Introduction

• Congenital narrowing of left ventricular outflow tract. Represents 7% of feline congenital cardiac anomalies.
• Cause: developmental malformation. Lesion is most commonly supravalvular in the cat, but may be valvular or subvalvular.
• Signs: asymptomatic, systolic murmur, weakness, lethargy, syncope, sudden death; left-sided congestive heart failure (CHF) Heart: congestive heart failure.
• Diagnosis: history, clinical signs, radiography, angiocardiography, electrocardiography, ultrasonography.
• Treatment: for mild cases none indicated; to treat CHF and arrhythmias use beta-blockers, calcium channel blockers; diuretics, anti-arrhythmics and rest.
• Prognosis: generally poor, most develop CHF, but some cases remain asymptomatic.

Pathogenesis

Pathophysiology

• Congenital narrowing of left ventricular outflow tract, aortic valves, or aortic root causes ventricular hypertrophy and may eventually lead to left-sided cardiac failure or sudden death.
• Sudden death may result from myocardial hypoxia and fatal dysrhythmias Heart: dysrhythmia.
• Syncope may result from outflow tract obstruction, hypoxia or arrythmias.

Severe cases

• Obstructed aortic outflow   →   reduced cardiac output and increased left ventricular pressure   →   pressure overload   →   ventricular concentric hypertrophy (LaPlace Law)   →   increased myocardial oxygen consumption   →   coronary perfusion not proportional to hypertrophy   →   myocardial hypoxia   →   ventricular dysrhythmias   →   syncope/sudden death.
• Rarely   →   myocardial failure   →   left-sided CHF.

Timecourse

• Signs <2 years old.

Diagnosis

Treatment

Outcomes