a Laboratory of Echocardiography, Heart Institute (InCor), University of São Paulo Medical School, Brazil
b Laboratory of Pathology, Heart Institute (InCor), University of São Paulo Medical School, Brazil
c Hemodynamics and Interventional Cardiology Laboratory, Heart Institute (InCor), University of São Paulo Medical School, Brazil
d Department of Nuclear Medicine, Heart Institute (InCor), University of São Paulo Medical School, Brazil
e Department of Paediatric Cardiology, Heart Institute (InCor), University of São Paulo Medical School, Brazil
f Department of Cardiology and General Director of the Heart Institute, Heart Institute (InCor), University of São Paulo Medical School, Brazil
Received February 25, 2004; revised June 22, 2004; accepted July 8, 2004 * Corresponding author. Tel.: + 55 11 3069 5252; fax: + 55 11 3069 5279 (E-mail: amussisoares{at}terra.com.br).
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Abstract |
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METHODS: After transcatheter closure of PDA with coils, 70 patients (mean age 8.6±3.4 years) were followed for a period of 3.6±0.9 years (range 2.15.9) and compared to 22 controls. Peak flow velocities and coil protrusion were assessed by Doppler echocardiography. A Doppler velocity index (DVI) was calculated by the difference between the LPA and right pulmonary artery (RPA) peak flow velocities relative to the pulmonary trunk (PT) expressed in percentage, as follows: DVI=(LPA velocityRPA velocity)/PT velocityx100. Lung scintigraphy was performed using 99mTc-labelled macro-aggregated albumin.
RESULTS: Device protrusion was observed in 94% of the patients, 10% of whom presented abnormal left lung perfusion. Peak LPA velocity and DVI were significantly greater in patients (p=0.001) and correlated negatively with left lung perfusion values (R2=0.21 and R2=0.65, respectively). A cut-off value of 50% for the DVI showed high sensitivity and specificity for reduced lung perfusion.
CONCLUSION: Impaired left lung perfusion may appear following transcatheter closure of PDA with coils and the determination of DVI may anticipate such alteration.
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Introduction |
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In order to evaluate the prevalence of coil protrusion to the LPA and its possible impact on the vessel diameters, flow disturbances and left lung perfusion, we studied prospectively, by echocardiography and radionuclide lung scintigraphy, a large group of patients submitted to transcatheter closure of PDA with coils.
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Patients and methods |
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Ten (14.3%) patients presented other associated congenital cardiac defects. Four of them had been previously operated on (one ventricular septal defect, one atrial septal defect, two sub-aortic stenoses) and submitted at the same operation to PDA closure, but showed recanalization in the post-operative evolution and were considered for transcatheter closure. Five other patients had minimal ventricular septal defects, all showing a Qp:Qs<1.2:1. The remaining patient had mild pulmonary valve thickening, without stenosis (peak flow velocity in the pulmonary trunk=1.3 m/s).
Eight patients (11.4%) were diagnosed as having congenital rubella syndrome but none of them presented stenosis of the pulmonary arterial branches.
Control group
The control group consisted of 22 children and adolescents (11 female, 11 male, mean age 9.37±4.2 years, range 3.719), 15 were normal and seven had minimal cardiac lesions (five small ventricular septal defects and one secundum atrial septal defect, all of them presenting Qp:Qs⩽1.1:1, and one non-stenotic bicuspid aortic valve).
This study was approved by the Institution's Ethics and Research Committee and an informed consent was obtained before all procedures for patients and controls.
Coil occlusion procedure
Left lateral aortograms were used to define the ductal angiographic type, according to Krichenko et al.6 Coil occlusion of PDA was performed in a retrograde fashion, via the femoral artery, using the methods of coil selection and implantation described in previous reports.7 Implantation was attempted using the Gianturco coils (Cook Inc., Bloomington, IN, USA) in 62 patients (88.6%) or Cook detachable coils (William Cook Europe, Bjaeverskov, Denmark) in eight patients.
Echocardiographic examinations
Transthoracic echocardiographic studies were performed using HDI 5000 equipment (Philips Medical Systems, Bothell, WA). Images were stored on 0.5 in. VHS format and were available for off-line analysis.
Measurements of the PDA minimal diameter and length were obtained prior to the transcatheter closure from the high left parasternal view.
In the follow-up period, the prevalence of residual shunt was evaluated by colour and pulsed wave Doppler, as well as the position of the coils and the presence of protrusion into the lumen of the LPA from high left and short axis parasternal views. The diameters of both pulmonary arteries were measured from the suprasternal views, at end-systole, and indexed by body surface area as shown in Figs. 1 and 2.
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All examinations were performed by the same investigator without knowledge of either the clinical data or the lung scintigraphy results.
Lung perfusion scintigraphy
Lung perfusion scans were performed using a peripheral intravenous injection of 100,000 to 150,000 particles (10 and 90 μm) of 99mTc-labelled macroaggregated albumin, at a dose of 0.03 mCi/kg. Two views were obtained in the anterior and posterior positions to evaluate the blood flow distribution between the lungs. The percentage of perfusion in both lungs was calculated by dividing the mean radioactivity obtained in both positions.
Predictors of decreased left lung perfusion
Several variables were examined in an attempt to predict which patients might be at increased risk for reduced left lung perfusion: age and weight during occlusion, other congenital cardiac defect or rubella syndrome associated, angiographic ductal type, PDA minimal diameter and length, amount and type of the coils, residual shunt, LPA diameter, coil protrusion into the LPA, peak LPA velocity and DVI.
Statistical analysis
Comparisons of means were performed by the paired or non-paired Student's t-test or the analysis of variance (ANOVA), according to the kind of data and number of tested groups. Correlation between continuous variables was evaluated by the Pearson productmoment correlation coefficient. The ROC curve was used to select an optimal decision regarding the cut-off value of the DVI to predict abnormal lung perfusion. Results are expressed as means±standard deviation and range p-value was set at 0.05 to achieve statistical significance.
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Results |
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The mean PDA minimal diameter obtained by echocardiography was 2.9±0.75 mm (range, 1.25.0 mm) and by angiography 2.1±0.8 mm (range, 0.74.1 mm). The mean lengths were, respectively, 7.9±2.7 mm (range, 416 mm), and 8.3±3.2 mm (range, 2.617.2 mm). The prevalence of residual shunt at the latest follow-up evaluation was 8.6%.
During the PDA occlusion procedure, coil embolization to the pulmonary artery was observed in three patients (2.1%), all of them being successfully retrieved. No embolic episode was noticed at the aorta.
Coil protrusion and pulmonary flow velocities
Sixty-six patients (94.3%) showed protrusion of the device. While the LPA mean peak velocity was significantly higher than in the RPA and the pulmonary trunk (p=0.001), there were no differences between the regional mean peak flow velocities in the control group (p=0.68, Fig. 3). Additionally, the peak LPA velocities and DVI were significantly greater in patients compared to controls (p=0.001) (DVI: 21.6±25.8% versus 1.7±7.3%).
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Correlation between left lung perfusion and LPA velocity and DVI
The mean time interval between the lung scintigraphy and the late echocardiographic study was 81±73.4 days (0287). Seven patients with abnormal left lung perfusion (mean 39±2.6%) presented mean LPA velocity and DVI greater than those with normal left lung perfusion (mean LPA velocity=1.59±0.33 m/s versus 1.09±0.26 m/s; mean DVI=55.5±32.96% versus 12.3±11.9%) (Table 1). Maximal LPA velocity and DVI showed significant negative correlations with left lung perfusion (p=0.001). However, the coefficient was stronger for the DVI (R2= 0.65) than for maximal LPA velocity (R2= 0.21) (Fig. 4). A regression equation was determined as follows: Left lung perfusion (%)=47.7970.0923xDVI.
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Discussion |
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The use of Gianturco coils to occlude the ductus is largely employed in developing countries, due to their low cost, easy manipulation and, above all, efficacy and safety. In the present series, Gianturco coils were used more frequently than Cook coils. The main difference between these two devices is the possibility of release control in the Cook model. Moreover, during the procedure implantation, some degree of protrusion into the pulmonary artery is normal, because in order to anchor the device, the first half of the first loop of the coil is positioned inside the pulmonary artery. This can be minimized by the mechanism of retrievability of the Cook coils. Consequently, Gianturco coils present higher rates of protrusion to the LPA when compared to other coils. While Stromberg et al.,8 described a 90% prevalence of Gianturco coil protrusion in a series of 31 patients, in the present study it was even higher (94.7%).
An alternative explanation for the high protrusion rate would be the greater thrombogenicity of Gianturco coils because of the presence of Dacron wool fibres. Cheung et al.,9 comparing different types of coils, found that the reduction of residual shunt with time tended to be greater when Gianturco coils were used.
When we studied the mean peak velocity in the LPA, we found a higher value than that observed in the RPA and in the PT (p=0.01). However, before trying to correlate such values to lung perfusion results, we tried to avoid possible sources of error, by establishing the DVI, which takes into account not only the LPA velocity, but also the velocities obtained in the pulmonary trunk and in the RPA. We believe that it is difficult to ascertain whether the absolute value of the velocity is normal or not in a specific segment of the pulmonary tree, as it may be influenced by factors such as the heart rate, ventricular function, volemia, etc. Therefore, the use of the proposed DVI may overcome these problems. Moreover, the evaluation of flow velocities in both right and left pulmonary arteries depends on the adequate alignment of the Doppler cursor with the long axis of the vessel, therefore compromising the calculation of the DVI. However, identical procedures were carried out for the control group, which showed a DVI close to zero.
Dessy et al.4 evaluated 49 patients submitted to transcatheter closure of PDA with the Rashkind prosthesis and detected device protrusion into the LPA in 10% of the cases. They also found a strong correlation between device protrusion and increased peak velocity, but a weak correlation with decreased lung perfusion values (they arbitrarily chose the value <40% as abnormal). Sreeram et al.,5 also studied lung perfusion after the utilization of Cook detachable coils. In their series of 35 patients, 40% showed device protrusion into the LPA, with a significant correlation with mean peak velocity evaluated by Doppler. Although patients with coil protrusion showed a tendency to have lower values of lung perfusion, no significant difference could be detected when compared to the ones without protrusion. Additionally, no significant association was detected between low lung perfusion values and number of coils used or increased flow velocity in the LPA.
The lack of association in their study could be explained by the fact that they considered flow velocity absolute values. Several findings of their study may be pointed out as different from the present investigation: the type of coil, a smaller prevalence of protrusion and lower incidence of decreased lung perfusion. We speculate that radionuclide lung scintigraphy being performed in the early post-procedural period could have minimized the perfusional alterations that could appear along the time. In this context, Hijazi et al.,10 demonstrated a decrease of 7% in left lung perfusion values based on scintigraphies performed immediately and 13 months after transcatheter closure of PDA.
Differently from Dessy et al.,3 who considered Doppler as a non-reliable method to evaluate possible alterations of lung perfusion, the proposed DVI was an excellent predictor of perfusional abnormalities. Based on the determination of normal values for lung perfusion, we verified that from eight patients presenting DVI⩾50%, seven had reduced left lung perfusion. Although we could also detect a negative correlation between peak LPA flow velocity and left lung perfusion, the coefficient was much lower than that obtained with the DVI. Furthermore, some apparently normal values of LPA velocities showed abnormal DVI (Table 1), which reinforces the concept of taking into account not only the LPA velocity but also the velocities in the pulmonary trunk and in the RPA.
The diameters of the pulmonary arteries should also be pointed out. This is a subject of some concern, as it has been argued that the closure procedure could impair the normal growth of such vessels. Our results depicted a difference between the right and left pulmonary artery diameters in patients, and even lower values for the left artery in the group showing an elevated DVI. These findings are in accordance with the hypothesis that the procedure can affect growth. However, we cannot completely rule out the possibility of it being related to a congenital abnormality or even if it is present due to an open-chest PDA closure.
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Limitations of the study |
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Perspectives |
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The utilization of the DVI may also be devised for other clinical situations where the presence of pulmonary arterial stenosis may be technically difficult to be confirmed, such as in the post-operative evaluation of the central pulmonary arteries in Fallot's tetralogy, Rastelli operation and arterial switch operation.14
Finally, the real long-term clinical relevance of left lung perfusion values lower than 39% detected in this study needs clarification which we believe may appear in the follow-up course of the affected patients.
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References |
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