Assessment of shunt volumes in children with ventricular septal defects:

Quantification of the area and shunt volume of multiple, circular, and noncircular ventricular septal defects: A 2D/3D echocardiography comparison and real time 3D color Doppler feasibility determination study

BACKGROUND

Quantification of defect size and shunt flow is an important aspect of ventricular septal defect (VSD) evaluation. This study compared three-dimensional echocardiography (3DE) with the current clinical standard two-dimensional echocardiography (2DE) for quantifying defect area and tested the feasibility of real time 3D color Doppler echocardiography (RT3D-CDE) for quantifying shunt volume of irregular shaped and multiple VSDs.

METHODS

Latex balloons were sutured into the ventricles of 32 freshly harvested porcine hearts and were connected with tubing placed in septal perforations. Tubing was varied in area (0.13-5.22 cm²), number (1-3), and shape (circle, oval, crescent, triangle). A pulsatile pump was used to pump "blood" through the VSD (LV to RV) at stroke volumes of 30-70 mL with a stroke rate of 60 bpm. Two-dimensional echocardiography (2DE), 3DE, and RT3D-CDE images were acquired from the right side of the phantom.

RESULTS

For circular VSDs, both 2DE and 3DE area measurements were consistent with the actual areas (R² = 0.98 vs 0.99). For noncircular/multiple VSDs, 3DE correlated with the actual area more closely than 2DE (R² = 0.99 vs 0.44). Shunt volumes obtained using RT3D-CDE positively correlated with pumped stroke volumes (R² = 0.96).

CONCLUSIONS

Three-dimensional echocardiography (3DE) is a feasible method for determining VSD area and is more accurate than 2DE for evaluating the area of multiple or noncircular VSDs. Real-time 3D color Doppler echocardiography (RT3D-CDE) is a feasible method for quantifying the shunt volume of multiple or noncircular VSDs.

Quantification of Shunt Volume Through Ventricular Septal Defect by Real-Time 3-D Color Doppler Echocardiography: An in Vitro Study

Quantification of shunt volume is important for ventricular septal defects (VSDs). The aim of the in vitro study described here was to test the feasibility of using real-time 3-D color Doppler echocardiography (RT3-D-CDE) to quantify shunt volume through a modeled VSD. Eight porcine heart phantoms with VSDs ranging in diameter from 3 to 25 mm were studied. Each phantom was passively driven at five different stroke volumes from 30 to 70 mL and two stroke rates, 60 and 120 strokes/min. RT3-D-CDE full volumes were obtained at color Doppler volume rates of 15, 20 and 27 volumes/s. Shunt flow derived from RT3-D-CDE was linearly correlated with pump-driven stroke volume (R = 0.982). RT3-D-CDE-derived shunt volumes from three color Doppler flow rate settings and two stroke rate acquisitions did not differ (p > 0.05). The use of RT3-D-CDE to determine shunt volume though VSDs is feasible. Different color volume rates/heart rates under clinically/physiologically relevant range have no effect on VSD 3-D shunt volume determination.

What radiologists need to know about the pulmonary-systemic flow ratio (Qp/Qs): what it is, how to calculate it, and what it is for

Cardiac magnetic resonance imaging (cMRI) provides abundant morphological and functional information in the study of congenital heart disease. The functional information includes pulmonary output and systemic output; the ratio between these two (Qp/Qs) is the shunt fraction. After birth, in normal conditions the pulmonary output is practically identical to the systemic output, so Qp/Qs = 1. In patients with « shunts » between the systemic and pulmonary circulations, the ratio changes, and the interpretation of these findings varies in function of the location of the shunt (intracardiac or extracardiac) and of the associated structural or postsurgical changes. We review the concept of Qp/Qs; the methods to calculate it, with special emphasis on cMRI; and the meaning of the results obtained. We place special emphasis on the relevance of these findings depending on the underlying disease and the treatment the patient has undergone.

Usefulness of electrocardiography-gated dual-source computed tomography for evaluating morphological features of the ventricles in children with complex congenital heart defects

PURPOSE

Improved time resolution using dual-source computed tomography (DSCT) enabled adaptation of electrocardiography (ECG)-gated cardiac CT for children with a high heart rate. In this study, we evaluated the ability of ECG-gated DSCT (ECG-DSCT) to depict the morphological ventricular features in patients with congenital heart disease (CHD).

MATERIALS AND METHODS

Between August 2006 and March 2010, a total of 66 patients with CHD (aged 1 day to 9 years, median 11 months) were analyzed using ECG-DSCT. The type of anomaly was ventricular septal defect (VSD) in 32 (malaligned type in 20, perimembranous type in 7, supracristal type in 3, muscular type in 2), single ventricle (SV) in 11, and corrected transposition of the great arteries (cTGA) in 3. All patients underwent ECG-DSCT and ultrasonography (US). We evaluated the accuracy of diagnosing the type of VSD. For the cases with SV and cTGA, we evaluated the ability to depict anatomical ventricular features.

RESULTS

In all 32 cases of VSD, DSCT could confirm the VSD defects, and the findings were identical to those obtained by US. Anatomical configurations of the SV and cTGA were correctly diagnosed, similar to that on US.

CONCLUSION

Our study suggests that ECG-DSCT can clearly depict the configuration of ventricles.

Cardiac output can be measured with the transpulmonary thermodilution method in a paediatric animal model with a left-to-right shunt

BACKGROUND

The transpulmonary thermodilution (TPTD) technique for measuring cardiac output (CO) has never been validated in the presence of a left-to-right shunt.

METHODS

In this experimental, paediatric animal model, nine lambs with a surgically constructed aorta-pulmonary left-to-right shunt were studied under various haemodynamic conditions. CO was measured with closed and open shunt using the TPTD technique (CO(TPTD)) with central venous injections of ice-cold saline. An ultrasound transit time perivascular flow probe around the main pulmonary artery served as the standard reference measurement (CO(MPA)).

RESULTS

Seven lambs were eligible for further analysis. Mean (sd) weight was 6.6 (1.6) kg. The mean CO(MPA) was 1.21 litre min(-1) (range 0.61-2.06 l min(-1)) with closed shunt and 0.93 litre min(-1) (range 0.48-1.45 litre min(-1)) with open shunt. The open shunt resulted in a mean Q(p)/Q(s) ratio of 1.8 (range 1.6-2.4). The bias between the two CO methods was 0.17 litre min(-1) [limits of agreement (LOA) of 0.27 litre min(-1)] with closed shunt and 0.14 litre min(-1) (LOA of 0.32 litre min(-1)) with open shunt. The percentage errors were 22% with closed shunt and 34% with open shunt. The correlation (r) between the two methods was 0.93 (P<0.001) with closed shunt and 0.86 (P<0.001) with open shunt. The correlation (r) between the two methods in tracking changes in CO (ΔCO) during the whole experiment was 0.94 (P<0.0001).

CONCLUSIONS

The TPTD technique is a feasible method of measuring CO in paediatric animals with a left-to-right shunt.

Resonancia magnética cardiovascular en la cuantificación de los cortocircuitos de izquierda a derecha en los defectos septales cardiacos con hipertensión arterial pulmonar

INTRODUCTION AND OBJECTIVES

As cardiac septal defects are frequently associated with pulmonary arterial hypertension, hemodynamic assessment is essential before deciding on surgery. The aim of this study was to evaluate the use of cardiovascular magnetic resonance imaging for assessing cardiac shunts and for quantifying pulmonary artery systolic pressure in patients with cardiac septal defects.

METHODS

This cross-sectional study involved patients with cardiac septal defects and clinically suspected severe pulmonary arterial hypertension who had an indication for cardiac catheterization and in whom magnetic resonance imaging was not contraindicated. Each test's results were evaluated independently by two expert radiologists and interventional cardiologists who were blinded to the results of the other test. The procedures were compared using confidence limits and intraclass correlation coefficients.

RESULTS

The study involved 29 patients (18 female and 11 male) aged from 30 days to 18 years; seven had an atrial septal defect, 14 had a ventricular septal defect, and eight had an atrioventricular septal defect. The correlation coefficients for measurements made using the two procedures were 0.80, 0.75, 0.81 and 0.58 for pulmonary output, systemic output, flow ratio, and systolic pressure in the pulmonary artery, respectively. Cardiovascular magnetic resonance tended to underestimate systemic output by 0.80 L/min, pulmonary output by 1.35 L/min, left-to-right shunt flow by 0.12 L/min, and systolic pressure in the pulmonary artery by 16.5 mmHg. The complication rate with cardiac catheterization was 31% compared with 3.4% with cardiovascular magnetic resonance imaging.

CONCLUSIONS

The evaluation of patients with cardiac septal defects and pulmonary arterial hypertension should initially be performed using noninvasive diagnostic techniques.

Evaluation of a resistance-based model for the quantification of pulmonary arterial hypertension using MR flow measurements

PURPOSE

To establish an estimate for the mean pulmonary arterial pressure (mPAP) derived from noninvasive data acquired with magnetic resonance (MR) velocity-encoded sequences.

MATERIALS AND METHODS

In seven sedated pigs synchronous catheter-based invasive pressure measurements (IPM) and noninvasive MR were acquired in the main pulmonary artery (MPA) at different severities of pulmonary arterial hypertension (PAH) that were caused by infusion of thromboxane A2 (TxA2). The invasively measured mPAP was correlated with the noninvasive MR velocity data and linear combination equations (LCE) were computed.

RESULTS

Intravenously applied TxA2 induced a dose dependent level of severity of PAH with an mPAP of up to 54 mmHg without systemic effects. The acceleration time (AT) measured with MR demonstrated the best correlation with the mPAP (r(2) = 0.75). The LCE with the highest correlation (R = 0.945, alpha < 0.01) between IPM and MR revealed a mean difference of 0, a SD of s = 4.66 and a maximal difference of 12.2 mmHg using the Bland-Altman analysis.

CONCLUSION

Applying the identified LCE allowed the estimation of the mPAP in an acute and resistance-based model of PAH with high accuracy using noninvasive MR velocity-encoded sequences.