Page 1894 - Cote clinical veterinary advisor dogs and cats 4th

Subaortic Stenosis 949

○ Increased blood flow velocity through the sensitive than a brief ECG, especially if • No definitive treatment exists for curing SAS.
LVOT Thoracic radiographs: • Excision of the stenotic tissue by open-heart
arrhythmias are precipitated by exercise.
VetBooks.ir ○ This process may rarely lead to left-sided • Often normal; unreliable as a screening tool vasive balloon valvuloplasty has not yet been Diseases and Disorders
surgery or dilation of the stenosis by nonin-
○ Compensatory left ventricular concentric
hypertrophy in moderate and severe cases
shown to provide an outcome that is superior
because hypertrophy of the LV is concentric.
CHF in some severe cases.
to conservative, medical management.
• With worsening SAS over time, left ventricu- • Variable left-sided cardiomegaly (left ven- • Recurrence of the stenotic lesion is often
tricular and atrial enlargement), usually only
lar thickening may exceed intramyocardial with moderate to severe cases observed after balloon dilation or surgery,
(coronary) blood supply, which does not • Helpful mostly to rule out congestive heart possibly as a result of anatomic characteristics
grow along with the hypertrophied myo- failure (rare), Post-stenotic dilation of the of the LVOT that were left unaltered after
cardial cells. Together with coronary arterial aortic root may be visible in some dogs, often surgery (e.g., abnormal aortoseptal angle).
changes, the result is inadequate perfusion greater in severe cases. It appears as a loss of the • A dilation technique using cutting and
of left ventricular tissue and ventricular cranial waist on the lateral views and widening high-pressure balloons has been described
arrhythmias or, less commonly, myocardial of the mediastinum on the dorsoventral view. and can be beneficial in symptomatic dogs.
infarction. These adverse consequences are Echocardiogram (p. 1094) for definitive Long-term and survival benefits of this
especially likely during high myocardial diagnosis: procedure remains controversial.
oxygen demand, which explains the value • Two-dimensional (2D)
of exercise restriction in severely affected dogs. ○ Often normal in mildly affected dogs Acute General Treatment
• Either process may be responsible for sudden ○ Subvalvular obstructive lesion or narrowed • Syncopal dogs should be kept at complete
death (common in severe SAS). left ventricular outflow tract rest until a complete cardivascular evalua-
○ A decreased/steeper aortoseptal angle can tion is performed (ECG, echocardiogram,
DIAGNOSIS be seen in severe cases. ± chest radiographs and Holter monitoring
○ Various degrees of left ventricular con- or “in-house” telemetry).
Diagnostic Overview centric hypertrophy
The diagnosis is first suspected on auscultation ○ Papillary muscles and the endocardial Chronic Treatment
of a systolic heart murmur loudest at the left surface of the LV may appear hyperechoic. Mild SAS:
heart base or cranial sternal region. Electro- ○ Various degrees of dilation of the left • No treatment
cardiography and thoracic radiographs may atrium Moderate SAS:
help raise or lower the likelihood of SAS, but ○ Dilated ascending aorta (poststenotic • Treatment not universally implemented
Doppler echocardiography is the most accurate dilation) in some cases • Mild exercise restriction (avoid vigorous
diagnostic test. • M-mode study activity) may be advised for dogs at the
○ Normal to increased left ventricular higher velocities of the moderate SAS range
Differential Diagnosis fractional shortening (80-100 mm Hg).
Other systolic heart murmurs heard at the left ○ Normal to increased left ventricular wall • Beta-blockade may be instituted in individual
heart base: thickness cases.
• Pulmonic stenosis ○ SAM sometimes observed Severe SAS:
• Tetralogy of Fallot • Doppler study • Open resection of the obstructing lesion is
• Atrial septal defect ○ Turbulent, high-velocity systolic signal in possible, but long-term survival is unchanged
• Incompletely ausculted PDA the LVOT and aortic root. Normal range compared with medical management.
High-output states: (controversial) = up to 2 m/s; gray zone • Balloon dilation of the stenosis: survival not
• Hyperthyroidism = 2-2.3 m/s; > 2.3 m/s = suggestive of longer than with medical management
• Anemia SAS when corresponding murmur and • Cutting balloon and high-pressure balloon
• Fever breed are also present; exception in the dilation may be beneficial short-term (12
• Exercise: physical activity increases the heart boxer breed and possibly others, where months) when aortoseptal angle > 160
rate, which may reveal a murmur of SAS such elevated velocities may be normal degrees. Promising but still unknown whether
that was not audible at rest. The distinction (requiring 2D aortic measurements for survival is superior to medical management
between this phenomenon and a benign, further evaluation) alone
exercise-induced heart murmur requires ○ Determination of the peak pressure • Exercise restriction: limit to walks on a leash
echocardiography. gradient in combination with the indexed and light exercising, and avoid vigorous
Juvenile innocent heart murmur: effective orifice area (IEOA) estimates the exercise.
• Puppies and kittens < 4 months old severity of disease; peak pressure gradient • Beta-blockers to prevent or control ventricu-
• Soft heart murmur, grade I-II/VI, short (early = 4 × (Doppler-derived LVOT peak veloc- lar arrhythmias, decrease myocardial oxygen
2
to midsystolic) ity in m/s ). This classification remains consumption, and improve coronary artery
• Sometimes disappears with a change in body arbitrary. flow
position or exercise/increase in heart rate ○ 16-40 mm Hg = mild SAS; 40-99 mm ○ Atenolol 0.5-1.5 mg/kg PO q 12h; begin
• Electrocardiogram (ECG), thoracic radio- Hg = moderate SAS at low dose and increase titration over 2-4
graphs, and echocardiogram are normal ○ >100 mm Hg = severe SAS. IEOA weeks until upper end of dose range or
2
2
< 0.6 cm /m = severe SAS signs of intolerance (lethargy, inappetence,
Initial Database ○ >125-130 mm Hg usually associated with hypotension) warranting dosage reduction,
ECG (p. 1096): clinical signs and worse prognosis or
• Often normal in mild to moderate cases ○ Diastolic signal of aortic regurgitation is ○ Sotalol 1-3 mg/kg PO q 12h, up-
• Left ventricular hypertrophy pattern often present in most cases of SAS. titration as per atenolol. Sotalol might
present (R wave > 3 mV in lead II) in severe be more effective in certain breeds (e.g.,
cases; unreliable as a screening tool TREATMENT boxers).
• ST segment may be slurred, depressed, or SAS with CHF (pp. 408 and 409)
elevated in severe cases (consistent with myo- Treatment Overview
cardial hypoxia) especially while exercising. • Only severe cases benefit from therapy. Mod- Behavior/Exercise
• Ventricular arrhythmias are seen in severe erate and mild cases are usually asymptomatic Severe SAS cases: exercise restriction is rec-
cases. Ambulatory ECG recording is more and do not need therapy. ommended, especially avoidance of vigorous
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