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Ventricular Septal Defect in a 1.5-year-old FS Boxer: Our Case Of the Month October 2017

Patient Information

1 Year
Female, Spayed


Exam Findings

Clinical Signs


4-chamber right parasternal view. Left to right color flow between the right ventricle and left ventricle (beneath the junction of the right and non-coronary cusps high in the ventricular system). There is no ventricular dilation suggests that shunting is not significant enough to put the dog at high risk for congestive heart failure or pulmonary hypertension.
Apical view from the left side. Thickened tricuspid valve leaflets that appear somewhat dysplastic. However, there is no tricuspid regurgitation.
Short axis heart base view showing the probable VSD with color flow.
Likely dilated coronary sinus which may be related to a persistent left cranial vena cava or anomalous pulmonary venous drainage.
A bubble study through the left cephalic would be necessary to confirm the possible coronary sinus.

Innocent murmur… I think not!  Here is a case where acting on a heart murmur, no matter the age or grade, is a prudent choice in clinical practice. A young, rambunctious boxer was presented for an echocardiogram and ECG, for a low grade (1/6) heart murmur that had continued to be auscultated after several puppy visits to her veterinarian. No obvious clinical signs were present, other than panting, but not unusual for an exuberant puppy in a clinic setting!  Many thanks to Dr. Shelly Knopsnyder of East Lane Veterinary Hospital and her awesome team in managing this case. SDEP-certified sonographer, Amanda Lacey of Animal Sounds NW provided the diagnostic images for this case study.


A 1.5-year-old, FS, Boxer was presented for an initial puppy wellness visit and a grade 1/6 cardiac murmur was detected; noted PMI (point of maximal impulse) right cranial. A grade 1-2/6 cardiac murmur was detected at several follow-up visits. The patient underwent ovariohysterectomy without event. More recently the patient was presented for further cardiac evaluations. PE found the patient with a heartrate of 140, panting but with no increased respiratory effort, and synchronous pulses. BP: 111/51, 95/53 MAP 67, 119/66 MAP 78. 2 ECG strips were submitted. The first strip (taken under sedation with butorphanol) showed periods of sinus rhythym and periods that appeared to be a high grade second degree AV block (ventricular rate 40-100 bpm). The second strip showed a sinus rhythm (rate 114 bpm) with intermittent single premature ventricular complexes (RBBB morphology) once sedation had worn off and patient was stimulated. 

Image Interpretation

A sinus rhythm was observed during the echocardiogram. There is a dilated coronary sinus. Trivial mitral regurgitation is suspected. The tricuspid valve leaflets are thickened and the septal leaflet is thethered in some views, although there is no tricuspid regurgitation. There is an area of left to right flow (beneath the junction of the right and non-coronary aortic cusps high in the ventricular septum).

Sonographic Differential Diagnosis

The murmur appears to be secondary to a small left to right shunting ventricular septal defect (~5mm), suspected restrictive physiology. Probable tricuspid valve dysplasia. Dilated coronary sinus (Ddx persistent left cranial vena cava vs. anomalous pulmonary venous return vs. other). Ventricular premature complexes. Possible high grade AV block during sedation (Ddx high vagal tone vs. myocarditis vs. idiopathic nodal fibrosis vs. other).


Venticular septal defect.


Placement of a 24-hour Holter monitor was advised to better assess the arrhythmia documented in the ECG, which is unlikely to be related to the VSD. If concurrent AV block and ventricular arrhythmias are diagnosed, a myocarditis may be present; in this case tick titers, protozoal titers, and potential for treatment with doxycycline would be indicated. The dilated coronary sinus may be related to a persistent left cranial vena cava or anomalous pulmonary venous drainage. A bubble study in the left cephalic vein would confirm the suspicion of a persistent left cranial vena cava. This is typically a benign congenital change. The lack of tricuspid regurgitation is a favorable finding. No cardiac medications appear indicated at this point, given the lack of clinical signs and lack of congestive heart failure on radiographs. With a small VSD the prognosis is typically good; recheck echocardiogram is 6-9 months was recommended. Due to the patient being clinically normal at home. as she was prior to the ultrasound, owners elected to not pursue further care except for recheck/echo/ECG that was recommended by the cardiologist.


4-chamber long axis view without color flow
4-chamber long axis view of the left to right color flow turbulence at the site of the VSD
Video showing the thickened tricuspid valve. This view was taken from the left side with the patient in left lateral recumbency. The right atrium and right ventricle are in the far field. There is no tricuspid regurgitation and the right atrium and left atrium are not enlarged.
Video of short axis heart base view showing the turbulent left to right flow of the probable VSD
Second video of short axis heart base showing the turbulent left to right flow of the probable VSD