Ventricular septal defects in two dimensional imaging seen as a single defect on colour flow doppler imaging.

To the Editor,

A 2-month-old child with heart failure and recurrent lower respiratory tract infections since birth was planned for early closure of the ventricular septal defect (VSD). Intraoperative two dimensional echocardiography with micro Transesophageal echocardiography (TEE) probe (S8-3t, IE33, Philips Ultrasound, Bothell, WA) in midesophageal five chamber view showed two echo dropouts below the aorta (5.5 mm perimembranous VSD) and in the interventricular septum (3 mm muscular VSD) [Video 1] both separated by a thin piece of ventricular septal tissue. The colour flow Doppler (CFD) showed only a single large VSD of size 10 mm [Figure 1; Video 1]. But the CFD in midesophageal Left ventricle (LV) long axis view showed two separate colour flow [Figure 2]. Another VSD of size 3 mm at the apical region was also detected. After opening the right atrium, the VSD was found to be a single large perimembranous (PM-VSD) with an extension into the muscular septum. The PM VSD was divided by the chordae of the septal leaflet of Tricuspid valve (TV) (SLTV) into two openings [Figure 3]. The PM-VSD was closed with gore-tex patch while avoiding injury to the chordae or the SLTV. The apical VSD was closed directly with sutures.

Figure 1

TEE (CFD) in midesophageal 5 chamber view showing large perimembranous VSD with left to right shunt. Abbreviations: CFD = colour flow doppler, LV = left ventricle, RV = right ventricle, TEE = transesophageal echocardiography, VSD = ventricular septal defect

Figure 2

TEE (CFD) in midesophageal LV long axis view showing perimembranous VSD and a muscular VSD (*). Abbreviations: Ao = Aorta, CFD = colour flow doppler, LV = left ventricle, PM-VSD = perimembranous ventricular septal defect, RV = right ventricle, TEE = transesophageal echocardiography

Figure 3

Surgical image shows a large PM-VSD divided by the chordae of septal leaflet of tricuspid valve (*) into 2 VSDs. The yellow arrow indicates smaller VSD. Abbreviations: PM-VSD – perimembranous ventricular septal defect; VSD – ventricle septal defect

PM-VSD accounts for 80% of all the VSD and is seen adjacent to the SLTV. SLTV or its chordae can cause restriction of the PM-VSD, thus reducing the size and shunting across the VSD.[1] Sometimes they may divide a PM-VSD into two or more VSDs.[2] Colour flow imaging as compared to conventional 2D echocardiography has greater accuracy for the detection of multiple VSD. Its sensitivity is greater for the diagnosis of multiple restrictive defects than for multiple non-restrictive defects.[3] Unlike in a restrictive defect, an absence is seen in the turbulent flow across the septum in non-restrictive defects due to equal peak ventricular systolic pressures. Identification of defects becomes tricky if a large defect is in combination with a smaller defect, with the colour flow occurring across the larger defect. Occasionally, separation of the colour jets might not be seen if the defects lie within <5 mm of each other. As a result, multiple defects can sometimes be misdiagnosed as a single isolated VSD in CFD. This is because of inadequate lateral resolution which is a limitation of the colour flow imaging.[3] Lateral resolution refers to the ability to discriminate two closely spaced points at the same depth.[4] Knowledge of the physics of the ultrasound beam and equipment allows the operator for adequate optimization of image quality so that errors can be minimized during echocardiography. In our case, the occurrence of a single VSD defect in CFD, instead of two defects was because of beam width artifact due to poor lateral resolution.[4] This can be minimized by increasing the frequency, adjusting the focal zone to the structure of interest, or imaging in alternative planes [Figure 2].

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