Large Animal - Congenital Cardiac Defects

Question 1

What is the most common cardiac defect reported in large animals? What is the most common location of this defect?

Answer 1

Ventricular septal defect (VSD).

Perimembranous VSDs are more common than muscular.

Question 2

Define a ventricular septal defect (VSD).

Answer 2

Opening in the inter ventricular septum that creates a communication between the left and right ventricles.

Question 3

In what breeds of cattle are VSDs heritable?

Answer 3

Herefords and Limousins.

Question 4

In what breeds of horses are VSDs most common?

Answer 4

Welsh Mountain Pony (Type A), Arabian, Standardbred, Quarter Horse.

Question 5

What is the embryologic defect that results in formation of a VSD?

Answer 5

• Failure of fusion of the endocardial cushion and muscular ventricular septum, or
• Failure of fusion of the truncal and conal septa.

Question 6

What is the most common direction in which blood is shunted in large animals with VSDs?

Answer 6

Left to right.

Because pressure in LV exceeds pressure in RV.

Question 7

List the factors which influence the size of the shunt.

Answer 7

• Size of the defect.

- Pressures in the RV, LV and pulmonary a.

Question 8

Describe the murmur(s) heard in patients with VSD.

Answer 8

Loud, harsh, pancystolic murmur with PMI over tricuspid v on RHS and softer, holosystolic murmur with PMI over pulmonic v on LHS.
+/- palpable thrill.
+/- split S2.

Question 9

If the murmur is loudest on the LHS in an animal with VSD what should be suspected?

Answer 9

A subpulmonic VSD or a complex anomaly.

Question 10

What CSx may be seen in large animals with VSD, in addition to a cardiac murmur?

Answer 10

Poor growth, lethargy, dyspnoea, exercise intolerance, CHF (by 5yo).
Small defects may be asymptomatic.

Question 11

List three differential diagnoses for VSD.

Answer 11

• Tetralogy of Fallot.
• Mitral or tricuspid valvular anomalies.
• Neonate flow murmur.

Question 12

Describe echocardiographic findings in patients with VSD.

Answer 12

• Typical perimembranous VSD: long-axis LVOT view, located underneath the right and/or non-coronary leaflet of the aortic v and central to septal leaflet of the tricuspid v.
• Subpulmonic VSD (calves>foals): short axis view in septum between the LVOT and RVOT.
• Large/mod VSDs –> LA and LV enlargement, RV enlargement and pulmonary a dilation +/- aortic valve prolapse and aortic regurgitation.

Question 13

Horses can race with VSDs = ______.

Answer 13

• = 4.5m/s peak velocity.

Question 14

Haemodynamically significant VSDs (i.e. resulting in CHF and death) have > _____ diameter, peak shunt velocity _______.

Answer 14

• > 3.5cm diameter.
• ## 0.3 VSD:Ao root.

Question 15

What changes occur within the heart in patients with very large VSDs?

Answer 15

Pressure in LV and RV are almost equalised –> RV, pulmonary circ, LA and LV must compensate for volume overload –> dilation of cardiac chambers and pulmonary hypertension.

Question 16

What happens to pulmonary resistance in patients with concurrent VSD and pulmonary disease of LHF and what effect does this have on the RV?

Answer 16

Increased pulmonary resistance –> chronic volume AND pressure overload on RV –> reversed direction of shunt (i.e. R-L) = Eisenmenger Complex (more common in cattle).

Question 17

VSDs can create turbulent blood flow within the heart. What cardiac disease does this predispose to?

Answer 17

Endocarditis secondary to endocardial damage.

Question 18

Identify which type of valvular regurgitation in most like to occur in patients with VSD and why.

Answer 18

Aortic regurgitation, due to the location of the VSD resulting in loss of structural support for the aortic valve cusps.

Question 19

Define an atrial septal defect (ASD) and list the most common ASD described in large animals.

Answer 19

A connection between the left and right atrial at the septal level.
Most common is patent foramen ovale (PFO).

Question 20

In which species is PFO seen commonly and what other congenital cardiac defect is it often seen with?

Answer 20

Calves and PDA.

Question 21

What is the embryologic origin of a PFO?

Answer 21

Failure of the septum primum to adhere to the crista dividens after birth.

Question 22

Describe the murmur presents in patients with PFO?

Answer 22

Holocystolic, crescendo-decrescendo at the left heart base.

Question 23

In which direction in the shunt most commonly in PFO?

Answer 23

Left to right.

Question 24

PFO are frequently asymptomatic in large animals. In the case of a large defect, however, congenital remodelling may occur. What changes may be seen on echo in this case?

Answer 24

RA, RV and LA enlargement.

Question 25

Define a patent ductus arteriosus (PDA).

Answer 25

Persistent potency of the vessel that connects the pulmonary arterial system to the aorta.

Question 26

When should a PDA normally close after birth in calves and foals and why does it close?

Answer 26

• Very shortly after birth in calves, and within 4 days in foals.
• Closes in response to decreasing pulmonary vascular resistance, increased systemic vascular resistance, increased blood vol and increased LV pressure when breathing begins.

Question 27

Describe the murmur in an animal with a PDA.

Answer 27

Continuous, high-pitched, ‘machinery murmur’ on the left and right; PMI 3rd/4th ICS at the level of the point of the shoulder.
Murmur may be absent with large PDAs.

Question 28

What clinical signs may be seen in animals with PDAs in addition to a cardiac murmur?

Answer 28

• Bounding pulses (due to run-off of blood from systolic to pulmonary circulation).
• Cyanosis (if shunt reversed).
• Stunted growth.

Question 29

Describe diagnostic imaging findings in an animal with a PDA.

Answer 29

• Rads: may see enlarged cardiac silhouette and pulmonary congestion.
• Echo: may see PDA, enlarged LA and LV, enlarged LA:Ao root ratio.
• Angiography provides definitive diagnosis.

Question 30

Describe changes which occur in the heart secondary to the presence of a PDA.

Answer 30

PDA –> L-R shunt –> LV overload –> LV dilation and hypertrophy +/- CHF.
Pulmonary hypertension and congestion can occur –> RV hypertrophy.

Question 31

When does a right to left shunt occur in PDA patients?

Answer 31

When pulmonary resistance exceeds systemic vascular resistance.

Question 32

What is the prognosis for large animals with PDA?

Answer 32

May remain asymptomatic if small; poor prognosis if large.

Question 33

Is PDA a heritable condition in large animals?

Answer 33

No evidence at this time that it is a heritable defect.

Question 34

List the four components of a Tetralogy of Fallot (ToF).

Answer 34

• Overriding (biventricular origin) aorta.
• VSD.
• Pulmonic stenosis.
• RV hypertrophy.

Question 35

What congenital anomaly is present, in addition to the 4 present in cases of ToF, to make the condition a Pentalogy of Falot?

Answer 35

• ASD, plus…
• Overriding (biventricular origin) aorta.
• VSD.
• Pulmonic stenosis.
• RV hypertrophy.

Question 36

What is the embryologic origin of a ToF?

Answer 36

Abnormal development of the conal septum.

Question 37

Describe the typical murmur in animals with ToF.

Answer 37

Crescendo-decrescendo murmur or pulmonic stenosis, or harsh, plateau-shaped murmur of VSD.

Question 38

What clinical signs may be seen in animals with ToF in addition to a cardiac murmur?

Answer 38

• Small size or slow growth.
• Marked exercise intolerance –> dyspnoea and collapse.
• Cyanosis of the MMs, skin and nose.

Question 39

List differential diagnoses for oxygen-responsive cyanosis in young large animals.

Answer 39

• NARDs.
• CNS Dz.
• Heart failure with pulmonary oedema.

Question 40

List differential diagnoses for non-oxygen responsive cyanosis in young large animals (i.e. R-L shunt)

Answer 40

• ToF or PoF.
• Reverse PDA.
• Reverse VSD.
• Tricuspid or RV atresia.
• LV hyperplasia.
• Truncus arteriosus.
• Pseudotruncus arteriosus.

Question 41

Describe diagnostic findings suggestive of ToF.

Answer 41

• Echo: visualisation of defects and colour Doppler flow abnormalities.
• CBC: PCV, RBCC and Hg conc increased in some cases.
• Blood gas: arterial hypoxaemia (degree depends on amount of shunting).

Question 42

In which large animal species is ToF most common and is it an hereditary condition in large animal species?

Answer 42

• Calves > foals.

- No evidence of a hereditary link at this time.