Clinical and Echocardiographic Features of Primary Infundibular Stenosis with Intact Ventricular Septum in Dogs

Background:Primary infundibular stenosis is a rare congenital defect in which the right ventricle is divided into a proximal “high‐pressure” chamber and a distal “low‐pressure” chamber. The condition can be misdiagnosed as ventricular septal defect or valvular pulmonic stenosis and the disease severity underestimated. The purpose of this study was to provide a detailed clinical and echocardiographic description of this anomaly in a series of dogs. Hypothesis:Several anatomic forms of infundibular stenosis exist. High resolution two‐dimensional echocardiography could differentiate 3 gross anatomic substrates. Knowledge of the anatomy of the obstructing lesion could influence options for corrective interventions. Animals:Thirteen dogs examined at the Ontario Veterinary College teaching hospital from 1994 to 2005 with an ultrasound diagnosis of subpulmonic stenasis. Methods:A retrospective review was made of case records from 1994 to 2005. Results:Thirteen dogs were identified as having primary infundibular stenosis, with apparent increased prevalence in Golden Retrievers (8/13, 62%) and Siberian Huskies (3/13, 23%). Three types of infundibular lesions were identified by ultrasound in 11/13 dogs: a fibrous diaphragm (6), fibromuscular (4), and muscular obstruction (1). Two dogs with a fibrous diaphragm underwent direct surgical dilation without the use of cardiopulmonary bypass or inflow occlusion, resulting in substantial reduction of the severity of stenosis. Conclusion and Clinical Importance: Accurate determination of the severity of the stenosis and the anatomy of the obstructing lesion are important in devising a treatment strategy. Recognition of the fibrous diaphragm by echocardiography identifies a subset of dogs potentially amenable to surgical dilation without the need for cardiopulmonary bypass.