Closed Transventricular Dilation of Discrete Subvalvular Aortic Stenosis in Dogs

Discrete subvalvular aortic stenosis with peak systolic pressure gradients of more than 60 mm Hg was treated by closed transventricular dilation in six young dogs. Peak systolic pressure gradients were measured by direct catheterization before surgery, immediately after dilation, and 3 months after surgery. Maximum instantaneous pressure gradients were measured by continuous wave Doppler echocardiography before surgery and 6 weeks to 9 months after surgery. All dogs survived the procedure, and two dogs were clinically normal after 9 and 14 months. Two dogs died at week 6 and month 7. One dog was receiving medication for pulmonary edema 15 months after surgery. One dog underwent open resection of the subvalvular ring at month 3, and was clinically normal 6 months after the second procedure. Complications included intraoperative ventricular fibrillation in one dog, and mild postoperative aortic insufficiency in one dog. Closed transventricular dilation resulted in an immediate 83% decrease in the peak systolic pressure gradient from a preoperative mean of 97 +/- 22 mm Hg to a mean of 14 +/- 15 mm Hg. However, systolic pressure gradients measured by direct catheterization at month 3 (77 +/- 26 mm Hg), and by Doppler echocardiography at week 6 to month 9 (85 +/- 32 mm Hg) were not significantly different from preoperative values, which suggested recurrence of the aortic stenosis. Closed transventricular dilation should not be considered a definitive treatment for discrete subvalvular aortic stenosis in dogs, but may be useful in young dogs with critical aortic stenosis as a bridge to more definitive surgery.     

Survival times in dogs with severe subvalvular aortic stenosis treated with balloon valvuloplasty or atenolol

OBJECTIVE: To determine survival times in dogs with severe subvalvular aortic stenosis (SAS) treated by means of balloon valvuloplasty or with atenolol, a beta-adrenoceptor blocking drug. DESIGN: Prospective study. ANIMALS: 38 dogs < 24 months old with severe SAS (peak systolic pressure gradient > or = 80 mm Hg). PROCEDURE: 10 dogs underwent balloon valvuloplasty and were reexamined 6 weeks later to determine the feasibility of the procedure. The remaining 28 dogs were randomly assigned to undergo balloon valvuloplasty (n = 15) or to be treated with atenolol long term (13) and were reexamined annually for 9 years or until the time of death. RESULTS: For the first 10 dogs, mean pressure gradient 6 weeks after balloon valvuloplasty (mean +/- SD, 119 +/- 32.6 mm Hg) was significantly decreased, compared with mean baseline pressure gradient (167 +/- 40.1 mm Hg). Median survival time for dogs that underwent balloon valvuloplasty (55 months) was not significantly different from median survival time for dogs treated with atenolol (56 months). CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that balloon valvuloplasty can result in a significant decrease in the peak systolic pressure gradient in dogs with severe SAS, at least for the short term. No clear benefit in survival times was seen for dogs that underwent balloon valvuloplasty versus dogs that were treated with atenolol.     

The relationship of resting S-T segment depression to the severity of subvalvular aortic stenosis and the presence of ventricular premature complexes in the dog

Electrocardiograms (ECG) from 35 dogs with subvalvular aortic stenosis (SAS) with a left ventricular outflow tract pressure gradient (PG) of > or =50 mm Hg were retrospectively evaluated for S-T segment depression (STD, > or =0.2 mV in lead II). Pressure gradient, age, heart rate (HR), and number of ventricular premature complexes (VPCs) on a 24-hour ambulatory ECG for dogs with STD were not significantly different from those for dogs without STD. The S-T segment deviation did not correlate significantly with PG, age, HR, or VPCs. The significance of STD in the dog with SAS remains uncertain. Long-term prospective studies are needed to fully understand this observation.     

An experimental study of apico-aortic valved conduit (AAVC) for surgical treatment of aortic stenosis in dogs

A new valved conduit was developed using a canine aortic valve. The bioprosthetic valve was fixed with glutaraldehyde and epoxy compound (Denacol-EX313/810). A vascular graft composed of ultra-fine polyester fiber (10 mm in diameter, 200 mm in length) was used. Four dogs underwent apico-aortic valved conduit (AAVC) implantation and aortic banding (bypass group, BG), while another 4 dogs underwent aortic banding without AAVC implantation (control group, CG). Cardiac catheterization and angiocardiography were performed for assessment of hemodynamics 2 weeks and 6 months after surgery. Left ventricular systolic pressure, left ventricular end-diastolic pressure and the left ventricular-aortic pressure gradient differed significantly (P<0.01) between the BG and CG dogs. Left ventricular angiocardiography showed patency of the valved conduit in all the BG dogs. Echocardiography was performed before and 2, 4 and 6 months after surgery, and showed that while pressure overload caused concentric myocardial hypertrophy in the CG dogs, the left ventricle dilated eccentrically in the BG dogs. Furthermore, relief of left ventricular pressure overload by AAVC was maintained.     

Influence of open surgical correction on intermediate-term outcome in dogs with subvalvular aortic stenosis: 44 cases (1991-1998)

OBJECTIVE: To compare outcome and intermediate-term survival for dogs undergoing open surgical correction of subvalvular aortic stenosis (SAS) with those for dogs with SAS that did not undergo surgery. DESIGN: Retrospective study. ANIMALS: 44 dogs with congenital SAS. PROCEDURE: Maximum instantaneous systolic pressure gradients were determined by use of Doppler echocardiography. Cardiopulmonary bypass and open surgical correction of SAS (membranectomy with or without septal myectomy) was performed in 22 dogs, whereas 22 dogs did not undergo surgical correction. Cumulative survival was compared between surgical and nonsurgical groups, using Kaplan-Meier nonparametric analysis and a Mantel-Cox log-rank test. RESULTS: Initial systolic pressure gradients were not significantly different for dogs undergoing surgery (128 +/- 55 mm Hg), compared with those that did not undergo surgery (117 +/- 57 mm Hg). Systolic pressure gradients were significantly decreased after surgery in dogs that underwent surgery (54 +/- 27 mm Hg). Cumulative survival was not significantly different between dogs in the surgical and nonsurgical groups. Censoring surgery-related mortality in the analysis still did not reveal a significant difference in cumulative survival between the surgical and nonsurgical groups. CONCLUSIONS AND CLINICAL RELEVANCE: Despite reductions in the systolic pressure gradient and possible associated improvement in exercise tolerance, a palliative benefit on survival was not documented in dogs undergoing surgery for SAS.     

Surgical correction of subvalvular aortic stenosis using cardiopulmonary bypass in a dog

A three-month-old male Golden Retriever had symptoms including exercise intolerance, dyspnea and syncope and was diagnosed with subvalvular aortic stenosis. Cardiac catheterization revealed a left ventricular-aortic systolic pressure gradient of 90 mm Hg. Surgical correction of the condition was achieved using cardiopulmonary bypass. The subvalvular fibrous lesion was resected through an aortotomy. The stenosis was dilated from 8.5 mm to 12.0 mm in diameter. Postoperatively the dog was asymptomatic. Seven months after surgery, the pressure gradient decreased to 44 mm Hg. However, after another three months, the dog died suddenly without any premonitory signs. Postmortem examination revealed that pathologic changes caused by increased left ventricular pressure overload were not severe.     

Echocardiographic estimation of systemic systolic blood pressure in dogs with mild mitral regurgitation

BACKGROUND: Systemic hypertension is likely underdiagnosed in veterinary medicine because systemic blood pressure is rarely measured. Systemic blood pressure can theoretically be estimated by echocardiography. According to the modified Bernoulli equation (PG = 4v(2)), mitral regurgitation (MR) velocity should approximate systolic left ventricular pressure (sLVP), and therefore systolic systemic blood pressure (sSBP) in the presence of a normal left atrial pressure (LAP) and the absence of aortic stenosis. The aim of this study was to evaluate the use of echocardiography to estimate sSBP by means of the Bernoulli equation. HYPOTHESIS: Systemic blood pressure can be estimated by echocardiography. ANIMAL: Seventeen dogs with mild MR. No dogs had aortic or subaortic stenosis, and all had MR with a clear continuous-wave Doppler signal and a left atrial to aorta ratio of < or = 1.6. METHODS: Five simultaneous, blinded continuous-wave measurements of maximum MR velocity (Vmax) and indirect sSBP measurements (by Park's Doppler) were obtained for each dog. Pressure gradient was calculated from Vmax by means of the Bernoulli equation, averaged, and added to an assumed LAP of 8 mm Hg to calculate sLVP. RESULTS: Calculated sLVP was significantly correlated with indirectly measured sSBP within a range of 121 to 218 mm Hg (P = .0002, r = .78). Mean +/- SD bias was 0.1 +/- 15.3 mm Hg with limits of agreement of -29.9 to 30.1 mm Hg. CONCLUSION: Despite the significant correlation, the wide limits of agreement between the methods hinder the clinical utility of echocardiographic estimation of blood pressure.     

Treatment of Congenital Pulmonic Stenosis in Two Dogs by Balloon Valvuloplasty

Balloon valvuloplasty was performed on two dogs with pulmonic valve stenosis. Immediately following balloon valvuloplasty, peak right ventricular systolic pressure declined from 92 to 44 mm Hg in the first dog and from 108 to 46 mm Hg in the second dog. The peak systolic pressure gradient across the pulmonic valve declined from 60 to 12 mm Hg in the first dog and from 84 to 22 mm Hg in the second dog. Hemodynamic improvement was sustained in both dogs at the time of recatheterization 3 months later. Both dogs tolerated the procedure well and there were no serious complications. It was concluded that balloon valvuloplasty offers an alternative to surgery for the treatment of valvular pulmonic stenosis in dogs. The exact indications for and limitations of balloon valvuloplasty must await the results of additional and more long-term studies.     

Surgical correction of subaortic stenosis via right ventriculotomy and septal resection in a dog

After 2 years of medical management with a beta-adrenoreceptor blocking agent, a 30-month-old castrated male Golden Retriever with subaortic stenosis was treated surgically because of progression of its condition. In an attempt to achieve complete relief of the left ventricular outflow obstruction, a modified Konno procedure consisting of right ventriculotomy and septal myectomy from the infundibular portion of the right ventricle was performed; this combination of procedures allowed wide resection of the septal portion of the left ventricular outflow obstruction. Two years after surgery, the mass of the dog's left ventricle had decreased and the peak calculated pressure gradient across the aortic valve had decreased to 40 mm Hg, compared with a preoperative value of 240 mm Hg; at that evaluation, the dog had gained weight and was able to play normally. It is suggested that use of this modified approach to the outflow tract may have a positive effect on long-term survival time in dogs with subaortic stenosis.     

Echocardiographic and right-sidedcardiac pressure comparison of the mule and horse

There are few physiologic studies that substantiate thepopular belief that mules are superior to horses as working animals. The purpose of this study was to compare selected cardiac dimensions and right-sided cardiac pressures of mules and horses. Using 2-D real time and M-mode echocardiography and transjugular cardiac catheterization resting cardiac dimensions and right-sided pressures were recorded from 10 adult mules and 10 adult horses. The mules and horses were similar in size and physical condition, and both groups had served equally as pack animals. The end diastolic left ventricular lumen diameter, interventricular septal thickness, left ventricular free wall thickness, and aortic root diameter measured (mean ± SD) 9.51 ±0.92 cm, 2.63±0.34 cm, 2.28±0.31 cm, 7.9±0.57 cm, respectively, in mules, and 9.83±0.87 cm, 2.83±0.29 cm, 2.39±0.33 cm, 7.9±0.36 cm, respectively, in horses. The end systolic left ventricular lumen diameter measured 5.79 cm in mules and 5.94±0.99 cm in horses, yielding left ventricular luminal shortening fractions of 39.2±7.15% in mules and 39.7±6.91% in horses. Right atrial mean pressure was 5.3±2.3 mm of Hg in mules and 5.8±1.2 mm Hg in horses. Right ventricular peak systolic pressure was 47.9±4.9 mm Hg in mules and 47.7±3.5 mm Hg in horses. Pulmonary artery mean pressure was 27.3±3.2 mm Hg in mules and 28.1±3.6 mm Hg in horses. No significant differences were detected between mules and horses for the resting cardiac dimensions examined or right-sided pressures measured.     

Echocardiographic parameters in 14 healthy English Bull Terriers

OBJECTIVE: To determine the range of various cardiac parameters using echocardiography in apparently normal, healthy English Bull Terriers. DESIGN: Fourteen English Bull Terriers were selected for study. Cardiac auscultation of the parents of these dogs was normal. Echocardiographic examination of one parent of each animal showed: no mitral or aortic valve abnormalities; no myocardial lesions; no two dimensional evidence of fixed or dynamic left ventricular outflow tract obstruction; and no systolic aortic or left ventricular outflow tract turbulence on colour flow Doppler examination. The 14 selected dogs did not have arrhythmias or murmurs, and on echocardiographic examination had similar findings to their parents. Systolic blood pressure was measured in all dogs and they had no clinical evidence of Bull Terrier polycystic kidney disease or Bull Terrier hereditary nephritis. PROCEDURE: All dogs were auscultated and subjected to a sequential global echocardiographic assessment of the heart, including two dimensional long and short axis, and colour flow Doppler interrogation of the mitral and aortic valves. Dimensional measurements, including those from the left atrium, aortic annulus and left ventricle, were taken from a right parasternal window, and derived values such as fractional shortening, stroke volume and left atrial to aortic annulus ratio were calculated. Peak systolic aortic velocity was measured from the left parasternal window using two dimensional-guided pulsed wave Doppler with angle correction. Systolic blood pressure was measured using a Doppler monitor. The absence of Bull Terrier polycystic kidney disease was determined using renal ultrasonography, and of Bull Terrier hereditary nephritis using urinary protein to creatinine ratio. RESULTS: These 14 dogs had greater left ventricular wall thickness and smaller aortic root diameters than those reported as normal for other breeds of comparable body size. Left atrial dimensions were also larger, however this may have been due to the "maximising" method of measurement. These apparently normal English Bull Terriers also had higher aortic velocities than those reported for other breeds, possibly due to a smaller aortic root diameter or other anatomic substrate of the left ventricular outflow tract, lower systemic vascular resistance, or breed-specific "normal" left ventricular hypertrophy. While these dogs were selected to be as close to normal as possible, the breed may have a particular anatomy that produces abnormal left ventricular echocardiographic parameters. CONCLUSION: These echocardiographic parameters may be used to diagnose left ventricular outflow tract obstruction and left ventricular hypertrophy, and inaccurate diagnoses may result if breed-specific values are not used.     

Balloon valvuloplasty of congenital mitral stenosis

Radiographic, echocardiographic, fluoroscopic, and angiographic images from 2 dogs with severe congenital mitral valve stenosis that underwent cardiac catheterization and balloon valvuloplasty are presented. Both dogs displayed systolic doming of the mitral valve leaflets, increased diastolic pressure gradient across the left atrium and ventricle, and decreased mitral inflow E to F slope. Balloon valvuloplasty was performed on both dogs using atrial transeptal puncture.     

Cutting balloon and high-pressure balloon dilation for palliative treatment of congenital double-chambered right ventricle and primary infundibular stenosis in a Golden retriever dog

Combined cutting balloon and high-pressure balloon dilation was performed in a dog with a double-chambered right ventricle and severe infundibular stenosis of the right ventricular outflow tract. The peak systolic pressure gradient across the stenosis decreased by 65% after dilation (from 187 mmHg before to 66 mmHg after) affirming the intervention as successful. However, early re-stenosis occurred within 3 months leading to exercise intolerance, exercise-induced syncope, and right-sided congestive heart failure. Cutting balloon followed by high-pressure balloon dilation provided temporary but not long-term relief of right ventricular obstruction in this dog.     

Mitral valve dysplasia in a cat causing reversible left ventricular hypertrophy and dynamic outflow tract obstruction

A 6-month-old male European shorthair cat was examined because of a 2/6 systolic left apical cardiac murmur. Echocardiography revealed severe concentric left ventricular hypertrophy and severe dynamic left ventricular outflow tract obstruction (pressure gradient of 85 mmHg) caused by systolic anterior motion (SAM) of the septal mitral valve leaflet. After 2 months of oral treatment with atenolol, the cardiac murmur had disappeared. Echocardiography showed only slight thickening of the interventricular septum and resolution of the pressure gradient. The cat was discharged and its owner was advised to continue atenolol lifelong. Echocardiographic findings of a combination of left ventricular concentric hypertrophy and dynamic left ventricular outflow tract obstruction can be caused by hypertrophic obstructive cardiomyopathy (HOCM) or mitral valve dysplasia in the absence of hypertension and fixed aortic stenosis. In the case of HOCM, left ventricular hypertrophy is the primary process. In the case of mitral valve dysplasia, systolic anterior motion of the mitral valve is the primary problem, which leads to dynamic left ventricular outflow tract obstruction and ultimately to left ventricular concentric hypertrophy, due to pressure overload. If the left ventricular outflow tract obstruction is reduced with an oral beta-receptor blocker the secondary left ventricular hypertrophy may resolve. This would not happen in the case of hypertrophic obstructive cardiomyopathy. To the best of the authors' knowledge, this is the first documented case of severe dynamic left ventricular outflow tract obstruction and severe left ventricular hypertrophy in a cat successfully treated with oral atenolol.     

The Natural Clinical History of Canine Congenital Subaortic Stenosis

The demographics and natural clinical history of canine congenital subaortic stenosis (SAS) were evaluated by retrospective analysis of 195 confirmed cases (1967 to 1991), 96 of which were untreated and available for follow-up evaluation. Of these, 58 dogs had left ventricular outflow systolic pressure gradients available for assessment of severity. All 195 dogs were used for demographic analysis. Breeds found to be at increased relative risk included the Newfoundland (odds ratio, 88.1; P < .001), Rottweiler (odds ratio, 19.3; P < .001), Boxer (odds ratio, 8.6; P < .001), and Golden Retriever (odds ratio, 5.5; P < .001). Dogs with mild gradients (16 to 35 mm Hg) and those that developed infective endocarditis or left heart failure were diagnosed at older ages than those with moderate (36 to 80 mm Hg) and severe (>80 mm Hg) gradients. Of 96 untreated dogs, 32 (33.3%) had signs of illness varying from fatigue to syncope; 11 dogs (11.3%) developed infective endocarditis or left heart failure. Exercise intolerance or fatigue was reported in 22 dogs, syncope in 11 dogs, and respiratory signs (cough, dyspnea, tachypnea) in 9 dogs. In addition, 21 dogs (21.9%) died suddenly. Sudden death occurred mainly in the first 3 years of life, primarily but not exclusively, in dogs with severe obstructions (gradient, > 80 mm Hg; odds ratio, 16.0; P < .001). Infective endocarditis (6.3%) and left heart failure (7.3%) tended to occur later in life and in dogs with mild to moderate obstructions. Left heart failure was uncommon in the absence of additional congenital defects or infective endocarditis. Dogs with mild obstructions lived longer than other groups and tended to remain asymptomatic. The majority of dogs with severe obstructions died before 3 years of age and had a high prevalence (8 of 15) of sudden death. The prognosis for long-term survival in dogs with untreated mild or moderate SAS is favorable (median survival, 30.5 and 51.1 months, respectively), while the prognosis for dogs with severe SAS is very poor (median survival, 18.9 months).     

Heterotopic implantation of a porcine bioprosthetic heart valve in a dog with aortic valve endocarditis

CASE DESCRIPTION: A 5-year-old male German Shepherd Dog was evaluated because of a 5-month history of progressive lethargy, weight loss, and heart failure. CLINICAL FINDINGS: On physical examination, bounding femoral pulses and systolic and diastolic murmurs were detected. Echocardiography revealed severe aortic valve insufficiency (AVI) and a large vegetative lesion on the aortic valve consistent with aortic valve endocarditis. The AVI velocity profile half-time was 130 milliseconds; the calculated peak systolic pressure gradient across the aortic valve was 64 mm Hg. Left ventricular diameter during diastole was 63.6 mm (predicted range, 40.2 to 42 mm) and during systole was 42.9 mm (predicted range, 25.4 to 27 mm). Systolic, diastolic, and mean arterial blood pressures were 120, 43, and 65 mm Hg, respectively. TREATMENT AND OUTCOME: To palliate severe AVI, the descending aorta was occluded (duration, 16.75 minutes) and heterotopic implantation of a porcine bioprosthetic heart valve in that vessel was performed. After surgery, systolic, diastolic, and mean arterial blood pressures were 115, 30, and 61 mm Hg, respectively, in the forelimb and 110, 62, and 77 mm Hg, respectively, in the hind limb. Within 6 months, the AVI velocity profile half-time had increased to 210 milliseconds, indicating diminished severity of AVI. After 24 months, the dog was able to engage in vigorous exercise; no pulmonary edema had developed since surgery. CLINICAL RELEVANCE: Heterotopic bioprosthetic heart valve implantation into the descending aorta during brief aortic occlusion appears feasible in dogs and may provide substantial palliation for dogs with severe AVI.     

An Open Patch-Graft Technique for Correction of Pulmonic Stenosis in the Dog

An open patch-graft technique for correction of pulmonic stenosis was performed in four dogs. A synthetic patch-graft was presutured to a partial-thickness incision in the right ventricular outflow tract and to the pulmonary artery along its cranial border. The pulmonary artery and right ventricle were incised during venous inflow occlusion, and dysplastic pulmonic valve leaflets were excised. The arteriotomy was closed by suturing the caudal margin of the incision to the patch-graft. The entire procedure was performed during mild hypothermia (30 degrees - 32 degrees C). The mean circulatory arrest time was 5.5 +/- 0.2 minutes. The mean systolic pressure gradient across the pulmonic valve before surgery was 121 +/- 29 mm Hg; after surgery it was 9 +/- 2 mm Hg.     

Diagnosis of pulmonary hypertension

Pulmonary hypertension may complicate a variety of congenital or acquired cardiac and pulmonary conditions. This vascular disorder results from conditions that lead to a chronic increase in left atrial pressure, increased pulmonary blood flow, or increased pulmonary vascular resistance. Definitive diagnosis requires cardiac catheterization and detection of systolic and mean pulmonary artery pressures exceeding 30 and 20 mm Hg, respectively. Clinical signs and historical complaints reflect underlying cardiac or pulmonary conditions, although syncope may be a predominant finding. Radiographic changes are nonspecific; however, right ventricular enlargement and enlarged pulmonary arteries should increase suspicion for the disorder. Estimates of pulmonary arterial pressure may be obtained through Doppler echocardiography. This requires detection of a high-velocity regurgitant jet across the tricuspid or pulmonic valve. Further investigation is required to determine how pulmonary hypertension impacts therapy and prognosis for dogs and cats with cardiac and pulmonary diseases.     

Techniques for isolation and performance of the perfused guinea pig working heart

This study demonstrated new approaches which enabled evaluating the work performance in both ventricles of an isolated guinea pig heart. By changing the right atrial filling pressure (RAFP, preload) from 6 to 20 mm of Hg at a constant aortic pressure (Pa, 20 mm of Hg), cardiac output, stroke volume, aortic flow, coronary flow, cardiac work, O2 consumption, CO2 output, as well as end-diastolic ventricular, and pulmonary arterial pressures increased. Cardiac contractility and both ventricular systolic pressures reached peak values between 12 and 14 mm of Hg of RAFP and then gradually decreased. With graded increases of Pa (afterload) from 10 to 45 mm of Hg at a fixed RAFP (8 mm of Hg), coronary flow, cardiac contractility, cardiac work, cardiac O2 consumption, glucose utilization rate, and pulmonary arterial and both ventricular systolic pressures increased. Although aortic flow decreased with an increase in Pa, cardiac output, stroke volume, and coronary resistance did not show significant changes. Furthermore, cardiac mechanical efficiency decreased with an increase of pre- or afterload of the perfused isolated heart. These findings indicate that the total working heart model is suitable for studying cardiac functions.