Physiology
This equation estimates pressure gradients using Doppler-derived blood flow velocities (recorded via echocardiogram).
What is the Modified Bernoulli equation?
Delta P = 4v^2
Decreased diameter of a valve or vessel increases the velocity at which blood moves through. While we cannot measure pressure directly via echocardiogram, we can use Doppler to measure velocity. Bernoulli's equation allows us to estimate pressure generated by the ventricles in cases of stenotic congenital disease.
V = velocity in m/s
Delta P = pressure gradient in mmHg
This is the classic murmur that will be heard in a subaortic stenosis patient.
What is a left basilar systolic murmur?
Generated due to resistance of blood flow against the stenotic ventricular outflow tract.
This is the classic murmur heard that is heard in a patient with pulmonic stenosis.
What is a left basilar systolic murmur.
These are often LOUD (grade 5-6/6) and may radiate cranially and/or to the right side of the chest. Remember that in stenotic diseases, an increase in murmur intensity DOES correlate with disease severity.
Pulmonic stenosis is the most common CHD in dogs, consistently comprising ~ 1/3 of all cases.
This class of drug is used for its negative inotropic and chonotropic effects in severe cases of SAS and PS.
Bonus points for the drug of choice.
What are beta blockers?
Beta blocks such as atenolol decrease heart rate and myocardial oxygen demand, improve diastolic filling time, and may reduce ventricular arrhythmias.
Atenolol is the drug of choice, a cardiac-selective B-blocker.
Fun fact: in humans, surgical resection of fibrous tissue, +/- myectomy and an aortoventriculoplasty is the treatment of choice for SAS. Though, there's still a high recurrence rate. (Crofton et al. 2023)
This congenital stenotic disease generally responds much better to interventional therapy. (Hint: your choices are subaortic and pulmonic stenosis.. :))
What is pulmonic stenosis?
Balloon valvuloplasty is often highly successful in PS, whereas interventional outcomes for SAS are much less predictable and less effective.
Beta blockers produce no significant increase in MST of SAS patients (Eason et al. 2014).
These are the two "types" (A and B) of pulmonic stenosis.
What are fused valve leaflets (Type A) and hypoplastic annulus + dysplastic valve leaflets (Type B)
These two causes of pulmonic stenosis create extremely similar clinical disease. One main distinction is that balloon valvuloplasty is much more effective in treating type A (fused valves) than type B (hypoplastic opening).
This clinical sign (part of our physical exam) can help differentiate subaortic stenosis from pulmonic stenosis.
What are weak femoral pulses?
Reduced stroke volume (SV) in subaortic stenosis leads to weak pulses, as the cardiac output is diminished. Subaortic stenosis directly impacts systemic blood flow, whereas pulmonic stenosis affects pulmonary circulation.
Note: In one study (Bini et al. 2022), 13% of patients with PS presented with weak femoral pulses, all of which had severe disease.
This is the most common presenting complaint for SAS (and PS).
What is: Nothing!
Most patients with congenital stenotic disease will be asymptomatic, especially in the early stages of disease. Murmurs related to these disease processes are usually an incidental finding on first puppy visits.
This procedure is a first-line therapy for severe pulmonic stenosis.
What is balloon valvuloplasty?
Balloon valvuloplasty is a minimally invasive procedure that mechanically widens the stenotic pulmonic valve and significantly reduces pressure gradients in many PS patients. A second procedure is rarely required.
A "successful" BVP is defined as a reduction in PG >50% or PG reduced to <80mmHg. Some studies disagree, but BVP may have a greater long-term efficacy rate with type A PS (fused leaflets).
This clinical sign may occur during exercise in severe SAS or PS due to diminished cardiac output.
What is syncope?
During exercise, affected patients cannot adequately increase cardiac output against the stenotic outflow tract, leading to transient cerebral hypoperfusion and collapse.
This type of heart enlargement occurs in severe cases of subaortic or pulmonic stenosis.
What is concentric hypertrophy?
Pressure overload caused by an outflow obstruction increases the force necessary for the ventricle to eject blood. In response, ventricular walls thicken to reduce stress on individual myocytes. This hypertrophy lead to diminished stroke volume and cardiac output.
PS -> Concentric RV hypertrophy
SAS -> Concentric LV hypertrophy
This is the signalment of subaortic stenosis.
What are young large-breed dogs, such as Newfoundlands, Golden Retrievers, Rottweilers, Boxers, and German Shepherds?
Males > females
These breeds are predisposed to pulmonic stenosis.
What are small breed dogs and Boxers, English Bulldogs, and French bulldogs.
The latter three breeds are predisposed due to abnormal coronary artery anatomy.
Mild-to-moderate cases of SAS and PS generally require what treatment?
What is... nothing!
Patients with mild disease are often asymptomatic and have excellent prognosis to live a long, healthy life.
This imaging modality is the gold standard for diagnosis and grading of SAS and PS.
What is echocardiography?
Echo allows direct visualization of stenotic lesions, doppler-derived pressure gradients, and potential secondary changes.
Note: One study (Bini et al. 2022) showed that right deviation of the MEA in patients that develop PS can be detected at birth in Golden Retriever puppies and that ECG could be a useful modality in predicting PS severity.
This is the most common lesion associated with stenosis of the LVOFT (SAS).
What is a fibromuscular ridge/ring/nodule below the aortic valve?
This clinical sign can be seen in severe cases of subaortic stenosis, but not pulmonic stenosis.
What is respiratory distress/ coughing related to left-sided CHF?
Severe SAS may lead to pulmonary edema and respiratory compromise due to elevated left-sided filling pressures and eventual backup of fluid.
This clinical sign can be seen in severe cases of pulmonic stenosis, but not subaortic stenosis.
What is Ascites/ right-sided congestive heart failure?
Severe pulmonic stenosis causes chronic right ventricular pressure overload, which can progress to right-sided heart failure and abdominal effusion/ ascites.
Patients with severe subaortic stenosis carry a median survival time as low as this.
What is 7 years.
The "severe" classification of subaortic stenosis is dictated by an 80-130 mmHg increase in pressure required to expel blood from the ventricle.
In "severe severe" cases (>130 mmHg additional pressure), the MST is ~3 years. :(
This vascular change may occur distal to turbulent blood flow in pulmonic stenosis.
What is post-stenotic dilation of the pulmonary artery?
High-velocity turbulent blood flow damages the walls of the vessel distal to the stenosis, causing dilation of the main pulmonary artery.
Periods of (bradycardia/ tachycardia) pose the greatest risk for myocardial ischemia in patients with SAS or PS.
What is tachycardia?
Tachycardia shortens diastole, reducing coronary perfusion time. Thickened ventricles already have increased oxygen demand, so tachycardic states predispose patients to myocardial ischemia and ventricular arrhythmias.
These two ECG changes can be seen in subaortic stenosis patients due to enlargement of the left heart chambers.
What are wide P waves and tall R waves?
Wide P waves indicate left atrial enlargement, and tall R waves indicate left ventricular enlargement.
Note: In PS, there will be tall P waves that indicate right atrial enlargement and deep S waves that indicate right ventricular enlargement.
This is the minimum pulse gradient (PG) that classifies a patient as having "severe" PS or SAS.
What is 80 mmHg?
This catastrophic outcome is significantly more common in SAS than in PS.
What is sudden death?
Malignant ventricular arrhythmias secondary to myocardial ischemia and fibrosis make sudden death a major concern. Sudden death accounted for 45% of all mortality in one study of 60 dogs with severe SAS. (Eason et al. 2014)
This congenital stenotic disease may progress during the first year of life as fibrous tissue develops.
What is subaortic stenosis?
SAS lesions may worsen as puppies mature due to progressive fibrous proliferation within the left ventricular outflow tract.