Detection of edema associated with myocardial ischemia by computerized tomography in isolated, arrested canine hearts

The ebb and flow of cardiac lymphatics: a tidal wave of new discoveries

The heart is imbued with a vast lymphatic network that is responsible for fluid homeostasis and immune cell trafficking. Disturbances in the forces that regulate microvascular fluid movement can result in myocardial edema, which has profibrotic and proinflammatory consequences and contributes to cardiovascular dysfunction. This review explores the complex relationship between cardiac lymphatics, myocardial edema, and cardiac disease. It covers the revised paradigm of microvascular forces and fluid movement around the capillary as well as the arsenal of preclinical tools and animal models used to model myocardial edema and cardiac disease. Clinical studies of myocardial edema and their prognostic significance are examined in parallel to the recent elegant animal studies discerning the pathophysiological role and therapeutic potential of cardiac lymphatics in different cardiovascular disease models. This review highlights the outstanding questions of interest to both basic scientists and clinicians regarding the roles of cardiac lymphatics in health and disease.

Myocardial Fluid Balance and Pathophysiology of Myocardial Edema in Coronary Artery Bypass Grafting

Myocardial edema is one of the most common complications of coronary artery bypass grafting (CABG) that is linearly related to many coronary artery diseases. Myocardial edema can cause several consequences including systolic dysfunction, diastolic dysfunction, arrhythmia, and cardiac tissue fibrosis that can increase mortality in CABG. Understanding myocardial fluid balance and tissue and systemic fluid regulation is crucial in order to ultimately link how coronary artery bypass grafting can cause myocardial edema in such a setting. The identification of susceptible patients by using imaging modalities is still challenging. Future studies about the technique of imaging modalities, examination protocols, prevention, and treatment of myocardial edema should be carried out, in order to limit myocardial edema occurrence and prevent complications.

Relationship between surface area of nonperfused myocardium and extravascular extraction of contrast agent following coronary microembolization

Myocardial microvascular permeability and coronary sinus concentration of muscle metabolites have been shown to increase after myocardial ischemia due to epicardial coronary artery occlusion and reperfusion. However, their association with coronary microembolization is not well defined. This study tested the hypothesis that acute coronary microembolization increases microvascular permeability in the porcine heart. The left anterior descending perfusion territories of 34 anesthetized pigs (32 ± 3 kg) were embolized with equal volumes of microspheres of one of three diameters (10, 30, or 100 μm) and at three different doses for each size. Electron beam computed tomography (EBCT) was used to assess in vivo, microvascular extraction of a nonionic contrast agent (an index of microvascular permeability) before and after microembolization with microspheres at baseline and during adenosine infusion. A high-resolution three-dimensional microcomputed tomography (micro-CT) scanner was subsequently used to obtain ex vivo, the volume and corresponding surface area of the embolized myocardial islands within the perfusion territories of the microembolized coronary artery. EBCT-derived microvascular extraction of contrast agent increased within minutes after coronary microembolization (P < 0.001 vs. baseline and vs. control values). The increase in coronary microvascular permeability was highly correlated to the micro-CT-derived total surface area of the nonperfused myocardium (r = 0.83, P < 0.001). In conclusion, myocardial extravascular accumulation of contrast agent is markedly increased after coronary microembolization and its magnitude is in proportion to the surface area of the interface between the nonperfused and perfused territories.

T2-weighted cardiovascular magnetic resonance in acute cardiac disease

Cardiovascular magnetic resonance (CMR) using T2-weighted sequences can visualize myocardial edema. When compared to previous protocols, newer pulse sequences with substantially improved image quality have increased its clinical utility. The assessment of myocardial edema provides useful incremental diagnostic and prognostic information in a variety of clinical settings associated with acute myocardial injury. In patients with acute chest pain, T2-weighted CMR is able to identify acute or recent myocardial ischemic injury and has been employed to distinguish acute coronary syndrome (ACS) from non-ACS as well as acute from chronic myocardial infarction.T2-weighted CMR can also be used to determine the area at risk in reperfused and non-reperfused infarction. When combined with contrast-enhanced imaging, the salvaged area and thus the success of early coronary revascularization can be quantified. Strong evidence for the prognostic value of myocardial salvage has enabled its use as a primary endpoint in clinical trials. The present article reviews the current evidence and clinical applications for T2-weighted CMR in acute cardiac disease and gives an outlook on future developments."The principle of all things is water"Thales of Miletus (624 BC - 546 BC).

Myocardial microvascular permeability, interstitial oedema, and compromised cardiac function

The heart, perhaps more than any other organ, is exquisitely sensitive to increases in microvascular permeability and the accumulation of myocardial interstitial oedema fluid. Whereas some organs can cope with profound increases in the interstitial fluid volume or oedema formation without a compromise in function, heart function is significantly compromised with only a few percent increase in the interstitial fluid volume. This would be of little consequence if myocardial oedema were an uncommon pathology. On the contrary, myocardial oedema forms in response to many disease states as well as clinical interventions such as cardiopulmonary bypass and cardioplegic arrest common to many cardiothoracic surgical procedures. The heart's inability to function effectively in the presence of myocardial oedema is further confounded by the perplexing fact that the resolution of myocardial oedema does not restore normal cardiac function. We will attempt to provide some insight as to how microvascular permeability and myocardial oedema formation compromise cardiac function and discuss the acute changes that might take place in the myocardium to perpetuate compromised cardiac function following oedema resolution. We will also discuss compensatory changes in the interstitial matrix of the heart in response to chronic myocardial oedema and the role they play to optimize myocardial function during chronic oedemagenic disease.

Controlled myocardial infarction induced by intracoronary injection of n-butyl cyanoacrylatein dogs: a feasibility study

Concentrated ethanol has been used to induce controlled myocardial infarct in patients with hypertrophic obstructive cardiomyopathy. We report the acute and early follow-up results of an alternative agent, n-butyl cyanoacrylate (n-BCA) glue, in a dog model. In 11 mongrel dogs, we injected n-BCA into different branches of the left anterior descending artery. Biplane left ventriculogram and coronary angiogram were performed before and after injection. In the surviving animals, we performed programmed stimulation (PS) to test for inducible ventricular tachycardia (VT) 48 days later. Following euthanasia, the removed hearts were studied with computer tomography (CT) and gross and histologic examination. Three dogs were lost before injection. Four dogs died within 2 hr to 4 days, and four animals survived 48 days. Accidental embolization of n-BCA into nontarget vessels was documented in four subjects. In the n-BCA-injected animals, homogeneous circumscribed scar was demonstrated by CT and histology. The glue was confined strictly to the tributary of the injected vessel, infiltrating arterioles of 14 mum. There was intense granulomatous reaction (GR) in the vessel wall and in the surrounding myocardium. Remote areas were unaffected. Monomorphic VT was not inducible with PS. We report a feasibility study of n-BCA injection to selected coronary arteries of dogs to cause controlled myocardial infarction. We demonstrated that the glue does not escape from the target artery through capillaries or small collateral vessels and thus produces a sharply demarcated and homogeneous scar, which is confined strictly to the supply zone of the injected vessel. Improvement of the delivery system is necessary to eliminate inadvertent embolization. Long-term follow-up is needed to study the GR induced by n-BCA.

Cardiac computed tomography imaging: a history and some future possibilities

Cardiac computed tomography (CT) is a special subset of CT, a subject about which much has been written in terms of the underlying concepts and mathematics and the sociologic impact. Cardiac CT has passed through three, chronologically overlapping, developmental stages and is now in its fourth stage of development. The first stage was fluoroscopy-based CT (1972-1995) stimulated by physiologic research needs, and the next was clinical CT-based exploration (1975-1980) of the potential of clinical CT in cardiology. This was followed by the electron beam CT-based stage (1980-present), which was the first CT approach applicable to clinical cardiology. Finally, volume-scanning CT imaging methods achieved with multislice scanning approaches of helical CT and by flat panel-based CT (1990-present), show great promise for clinically applicable CT of the cardiovascular system.

Myocardial fluid balance

Fluid accumulation in the cardiac interstitium or myocardial edema is a common manifestation of many clinical states. Specifically, cardiac surgery includes various interventions and pathophysiological conditions that cause or worsen myocardial edema including cardiopulmonary bypass and cardioplegic arrest. Myocardial edema should be a concern for clinicians as it has been demonstrated to produce cardiac dysfunction. This article will briefly discuss the factors governing myocardial fluid balance and review the evidence of myocardial edema in various pathological conditions. In particular, myocardial microvascular, interstitial, and lymphatic interactions relevant to the field of cardiac surgery will be emphasized.

High-frequency ultrasound for quantitative characterization of myocardial edema

Myocardial edema has been associated with impaired ventricular compliance and diastolic filling. To determine the sensitivity of high-frequency (40 MHz) ultrasound to myocardial edema, we employed a model in which myocardial edema was induced by immersion of tissue in isotonic saline. The effect of freezing tissue on edema formation was also evaluated. Rat hearts were arrested at end-diastole and insonified fresh within 15 min of excision (n = 5) or following being frozen for 24 h and thawed (n = 4). Measurements of attenuation, backscatter, tissue thickness and speed of sound were performed at baseline and hourly for 4 h, and compared with direct measurements of myocardial edema. Fresh tissue demonstrated a greater propensity for the development of edema than frozen tissue. Integrated backscatter increased in both tissues, whereas the magnitude and slope of attenuation decreased as edema evolved. We conclude that high-frequency ultrasound sensitively detects myocardial edema, and we propose that the extension of these methods to clinical frequencies may prove useful for monitoring and treatment of cardiac edematous disease states.

Effect of hyperosmotic mannitol on magnetic resonance relaxation parameters in reperfused canine myocardial infarction

To determine how administration of a hyperosmotic agent alters regional nuclear magnetic resonance (NMR) relaxation parameters and imaging characteristics in ischemic-reperfused myocardium, 7 dogs were infused with mannitol for 15 minutes before and after the release of a 3 hour left anterior descending coronary artery (LAD) occlusion. Nine control animals received normal saline during the 3 hour occlusion and 1 hour reperfusion periods. Normal posterior left ventricular (LV) wall and the ischemic anterior LV wall (risk area) myocardium was sampled for calculation of segmental microsphere myocardial blood flow, % tissue water content, NMR relaxation times (T1, T2) and myocyte ultrastructure using electron microscopy. Mean infarct T1 values were 14% greater than normal segments in saline-treated controls, but only 5% greater after mannitol. The difference in tissue water content between infarcted and normal segments was 4% in saline-treated (83 vs. 79%) compared to 2% in mannitol-treated dogs (79 vs. 77%). T1, T2 and % water content of control infarct segments were greater than treated infarcts (p less than 0.01). T1 and T2 rose as occlusion flow fell below 0.5 ml/min/g in control hearts but did not rise until flows were reduced to 0.1 ml/min/g in mannitol-treated hearts. Areas of increased signal in T1 and T2 NMR images correlated well with histochemical infarct volume (r = 0.98, SEE = 1.1 cc) in mannitol-treated dogs, but infarct borders were qualitatively less well-defined than in controls. We concluded that mannitol (1) diminishes tissue edema and reduces NMR relaxation parameters (T1, T2) in infarcted myocardium; and (2) attenuates the rise in T1 and T2 and ultrastructural myocyte injury in ischemic-reperfused myocardium.

Myocardial infarction and risk region relationships: evaluation by direct and noninvasive methods

Optimal quantitation of myocardial infarction requires resolution of the three-dimensional geometry of the ischemic region at a time that progression of tissue necrosis has been completed and can be sharply delineated from noninfarcted myocardium but before significant remodeling of the ventricular chamber. Although this can be achieved at two to three days after coronary occlusion by histologic techniques, a variety of technologies including two-dimensional echo, CTT, SPECT, PET, and NMR have demonstrated potential for providing noninvasive quantitative measurements of the extent of myocardial infarction. Additional studies are needed to clarify the utility of these technologies for resolving the highly variable transmural distribution of infarction that is present in the clinical setting. Assessment of the region at risk for infarction, the ischemic zone, requires quantitative measurements of the degree of ischemia as well as the size of the ischemic region. Although the above technologies may provide quantitative measurements of the dimensions of the ischemic zone, the utility for resolving the highly variable transmural distribution of regional myocardial blood flow using clinically applicable methodologies has not been convincingly established at present. It is possible that cine CT, new generation PET, and NMR technologies may eventually provide noninvasive quantitative measurements of regional myocardial blood flow.

Infarct size--can it be measured or modified in humans?

Despite more than 15 years of intensive experimental and clinical research in the general area of limiting infarct size, no treatment has been shown to be so efficacious and relatively free of side effects that its routine use can be recommended. In addition, there is no ideal means of measuring infarct size as yet. However, considerable progress has been made in understanding mechanisms responsible for irreversible cellular injury and in identifying factors and anatomic alterations responsible for or contributing to the development of transmural (Q wave) and non-transmural (non-Q wave) myocardial infarcts. Interventions are available that are capable of causing rapid coronary thrombolysis, and techniques are becoming available tht have increasing power to size myocardial infarcts and estimate both segmental and ventricular function. Experimental studies have also suggested a potential benefit from a combination of reperfusion therapy with selected pharmacologic intervention in reducing infarct size and preserving ventricular function. It seems likely that this general area will remain an intensive area of clinical research in the immediate future.

In vivo evaluation of myocardial infarction by computed tomography: an experiment with electrocardiographic gating

Retrospectively gated and ungated images of normal and 24 h post-infarction mini-pig hearts were obtained. The 11 imaged infarcts were transcatheter embolisation of the branches of the left anterior descending coronary artery. Using a contrast infusion technique and scanning during infusion, four infarcts were clearly detected as low-attenuation areas in the myocardium, one of these showing adjacent contrast enhancement. Two other infarcts showed as enhancing regions. Two small infarcts (0.8-1.0 cm3) were not detected and three others were in doubt. Streaking and other artefacts presented difficulties in image interpretation, which were sometimes resolved by gating. A comparison is made of these findings with those obtained from experiments with dogs, of comparable methodology. Differences are considered to result from anatomical differences between the two species, more particularly in the collateral blood supply to the myocardium.

Myocardial blood flow conditions at re-perfusion following acute ischaemia

The purpose of this study was to investigate the effect of re-perfusion upon distribution of radioactive microspheres in ischaemic myocardium. Ten anaesthetized cats were given 15-micron microspheres prior to left anterior coronary artery occlusion, at 1 h of occlusion, and after 1 h of subsequent re-perfusion. Pre-occlusion blood flow estimates were lower in tissue which had been ischaemic compared with nonischaemic regions in the same heart (1.44 versus 1.87 ml X min-1 X g-1, p less than 0.001), corresponding to 23% apparent loss. Loss also occurred in ischaemic right ventricular tissue (32%). In left ventricular ischaemic endocardium, apparent loss was due to development of oedema. Oedema was also significant in epicardial ischaemic tissue. Correction for oedema eliminated two-fifths of the loss, while three-fifths was due to physical loss. Oedema increased linearly with the level of re-perfusion. During re-perfusion, myocardial blood flow in previously ischaemic tissue was inhomogeneously distributed and, on average, 28% lower than in non-ischaemic myocardium. The 15-micron spheres appeared to pass through capillaries in the ischaemic subepicardium, but this process was not enhanced by reperfusion.

Assessment of myocardial ischemia with proton magnetic resonance: effects of a three hour coronary occlusion with and without reperfusion

Proton (hydrogen-1) magnetic resonance imaging techniques have potential for the detection and characterization of changes associated with myocardial ischemia. Since image contrast is dependent on T1 and T2 relaxation times, we examined these parameters in a canine preparation of occlusion of the left anterior descending coronary artery. Of 16 dogs studied, seven underwent 3 hr of coronary artery occlusion and nine underwent 3 hr of occlusion followed by 1 hr of reperfusion. After the dogs were killed, the hearts of four from each group were imaged in a small bore, 1.4 tesla magnet. From all hearts myocardial segments were obtained from the normal zone and the central ischemic zone (CZ). These segments were divided into epicardial and endocardial sections and studied in a spectrometer (20 MHz). After 3 hr of occlusion, CZ endocardial T1 and T2 increased significantly (p less than .01 and p less than .05, respectively). Changes in CZ epicardial relaxation times were not as marked. Although T1 and T2 tended to be higher in the reperfused group compared with the nonreperfused group, the differences did not reach statistical significance. In keeping with the spectrometric findings, T1-dependent inversion recovery images and T2-dependent spin-echo images of the excised hearts demonstrated excellent contrast between normal and ischemic myocardium. Modest correlations were noted for both groups between blood flows during occlusion measured by the microsphere technique and T1 and T2 relaxation times. In summary, relaxation times T1 and T2 increase regionally after 3 hr of coronary artery occlusion and tend to be accentuated by reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of myocardial infarction in dogs by contrast enhanced sequential CT scans

Surgically induced myocardial infarcts were studied in ten dogs by contrast enhanced computer transmission tomography at several stages of the infarct evolution. The hearts were scanned sequentially at 3.4 second intervals during intravenous bolus injection of contrast medium and every five minutes following the completion of a ten minute contrast medium infusion. Cardiac borders including those of the infarctions were defined by computer graphic techniques. Data from several consecutive scans were combined into one image; the ventricular chamber boundaries and those of the epicardium were reconstructed from images taken during the bolus injection. Images taken during the contrast medium washout phase were used for infarct area determination. A statistical definition of the boundary between normal tissue and infarcted myocardium was obtained which correlated well with autopsy measurements. Image analysis as described here may serve as a basis for infarct volume estimates as well as differentiation between acute and chronic infarctions.

The usefulness of x-ray computed tomography for the diagnosis of myocardial infarction

Conventional and enhanced computed tomographic (CT) examinations were performed in 103 patients with myocardial infarction for evaluation of the diagnostic usefulness of CT. After intravenous bolus injection of contrast material, an initial filling defect and late enhancement of the infarcted myocardium appeared on the cardiac CT images. These two findings were direct evidence of myocardial infarction; the former was found mostly in the patient with recent myocardial infarctions, and the latter was recognized both in those with recent and those with "remote" infarctions. Wall thinning at the site of infarction was found by enhanced CT mostly in patients with anteroseptal or extensive anterior infarctions, and was rarely found in patients with inferoposterior infarctions. Left ventricular aneurysms and ventricular thrombi were found by enhanced CT in 39 and 23 of the 103 subjects, respectively, and the sensitivity of CT in detecting intracardiac thrombi was higher than that of two-dimensional echocardiography. Calcification of the myocardium and pericardial effusion associated with myocardial infarction were also detected by conventional nonenhanced CT. Thus, cardiac CT was found to be a useful test in evaluating patients with myocardial infarction.

Effects of transient coronary ischemia and reperfusion on myocardial edema formation and in vitro magnetic relaxation times

The effects of transient ischemia and reperfusion on regional myocardial function, salvage and swelling have been systematically analyzed in experimental canine preparations. The results of these interventions on myocardial in vitro measurements of magnetic relaxation times (T1 = magnetization recovery, T2 = spin echo) are of significant importance with respect to future nuclear magnetic resonance tomographic imaging. Thus, using a pulsed magnetic resonance spectrometer (10.7 MHz), myocardial tissue samples from two groups of dogs were evaluated. In group 1 (n = six dogs), the left anterior descending artery was occluded for 3 hours before sacrifice; in group 2 (six dogs), 3 hours of occlusion was followed by 1 hour of reperfusion. Multiple tissue samples from normal and ischemic (or ischemic and reperfused) myocardium were obtained for measurement of T1, T2 and % water content (wet weight--dry weight/wet weight). Water content increased with ischemia (78 +/- 4%) and reperfusion (81 +/- 4%) (both p less than 0.01 versus control values). Values for T1 increased with ischemia (598 +/- 39 versus 487 +/- 23 ms in normal tissue from the same heart, p less than 0.01). Even greater T1 changes occurred in the animals with reperfusion (654 +/- 52 ms, p less than 0.01 versus the intra-animal control values). Changes in T2 were similar but less marked (ischemic zone 43.9 +/- 1.0 versus 41.2 +/- 1.0 ms in nonischemic tissue in the corresponding heart, p less than 0.05; reperfusion zone 48.3 +/- 3.5 versus 41.9 +/- 2.3 ms in the normal zone, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Use of computerized tomography to assess myocardial infarct size and ventricular function in dogs during acute coronary occlusion and reperfusion

Prospectively ECG-gated and nongated computed tomography (CT) can be used to assess global and regional left ventricular (LV) function and to measure myocardial infarct (MI) size. In the current study, CT was used to assess the effects of coronary occlusion and reperfusion in 16 dogs. Ten dogs were subjected to permanent occlusion of the proximal left anterior descending coronary artery and 6 dogs were reperfused after a 2-hour period of total coronary occlusion. Gated scans were used to quantitate the extent of wall thickening in the ischemic zone and to assess changes in mid-LV cross-sectional chamber area at end-diastole and end-systole. Nongated scans were used to estimate the size of the initial perfusion defect during contrast injection shortly after coronary occlusion and the size of the MI as indicated by delayed enhancement of the infarct 10 to 30 minutes after cessation of contrast administration. Neither group showed significant changes in end-diastolic chamber area during acute occlusion or 3 days later. Both groups showed a significant deterioration in percent change in chamber area both early after coronary occlusion and 3 days later; however, in the permanent occlusion group, percent wall thickening in the ischemic zone decreased from 46.2 +/- 16.5% (mean +/- standard deviation) to 1.6 +/- 9.0% during acute occlusion (p less than 0.01) and thickening remained depressed 3 days later (2.4 +/- 10.1%, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of myocardial ischemia on quantitative ultrasonic backscatter and identification of responsible determinants

Quantitative characterization of myocardial properties represent a rapidly emerging area of echocardiographic investigation. Because measurement of the ultrasonic integrated backscatter is theoretically applicable to analysis in vivo with reflected ultrasound, this study was performed to develop and evaluate a suitable method for measurement of quantitative backscatter in vivo. In view of the desirability of characterizing ischemic myocardium noninvasively, the study was performed with animal preparations simulating myocardial ischemia in humans. In one series of open-chest dogs, integrated backscatter among 22 ischemic regions was increased by 200% (P less than 0.01) compared to values in control regions within 1 hour after coronary occlusion and by 400% (-45.1 +/- 0.7 dB compared to -50.9 +/- 0.4 dB) (P less than 0.001) within 6 hours. In a second series of open-chest dogs, ischemia was quantified with 141Ce microspheres, and mean integrated backscatter was found to increase (280% of control) (P less than 0.01) in regions with flow less than 20% of control 2 hours following coronary occlusion. Additional studies with perfused hearts revealed two determinants of the increased ultrasonic backscatter observed: (1) an increase in cardiac fluid content reflected by the wet-to-dry weight ratio, and (2) the contributions of formed elements in whole blood. The results indicate that ultrasonic integrated backscatter distinguishes severely ischemic from nonischemic myocardium in vivo in open-chest animals. Because it was possible to obtain these results in the reflection mode, potential extension of the approach to clinical applications is promising.

Detection of left ventricular thrombi by computerised tomography. A preliminary report

Images

Detection and quantitation of myocardial infarction in vivo using transmission computed tomography

In vivo studies were performed on 28 dogs to evaluate the usefulness of transmission computed tomography (CT) in the detection and quantitation of experimentally induced myocardial infarction. Intravenously administered contrast material was required to define the internal structure of the heart and to differentiate normal from infarcted tissue. Transmural infarcts with homogeneous central regions were visualized as areas of diminished contrast enhancement compared with the normal myocardium. All transmural infarcts of at least 24 hours' duration showed a surrounding border zone of patchy necrosis that was variable in size and had high CT numbers due to slow washout of the contrast material from this region. Infarct area determined from the images for individual slices correlated well (r = 0.976) with that calculated using pathology. The technique is very sensitive and can detect infarction within a papillary muscle. Nontransmural or patchy infarcts show up as areas of diffuse contrast enhancement without a central core of diminished enhancement. The distribution of the contrast material is similar to that of technetium-99m pyrophosphate in the border zone of the infarct in infusion studies, but in bolus studies it behaves more like thallium-201.

Myocardial infarction in dogs, demonstrated by non-enhanced computed tomography

The capability of non-enhanced and enhanced CT scanning of the heart without ECG gating to detect myocardial infarction in living dogs was explored. CT findings were correlated with those at post mortem. In large transmural infarctions, areas of lower attenuation were detected without contrast medium enhancement and appeared as defects when intravenous contrast medium was administered. The infarct size as estimated on each CT scan correlated closely with post mortem values.

Noninvasive three-dimensional viewing of the motion and anatomical structure of the heart, lungs, and circulatory system by high speed computerized X-ray tomography

A new generation X-ray computerized tomography system now under construction, the Dynamic Spatial Reconstructor (DSR), will record 1680 multiple view X-ray video images of the chest or other segments of the body per second. This allows com0utation of stop-action and 60-per-second instant replay motion pictures of the dynamic three-dimensional changes in shape and dimensions of the full anatomic extents of the internal and external surfaces of the heart chambers or the vascular anatomy and circulatory dynamics in any region of the body. Current commercially available scanners require one or more seconds per cross-sectional scan and lack the synchronous volumetric scanning capabilities of the DSR. These capabilities allow nondestructive mathematical selection and removal of any subvolume of interest from a reconstructed volume. The associated abilities to "zoom in" and "section" this subvolume so as to examine its structure and physiologic function in detail allow direct visualization of the internal anatomy and function of organ systems within the body. These capabilities of "noninvasive numerical biopsy" and "vivisection" have heretofore been the preserve of pathologists at autopsy or surgeons at the operating table. Possible future availability of these techniques to the practicing internist carries promise of revolutionary improvements in clinical diagnosis and treatment of the myriad of disease processes, including cancer, which may affect the heart, lungs, vascular anatomy or circulatory dynamics in any region of the body.

Evaluation of myocardial ischemic damage of various ages by computerized transmission tomography. Time-dependent effects of contrast material

The potential role of computerized transmission tomography (CTT) in the detection and quantitation of acute myocardial ischemic damage was assessed in 42 excised canine hearts at 2 hours, 8 hours, and 48 hours after coronary occlusion. The CTT scan detected by myocardial damage that was 2-48 hours old each time the presence of regional ischemia was confirmed by histochemical straining or epicardial electrocardiographic mapping. Intravenous administration of contrast material enhanced the x-ray attenuation of areas of ischemic damage of 8 and 48 hours duration compared with normal myocardium, but enhanced only normal myocardium in those of 2 hours duration. Volumetric estimation of the extent of damage from the CTT scans in dogs with ischemia of 48 hours duration showed a close linear relationship with the morphometric volume in the absence of contrast material. Quantitation of the area of ischemic damage from the CTT scan after contrast administration resulted in substantial underestimation of the volume of damaged tissue.

Assessment of drug intervention on the ischemic myocardium: serial imaging and measurement with computerized tomography

Computerized tomography was evaluated as a technique for imaging and measuring the effect of an intervention on acutely ischemic myocardium. Because cell edema occurs with acute myocardial ischemia and decreases the X-ray attenuation coefficients (tissue density) of myocardium, computerized tomographic images were used to quantitate the effect of hyperosmotic mannitol on ischemia-induced edema. Canine hearts were arrested and scanned after (1) temporary occlusion of the proximal circumflex artery followed by reflow of blood, or (2) continued occlusion of the distal left anterior descending coronary artery. X-ray attenuation values (Hounsfield units) were linearly related to tissue wet/dry weight ratios (r = 0.87, P less than 0.001). After 2 hours of occlusion of the left anterior descending coronary artery the hearts that received mannitol manifested a significant reduction (P less than 0.05) in the volume of left ventricular wall involved with edema. Although the area of edema measured with computerized tomography tended to be smaller in the hearts treated with mannitol than in untreated hearts subjected to a 6 hour occlusion of the left anterior descending coronary artery, the size of the lesion was variable and did not differ significantly from that in untreated hearts. With either short periods of circumflex arterial occlusion followed by blood reflow or with 2 or 6 hours of prolonged occlusion of the left anterior descending coronary artery, the difference in mean attenuation coefficients between the ischemic and nonischemic areas of myocardium in mannitol-treated and untreated hearts was significantly less. These results indicate that computerized tomography in the arrested heart can detect and quantitate the lesion of early acute myocardial ischemia and can quantitate the effect of drug intervention.

Differential accumulation of radiopaque contrast material in acute myocardial infarction

The differential accumulation of radiographic contrast materials in ischemically damaged and normal myocardium was assessed with direct measurement (fluorescent excitation analysis) of the iodine content of tissue samples from dogs with 48 hour old myocardial infarctions. Tissue samples were obtained 10, 30, 60 and 180 minutes after the intravenous administration of 2 ml/kg body weight of diatrizoate meglumine and sodium (Renografin-76). At all time intervals, the iodine concentration of infarcted tissue was at least threefold greater than that of normal myocardium. At 180 minutes the ratio between iodine concentration in infarcted myocardium and that in normal myocardium was 8.5 and between that in infarcted myocardium and that in blood was 2.6. The iodine concentration in the liver was similar to or greater than that in the infarcted area at time intervals after 10 minutes. These results suggest that the intravenous administration of contrast material may facilitate the identification of acutely infarcted myocardium with computerized X-ray transmission tomography.

Lack of effect of methylprednisolone on lysosomal and microsomal enzymes after two hours of well-defined canine myocardial ischemia

Myocardial ischemia was produced for 2 hours by coronary ligation in 11 dogs pretreated with methylprednisolone (MP, 30 mg/kg). Myocardial blood flow (MBF) was measured with microspheres (15 micrometer) in each tissue sample used for enzymatic analysis. Homogenates of these tissue samples were separated by ultracentrifugation into lysosome-rich and microsomal fractions and were analyzed for N-acetyl-beta-glusosaminidase (NAGA), beta-glucuronidase (beta-gluc), rotenone-insensitive-NADH-cytochrome c reductase (RINCR), and cytochrome oxidase. The enzymatic data from centrifugal fractions were grouped according to MBF values for statistical analysis of inter-group effects of ischemia. Significant losses (P less than 0.001) of NAGA and beta-gluc were seen in all MP-treated lysosome-rich particulate fractions that were isolated from zones demonstrating MBF values less than 25% of control (L-ischemia). Similar significant losses (P less than 0.001) of RINCR were seen in microsomal fractions from L-ischemia zones. Samples with MBF values greater than 25% but less than 75% of control (M-ischemia) also demonstrated significant decreases of lysosomal and microsomal enzymatic activity in specific fractions. When the data of the above MP-treated group were compared with the untreated control group, no significant intergroup effects of treatment with MP were observed. In addition, enzymatic data (NAGA, RINCR) were normalized prior to performing linear regression analyses; percent loss of particulate enzymatic activity was plotted against percent decrease in MBF. The effects of 2 hours of ischemia on the above biochemical parameters were comparable between untreated and MP-treated groups. Finally, when myocardial samples were grouped according to similar levels of MBF, statistical analysis using the general linear models procedure revealed no beneficial effect of MP treatment on changes in lysosomal hydrolases, microsomal RINCR, or latency of lysosomes.

Effects of well-defined ischemia on myocardial lysosomal and microsomal enzymes in a canine model

We have used a new technique for extraction of myocardial membranes (0.25 M sucrose, 0.6 M KCl) to isolate particulate and soluble proteins and enzymatic activities in an effort to quantify changes characteristic of progressive ischemia. Myocardial blood flow (MBF) was measured with microspheres (15 micrometer diameter) in all samples of tissue used for assay of proteins and enzymatic activities; MBF to the moderately ischemic areas (M-ischemia) was 53% of control (H-control); MBF to the severely ischemic areas (L-ischemia) was 9% of control. Significant decreases (P less than 0.001) in content of protein were seen in all post 1,000 g pellets and supernatant fluids in the L-ischemia zones; particulate lysosomal enzymatic activity was significantly decreased (P less than 0.001) in all four post 1,000 g pellets (2,500 g to 140,000 g) of the L-ischemic areas (for N-acetyl-beta-glucosaminidase and beta-glucuronidase). The increase in percent free activity of lysosomal enzymes (index of loss of latency) also was highly significant (P less than 0.001) in all particulate fractions of the L-ischemic areas. In addition, about 45% of the total activity of the microsomal marker enzyme, rotenone-insensitive NADH cytochrome C reductase (RINCR), was found in the 140,000 g pellet of H-control tissue (9.9 micronmol/min per g); this activity fell to 8.1 micronmol/min per g in M-ischemic areas (P less than 0.001) and to 5.3 micronmol/min per g in L-ischemic areas (P less than 0.001). This study demonstrates that changes in myocardial proteins, lysosomes, and other membrane-bound enzymes (RINCR) may provide reproducible bichemical parameters for assessing ischemic myocardial injury.

Computed tomography for localization and sizing of experimental acute myocardial infarcts

Computed tomography (CT) has been used to quantitate acute myocardial infarct size in isolated, arrested canine hearts. Acute myocardial infarcts were produced in 20 hearts by either left anterior descending (13 dogs) or circumflex coronary artery ligation (seven dogs). Each animal was given iodinated contrast media intravenously immediately before sacrifice 24--72 hours postinfarction. All infarcts greater than 1 g and one of three infarcts 0.5 g or less were detected by CT imaging. Infarct volume determined by CT correlated with gross infarct weight (r=0.83). CT imaging, however, consistently underestimated infarct volume; underestimation was largest in a group of patchy, predominantly subendocardial infarcts. As adequate equipment and techniques for in vivo studies are developed, CT imaging of the heart may become important in clinical evaluation of myocardial infarction.

Heart imaging from computerized tomography

In vitro and in vivo animal experiments have demonstrated the potential for using computerized tomography in heart imaging. This paper summarizes some of the work done in our laboratory related to heart imaging of dogs, of cadavers, and of live subjects using the CT approach. We have also provided examples demonstrating a method for computing the heart volume from serial CT images.

New vistas for the study of structural and functional dynamics of the heart, lungs, and circulation by noninvasive numerical tomographic vivisection

Major segments of the biologic sciences and the practice of medicine are based on study and knowledge of the relationships of anatomic structure to biologic function. Traditionally, this knowledge has been gained by indirect means, inference, or by direct surgical vivisection or postmortem examination. The revolutionary capability of nondestructive, operator interactive, mathematical vivisection provided by synchronous cylindrical scanning tomography to obtain similar information non-invasively and painlessly will provide these data to the internist for individual patients. Furthermore, this information will be in a computerized format which can be subjected to myriad types of objective measurements and display. These developments promise beneficial effects of clinical diagnosis and health care which may approach those associated with the discoveries of the biomedical investigative and clinical diagnostic value of X-rays and cardiac catheterization.