Prevalence of murmurs consistent with aortic stenosis among boxer dogs in Norway and Sweden

The influence of emotional stress on Doppler-derived aortic peak velocity in boxer dogs

Background

Subaortic stenosis (SAS) is a common congenital heart disease in Boxers. Doppler‐derived aortic peak velocity (AoPV) is a diagnostic criterion for the disease.

Objectives

To investigate the influence of emotional stress during echocardiographic examination on AoPV in normal and SAS‐affected Boxers. To evaluate the effects of aortic root diameters on AoPV in normal Boxers.

Dogs

Two hundred and fifteen normal and 19 SAS‐affected Boxers.

Methods

The AoPV was recorded at the beginning of echocardiographic examination (T0), and when the emotional stress of the dog was assumed to decrease based on behavioral parameters and heart rate (T1). AoPV0–AoPV1 was calculated. In normal dogs, stroke volume index was calculated at T0 and T1. Aortic root diameters were measured and their relationship with AoPV and AoPV0–AoPV1 was evaluated.

Results

In normal dogs, AoPV was higher at T0 (median, 1.95 m/s; range, 1.60–2.50 m/s) than at T1 (median, 1.76 m/s; range, 1.40–2.20 m/s; P < .0001; reduction 9.2%). The stroke volume index at T0 also was greater than at T1 (P < .0001). Weak negative correlations were detected between aortic root size and aortic velocities. In SAS‐affected dogs, AoPV0 was higher than AoPV1 (P < .0001; reduction 7.3%).

Conclusion and Clinical Importance

Aortic peak velocity was affected by emotional stress during echocardiographic examination both in SAS‐affected and normal Boxers. In normal Boxers, aortic root size weakly affected AoPVs, but did not affect AoPV0–AoPV1. Stroke volume seems to play a major role in stress‐related AoPV increases in normal Boxers. Emotional stress should be taken into account when screening for SAS in the Boxer breed.

A prospective study of systolic ejection murmurs and left ventricular outflow tract in boxers

OBJECTIVES

To investigate the prevalence and progression of murmurs and the development of the left ventricular outflow tract (LVOT) and flow velocities in the great arteries in boxer puppies through adolescence until three years of age.

METHODS

Nineteen boxer puppies with or without a low-intensity murmur, but without evidence of congenital heart disease, were studied prospectively. Examinations were carried out at 7 weeks, 3, 4, 6, 9, 12 and 36 months of age by cardiac auscultation and Doppler echocardiography.

RESULTS

Presence and intensity of heart murmurs varied in the same dog and between dogs, but flow velocities did not change. Estimated effective orifice diameter (EOD) and indexed EOD was significantly narrower than measured subvalvular and valvular diameters.

CLINICAL SIGNIFICANCE

The variability in presence and intensity of low-intensity ejection murmurs is high during growth in boxers.

Aorto-septal angle in Boxer dogs with subaortic stenosis: an echocardiographic study

The present study was designed to determine the aorto-septal angle (AoSA) in Boxer dogs with or without subaortic stenosis (SAS) by using two-dimensional echocardiography. Forty-five Boxer dogs were prospectively included in the study. The AoSA was steeper in the group with SAS than in healthy Boxers with a mean difference of 10 degrees . According to the proposed regression model, the AoSA is associated with SAS in Boxers, particularly because it becomes steeper as SAS severity increases. Several studies in humans demonstrate that small changes in the AoSA produce important changes in septal shear stress, which in turn causes proliferation of the endocardial cells resulting in subaortic obstruction. A definite conclusion about the role of the AoSA on the formation and/or progression of subvalvular lesions in Boxers cannot be drawn from the data analysed due to the transversal nature of the observations.

Use of auscultation and Doppler echocardiography in Boxer puppies to predict development of subaortic or pulmonary stenosis

BACKGROUND

Boxers are predisposed to subaortic and pulmonic stenosis (SAS, PS). Screening of puppies may be useful in estimating the risk of their developing a defect that potentially compromises life expectancy or exercise tolerance.

HYPOTHESIS

Presence of SAS or PS in adult Boxers can be predicted by auscultation and Doppler echocardiography at 9-10 weeks of age.

ANIMALS

Eighty-five Boxer puppies examined at 9-10 weeks of age and at 12 months of age.

METHODS

Prospective, longitudinal observational study. Auscultation by stethoscope and continuous wave-Doppler echocardiography for peak velocities (V(max)) in the aorta (Ao) and pulmonary artery (PA).

RESULTS

Intensity of heart murmurs in puppies correlated with V(max)Ao and V(max)PA in adults. V(max)Ao and V(max)PA in puppies correlated with V(max)Ao and V(max)PA in adults, respectively. From puppy to adult, V(max)Ao increased and V(max)PA remained unchanged. The negative predictive value for absent or only a soft (< or =II/VI) murmur in puppies being associated with V(max)Ao and PA < or = 2.4 m/s as an adult was 90% and < or =3.5 m/s 100%. The negative predictive value of a V(max)< or = 2.4 m/s as a puppy still being < or =2.4 m/s as an adult was 94% for Ao and 96% for PA, and of a V(max)< or = 3.5 m/s, 99% for Ao and 100% for PA.

CONCLUSIONS AND CLINICAL IMPORTANCE

Even though V(max)Ao increases during growth in Boxer puppies, indicating relative narrowing of the aorta, puppies with V(max)Ao < or = 2.4 m/s do not usually progress to clinically have relevant SAS at 12 months of age.

Echocardiographic ratio indices in overtly healthy Boxer dogs screened for heart disease

BACKGROUND

Boxer dogs are routinely screened by echocardiography to exclude congenital and acquired heart disease. Individuals of a given breed may span a large range of body sizes, potentially invalidating linear regression of M-mode measurements against body weight. Echocardiographic ratio indices (ERIs) provide a novel method of characterizing echocardiographic differences between Boxers and other dog breeds.

HYPOTHESIS

ERIs obtained from overtly healthy Boxer dogs presented for cardiac screening will be different from ERIs established for normal non-Boxer dogs, and those differences will be unrelated to aortic velocity or systolic blood pressure.

ANIMALS

Eighty-one Boxers with no outward clinical signs of heart disease were studied.

METHODS

All dogs were examined by 2-dimensional, M-mode, and Doppler echocardiography. M-mode measurements were used to perform ERI calculations, and the indices in Boxers were compared between Boxers with varying severity of arrhythmia and those of normal non-Boxer dogs.

RESULTS

Differences in weight-based ERIs, which reflect increased thickness of the left ventricular free wall (LVW) and interventricular septum (IVS) and smaller aortic size, were found in overtly healthy Boxer dogs compared with normal non-Boxer dogs. ERIs of left atrial and LV cavity size in overtly healthy Boxers were not significantly different from those of non-Boxer dogs.

CONCLUSIONS AND CLINICAL IMPORTANCE

Boxer dogs may have an increased relative thickness of the LVW and IVS that is independent of aortic size, aortic velocity, or arterial blood pressure, and this morphology should be taken into consideration when screening Boxers by echocardiography.

Assessing aortic stenosis using sample entropy of the phonocardiographic signal in dogs

In aortic valve stenosis (AS), heart murmurs arise as an effect of turbulent blood flow distal to the obstructed valves. With increasing AS severity, the flow becomes more unstable, and the ensuing murmur becomes more complex. We hypothesize that these hemodynamic flow changes can be quantified based on the complexity of the phonocardiographic (PCG) signal. In this study, sample entropy (SampEn) was investigated as a measure of complexity using a dog model. Twenty-seven boxer dogs with various degrees of AS were examined with Doppler echocardiography, and the peak aortic flow velocity ( V(max)) was used as a reference of AS severity. SampEn correlated to V(max) with R = 0.70 using logarithmic regression. In a separate analysis, significant differences were found between physiologic murmurs and murmurs caused by AS ( p << 0.05), and the area under a receiver operating characteristic curve was calculated to 0.96. Comparison with previously presented PCG measures for AS assessment showed improved performance when using SampEn, especially for differentiation between physiological murmurs and murmurs caused by mild AS. Studies in patients will be needed to properly assess the technique in humans.

Screening for aortic stenosis in the Boxer: Auscultatory, ECG, blood pressure and Doppler echocardiographic findings

OBJECTIVES

This study was conducted to estimate the incidence of aortic stenosis (AS) in a group of Boxers evaluated by auscultation, ECG, blood pressure measurement and Doppler-echocardiography.

BACKGROUND

The Boxer is a breed at significantly increased risk of AS. The prevalence of murmurs and Doppler-echocardiographic findings consistent with AS in this breed is reportedly high.

ANIMALS, MATERIALS AND METHODS

Eighty-nine Boxers were evaluated by auscultation, and final murmur grade recorded after stress testing. Doppler echocardiography was performed in fifty-five adult Boxers. Electrocardiograms (ECG, n=53), non-invasive blood pressure measurement (n=32), and Holter monitoring (n=24) were performed in selected dogs. Degree of AS was based on the aortic peak flow velocity (Ao PFV). Final Ao PFV was recorded as the highest value obtained after stress testing. AS was defined as an Ao PFV>2m/s on continuous wave Doppler, using the subcostal window. Pressure gradients (Deltap) were calculated using the modified Bernoulli equation (Deltap=4V(2)). Mild AS was defined as Deltap=16-40mmHg, moderate AS Deltap=40-75mmHg, and severe AS Deltap>75mmHg.

RESULTS

62% of adult Boxers evaluated by echocardiography had an Ao PFV>2m/s suggestive of AS. Systolic basilar ejection murmurs were diagnosed in 73%. Murmur intensity showed a statistically significant correlation with Ao PFV (p<0.05). ECG abnormalities were only detected in dogs with severe AS.

CONCLUSION

The study reports on systolic murmurs and Doppler-echocardiographic findings consistent with AS, as well as ECG and blood pressure measurements in a sample of pure-breed Boxers.

Congenital Heart Diseases in the Boxer Dog: A Retrospective Study of 105 Cases (1998–2005)

Subaortic stenosis (SAS) is one of the most common congenital heart diseases (CHD) in dogs with Boxers being predominantly affected. However, the increasing availability of modern diagnostic imaging systems now allows a better assessment of cardiac morphology and function, thereby facilitating early detection of CHD in awake animals. In this context, the case records of Boxer dogs diagnosed with CHD using echocardiography combined with Doppler mode, were retrospectively reviewed (1998-2005). One hundred and five Boxers exhibiting either a single CHD (53/105, 50.5%) or association of several CHD (52/105, 49.5%) were included. The most common CHD was atrial septal defect (ASD) observed in 56.2% of these animals (59/105), followed by mitral dysplasia (58/105, 55.2%), and SAS (49/105, 46.7%). SAS was associated with one or two CHD in 29.5% of cases (31/105). Most of the dogs with a low intensity left heart base systolic murmur had an isolated ASD whereas most of the dogs with a similar but high intensity murmur had SAS, either isolated or associated with a concurrent CHD. The incidence of ASD and mitral dysplasia in Boxer dogs is higher than previously assumed, and ASD is a common cause of left heart base systolic murmur in this breed of dog. This confirms that the detection of such a murmur should not be used as the unique criterion for diagnostic confirmation of SAS.

TRANSESOPHAGEAL ECHOCARDIOGRAPHY OF THE LEFT VENTRICULAR OUTFLOW TRACT, AORTIC VALVE AND ASCENDING AORTA IN BOXER DOGS WITH HEART MURMURS

The study was aimed at evaluating the anatomy of the left ventricular outflow tract, aortic valve, and ascending aorta by means of multiplane transesophageal echocardiography in Boxer dogs with left basilar heart murmurs and at comparing two-dimensional (2D) transthoracic to transesophageal echocardiography for the diagnosis of subaortic stenosis in this breed. Twenty-eight Boxers were included in the study and allocated to four groups according to physical and routine transthoracic 2D and Doppler echocardiography findings: group A--dogs with low grade (I-II/VI) heart murmurs without overt evidence of aortic stenosis (14 dogs); group B--dogs with type 1 subaortic stenosis (seven dogs); group C--dogs with type 2 subaortic stenosis (five dogs); group D--dogs with type 3 subaortic stenosis (two dogs). Anatomic lesions were not discovered by transesophageal echocardiography in dogs belonging to group A. Transesophageal imaging confirmed the type of subaortic stenosis, as graded by transthoracic echocardiography, in diseased animals (groups BCD). Morphologic information obtained by transesophageal echocardiography in Boxer dogs was similar to that obtained by transthoracic echocardiography.

Low intensity heart murmurs in boxer dogs: inter-observer variation and effects of stress testing

Inter-observer variation in the detection and grading of low intensity heart murmurs in boxer dogs was investigated. Six veterinarians with different levels of experience examined 27 boxers by cardiac auscultation. The dogs were auscultated before and after exercise, and the results were compared with phonocardiographic and echocardiographic examinations performed at rest and during two different stress tests. A subvalvular aortic ridge was identified in six dogs on two-dimensional echocardiography. Using dogs with low intensity murmurs or dogs free of heart murmurs, inter-observer agreement was positively correlated to the level of experience at rest (weighted kappa [kappa] 0.14 to 0.75), while the agreement was poor after exercise (weighted kappa 0.01 to 0.36). The presence of a subvalvular aortic ridge was associated with higher aortic flow velocities (P<0.002) and higher auscultatory murmur grading (P<0.001). There was an increase in murmur duration during one kind of stress test (P<0.001) and in aortic flow velocity during the other (P=0.001).

Aortic ejection velocity in healthy Boxers with soft cardiac murmurs and Boxers without cardiac murmurs: 201 cases (1997-2001)

OBJECTIVE

To determine aortic ejection velocity in healthy adult Boxers with soft ejection murmurs without overt structural evidence of left ventricular outflow tract obstruction and in healthy Boxers without cardiac murmurs.

DESIGN

Retrospective study.

ANIMALS

201 Boxers.

PROCEDURE

Dogs were examined independently by 2 individuals for evidence of a cardiac murmur, and a murmur grade was assigned. Maximal instantaneous (peak) aortic ejection velocity was measured by means of continuous-wave Doppler echocardiography from a subcostal location. Forty-eight dogs were reexamined approximately 1 year later.

RESULTS

A soft (grade 1, 2, or 3) left-basilar ejection murmur was detected in 113 (56%) dogs. Overall median aortic ejection velocity was 1.91 m/s (range, 1.31 to 4.02 m/s). Dogs with murmurs had significantly higher aortic ejection velocities than did those without murmurs (median, 2.11 and 1.72 m/s, respectively). Auscultation of a murmur was 87% sensitive and 66% specific for the identification of aortic ejection velocity > 2.0 m/s. An ejection murmur and aortic ejection velocity > 2.0 m/s were identified in 73 (36%) dogs. For most dogs, observed changes in murmur grade and aortic ejection velocity during a follow-up examination 1 year later were not clinically important.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that ejection murmurs were common among healthy adult Boxers and that Boxers with murmurs were likely to have high (> 2.0 m/s) aortic ejection velocities. The cause of the murmurs in these dogs is unknown.