299

THE LANCET Hot Spots of the Heart

diagnosis of myocardial infarction, myocardial scintigraphy has its apologists and its As

an

aid

to

critics.2The detached clinician may find the arguments hard to disentangle from a bewildering number of reports. A wide variety of radiopharmaceuticals are taken up by acutely damaged myocardium. In one study of eighteen different tracers, the most favourable uptake occurred with an iodinated derivative of hydroxymercurifluorescein labelled with 1251 or 203Hg, but unsuitable gamma-ray energies and physical half-life limit its use.3 Most recent work has been with substances that can be labelled with technetium-99m, since this isotope is widely available and has a suitable energy for work with modern gamma cameras. The bone-scanning agents pyrophosphate,4polyphosphate,4 hydroxyethylidene-1, -1 disodium phosphonate,4and imidodiphosphonateare all taken up much more readily by damaged myocardium than by healthy myocardium. 99"’Tc-pyrophosphate has been used widely in clinical infarct detection.6 How do the agents work? They become concentrated in damaged muscle irrespective of the cause of muscle necrosis. In the early hours after infarction the scans are usually negative and the best time to obtain a positive scan is about 24-48 hours after the onset of chest pain, 1 hour after intravenous injection of the tracer. The intensity of the scan is related to the perfusion of the infarcted zone as well as to its size; thus a small infarct well perfused by collaterals may show more intense radioactivity than a large infarct poorly perfused.7 Experimentally the uptake of tracer is highest in the peripheral zones of the infarct, though the central zones still have higher uptakes than healthy myocardium.8 Special stains show discrete calcium deposits, more numerous in the peripheral zones of the infarct, and the peripheral myocardial cells show consistent alterations of the mitochondria, stern

__

the

most

common

being

electron-dense

spicules

which may represent apatite crystals. The timecourse of these changes runs parallel with the intensity of the scintiscans, and the uptake of the radio-tracer may be due to formation of calcium’salt precipitates. Two types of scintigraphic abnormality are described—diffuse uptake by the myocardium, and welldefined regional uptake. Of patients with no cardiac lesion, 13-35 % show a diffuse pattern,9 and much of this may represent blood-pool background ; these false-positives will doubtless be reduced with better radiopharmaceutical preparations and computer subtraction techniques. Localised uptake occurs almost exclusively in patients with heart-disease. Myocardial infarction apart, such abnormalities have been detected in patients with ventricular aneurysm,lO valvular calcification," myocardial contusion, 12 and cardiomyopathy,13 and after repeated cardioversion.14 What about ischaemic as opposed to necrotic muscle? With 99m Tc-pyrophosphate several groups have reported a mild diffuse uptake pattern in patients with unstable angina; perhaps these patients had subclinical infarction, but the possibility of uptake by ischaemic muscle remains, and this, along with other causes of false-positive images, detracts from the value of 99mTc-pyrophosphate as a tracer for myocardial infarction.15 Much interest has centred on the ability of this technique to show the extent of infarcted muscle, and experimentally there is good correlation between infarct size as judged from abnormal uptake of the tracer and the extent of histological infarction. 16 17 HENNING and colleagues,18 in patients with anterior infarction, reported good correlation between infarct size determined by isotope uptake and by serum enzyme activity. No such correlation was found by SHARPE et al., but the area of uptake of 99mTc-pyrophosphate did correlate well with the extent of reduced thallium uptake (cold-spot scanning) and with abnormal regional wall contraction as indicated by multiple images derived from a gated cardiac blood-pool isotope method. The poor agreement between enzyme and isotope methods may partly reflect the perfusion or lack of perfusion of infarcted muscle since both techniques are per9.

Prasquier, R., Taradash, M. R., Botvinick, E. H., Shames, D. M., Parmley, W. W. ibid. 1977, 55, 61. 10. Ahmad, M., Dubiel, J. P., Verdon, T. A. Jr., Martin, R. H. ibid. 1976, 53, 833. 11.

1.

Willerson, J. T., Parkey, R. W., Bonte, F. J., Meyer, S. L., Atkins, J. M., Stokely, E. M. Circulation, 1975, 51, 1046. 2. Ter-Pogossian, M. M. ibid. 1976, 53, suppl. 1, p. 119. 3. Davis, M. A., Holman, B. L., Carmel, A. N. J. nucl. Med. 1976, 17, 911. 4. Bonte, F. J., Parkey, R. W., Graham, K. D., Moore, J. G. ibid. 1975, 16, 132. 5.

Ell, P. J., Langford, R., Pearce, P., Lui, D., Elliott, A. T., Woolf, N., Williams, E. S. Br. Heart J. 1978, 40, 226. 6. Marcus, M. L., Kerber, R. E. Circulation, 1977, 56, 335. 7. Sharpe, D. N., Botvinick, E. H., Shames, D. M., Norman, A., Chatterjee, K., Parmley, W. W. ibid. 1978, 57, 307. 8. Buja, L. M., Parkey, R. W., Dees, J. H., Stokely, E. M., Harris, R. A. Jr., Bonte, F. J. Willerson, J. T. ibid. 1975, 52, 596.

Righetti, A., O’Rourke, R. A., Schelbert, H., Henning, H., Hardarson, T., Daily, P. O., Ashburn, W., Ross, J. Jr. Am. J. Cardiol. 1977, 39, 43. 12. Go, R. T., Doty, D. B., Chiu, C. L., Christie, J. H. Radiology, 1975, 116, 107.

Perez, L. A., Hayt, D. B., Freeman, L. M. J. nucl. Med. 1976, 17, 241. Pugh, B. R., Buja, L. M., Parkey, R. W., Poliner, L. R., Stokely, E. M., Bonte, F. J., Willerson, J. T. Circulation, 1976, 54, 399. 15. Wynne, J., Holman, B. L., Lesch, M. Prog. cardiovasc. Dis. 1978, 20, 243. 16. Stokely, E. M., Buja, L. M., Lewis, S. E., Parkey, R. W., Bonte, F. J., Harris, R. A. Jr., Willerson, J. T. J. nucl. Med. 1975, 17, 1. 17. Botvinick, E. H., Shames, D., Lappin, H., Tyberg, J. V., Townsend, R., Parmley, W. W. Circulation, 1975, 52, 909. 18. Henning, H., Schelbert, H., Righetti, A., O’Rourke, R., Ashburn, W. Clin. Res. 1977, 25, 91A.

13. 14.

300

fusion dependent, but some of the explanation may be that the enzyme method is related to the mass of muscle involved whereas the isotope method is more related to the area of infarcted muscle. The scintillation camera can only view a three-dimensional object in a two-dimensional plane. The field of view and resolution of the camera vary with depth, and the attenuation of the gamma radiation in tissues allows only a qualitative relationship between image and the distribution of activity in the myocardium.2 Originally the main aim of infarct size was to determine whether treatment in the first few hours could limit subsequent damage, but positive scans develop too slowly for this. Moreover, the long half-life of 99mTC (6 h) limits the frequency of repeat studies. Myocardial scintigraphy can be used to localise the site of infarction, particularly when electrocardiographic abnormalities such as left-bundlebranch block make diagnosis difficult. It may be helpful in reinfarction or infarction after cardiac surgery. Right-ventricular infarction can be diagnosed more easily by scintigraphy than by any other method.19 In most other patients the diagnosis of myocardial infarction is easily confirmed from E.C.G. and serum-enzyme changes. Myocardial scintigraphy does not yet provide information which is essential for management of patients with infarction. However, it has contributed to understanding of the pathogenesis of ischsemia and infarction. Radio-iodinated antibody specific for cardiac myosin,2o neutrally charged liposomes,21 three-dimensional imaging with positron emitters,22 and advances in computerised axial tomography23 may all enable us to assess much more accurately the extent and location of myocardial

damage.

Water with

Sugar and Salt

discovery that sodium transport and glucose transport are coupled in the small intestine, so that glucose accelerates absorption of solute and water, was potentially the most important medical advance this century.It opened the way to oral hydration treatment for severe diarrhœa—the main cause of infant death in the developing world. HIRSCHHORN and others2 showed that an oral gluTHE

Sharpe, D. N., Botvinick, E. H., Shames, D. M., Schiller, N. B., Massie, B. M., Chatterjee, K., Parmley, W. W. Circulation, 1978, 57, 483. 20. Khaw, B. A., Beller, G. A., Haber, E. ibid. p. 743. 21. Caride, V. J., Zaret, B. L. Clin Res. 1977, 25, 211A. 22. Weiss, E. S., Ahmed, S. A., Welsh, M. J., Williamson, J. R., Ter-Pogossian, M. M., Sobel, B. E. Circulation, 1977, 55, 66. 23. Powell, W. J. Jr., Wittenberg, J., Maturi, R. A., Dinsmore, R. E., Miller, S. W. ibid. p. 99. 1. See Lancet, 1975, i, 79. 2. Hirschhorn, N., Kinzie, J. L., Sachar, D. B., Northrup, R. S., Taylor, J. O., Ahmed, S. F., Phillips, R. A. New Engl. J. Med. 1968, 279, 176. 19.

cose electrolyte solution could replace intravenous fluids for cholera, and similar solutions have proved equally useful in enterotoxigenic Escherichia coli enteritis and other forms of infective diarrhoea.3Three years ago the main obstacles to wide application seemed to be practical. How might these oral glucose electrolyte preparations be brought into remote homes and health centres? But there were other questions: would a single fluid do for all forms of diarrhoea in all age-groups? For maintenance of hydration, as opposed to rehydration, would it be permissible to leave out the potassium and bicarbonate (the most perishable ingredients) and treat the patient simply with salt and glucose-or even better, salt and sucrose? Some answers have emerged. Controlled trials in London have shown that, in mild diarrhoeal disease, oral sucrose electrolyte solution is as effective as oral glucose electrolyte solution. 4 5 probably many of these patients were infected with rotaviruses.In piglets DAVIDSON and others detected abnormalities of carbohydrate handling in viral diarrhoea -which are absent in toxigenic diarrhoea. Could these interfere with sugar absorption and with the splitting of sucrose into glucose and fructose, rendering the oral solution less effective? Dr SACK and his co-workers address this question on p. 280 this week, and the answer is broadly no. In Bangladeshi children with rotavirus diarrhoea, oral sucrose was as good as oral glucose. What is more, despite the lower sodium losses in rotavirus infection than in toxigenic diarrhoeas, no patient became hypernatraemic on the standard World Health Organisation-style electrolyte regimen (perhaps because additional fluids were allowed). On p. 277 Dr NALIN and his co-workers report another comparison of glucose and sucrose in oral solutions, this time in various kinds of diarrhoea in Costa Ricans. Glucose had a distinct edge, but not a crucial one. Ideally, every household would have a few packets of glucose electrolyte powder and a measuring vessel for mixing it with water. This ideal is far from reality. Apart from the expense and perishability of existing preparations (such as W.H.O. glucose electrolyte powder), there is great difficulty in getting them into people’s homes. Health centres can cope with them, or can stock and measure out the separate ingredients.8 But the first object is to

3. Hirschhorn, N., McCarthy, B. J., Ranney, B., Hirschhorn, M. A., Woodward, S. T., Lacapa, A., Cash, R. A., Woodward, W. E. J. pediat. 1973,

5.

83, 562. Rahilly, P. M., Shepherd, R., Challis, D., Walker-Smith, J. A., Manly, J. Archs Dis. Childh. 1976, 51, 152. Hutchins, P. M., Matthews, T., Lawrie, B., Manly, J., Walker-Smith, J. A.

6.

Bishop,

4.

Lancet, 1978, i, 1211. R.

F., Davidson, G. P., Holmes, I. H., Ruck, B. J. ibid. 1973, ii,

1497.

7. 8.

Davidson, G. P., Gall, D. G., Petrii, M., Butler, clin. Invest. 1977, 60, 1402. Morley, D., King, M. Lancet, 1978, i, 53.

D.

G., Hamilton, J. R. J.

Hot spots of the heart.

299 THE LANCET Hot Spots of the Heart diagnosis of myocardial infarction, myocardial scintigraphy has its apologists and its As an aid to critic...
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