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VETERINARY CLINICAL CARDIOLOGY
CARDIOLOGY CONCEPTS
Congenital Heart Disease
General
1. Dog Breed Predilections
Dog Breed Predilections For Congenital Heart Disease

Airedale Pulmonic stenosis (PS), Patent Ductus Arteriosus (PDA), Ventricular septal defect (VSD)
Akita Ventricular septal defect (VSD)
Australian shepherd Patent ductus arteriosus (PDA)
Basset hound PS
Beagle PS, VSD
Bernese Mountain Dog Subaortic stenosis (SAS)
Bichon frise PDA
Border Terrier SAS
Bouvier de Flanders SAS, PDA
Boxer SAS, PS, atrial septal defect (ASD), VSD
Boykin spaniel PS
Bulldog English Tetralogy of Fallot, VSD, PS, SAS, single coronary artery (Right coronary)
Bulldog French PS
Bull terrier Mitral dysplasia, aortic stenosis, SAS
Cairn Terrier SAS
Cavalier King Charles Spaniel PDA, PS, mitral valve dysplasia
Chihuahua PDA, PS
Chesapeake Bay Retriever SAS
Chow chow Cor triatriatum dexter, PS
Cocker spaniel PDA, PS
Collie PDA, tricuspid valve dysplasia
Doberman pinscher ASD, PDA, PS, VSD, atrial septal defect (ASD)
Dogue de Bordeaux SAS, tricuspid valve dysplasia
English bulldog Tetralogy of Fallot, VSD, PS, SAS
English Springer spaniel PDA, VSD
French Bulldog PS
German shepherd SAS, aortic stenosis, mitral and tricuspid valve dysplasia, PDA, persistent right aortic arch, ventricular arrhythmias
German shorthair pointer SAS
Golden retriever SAS, tricuspid valve and mitral valve dysplasia, PS
Great Dane Mitral and tricuspid valve dysplasia, SAS, PS
Ibizan Hound SAS, PS
Irish setter Persistent right aortic arch
Keeshond Tetralogy of Fallot, PDA, PS
Labrador retriever Tricuspid valve dysplasia, PDA, PS, SAS
Malamute PS
Maltese PDA, PS, VSD
Mastiff PS, SAS, mitral valve dysplasia
Mastiff English SAS
Miniature Schnauzer PS, PDA
Neapolitan Mastiff PS
Newfoundland SAS, mitral valve dysplasia, PS
Nova Scotia Duck Tolling Retriever PS
Poodle PDA
Poodle Standard Atrial septal defect (ASD)
Pomeranian PDA
Portuguese Water Dog DCM
Rhodesian Ridgeback Mitral valve dysplasia
Rottweiler SAS, PDA, Mitral valve dysplasia
Saluki Tricuspid valve dysplasia
Samoyed PS, ASD, SAS
Schnauzer PS
Shetland sheepdog PDA
Shih tzu VSD, PDA
Siberian husky VSD
St Bernard SAS, tricuspid valve dysplasia
Terrier breeds PS
Weimaraner Tricuspid dysplasia, peritoneopericardial hernia
West Highland White Terrier PS, VSD, Tetralogy of Fallot,coronary artery to pulmonary artery fistula, single coronary artery (Right coronary)
Whippet PS
Wirehaired Fox Terrier PS
Yorkshire terrier PDA
2. Congenital heart disease - general features about shunts
Some general features about congenital heart disease:

  1. Cyanosis: occurs when the reduced hemoglobin concentration (unoxygenated) is (5 gm/dl) 50 gm/l or greater.
    • If severe anemia is present (<15% PCV) than cyanosis cannot be detected
    • Cyanosis may occur due to:
      1. Severe respiratory disease and the inability to oxygenate blood.
      2. Right to left shunt located:
        • at the level of the atria
        • at the level of the ventricles
        • at the level of the aorta and pulmonary artery
        • arterio-venous shunt in the lungs
  2. Weakness occurs when:
    • Cardiac output to the skeletal muscles is reduced.
    • Cardiac output may be normal but due to a shunt, the level of oxygen delivered to the skeletal muscles is reduced.
  3. Syncope: occurs for the same etiologies as weakness, however, it is defined as a transient loss of consciousness caused by a reduction in cerebral oxygen or glucose delivery that is due either to decreased amounts of these constituents in blood or, more commonly, to decreased cerebral blood flow. Syncope can be difficult to differentiate from a seizure. See more about syncope.
-
Syncope Seizure
+ generalized muscle weakness + aura
+/- ataxia + loss of consciousness
+ collapse -
+/- loss of consciousness + tonic/clonic activity
+/- muscular activity -
+/- flaccid muscle +/- defecation
+/- urination +/- hypersalivation
+/- defecation +/- vomiting
- vomiting + post ictal period
+/- cry out + occurs during sleep
+ rapid recovery -
- post ictal period + post ictal period
+ usually preceded by activity or excitement -
  • Differential diagnosis for syncope includes:
    1. seizure, narcolepsy, cataplexy
    2. electrolyte disorders
    3. neuro-muscular junctional disorders
  1. Pulmonary vasculature as determined radiographically.
    • Pulmonary overcirculation:
      • An increased volume of blood flow through the pulmonary vasculature associated with left to right shunts.
    • Pulmonary undercirculation:
      • A reduced volume of blood flow through the pulmonary vasculature associated with right to left shunts.
  2. Polycythemia:
    • is a compensatory response to an inadequate delivery of oxygen to the metabolizing tissues
    • is seen primarily with right to left shunts
  3. The recirculation circuit:
    • The recirculation circuit determines the vessels and intracardiac chambers that become enlarged (undergo dilation/eccentric hypertrophy) associated with congenital disorders or acquired disorders that cause volume overload.
    • This involves disorders of valvular insufficiency or shunting.
    • The recirculation circuit is the path that a red blood cell would take if it continuously traversed across the defect on every occasion when it encounters the defect.
    • The structures within the recirculation circuit are subject to volume overload; that is they carry an increase in blood volume.
    • The cardiac structures within the recirculation circuit respond to volume overload by eccentric hypertrophy (dilation).
    • The arteries and veins within the recirculation circuit respond to volume overload by dilation.

3. Patent ductus arteriosus: What is the abnormality?

PDA Recirculation Circuit:

  • The recirculation circuit is the path that a red blood cell would take if it continuously traversed across the defect on every occasion when it encounters the defect.
  • The structures within the recirculation circuit are subject to volume overload; that is they carry an increase in blood volume.
  • The cardiac structures within the recirculation circuit respond to volume overload by eccentric hypertrophy (dilation).
  • The arteries and veins within the recirculation circuit respond to volume overload by dilation.
  • For a left to right PDA the recirculation circuit is: the main pulmonary artery; the pulmonary arteries; the pulmonary veins; the left atrium; the left ventricle; the ascending aorta; the arch of the aorta; and the descending aorta up to the ductus arteriosus.

The abnormality:

  • Failure of the ductus arteriosus to close shortly after birth and thereby allowing continued flow of blood between the aorta and pulmonary artery.
  • Ductal smooth muscle hypoplasia is responsible for failure of the ductus to close.
  • A polygenic mode of inheritance is proposed for Miniature and toy poodles.

The Incidence:

PDA is reported to be the most frequently encountered congenital cardiac defect in the dog. We now believe that aortic stenosis is the most common cardiac congenital disorder in the dog.

1. Classical Patent Ductus Arteriosus (PDA) (Left to Right Shunt):

  • most cases of PDA involve blood flow from the higher pressure region (aorta) to the lower pressure region (pulmonary artery)

2. Reverse PDA (Right to Left Shunt):

  1. This may occur secondary to a hypoplastic pulmonary artery disorder or pulmonary artery hypertension resulting in a markedly elevated pulmonary artery pressure such that the pulmonary artery pressure is greater than the pressure in the aorta.
  2. In people, a reverse PDA may occur secondary to a large volume of blood flowing into the pulmonary artery due a left to right shunt. Chronic left to right shunting of blood is reported to increase pulmonary artery tone and result in elevated pulmonary artery pressure. To the authors' knowledge this has never been demonstrated to occur in the dog.
4. How does patent ductus arteriosus present?
Signalment:

  • Common breeds:
    • Miniature Poodle
    • German Shepherd
    • Collie
    • Sheltie
    • Pomeranian
  • Usually presented at 6 - 12 wks of age
  • More common in females, approximately 70% of cases are in females

History:

  • The majority of cases present for an incidental heart murmur detected at the time of first vaccination
  • Rarely they present for signs of congestive heart failure
  • Also rarely they present for hind leg weakness (with reverse PDA)
  • Cats are reported to show severe heart failure by a few weeks of age (this has not been the authors experience)

Continuous Murmur:

  • PDA
  • A-V Fistula

Physical Examination:

  • The hall mark of PDA is the finding of a continuous heart murmur with a PMI in the left axilla or thoracic inlet. Although the murmur can be heard in systole and diastole, the intensity is always stronger in systole and fades in diastole. Also, if one listens over the left apex, the murmur is usually only systolic; therefore the PMI must be sought out (deep in the axillary region) to find the continuous nature of the murmur.
  • Signs of heart failure are usually absent, but in some cases may be noted, especially congestive heart failure
  • If heart failure is present, reduced stature may be noted
  • The femoral arterial pulse is usually exuberant (another typical feature of PDA). Often a prominent pulse may be noted in many unusual areas on the body (i.e. along the gingival mucous membranes)
  • When reverse PDA occurs, it presents with:
    • differential cyanosis - cyanosis of the rear half of the body, pink head area and forelegs
    • the polycythemia that develops may mask the murmur which is usually systolic
5. How is patent ductus arteriosus diagnosed?
A definitive diagnosis of PDA is obtained with cardiac catheterization. A presumptive diagnosis of PDA can be obtained by auscultation.

  1. Auscultation:
  2. Radiology may see:
    • Left ventricular enlargement
    • Left atrial enlargement
    • Aortic bulge (12:00 - 1:00 o'clock on the V/D or D/V view)
    • Main pulmonary artery bulge (1:00 - 2:00 o'clock on the V/D or D/V view)
    • Left auricular bulge (2:00 - 3:00 o'clock on the V/D or D/V view)
    • Pulmonary venous congestion/pulmonary edema
    • Pulmonary overcirculation
  3. ECG may see:
    • normal ECG
    • left ventricular enlargement (tall R waves)
    • left atrial enlargement (tall P waves)
    • dysrhythmias both supraventricular and ventricular
    • signs of right ventricular enlargement with reverse PDA
  4. Blood Gas
    • normal with classical PDA
    • markedly reduced femoral arterial oxygen content with reverse PDA
  5. Echocardiography
    • left ventricular enlargement
    • left atrial enlargement
    • turbulence in main pulmonary artery (presumptive evidence of PDA) by Doppler
    • identification of the ductus arteriosus entering the pulmonary and color Doppler demonstrating left to right flow through the ductus arteriosus
    • signs of right heart enlargement with reverse PDA
  6. Cardiac Catheterization
    • Selective angiography of the ductus arteriosus confirming a PDA with left to right or right to left shunt

Comments: The finding of a continuous murmur is strong evidence for PDA and is usually sufficient to warrant surgery

6. How is patent ductus arteriosus treated?
  • The only definitive treatment for PDA is ductal occlusion
    • Surgical correction
    • Coil embolization
    • If left untreated 50% to 64% of dogs are expected to die within 12 months
  • Compare and contrast these procedures:
    • Cost: almost identical
    • Morbidity: surgical correction involves a thoracotomy with the pain inherent in that procedure and the potential for hemothorax, hydrothorax, pyothorax, and pneumothorax. These complications the authors have not experienced with coil embolization. In children coil embolization is an outpatient procedure and the preferred method of closure.
    • Mortality: surgical mortality is reported at 8% - 11%; we have experienced no mortality with coil occlusion
    • Complications: with surgery include all those encountered with a thoracotomy. With coil embolization dislodgement of the coil with embolization of the pulmonary arterial tree or the systemic tree. Pulmonary arterial embolization has been described by most centers and if left in place has never resulted in any long-term sequelae. Angiography performed at 1 year after pulmonary artery embolization reveal not difference in perfusion of either lung. Arterial embolization has been rarely encountered by the authors and necessitated coil extraction. This was accomplished with a snare retrieval device. Hemolysis and recanalization have been reported but not observed by the authors.
    • Residual flow post correction: we believe similar results occur with both procedures - up to 20%. This appears to be insignificant
    • From one to 11 coils have been required to close the ductus.
  • Those cases with pulmonary edema are usually readily controlled with diuretics (furosemide) prior to correction. One week of diuretic therapy is usually sufficient
  • Cases of reverse PDA cannot be corrected, fulminant right heart failure will develop. Patients with reverse PDA can be treated with hydroxyurea to deal with polycythemia; hydroxyurea suppresses bone marrow production of red blood cells (RBCs).
7. What is the prognosis with patent ductus arteriosus?
In the hands of a skilled surgeon the prognosis for surviving surgery is 90%. If the dog survives surgery the prognosis for a full life is excellent. The radiographic changes should resolve in 6 - 12 months.

It is reported that >60% of cases will die within 1 year without surgery. These findings are incompletely substantiated.

In the authors' experience the prognosis is excellent with both the coil embolization and surgical ligation procedures.

In reverse PDA, animals may live for a few years, however debilitated by cyanosis.

8. Aortic Stenosis: What is the abnormality?

Aortic stenosis is reported to be the 2nd most prevalent congenital cardiac disorder in the dog. Our experience suggests that aortic stenosis is by far the most common congenital cardiac defect in the dog. The stenotic lesion may occur in the subvalvular position, valvular position, or supravalvular position.

The subvalvular disorder is the most common form of aortic stenosis in the dog. Aortic stenosis is a relatively uncommon congenital heart disorder in the cat. When present, it is reported to usually occur in the supraaortic valve position.

The hemodynamic consequences of aortic stenosis is the development of left ventricular concentric hypertrophy due to pressure overload. This results in reduced left ventricular distensibility and the hypertrophied left ventricular wall is prone to initiating dysrhythmias.

9. How does aortic stenosis present?
  1. Signalment
    • Breeds:
      • Newfoundland
      • German Shepherd
      • Boxer
      • Golden Retriever
      • Rottweiler
      • Bull Terriers
      • Bouvier de Flanders
      • Bernese Mountain Dogs
      • And many other breeds
    • Age:
      • presented as puppies at the time of the first vaccination - an incidental finding
      • may present as adults with an incidental murmur
    • Inheritance:
      • Polygenic or
      • Autosomal dominant with gene modifiers
  1. History:
    • Presented for vaccination, the heart murmur is an incidental finding
    • Usually asymptomatic
    • Syncope, sudden death may occur
  2. Physical examination:
    • Systolic heart murmur with a PMI over the left heart base radiating up the neck, and to the right hemothorax
    • The femoral arterial pulse may be weak
    • Signs of heart failure are rare
    • Dysrhythmias with pulse deficits may be noted
    • At times the PMI for this disorder is over the right heart base
10. How is aortic stenosis diagnosed?
The definitive diagnostic test for aortic stenosis is:

  1. Doppler echocardiography
  2. Cardiac catheterization

A presumptive diagnosis can be made with:

    1. Auscultation of a left basilar systolic heart murmur
    2. Weak femoral arterial pulse
      • Weak pulses are noted only in severe cases
    3. Left ventricular enlargement on ECG and
      • Usually LVE is not evident on the ECG
    4. A bulge in the ascending aorta on radiography
      • Usually in ascending aortic bulge is not evident on the radiographs

    Diagnostic Findings:

    1. Radiology may see:
      • left ventricular enlargement
      • dilation of the aortic arch particularly on the lateral view in the region of the "right auricle/main pulmonary artery /ascending aorta"
      • frequently radiographs are normal
    2. ECG:
      • usually normal
      • may see criteria of left ventricular enlargement
      • may see ventricular ectopy (PVC's)
    3. Echocardiography:
      • left ventricular hypertrophy (concentric)
      • subvalvular lesion in the left ventricular outflow tract
      • increased velocity across the aortic valve by Doppler
        • Not only does this data provide a diagnosis but it remains the most critical data to address severity of the stenosis
        • aortic regurgitation by Doppler in about 85% of cases
11. How is aortic stenosis treated?
Goals of therapy:

  • Correct dysrhythmias:
    • Beta blocker therapy
      • Propranolol
      • Metoprolol
      • Atenolol
    • Class I antidysrhythmic therapy
      • Lidocaine analog (tocainide, mexiletine)
      • Procainamide (sustained release)

  • Improve left ventricle distensibility:
    • Beta blocker therapy:
      • Propranolol
      • Metoprolol
      • Atenolol
  • Definitive treatment:
    • Surgical correction:
      • Require cardiopulmonary bypass - thus technically challenging
        • Very few centers in North America can address these cases
      • Dilation of the stenosis with a metal dilator - generally not effective
    • Balloon Valvuloplasty:
      • Ineffective against the firm fibrotic lesion of SAS
    • Thus no definitive treatment is available
    • Dosages:

      1. Propranolol dog: 0.2-1 mg/kg TID (PO); 0.04-0.06 mg/kg slowly IV
      2. Metoprolol dog: 0.5-1 mg/kg TID (PO)
      3. Atenolol dog: 5-12.5 mg SID (PO)
      4. Lidocaine dog: 2-4 mg/kg slow (IV), repeat q 10 min to max. of 8 mg/kg; 25-75 ug/kg/min (CRI)
      5. Tocainide dog: 5-10 mg/kg TID-QID (PO); Dr. Hamlin suggests 25 mg/kg QID (PO)
      6. Mexiletine dog: 2-5 mg/kg BID-TID (PO) we have dosed some dogs at 8-10 mg/kg
      7. Procainamide dog: 6-8 mg/kg (IV) over 5 min; 25-40 ug/kg/min (CRI); 8-20 mg/kg q 4-6 hr (IM), TID (PO) sustained release

      Comment: The prophylactic use of beta-blocker therapy is controversial. Repeated reports in the veterinary literature support this indication for beta-blocker therapy.

    Consequences:

    • Congestive heart failure:
      • Uncommon
        • Occurs in older dogs
        • More likely to manifest if moderate to severe MR and/or AI are/is also present
    • Syncope/sudden death
      • Ventricular arrhythmias are common
      • Exertional syncope is common
      • Sudden death is the most common outcome with SAS, most occurring by 3 years of age
      • Weakness may also manifest
      • Average survival is 14.4 months
  • 12. What is the prognosis with aortic stenosis?
    • Most cases of aortic stenosis of marked severity result in malignant dysrhythmias and sudden death.
    • Mild cases of aortic stenosis live a full life (both normal quality and duration).
    • Even cases of moderate stenosis can anticipate a life of normal length and quality.
    • The severity of the stenosis can be predicted by Doppler echocardiography.
      • Mild SAS: has a pressure gradient between the LV and Ao of <50 mmHg
      • Moderate SAS: has a pressure gradient between the LV and Ao of 50 to 80 mmHg
      • Severe SAS: has a pressure gradient between the LV and Ao of >80 mmHg
        • The authors have observed many dogs with pressure gradients of 100 mmHg experience lives of normal length and quality
        • The authors therefore use a threshold of >100 mmHg as a threshold gradient in the mature dog identifying dogs with a poor prognosis.
    • Work with Doppler echocardiography indicates that aortic stenosis is a progressive and that the rate of progression is greatest in the immature dog and progresses at a very slow rate in the mature dog.
    • It has been reported that if dogs survive with aortic stenosis beyond 3 years, they usually do not have aortic stenosis severe enough to produce a marked effect on LV performance.
    13. Pulmonic Stenosis: What is the abnormality?

    • Pulmonic stenosis is reported to be the 3rd most prevalent congenital cardiac disorder in the dog.
    • The stenotic lesion may occur in the:
      • subvalvular position
      • valvular position or
      • supravalvular position
    • The valvular disorder is the most common in the dog (88% incidence). Usually the commissures of the valve are fused and the free edges are thickened. Pulmonic stenosis is a very uncommon congenital heart disorder in the cat.
    • The hemodynamic consequences of pulmonic stenosis are the development of right ventricular concentric hypertrophy and reduced filling of the left ventricle. The right ventricular concentric hypertrophy causes reduced right ventricular compliance with reduced distensibility. The hypertrophied right ventricular wall is prone to initiate dysrhythmias.
    14. How does pulmonic stenosis present?
    1. Signalment:
      1. Breeds
        • Samoyed
        • English Bulldog
        • Mastiff
        • Fox terrier
        • Miniature Schnauzer
        • Chihuahua
        • Beagle
        • Keeshond
        • American Cocker Spaniel
        • West Highland White Terrier
      2. Inheritance: Polygenic
      3. Age: presented as puppies
    2. History:
      • An incidental finding at the time of puppy vaccination is the usual presentation
      • Syncope/fatigue/exercise intolerance may occur
      • Signs of right heart failure in cases of severe pulmonic stenosis
      • Could present as an incidental murmur in an adult
    3. Physical examination:
      • systolic heart murmur with a PMI over the left heart base which may radiate up the neck
      • femoral arterial pulse is normal
      • signs of right heart failure may be present
      • concurrent tricuspid valve insufficiency may be present
      • dysrhythmias with pulse deficits may be present
    15. How is pulmonic stenosis diagnosed?
    The definitive diagnostic test for pulmonic stenosis is:

    1. Doppler echocardiography
    2. Cardiac catheterization

    A presumptive diagnosis can be made with:

    1. Auscultation of a left basilar systolic heart murmur
    2. Normal femoral arterial pulse
    3. Right ventricular enlargement on ECG and
    4. Right ventricular enlargement on radiography
    5. Main pulmonary artery bulge on radiographs
    6. Diagnostic Findings

      1. Radiology may show:
        • right ventricular enlargement
        • bulge in the main pulmonary artery
        • ascites
        • hepatomegaly
      2. ECG may show:
        • normal ECG
        • right ventricular enlargement criteria with moderate to severe pulmonic stenosis
        • right atrial enlargement
        • may be normal with mild cases
        • dysrhythmias may be noted
      3. Echocardiography:
        • right ventricular hypertrophy
        • stenosis of the pulmonic valve
        • increased velocity of flow across the pulmonic valvular orifice by Doppler
          • Not only does this data provide a diagnosis but it remains the most critical data to address severity of the stenosis
        • pulmonic regurgitation by Doppler
        • right ventricular enlargement
        • tricuspid regurgitation by Doppler
    16. How is pulmonic stenosis treated?
    The treatment of choice for severe pulmonic stenosis is reduction of the stenosis.
    • Surgical correction
      • Objective of correction is not to completely relieve the obstruction but to substantively increase the size of the orifice.
      • Several procedures have been described
        • Patch graft procedure
        • Valvulotomy via the MPA
        • Valvuloplasty with a closed knife and/or valve dilator introduced into the RVOT
        • Implantation of a valved or non-valved conduit detouring the stenosis (from the RVOT to the MPA)
    • Balloon valvuloplasty
      • Single balloon procedure
        • Introduced via the jugular vein or femoral vein
      • Double balloon procedure
        • One introduced via each femoral vein
    • Compare and contrast these procedures:
      • Cost: almost identical
      • Morbidity: surgical correction involves a thoracotomy with the pain inherent in that procedure and the potential for hemothorax, hydrothorax, pyothorax, and pneumothorax. With balloon valvuloplasty severe arrhythmias can develop and it is possible for ventricular fibrillation and death to occur. Arrhythmic death can occur with either procedure. In children balloon valvuloplasty is an outpatient procedure and the preferred method of treatment.
      • Mortality: surgical mortality is not reported, however the authors would expect comparable mortality with both procedures.
      • Complications: with surgery include all those encountered with a thoracotomy. Balloon valvuloplasty is associated at times with trauma to the tricuspid valve. English bulldogs and boxers have been described to possess, at times, an aberrant single right coronary artery (type R2A) which gives rise to the left coronary that encircles the base of the MPA at the level of the pulmonic annulus. Patch Graft surgery and balloon dilation have both had fatal results if this anomaly is present at the time of correction of the pulmonic stenosis.
      • Efficacy of correction: The authors have not been impressed with the Patch Graft technique. As the surgical experience with the other methods is limited it is not possible to comment on efficacy. Although data is limited it appears that dogs that have undergone successful balloon valvuloplasty are at least 2 times more likely to reach 2 years of age compared with untreated dogs.

      However the efficacy of surgical intervention remains to be substantiated. Surgery should be reserved for cases of moderate to severe pulmonic stenosis (a Doppler velocity of >5 m/s)

      Other goals of therapy:

    • Control dysrhythmias
      • as for aortic stenosis
    • Control signs of right heart failure
      • diuretics - furosemide (these should be used sparingly)
    • Infundibular hypertrophy may be controlled with beta blocker therapy. This remains unsubstantiated.
      • Dosages:

        • Furosemide (Lasix):
          • dog: 2-4 mg/kg BID-TID (IV, IM, SQ, PO); 2-8 mg/kg q 1 hr (IV) in severe pulmonary edema
          • cat: 1-2 mg/kg BID-TID (PO, IM, IV) do not exceed 2 mg/kg (IV)
        • Propranolol:
          • dog: 0.21-1.0 mg/kg TID (PO); 0.04-0.06 mg/kg (IV) slowly
          • cat: 0.21-1.0 mg/kg BID-TID (PO); 0.04 mg/kg (IV) slowly
        • Metoprolol:
          • dog: 0.5-1 mg/kg TID (PO)
          • cat: 2-15 mg TID (PO)
        • Atenolol:
          • dog: 5-12.5 mg SID (PO)
          • cat: 5-12.5 mg SID-BID (PO)

      Comment: Balloon valvuloplasty has been shown to be of use to dilate the valvular lesion. This procedure will reduce the morbidity and mortality associated with thoracic surgery.

    17. What is the prognosis with pulmonic stenosis?
    1. Most cases of severe pulmonic stenosis result in:
      • Malignant dysrhythmias and sudden death,
      • Exertional weakness, or
      • Right heart failure with ascites and pleural effusion
    2. Mild cases of pulmonic stenosis live a full life (both normal quality and duration).
    3. Even cases of moderate pulmonic stenosis can anticipate a life of normal length and quality
    4. The severity of the stenosis can be predicted by Doppler echocardiography
      • Mild PS: has a pressure gradient between the LV and Ao of <50 mmHg
      • Moderate PS: has a pressure gradient between the LV and Ao of 50 to 80 mmHg
      • Severe PS: has a pressure gradient between the LV and Ao of >80 mmHg
        • The authors have observed many dogs with pressure gradients of > 100 mmHg experience lives of normal length and quality
        • The authors therefore use a threshold of >100 mmHg as a threshold gradient in the mature dog identifying dogs with a poor prognosis.
        • Dogs appear to handle more severe pulmonic stenosis than comparable subaortic stenosis.

    Comment:

  • We have encountered dogs with relatively mild pulmonic stenosis that have developed severe ventricular or supraventricular dysrhythmias which have prematurely shortened their lives. Thus the consequences of the disorder may cause more problems than the stenosis itself.
  • Work with Doppler echocardiography indicates that like subaortic stenosis, pulmonic stenosis is progressive and the rate of progression is greatest in the immature dog and progresses at a very slow rate in the mature dog.
  • 18. Ventricular Septal Defect: What is the abnormality?

    Abnormality: A defect allowing blood flow between the left and right ventricle. The defect on the right side is usually beneath the septal leaflet of the tricuspid valve. The defect on the left side is usually beneath the aortic valve.

    The hemodynamic consequences of VSD consist of:

    1. eccentric hypertrophy of the left ventricle, and right ventricle. The right ventricle is more distensible than the left ventricle thus reduced left ventricular distensibility becomes the main problem leading to congestive heart failure. It appears that flow across the defect usually streams directly into the pulmonary artery without significant mixing and distention of the right ventricle
    2. a marked % of LV cardiac output is detoured from its true target
    3. if the volume of shunt flow is very high, the pulmonary vasculature may respond with profound pulmonary artery hyperplasia resulting in severe pulmonary artery hypertension. This will result in a reversal of blood shunt flow from right to left. This causes systemic hypoxemia. We have never documented such a scenario.
    19. How does ventricular septal defect present?
    1. Signalment:
      1. Breeds:
        • English Springer Spaniels
        • English Bulldog
        • Keeshond
      2. Inheritance: Polygenic
      3. Age: Usually presented as puppies
    2. History:
      • An incidental finding at the time of puppy vaccination if small defect
      • large defect - stunted growth, fail to thrive
      • A murmur may be detected as an incidental finding in the adult
    3. Physical examination:
      • A systolic heart murmur with a PMI over the right sternal border
      • Thrill may be present over right hemithorax
      • If shunt flow reverses - signs of right to left shunt flow will be noted and signs of right heart failure
      • Large defects may show congestive heart failure
    20. How is ventricular septal defect diagnosed?
    The definitive diagnostic test for ventricular septal defect is:

    1. Doppler echocardiography
    2. Cardiac catheterization

    A presumptive diagnosis can be made with:

    1. Auscultation of a right sternal border systolic heart murmur.
    2. Radiographic evidence of pulmonary overcirculation.

    The re-circulation circuit is: right ventricle, right ventricular outflow tract, pulmonary arteries, pulmonary veins, left atrium and left ventricle.

    Diagnostic Findings:

    1. Radiology may show:
      • generalized heart enlargement
      • pulmonary overcirculation
    2. ECG may show:
      • usually normal ECG
      • possibly left ventricular enlargement
      • variable right ventricular enlargement
    3. Echocardiography:
      • VSD defect
      • Generalized heart enlargement
      • Doppler evidence of a left to right VSD

    Comment (Right to left VSD): It is reported that chronic large volume of flow across the VSD into the pulmonary arteries can result in pulmonary artery hypertension and elevated right ventricular pressure. This can eventually result in right to left flow across the VSD.

    It is my belief that a right to left shunt does not occur due to this etiology of excessive blood flow as described in man. When a right to left shunt does occur it is a result of a hypoplastic pulmonary vasculature or congenital pulmonary artery hypertension.

    When right to left flow occurs across the VSD:

    1. Historical signs develop:
      • reduced exercise tolerance
      • syncope
      • fatigue
    2. Physical examination signs develop:
      • jugular venous distention
      • cyanosis
      • weakness
      • possibly heart murmur
    3. Radiologic signs develop:
      • right ventricular enlargement
      • right atrial enlargement
      • pleural effusion
      • ascites
    4. Electrocardiographic signs develop:
      • right ventricular enlargement
      • right atrial enlargement
    5. Blood work findings develop:
      • reduced arterial oxygen content
    6. Echocardiographic findings develop:
      • right ventricular enlargement
      • right atrial enlargement
      • right to left contrast flow across VSD
    21. How is ventricular septal defect treated?
    1. Mild VSD
      • causes no hemodynamic embarrassment and thus warrants no therapy
    2. Severe VSD
      • may require surgical repair of the defect
      • a number of procedures are available
    3. Arterial vasodilators will reduce the degree of left to right shunting.
    4. Pulmonary artery banding procedures can spare pulmonary vascular damage a result of excessive fluid flowing through the pulmonary circulation.
    22. What is the prognosis with ventricular septal defect?
    1. Mild VSD - presents no morbidity.
    2. Severe VSD - if pulmonary hypertension develops:
      • response to therapy and prognosis are unknown, but likely very poor
      • if heart failure develops, the animal will likely succumb within 6 months.

    Comments:

    • chronic excessive fluid flow through the pulmonary circulation may result in pulmonary hypertension and right to left shunt flow.
    • this is likely a rare occurrence.
    • if it does occur, polycythemia (increase in RBC mass of the blood) may develop and can be treated with hydroxyurea, which suppresses bone marrow production of RBCs.
    23. Tetralogy of Fallot - What is the abnormality?

    Abnormality: Tetralogy of Fallot is a complex congenital cardiac defect consisting of:

    1. pulmonic stenosis
    2. overriding aorta
    3. VSD
    4. hypertrophic right ventricle

    The hemodynamic consequences of Tetralogy of Fallot consist of:

    1. systemic hypoxemia
    2. polycythemia with reduced peripheral circulation and seizures
    3. reduced right ventricular distensibility due to concentric hypertrophy. This can result in dysrhythmias.
    24. How does Tetralogy of Fallot present?
    1. Signalment:
      1. Breeds - Keeshond
      2. Age - 3 to 6 months
    2. History:
      1. may present with an incidental heart murmur at vaccination
      2. may have:
        • stunted growth
        • reduced exercise tolerance
        • respiratory distress
        • syncope
    3. Physical examination:
      1. cyanotic mucus membranes
      2. systolic heart murmur of pulmonic stenosis
      3. if polycythemia is present no murmur may be noted
      4. jugular venous distention
    25. How is Tetralogy of Fallot diagnosed?
    The definitive diagnostic test for Tetralogy of Fallot is:

    1. Cardiac catheterization
    2. Doppler Echocardiography

    A presumptive diagnosis can be made with:

    1. Systemic cyanosis.
    2. Radiographic evidence of pulmonary undercirculation and right heart enlargement
    3. Electrocardiographic evidence of right ventricular enlargement.

    Results of Diagnostic Tests:

    1. Radiology may show:
      • Criteria for right ventricular enlargement
      • Pulmonary undercirculation
      • Main pulmonary artery may be small
    2. ECG may show:
      • Criteria for right ventricular enlargement
      • Ventricular ectopy
    3. Blood Work may show:
      • Polycythemia
      • Evidence of reduced glomerular filtration (increase BUN/creatinine)
    4. Echocardiography: may show:
      • Right ventricular hypertrophy
      • Doppler evidence of pulmonic stenosis
      • Overriding aorta
      • High ventricular septal defect
      • Color Doppler or contrast echocardiographic evidence of a right to left shunt.

    Comment:

    • pulmonary artery hypoplasia is common
    • anomalies of the aorta are common
    26. How is Tetralogy of Fallot treated?
    Tetralogy of Fallot can be treated by:

    1. Several palliative surgical procedures are described which involve detouring flow from the aorta to the pulmonary artery (via a surgically created shunt) to enhance pulmonary artery flow.
    2. There is no definitive medical therapy.
    3. Polycythemia can be treated with hydroxyurea (50 mg/kg PO QOD) to suppress bone marrow production of RBCs.

    If arrhythmias are present, manage as per pulmonic stenosis. Beta blocker therapy is recommended by some, efficacy is unsubstantiated. Intermittent phlebotomies may manage some of the symptoms of Tetralogy of Fallot.

    27. What is the prognosis with Tetralogy of Fallot?
    1. If activity is severely restricted some individuals may live with their disorder through a long life.
    2. The efficacy of surgical intervention is undetermined.
    3. Most individuals can be expected to experience a life of reduced stamina
    28. How does congenital heart disease of cats differ from that of dogs?
    1. Incidence:
      • Less common in cats than dogs
    2. Breed, Sex:
      • No overall breed or sex predilection in cats
    3. Frequency of congenital disorders:
      1. A-V valve insufficiency - (17%)
      2. Ventricular septal defect - (15%)
      3. Endocardial fibroelastosis - (11%)
      4. Patent ductus arteriosus - (11%)
      5. Aortic stenosis - (6%)
      6. Tetralogy of Fallot - (6%)
    4. General Comments:
      • A-V valve insufficiency:
        • if severe - heart failure and death likely occur in the first few weeks of life
        • most cases are likely mild with no symptoms but do have a heart murmur of mitral or tricuspid regurgitation
        • a great deal of data is lacking with respect to the significance of this disorder
      • Ventricular septal defect:
        • the prognosis of this disorder depends on the size of the defect
        • it is well known that many cats can have small defects and live long normal lives
        • the clinical picture is identical to that of the dog
        • in that spontaneous closure of VSD is common in man, it may also occur in cats
        • in that VSD forms a part of a number of other complex anomalies, the VSD disorder is considered by many to be the most common defect in the cat
      • Endocardial fibroelastosis (EFE):
        • primarily seen in Burmese and Siamese cats
        • a fatal short coursed disorder in young cats (3 wk to 4 months) characterized by fibrosis of the ventricular endocardium causing a marked loss in distensibility
        • LV and left atrial dilation occur with fulminant heart failure
        • no treatment is effective
      • Patent ductus arteriosus:
        • some cats may die with this disorder soon after birth
        • it is reported that if they survive the immediate neonatal period, most will develop signs of CHF and die by one year of age
        • the incidence of reverse PDA in cats is said to be 15-20% of cases of PDA
        • the clinical picture is as for dogs with PDA
        • surgical correction is the only definitive cure
      • Aortic stenosis:
        • A.S. is usually supravalvular in the cat
        • the clinical picture is as for dogs
      • Tetralogy of Fallot:
        • similar to the dog in presentation and clinical course
    29. What are the causes for syncope?
    Syncope refers to the sudden loss of consciousness due to the temporary loss of cerebral perfusion. The metabolism of the brain, unlike other organs, is exclusively dependent on perfusion. In contrast to skeletal muscle, for example, storage of high-energy phosphate in the brain is limited, and energy supply depends largely on the oxidation of glucose extracted from the blood. Thus, cessation of cerebral blood flow causes a loss of consciousness within about 10 seconds.

    The loss of blood flow is related to a fall in blood pressure. Recall the factors that maintain blood pressure:

    • BP = CO x Arterial Resistance; since CO = HR x SV
    • BP = HR x SV x Arterial Resistance; since Arterial Resistance is proportional to 1/radius4
    • BP = HR x SV x 1/R4; note SV depends on preload, afterload, contractility

    Causes of syncope:

    1. Sudden changes in heart rate: bradycardia, tachycardia
    2. Obstruction to blood flow: aortic stenosis, pulmonic stenosis, mitral stenosis, tricuspid stenosis, pulmonary hypertension, pulmonary embolism, obstructive HCM, cardiac tamponade
    3. Right to left shunting: Tetralogy of Fallot, Eisenmenger's Syndrome
    4. Reduced preload: dehydration, hemorrhage, hypotensive drugs
    5. Vascular or neurogenic dysfunction: carotid sinus hypersensitivity (vasovagal), postmicturition, post-tussive.
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