I typically rescan at 6

I typically rescan at 6 months then at full grown 1 year and am nebulous on px til I see any changes in pulmonic pressure gradients. Typically noone considers intervening til pulmonic velocities start to get near 4.5- 5 m/sec and or if structural changes are developing RV hypertrophy.

 

Heres an unedited excerpt on the subject we wrote for the upcoming curbside guide that you can see in products:

http://sonopath.com/products

 

 

Pulmonic Stenosis

 

 

Pulmonic stenosis is a congenital anomaly which causes right ventricular outflow obstruction and is classified into valvular, subvalvular, and supravalvular forms.^1,2,3 Various reports describe pulmonic stenosis as one of the top three congenital heart defects in dogs with a frequency of 11-20% ^1,4,5,6,7 accompanied by subaortic stenosis (SAS) (25.5-41%) and patent ductus arteriosis (PDA) (11-27.7%).^7,8 English Bulldogs, Boxers, West Highland White and other terriers, Miniature Schnauzers, Chihuahuas, Samoyeds, Mastiffs, Boykin Spaniels and Beagles have a prominent breed predisposition for PS.^3,4,7,9 Occasionally German Shepherds, Spaniels and Retrievers can be affected.^{4, 6} It has been reported to be inherited in Beagles. Males are affected more often than females in English Bulldogs and Mastiffs.⁹  

            Signs of this disease vary with the degree of stenosis in the individual. In moderate to severe cases, exercise intolerance, failure to grow, syncope, ascites, and abnormal jugular pulsations all may occur.^{1,4, 6} The latter two symptoms usually occur after chronic right-sided failure has occurred in patients over one year of age.⁴ Patients afflicted with PS present a left heart base, harshly auscultable, crescendo-decrescendo murmur, which is quite similar to the heart murmur caused by SAS.^3,4 Dogs with atrial septal defect (ASD) and right sided volume overload, tetralogy of Fallot, left-to-right PDA can all present with left heart based murmurs. These conditions should be kept on the differential list until further diagnostic investigation can be performed.^2,3,10 The PS murmur may radiate to the right side.^3,11 SAS, and tetralogy of Fallot can also present similar right-sided extension of the murmur.¹⁰ Right-sided heart failure, diminished cardiac output, arrhythmias, and right-to-left shunting through a patent foramen ovale may also occur.^1,12 Pulses may be diminished in severe cases but typically are of normal quality. A secondary right apical tricuspid murmur may also be present as right-sided volume overload induces insufficiency of this valve.⁴

            Electrocardiogram readings in moderate to severe cases often reveal deep S waves in leads I, II, III, and aVF, with the occasional presence of premature ventricular complexes.^{2, 3, 9,} Cases with SAS, on the other hand, will often present with large R waves, which may aid in achieving a tentative diagnosis differentiating the two diseases.⁴ Radiographs may not reveal any visible abnormality especially in mild to moderate cases. Moderate to severe cases will reveal a prominent cranial waist on lateral views and a poststenotic bulge of the pulmonary artery at the one o’clock position on dorsal-ventral or ventral-dorsal views.^{3, 4, 11, 13} Right atrial enlargement and tracheal elevation at the cranial heart base may also be present. ⁴ Pulmonary output may be decreased resulting in smaller than normal pulmonary arteries. ³ Pulmonic and aortic stenoses result in concentric hypertrophy, which is less apparent on survey radiographs in early and mild cases than eccentric hypertrophy which is found in cases of volume overload (i.e.VSD or ASD). Hence, PS and SAS changes are frequently unappreciated radiographically. ¹³ Other factors affecting radiographic interpretation are thoracic conformation due to breed, body score, positioning, practitioner experience, and variations in respiratory and cardiac phases. ¹³

            An NT-proBNP level may be useful in young puppies with murmurs to screen for congenital anomalies. NT-proBNP levels have been demonstrated to be elevated in dogs with various congenital diseases. In a recent study by Saunders et al, the median value of NT-proBNP in dogs with PS was reported at 815 pmol/L whereas normal dogs had a median value of 333 pmol/L (JVIM 2009 Abstract). While the elevation of NT-proBNP is not specific for PS, an elevated level should  – like a heart murmur – prompt additional diagnostic tests specifically, echocardiography.

The definitive diagnosis of pulmonic stenosis is reached by echocardiogram with structural evaluation of the heart and Doppler quantification of pulmonic velocities and pressure gradients. ^{3, 4, 11, 14} Intracardiac catheterization can also measure these gradients yet are usually lower due to the necessary sedation involved in the procedure. ^9,11 Normal pulmonic velocity in non-sedated dogs is considered to be less than 1.7 m/s with right ventricular outflow tract (RVOT) pressures between 20-25 mmHg. ¹⁵ Right parasternal short axis and left short and long axis views avoid lung air interference thus visualizing the RVOT adequately. ¹⁴ Pulse wave (PW) Doppler is used to identify the location of the murmur, while continuous wave (CW) Doppler demonstrates the severity of the lesion by means of quantification of the velocity and pressure gradient across the defect. PW may reveal turbulence and localize an increase in outflow velocity at level of the stenosis that CW can later quantify. ¹⁴ Doppler echocardiography pressure gradients and velocity measurements of the pulmonic apparatus, measured between the right ventricle and main pulmonary artery, classifies the severity of stenosis as follows: mild 20-50 mmHg (2-3.5 m/sec); moderate 50-80 mmHg (3.5-4.5 m/sec); and severe > 80 mmHg (>4.5 m/sec). ¹⁹ Variable degrees of concurrent pulmonic insufficiency may also be detectable. ^{6, 7, 11, 14} Further investigation can evidence turbulence and dynamic obstruction in the RVOT as well as identify any secondary tricuspid insufficiency or shunting lesions such as ASD and VSD, which can occur simultaneously. ¹¹ Concentric hypertrophy of the right ventricular free wall and interventricular septum, flattened septum due to excessive RV pressure, prominent papillary muscle formation, variable narrowing of the RVOT, varying degrees of right atrial enlargement, and post-stenotic main pulmonary artery dilation are typical findings. ^{3, 11, 15} A “double chambered right ventricle” may be seen in cases of severe obstruction. This term is used to describe the right ventricle when it is structurally divided into a low-pressure region (infundibulum) and a high- pressure region (right ventricular apex) by a fibromuscular ridge. ¹¹

            The pathophysiology of PS lies within the right ventricular outflow obstruction from structural impedance proximal to the valve (subvalvular), at the valve (valvular), or distal to the valve in the pulmonary artery (postvalvular). Subvalvular stenosis is visualized as an ill-defined narrowing proximal to the pulmonic valve.  The subvalvular form may be accompanied by an anomalous left coronary artery with an enlarged right coronary counterpart in Boxers and English Bulldogs. ¹⁴

            Valvular stenosis is by far the most frequent form of PS ^{1, 4, 6, 7, 9, 14, 15} in which excessive thickening or fusion at the leaflet extremities may be present. ^{7, 14, 15} More than 80% of dogs with PS have some degree of valvular dysplasia.^{16, 18} Thickened valvular conformation causes the valve to be less mobile, while thin fused valves tend to be excessively mobile bowing toward the pulmonary artery during systole.^{14, 15} In cases of annulus hypoplasia there is no fusion of the cusps and minimal valvular mobility.¹⁵ Histologically, spongiosa thickening of the valve with overproduction of valve collagen elements has been demonstrated. ¹¹ Failure of embryonic valve primordial conversion has been postulated as the cause of abundant tissue formation. ¹¹

            Further classification of valvular stenosis has been suggested by Bussadori et al. ⁹ by dividing valvular stenosis into types A and B. Type A PS presents minimal leaflet thickening, fused commisures with systolic doming, aortic/pulmonary annulus ratio of less than 1.2, and poststenotic dilation of the pulmonary trunk without subvalvular obstruction. This seems to be the prominent type in larger breeds such as German Shepherds. Type B PS morphologically presents marked valvular thickening, annulus hypoplasia, an aortic/pulmonary annulus ratio greater than 1.2, and severe infundibular hypertrophy.

             Regardless of the type of obstruction, evolution of the pathology begins with increased resistance to systolic ejection resulting in concentric right ventricular hypertrophy. ¹¹ Dynamic obstruction during systole can also occur secondarily to right ventricular concentric hypertrophy and papillary prominence due to pressure overload ^{1, 2, 6, 7, 11, 15}, particularly during exercise or stress. ¹¹ Severe cases may present with right ventricular hypertrophy that supersedes the left ventricular thickness. ⁷ In moderate to severe cases, concentric left ventricular hypertrophy may occur due to poor right ventricular output and resultant poor left sided volume. ¹⁵ Rarely, severe hypertrophy of the ventricular septum can secondarily narrow the left ventricular outflow tract and cause dynamic left ventricular outflow tract (LVOT) obstruction similar to that found in hypertrophic cardiomyopathy. ¹¹ Configuration changes of the RV lead to tricuspid regurgitation, right atrial dilation, increased right-sided diastolic pressures and eventual right-sided heart failure in moderate to severe cases. Flattening of the ventricular septum may occur as right-sided pressures approach that of the left side. ⁷ If right ventricular pressures exceed those of the left ventricle, paradoxical septal motion may be seen.¹⁵ Pulmonary artery dilation may also be present.^{6, 15} Impeded coronary artery flow may cause sudden death, especially in English Bulldogs in which anomaly of the left main coronary artery is prominent. This coronary anomaly is a frequent obstacle in ballooning procedures in this breed, thus impeding success percentages from reaching 100% in many studies.^{7, 17}An aberrant coronary artery may be found as a slight bulge at the aortic root during an angiogram in English Bulldogs and Boxers, and is known as the “aortic root sign” in human cardiology. ^{16, 17} This aberrant left coronary arises from the right coronary ostia and courses across the right ventricular outflow tract where it can be injured during BV or patch graft procedures.¹⁶ In cases of subvalvular stenosis a dilated right coronary artery and anomalous left coronary artery may be seen sonographically in some cases. ¹⁴

            Treatment of pulmonic stenosis is typically performed in moderate to severe cases (pressure gradient greater than 60 mmHg) either through balloon valvuloplasty (BV) ^{3, 9, 11}, surgical patch graft technique, or surgical right ventricle/pulmonary artery (RV/PA) bypass. ^{2, 3, 11}However, full grown patients with Doppler gradients less than 50 mmHg according to Fossum², or less than 80 mmHg according to Sisson et al.¹¹, without other complicating lesions (ASD, VSD, tricuspid insufficiency) can lead relatively normal lives and do not necessarily require treatment. Recently, Rausch and Atkins ¹ suggest that BV should be considered in pets over 2 kg body weight, pressure gradient greater than 80 mmHg, marked right ventricular hypertrophy, or clinical signs consistent with PS. The goal in treatable cases is to reduce the systolic pressure gradient to a mild range (less than 60-80 mmHg ^{5, 9, 11}) prior to the development of heart failure symptoms. ¹¹ Balloon valvuloplasty should as well be considered in patients with pressure gradients greater than 60 mm Hg and concomitant tricuspid dysplasia or significant right ventricular concentric hypertrophy. Beta-blockers may prevent sudden death by limiting excessive tachycardia if BV is not an option. ⁴ BV is most successful when the pulmonary annulus is adequately developed with thin, fused valves. Results vary with complicating lesions such as annulus hypoplasia, RVOT obstruction, concurrent arrhythmia, double chambered right ventricle, and anomalous right coronary artery. ¹¹ There is difficulty in these cases regarding the passage of the balloon catheter with a higher risk of complications. In patients afflicted by such complicating lesions, and in those that have received BV and have recurrent stenosis, patch graft or bypass surgery is available. ^{2, 11, 16}

            The patch graft technique requires placement of a Gore-Tex® material or pericardial patch into a partial thickness, right ventriculotomy that extends into the pulmonary artery under inflow occlusion or cardiopulmonary bypass and mild hypothermia through a left fifth intercostal thoracotomy.^{2, 18} Redundant valvular tissue can be removed at this time. Pulmonic insufficiency results from this procedure but is tolerated as long as tricuspid integrity is present and pulmonary hypertension is not a factor. ² Operative mortality is approximately 20-25% in the hands of an experienced surgeon.^{2, 16} Patients with an aberrant coronary artery contributing to their pulmonic stenosis are not considered candidates for balloon valvuloplasty or patch graft techniques and require surgical cardiopulmonary bypass via a RV/PA conduit placement to circumvent the stenosis.^{11, 16, 18} This carries a lower risk than a simple patch graft procedure due to more direct graft placement by use of the bypass. ¹⁶ The majority of PS patients, however, are responsive to BV and, therefore, this is the usual treatment of choice. ^{9, 11}

            The BV procedure was first developed in dogs at Johns Hopkins University prior to utilization in humans. An English Bulldog with pulmonic stenosis was first successfully treated by BV at Johns Hopkins in 1980 after transfer from the University of Pennsylvania. ¹⁷ BV is performed by insertions of a series of catheterizations of the right heart via the femoral or jugular veins. Direct arterial blood pressure and electrocardiogram monitoring is essential during the procedure. An introducing needle is passed percutaneously into the vein followed by an exchange wire, which is passed through the needle. After the needle is removed, a wide introducer is placed over the wire. The wire is then, in turn, removed. This catheter is used as an exchange port for the remainder of the procedure. With the aid of right ventricular fluoroscopy, an angiographic catheter is passed through the port catheter and guided into the right ventricle. Radiopaque contrast medium is injected into the right ventricle to enhance visualization of the right ventricular chamber, right ventricular outflow tract, pulmonary artery, and stenotic lesion. The angiographic catheter is removed and replaced with a end-hole wedge pressure catheter to measure intravascular pressures. Pressures are measured in the right ventricle and pulmonary artery. This pressure catheter is replaced with a compressed balloon tipped catheter. The width and length of this catheter is determined by the patient’s PA width and degree of stenosis. The balloon is guided to the stenotic area over a rigid exchange wire followed by numerous short inflations. RV and PA pressure gradients are again measured intraoperatively to assess the necessity for repeated inflations. At the completion of the procedure the catheters are removed and a pressure wrap is placed across the vein. ¹

            Follow up echocardiogram measurements of the pulmonic pressure gradients and velocities are typically performed the following day, at 3-6 months, and at one year. Success of the procedure is defined as a 50% drop in the RV/PA systolic pressure gradient with or without a drop of pulmonic pressure gradient below 75-80 mmHg, as well as an absence of clinical signs after one year.^{1, 4, 9} The study by Bussadori et al ⁹ revealed 100% success rate in type A stenosis cases and a 50% success rate in type B cases. The diminished success in the type B cases was due to the difficulty with balloon passage through the hypertrophied right ventricular, severe ventricular arrhythmias (2 cases), cardiac arrest due to possible coronary anomaly (2 cases), and recurrent stenosis within one year (50% of survivors). It was found that annulus hypoplasia, leaflet dysplasia, and infundibular stenosis typical of type B patients were the primary factors in restenosis post BV. These difficulties have also been confronted by other cardiologists primarily when treating brachycephalic breeds. Gordon et al. ⁵ revealed an overall short-term success rate of PS cases (type A/B classification not utilized) of 87% in 45 patients evaluated with a mean percent gradient reduction of 58%. Long-term evaluation demonstrated 78% successful gradient reduction in 23 available patients, while 71% of symptomatic patients became and remained asymptomatic. ⁵ Mortality during the procedure due to myocardial rupture, vascular perforation, hemorrhage, or arrhythmia can occur in approximately 5% of cases overall.^{1, 5, 9}

            Therefore, balloon valvuloplasty is minimally invasive, does not require thoracotomy and patients have a short recovery time. This is the ideal procedure for type A stenosis and for mild/moderate type B cases.  More invasive patch graft and bypass procedures are considered to be better definitive, long-term solutions in moderate to severe type B obstructive cases or in cases of coronary artery anomaly. Patients should, therefore, have angiographic exams to evaluate coronary anomaly prior to procedure selection as well as further visualize the degree of stenotic flow.

 

Johanna Frank DVM, DVSc, DACVIM (Internal Medicine)

Eric Lindquist DMV, Dip ABVP (Canine & Feline Practice), Cert./Pres. IVU

 

¹ Rausch W, Atkins C. Treatment of canine pulmonic stenosis with percutaneous balloon valvuloplasty. Vet Med, 2002: Nov; 97(11): 819-21.

² Fossum T. Surgery of the cardiovascular system. Small Animal Surgery; Second ed., St.Louis: Mosby 2002; 690-2.

³ Goodwin J, Tilley L. Congenital heart disease. Manual of Canine and Feline Cardiology; Third Ed.; Philadelphia: W.B. Saunders Co, 2001; 282-5.

⁴ Layer C, Abbott J. Pulmonic stenosis. Small Animal Cardiology Secrets. Philadelphia: Hanley and Belfus, Inc, 2000; 306-09.

⁵ Gordon S, Miller M, Baig S. A retrospective review of balloon valvuloplasty in 50 dogs with pulmonic stenosis. Effect of valve morphology and annular size on initial and 1-year outcome. In Proceedings of the 20^th American College of Veterinary internal Medicine Forum, Dallas, TX, 2002: 775.

⁶ Tidholm A. Retrospective study of congenital heart defects in 151 dogs. J of Small Animal Practice 1997; 38(3): 94-98.

⁷ Oyama M, Sisson D. Evaluation of canine congenital heart disease using an echocardiogram algorithm. J Am Anim Hosp Assoc 2001; Nov-Dec; 37(6): 519-35.

⁸ Schneider M, Schneider I, Neu H. Feasibility of sonography in the diagnosis of congenital heart disease in dogs. Tierarztl Prax Ausg K Klientiere Heimtiere 1998; May; 26(3): 170-9.

⁹ Bussadori C, DeMadron E, Santilli R, Borgarelli M. Balloon valvuloplasty in 30 dogs with pulmonic stenosis: Effect of valvular morphology and annular size on initial and 1-year outcome. J Vet Intern Med 2001; 15:553-558.

¹⁰ Pion P. Cardiology, Making the diagnosis. In Proceedings of the Atlantic Coast Veterinary Conference, Atlantic City, New Jersey, 2001; 597-607.

¹¹ Sisson D, Thomas W, Bonagura J, Ettinger S. Ventricular outflow obstructions. Textbook of Veterinary Internal Medicine; Fifth ed. W.B. Saunders Co, Philadelphia, 2000: 759-67.

¹² Bonagura J, Lehmkul, L. Congenital heart disease. Textbook of Canine and Feline Cardiology: Principles and Clinical Practice. W.B. Saunders Co, Philadelphia, 1999: 471-535.

¹³ Lamb C, Boswood A, Volkman A, Connolly D. Assessment of survey radiography as a method of diagnosis of congenital cardiac disease in dogs. J Small Animal Practice 2001; Nov; 42(11): 541-5.

¹⁴ Kienle R, Thomas W, Nyland T, Mattoon J. Pulmonic stenosis; anatomy and physiology. Small Animal Diagnostic Ultrasound; Second ed. Philadelphia, W.B. Saunders Co, 2002; 382-4.

¹⁵ Boone J. Pulmonic stenosis. Manual of Veterinary Echocardiography. Baltimore, Williams & Wilkins Co, 1998; 397-404.

¹⁶ Orton E, Bonagura J. Current indications for cardiac surgery. Current Veterinary Therapy XIII. Philadelphia, W. B. Saunders Co, 2000; 745-6.

¹⁷ Buchannan J, Anderson J, White R. The first balloon angioplasty: a historical note. J Vet Intern Med 2002; Jan-Feb; 16(1): 116-7.

¹⁸ Fossum T. Cardiovascular surgery: Where are we, and where are we going. In Proceedings of the 20^th American College of Veterinary internal Medicine Forum, Dallas, TX, 2002: 82-4.

¹⁹: C. Bussadori, C. Amberger, G. Le Bobinnec, C.W. Lombard Guidelines for the echocardiographic studies of suspected subaortic and pulmonic stenosis.