- Email: [email protected]
Range of normal valve annulus size in neonates
plasty cases(42.9%). Accordingly, the 3 interventional cardiologists who performed all the interventions in this study began to preselect patients to be imaged by IVUS in whom the angiographic findings were limited and the IVUS images were expected to provide more definitive information. Thus imaging of poststent casesincreased from 15.2% (5 of 33) to 40.5% (15 of 37) (p = 0.032), pre/post ELCA or DCA imaging increased from 12.1% (4 of 33) to 32.4% (12 of 37) (p = 0.052), and the imaging of angiographically ambiguous lesions including ostial segmentsincreasedfrom 24.2% (8 of 33) to 45.9% (17 of 37) of cases(p = 0.081). Postballoon angioplasty imaging decreasedfrom 60.6% (20 of 33) to 27.0% (10 of 37) (p = 0.008). There were 3 complications attributed to IVUS imaging. One patient had an angiographically apparent dissection of the left anterior descending coronary artery that developedafter postballoon angioplasty TVUSimaging, which had not been observedby angiography immcdiately after balloon angioplasty. A coronary stent was placed in this vessel without complication. Two patients had coronary vasospasm during IVUS imaging; both were relieved promptly by the intracoronary injection of nitroglycerin. All 3 patients were treated in the catheterization laboratory without further clinical sequelae. ... The use of IVUS imaging for studying the mechanisms of coronary atherosclerosis, coronary intervcntions, and coronary restenosis, and its utility before or after the specific intervention has beenreported by many investigators.‘A However the utility of IVUS for contributing to intervcntional decision making has not been fully assessed.Mints et al? focusing on only preintcrventional imaging, showed that planned interventional therapies were altered after preinterventional IVUS
Range
of Normal
Valve
imaging in 40% of patients. Accordingly, our study included IVUS assessmentof diagnostic cases and a spectrum of interventional therapies using the same imaging console and a 30 MHz, 3.5Fr catheter. In the past year, the frequency of decision making basedon IVUS findings has increaseddramatically (from 49% in the early seriesto 84% in the late series),although there was no change in the composition of total interventional procedures baween these 2 periods. This increase is related to preselection of patients for IVUS associatedwith stent placement,DCA. laser angioplasty, and coronary angiographic lesions of uncertain severity. We conclude that IVUS imaging has become a method for supporting interventional decision making in our laboratory. By selecting patients for IVUS imaging who are undergoing stent placement, DCA, and laser angioplasty, and who have coronary angiographic lesions of uncertain severity, there has been an increase in the clinical utility of IVUS imaging in our laboratory.
1. Honye J, Wd~on DJ. Jam A, Wute CJ. Ramee SR, Wallis JR. .A-parka A, Tohis JM. Morphological effects of coronary hallow angioplas~)’ in YIVO assessed by intravascular ultrasound Imaging. Crrrrrlorion 1992:X5: l~l2-lO2S. 2. Hodgaon JMB. Rcddy KG. Suncja R, Nair RS. Lancfsky Il. Sheehan H&l. Intracoronary uhmtound imaging: am-elation of plaque mwphology with angmgraphy. clinical syndrome and pnrcdural results in paienfs undergoing coronary angioplasty. J Am Co// Cnrdiol 1993;21:354l. 3. Tenaglia AS, Duller EC. Kisslo KR. Stack RS. Davidson CJ. Mechamsms 01 balloon angiopla\ly and dircctmnal aherecromy as assessed by inrracoronary uluasound. J Am Co// Car-&~/ lYY2:20:685-69 I. 4. Xakamura S. Colombo A. Gaglion .A. Almagor Y. Goldbeg SL. Maicllo L. Finci L. ‘I’obis JM. Irnracoronary ultrasound obwvariom during s~cnt implanuion. Circ-darion I YY4:X9:202&2034. 5. Mina GS. Pichard AD, Kovach Jr\, Kent KM, Sadler 1.1:. Javicr SP. Popma JL, Leon MB. Impact of preinrervcnlion inuwarcular ultr~~sound unaging on trascatheter ~rcatment rrrategie\ in coromq anery ditease. Am .I Cardk~l lYY4:73: 423130.
Annulus
Theresa A. Tacy, MD, Roger P. Vermilion, etermination of valve annulus size is often performed in the neonatal period by 2-dimensional D echocardiography. These measurementsare compared with values generatedfrom formalin-fixed heartsin order to determine adequacy of size.’ Annulus dimensions determined by echocardiography diRer by an averageof 17% from the same measurementsperformed in hearts fixed in formalin.* Echocardiographic dimensions measured by M-mode in 93 normal patients ranging in age from 1 day to 18 years have been rcportcd.’ Comparing these data with measurementsperformed with 2-dimensional imaging is inappropriate. Furthermore, the atrioventricular valve dimensions were measured at maximal valve leaflet excursion and were not measurements Frorr :he Deportment of Wio1’1cs. Children’s hospital. Lniversi;y of Wburgh, P&nsy’vanio, end tke Deportmert of Ped;a+rts. C. S r(kztt Children’s Hosoi!ci. Ilnlvcrcltv of Mich’aan. Ann Arbx. Mic?laar Cr. Tocy’s current cddr’ess is’ CiJdre~‘s H&pi&i of Pittsburgh. 3i;iwn of Cardiology, 3705 F-if-h Avenue, Pit’sburgh, Pennsylvania 152 13 r\Aont,script received September 19, 1994; revised mor,Jscrlpt recewcd Novemkxr A, ‘994, and accepted i\rovcmber 7, 1994.
Size in Neonates
MD, and Achi Ludomirsky, MD
of the atrioventricular valve annulus. The range of normal atrioventricular valve annulus sizes in the pediatric population estimated by 2-dimensional echocardiography has been described by King et aL4 This study included 103 patients ranging in age from 1 day to 15 years, with few patients in the neonatal period. These data do not include preterm infants or neonateswho are small for gcstational age. Similarly, Snider et al” determined the aortic dimensions at the level of the sinus of Valsalva and the pulmonary annulus diameter in 110normal children, with 10subjectssmaller than 0.25 m2. Data about the range of normal valve annulus size in the nconatal population, inclusive of pretcrm infants, are therefore lacking. This study determines the range of nonnal valve annulus sizes in pretcrm and term neonates. ... Two-dimensionalechocardiographicstudiesperformed between June 1989 and June 1993 on neonates0 to 10 days old were reviewed and selected using the following criteria: (I) The first IO normal patients in each of 7 weight groups (in kg) (0.5 to 0.99. 1.00 to 1.49, 1.50to 9RIkt
iEPOKlS
541
1.99, 2.00 to 2.49, 2.50 to 2.99, 3.00 to 3.49, and 3.50 to 4.00) were included in the study. This selection processwas designed to ensure an equal distribution of patients across the range of weights. (2) The patients included in the study had no echocardiographic evidence of abnormal intracardiac anatomy or myocardial dysfunction. (3) Patients with a patent ductus arteriosus or chromosomal abnormalities were excluded from the study. (4) Only patients with a complete 2-dimensional echocardiographic examination that was technically adequate for measurementwere included in the study. The study group selectedusing these criteria consisted of 46 male and 24 female infants. The 2-dimensional echocardiographic studies were performed using a 5.0- or a 7.5MHz phased-arraytransducer and were recorded on Kinch super VHS videotape for subsequent analysis. Measurements were obtained with electronic calipers from recorded images
A
Weight
I-
(kg)
16 ---
--r-
--
I
6 6 4
4 I
2 0
.-.-I
2 --L..Il 0
1
B
2
3
Weight
(kg)
4
5
.-
r
.--
=
1.04
-.
L-.-I.. 2
3
Weight
(kg)
4
I 5
16
--
16
see
1
I-.
---/
8
6
6 4 -0
-1
D
1 2
I 3
Weight
(kg)
-..-4
5
E
Weight
(kg)
FIGURE 1. Pane/s A rhroug/~ E demonstmte he relation between annular dimension and patient weight. Sdid lines represent 95% prediction intervals. The regression equation, corrdation coefficient (rs), and SEE are shown far eachvalve.
542
THt AIvI;RICAK.JOU~NA,
OF CARDClOGY*
VOL. 75
h/ARCH 1, ‘995
reviewed on a 9-inch. high-resolution monitor using a commercially available off-line digitizing system (Freeland Systems,Broomfield, Colorado). Five valve annuli were measuredfor each patient. The aortic valve annulus was measuredin the parastemal long-axis view. The mitral valve anteroposterior dimension was measuredin the parastcmal long-axis view, and the lateral dimension was measuredfrom the apical view. The lateral dimension of the tricuspid valve annulus was measuredfrom the apical 4-chamber view. The parastemal short-axis view was utilized for measurement of the pulmonary valve annulus. Each valve annulus measurementwas performed at the onset of valve opening; the average of 3 measurementswas recorded. Valve annulus measurcments were obtained at the baseof the valve leaflets from the apparent hingepoint of valve movement. Two rcaders obtained measurements independently, and each reader was blinded to the results of the other reader.The average of the 2 investigators’ measurementswas used for analysis. Linear regression analysis of the data was used to determine the relation between each annulus diameter and patient weight. The 95% prediction intervals for future observations were determined for the regression functions using the method described by Draper and Smith.” Interobserver variability was assessedby comparing the mean difference in valve annulus measurement,and by use of a linear regression of the valve annulus dimensions between 2 readers. Linear regression analysis demonstratedthat patient weight was a good predictor of normal valve dimensions (Figure 1). Interrater variability was assessedas the mean difference between the valve measurementsperformed by the 2 raters. The mean interobserver difference was 13.S%,ranging from a mean of 11.3%for pulmonary valve measurementsto a mean of 15.8% for tricuspid valve measurements.Interrater measurements had excellent correlation, with an r2 of 0.99 for all valve measurements. Gender was added to the regression equation as a dummy variable in order to investigate possible differences in the relation between weight and valve annulus size between sexes.For each valve, there was no significant difference in the relation between weight and annulus dimension between sexes (p value range 0.817 to 0.978). ... These data provide the tirst reference information for normal valve annulus size of all valves in preterm to term neonates.Often the measurementof atrioventricular or semilunar valve dimensions is performed by 2-dimensional cchocardiography to determine the adequacy of valve size. The valve dimensions are then comparedwith values that have been obtained by identical techniques
in the normal population. However?for the neonatal population, thesedata are lacking. The 5 nomogramsincluded in this study provide these data for patients weighing between 0.5 and 4.0 kg. All of the valve measurementshad excellent interrobserver correlation, indicating that 2-dimensional determination of valve annulus dimension is a reliable and reproducible measurement. Previous studies relating vah!e dimensions to patient size over a wide range of body surfaceareahave demonstrated a complex relation between cardiac dimensions and patient body surface area. Several investigations have noted a linear relation bctwcen the atrioventricular valve dimensions and the natural log of the body surface area.‘,X Snider et al’ found a linear relation with the squareroot of body surfacearea.However, in the neonatal population studied, an excellent correlation was found with a linear relation between atrioventricular and semilunar valve dimensions and patient weight. This linear relation between cardiac measurementsand weight has been previously noted by Baylcn et al? who reported a linear relation between left ventricular dimension and patient weight in prematureinfants. It hasbeensuggested previously that cchocardiographic dimensions be correlated to patient weight as opposed to body surface area in the premature infant or small neonate, since large changesin weight arc associatedwith minimal changes in body surface area in these newboms.3 In our study, linear regression comparison of valve annulus size with patient weight resulted in a good lit for the annulus measurements.These data support the use of patient weight as the independent variable in this assessment. In preterm and term infants, weight can be used as a predictor of normal valve annulus dimensions measured by 2-dimensional echocardiography. The relation of weight and annulus size in neonates without heart disease may be used as a reference standard for determining adequacy of valve annular dimensions. 1. Rou Ia L:F. Rmwldi IIJ. La M. The quanlitar~vc anatomy of rhc normal child’s hean. In: Gxuxr L, cd. Pediatric Clinics of Sorth America: Sympwum on Gcnetits. Philadelphia: WB Saunders. Io63:499-5XX. 2. Gutge\cll HP. Rrickcr JT. Calvin EV, I.atwn LA. Hawkins El’. .Atrio\cntricular \alvc anular diameter: two-dimensional ech(rar[lioe~lpllic-autopsy corxlation.
Am J Cordial 1984:53: l652-16.55. 3. Rqe CL. S~lvcrman XII. Han PA. Raj RM. Canhx
stmc,ure growh partcm detcmuned hy echocardwgraphy. Cir-rulorrofr 197X:57:285-.2(X). King DH, O’Bnan Smith E, Iluhta JC. Gu~gcsell IIP. Mitral and wicurpid anular diameter in nomlal chddrcn deremlined by two-dimensional echocardiography. Am J Cordwl 1985:.59:7X7-789. 5. Snider I\R, Enderlcin MA. Tcitrl DI,, Jucrer RI’. Two-dimenwnal echocardmgraphic detemnnation of sonic and pulmonar) aneq wes from infancy 10 adulthood in nunnal subJec&. An? J Cnrdiol 1984;.53:218 224, 6. Draper UR, Smith H. Fitting a straigh! line by lea square\. In: Applied Rcgression Analysis, Second Edition. ?iew York: John Wiley. 19Rl:l~9. 7. Baylcn R. .Ms)er RA, KoRagcn J. Bewing G III. Bubb ME. Kaplan S. Left ventricular performance in the critically ill prcmalure inf’anr with pxcm ductus anermcus and pulmonary disease. C~rcr&xron 197755: 1X2-188.
4.
Range
of Normal
Valve
imaging in 40% of patients. Accordingly, our study included IVUS assessmentof diagnostic cases and a spectrum of interventional therapies using the same imaging console and a 30 MHz, 3.5Fr catheter. In the past year, the frequency of decision making basedon IVUS findings has increaseddramatically (from 49% in the early seriesto 84% in the late series),although there was no change in the composition of total interventional procedures baween these 2 periods. This increase is related to preselection of patients for IVUS associatedwith stent placement,DCA. laser angioplasty, and coronary angiographic lesions of uncertain severity. We conclude that IVUS imaging has become a method for supporting interventional decision making in our laboratory. By selecting patients for IVUS imaging who are undergoing stent placement, DCA, and laser angioplasty, and who have coronary angiographic lesions of uncertain severity, there has been an increase in the clinical utility of IVUS imaging in our laboratory.
1. Honye J, Wd~on DJ. Jam A, Wute CJ. Ramee SR, Wallis JR. .A-parka A, Tohis JM. Morphological effects of coronary hallow angioplas~)’ in YIVO assessed by intravascular ultrasound Imaging. Crrrrrlorion 1992:X5: l~l2-lO2S. 2. Hodgaon JMB. Rcddy KG. Suncja R, Nair RS. Lancfsky Il. Sheehan H&l. Intracoronary uhmtound imaging: am-elation of plaque mwphology with angmgraphy. clinical syndrome and pnrcdural results in paienfs undergoing coronary angioplasty. J Am Co// Cnrdiol 1993;21:354l. 3. Tenaglia AS, Duller EC. Kisslo KR. Stack RS. Davidson CJ. Mechamsms 01 balloon angiopla\ly and dircctmnal aherecromy as assessed by inrracoronary uluasound. J Am Co// Car-&~/ lYY2:20:685-69 I. 4. Xakamura S. Colombo A. Gaglion .A. Almagor Y. Goldbeg SL. Maicllo L. Finci L. ‘I’obis JM. Irnracoronary ultrasound obwvariom during s~cnt implanuion. Circ-darion I YY4:X9:202&2034. 5. Mina GS. Pichard AD, Kovach Jr\, Kent KM, Sadler 1.1:. Javicr SP. Popma JL, Leon MB. Impact of preinrervcnlion inuwarcular ultr~~sound unaging on trascatheter ~rcatment rrrategie\ in coromq anery ditease. Am .I Cardk~l lYY4:73: 423130.
Annulus
Theresa A. Tacy, MD, Roger P. Vermilion, etermination of valve annulus size is often performed in the neonatal period by 2-dimensional D echocardiography. These measurementsare compared with values generatedfrom formalin-fixed heartsin order to determine adequacy of size.’ Annulus dimensions determined by echocardiography diRer by an averageof 17% from the same measurementsperformed in hearts fixed in formalin.* Echocardiographic dimensions measured by M-mode in 93 normal patients ranging in age from 1 day to 18 years have been rcportcd.’ Comparing these data with measurementsperformed with 2-dimensional imaging is inappropriate. Furthermore, the atrioventricular valve dimensions were measured at maximal valve leaflet excursion and were not measurements Frorr :he Deportment of Wio1’1cs. Children’s hospital. Lniversi;y of Wburgh, P&nsy’vanio, end tke Deportmert of Ped;a+rts. C. S r(kztt Children’s Hosoi!ci. Ilnlvcrcltv of Mich’aan. Ann Arbx. Mic?laar Cr. Tocy’s current cddr’ess is’ CiJdre~‘s H&pi&i of Pittsburgh. 3i;iwn of Cardiology, 3705 F-if-h Avenue, Pit’sburgh, Pennsylvania 152 13 r\Aont,script received September 19, 1994; revised mor,Jscrlpt recewcd Novemkxr A, ‘994, and accepted i\rovcmber 7, 1994.
Size in Neonates
MD, and Achi Ludomirsky, MD
of the atrioventricular valve annulus. The range of normal atrioventricular valve annulus sizes in the pediatric population estimated by 2-dimensional echocardiography has been described by King et aL4 This study included 103 patients ranging in age from 1 day to 15 years, with few patients in the neonatal period. These data do not include preterm infants or neonateswho are small for gcstational age. Similarly, Snider et al” determined the aortic dimensions at the level of the sinus of Valsalva and the pulmonary annulus diameter in 110normal children, with 10subjectssmaller than 0.25 m2. Data about the range of normal valve annulus size in the nconatal population, inclusive of pretcrm infants, are therefore lacking. This study determines the range of nonnal valve annulus sizes in pretcrm and term neonates. ... Two-dimensionalechocardiographicstudiesperformed between June 1989 and June 1993 on neonates0 to 10 days old were reviewed and selected using the following criteria: (I) The first IO normal patients in each of 7 weight groups (in kg) (0.5 to 0.99. 1.00 to 1.49, 1.50to 9RIkt
iEPOKlS
541
1.99, 2.00 to 2.49, 2.50 to 2.99, 3.00 to 3.49, and 3.50 to 4.00) were included in the study. This selection processwas designed to ensure an equal distribution of patients across the range of weights. (2) The patients included in the study had no echocardiographic evidence of abnormal intracardiac anatomy or myocardial dysfunction. (3) Patients with a patent ductus arteriosus or chromosomal abnormalities were excluded from the study. (4) Only patients with a complete 2-dimensional echocardiographic examination that was technically adequate for measurementwere included in the study. The study group selectedusing these criteria consisted of 46 male and 24 female infants. The 2-dimensional echocardiographic studies were performed using a 5.0- or a 7.5MHz phased-arraytransducer and were recorded on Kinch super VHS videotape for subsequent analysis. Measurements were obtained with electronic calipers from recorded images
A
Weight
I-
(kg)
16 ---
--r-
--
I
6 6 4
4 I
2 0
.-.-I
2 --L..Il 0
1
B
2
3
Weight
(kg)
4
5
.-
r
.--
=
1.04
-.
L-.-I.. 2
3
Weight
(kg)
4
I 5
16
--
16
see
1
I-.
---/
8
6
6 4 -0
-1
D
1 2
I 3
Weight
(kg)
-..-4
5
E
Weight
(kg)
FIGURE 1. Pane/s A rhroug/~ E demonstmte he relation between annular dimension and patient weight. Sdid lines represent 95% prediction intervals. The regression equation, corrdation coefficient (rs), and SEE are shown far eachvalve.
542
THt AIvI;RICAK.JOU~NA,
OF CARDClOGY*
VOL. 75
h/ARCH 1, ‘995
reviewed on a 9-inch. high-resolution monitor using a commercially available off-line digitizing system (Freeland Systems,Broomfield, Colorado). Five valve annuli were measuredfor each patient. The aortic valve annulus was measuredin the parastemal long-axis view. The mitral valve anteroposterior dimension was measuredin the parastcmal long-axis view, and the lateral dimension was measuredfrom the apical view. The lateral dimension of the tricuspid valve annulus was measuredfrom the apical 4-chamber view. The parastemal short-axis view was utilized for measurement of the pulmonary valve annulus. Each valve annulus measurementwas performed at the onset of valve opening; the average of 3 measurementswas recorded. Valve annulus measurcments were obtained at the baseof the valve leaflets from the apparent hingepoint of valve movement. Two rcaders obtained measurements independently, and each reader was blinded to the results of the other reader.The average of the 2 investigators’ measurementswas used for analysis. Linear regression analysis of the data was used to determine the relation between each annulus diameter and patient weight. The 95% prediction intervals for future observations were determined for the regression functions using the method described by Draper and Smith.” Interobserver variability was assessedby comparing the mean difference in valve annulus measurement,and by use of a linear regression of the valve annulus dimensions between 2 readers. Linear regression analysis demonstratedthat patient weight was a good predictor of normal valve dimensions (Figure 1). Interrater variability was assessedas the mean difference between the valve measurementsperformed by the 2 raters. The mean interobserver difference was 13.S%,ranging from a mean of 11.3%for pulmonary valve measurementsto a mean of 15.8% for tricuspid valve measurements.Interrater measurements had excellent correlation, with an r2 of 0.99 for all valve measurements. Gender was added to the regression equation as a dummy variable in order to investigate possible differences in the relation between weight and valve annulus size between sexes.For each valve, there was no significant difference in the relation between weight and annulus dimension between sexes (p value range 0.817 to 0.978). ... These data provide the tirst reference information for normal valve annulus size of all valves in preterm to term neonates.Often the measurementof atrioventricular or semilunar valve dimensions is performed by 2-dimensional cchocardiography to determine the adequacy of valve size. The valve dimensions are then comparedwith values that have been obtained by identical techniques
in the normal population. However?for the neonatal population, thesedata are lacking. The 5 nomogramsincluded in this study provide these data for patients weighing between 0.5 and 4.0 kg. All of the valve measurementshad excellent interrobserver correlation, indicating that 2-dimensional determination of valve annulus dimension is a reliable and reproducible measurement. Previous studies relating vah!e dimensions to patient size over a wide range of body surfaceareahave demonstrated a complex relation between cardiac dimensions and patient body surface area. Several investigations have noted a linear relation bctwcen the atrioventricular valve dimensions and the natural log of the body surface area.‘,X Snider et al’ found a linear relation with the squareroot of body surfacearea.However, in the neonatal population studied, an excellent correlation was found with a linear relation between atrioventricular and semilunar valve dimensions and patient weight. This linear relation between cardiac measurementsand weight has been previously noted by Baylcn et al? who reported a linear relation between left ventricular dimension and patient weight in prematureinfants. It hasbeensuggested previously that cchocardiographic dimensions be correlated to patient weight as opposed to body surface area in the premature infant or small neonate, since large changesin weight arc associatedwith minimal changes in body surface area in these newboms.3 In our study, linear regression comparison of valve annulus size with patient weight resulted in a good lit for the annulus measurements.These data support the use of patient weight as the independent variable in this assessment. In preterm and term infants, weight can be used as a predictor of normal valve annulus dimensions measured by 2-dimensional echocardiography. The relation of weight and annulus size in neonates without heart disease may be used as a reference standard for determining adequacy of valve annular dimensions. 1. Rou Ia L:F. Rmwldi IIJ. La M. The quanlitar~vc anatomy of rhc normal child’s hean. In: Gxuxr L, cd. Pediatric Clinics of Sorth America: Sympwum on Gcnetits. Philadelphia: WB Saunders. Io63:499-5XX. 2. Gutge\cll HP. Rrickcr JT. Calvin EV, I.atwn LA. Hawkins El’. .Atrio\cntricular \alvc anular diameter: two-dimensional ech(rar[lioe~lpllic-autopsy corxlation.
Am J Cordial 1984:53: l652-16.55. 3. Rqe CL. S~lvcrman XII. Han PA. Raj RM. Canhx
stmc,ure growh partcm detcmuned hy echocardwgraphy. Cir-rulorrofr 197X:57:285-.2(X). King DH, O’Bnan Smith E, Iluhta JC. Gu~gcsell IIP. Mitral and wicurpid anular diameter in nomlal chddrcn deremlined by two-dimensional echocardiography. Am J Cordwl 1985:.59:7X7-789. 5. Snider I\R, Enderlcin MA. Tcitrl DI,, Jucrer RI’. Two-dimenwnal echocardmgraphic detemnnation of sonic and pulmonar) aneq wes from infancy 10 adulthood in nunnal subJec&. An? J Cnrdiol 1984;.53:218 224, 6. Draper UR, Smith H. Fitting a straigh! line by lea square\. In: Applied Rcgression Analysis, Second Edition. ?iew York: John Wiley. 19Rl:l~9. 7. Baylcn R. .Ms)er RA, KoRagcn J. Bewing G III. Bubb ME. Kaplan S. Left ventricular performance in the critically ill prcmalure inf’anr with pxcm ductus anermcus and pulmonary disease. C~rcr&xron 197755: 1X2-188.
4.