1. Oregon Health & Science University, Portland, Oregon, USA
Accuracy of 3D Echocardiography on Imaging Ventricular Septal Defect Size: An In Vitro Validation Study
Rebecca Luoh; Darya Gratcheva; Aarti Jayaraman, MD; Muhammad Ashraf, MD; David J Sahn, MD, FAHA
Oregon Health & Science University, Portland, Oregon, USA
ABSTRACT
Background: Ventricular septal defect (VSD) is one of the most common congenital heart diseases, but the accuracy of defining VSD orifices has not been validated for 3D echo. Methods: We studied 4 fresh porcine hearts due to their anatomical similarity with human hearts. Each heart was connected to a calibrated pulsatile pump with different stroke volumes (SV, 30-80ml) on the left ventricular (LV) side and constant 40ml on the right ventricular (RV) side through a balloon VSD model, secured in LV and RV, that contained a tube of various size to define the VSD orifice (0.700cm, 1.00cm, 1.25cm, 1.59cm in diameter). Each heart was mounted in a water bath to facilitate ultrasound scanning and driven passively by 2 pumps at a constant rate of 50bpm. 3D images were gathered on GE Vivid 9, BT10 & BT09 and analyzed by EchoPac PC. Results: 3D echo detected the VSD orifice, and the size can be measured accurately by the program. The measured orifice sizes increase as SVs increase except SV40. The measured value at SV60 is the closest to the actual orifice size, while the measured value is the smallest at SV40. Conclusions: 3D echo can accurately measure the VSD orifice size, and the variation of VSD orifice with SV can be explained by mechanism of expanding and contracting of the myocardium surrounding the simulated VSD orifice by difference in stroke volumes of the two chambers.
BACKGROUND
Ventricular Septal Defect (VSD) is one of the most common congenital heart diseases. Approximately, one in 500 infants will be born with a VSD. Previous studies have found that children with VSD have reduced systemic cardiac output and reduced stroke volume. In addition, patients with VSD have impaired contractile function, increased afterload, and reduced preload. Small VSD hole does not cause much problem and usually closes on its own, but large VSD hole increases the amount of pressure exerted on the lungs, thereby causing breathing difficulties. VSD could be detected by 2D and 3D Echo with Doppler due to the presence of shunting, but the orifice size could not be determined.
  Our lab has a pulsatile heart model in water tank for ultrasound scanning to study freshly harvested porcine hearts which have anatomical similarity with human hearts. The heart was driven by a calibrated pulsatile pump through a latex balloon secured in the left ventricular cavity. The model simulates the beating of a normal human heart.
  The goal of the study was to establish a porcine heart model for the VSD and study whether 3D Echo can detect and precisely measure the orifice size of the interventricular component.
METHODS
The model was made by cutting a hole in 2 balloons, and connecting them with a one-inch PVC tubing of a certain diameter as a conduit to mimic an orifice, between the two balloons. The two junctions were superglued to prevent leaking. The left and right atria of a pig heart were removed. An orifice was cut at the interventricular septum wall. The balloon model was inserted into the heart and sewn to filling tubes. The PVC tube passed through the orifice in heart. The tubes were then connected to calibrated pulsatile pumps to simulate the pumping of the heart. The heart was driven passively by 2 calibrated pulsatile pumps at a constant rate of 50 bpm and mounted in water bath for ultrasound imaging.
Protocol
Four different models with varying tube sizes on 4 different porcine hearts were made. For each tube size, the LV was changed with 6 varied stroke volumes of LV were set at 6 different settings, 30, 40, 50, 60, 70 and 80, while RV fixed at 40.
GE Vivid ultrasound systems BT10 and BT09 were used for imaging. Measurements were repeated 3 times. EchoPac was used for analysis. VSD orifice size was measured in diameter (cm).
RESULTS
Images taken from an angle parallel to the tube were clear and the orifice of the interventricular septal defect was clearly imaged in 3D space.
As shown in the Table and Figure, several trends were observed when RV was fixed at 40:
1. The measured orifice size values increase with SV except SV40.
2. The measured orifice size values are the smallest at SV40, where the pressure difference between LV and RV is the smallest.
3. The measured orifice size values in SV60 are closest to the actual orifice size.
 Table. Orifice size Measured by 3D Echo versus Actual orifice size in diameter (cm).
DISCUSSION
The measured orifice size, in general, increases when the SV increases. It is closest to the actual orifice size at SV 60, while it is the smallest at SV 40. This is because the tube was compressed when there is no shunting, i.e. ΔSV=0, while it was expanded when SV was high, i.e. when the ΔSV is the greatest. In a real VSD heart, the VSD orifice compresses and expands with the heartbeat.
Nine different combinations of materials including Plaster of Paris, latex, superglue, balloons, and tubes were tried. Acoustic shadowing by some of these materials may cause artifact. The balloons connected with plastic tubes sealed with superglue cast the least shadow on imaging.
Our preliminary study yielded a second model that might be able to measure strain in the septum adjacent to the VSD. This model was made by cutting a hole in each of the two balloons and connecting them with superglue to prevent leaking. Images were great, and orifice was clear.
CONCLUSIONS
The orifice, i.e. the interventricular septal defect, can be clearly visualized by 3D Echo and precisely measured from these images in EchoPac. With this model, more research on VSD can be done.
DISCLOSURE
No relationships to disclose:
Rebecca Luoh Darya Gratcheva
Aarti Jayaraman Muhammad Ashraf
David J Sahn
Rebecca Luoh and Darya Gratcheva are high school students in Portland, Oregon. LV RV LV RV
SV(ml)/
tube Size
1.59
1.25
1.00
0.700 30
1.36±0.089
0.933±0.153
0.833±0.058
0.650±0.071 40
1.32±0.130
0.900±0.100
0.800±0.173
0.567±0.058 50
1.52±0.084
1.17±0.153
0.967±0.153
0.650±0.100 60
1.56±0.055
1.30±0.000
1.03±0.058
0.600±0.000 70
1.66±0.055 NA 80
1.72±0.130