Congenital heart disease in the dog and cat 1 + 2 Flashcards
Which congenital condition causes a continuous heart murmur?
Patent ductus ateriosus
List some examples of congenital heart conditions that cause systolic murmurs
- Aortic stenosis
- Pulmonic stenosis
- Ventricular septal defect
- Mitral dysplasia
- Tricuspid dysplasia
Describe the features of an innocent flow murmur
Low intensity, systolic, localised at the left heart base, musical
puppies and kittens - should disappear by 20wo
Which congenital heart defect causes a weak pulse quality?
Aortic stenosis
A ‘bounding’ pulse can be seen in which 2 congenital heart defects?
Patent ductus arteriosus
Ventricular septal defect
Where does a patent ductus arteriosus run in the heart?
PDA runs from the descending aorta into the pulmonary artery
What is the main consequence of a patent ductus arteriosus?
Left sided volume overload
Describe the pathophysiology of a patent ductus arteriosus
- Shunt from desc. Aorta to Pulmonary artery
- Aortic pressure > Pulmonic in both systole & diastole (continuous murmur)
- Continuous “run-off” of blood into pulm. circ. (femoral pulse may be “tapping” or “waterhammer”)
- Pulmonary over-circulation (Radiographs: can see increased pulmonary vessel size)
- Volume overload of LA & LV
- Dilation of Mitral valve annulus: secondary mitral regurgitation
- Increased LA & LV EDP results in LHF
- Myocardial failure is a common consequence
Describe the direction of the shunt in a PDA
Left to right
Describe the predispositions for a PDA
Rare in cats: common defect in dogs
Bitches much more commonly affected than males
Breeds: German shepherd dog, collies, bichon, poodle, CKCS, Irish setter
Describe how the clinical signs develop in a patient with a PDA
- Initially, pup may be completely asymptomatic
- Continuous murmur, left axilla, may be very localised (so often missed at first puppy exam)
- Murmur may radiate (esp. systolic component)
- Secondary murmur (systolic) of MR
- Rapidly collapsing femoral pulse: “tapping”, “waterhammer” “hyperkinetic”; due to large systolic - diastolic pulse pressure difference.
What happens if a PDA goes untreated/unnoticed?
By about 7yo CHF will develop
How will a PDA present on a radiograph?
- Left atrial & LV enlargement
- “Apparent” right sided enlargement
- On DV, may have pathognomic “triple knuckle” (Aortic, pulmonic and left auricular appendage bulges).
- Pulmonary over-circulation (arteries & veins increased)
- +/- Radiographic evidence of LHF
Describe the ECG changes seen in patients with a PDA
Evidence of LA and LV enlargement
P mitrale
Tall R waves (can be VERY tall)
Arrhythmias may occur (e.g. atrial fibrillation)
How is a PDA treated?
- Before CHF develops
- Surgery: ligation of the ductus
- Device based occlusion of the ductus by cardiac catheterization
Patient will be cured
Name the most common congenital heart defect in dogs?
Sub-aortic stenosis
Describe the predisposition of subaortic stenosis
- Breeds: Boxers, Newfoundlands, golden retrievers, Rottweilers, Bull terrier, miniature bull terrier
- No sex predisposition
- Uncommon in cats but severe
Describe the pathophysiology of aortic stenosis
- Fixed (or dynamic) obstruction at aortic valve or LVOT level
- Increased afterload on LV: develops concentric hypertrophy (LVH) (Pressure overload)
- Increased aortic velocities
- Coronary perfusion compromised (poor coronary filling and increased wall stress; coronaries do not “keep up” with LVH)
- Myocardial ischaemia may result in ventricular arrhythmias
Describe the clinical signs of aortic stenosis
- Harsh, ejection type mid to holosystolic heart murmur
- Grade of heart murmur corresponds to severity of stenosis
- Radiates up carotids and on right chest
- Femoral pulses may be weak
- Left heart base murmur
Aortic regurgitation may cause what kind of murmur?
Audible (diastolic) murmur: gives a “to-and-fro” murmur
Which diagnostic method is best to diagnose aortic stenosis?
Doppler echocardiography
Describe how doppler echocardiography is used to diagnose aortic stenosis
- 2D sub-valvular or valvular (rarely supra-valvular) lesions may be appreciated
- Post-stenotic dilation of the aorta may be recognised.
- Colour flow Doppler shows turbulence in the LV outflow tract and aorta, around the obstruction
Describe how aortic outflow velocity (measure on doppler) is used in diagnosis of aortic stenosis
In normal dogs, aortic velocity is less than 1.7 m/s.
Velocities >2.0 or 2.2 m/s are usually consistent with aortic stenosis.
The higher the velocity, the more severe the stenosis.
Describe the equation used to assess the pressure gradient across the valve in aortic stenosis
The modified Bernouilli equation can be used to convert Doppler velocity (v) into pressure gradient (PG) across the valve
0 - 50 mmHg MILD
50 - 80 mmHg MODERATE
> 80 mmHg SEVERE
How is aortic stenosis controlled in the UK?
Breed schemes in boxers and Newfoundlands so affected dogs are not used for breeding
Only boxers which are heart murmur free or a grade 1/6 murmur are acceptable for breeding
How is aortic stenosis treated?
- Poor prognosis: may cause sudden death
- No surgical treatment is possible (would require cardiopulmonary bypass)
- If CHF, requires diuretics etc.
- AVOID positive inotropes (Pimobendan) or arteriodilators in fixed obstruction
Which breeds are predisposed to pulmonic stenosis?
Cocker spaniels, CKCS, Terriers, Beagle, Bull dog, Bull mastiff, Boxer
Describe the murmur heard in pulmonic stenosis
- Left heart base systolic murmur
- Mid to Holo-systolic murmur cranially left heart base, radiating dorsally up the intercostal space
- Grade of murmur correlates with disease severity
Describe the pathophysiology of pulmonic stenosis
- Fixed obstruction at pulmonic valve
- Stenosis causes a pressure overload on the right ventricle –> concentric right ventricular hypertrophy
- If RV pressures equal/exceed LV pressures, altered intraventricular septal motion (may be paradoxical) and LV can appear “squashed”.
- RV hypertrophy may lead to myocardial ischaemia; ventricular arrhythmias may result
Describe the clinical signs of pulmonic stenosis
- Incidental heart murmur – not usually symptomatic
- Exercise intolerance
- Syncope
- Normal pulses
During echocardiography of pulmonic stenosis, describe the appearance of the heart on the short and long axis views
Long axis – septum and left side of the heart are ‘squashed’
Short axis – ‘mushroom view’ at the level of the papillary muscles. Top of the ‘mushroom’ has been squashed/flattened
Mushroom = LV
How does pulmonic stenosis appear on radiography?
- Right sided enlargement: increased sternal contact. Apex tipping on lateral view due to right ventricular hypertrophy. Marked “reverse D” shape on DV view.
- A post-stenotic dilation of the pulmonary artery may be recognised (bulge in 1 –2 o’clock position on DV view). On the lateral view, the PA may overlie the air filled trachea cranial to the carina, giving a “pulmonary cap”.
Describe the changes seen on an ECG in cases of pulmonic stenosis
Negative QRS in lead I
Deep S waves in leads I, II & aVF
Right axis deviation
Describe how pulmonic stenosis can be treated?
- Cardiac Catheterisation approach: balloon Valvuloplasty of valvular stenosis, good response
- Surgery: various techniques to “dilate” pulmonic annulus. Indicated if significant RVH and infundibular hypertrophy
Name the dog breed most commonly affected by supravalvular stenosis
French bulldog
Describe the predisposition of a ventricular septal defect
One of the more common congenital defects in cats
Less common in dogs. Breeds: cocker spaniels, WHWT
Describe the murmur heard when a patient has a ventricular septal defect
- The murmur reflects the left to right shunt, with the point of maximal intensity on the right hemithorax, although it is heard more caudally on the left also (diagonal murmur).
- The murmur is holo- or pan-systolic.
- Murmur grade is INVERSELY proportional to the size of the defect
- Small defect = very fast, turbulent flow & very loud heart murmur
- Large defect = less fast, turbulent flow, lower grade murmur
Describe the pathophysiology of a ventricular septal defect
- Left to right shunt
- Volume overload of RV
- Pulmonary over-circulation
- Volume overload of LA & LV
- Left sided heart failure may result
What occurs in sequalae to a ventricular septal defect?
- Small, restrictive VSDs; remain asymptomatic
- Left sided heart failure with large defects
- With growth, some VSDs may close
- Aortic valve leaflets may prolapse into VSD; VSD functionally “closed” but Aortic regurgitation develops
What are the consequences of pulmonary hypertension associated with a VSD?
High RV pressures may result in shunt reversal (right to left) (Eisenmenger’s syndrome).
How does a ventricular septal defect appear on radiography?
- Left sided (LAE, LVE) and right ventricular enlargement
- Pulmonary over-circulation (increased size of lobar vessels (arteries and veins) and increased vascularity.
Describe the predisposition of mitral valve dysplasia
- It is one of the more common congenital heart defects in cats (no particular breed predisposition).
- Dog breeds predisposed: Bull terriers, great Danes, golden retrievers, German shepherd dogs, English Springer spaniels.
Describe the gross pathology of mitral dysplasia seen on PME
- Thickened mitral valve
- Mitral stenosis
- Aortic Stenosis
- Valves are stiff and don’t open properly
Describe the pathophysiology of mitral and tricuspid dysplasia
- Incompetence of MV/TV, with MR / TR
- Volume overload of LA/LV or RA/RV
- Left / Right sided heart failure
- Possible arrhythmias (especially atrial, e.g. supraventricular tachycardia, AF)
- Occasionally get STENOSIS of MV (or TV)
- Rarely detect a diastolic murmur (mitral inflow)
- Gross atrial enlargement results
How does mitral dysplasia appear on radiography
Big left side of the heart, pulmonary oedema
Describe the main features of an atrial septal defect
Usually left to right shunt
Normally identified incidental to another congenital heart defect
List the 4 components that make up the tetralogy of Fallot defect
- Ventricular septal defect
- Pulmonic stenosis
- Right ventricular hypertrophy
- Dextrapposed aorta
What are the consequences of a tetralogy of fallot defect?
- Pulmonic stenosis results in high RV pressure
- The shunt is right to left across the VSD when RV pressure exceeds LV pressure.
- Flow from the right ventricle may exit into a severely Dextrapposed aorta straddling the VSD
How does a patient with a Tetralogy of Fallot present?
The animal will be cyanotic. The cyanosis fails to respond to oxygen supplementation (the animal stays “blue” and does not “pink-up”).
Name 2 congenital heart lesions not associated with a murmur
Vascular ring anomalies
Pericardio-peritoneal diaphragmatic hernia (PPDH)
What is a vascular ring anomaly?
Usually a persistent right fourth aortic arch
This results in a vascular ring surrounding the oesophagus, so patients show regurgitation at the onset of weaning or intake of solid foods.
Mega-oesophagus rostral to the constriction can result, evident on radiographs or fluoroscopy
