An Echocardiographic Index for Separation of Right Ventricular Volume and Pressure Overload

View metadata, citation and similar papers at core.ac.uk brought to you by CORE

918 provided bylACC ElsevierVol. - Publisher 5, No.4 Connector April 1985:918-24

THOMAS RYAN, MD, OLIVERA PETROVIC, MD, JAMES C. DILLON, MD, FACC, HARVEY FEIGENBAUM, MD, FACC, MARY JO CONLEY, WILLIAM F. ARMSTRONG, MD, FACC Indianapolis, Indiana

Abnormal motion oftheinterventricularseptum has been In all normal subjects, the eccentricity index at both described as an echocardiographic feature of both right end-systole and end-diastole was essentially 1.0, as would ventricular volume and pressure overload. To determine be expected if the left ventricular cavity was circular in if two-dimensional echocardiography can separate these the short-axis view. In patients with right ventricular two entities and distinguish them from normal, geometry volume overload, the eccentricity index was approxi and motion of the interventricular septum in short-axis mately 1.0 at end-systole, but was significantly increased views of the left ventricle were evaluated in 12 normal at end-diastole (mean eccentricity index = 1.26 ± 0.12) subjects and 35 patients undergoing cardiac catheter (p < 0.001). In patients with right ventricular pressure ization. Thirteen of the 35 patients had uncomplicated overload, the eccentricity index was significantly greater atrial septal defect with associated right ventricular vol than 1.0 at both end-systole and end-diastole (1.44 ± ume overload, but no elevation in pulmonary artery 0.16 and 1.26 ± 0.11, respectively) (p < 0.001). These pressure. The 22 remaining patients had a pulmonary results suggest that an index of eccentric left ventricular artery systolic pressure greater than 40 mm Hg and, shape which reflects abnormal motion of the interven thus, constituted the group with right ventricular pres tricular septum can be defined. This index is easily ob sure overload. An eccentricity index, defined as the ratio tained and allows separation of normal subjects, patients of the length of two perpendicular minor-axis diameters, with right ventricular volume overload and patients with one of which bisected and was perpendicular to the in. right ventricular pressure overload. terventricular septum, was obtained at end-systole and (J Am Coil CardioI1985;5:918-24) end-diastole.

Abnormal motion of the interventricular septum has been normal motion may be manifest in systole or diastole, or described as an echocardiographic feature of several patho both, depending on the pathologic state. logic states (1-9). As a structure common to both ventricles, Two conditions often associated with abnormal septal the shape and motion of the septum reflects the functional motion are right ventricular volume overload and right ven dynamics of these two chambers. Although the normally tricular pressure overload. Both are characterized by a dis functioning septum behaves as an integral part of the left placement during either systole or diastole of septal position ventricle, certain conditions permit the septum to more closely toward the left ventricle. As a result, left ventricular ge reflect right ventricular hemodynamics. The pattern of ab- ometry becomes altered, with a characteristic flattening of septal contour. The purpose of this investigation was to determine if two-dimensional echocardiography can distin From the Department of Medicine, Krannert Institute of Cardiology, guish right ventricular volume from pressure overload. We Indiana University School of Medicine, Indianapolis, Indiana. This study evaluated left ventricular geometry in the short-axis view was supported in part by the Herman C. Krannert Fund, Indianapolis, Indiana; Grants HL-06308 and HL-071820 and Clinical Investigator Award using an index of septal flattening which can be applied to HL-01041-02 from the National Heart, Lung, and Blood Institute, National patients to distinguish pressure from volume overload of the Institutes of Health, Bethesda, Maryland; the American Heart Association, right ventricle. Indiana Affiliate, Indianapolis and a Grant-in-Aid from the Whitaker Foun dation, Camp Hill, Pennsylvania. Dr. Armstrong is a recipient of a Clinical Investigator Award from the National Institutes of Health/National Heart, Lung, and Blood Institute. Manuscript received August 20, 1984; revised Methods manuscript received October 30, 1984, accepted October 30, 1984. Address for reprints: Thomas Ryan, MD, Indiana University Medical Subjects (Table 1). Thirty-five consecutive patients with Center, UH N-563, 926 West Michigan Street, Indianapolis, Indiana 46223. right ventricular overload who underwent right heart cath-

Table 1. Clinical Data and Primary Diagnoses in 12 Normal Subjects and 35 Patients With Right Ventricular Overload

Underlying Disorders Age PASP Group (yr) (mmHg) None ASD PS RHD PHT PDA CM

Normal 36 ± 7 12 0 0 0 0 0 0 (n = 12) RVVO 35 ± 14 27.9 ± 6 0 13 0 0 0 0 0 (n = 13) RVPO 43 ± 14 89.7 ± 30* 0 3 3 12 2 (n = 22) *For three patients with pulmonary stenosis, right ventricular systolic pressure was substituted for pulmonary artery systolic pressure. Values are mean ± standard deviation. ASD = uncomplicated atrial septal defect; CM = cardiomyopathy; PASP = pulmonary artery systolic pressure; PDA = patent ductus arteriosus; PHT = primary pulmonary hypertension; PS = pulmonary stenosis; RHD = rheumatic heart disease; RVPO = right ventricular pressure overload; RVVO = right ventricular volume overload. eterization within 2 weeks of echocardiographic examina Echocardiographic measurements. The videotape was tion were identified retrospectively. The group with right analyzed on a commercially available off-line system with ventricular volume overload included 13 patients (10 women) a self-contained video disc (Micro Sonics, Inc). An eccen with uncomplicated atrial septal defect and a pulmonary to tricity index was derived as defined previously (11). Ini systemic flow ratio of 1.3: 1 to 4: I. All 13 patients had a tially, two methods were employed to obtain the diameters pulmonary artery systolic pressure of 40 mm Hg or less used to compute the eccentricity index. The endocardial (range 18 to 40). No patient in this group had tricuspid or contour was traced electronically at end-systole and end pulmonary insufficiency as the cause of their right ventric diastole using a regional wall motion software package (Mi ular volume overload. cro Sonics, Inc). For the purpose of this study, papillary The group with right ventricular pressure overload in muscles were ignored and the circumference was extended cluded 22 patients (17 women) with pulmonary artery sys by means of a hypothetical line at the base. Once traced, tolic pressure of 45 mm Hg or greater (range 45 to 148). the endocardial center of area was determined and used as Included within this group were nine patients with an ele a point through which several diameters were automatically ment of right ventricular volume overload, either due to drawn. One diameter, which bisected and was perpendicular atrial septal defect or tricuspid regurgitation. The underlying to the plane of the interventricular septum, was designated disorders in these patients are outlined in Table I. Patients D I. A second diameter, D2 , was perpendicular to D I and, with segmental wall motion abnormalities, left bundle branch thus, parallel to the septum (Fig. I). block or Ebstein's anomaly were excluded from the study. The control group included 12 subjects (5 women) with Figure 1. Schematic representation of the parasternal short-axis no evidence of heart disease. view at the level of the mitral valve-chordae tendineae transition, Echocardiographic methods. Two-dimensional echo illustrating derivation of the eccentricity index. See text for further cardiograms were performed using one of two commercially discussion. 0 1 = left ventricular minor-axis diameter perpendic available instruments: an ATL 300 with a 3 MHz transducer ular to the septum; O2 = left ventricular minor-axis diameter or a Smith Kline 10 with a 2.25 MHz transducer. Inter parallel to the septum. ventricular septal motion and configuration were analyzed in the standard parasternal short-axis view at the level of the papillary muscles, chordae tendineae or tips of the mitral leaflets (10). All studies were reviewed in real time with the capability of slow motion and frame by frame analysis. Appropriate stop frame images depicting end-systole and end-diastole were measured using a calibrated electronic caliper system. End-systole was defined as the frame in which the smallest short-axis area was contained. End-di astole was defined as the peak of the R wave on a simul taneously derived electrocardiogram. Extrasystolic and first End-diastole End-systole postextrasystolic beats were not analyzed. Measurements were performed independently by one nonblinded and one blinded observer. Eccentricity Index =O2/01 920 RYAN ET AL. JACC Vol. 5, No.4 RIGHT VENTRICULAR OVERLOAD April 1985:918-24

Later, a second. more simple method was employed to Table 2. Eccentricity Index at End-Diastole and End-Systole derive D and D • This involved the use of an electronic 1 2 Group El/ED EVES caliper system. The two perpendicular minor-axis diame Normal 1.01 :t 0.04* 1.00 :t 0.06* ters, D] and D , were drawn manually. Care was taken to 2 (n = 12) ensure that the two diameters were oriented properly with RVVO 1.26 :t 0.12t 1.02 :t 0.04* respect to one another and the interventricular septum and (n = 13) to ensure passage of the lines through the center of the cavity RVPO 1.26 :t 0.11 t 1.44 :t 0.16t to avoid any foreshortening of the measurement. Measure (n = 22) ments were obtained at end-systole and end-diastole. For *p < 0.001 versus right ventricular pressure overload; tp < 0.001 each patient, three or more representative images were mea versus normal subjects. Values are mean :t standard deviation. El/ED = sured and the results averaged. When these two methods eccentricity index at end-diastole; EVES = eccentricity index at end were compared in 20 randomly selected patients, it was systole; other abbreviations as in Table I. determined that the latter method was as accurate and less time consuming. Consequently, this method was used for significance using Student's t test for paired observations, the derivation of all the data presented in this report. Interobserver variability was evaluated with correlation

An eccentricity index was defined as the ratio D21D] and coefficients and paired t tests. was calculated at both end-systole and end-diastole. Thus, an eccentricity index equal to unity would describe a situ ation in which the lengths of the two minor-axis diameters Results were the same. This would occur if the left ventricular cavity The results for all study subjects are summarized in Table were circular in the short-axis view. Septal flattening would 2 and Figure 2. be detected as a relative decrease in D] and would result in Normal subjects. For normal subjects and patients with an eccentricity index greater than one. The degree of flat out right ventricular overload, normal left ventricular shape tening would be directly proportional to the eccentricity in the short-axis view is circular at both end-systole and index and would, thus, provide a quantitative assessment end-diastole (Fig. 3). The eccentricity index in 12 normal of the magnitude of septal deformity at both end-systole and volunteers was l.00 ± 0.06 and l.01 ± 0.04 at end-systole end-diastole. and end-diastole, respectively. Although the range of values Hemodynamic measurements. Cardiac catheterization is slightly greater at end-systole, in no case did the eccen was performed using standard hemodynamic and angio tricity index exceed l.1O. graphic methods. Right ventricular or pulmonary artery Right ventricular volume overload. Patients with right pressure, or both, were measured using a fluid-filled catheter ventricular volume overload (Fig. 4) were also characterized system. Systemic and pulmonary flows were calculated by by a circular left ventricular configuration at end-systole the Fick method (12). (eccentricity index = 1.02 ± 0.04). At end-diastole, how Statistical methods. Within each group, eccentricity in ever, the eccentricity index was significantly greater (ec dex was expressed as the mean ± standard deviation. The centricity index = 1.26 ± 0.12, P < 0.001 compared with mean values from the groups were compared for statistical normal subjects). In each case, the eccentricity index in-

1.6 - -1.6

x Q) "0 .E 1.4 - - 1.4 > Figure 2. Summary of eccentricity index :!: o values obtained at end-diastole and end '':::: systole. Vertical bars represent mean ± ....c: Q) 1.2 - -1.2 standard deviation. RVPO = right ven o o tricularpressure overload; RVVO = right UJ ventricular volume overload. 1.0- I~l -1.0

I I I II DIASTOLE SYSTOLE DIASTOLE SYSTOLE DIASTOLE SYSTOLE Normal RVVO RVPO n=12 n=13 n=22 lACC Vol. 5. No.4 RYANET AL. 921 April 1985:918-24 RIGHT VENTRICULAR OVERLOAD

Figure 3. Normalsubject. Parasternal short axis views atend-diastole (OIAST) (left)and end-systole (SYST) (right) demonstrating a circular left ventricular configuration. Ec centricity index (0110\) equals 1.04 and1.06 atend-diastole andend-systole, respectively.

0\ :0 left ventricular minor-axis diameter perpendicular to the septum; O2 = left ven tricular minor-axis diameter parallel to the septum; RV = right ventricle.

creased fromend-systole to end-diastole. There was no over volume overload. In two patients, the eccentricity index was lap in eccentricity index values obtained at end-diastole less at end-systole than at end-diastole. One of these patients between normal subjects and patients with right ventricular had mitral stenosis and significant pulmonary hypertension volume overload. Thus, the eccentricity index at end-di (pulmonary artery pressure of 81140 mm Hg) and the other astole served to clearly separate these two groups. had an atrial septal defect with pulmonary artery pressure Among patients with right ventricular volume overload, of 45/22 mm Hg (the lowest pulmonary artery systolic pres the range of values for eccentricity index at end-diastole sure in the group). was relatively broad (1.10 to I. 55). Although there was no Neither the cause of the pressure overload nor the pres significant correlation between eccentricity index and pul ence of concurrent volume overload interfered with the abil monary artery systolic pressure within this group, pulmo ity of the eccentricity index to identify patients within this nary artery systolic pressures fell within a relatively narrow group. At least nine patients within this group had some range (18 to 38 mm Hg). element of volume overload. This included three patients Right ventricular pressure overload. Among patients with atrial septal defect and Eisenmenger's physiology and with right ventricular pressure overload (Fig. 5), defined as six patients with tricuspid insufficiency. The pattern of left pulmonary artery systolic pressure of 45 mm Hg or greater, ventricular deformity observed in these patients, as defined eccentricity index at end-systole was significantly greater by the eccentricity index, was indistinguishable from those than I (1.44 ± 0.16) and this allowed separation of these with pure pressure overload. The eccentricity index at end patients from normal subjects (p < 0.(01) and patients with systole allows separation of patients with both pressure and right ventricular volume overload (p < 0.(01). Again, there volume overload from those with pure volume overload. was no overlap between the eccentricity index at end-systole No significant correlation existed between the eccentricity in patients with right ventricular pressureoverload and those index atend-systole andthepulmonary arterysystolic pressure. from the other two groups. In 20 (91%) of the 22 patients, Reproducibility. Interobserver variability was evalu the eccentricity index was greater at end-systole than at end ated by comparing eccentricity index values measured by diastole, a change which separated patients with right ven two independentobservers, one blinded and one not blinded. tricular pressure overload from those with right ventricular Agreement was excellent between paired observations as

Figure 4. Right ventricular volume over load. Parasternal short-axis views from a 20 yearold woman with an atrial septal defect and a pulmonary artery systolic pressure of 18 mm Hg. Abnormal leftventricular shape, apparent atend-diastole, resolved atend-sys tole. Eccentricity index was 1.52 and 1.04, respectively. Abbreviations as in Figure 3. 922 RYANET AL. lACC Vol. 5, No.4 RIGHT VENTRICULAR OVERLOAD April 1985:918-24

Figure 5. Right ventricular pressure over load. Parasternal short-axis views from a 28 year old woman with primary pulmonary hy pertension (pulmonary artery systolic pres sure of 68 mm Hg). Left ventricular deform ity due to septal flattening is evident at both end-diastole and end-systole. Eccentricity in dex was 1.45 and I. 68, respectively. Ab breviations as in Figure 3.

measured by Student's t test (r = 0,92 at end-systole and One final potential problem in deriving the eccentricity r = 0.83 at end-diastole). Paired t test analysis revealed no index is the timing of sampling points. End-diastole was systematic deviation between observers. defined in this study as the peak of the R wave. This sam pling point, which preceeds atrioventricular valve closure, was chosen for reproducibility and convenience. Particular Discussion care must be taken to avoid sampling later (that is, very Abnormal motion of the interventricular septum was first early systole) in patients with right ventricular volume over described using echocardiography in 1969 by Popp et al. load because of the rapid normalization of left ventricular (1). Although initially reported in patients with right ven shape that occurs during this phase. End-systole was defined tricular volume overload, it has since been described in a as the frame in which the smallest short-axis area was viewed. variety of clinical settings including right ventricular pres Admittedly, this ignores changes in septal configuration that sure overload (4,13-15). Two-dimensional echocardio might occur during isovolumic relaxation. Previous studies graphic studies have emphasized abnormal left ventricular in patients with right ventricular pressure overload are in shape, primarily due to a reversal in normal septal curvature, disagreement as to when septal deformity is most profound. to account for what earlier investigators using M-mode echo In children with pulmonary hypertension, King et al. (13) cardiography had referred to as paradoxical septal motion. observed that left ventricular configuration was most ab Derivation of the eccentricity index. In this study, we normal immediately before mitral valve opening. A study used an index of left ventricular deformity that provides a in adults with elevated right ventricular systolic pressure quantitative assessment of septal flattening. Previous work (15), however, suggests that septal deformity is greatest in from our laboratory (11) demonstrated that end-diastolic early diastole. We noted that the degree of septal flattening, septal flattening, as defined by an elevated eccentricity in as seen in this group of patients, changes relatively little dex, occurs in the setting of an atrial septal defect and during this phase of the cycle. Thus, the exact timing of normalizes when the volume overload is eliminated. The end-systole does not appear to be a crucial factor in deter eccentricity index is easily obtained, reproducible and can mining an accurate eccentricity index. be applied to most patients with abnormal patterns of septal Normal subjects. In all normal volunteers, left ventric motion. Good separation can be achieved by sampling at ular shape was essentially circular at end-systole and end end-systole and end-diastole among normal subjects, pa diastole. Similar observations have been reported in pre tients with right ventricular volume overload and patients vious studies of adults (15,17). In a normal pediatric pop with right ventricular pressure overload. ulation, however, King et al. (13) observed that while the Despite the ease and reproducibility of this method, sev left ventricular cavity appears round, a slight degree of septal eral details must be considered when deriving the index in flattening exists, particularly at end-systole. Our technique an individual patient. The first is the problem of where to would support these observations. The range of eccentricity measure. We chose the mid left ventricular level between index values among normal volunteers was 0.92 to 1.10, the papillary muscles and the tips of the mitral leaflets. certainly within the limits of the technique. Although two Sampling too near the base results in distortion of septal perpendicular diameters of equal length do not necessarily motion by aortic root motion (16). Sampling too near the define a circle, by our methods, an eccentricity index ap apex may lead to a failure to detect abnormalities as pointed proximately equal to unity would be anatomically unlikely out in previous studies (3). Scans that are slightly off axis in the presence of any significant deformity. can result in an artifactually flattened septum and, thus, an Right ventricular volume overload. In patients with inaccurate eccentricity index. right ventricular volume overload, significant left ventricular lACC Vol. 5, No.4 RYAN ET AL. 923 April 1985:918-24 RIGHT VENTRICULAR OVERLOAD

deformity was observed only at end-diastole. By end-sys would be critical in establishing such a relation . Since our tole, normalization of left ventricular configuration had oc definition of end-systole differed from either of these two curred. Similar findings have been reported using two-di previous studies (13,15), this may partially explain our re mensional echocardiography (3), as well as contrast (18) sults. Finally, our group of patients with right ventricular and radionuclide ventriculography (19). This observation is pressure overload included a variety of underlying disorders consistent with the concept that, in the absence of elevated that could independently affect systolic septal motion. right-sided systolic pressure, right ventricular volume over Conclusion. Abnormal left ventricular configuration is load is primarily a diastolic event. commonly observed in patients with right ventricular vol The observation that left ventricular deformity was pres ume or pressure overload. This change in shape is primarily ent at end-diastole but not end-systole would support the the result of leftward displacement of the interventricular hypothesis that septal flattening reflects relative right and septum, due to overload of the right ventricle. We have left ventricular filling. Thus, left to right shunting augments described a method for quantitating this phenomenon, which right ventricular diastolic volume at the expense of left ven can be applied at end-systole and end-diastole. This may be tricular diastolic volume. A leftward shift in septal position useful in identifying patients with right ventricular volume is the anatomic correlate of this phenomenon. Others (20) overload or right ventricular pressure overload, or in dis have noted that abnormal motion of the interventricular sep tinguishing patients with an uncomplicated right ventricular tum is generally associated with relatively large interatrial volume overload from those with superimposed pressure shunts . Chazal et al. (21) correlated the magnitude of early overload. diastolic septal motion with the pulmonary to systemic flow ratio and suggested an imbalance in ventricular filling rates We gratefully acknowledge the assistance of Naomi Fineberg, PhD in the to account for this relation. A limitation of our study is that statistical analysis of the data, and Nancy Naan for secretarial support. other forms of right ventricular volume overload, such as isolated tricuspid or pulmonary insufficiency, were not in cluded. Weymen et al. (3) observed that septal motion ab References normalities were more striking in this group of patients than l. Popp RL, Wolfe SB, Hirata T, Feigenbaum H. Estimation of right in patients with an atrial septal defect. We excluded these and left ventricular size by ultrasound. A study of the echoes from patients for two reasons: I) because of the difficulty in the interventricular septum. Am J Cardiol 1969;24:523-30. quantitating the degree of volume overload in the setting of 2. DiamondMA, DillonJC, HaineCL, Chang S, Feigenbaum H. Echo valvular insufficiency, and 2) these conditions rarely exist cardiographic features of atrial septaldefect.Circulation 1971 ;43:129-35. in isolation in adult patients . 3. Weyman AE, Wann S, Feigenbaum H, Dillon Je. Mechanism of abnormal septal motionin patients with right ventricularvolumeover Right ventricular pressure overload. In patients with load. Circulation 1976;54:179-86. right ventricular pressure overload, left ventricular deform 4. Tanaka H, Chuwa T, Shoichero N, et al. Diastolic bulging of the ity persisted throughout the cardiac cycle. In most patients interventricular septumtowardthe left ventricle. Anechocardiographic (91%), the degree of deformity was greater at end-systole. manifestation of negative interventricular pressure gradient between left and right ventriclesduring diastole. Circulation 1980;62:558-63. End-systolic septal flattening has been shown to be a sen 5. Payvandi MN, Kerber RE. Echocardiography in congenital and ac sitive marker for right ventricular systolic hypertension in quired absence of the pericardium. Circulation 1976;53:86-92. children (13). Shimada et al. (15) demonstrated end-systolic 6. DillonJC, ChangS, FeigenbaumH. Echocardiographic manifestations septal deformity in adults with pulmonary hypertension. In of left bundle branch block. Circulation 1974;49:876-80. both of these studies (13,15), the magnitude of septal de 7. Kerber RE. Litchfield R. Postoperative abnormalities of interventric formity was correlated with right ventricular systolic pres ular septal motion: two-dimensional and M-mode echocardiographic correlations. Am Heart J 1982;104:263-8 . sure . However, we found no such relation. There may be 8. WeymanAE, HegerJJ, Krenik G, Wann LS, DillonJC, Feigenbaum several reasons for this. In animals as well as human sub H. Mechanism of paradoxical early diastolic septal motion in patients jects, septal position has been shown to reflect the instan with mitral stenosis: a cross-sectionalechocardiographic study. Am J taneous transseptal pressure gradient (4, 14). With right ven Cardiol 1977;40:691-9. tricular pressure overload, peak right ventricular pressure 9. AjisakaR, lesakaY. TakamotoT. et al. Echocardiographic assessment of left ventricularvolumeoverloadinginaorticinsufficiency and mitral mayor may not exceed peak left ventricular pressure. Char insufficiency. J Cardiogr 1978;8:209-16 . acteristically, however, right ventricular ejection is pro 10. Feigenbaum H. Echocardiography. 3rd ed. Philadelphia: Lea & Fe longed , with subsequent delay in right ventricular isovol biger, 1981 :79. umic relaxation. Thus, late systolic septal flattening would II . Schreiber TL. Feigenbaum H. Weyman AE. Effect of atrial septal be expected to occur relatively independently of the mag defect repair on left ventriculargeometry and degree of mitral valve prolapse. Circulation 1980;61 :888-96 . nitude of peak right ventricular pressure. Therefore, the lack 12. GrossmanW. CardiacCatheterization and Angiography,2nded. Phil of correlation between peak right ventricular pressure and adelphia: Lea & Febiger, 1980:131-43. the degree of septal deformity observed in our study was 13. King ME, Braun H, Goldblatt A. LiberthsonR, Weyman AE. Inter not unexpected. It would appear that the timing of sampling ventricularseptal configuration as a predictor of right ventricularsys- 924 RYAN ET AL. lACC Vol. 5, No.4 RIGHT VENTRICULAR OVERLOAD April 1985:918-24

tolic hypertension in children: a cross-sectionalechocardiographicstudy. 18. Popio KA, Gorlin R, Teichholz LE, Cohn PF, Bechtel 0, Herman Circulation 1983;68:68-75. MV. Abnormalities of left ventricular function and geometry in adults 14. Kingma I, Tyberg lV, Smith ER. Effects of diastolic transseptal pres with an atrial septal defect. Ventriculographic, hemodynamic and sure gradient on ventricular septal position and motion. Circulation echocardiographic studies. Am 1 Cardiol 1975;36:302-8. 1983;68:1304-14. 19. Hung 1, Uren RF, Richmond DR, Kelly DT. The mechanism of 15. Shimada R, Takeshita A, Nakamura M. Noninvasive assessment of abnormal septal motion in atrial septal defect: pre- and postoperative right ventricular systolic pressure in atrial septal defect: analysis of study by radionuclide ventriculography in adults. Circulation the end-systolic configuration of the ventricular septum by two-di 1981;63:142-8. mensional echocardiography. Am 1 CardioI1984;53:1117-23. 20. Radtke WE, Tajik Al, Gau GT, Schattenberg TT, Giuliani ER, Tan 16. Hagan AD, Francis GS, Sahn 01, Karliner lS, Friedman WF, credi RG. Atrial septal defect: echocardiographic observations. Studies O'Rourke RA. Ultrasound evaluation of systolic anterior septal motion in 120 patients. Ann Intern Med 1976;84:246-52. in patients with and without right ventricular volume overload. Cir 21. Chazal RA, Armstrong WF, Dillon lC, Feigenbaum H. Diastolic culation 1974;50:248-54. ventricular septal motion in atrial septal defect: analysis of M-mode 17. Rogers EW, Mirro Ml, Godley RW, Caldwell RL, Weyman AE, echocardiograms in 31 patients. Am 1 Cardiol 1983;52:1088-90. Feigenbaum H. Abnormalities of left ventricular geometry and rotation in endocardial cushion defect (abstr). Circulation I979;60(suppl II):II 145.