CLINICAL RESEARCH: CONGENITAL HEART DISEASE
Hearts late after fontan operation have normal mass, normal volume, and reduced systolic function
A magnetic resonance imaging study
Andreas Eicken, MD*,*,
Sohrab Fratz, MD*,
Christine Gutfried, MD*,
Gunter Balling, MD*,
Markus Schwaiger, PhD ,
Rüdiger Lange, PhD ,
Raymonde Busch, MS ,
John Hess, PhD* and
Heiko Stern, PhD*
* Department of Pediatric Cardiology and Congenital Heart Disease, Deutsches Herzzentrum, Technische Universität, München, Germany
Department of Nuclear Medicine, Technische Universität, München, Germany
Department of Thoracic and Cardiovascular Surgery, Deutsches Herzzentrum, Technische Universität, München, Germany
Institute of Medical Statistics and Epidemiology, Technische Universität, München, Germany
Manuscript received March 7, 2003;
revised manuscript received May 17, 2003,
accepted June 13, 2003.
* Reprint requests and correspondence: Dr. Andreas Eicken, Deutsches Herzzentrum, München, Lazarettstr. 36, D-80636 München, Germany.
eicken{at}dhm.mhn.de
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Abstract
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OBJECTIVES: The purpose of this study was to assess ventricular mass, volume, and systolic function in patients late after Fontan operation by cardiac magnetic resonance imaging.
BACKGROUND: An assessment of determinants for ventricular function in post-Fontan patients was intended.
METHODS: Twenty-three unselected patients (9 female, 14 male) at a median age of 19.4 years (range, 7.8 to 31.3 years), at a median time of 10.5 years (range, 4.1 to 18 years) after Fontan operation were studied. A standard 1.5-T scanner was used, and analysis was performed using dedicated software. Ten healthy volunteers (median age 26.4, range 18 to 39.3 years) served as the control group.
RESULTS: Median end-systolic mass index was 72.2 g/m2 (range, 43 to 138 g/m2) and 86.6 g/m2 (range, 52 to 123 g/m2) in the control group (p = NS). Median end-diastolic ventricular volume was 64 ml/m2 (range, 32 to 117 ml/m2) compared with 67.7 ml/m2 (range, 59 to 75 ml/m2) in the control group (p = NS). Median ejection fraction was 49.3% (range, 20% to 63%) compared with 64.8% (range, 57% to 79%) in normals (p = 0.00001).
CONCLUSIONS: We conclude that long-term survivors of a Fontan operation have normal ventricular mass, normal volume, but reduced systolic ventricular function.
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Abbreviations and Acronyms
| | BSA | | body surface area | | EF | | ejection fraction | | MRI | | magnetic resonance imaging |
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Today the concept of total right ventricular bypass, first performed by Fontan in 1968 (1), is applied in modifications for definite surgical palliation of complex cardiac defects with functionally one ventricle, precluding biventricular repair (2). Separation of the pulmonary and systemic circulation results in normal oxygenation, and therefore patients with univentricular heart disease will generally benefit from this operation. However, the absence of a subpulmonary pumping chamber results in an elevated central venous pressure, low cardiac output, and non-pulsatile pulmonary arterial flow. Long-term postoperative follow-up studies demonstrate significant late morbidity and mortality (3,4). The detrimental effect of ventricular hypertrophy and increased ventricular mass after pulmonary arterial banding in the early postoperative period is well known (5–7).
Cardiovascular magnetic resonance imaging (MRI) is the method of choice for determination of ventricular function, mass, and volume in patients with heart failure and normal cardiac anatomy (8). The superb imaging quality of comtemporary MRI technology yields precise information even in studies with small sample size (9). So far, only few reports exist on MRI studies on ventricular mass and volume after Fontan operation (10–13). Therefore, the aim of this study was to determine ventricular mass, volume, and function late after this operation by MRI.
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Methods
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Patients.
From January 1999 to January 2001, a total of 23 unselected patients (9 female and 14 male) were included in the study. Median age was 19.4 years (range, 7.8 to 31.3 years), median weight was 55.9 kg (range, 21 to 103 kg), and median time after Fontan operation was 10.5 years (range, 4.1 to 18 years). Details for each patient are listed in Table 1. Twenty patients had a morphologic left systemic ventricle, and three patients had a morphologic right systemic ventricle. All patients were in sinus rhythm.
Before the Fontan operation, palliative operations were carried out in 17 of 23 patients (aorto-pulmonary shunt n = 11, pulmonary arterial banding n = 6). In six patients, the Fontan operation was the initial surgical procedure. Seventeen patients were treated with a Fontan operation (right atrium to pulmonary artery anastomosis n = 11, right atrium to right ventricle anastomosis n = 6), and in six a total cavopulmonary connection was performed (baffle fenestration n = 5).
The control group consisted of 10 healthy volunteers with a median age of 26.4 years (range, 18 to 39.3 years). Median body surface area (BSA) was 1.6 m2 (range, 0.84 to 2.27 m2) for the Fontan patients and 1.83 m2 (range, 1.72 to 2.38 m2) in the control group (p = 0.001). Because there was a significant difference in BSA, all measured values were indexed to BSA.
MRI.
All studies were performed on a standard 1.5-T scanner (Gyroscan ACS NT, Philips Best NL), using a surface coil with five elements. Short-axis scans covering the entire heart were acquired using a balanced FFE (bFFE) sequence, as previously described (14). Scans were electrocardiogram-triggered and performed under breath-hold. Slice thickness was 6 mm without slice gap, field of view was 350 to 400 mm, and the matrix was 256 x 256 yielding an in-plane resolution of 1.4 to 1.6 mm. Each slice was imaged in 12 phases of the cardiac cycle.
Out of the short-axis cuts of the heart, ventricular end-diastolic and end-systolic volumes as well as myocardial mass were calculated using dedicated software (MASS; Medis, Leiden, The Netherlands) (15). Both ventricular volume and mass were defined as the sum of the volumes and masses from the systemic ventricle and the hypoplastic second ventricle, if present. Myocardial mass was calculated as myocardial volume times 1.05 g/cm3 (16). For calculation of ventricular mass in the control subjects, the right ventricle was also included. Written informed consent was obtained in every patient and control subject.
Statistical analysis.
For statistical analysis, nonparametric tests (Mann-Whitney U test, Spearman) were applied owing to the relatively small patient and control groups. Box plots express median, 25% to 75% quartiles, minimum, maximum, and outliers, respectively. In the text, groups are characterized with median (minimum, maximum) values. Statistical analysis was performed using SPSS version 10.0.5 (SPSS Inc., Chicago, Illinois). The Mann-Whitney U test was done. Statistical significance was accepted at p < 0.05.
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Results
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End-systolic mass index.
There was no significant difference in the end-systolic mass indexes in Fontan patients with (median 75 g/m2, minimum 54, maximum 124 g/m2) or without (median 72.2 g/m2, minimum 42.6, maximum 138 g/m2) previous pulmonary arterial banding (p = NS) (Table 2). Median end-systolic mass index was 72.2 g/m2 (range, 43 to 138 g/m2) in the entire Fontan group and 86.5 g/m2 (range, 52 to 123 g/m2) in the control group (p = NS) (Fig. 1).
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Table 2 Ejection Fraction, End-Diastolic Ventricular Volume, and End-Systolic Ventricular Mass: Magnetic Resonance Imaging Values
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Figure 1 End-systolic myocardial mass/body surface area in g/m2. Comparison of patients after Fontan operation with control subjects (p = NS). Box plots express median, 25% and 75% quartiles, minimum, maximum, and outliers (>1.5 interquartile length values). White rectangles = Fontan; striped rectangles = control. p = 0.12.
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End-diastolic ventricular volume.
There was no significant difference in end-diastolic ventricular volume indexes in Fontan patients with (72.7 ml/m2, minimum 45.3, maximum 104 ml/m2) or without (median 61.2 ml/m2, minimum 32, maximum 117 ml/m2) previous pulmonary arterial banding (p = NS). Median end-diastolic ventricular volume in the entire Fontan group was 64 ml/m2 (range, 32 to 117 ml/m2) compared with 67.7 ml/m2 (range, 59 to 75 ml/m2) in the control group (p = NS) (Fig. 2).
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Figure 2 End-diastolic ventricular volume/body surface area in ml/m2. Comparison of patients after Fontan operation with control subjects (p = NS). Box plots express median, 25% and 75% quartiles, minimum, maximum, and outliers (>1.5 interquartile length values). White rectangles = Fontan; striped rectangles = control. p = 0.29.
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Ejection fraction (EF).
There was no significant difference in EF in previously banded patients (median EF 51.5%, minimum 35%, maximum 60%) in comparison to nonbanded patients (median EF 48.8%, minimum 20%, maximum 63%) (p = NS). Median EF for all Fontan patients was 49.3% (range, 20% to 63%) compared with 64.8% (range, 57% to 79%) in normals (p = 0.00001) (Fig. 3). Ventricular morphology did not significantly affect EF.
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Figure 3 Ventricular ejection fraction (EF) in percent. Comparison of patients after Fontan operation with control subjects (p < 0.0001). Box plots express median, 25% and 75% quartiles, minimum, maximum, and outliers (>1.5 interquartile length values). White rectangles = Fontan; striped rectangles = control. p < 0.0001.
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Discussion
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The results of our study show that hearts late after Fontan operation have normal mass, normal volume, and reduced systolic function. As geometrical assumptions are not necessary, the inclusion of a hypoplastic ventricle in the volume calculation can readily be performed by MRI.
Ventricular mass.
Increased ventricular mass is a risk factor in the early postoperative period after Fontan operation (6,7,17). A previous study from our institution defined pulmonary arterial banding as a risk factor after Fontan operation (5). Ventricular mass index was significantly higher in patients with previous pulmonary arterial banding (125.8 g/m2 vs. 87 g/m2, p < 0.05) at a mean time interval of 2.7 years after the operation. This resulted in a significantly increased incidence of effusions and subaortic stenosis postoperatively.
However, in the majority of our patients, ventricular mass was normal at long-term follow-up, even in patients after previous banding of the pulmonary artery. Left ventricular hypertrophy, assessed by MRI in the Framingham study, was defined as mass exceeding 95.0 and 74.7 g/m2 in men and women, respectively (18). In our study, ventricular mass comprised both right and left ventricular myocardium. Therefore, in patients with univentricular heart, ventricular hypertrophy was considered to be present when mass exceeded a value of 110 g/m2. According to this definition, three of our patients proved to have increased ventricular mass. Of these, two had dilated ventricles. Lower values than in the early postoperative period were assessed. In a report by Fogel et al. (11), ventricular mass, assessed by MRI, was elevated to a mean value of 120 g/m2 two years after Fontan operation. Normalization of ventricular mass has not been reported previously.
The Fontan physiology is characterized by decreased cardiac index with increased systemic vascular resistance (19). It can be speculated that this chronic state of low cardiac output results in small ventricles with normal, or even reduced ventricular mass. Although Gewillig et al. (20) demonstrated in animal experiments that ventricular mass was the last parameter to reach normal values after unloading of systemic ventricles, this has not been reported in patients long-term after Fontan operation.
Ventricular volume.
Our results define long-term (median 10.5 years) MRI-derived ventricular dimensions after Fontan operation. Mean ventricular end-diastolic volume was normal in our study group. This is in concordance with early postoperative findings of other investigators (11,20). Again the group of Fogel et al. (11) found a mean ventricular volume of 68.4 ml/m2 early after operation. Our data extend this experience to the long-term postoperative course. Two patients, as previously mentioned, had large ventricles (>100 ml/m2 ) with poor EF. In both patients, unloading of the systemic ventricle was performed late in life after previous palliation (age 14.5 and 15.7 years, respectively). Possibly, as argued by Gewillig et al. (21), for these patients volume unloading came too late. A "point of no return" is known to exist for patients with ventricular overload as due to aortic regurgitation (22). These patients may have been beyond the point where reversal of ventricular dilation would have been possible. Retrospectively, they probably should not have undergone a Fontan operation. End-diastolic ventricular volume was higher in patients after previous pulmonary arterial banding. However, the difference was statistically not significant. Six of 23 patients (26%) had a ventricular volume above 72 ml/m2 (mean control value ± 1 SD).
Systolic ventricular function.
Additionally, ventricular EF was significantly reduced in comparison to normal control subjects (p = 0.00001). Another investigator also found decreased systolic ventricular function after Fontan operation (11). Previous pulmonary arterial banding had no impact on ventricular function.
Deterioration of systolic or diastolic ventricular function results in a rise of venous pressures. Failure of the Fontan circulation may then occur. Thus, the assessment of cardiac volumes, mass, and EF yields valuable diagnostic, prognostic, and therapeutic implications.
Echocardiography has been widely used as it is readily available and noninvasive. In conjunction with stress echocardiography, ventricular function was assessed after Fontan operation (21,23). M-mode echo relies on geometric assumptions that do not take into account the complex anatomy in a functional single ventricle. Furthermore, regional changes in ventricular architecture or wall motion abnormalities prevent precise measurements. Two-dimensional echo (transthoracal or transesophageal) also extrapolates data from limited measurements of the systemic ventricle (24). We used cardiac MRI to measure ventricular dimensions. Cardiac MRI has been shown to be accurate and reproducible to determine cardiac mass, volume, and function in adults with normal and dilated hearts (16,25,26). Magnetic resonance imaging evaluation of the systemic ventricle is feasible in patients after Fontan operation (10,11,14,27).
Study limitations.
The number of patients is relatively small in this study. Natural bias occurs if a small patient group is broken down by categories. Hence the statement that ventricular mass is not significantly different in patients with and without previous banding during long-term follow-up after a Fontan operation needs to be regarded with caution. The lack of statistical significance may be explained by the low number of included patients with previous pulmonary arterial banding. Reliable information on ventricular function can be gained even in studies with small sample size, owing to excellent data collection by MRI scanners (9). Furthermore, study bias may occur because during long-term observation assessement is restricted to survivors. Fontan et al. (3) reported a 10-year survival of only 60% of all patients undergoing a Fontan operation.
Conclusions.
We conclude that hearts late after Fontan operation have normal mass, normal volume, and reduced systolic function.
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Footnotes
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This work was supported by the 1999 grant "Maximilian-Forschungs-Förderpreis (Herzkind.e.V.)."
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References
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Abstract
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