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Ventricular septal defects in dogs & cats | VETgirl Veterinary CE Podcasts

In this VETgirl online veterinary CE podcast, we review ventricular septal defects (VSDs) in dogs and cats. VSDs are defined as an opening or communication in the interventricular septum due to defects in closure or alignment of the septum during fetal development. VSDs are a regularly identified form of congenital heart disease in animals, albeit less common than the incidence of VSDs in humans. VSDs are subclassified based on anatomic location and include the following varieties:

  • Supracristal
  • Membranous
  • Perimembranous
  • Muscular
  • Atrioventricular (AV) canal.

VSDs may occur in isolation or with other forms of congenital heart disease. Direction of flow across a VSD is most commonly identified as left-to-right but is specifically dictated by defect size as well as the presence or absence of elevated pulmonary vascular resistance. Up to this point, data of any kind (retrospective or other) evaluating large populations of VSDs in dogs and cats was lacking. For this reason, Bomassi et al from France retrospectively evaluated this in a study called “Signalment, clinical features, echocardiographic findings, and outcome of dogs and cats with ventricular septal defects: 109 cases (1992-2013)” in JAVMA.

In this retrospective study, they wanted to evaluate signalment, clinical features, echocardiography results, and overall survival or outcome of dogs and cats diagnosed with ventricular septal defects (VSDs).1 The size of the VSD was measured using color flow Doppler echocardiography in each patient. A total of 109 animals (which included 56 dogs and 53 cats) were diagnosed with VSD over a 21 year period (which just goes to show you that it takes a lot of years to accumulate all those cases!).The canine breeds that often were identified with VSD? Terriers and French bulldogs. Overall, 75.2% (82/109) of VSDs were membranous or perimembranous.

Of all the 109 cases, 53 animals (48.6%) had isolated VSD (46% of dogs, 51% of cats).  All animals with isolated VSDs presented with systolic heart murmurs with the PMI at the right sternal border. Nearly all (96%) of animals with isolated VSDs had left-to-right shunting across the VSD. The vast majority (81%) of animals with isolated VSDs had no clinical signs. Of those animals with follow up data available (37/52 or 71%), none of the animals with isolated VSDs AND no clinical signs at diagnosis were observed to develop clinical signs in their lifetime.

The remaining 51.4% had other concomitant congenital heart disease. Tetralogy of Fallot, a combination of severe cardiac defects, was the most common in non-isolated VSDs and found in 20 animals in this study. VSD with some form of pulmonic stenosis was the most common association for VSD w/concomitant congenital heart disease.

When looking specifically at echocardiographic findings in this study, the pulmonary-to-systemic flow ratio (which is a calculated echocardiographic parameter used to quantify shunt magnitude) was highly correlated with measured VSD diameter and measured VSD-to-aortic diameter ratio.
The VSD diameter, VSD-to-aortic diameter ratio and pulmonary-to-systemic flow ratio were highly correlated with the presence or absence of clinical signs at the time of diagnosis (with larger values being more likely to have clinical signs). The presence or absence of aortic regurgitation did not influence clinical status or outcome and was predominantly mild, when identified, in animals with isolated VSD.

Despite all this  “echo heavy” info, this study provided a plethora of data, from which some simple and valuable conclusions can be made (which thankfully support what one would speculate based on the pathophysiology of VSDs). More than half of animals with VSDs in this study had other forms of concurrent congenital heart disease, which places great importance on the value of having veterinary cardiologists perform echocardiography where congenital disease is suspected. It is reasonable to conclude that in most animals with isolated VSDs, they present with no clinical signs, isolated right parasternal murmurs, and do not develop clinical signs in their lifetime. This appears to be directly correlated to the size of the VSD as would be expected (In other words, most VSDs are small in dogs/cats). Various echocardiographic parameters (e.g., VSD-to-aortic diameter ratio, pulmonary-to-systemic flow ratio) can be used to accurately assess and classify VSD size in animals although some of these parameters (pulmonary-to-systemic flow ratio) are technically challenging and should be performed by experienced cardiologists.

So, what do we take from this VETgirl podcast? When it comes to VSD in dogs and cats, it often occurs in conjunction with other forms of congenital heart disease. Clinical sequelae in these patients will more commonly be dictated by the nature of the other concurrent form(s) of congenital heart disease present in these animals. Thankfully, VSDs by itself (e.g., in isolation) are typically small and do not result in clinical consequences.

References:
1. Bomassi E, Misbach C, Tissier R, et al. Signalment, clinical features, echocardiographic findings, and outcome of dogs and cats with ventricular septal defects: 109 cases (1992-2013). J Am Vet Med Assoc 2015;247:166-175

Abbreviations:
VSD: ventricular septal defect
CHD: congenital heart disease
PMI: point of maximal murmur intensity
Qp:Qs: pulmonary-to-systemic flow ratio
VSD:Ao: VSD-to-aortic diameter ratio

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