disease severity in arteries with greater than or equal to 50% diameter stenosis (except for right coronary lesions) and underestimated severity in all arteries with less than 50% diameter stenosis. Of the 241 arteriograms, 40 had quantitative and visual analysis of all three coronary arteries for assessment of significant disease. In only 62% of the cases did visual and quantitative methods agree on the presence of severe disease; visual estimates diagnosed significantly (p less than 0.05) more three-vessel disease. In part 3 of the study, comparison of percent diameter stenosis by visual estimate with quantitative coronary arteriographic assessment before and after balloon angioplasty of 38 stenoses showed that visual interpretation significantly (p less than 0.001) overestimated initial lesion severity and underestimated stenosis severity after angioplasty.

Clinical cardiac positron emission tomography: state of the art

Cardiac positron emission tomography (PET) has evolved rapidly from a relatively esoteric research tool into clinical applications providing unique, quantitative information on myocardial perfusion, metabolism, and cell membrane function and having a potentially significant impact on cardiovascular medicine. Although there are many different positron radionuclides for imaging diverse myocardial behavior, three radionuclides have reached accepted clinical utility. Cardiac PET using nitrogen-13-ammonia, rubidium-82, and fluoro-18-deoxyglucose has proved accurate and definitive in multiple university and private-practice sites for diagnosing and assessing severity and location of coronary artery disease in symptomatic or asymptomatic patients, for identifying injured but viable myocardium potentially salvageable by revascularization, and for ruling out clinically significant coronary artery stenosis with a high specificity in patients who might otherwise undergo coronary arteriography to document the absence of significant disease.

Regulation of cdc2 activity in Schizosaccharomyces pombe: the role of phosphorylation

The cdc2 protein kinase, first identified as a cell cycle gene required for transition into the S- and M-phases of budding and fission yeast, has been shown to act as a key component in the regulation of the eukaryotic cell cycle. The periodic activation of cdc2 kinase, which is required for entry into M-phase, is regulated by subunit association with cyclin B, the cdc25, wee1, mik1 gene products and differential phosphorylation of the cdc2 protein. Phosphorylation at Tyr 15 inhibits activation of the cdc2/cdc13 complex whereas phosphorylation of Thr 167 is required for kinase activity.

Quantitation of the critically ischemic zone at risk during acute coronary occlusion using PET

Critical myocardial ischemia has been defined experimentally during acute coronary occlusion as flow reduction of 50% or more since cellular ATP depletion begins to occur beyond this flow reduction threshold, placing tissue at risk of cellular injury. To test the hypothesis that critically ischemic fractional left ventricular mass can be measured noninvasively with PET, nine dogs were imaged in a multi-slice positron camera using the perfusion tracer 13N-ammonia, while radiolabeled microspheres were injected into the left atrium during acute coronary occlusion. Images were processed using a 50% threshold and the size of the resulting perfusion defect was expressed as a fraction of total left ventricular image volume. The critically ischemic left ventricular fraction determined in vitro from the microsphere perfusion data, ranged from 5% to 30% of the total left ventricular weight and correlated closely with that determined noninvasively by PET with r = 0.94 (y = 1.05X - 2.0%). We conclude that the fraction of left ventricular myocardium rendered critically ischemic during acute coronary occlusion can be measured accurately and noninvasively in vivo using perfusion imaging with positron emission tomography.

The poststenotic vessel segment during dynamic exercise: effect of oral isosorbide-dinitrate

Coronary vasomotion of normal, stenotic, and poststenotic vessel segments was studied in 18 patients with coronary artery disease at rest, during submaximal bicycle exercise, and 5 min after sublingual nitroglycerin or oral isosorbide-dinitrate (ISDN) spray. Patients were divided into two groups: group 1 consisted of 10 patients with no premedication prior to exercise, and group 2 consisted of 8 patients receiving 120 mg long-acting ISDN orally 1 h before the procedure. Quantitative coronary arteriography was carried out in biplane projection using a semi-automatic computer system. The normal vessel segment showed a trend toward a small increase in cross-sectional area during exercise in both groups (+3% in group 1 and +4% in group 2, both NS). After sublingual nitroglycerin following exercise, there was a significant increase in group 1 (+29%, p less than 0.001 vs rest) but not after ISDN spray in group 2 (+5%, NS vs rest). The stenotic vessel segment showed exercise-induced stenosis narrowing in group 1 (-31%, p less than 0.01 vs rest) which was prevented by oral ISDN (+6%, NS vs rest). After exercise, sublingual administration of nitroglycerin or ISDN spray was associated with no significant change in stenosis area in either group. The poststenotic vessel segment showed no significant vasomotion during exercise in both groups (area change +6% in group 1 and +7% in group 2), but poststenotic luminal area increased after sublingual nitroglycerin (group 1: +15%, p less than 0.01 vs rest) or ISDN spray (group 2: +15%, p less than 0.05 vs rest). The mean pulmonary artery pressure increased during exercise from 22 to 39 mmHg (p less than 0.001) in group 1 and from 14 to 27 mmHg (p less than 0.001) in group 2. At rest (p less than 0.001) and during exercise (p less than 0.01) mean pulmonary pressure was lower in group 2 than in group 1. Thus, it is concluded that coronary vasomotion of the poststenotic vessel segment is only minimal during exercise and is not affected by coronary vasomotion of the stenotic vessel segment. Pretreatment with oral ISDN did not influence coronary vasomotion of the poststenotic vessel segment, but prevented exercise-induced stenosis narrowing. In the untreated patients, vasoconstriction of the stenotic vessel segment is limited to the site of the stenosis, and it appears that there is no release of vasoactive substances with vasoconstrictive influences on the poststenotic segment.

A segmented attenuation correction for PET

A segmented attenuation correction technique has been developed for positron emission tomography which computes attenuation correction factors automatically from transmission images for use in the final image reconstruction. The technique segments the transmission image into anatomic regions by thresholding the histogram of the attenuation values corresponding to different regions such as soft tissue and lungs. Average values of attenuation are derived from these regions and new attenuation correction factors are computed by forward projection of these regions into sinograms for correction of emission images. The technique has been tested with phantom studies and with clinical cardiac studies in patients for 30- and 10-min attenuation scan times. This method for attenuation correction was linearly correlated (slope = 0.937 and r2 = 0.935) with the standard directly measured method, reducing noise in the final image, and reducing the attenuation scan time.

Complementation of the mitotic activator, p80cdc25, by a human protein-tyrosine phosphatase

The onset of M phase requires the activation of the pp34 protein kinase in all eukaryotes thus far examined. In Schizosaccharomyces pombe, pp34 is phosphorylated on Tyr15, and dephosphorylation of this residue regulates the initiation of mitosis. In this study, it is shown that dephosphorylation of Tyr15 triggered activation of the pp34-cyclin complex from fission yeast, that a human protein-tyrosine phosphatase can catalyze this event both in vitro and in vivo, and that activation of fission yeast pp34 does not require threonine dephosphorylation. The complementary DNA that encoded the tyrosine phosphatase replaced the mitotic activator p80cdc25, closely associating the cdc25(+)-activating pathway with tyrosine dephosphorylation of pp34.

Positron emission tomography and interventional cardiology

Current noninvasive diagnostic techniques have limited accuracy for detection of coronary artery disease (CAD) in symptomatic and (particularly) asymptomatic patients with silent disease. Furthermore, no standard noninvasive method provides reliable diagnostic information on the location of the coronary arteries involved, the severity of stenosis, the presence of collaterals and myocardial viability. Based on greater than 1,000 cardiac studies at the University of Texas, cardiac positron emission tomography (PET) with either generator-produced rubidium-82, cyclotron-produced N-13 ammonia, or F-18 deoxyglucose is suitable for 4 routine diagnostic purposes: (1) noninvasive diagnosis of CAD in either symptomatic or asymptomatic subjects with a sensitivity of 95 to 98% and specificity of 95 to 100%. This accuracy is now sufficient to schedule diagnostic catheterization and multivessel angioplasty with surgical backup on the basis of the PET scan. At the University of Texas we carry out PET in asymptomatic and symptomatic patients to direct those with mild disease to cholesterol-lowering reversal therapy and those with severe disease to percutaneous transluminal coronary angioplasty (PTCA); (2) assessment of physiologic severity of coronary artery stenosis as compared to automated quantitative coronary arteriographic analysis. Changes in stenosis severity are followed before and after interventions including PTCA, bypass surgery, vasodilator drugs and cholesterol control regimens for reversal of coronary atherosclerosis; (3) imaging myocardial infarction, ischemia, viability, zone at risk and sizing of these pathophysiologic processes.(ABSTRACT TRUNCATED AT 250 WORDS)