Page 155 - Problem-Based Feline Medicine

9 – THE CAT WITH ABNORMAL HEART SOUNDS AND/OR AN ENLARGED HEART 147

poor motility during systole, resulting in fixed A subvalvular or supravalvular fibrous ridge may be
obstruction of outflow of blood. In some cases, identified.
supravalvular or subvalvular stenosis may be found.
In some cases, left atrial enlargement may be present.
Secondary left ventricular hypertrophy may develop.
Doppler study of the left ventricular outflow reveals
The degree of hypertrophy is directly dependent on the
increased velocity of blood flow (> 2.0 m/s).
severity of the stenosis. Valvular gradients above 100
mmHg are classified as severe.
Clinical signs Cardiac catheterization findings
Cardiac catheterization is not routinely done, since the
A systolic murmur is heard over the left heart base or over
introduction of echocardiography.
the cranial aspect of the sternum.
Injection of contrast in the left ventricle will show:
Most cats are asymptomatic. Most common symptoms
● Left ventricular hypertrophy.
in severe cases are exercise intolerance and syncope.
● Narrow left ventricular outflow.
If severe, in the first 1–2 years of life, cats may die sud- ● Filling defect at the aortic valve level (due to a
denly or develop congestive heart failure. thickened valve).
● Post-stenotic dilatation of the aortic arch.
Diagnosis
● Subvalvular or supravalvular filling defects may be
seen.
Radiographic findings
There is widening of the cranial mediastinum as a result
of post-stenotic dilation of the aortic arch. This is evi- Differential diagnosis
dent on both views (dorsoventral view and lateral view).
Hypertrophic obstructive cardiomyopathy (HOCM) dif-
Left ventricular enlargement with elongation of the fers from aortic stenosis in the location and pathophysi-
left heart occurs secondary to hypertrophy. ology of the stenosis. With HOCM the stenosis is
If congestive heart failure is present, pulmonary venous dynamic (changes with heart rate) while in aortic steno-
distention (pulmonary vein larger than accompanying sis the obstruction to blood flow is fixed.
pulmonary artery) and evidence of pulmonary edema
may be seen (focal areas of marked interstitial or alve-
olar densities). Treatment
In mild and moderate cases (Doppler-derived pres-
Electrocardiographic findings
sure gradient less than 100 mmHg and asymptomatic),
The electrocardiogram may be normal or have evidence
there is no benefit from medical therapy.
of left ventricular hypertrophy with a tall R wave in
lead II (> 0.9 mV). In cases complicated with ventricular arrhythmias
and/or left ventricular concentric hypertrophy,
Left axis deviation and/or left fascicular anterior block
beta-blockers may reduce the likelihood of sudden
may be present.
death and/or collapse. Refer to section in hypertrophic
Ventricular arrhythmias may be present, but are not cardiomyopathy (page 130).
common.
If congestive heart failure is present, refer to hyper-
trophic cardiomyopathy section (page 130).
Echocardiographic findings
Left ventricular hypertrophy is seen (diastolic Caution with the use of angiotensin-converting
dimension of the interventricular septum and/or LV enzyme inhibitors, which may increase the pressure
posterior wall greater than 6 mm). gradient across the stenosis.

If valvular stenosis is present, the valve appears thick No surgical therapy is currently being offered for treat-
and has restricted opening. ment of this disease.