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BEDSIDE DETECTION OF INTRACARDIAC SHUNTS
610
hereditary ovalocytosis proves to be an entirely benign condition, will the gene(s) responsible proceed to fixation under malarial pressure and provide us with the first identified example in man of eugenics in the wild?
BEDSIDE DETECTION OF INTRACARDIAC SHUNTS AN intracardiac shunt may be suspected when cyanosis is observed or a cardiac murmur is found. A right-to-left shunt, even when small, may be diagnosed in newborn babies or infants by the presence of central cyanosis, whereas much larger left-to-right shunts in older children may not be readily apparent. Once a shunt is detected it is important to determine its magnitude to guide subsequent management. What are the most appropriate methods of diagnosis and assessment? Oximetry of blood samples taken from various cardiac chambers has long been the gold standard for diagnosis and quantification of intracardiac shunts.l This investigation requires cardiac catheterisation and is usually carried out at the time of angiocardiography. The disadvantages of the technique include the invasive nature of the investigation and exposure to ionising radiation. Moreover, the indications for cardiac catheterisation or angiography in the diagnosis or assessment of such patients have greatly diminished with the introduction of two-dimensional
echocardiographic imaging.2 Almost all structural abnormalities can be imaged with two-dimensional echocardiography provided care is taken to obtain the appropriate views. Other valuable information can be obtained with simultaneous doppler assessment of blood flow velocity. Abnormal blood flow patterns can be characterised by careful mapping of doppler flow velocities within cardiac chambers while two-dimensional imaging allows precise definition of any anatomical abnormalities. Although doppler assessment of flow velocity cannot directly evaluate the extent of intracardiac shunting, it can estimate the cardiac output by indirect measurement of stroke volume. The product of aortic flow velocity integral over systole and the estimated cross-sectional area of the ascending aorta is directly proportional to the stroke volume.4 The ratio of the same measurements taken from the pulmonary artery to those from the aorta will provide an estimate of pulmonary to systemic flow and therefore the degree of shunting. 5,6 Rapid intravenous injection of dextrose, saline, or
indocyanine-green dye normally appears on a twodimensional echocardiogaphic image as a discrete bolus of contrast passing through the right-sided chambers of the 1. Grossman W, ed Cardiac catheterization and angiography 3rd ed Philadelphia: Lea and Febiger, 1986: 155-69. 2. Bull C. Interventional catheterisation in infants and children Br Heart J 1986; 56: 197-200
Armstrong WF Congenital heart disease. In Feigenbaum H, ed. Echocardiography. 4th ed Philadelphia: Lea and Febiger, 1986: 397-437 4. Editorial Measurement of cardiac output. Lancet 1988, ii: 257-58. 5 Sanders SP, Yeager S, Williams RG Measurement of systemic and pulmonary blood
3.
flow and Qp Qs ratio using Doppler and two-dimensional echocardiography. Am J Cardiol 1983; 51: 952-56 6 Barron JV, Sahn DJ, Valdes-Cruz LM, et al. Clinical utility of two-dimensional Doppler echocardiographic techniques for estimating pulmonary to systemic blood flow ratios in children with left to right shunting atnal septal defect, ventricular septal defect or patent ductus arteriosus. JACC 1984, 3: 169-78.
heart.7-8The simultaneous appearance of the contrast material in a left-sided cardiac chamber indicates the presence but not the extent of right-to-left intracardiac shunting; the appearance of "negative" contrast in rightsided chambers is a less reliable indication of left-to-right shunting.9 Contrast echocardiography is an especially useful technique in children. Several radionuclide techniques have been devised for the diagnosis and assessment of intracardiac shunts. The most commonly used isotope is 99Tc, which has a half-life of 6 h, although 195Au with a half-life of 30-5 s results in a much lower radiation dose and permits several rapid sequential first-pass studies to be carried out.lO,l1 Advanced computerised analysis of the precordial time/activity curve enables the degree of left-to-right shunting to be quantified.12,13 The use of a bedside nuclear probe (nuclear stethoscope) compares well with gamma camera and oximetric estimations of such shunts.14 The disadvantage of these techniques is again the use of ionising radiation; in addition, the nuclear probe does not image and the resolution of the gamma camera image is poor. The techniques used for quantification of intracardiac shunts are based on measurement of blood flow and cardiac output and are prone to considerable errors.4 The most appropriate technique for the initial diagnosis and assessment of suspected intracardiac shunts is a noninvasive procedure that can be used at the bedside if necessary for ill patients. Overall, echocardiography is clearly the best method, but in certain cases cardiac catheterisation will still be required for complete assessment, particularly when complex congenital abnormalities are present.
ARE INSECT REPELLENTS SAFE? INSECT repellents have been used widely for many years both by the general public and by military personnel. Diethyltoluamide (DEET), the commonest agent, has been available since 1957; it is effective against various
mosquitoes, ticks, fleas, gnats, biting flies, and chiggers. DEET is available in liquid form (usually with ethanol or isopropanol), in pressurised or pump spray containers, in sticks, and in impregnated towelettes; it is sometimes combined with other repellents such as ethohexadiol (ethylhexanediol) and dimethyl phthalate. R, Shah PM, Kramer DH. Ultrasound cardiography: contrast studies in Radiology 1969; 92: 939-48 8. Valdes-Cruz LM, Sahn DJ. Ultrasonic contrast studies for the detection of cardiac shunts. JACC 1984; 3: 978-85. 9. Weyman AE, Wann LS, Caldwell RL, Hurwitz RA, Dillon JC, Feigenbaum H Negative contrast echocardiography: a new method for detecting left-to-right shunts Circulation 1979; 59: 498-505. 10. Parker A, Treves S. Radionuclide detection, localization and quantification of intracardiac shunts and shunts between the great arteries. Progr Cadiovasc Dis 1977; 20: 121-50. 11. Dymond DS, Elliott AT, Flatman W, et al. The clinical validation of gold-195m a new short half-life radiopharmaceutical for rapid, sequential, first pass angiography in patients. JACC 1983; 2: 85-92. 12. Maltz DL, Treves S Quantitative radionuclide angiography determination of Qp Qs in children. Circulation 1973; 47: 1049-56. 13. Bourguignon MH, Links JM, Douglas KH, Alderson PO, Roland JM, Wagner HN Quantification of left to right shunts by multiple deconvolution analysis Am J Cardiol 1981; 48: 1086-90. 14. Gould BA, Turner J, Keeling DH, Ring NJ, Cox RR, Marshall AJ. Beside nuclear probe for detection and quantification of left to right intracardiac shunts. Br Hear: J 1988; 59: 463-67. 7. Graniak
anatomy and function.
hereditary ovalocytosis proves to be an entirely benign condition, will the gene(s) responsible proceed to fixation under malarial pressure and provide us with the first identified example in man of eugenics in the wild?
BEDSIDE DETECTION OF INTRACARDIAC SHUNTS AN intracardiac shunt may be suspected when cyanosis is observed or a cardiac murmur is found. A right-to-left shunt, even when small, may be diagnosed in newborn babies or infants by the presence of central cyanosis, whereas much larger left-to-right shunts in older children may not be readily apparent. Once a shunt is detected it is important to determine its magnitude to guide subsequent management. What are the most appropriate methods of diagnosis and assessment? Oximetry of blood samples taken from various cardiac chambers has long been the gold standard for diagnosis and quantification of intracardiac shunts.l This investigation requires cardiac catheterisation and is usually carried out at the time of angiocardiography. The disadvantages of the technique include the invasive nature of the investigation and exposure to ionising radiation. Moreover, the indications for cardiac catheterisation or angiography in the diagnosis or assessment of such patients have greatly diminished with the introduction of two-dimensional
echocardiographic imaging.2 Almost all structural abnormalities can be imaged with two-dimensional echocardiography provided care is taken to obtain the appropriate views. Other valuable information can be obtained with simultaneous doppler assessment of blood flow velocity. Abnormal blood flow patterns can be characterised by careful mapping of doppler flow velocities within cardiac chambers while two-dimensional imaging allows precise definition of any anatomical abnormalities. Although doppler assessment of flow velocity cannot directly evaluate the extent of intracardiac shunting, it can estimate the cardiac output by indirect measurement of stroke volume. The product of aortic flow velocity integral over systole and the estimated cross-sectional area of the ascending aorta is directly proportional to the stroke volume.4 The ratio of the same measurements taken from the pulmonary artery to those from the aorta will provide an estimate of pulmonary to systemic flow and therefore the degree of shunting. 5,6 Rapid intravenous injection of dextrose, saline, or
indocyanine-green dye normally appears on a twodimensional echocardiogaphic image as a discrete bolus of contrast passing through the right-sided chambers of the 1. Grossman W, ed Cardiac catheterization and angiography 3rd ed Philadelphia: Lea and Febiger, 1986: 155-69. 2. Bull C. Interventional catheterisation in infants and children Br Heart J 1986; 56: 197-200
Armstrong WF Congenital heart disease. In Feigenbaum H, ed. Echocardiography. 4th ed Philadelphia: Lea and Febiger, 1986: 397-437 4. Editorial Measurement of cardiac output. Lancet 1988, ii: 257-58. 5 Sanders SP, Yeager S, Williams RG Measurement of systemic and pulmonary blood
3.
flow and Qp Qs ratio using Doppler and two-dimensional echocardiography. Am J Cardiol 1983; 51: 952-56 6 Barron JV, Sahn DJ, Valdes-Cruz LM, et al. Clinical utility of two-dimensional Doppler echocardiographic techniques for estimating pulmonary to systemic blood flow ratios in children with left to right shunting atnal septal defect, ventricular septal defect or patent ductus arteriosus. JACC 1984, 3: 169-78.
heart.7-8The simultaneous appearance of the contrast material in a left-sided cardiac chamber indicates the presence but not the extent of right-to-left intracardiac shunting; the appearance of "negative" contrast in rightsided chambers is a less reliable indication of left-to-right shunting.9 Contrast echocardiography is an especially useful technique in children. Several radionuclide techniques have been devised for the diagnosis and assessment of intracardiac shunts. The most commonly used isotope is 99Tc, which has a half-life of 6 h, although 195Au with a half-life of 30-5 s results in a much lower radiation dose and permits several rapid sequential first-pass studies to be carried out.lO,l1 Advanced computerised analysis of the precordial time/activity curve enables the degree of left-to-right shunting to be quantified.12,13 The use of a bedside nuclear probe (nuclear stethoscope) compares well with gamma camera and oximetric estimations of such shunts.14 The disadvantage of these techniques is again the use of ionising radiation; in addition, the nuclear probe does not image and the resolution of the gamma camera image is poor. The techniques used for quantification of intracardiac shunts are based on measurement of blood flow and cardiac output and are prone to considerable errors.4 The most appropriate technique for the initial diagnosis and assessment of suspected intracardiac shunts is a noninvasive procedure that can be used at the bedside if necessary for ill patients. Overall, echocardiography is clearly the best method, but in certain cases cardiac catheterisation will still be required for complete assessment, particularly when complex congenital abnormalities are present.
ARE INSECT REPELLENTS SAFE? INSECT repellents have been used widely for many years both by the general public and by military personnel. Diethyltoluamide (DEET), the commonest agent, has been available since 1957; it is effective against various
mosquitoes, ticks, fleas, gnats, biting flies, and chiggers. DEET is available in liquid form (usually with ethanol or isopropanol), in pressurised or pump spray containers, in sticks, and in impregnated towelettes; it is sometimes combined with other repellents such as ethohexadiol (ethylhexanediol) and dimethyl phthalate. R, Shah PM, Kramer DH. Ultrasound cardiography: contrast studies in Radiology 1969; 92: 939-48 8. Valdes-Cruz LM, Sahn DJ. Ultrasonic contrast studies for the detection of cardiac shunts. JACC 1984; 3: 978-85. 9. Weyman AE, Wann LS, Caldwell RL, Hurwitz RA, Dillon JC, Feigenbaum H Negative contrast echocardiography: a new method for detecting left-to-right shunts Circulation 1979; 59: 498-505. 10. Parker A, Treves S. Radionuclide detection, localization and quantification of intracardiac shunts and shunts between the great arteries. Progr Cadiovasc Dis 1977; 20: 121-50. 11. Dymond DS, Elliott AT, Flatman W, et al. The clinical validation of gold-195m a new short half-life radiopharmaceutical for rapid, sequential, first pass angiography in patients. JACC 1983; 2: 85-92. 12. Maltz DL, Treves S Quantitative radionuclide angiography determination of Qp Qs in children. Circulation 1973; 47: 1049-56. 13. Bourguignon MH, Links JM, Douglas KH, Alderson PO, Roland JM, Wagner HN Quantification of left to right shunts by multiple deconvolution analysis Am J Cardiol 1981; 48: 1086-90. 14. Gould BA, Turner J, Keeling DH, Ring NJ, Cox RR, Marshall AJ. Beside nuclear probe for detection and quantification of left to right intracardiac shunts. Br Hear: J 1988; 59: 463-67. 7. Graniak
anatomy and function.