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Evaluation of atrioventricular septal defect by magnetic resonance imaging
Evaluationof Attioventricular Septal Defect by Magnetic ResonanceImaging MARK D. JACOBSTEIN,MD, BARRY D. FLETCHER,MD, STANLEY GOLDSTEIN,MD, and THOMAS A. RIEMENSCHNEIDER, MD
Electrocardiographically gated magnetic resonance imaging (MRI) was successfully performed in 9 patients with atrioventricular (AV) septal defect: 6 had complete AV canal and 3 had partial AV canal. The defect was readily visualized in all patients on transverse scans taken at the level of the AV valve. The size and extent of the defect could be easily determined. All patients demonstrated a similar underlying morphologic pattern on MRI scans, consisting of deficiency of the primum atrial septum and inlet ventricular septum and a “common” AV valve ring with absence of the cardiac crux. The 3 patients with isolated atriai septal defect could be distinguished from the 6 with complete AV canal by
the dense, fibromuscuiar bridging tissue, which coursed from the AV valve to the crest of the ventricular septum, obliterating the interventricular communication. Four patients had angiographically proved ventricular hypopiasia, which was also detected by MRI. AV valves and their patterns of chordal attachment were accurately imaged in 7 patients on systolic sections; accessory chordae were identified in 6 patients. MRI is a useful noninvasive imaging modality that can depict the underlying morphologic abnormalities in AV septal defect as well as important anatomic variations.
Atrioventricular (AV) septal defect is a cardiac malformation with a characteristic morphologic pattern at the AV septal junction.’ This includes deficiency of the atria1 septum primum, a “scooped-out” appearing left ventricle resulting from deficiency of the inlet ventricular septum, and a 5-leaflet, more-or-less common AV valve.l Despite these basicsimilarities, AV septal defect is a diversegroup of malformations ranging from ostium primum defect to complete AV canal. This diversity results from variations in the morphologic pattern of the AV valve leaflets and differences in their degree of attachment to the crest of the ventricular septum.’ Further variability results during cardiogenesis from unequal apportioning of the ventricular massinto rightand left-sided chambers, producing hypoplasia of one of the ventricles2y3Ventricular hypoplasia has been implicated as an important cause of a high mortality rate after surgical correction of AV canal defects.4
Electrocardiographically gated magnetic resonance imaging (MRI) is a new noninvasivetechnique that can provide excellent spatial and contrast resolution of vascular structures.“-9 By timing information acquisition to the patient’s electrocardiogram (gating), normal and abnormal intracardiac anatomy, including congenital heart defects, can be imaged.5y6This report is a description of the morphology of AV septal defect as demonstrated by MRI.
From the Division of Pediatric Cardiology and the Department of Radiology, Rainbow Babies and Childrens Hospital, and University Hospitals Of Cleveland, Gase Western Reserve University, Cleveland, Ohio. Manuscript received September 24, 1984; revised manuscript received December 5, 1984, accepted December 7, 1984. Address for reprints: Mark D. Jacobstein, MD, Rainbow Babies and Childrens Hospital, 2101 Adelbert Road, Cleveland, Ohio 44106.
(Am J Cardiol 1965;55:1156-1161)
Methods Eleven patients with AV septal defect were entered in the study. All patients had undergone prior evaluation by echocardiography and cardiac catheterization. In 2 infants, sedation was inadequate and images could not be obtained. In 9 patients, 8 months to 33 years, imaging was successful and these patients constitute the study population. Images were obtained with a superconducting magnet operating at 0.3 Tesla. At this field strength, the resonance frequency for protons is 12.85 MHz. Single-echo radiofrequency pulses were applied in sequences consisting of 90” saturation-recovery pulses followed in 15 ms by 180” inversion pulses, resulting in peak ethos 30 ms after the 90” pulse. Because the repetition time (TR) varied with heart rate, relative Tl and T2 contributions to the image were also variable. However, image contrast was not appreciably affected. Multiple, nonsimultaneous, parallel sections (1.0 to 1.4 cm thick)
April 15. 1985 THE AMERICAN JOURNAL OF CARDIOLOGY Volume 55
were obtained in 3 orthogonal planes, transverse (horizontal), coronal and sagittal, and were displayed tomographically. The section thickness was chosen so as to maximize signal-to-noise ratio at the available field strength while acquiring an image within a reasonable length of time. The pulse sequenceswere initiated by the R wave of the patient’s electrocardiogram and were telemetrically transmitted to the controlling computer as previously described.s Data for each section were acquired at the same point in the cardiac cycle for more than 256 heartbeats, requiring 3 to 5 minutes per section. For images acquired during diastole, the pulse sequence immediately
1159
followed receipt of the R wave, whereas for systolic images, a time delay after the R wave was preset according to the heart rate. Examinations were completed within 60 minutes.
Results Atrioventricular septal defect and atrioventricular valve morphology: The AV septal defect was well visualized in all 9 patients. Transverse sections clearly imaged the remnants of the atrial and ventricular septa, delineating the size and extent of the defect. Six patients had large AV canals demonstrated by MRI (Fig. 1, 2 and 3), while 3 had defects confined to the atria1 level (partial AV canal or primum atria1 septal defect) (Fig. 4 and 5). Tomographic sections obtained at the level of the AV valve revealed deficiency of the primum atria1 septum and the inlet ventricular septum in all patients, including the 3 without interventricular communication. In the latter patients, bridging tissue
FIGURE 1. Systolic frame from a patient with atrioventricular (AV) canal, tetralogy of Fallot and mild right ventricular hypoplasia. White arrow indicates the tip of the atrial septum. Note papillary muscle in the left ventricle. accessory chordae faintly seen on the ventricular septal crest and right-sided descending aorta (black arrowhead). The common AV valve is identified between bright signals arising from the AV valve ring.
FIGURE 2. Complete atrioventricular canal with left ventricular hypoplasia. A, marked right ventricular hypertrophy and small left ventricle. Accessory chordal tissue completes the ventricular septum at this level. B, note common atrioventricular valve and discrepant ventricular sizes with septal curvature toward hypoplastic left ventricle. The ventricular component of the defect is visible. LV = left ventricle; RV = right ventricle.
FIGURE 3. Three different transverse sections in a patient with polysplenia syndrome, dextrocardia, atrioventricular canal and hypoplastlc left ventricle. A, the common atrioventrlcular valve and large defect are well seen, as is the common atrial chamber (A). B, accessory chordal tissue (arrow) is seen. C, left ventricular hypoplasia can be appreciated in all views, but is especially well Seen in this section. Note the moderator band (arrow), which identifies the right ventricle. The aorta descends on the left. LV = left ventricle: RV = right ventricle.
1160
MAGNETIC
RESONANCE
IMAGING
OF ATRIOVENTRICULAR
SEPTAL
could be identified from the AV valve to the crest of the ventricular septum (Fig. 4 and 5). This tissue, which obliterated the interventricular communication, could be distinguished from septal musculature by its thinner size and less intense (grayer) signal intensity. In all patients, including those with partial AV canal, there appeared to be a single, common AV valve ring with absence of the cardiac crux and AV septum. As a result, the “mitral” and “tricuspid” components of the common valve are located at the same level. This is different from hearts without AV septal defect (Fig. 6), in which the tricuspid ring is distinctly more anterior or apical in position than the mitral ring. AV valve leaflets were readily imaged on systolicgated scans in 7 patients, including 4 of 6 complete canals and all 3 partial canals. In 2 early studies, only diastolic sections were obtained and leaflets could not be visualized. The AV valve in the 4 complete canals guarded a single, common orifice between atria1 and ventricular chambers, with leaflets spanning the defect. In 3, the AV valve was shown to be loosely attached to the crest of the ventricular septum by accessorychordae (Fig. 1,2 and 3). These chordae did not distort the basic
FIGURE 4. Partial atrioventricular (AV) canal (primum atrlal septal defect). The underlying septal and AV valve morphology are essentially the same as in complete AV canals. Note chordal tissue (small arrow) from AV valve to crest of ventricular septum. No interventricular communication was present on the gated magnetic resonance imaging study or by angiography. Larger arrow indicates edge of the atrial septum which is faintly visualized.
L
--.
DEFECT
architecture of the AV valve. Furthermore, septal bridging was incomplete and large interventricular communications could be visualized. In patients with partial AV canal (ostium primum atrial septal defect), no interventricular communication could be found on MRI study due to complete chordal bridging. In 1 patient (Fig. 4), the morphologic pattern of the AV valve was identical to those in the complete canals. In the 2 other cases, the AV valve architecture was distorted by short, dense chordae that appeared to bind the leaflets to the deficient ventricular septum during systole (Fig. 5). Ventricular size and configuration: Five patients had nearly equal and adequate sized ventricles, demonstrated on MRI (Fig. 4 and 5). In these patients, an imaginary line drawn through the remnant of the ventricular septum would intersect the AV valve ring perpendicularly, dividing it into 2 equal parts. Four patients, 3 with large AV canal defects, and 1 with a partial AV canal, had malapportionment of their ventricles, including 2 with a small left ventricle (Fig. 2 and 3) and 2 with a mildly hypoplastic right ventricle (Fig. 1). In patients with hypoplasia, the ventricular chambers were unequal in size, with the nonhypoplastic chamber exhibiting compensatory dilatation. In addition, the remnant of ventricular septum was frequently deviated toward the smaller chamber (Fig. 2) and a line drawn through the septum would bisect the AV valve obliquely and unequally. Qualitative assessmentof chamber sizes was facilitated by evaluation from multiple planes and by obtaining parallel, contiguous sections. Discussion MRI is ideally suited to evaluation of the cardiovascular system because of the high-resolution of vascular structures, the wide range of spatial resolution (particularly compared to ultrasound), and the lack of interference from the lungs and bony thorax. It is noninvasive and avoids the hazards of ionizing radiation and contrast agents; therefore, it can be repeated frequently. Diagnostic cardiovascular imaging has been made possible with the advent of electrocardiographic gating
.d
FIGURE 5. Partial atrioventricular canal (primum atrial septal defect) with balanced ventricular sizes. Dense bridging of the atrioventricular valve to the ventricular septal crest is seen, resulting in 2 separate orifices despite a common ring. The arrow indicates the tip of the secundum atrial septum, seen separating right from left atrium.
FIGURE 6. Secundum atrial septal defect. The primum atrial septum (arrow), cardiac crux and inlet ventricular septum are present. In contrast to patients with atrioventricular septal defects, 2 separate atrioventricular valves at different levels are imaged. The right ventricle is dilated.
April 15. 1985
techniques that circumvent the loss of detail produced by cardiac motion. Sg Gating also permits images to be obtained at specific intervals during the cardiac cycle. This study suggests that MRI can be a valuable adjunct to angiography and echocardiography in the assessment of patients with AV septal defect. Transverse tomographic sections at the level of the AV valve reveal the underlying morphologic pattern of the AV septal defect: absence of the cardiac crux, deficiency of the primum atria1 septum, variable deficiency of the inlet ventricular septum and a common AV valve ring. This results in a large, central defect that is readily apparent on MRI scans (Fig. 1 to 5). Furthermore, these findings differentiate AV septal defect from other defects. The MRI study in a patient with a secundum atria1 septal defect is shown for comparison in Figure 6. The cardiac crux, primum atria1 septum, inlet ventricular septum and 2 separate AV valve rings are clearly present. Patients with complete AV canal have common AV valves that may be loosely connected to the ventricular septal crest by accessory chordae (Fig. 1,2 and 3). This bridging is incomplete and large interventricular communications can be demonstrated. The AV valve lies wholly within the plane of the AV ring and is not distorted by these accessory chordae. Patients with partial AV canal have similar appearing inlet septal deficiencies and “common” AV valves (Fig. 4 and 5). However, MRI demonstrates accessorychordal tissue which completely bridges the AV valve to the ventricular septal crest, obliterating the interventricular communication. Two types of AV valve morphology were found in patients with partial AV canal. In one (Fig. 4), the AV valve is not distorted and lies within the plane of the AV ring, indistinguishable from the morphology found in complete AV canal. In the other type (Fig. 5), dense, short chordal tissue tightly anchors the valve to the deficient ventricular septal crest, distorting the valve in systole by preventing it from closing within the plane of the AV ring. Ventricular hypoplasia, an important cause of increased surgical risk, is a relatively common finding in otherwise uncomplicated AV septal defect, being present in one series in nearly 20% of hearts with this malformation.* Although the detection of associated ventricular hypoplasia has been described using standard imaging modalities (angiography and echocardiography),3 diagnosis of diminished chamber capacity
THE AMERICAN
JOURNAL
OF CARDIOLOGY
Volume 55
1161
may still be difficult in the presence of a large AV canal defect. MRI is especially well suited to evaluation of ventricular sizes. Four patients in this study showed ventricular hypoplasia. Patients with balanced AV canal have equal sized ventricles and a septum that is midline and straight (Fig. 4 and 5). In contrast, patients with unbalanced AV canal have MRI studies that are characterized by discrepant ventricular sizes and a septum that is deviated toward the smaller chamber (Fig. 1,2 and 3). Since MRI uses a tomographic display format, recognition of normal and abnormal cardiac anatomy is facilitated by sequential imaging in parallel planes through the chest and heart. In this fashion, true defects can be distinguished from image loss created when a structure leaves the plane of imaging. Furthermore, chamber sizes, connections and spatial relations can be appreciated more accurately. Future improvements in MRI technology should produce better resolution, perhaps with 3-dimensional rather than tomographic reconstruction. Along with the additional development of quantitative capabilities, including assessment of ventricular volumes, MRI should prove even more valuable in the evaluation of AV septal defect. Acknowledgmenti We expressour appreciation to Mark Clampitt, RT, and GingerG. Haddad,RT, for expert technical assistance.
References 1. Becker AE, Anderson RH. Atrioventricular septal defects. In: Crawford T, ed.Ethology of Congenital Heart Dlsease. London: Butterworths, 1961; ,
,
IS.
2. Bharati S, Lev M. The spectrum of common atrioventricular orifice (canal). Am Heart J 1973;86:553-581. 3. Mehla ST Hirschfold S, Riggs T, M&man J. Echocardiographic estimation of ventricular hy oplasia in complete atrioventricular canal. Circulation 1979;59:888-89 !. 4. Bhbr M, Blackstone EH. Khidh JW, Paclfko AD, Soto 8, Chuq GK, KHclln JK, Bargeron LY. Determinants of early and late results of repair of atrioventricular septal (canal) defects. J Thorac Cardiovasc Surg 1982;84: 523-542. 5. JacobsteIn MD, Fletcher BD, Nelson AD, Goldstein S, Atftdl RJ, Rlemensdmkler TA. ECGgated nuclear magnetic resonance imaging: appekrance of the congenitally malformed heart. Am Heart J 1984;107:1014-1019. 6. Fletcher BD, Jacobsteln MD, Nelson AD, Rlemenschnekler TA, Alfldl RJ. Gated magnetic resonance imaging of congenital cardiac malformations. Radiology 1984;150:137-140. 7. HerRwns RJ, Hl~lns CB, Hrlcak H, Upton MJ, Crooks LE, Lanzer P, Botvlnkk E, Brunda9e B, Sheldon PE, Kaufman L. Nuclear magnetic resonance imaging of the cardiovascular system: normal and pathologic findings. Radiology 1983;147:749-759. 8. HiOgins CB, Stark D, McNamara M, Lanzer P, Crooks LE, Kaufman L. Multiplane magnetic resonance imaging of the heart and major vessels: studies in normal volunteers. Am J Roentgen01 1984; 142:66 l-667. 9. Jacohsteln MD, Fletcher BD, Nelson AD. Clamottt M. Alfldl RJ. Rlemenschnelder TA. magnetic resonance lmaiing: e\ialuatibn of palliative systemic-pulmonary artery shunts. Circulation 1984;70:650-658.
Electrocardiographically gated magnetic resonance imaging (MRI) was successfully performed in 9 patients with atrioventricular (AV) septal defect: 6 had complete AV canal and 3 had partial AV canal. The defect was readily visualized in all patients on transverse scans taken at the level of the AV valve. The size and extent of the defect could be easily determined. All patients demonstrated a similar underlying morphologic pattern on MRI scans, consisting of deficiency of the primum atrial septum and inlet ventricular septum and a “common” AV valve ring with absence of the cardiac crux. The 3 patients with isolated atriai septal defect could be distinguished from the 6 with complete AV canal by
the dense, fibromuscuiar bridging tissue, which coursed from the AV valve to the crest of the ventricular septum, obliterating the interventricular communication. Four patients had angiographically proved ventricular hypopiasia, which was also detected by MRI. AV valves and their patterns of chordal attachment were accurately imaged in 7 patients on systolic sections; accessory chordae were identified in 6 patients. MRI is a useful noninvasive imaging modality that can depict the underlying morphologic abnormalities in AV septal defect as well as important anatomic variations.
Atrioventricular (AV) septal defect is a cardiac malformation with a characteristic morphologic pattern at the AV septal junction.’ This includes deficiency of the atria1 septum primum, a “scooped-out” appearing left ventricle resulting from deficiency of the inlet ventricular septum, and a 5-leaflet, more-or-less common AV valve.l Despite these basicsimilarities, AV septal defect is a diversegroup of malformations ranging from ostium primum defect to complete AV canal. This diversity results from variations in the morphologic pattern of the AV valve leaflets and differences in their degree of attachment to the crest of the ventricular septum.’ Further variability results during cardiogenesis from unequal apportioning of the ventricular massinto rightand left-sided chambers, producing hypoplasia of one of the ventricles2y3Ventricular hypoplasia has been implicated as an important cause of a high mortality rate after surgical correction of AV canal defects.4
Electrocardiographically gated magnetic resonance imaging (MRI) is a new noninvasivetechnique that can provide excellent spatial and contrast resolution of vascular structures.“-9 By timing information acquisition to the patient’s electrocardiogram (gating), normal and abnormal intracardiac anatomy, including congenital heart defects, can be imaged.5y6This report is a description of the morphology of AV septal defect as demonstrated by MRI.
From the Division of Pediatric Cardiology and the Department of Radiology, Rainbow Babies and Childrens Hospital, and University Hospitals Of Cleveland, Gase Western Reserve University, Cleveland, Ohio. Manuscript received September 24, 1984; revised manuscript received December 5, 1984, accepted December 7, 1984. Address for reprints: Mark D. Jacobstein, MD, Rainbow Babies and Childrens Hospital, 2101 Adelbert Road, Cleveland, Ohio 44106.
(Am J Cardiol 1965;55:1156-1161)
Methods Eleven patients with AV septal defect were entered in the study. All patients had undergone prior evaluation by echocardiography and cardiac catheterization. In 2 infants, sedation was inadequate and images could not be obtained. In 9 patients, 8 months to 33 years, imaging was successful and these patients constitute the study population. Images were obtained with a superconducting magnet operating at 0.3 Tesla. At this field strength, the resonance frequency for protons is 12.85 MHz. Single-echo radiofrequency pulses were applied in sequences consisting of 90” saturation-recovery pulses followed in 15 ms by 180” inversion pulses, resulting in peak ethos 30 ms after the 90” pulse. Because the repetition time (TR) varied with heart rate, relative Tl and T2 contributions to the image were also variable. However, image contrast was not appreciably affected. Multiple, nonsimultaneous, parallel sections (1.0 to 1.4 cm thick)
April 15. 1985 THE AMERICAN JOURNAL OF CARDIOLOGY Volume 55
were obtained in 3 orthogonal planes, transverse (horizontal), coronal and sagittal, and were displayed tomographically. The section thickness was chosen so as to maximize signal-to-noise ratio at the available field strength while acquiring an image within a reasonable length of time. The pulse sequenceswere initiated by the R wave of the patient’s electrocardiogram and were telemetrically transmitted to the controlling computer as previously described.s Data for each section were acquired at the same point in the cardiac cycle for more than 256 heartbeats, requiring 3 to 5 minutes per section. For images acquired during diastole, the pulse sequence immediately
1159
followed receipt of the R wave, whereas for systolic images, a time delay after the R wave was preset according to the heart rate. Examinations were completed within 60 minutes.
Results Atrioventricular septal defect and atrioventricular valve morphology: The AV septal defect was well visualized in all 9 patients. Transverse sections clearly imaged the remnants of the atrial and ventricular septa, delineating the size and extent of the defect. Six patients had large AV canals demonstrated by MRI (Fig. 1, 2 and 3), while 3 had defects confined to the atria1 level (partial AV canal or primum atria1 septal defect) (Fig. 4 and 5). Tomographic sections obtained at the level of the AV valve revealed deficiency of the primum atria1 septum and the inlet ventricular septum in all patients, including the 3 without interventricular communication. In the latter patients, bridging tissue
FIGURE 1. Systolic frame from a patient with atrioventricular (AV) canal, tetralogy of Fallot and mild right ventricular hypoplasia. White arrow indicates the tip of the atrial septum. Note papillary muscle in the left ventricle. accessory chordae faintly seen on the ventricular septal crest and right-sided descending aorta (black arrowhead). The common AV valve is identified between bright signals arising from the AV valve ring.
FIGURE 2. Complete atrioventricular canal with left ventricular hypoplasia. A, marked right ventricular hypertrophy and small left ventricle. Accessory chordal tissue completes the ventricular septum at this level. B, note common atrioventricular valve and discrepant ventricular sizes with septal curvature toward hypoplastic left ventricle. The ventricular component of the defect is visible. LV = left ventricle; RV = right ventricle.
FIGURE 3. Three different transverse sections in a patient with polysplenia syndrome, dextrocardia, atrioventricular canal and hypoplastlc left ventricle. A, the common atrioventrlcular valve and large defect are well seen, as is the common atrial chamber (A). B, accessory chordal tissue (arrow) is seen. C, left ventricular hypoplasia can be appreciated in all views, but is especially well Seen in this section. Note the moderator band (arrow), which identifies the right ventricle. The aorta descends on the left. LV = left ventricle: RV = right ventricle.
1160
MAGNETIC
RESONANCE
IMAGING
OF ATRIOVENTRICULAR
SEPTAL
could be identified from the AV valve to the crest of the ventricular septum (Fig. 4 and 5). This tissue, which obliterated the interventricular communication, could be distinguished from septal musculature by its thinner size and less intense (grayer) signal intensity. In all patients, including those with partial AV canal, there appeared to be a single, common AV valve ring with absence of the cardiac crux and AV septum. As a result, the “mitral” and “tricuspid” components of the common valve are located at the same level. This is different from hearts without AV septal defect (Fig. 6), in which the tricuspid ring is distinctly more anterior or apical in position than the mitral ring. AV valve leaflets were readily imaged on systolicgated scans in 7 patients, including 4 of 6 complete canals and all 3 partial canals. In 2 early studies, only diastolic sections were obtained and leaflets could not be visualized. The AV valve in the 4 complete canals guarded a single, common orifice between atria1 and ventricular chambers, with leaflets spanning the defect. In 3, the AV valve was shown to be loosely attached to the crest of the ventricular septum by accessorychordae (Fig. 1,2 and 3). These chordae did not distort the basic
FIGURE 4. Partial atrioventricular (AV) canal (primum atrlal septal defect). The underlying septal and AV valve morphology are essentially the same as in complete AV canals. Note chordal tissue (small arrow) from AV valve to crest of ventricular septum. No interventricular communication was present on the gated magnetic resonance imaging study or by angiography. Larger arrow indicates edge of the atrial septum which is faintly visualized.
L
--.
DEFECT
architecture of the AV valve. Furthermore, septal bridging was incomplete and large interventricular communications could be visualized. In patients with partial AV canal (ostium primum atrial septal defect), no interventricular communication could be found on MRI study due to complete chordal bridging. In 1 patient (Fig. 4), the morphologic pattern of the AV valve was identical to those in the complete canals. In the 2 other cases, the AV valve architecture was distorted by short, dense chordae that appeared to bind the leaflets to the deficient ventricular septum during systole (Fig. 5). Ventricular size and configuration: Five patients had nearly equal and adequate sized ventricles, demonstrated on MRI (Fig. 4 and 5). In these patients, an imaginary line drawn through the remnant of the ventricular septum would intersect the AV valve ring perpendicularly, dividing it into 2 equal parts. Four patients, 3 with large AV canal defects, and 1 with a partial AV canal, had malapportionment of their ventricles, including 2 with a small left ventricle (Fig. 2 and 3) and 2 with a mildly hypoplastic right ventricle (Fig. 1). In patients with hypoplasia, the ventricular chambers were unequal in size, with the nonhypoplastic chamber exhibiting compensatory dilatation. In addition, the remnant of ventricular septum was frequently deviated toward the smaller chamber (Fig. 2) and a line drawn through the septum would bisect the AV valve obliquely and unequally. Qualitative assessmentof chamber sizes was facilitated by evaluation from multiple planes and by obtaining parallel, contiguous sections. Discussion MRI is ideally suited to evaluation of the cardiovascular system because of the high-resolution of vascular structures, the wide range of spatial resolution (particularly compared to ultrasound), and the lack of interference from the lungs and bony thorax. It is noninvasive and avoids the hazards of ionizing radiation and contrast agents; therefore, it can be repeated frequently. Diagnostic cardiovascular imaging has been made possible with the advent of electrocardiographic gating
.d
FIGURE 5. Partial atrioventricular canal (primum atrial septal defect) with balanced ventricular sizes. Dense bridging of the atrioventricular valve to the ventricular septal crest is seen, resulting in 2 separate orifices despite a common ring. The arrow indicates the tip of the secundum atrial septum, seen separating right from left atrium.
FIGURE 6. Secundum atrial septal defect. The primum atrial septum (arrow), cardiac crux and inlet ventricular septum are present. In contrast to patients with atrioventricular septal defects, 2 separate atrioventricular valves at different levels are imaged. The right ventricle is dilated.
April 15. 1985
techniques that circumvent the loss of detail produced by cardiac motion. Sg Gating also permits images to be obtained at specific intervals during the cardiac cycle. This study suggests that MRI can be a valuable adjunct to angiography and echocardiography in the assessment of patients with AV septal defect. Transverse tomographic sections at the level of the AV valve reveal the underlying morphologic pattern of the AV septal defect: absence of the cardiac crux, deficiency of the primum atria1 septum, variable deficiency of the inlet ventricular septum and a common AV valve ring. This results in a large, central defect that is readily apparent on MRI scans (Fig. 1 to 5). Furthermore, these findings differentiate AV septal defect from other defects. The MRI study in a patient with a secundum atria1 septal defect is shown for comparison in Figure 6. The cardiac crux, primum atria1 septum, inlet ventricular septum and 2 separate AV valve rings are clearly present. Patients with complete AV canal have common AV valves that may be loosely connected to the ventricular septal crest by accessory chordae (Fig. 1,2 and 3). This bridging is incomplete and large interventricular communications can be demonstrated. The AV valve lies wholly within the plane of the AV ring and is not distorted by these accessory chordae. Patients with partial AV canal have similar appearing inlet septal deficiencies and “common” AV valves (Fig. 4 and 5). However, MRI demonstrates accessorychordal tissue which completely bridges the AV valve to the ventricular septal crest, obliterating the interventricular communication. Two types of AV valve morphology were found in patients with partial AV canal. In one (Fig. 4), the AV valve is not distorted and lies within the plane of the AV ring, indistinguishable from the morphology found in complete AV canal. In the other type (Fig. 5), dense, short chordal tissue tightly anchors the valve to the deficient ventricular septal crest, distorting the valve in systole by preventing it from closing within the plane of the AV ring. Ventricular hypoplasia, an important cause of increased surgical risk, is a relatively common finding in otherwise uncomplicated AV septal defect, being present in one series in nearly 20% of hearts with this malformation.* Although the detection of associated ventricular hypoplasia has been described using standard imaging modalities (angiography and echocardiography),3 diagnosis of diminished chamber capacity
THE AMERICAN
JOURNAL
OF CARDIOLOGY
Volume 55
1161
may still be difficult in the presence of a large AV canal defect. MRI is especially well suited to evaluation of ventricular sizes. Four patients in this study showed ventricular hypoplasia. Patients with balanced AV canal have equal sized ventricles and a septum that is midline and straight (Fig. 4 and 5). In contrast, patients with unbalanced AV canal have MRI studies that are characterized by discrepant ventricular sizes and a septum that is deviated toward the smaller chamber (Fig. 1,2 and 3). Since MRI uses a tomographic display format, recognition of normal and abnormal cardiac anatomy is facilitated by sequential imaging in parallel planes through the chest and heart. In this fashion, true defects can be distinguished from image loss created when a structure leaves the plane of imaging. Furthermore, chamber sizes, connections and spatial relations can be appreciated more accurately. Future improvements in MRI technology should produce better resolution, perhaps with 3-dimensional rather than tomographic reconstruction. Along with the additional development of quantitative capabilities, including assessment of ventricular volumes, MRI should prove even more valuable in the evaluation of AV septal defect. Acknowledgmenti We expressour appreciation to Mark Clampitt, RT, and GingerG. Haddad,RT, for expert technical assistance.
References 1. Becker AE, Anderson RH. Atrioventricular septal defects. In: Crawford T, ed.Ethology of Congenital Heart Dlsease. London: Butterworths, 1961; ,
,
IS.
2. Bharati S, Lev M. The spectrum of common atrioventricular orifice (canal). Am Heart J 1973;86:553-581. 3. Mehla ST Hirschfold S, Riggs T, M&man J. Echocardiographic estimation of ventricular hy oplasia in complete atrioventricular canal. Circulation 1979;59:888-89 !. 4. Bhbr M, Blackstone EH. Khidh JW, Paclfko AD, Soto 8, Chuq GK, KHclln JK, Bargeron LY. Determinants of early and late results of repair of atrioventricular septal (canal) defects. J Thorac Cardiovasc Surg 1982;84: 523-542. 5. JacobsteIn MD, Fletcher BD, Nelson AD, Goldstein S, Atftdl RJ, Rlemensdmkler TA. ECGgated nuclear magnetic resonance imaging: appekrance of the congenitally malformed heart. Am Heart J 1984;107:1014-1019. 6. Fletcher BD, Jacobsteln MD, Nelson AD, Rlemenschnekler TA, Alfldl RJ. Gated magnetic resonance imaging of congenital cardiac malformations. Radiology 1984;150:137-140. 7. HerRwns RJ, Hl~lns CB, Hrlcak H, Upton MJ, Crooks LE, Lanzer P, Botvlnkk E, Brunda9e B, Sheldon PE, Kaufman L. Nuclear magnetic resonance imaging of the cardiovascular system: normal and pathologic findings. Radiology 1983;147:749-759. 8. HiOgins CB, Stark D, McNamara M, Lanzer P, Crooks LE, Kaufman L. Multiplane magnetic resonance imaging of the heart and major vessels: studies in normal volunteers. Am J Roentgen01 1984; 142:66 l-667. 9. Jacohsteln MD, Fletcher BD, Nelson AD. Clamottt M. Alfldl RJ. Rlemenschnelder TA. magnetic resonance lmaiing: e\ialuatibn of palliative systemic-pulmonary artery shunts. Circulation 1984;70:650-658.