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Angiocardiographic determination of ejection fraction in coronary artery disease
Angiocardiographic Determination of Ejection Fraction in Coronary Artery Disease MURRAY
G. BARON. MD, FACC
New York, New York
The functional state of the left ventricle reflects the extent of the cardiac damage caused by coronary artery disease and provides an indication of the risk of coronary surgery. All other factors being equal, the patient with normal or near normal ventricular function is considered a good surgical candidate, whereas the patient with a baggy, dilated ventricle that seems to quiver rather than contract with each heart beat usually presents an unacceptably high risk. In the latter case, myocardial function is so poor that, even if the surgical procedure is a technical success, it is unlikely that any benefit will be derived from the increase in coronary flow. Between the two extremes, there is a sizable group of patients in whom it is very difficult, because of the absence of clear-cut objective criteria, to evaluate accurately the degree of ventricular impairment. The left ventricular ejection fraction has been proposed as an objective measurement of the functional potential and possibly the viability of the myocardium. If coronary surgery should be shown to preserve or improve cardiac function, this measurement may be of prime importance in differentiating the patient with a “salvageable” ventricle from the patient with ischemic changes that have progressed beyond the point of rehabilitation. Whether the ejection fraction is the proper index for this purpose is beyond the scope of this discussion. However, no evaluation of the role of the ejection fraction is possible until this value can be accurately determined so that it truly reflects the stroke work of the heart under physiologic conditions. The ejection fraction is derived from the end-systolic volume and the end-diastolic volume of the left ventricle and is dependent on the ventricular diameters as measured on the angiocardiogram. The mathematics involved are considered to be valid, with an acceptable degree of error. However, because the angiographic procedure alters cardiac hemodynamics and function, it introduces additional variables that can make the final result considerably less accurate than desired. From the Department of Radiology, the Mount Sinai School of Medicine, City University of New York, 1 East 100th St. New York, N.Y. 10029.
Injection of contrast material into the heart causes an increase in the left ventricular end-diastolic pressure and volume, peripheral hypotension, an increase in blood volume and a decrease in hematocrit.1*2 Several studies have shown these changes to be present at the end of the angiocardiographic study and to increase to a maximum within the next 2 to 4 minutes. The values gradually return to normal levels over a 15 to 20 minute period. Since the ejection fraction is calculated from measurements obtained from the earliest phase of the angiocardiogram, when the left ventricle is optimally opacified, these late changes are of no concern. It is important to determine exactly at which point in the study the alterations in ventricular function begin to occur. Hammermeister and Warbasse, in their study in the March issue of this Journal,3 could find no significant variation in ventricular volumes during the first 3 or 4 cardiac cycles after the start of injection of contrast material into the left ventricle. A similar study in this Journal by Carleton4 showed some change occurring by the third heartbeat and a significant change in the ventricular volume by the fifth beat. These studies suggest that the data obtained from the first few cardiac cycles are essentially the same as those observed in the preangiographic phase. However, because the ventricle cannot be measured unless it is opacified, it must be assumed that no change occurs between the first heartbeat recorded on the angiocardiogram and the beats that immediately precede it. These studies, however, are based on selected cases and are not completely applicable to the data collected in the day to day practice of a cardiac catheterization laboratory. Ventricular diameters are measured when the chamber is well opacified and when the heart is in sinus rhythm. Extrasystolic contractions and the compensatory beat that follows must be excluded from the calculations. In one of the data were obtained from the studies3 satisfactory angiocardiogram in 14 of 21 patients, while in the other,4 only 7 of 100 consecutive left ventriculograms were considered suitable for measurement. A run of extrasystoles is very common during the pressure injection of contrast material into the left ventricle. Often, 4 or more ectopic beats precede the first nor-
June 1973
The American
Journal of CARDIOLOGY
Volunte 31
803
EDITORIALS
ma1 ventricular contraction. Because of the delay caused by the arrhythmia, measurements must be made when induced alterations in cardiac function are becoming manifest. An additional complicating factor is that the angiocardiogram usuglly does not represent the first injection of contrast material, but follows one or more test injections made during manipulation of the catheter. Whether the small amounts of contrast material used for test injections have a significant cumulative effect on cardiac hemodynamics is not certain. The pressure5 and speed3 of the injection may have some influence on the magnitude of hemodynamic changes. Presumably, this is in part a mechanical effect related to the force of the fluid jets from the catheter.5 Standardization of catheters, contrast media and pressures will not completely exclude this variable because it is also affected by the size of the ventricular cavity and the proximity of the catheter to the ventricular wall. A more serious drawback to the ejection fraction as determined from the angiocardiogram is that the error in the method is not constant from patient to patient. Cardiac response to hypertonic contrast material can vary both in magnitude and direction with the severity of the myocardial disease. When there is stenosis of the coronary arteries, instead of the normally expected increase in ventricular stroke work, there may be no response to angiocardiography in some patients, whereas a’ definite decrease in cardiac function may occur in others.6 It is exactly in this group of patients with moderate to severe coronary artery disease that the most accurate ejection fraction is needed if it is to be of practical value. To limit possible inaccuracies in the angiocardiographic ejection fraction, the number of test injections should be kept to a minimum, and the left ventriculogram should be obtained before the study of the coronary arteries. The latter almost always produces a transient decrease in myocardial contractility.l.7 This is a logical sequence of study, because if the left ventricle is hopelessly compromised there is
little rationale or justification for submitting the patient to the added risks of coronary arteriography. The problem of extrasystoles can be obviated by introducing the contrast material into the pulmonary artery rather than directly into the left ventricle. Unfortunately, although this solves one problem, it exaggerates another. The alterations in left ventricular end-diastolic pressure and volume are similar if the contrast material is injected into the right side of the heart or the left. Since it takes several cardiac cycles for contrast material injected in the pulmonary artery to transverse the pulmonary circulation, by the time the left ventricle is sufficiently opacified to be measured, variations in cardiac function are already occurring. As more physiologic contrast media are developed,s a decrease in the cardiac reaction to angiocardiography can be expected, with a resultant increase in the accuracy of the ejection fraction determination. However, the basic invasive nature of the angiographic procedure is such that some artifacts will almost certainly remain. Despite these objections, the fact remains that at this time angiocardiography is the only practical technique for determining the ejection fraction. Although the results are more likely to be approximations than absolute values, they still provide information that is helpful in the selection of patients for coronary arterial surgery. In practice, a useful estimate of left ventricular function can also be made by simply observing the ventricle on the cineangiocardiogram as it contracts and distends. In this manner, an experienced observer can usually distinguish between the moderately impaired ventricle and the severely impaired one. Obviously, a borderline group of patients will remain in whom a clear-cut decision cannot be made. On the other hand, indeterminate cases also result from the use of the numerical ejection fraction. Unless the calculation of ejection fraction results in a significantly smaller borderline group, it is questionable whether it is worth the expenditure of money for the equipment and time that the procedure requires.
References 1. Friesinger GC, Schaffer J, Criley JM, et al: Hemodynamic consequences of the injection of radiopaque material. Circulation 31:730, 1963 2. Brown, R., Rahimtoola, SH, Davis, GD, et al: The effect of angiocardiographic contrast medium on circulatory dynamics in man. Cardiac output during angiocardiography. Circulation 31:234-240, 1963 3. Hammermeister KE, Warbasse JR: The immediate hemodynamic effects of cardiac angiography in man. Amer J Cardiol 31:307-314,1973 4. Carleton RA: Change in left ventricular volume during angiocardiography. Amer J Cardiol 27:460-463, 1971
804
June 1973
The American
Journal of CARDIOLOGY
5. Krovetz LJ, Simon AL, Levy RJ, et al: Effects of angiocardiographic contrast media on left ventricular function. Johns Hopkins Med J 127:172-183, 1970 6. Rahimtoola MB, Duffy JP, Swan HJC: Ventricular performance after angiocardiography. Circulation 35: 70-77, 1967 7. Levin DC, Baltaxe HA: Effect of radiopaque contrast material on left ventricular end-diastolic pressure. NY State J Med 72:2619-2622,1972 6. Ovitt T, Ritk G, Frech RS, et al: Electrocardiographic changes in selective coronary arteriography: the importance of ions. Radiology 104:705. 1972
Volume 31
G. BARON. MD, FACC
New York, New York
The functional state of the left ventricle reflects the extent of the cardiac damage caused by coronary artery disease and provides an indication of the risk of coronary surgery. All other factors being equal, the patient with normal or near normal ventricular function is considered a good surgical candidate, whereas the patient with a baggy, dilated ventricle that seems to quiver rather than contract with each heart beat usually presents an unacceptably high risk. In the latter case, myocardial function is so poor that, even if the surgical procedure is a technical success, it is unlikely that any benefit will be derived from the increase in coronary flow. Between the two extremes, there is a sizable group of patients in whom it is very difficult, because of the absence of clear-cut objective criteria, to evaluate accurately the degree of ventricular impairment. The left ventricular ejection fraction has been proposed as an objective measurement of the functional potential and possibly the viability of the myocardium. If coronary surgery should be shown to preserve or improve cardiac function, this measurement may be of prime importance in differentiating the patient with a “salvageable” ventricle from the patient with ischemic changes that have progressed beyond the point of rehabilitation. Whether the ejection fraction is the proper index for this purpose is beyond the scope of this discussion. However, no evaluation of the role of the ejection fraction is possible until this value can be accurately determined so that it truly reflects the stroke work of the heart under physiologic conditions. The ejection fraction is derived from the end-systolic volume and the end-diastolic volume of the left ventricle and is dependent on the ventricular diameters as measured on the angiocardiogram. The mathematics involved are considered to be valid, with an acceptable degree of error. However, because the angiographic procedure alters cardiac hemodynamics and function, it introduces additional variables that can make the final result considerably less accurate than desired. From the Department of Radiology, the Mount Sinai School of Medicine, City University of New York, 1 East 100th St. New York, N.Y. 10029.
Injection of contrast material into the heart causes an increase in the left ventricular end-diastolic pressure and volume, peripheral hypotension, an increase in blood volume and a decrease in hematocrit.1*2 Several studies have shown these changes to be present at the end of the angiocardiographic study and to increase to a maximum within the next 2 to 4 minutes. The values gradually return to normal levels over a 15 to 20 minute period. Since the ejection fraction is calculated from measurements obtained from the earliest phase of the angiocardiogram, when the left ventricle is optimally opacified, these late changes are of no concern. It is important to determine exactly at which point in the study the alterations in ventricular function begin to occur. Hammermeister and Warbasse, in their study in the March issue of this Journal,3 could find no significant variation in ventricular volumes during the first 3 or 4 cardiac cycles after the start of injection of contrast material into the left ventricle. A similar study in this Journal by Carleton4 showed some change occurring by the third heartbeat and a significant change in the ventricular volume by the fifth beat. These studies suggest that the data obtained from the first few cardiac cycles are essentially the same as those observed in the preangiographic phase. However, because the ventricle cannot be measured unless it is opacified, it must be assumed that no change occurs between the first heartbeat recorded on the angiocardiogram and the beats that immediately precede it. These studies, however, are based on selected cases and are not completely applicable to the data collected in the day to day practice of a cardiac catheterization laboratory. Ventricular diameters are measured when the chamber is well opacified and when the heart is in sinus rhythm. Extrasystolic contractions and the compensatory beat that follows must be excluded from the calculations. In one of the data were obtained from the studies3 satisfactory angiocardiogram in 14 of 21 patients, while in the other,4 only 7 of 100 consecutive left ventriculograms were considered suitable for measurement. A run of extrasystoles is very common during the pressure injection of contrast material into the left ventricle. Often, 4 or more ectopic beats precede the first nor-
June 1973
The American
Journal of CARDIOLOGY
Volunte 31
803
EDITORIALS
ma1 ventricular contraction. Because of the delay caused by the arrhythmia, measurements must be made when induced alterations in cardiac function are becoming manifest. An additional complicating factor is that the angiocardiogram usuglly does not represent the first injection of contrast material, but follows one or more test injections made during manipulation of the catheter. Whether the small amounts of contrast material used for test injections have a significant cumulative effect on cardiac hemodynamics is not certain. The pressure5 and speed3 of the injection may have some influence on the magnitude of hemodynamic changes. Presumably, this is in part a mechanical effect related to the force of the fluid jets from the catheter.5 Standardization of catheters, contrast media and pressures will not completely exclude this variable because it is also affected by the size of the ventricular cavity and the proximity of the catheter to the ventricular wall. A more serious drawback to the ejection fraction as determined from the angiocardiogram is that the error in the method is not constant from patient to patient. Cardiac response to hypertonic contrast material can vary both in magnitude and direction with the severity of the myocardial disease. When there is stenosis of the coronary arteries, instead of the normally expected increase in ventricular stroke work, there may be no response to angiocardiography in some patients, whereas a’ definite decrease in cardiac function may occur in others.6 It is exactly in this group of patients with moderate to severe coronary artery disease that the most accurate ejection fraction is needed if it is to be of practical value. To limit possible inaccuracies in the angiocardiographic ejection fraction, the number of test injections should be kept to a minimum, and the left ventriculogram should be obtained before the study of the coronary arteries. The latter almost always produces a transient decrease in myocardial contractility.l.7 This is a logical sequence of study, because if the left ventricle is hopelessly compromised there is
little rationale or justification for submitting the patient to the added risks of coronary arteriography. The problem of extrasystoles can be obviated by introducing the contrast material into the pulmonary artery rather than directly into the left ventricle. Unfortunately, although this solves one problem, it exaggerates another. The alterations in left ventricular end-diastolic pressure and volume are similar if the contrast material is injected into the right side of the heart or the left. Since it takes several cardiac cycles for contrast material injected in the pulmonary artery to transverse the pulmonary circulation, by the time the left ventricle is sufficiently opacified to be measured, variations in cardiac function are already occurring. As more physiologic contrast media are developed,s a decrease in the cardiac reaction to angiocardiography can be expected, with a resultant increase in the accuracy of the ejection fraction determination. However, the basic invasive nature of the angiographic procedure is such that some artifacts will almost certainly remain. Despite these objections, the fact remains that at this time angiocardiography is the only practical technique for determining the ejection fraction. Although the results are more likely to be approximations than absolute values, they still provide information that is helpful in the selection of patients for coronary arterial surgery. In practice, a useful estimate of left ventricular function can also be made by simply observing the ventricle on the cineangiocardiogram as it contracts and distends. In this manner, an experienced observer can usually distinguish between the moderately impaired ventricle and the severely impaired one. Obviously, a borderline group of patients will remain in whom a clear-cut decision cannot be made. On the other hand, indeterminate cases also result from the use of the numerical ejection fraction. Unless the calculation of ejection fraction results in a significantly smaller borderline group, it is questionable whether it is worth the expenditure of money for the equipment and time that the procedure requires.
References 1. Friesinger GC, Schaffer J, Criley JM, et al: Hemodynamic consequences of the injection of radiopaque material. Circulation 31:730, 1963 2. Brown, R., Rahimtoola, SH, Davis, GD, et al: The effect of angiocardiographic contrast medium on circulatory dynamics in man. Cardiac output during angiocardiography. Circulation 31:234-240, 1963 3. Hammermeister KE, Warbasse JR: The immediate hemodynamic effects of cardiac angiography in man. Amer J Cardiol 31:307-314,1973 4. Carleton RA: Change in left ventricular volume during angiocardiography. Amer J Cardiol 27:460-463, 1971
804
June 1973
The American
Journal of CARDIOLOGY
5. Krovetz LJ, Simon AL, Levy RJ, et al: Effects of angiocardiographic contrast media on left ventricular function. Johns Hopkins Med J 127:172-183, 1970 6. Rahimtoola MB, Duffy JP, Swan HJC: Ventricular performance after angiocardiography. Circulation 35: 70-77, 1967 7. Levin DC, Baltaxe HA: Effect of radiopaque contrast material on left ventricular end-diastolic pressure. NY State J Med 72:2619-2622,1972 6. Ovitt T, Ritk G, Frech RS, et al: Electrocardiographic changes in selective coronary arteriography: the importance of ions. Radiology 104:705. 1972
Volume 31