Download BALLOON VALVULPLASTY OF PULMONIC STENOSIS

Veterinary Cardiorespiratory Centre
Martin Referral Services, Thera House, 43 Waverley Road, Kenilworth, Warwickshire CV8 1JL
Tel: 01926 863445
INFORMATION SHEET - VETS
BALLOON VALVULOPLASTY OF PULMONIC STENOSIS
Indications
Balloon valvuloplasty is indicated when there are clinical signs (symptoms) of forward heart failure, or right
sided congestive heart failure, attributable to the pulmonic stenosis.
In the absence of obvious clinical signs the following are also indications:
 The trans-stenotic pressure gradient exceeds 80mmHg.
 There is dynamic right ventricular outflow tract obstruction (also warrants beta blockers)
 There is severe right ventricular hypertrophy with flattening of the ventricular septum
Outcome
The Veterinary Cardiorespiratory Centre is one of the few specialist centres in the UK to regularly perform
this procedure. This is one of the more difficult interventions and better results will be achieved with
experienced veterinary cardiologists.
The success rate varies in relation to the pathology of the stenosis, ie. commissural fusion, dysplasia or
hypoplasia. However as a guideline in our experience >85% of cases will show a significant clinical
improvement with a 40 - 60% drop in the pressure gradient through the stenosis. The procedure is not
without risk and a small number of patients (approx. 5 - 7%) do not survive anaesthesia and surgery.
Subvalvular stenosis, such as seen in Bulldogs, does not respond as well.
Complications
 Aberrant coronary arteries can be present, particularly in Bulldogs, that would be a contraindication to
balloon dilatation (see later). Where this is suspected, coronary angiograms will also be performed at the
time of cardiac catheterisation (which will additionally require arterial catheterisation via the femoral
artery). It’s presence then precludes proceeding to balloon dilatation.
 A patent foramen ovale is not uncommon; if this is reverse shunting (ie. right to left) an echo-contrast
study should reveal this and the PCV also measured. A reverse shunting defect increases the anaesthetic
complications, although in severe cases this is a risk that has to be taken.
 Arrhythmias are not uncommon with severe pulmonic stenosis, in particular during the passing of
relatively large catheters through the heart during surgery. Pre-medication with beta blockers prior to
surgery, in our experience, appears to reduce the incidence of arrhythmias and anaesthetic complications.
Prior to surgery
It is preferable if dogs are medicated with beta blockers before referral and these should normally be
continued until a follow-up scan some months later.
 propranolol: 0.3 to 0.5mg/kg tid, or
 atenolol: 0.3 - 0.5mg/kg bid
The dog should be free of any infections especially pyodermas and skin parasites - if present these should be
treated before surgery can proceed.
Post surgery follow-up
 Sutures from the left jugular area (or right femoral area) are due for removal 8 to 10 days post surgery.
 Beta blockers should be continued (in many cases) until a follow-up scan is performed in approximately
6 months time.
References
Martin M W S., Godman M, Luis Fuentes V, Clutton R E, Haigh A L and Darke P G G. (1992) Assessment of balloon
pulmonary valvuloplasty in six dogs. Journal of Small Animal Practice 33, 443 - 449.
Stafford Johnson MJ & Martin M (2003) Balloon valvuloplasty in a cat with pulmonic stenosis. JVIM 17: 928-930
Stafford Johnson MJ & Martin MWS (2004). Results of balloon valvuloplasty in 40 dogs with pulmonic stenosis. JSAP,
45, 148-153
Stafford Johnson MJ & Martin MWS, Edwards D, French A & Henley W. (2004). Pulmonic stenosis in dogs: balloon
valvuloplasty improves clinical outcome. Journal of Veterinary Internal Medicine 18: 656-662
A review of pulmonic stenosis in small animals
~ Mike Martin
Pathology of pulmonic stenosis
The most common form of pulmonic stenosis in dogs and cats is valvular (supravalvular and
subvalvular stenosis are rare), which is the form for which balloon valvuloplasty is
appropriate.
The valvular form consists of three types:
1. Fusion of the cusp - thus they do not open fully
2. Valve dysplasia - abnormal morphology with thickening of the cusps
3. Narrowed annulus
In dogs and cats, these three types of stenosis occur in differing proportions and it is not
possible to identify clearly which type predominates by currently available diagnostics. Cusp
fusion is the type that responds best to ballooning and it is generally believed this type
predominates in the majority of dogs, which is also our experience.
Aberrant coronary arteries
In Bulldogs, there have been reports of aberrant coronary arteries in association with the
pulmonic stenosis - we have seen a few such Bulldogs, but also seen similar complications in
a Shih Tzu and a Staffie cross bred dog. In this condition the left coronary artery has not
formed and instead the left ventricle is fed by an aberrant branch of the right coronary artery.
However this aberrant branch encircles the subvalvular pulmonic stenosis, thus either
ballooning or traditional surgery (eg. patch graft technique) would result in rupture of the
coronary and death.
Pathophysiology
The stenosis restricts cardiac output, in proportion to severity. The right ventricular
myocardium must generate increased strength of contractility and chamber pressure to sustain
cardiac output through the stenosis resulting in an increase in blood flow velocity through the
stenosis. The right ventricular myocardium hypertrophies in proportion to the severity of the
stenosis. The hypertrophy is concentric causing a marked change in shape of the right
ventricle for which the tricuspid valve cannot compensate. The valve therefore can become
incompetent in many cases, leading to right atrial dilation and right sided congestive heart
failure. The ventricular hypertrophy can result in additional obstruction to blood flow
through the right ventricular outflow tract during systole (dynamic outflow tract obstruction).
History and Clinical Signs
 In the majority of cases a systolic murmur may be the only finding. This is usually heard
maximally over the left heart base and on the right side of the thorax and close to the
sternum.
 In moderately or severely affected dogs, there may be a history of exercise intolerance,
right sided congestive heart failure or syncope.
ECG
 There is a right ventricular enlargement patternin >90% of cases
 Ventricular tachydysrhythmias (ventricular premature complexes, ventricular tachycardia)
may be present in more severely affected cases.
Radiography
 Right ventricular enlargement is often seen (enlargement and rounding of the right heart
border on the lateral and DV views).
 On the DV view, a post-stenotic bulge in the pulmonary artery may be evident but its size
does not appear to correlate with severity.
 Right atrial enlargement may be present in cases with tricuspid regurgitation, often better
appreciated on the DV view.
Echocardiography
2-D echocardiography may visualise the valvular pulmonic stenosis as abnormally thickened
valves particularly when there is a severe lesion, but is often difficult to reliably and
accurately appreciate. The post-stenotic bulge is sometimes seen and the right ventricle is
often seen to be hypertrophied. Right atrial dilation may be evident.
Subvalvular stenosis with aberrant coronaries
It can sometimes be difficult to reliably distinguish subvalvular stenosis from valvular
stenosis. Subvalvular stenosis is the type that can be associated with aberrant coronaries. This
type of stenosis often appears to have a very narrowed annulus compared to the more usual
valvular stenosis. In addition, sometimes an abnormal coronary artery can be appreciated on
the right parasternal long axis view maximised to show the aorta. The aberrant coronary is
sometimes seen to course in an unusual direction from the sinus of valsalva (septal side). In
short axis view it can sometimes also be appreciated at the same level of the stenosis and
appears to course around it.
Doppler echocardiography is currently the definitive means of diagnosis. It will demonstrate
an increase in velocity through the stenosis (V2) compared to the velocity proximal to it
(V1), ie. there is a step up in velocity. The pressure gradient is proportional to the velocity,
which can be estimated from the modified Bernoulli equation [the pressure gradient = 4 (V2
- V1)2 ]. As a guide a pressure gradient (PG) <50mmHg is considered mild, a PG between 50
and 100mmHg is moderately severe and a PG >100mmHg is severe.
If there is dynamic outflow tract obstruction this is best seen on spectral Doppler as an
exponential increase in velocity. In this situation estimating the true PG becomes difficult as
V1 is not elevated and accurate measurement of this is difficult. If there is tricuspid valve
incompetence the PG between the right ventricle and atrium can also be estimated - this
provides a second method in which right ventricular pressure can be measured.
Treatment
Treatment is usually only required in moderately or severely affected cases and those
producing clinical signs.
 If there is congestive heart failure this is controlled with diuretics (eg. frusemide) and
ACE inhibitors.
 Primary treatment of ventricular dysrhythmias may be managed with anti-arrhythmics
such as beta blockers.
 Balloon valvuloplasty has been shown to be associated with good success in dogs
resulting in a long term imporvement in 85% of cases.
Indications for balloon valvuloplasty
1. The presence of clinical signs (symptoms)
2. Doppler derived trans-stenotic pressure gradient > 80mmHg
3. Dynamic right ventricular outflow tract obstruction (also warrants beta blockers)
4. Severe right ventricular hypertrophy with flattening of the ventricular septum
Prognosis
A prognosis can be offered based upon severity, assessed by Doppler echocardiography. A
dog with a mild stenosis (pressure gradient less than 40mmHg) will usually live a full and
normal life. Dogs with a more severe stenosis may develop clinical signs in the second half of
life, and those with a pressure gradient in excessive of 80mmHg usually do so within the first
few years of life. The presence of right sided congestive failure warrants a more guarded
prognosis.
REFERENCES
Bonagura, J.D. (1989) Congenital heart disease. In: Textbook of Veterinary Internal
Medicine, 3rd edn. Ed: S.J. Ettinger. W.S. Saunders Company, Philadelphia.
Martin, MWS, Godman, M, Luis Fuentes, V, et al (1992) Assessment of balloon pulmonary
valvuloplasty in six dogs. Journal of Small Animal Practice 33: 443.
Patterson, D.F. and others (1981). Hereditary dysplasia of the pulmonic valve in beagle dogs.
Am. J. Cardiology 47, 631.