Automated echocardiographic left ventricular dimension assessment in dogs using artificial intelligence: Development and validation.

BACKGROUND: Artificial intelligence (AI) could improve accuracy and reproducibility of echocardiographic measurements in dogs. HYPOTHESIS: A neural network can be trained to measure echocardiographic left ventricular (LV) linear dimensions in dogs. ANIMALS: Training dataset: 1398 frames from 461 canine echocardiograms from a single specialist center. VALIDATION: 50 additional echocardiograms from the same center. METHODS: Training dataset: a right parasternal 4-chamber long axis frame from each study, labeled by 1 of 18 echocardiographers, marking anterior and posterior points of the septum and free wall. VALIDATION DATASET: End-diastolic and end-systolic frames from 50 studies, annotated twice (blindly) by 13 experts, producing 26 measurements of each site from each frame. The neural network also made these measurements. We quantified its accuracy as the deviation from the expert consensus, using the individual-expert deviation from consensus as context for acceptable variation. The deviation of the AI measurement away from the expert consensus was assessed on each individual frame and compared with the root-mean-square-variation of the individual expert opinions away from that consensus. RESULTS: For the septum in end-diastole, individual expert opinions deviated by 0.12 cm from the consensus, while the AI deviated by 0.11 cm (P = .61). For LVD, the corresponding values were 0.20 cm for experts and 0.13 cm for AI (P = .65); for the free wall, experts 0.20 cm, AI 0.13 cm (P < .01). In end-systole, there were no differences between individual expert and AI performances. CONCLUSIONS AND CLINICAL IMPORTANCE: An artificial intelligence network can be trained to adequately measure linear LV dimensions, with performance indistinguishable from that of experts.

Evaluation of a smartphone electrocardiograph in healthy foals and comparison to standard base-apex electrocardiography.

Smartphone-based technology for ECG recording has recently spread as a complementary tool for electrocardiographic screening and monitoring in adult horses and in other animal species. The present study aimed to assess the feasibility and accuracy of a smartphone-based ECG in healthy foals. This was a prospective observational study (authorization n. 45,865/2016) including 22 foals aged less than 21 days. A reference standard base-apex ECG (rECG) was acquired, and a smartphone ECG (sECG) was recorded immediately after by using a smartphone-based single lead electrocardiograph. All ECG tracings were evaluated in a blind fashion by a single board-certified cardiologist, who judged whether the tracings were acceptable for interpretation and performed ECG measurements and diagnosis. The Spearman correlation coefficient, the Cohen's k test and the Bland-Altman test were used to assess the agreement between sECG and rECG. All sECG tracings were acceptable for interpretation. All foals showed sinus rhythm on both rRCG and sECG tracings, with perfect agreement in heart rate classification (κ = 0.87; p < 0.001). No clinically relevant differences were found in the assessment of waves and intervals duration. Concerning P wave and QRS complex polarity, the percentage of agreement between rECG and sECG was 78% and 83%, respectively. About ECG tracing quality, rECG and sECG showed a substantial agreement (κ = 0.624; p < 0.001). In conclusion, the smartphone-based ECG device tested in the present study recorded good quality single-lead ECG tracings in foals, reliable for heart rate and ECG measurements, but different polarity of P waves and QRS complexes was found in some foals in comparison to rECG.

Right heart echocardiographic variables and prediction of clinical severity in dogs with pulmonary stenosis.

BACKGROUND: Pulmonary stenosis (PS) usually is evaluated using echocardiography. A multiparametric approach, in addition to the maximum pressure gradient (PG), might be indicated to better characterize PS severity and address its management. HYPOTHESIS/OBJECTIVES: Our hypothesis was that right heart size and function are associated with echocardiographic and clinical severity of pulmonary stenosis in dogs. ANIMALS: Client-owned dogs with PS. METHODS: Prospective, multicenter, observational study. Enrolled dogs underwent complete echocardiographic examination. Associations among right heart echocardiographic variables, PS transvalvular PG >80 mm Hg and presence of clinical signs (exercise intolerance, syncope, right-sided congestive failure, or some combination of these) were assessed using logistic regression analysis. RESULTS: Eighty-eight dogs with PS. Twenty-eight dogs were symptomatic. Increased right ventricular end-diastolic free wall thickness (odds ratio [OR] > 100; 95% confidence interval [95%CI], 50- > 100; P = .01) and decreased aorta-to-pulmonary artery velocity time integral ratio (OR, < 0.001; 95%CI, 0.0-0.001; P = .005) were independently associated with PS PG >80 mm Hg. Decreased tricuspid annular plane systolic excursion (OR, 0.35; 95%CI, 0.15-0.77; P = .01) and increased right ventricular end-diastolic area (OR, 1.4; 95%CI, 1.08-2.02; P = .01) were independently associated with clinical severity. CONCLUSION AND CLINICAL IMPORTANCE: Structural and functional right heart echocardiographic variables are associated with echocardiographic and clinical severity in dogs with PS. A multiparametric approach is advised to better assess PS severity.

Equine echocardiography: Can dobutamine infusion correct alterations due to sedation with alpha-2 agonists?

For the echocardiographic examination horses should not be sedated unless absolutely necessary because this alters cardiac dimensions and indices of function. However, some horses do not tolerate the echocardiographic procedure and require sedation to conduct the examination safely and obtain good quality images. The objective of this study was to evaluate whether the concurrent infusion of dobutamine in horses sedated with romifidine counteracts the cardiovascular changes observed with sedation alone. Twelve healthy untrained Standardbred mares were used. Three echocardiographic examinations were performed on the same day for each subject: a) without any treatment under resting conditions (WT); b) under sedation with romifidine administered intravenously (RT); c) under sedation with romifidine and concurrent intravenous infusion with dobutamine (RDT). A three-hour washout period was observed between each examination and the order of the examinations was randomly decided by rolling a dice. The measurements on the images recorded were performed offline at the end of the study protocol and at this point the operator was blinded to the horse and treatment administered. Left ventricular internal diameter (LVID) in diastole, left ventricular free wall (LVFW) in systole, and fractional shortening (FS) were higher in the WT group compared with the other two groups. No differences in the other M-mode and B-mode values were observed. A continuous rate infusion of dobutamine did not counteract the alterations caused by sedation and led to similar echocardiographic measurements to those obtained after romifidine administration.

Right ventricular size and function evaluated by various echocardiographic indices in dogs with pulmonary hypertension.

BACKGROUND: Three-dimensional (3D) echocardiography and 2-dimensional (2D) strain measurements of the right ventricle (RV) are important indices in humans with pulmonary hypertension (PH) and need further evaluation in dogs with PH. OBJECTIVES: To evaluate various RV size and function indices in dogs with PH and to examine differences between pre- and postcapillary PH. ANIMALS: A total of 311 client-owned dogs: 100 dogs with PH, 31 with postcapillary and 69 with precapillary PH, and 211 healthy control dogs. METHODS: Retro- and prospective, multicenter study. Size and function of the RV was determined using several indices, derived using dedicated RV software, including 3D RV end-diastolic volume (EDVn), end-systolic volume (ESVn), ejection fraction, 2D global and free wall RV longitudinal strain (RVLS), end-diastolic area, end-systolic area, fractional area change, tricuspid annular plane systolic excursion, and tissue Doppler imaging-derived systolic myocardial velocity of the lateral tricuspid annulus (S'n). RESULTS: The EDVn (1.8 vs 2.5 mL/kg0.942 , P < .01) and ESVn (0.8 vs 1.2 mL/kg0.962 , P < .001) were significantly larger in the PH group compared to healthy controls. Free wall RVLS was decreased in dogs with severe PH compared to controls (-24% vs -29.6%, P < .001). Dogs with precapillary PH had worse RV systolic function than dogs with postcapillary PH. CONCLUSION: Three-dimensional echocardiography of the RV is a promising tool to detect RV changes in dogs with PH. Also, 2D strain measurements are able to detect decreased RV function and offer several advantages compared to conventional indices.

Evaluation of a Novel Precordial Lead System for the Electrocardiographic Diagnosis of Right Ventricular Enlargement in Dogs.

The purpose of this study was to evaluate the reliability of precordial leads for the detection of right ventricular enlargement (RVE) in dogs. This was a prospective observational study. The RVE was defined by echocardiography. The amplitude (mV) of the Q, R, and S waves, the R/S ratio, and the mean electrical axis (MEA) of the QRS complex were assessed on the 12-lead ECG. The ROC curve and the Youden index yielded the best cutoffs for RVE detection. An area under the curve (AUC) > 0.7 defined suitable diagnostic accuracy. A total of 84 dogs, 27 with RVE and 57 healthy controls, were enrolled. Q wave amplitude in aVR (cutoff > 0.10 mV; AUC = 0.727), R/S ratio in V4 (cutoff < 1.15; AUC = 0.842), R/S ratio in V5 (cutoff < 1.95; AUC = 0.839) and S wave amplitude in V6 (cutoff > 0.70 mV; AUC = 0.703) showed suitable diagnostic accuracy in detecting RVE. Among dogs with RVE, only 9/27 (33%) presented a right shift of MEA. Differently, 19/27 (70%) showed at least one of the identified precordial lead criteria. Assessment of the R/S ratio in V4 and V5 and S wave amplitude in V6 increases the diagnostic accuracy of ECG in distinguishing between dogs with RVE and healthy dogs.

Percutaneous Balloon Dilation in Two Dogs with Cor Triatriatum Dexter.

Percutaneous balloon dilation was performed in a Rhodesian Ridgeback and in an American Staffordshire Terrier affected by cor triatriatum dexter (CTD). Both cases had ascites without jugular venous distension or pleural effusion. In both dogs the CTD presented a perforated membrane but with different morphology: in one case the coronary sinus entered the caudal chamber of the CTD together with the caudal vena cava. In the other case, the coronary sinus communicated with the cranial chamber of the CTD together with the cranial vena cava. Percutaneous balloon dilation of the CTD was successfully performed, and both dogs had uneventful surgery recoveries. At two years of follow-up, the dogs were free from clinical signs and cardiac medication.

Transjugular Patent Ductus Arteriosus Occlusion in Seven Dogs Using the Amplatzer Vascular Plug II.

Although vascular plugs for the closure of patent ductus arteriosus (PDA) have been validated in dogs, studies are lacking on its use as a first-choice device with a transjugular approach. The present case series describes the transvenous right jugular embolization of PDA using an Amplatzer Vascular Plug II in seven dogs of different ages, breeds, and body weights. Complete closure of the PDA was demonstrated in all cases. All dogs showed significant hemodynamic reduction of pulmonary overcirculation and left heart size after the procedure and at following echocardiographic check-ups. Transjugular PDA occlusion using an Amplatzer Vascular Plug II can thus be considered as a safe alternative to the arterial or venous femoral approach using an Amplatzer canine ductal occluder (ACDO), particularly in puppies with small femoral vessels.

Abnormalities of External Jugular Veins in Bulldogs with Pulmonary Valve Stenosis.

Two French bulldogs and one English bulldog affected by pulmonary valve stenosis and referred for pulmonary balloon valvuloplasty were diagnosed with different abnormalities of the external jugular veins. The diagnosis included unilateral absence of the right external jugular vein and bilateral hypoplasia of the external jugular veins, associated with persistent left cranial vena cava. Vascular ultrasound and computed tomography were used for the diagnosis. Jugular vein anomalies can affect decision-making regarding the central venous catheterization needed to perform procedures such as pulmonary balloon valvuloplasty or central catheter placement. Based on the results of the present case series, anomalies of external jugular veins should be considered in French and English bulldogs when the external jugular veins cannot be palpated or when echocardiography shows coronary sinus dilation. Vascular ultrasound or computed tomography may help identify jugular venous anomalies and should be considered in the preoperative evaluation of bulldogs that need to undergo interventional procedures requiring transjugular catheterization.

Clinical and Electrocardiographic Findings for Predicting the Severity of Pulmonary Valve Stenosis in Dogs.

Pulmonary valve stenosis (PS) in dogs is usually suspected due to the presence of a heart murmur and clinical signs. Echocardiography is needed to confirm the diagnosis and define the severity of PS. This retrospective study evaluated the utility of clinical and electrocardiographic (ECG) findings in the prediction of PS severity. Data regarding heart murmur and ECG analysis were gathered. Ninety-seven dogs with PS were included. A murmur grade ≥IV/VI was predictive of severe PS (area under curve (AUC) = 0.71; sensitivity (Se) = 95%; specificity (Sp) = 33%; p = 0.003). In lead II, P wave amplitude >0.35 mV (AUC = 0.67; Se = 31%; Sp = 100%; p = 0.038), Q wave < 0.15 mV (AUC = 0.70; Se = 70%; Sp = 59%; p = 0.0015), R wave < 0.87 mV (AUC = 0.66; Se = 67%; Sp = 69%; p = 0.006), and S wave > 0.37 mV (AUC = 0.80; Se = 72%; Sp = 85%; p < 0.0001) were predictive of severe PS. The extent of right deviation of the mean electrical axis of the QRS complex was correlated with the pulmonary pressure gradient (r = 0.648; p < 0.0001). In conclusion, a systolic murmur with intensity ≥IV/VI, a P wave amplitude >0.35 mV, low amplitude of Q and R waves, deep S waves in lead II, and right axis deviation of the QRS complex in a young dog are predictive of severe PS.

Echocardiographic reference intervals for right ventricular indices, including 3-dimensional volume and 2-dimensional strain measurements in healthy dogs.

BACKGROUND: There is currently a lack of reference intervals (RIs) for the novel measures like 3-dimensional (3D) echocardiography or speckle-tracking strain for assessment of right ventricular (RV) structure and function. OBJECTIVES: To generate RIs and to determine the influence of age, heart rate, and body weight (BW) on various RV function indices using a dedicated RV software for 3D RV end-diastolic volume (EDV), end-systolic volume (ESV), ejection fraction (EF), global and free wall RV longitudinal strain (RVLS), end-diastolic area (RVEDA), end-systolic area (RVESA), fractional area change (FAC), tricuspid annular plane systolic excursion (TAPSE), and tissue Doppler imaging (TVI)-derived systolic myocardial velocity of the lateral tricuspid annulus (S'). ANIMALS: Healthy adult client-owned dogs (n = 211) of various breeds and ages. METHODS: Prospective study. Reference intervals were estimated as statistical prediction intervals using allometric scaling for BW-dependent variables. Right-sided (upper limit) or left-sided (lower limit) 95% RIs were calculated for every variable. Inter- and intraobserver variability was determined. RESULTS: Most variables showed clinically acceptable repeatability with coefficient of variation less than 10. Upper or respectively lower RI after allometric scaling to normalize for different BWs were: EDVn ≤ 2.5 mL/kg0.942 , ESVn ≤ 1.2 mL/kg0.962 , TAPSEn ≥ 4.5 mm0.285 , RVEDAn ≤ 1.4 cm2 /kg0.665 , RVESAn ≤ 0.8 cm2 /kg0.695 , and TVI S'n ≥ 5.6 cm/s/kg0.186 . The calculated limits for indices without allometric normalization were: EF > 42.1%, FAC > 30.0%, free wall RVLS < -20.8%, and global RVLS < -18.3%. CONCLUSIONS: Echocardiographic RIs for RV structure and function are provided.

Evaluation of a new portable 1-lead digital cardiac monitor (eKuore) compared with standard base-apex electrocardiography in healthy horses.

Recently, the use of smartphone ECG devices has been reported in humans and animals. Nevertheless, as the electrodes of these devices are inseparable, they can create only a precordial reading in veterinary species. Thus, although the smartphone ECG devices are considered valuable as a screening tool for the detection of some common arrhythmias, they are not always a reliable method for the measurement of the duration of the electrical deflections. The objectives of this study were to evaluate the feasibility of a novel smartphone ECG device, to report the readings obtained recorded simultaneously with a reference ECG system, and to compare the heart rate and duration of cardiac deflections obtained with the two methods. A total of 28 healthy mares of different breeds and age were included in this study and ECG recordings were obtained simultaneously with a reference ECG telemetry system with surface electrodes attached to the skin with alligator clips using a standard base-apex system and a smartphone ECG device with electrodes positioned alternatively with a standard and a modified base apex derivation. All the recordings obtained were considered acceptable for interpretation. An excellent agreement was found between the two methods for the evaluation of heart rate and polarity of cardiac deflections. No differences regarding number, duration and percentage of artifacts were found. This technology could become a valid diagnostic tool in the cardiological assessment of horses, in particular on the field.

Breath-by-breath analysis of respiratory sinus arrhythmia in dogs.

Dogs differ greatly in size, heart (HR) and breathing rates (BR). In addition, they have a clear Respiratory Sinus Arrhythmia (RSA) at rest. Therefore, better than any other mammalian species, dogs offer an opportunity to test whether resting RSA varies with body weight, HR or BR. Sequences of inter-beat-intervals (IBI, ms) a few-minutes long were collected in twenty-three resting dogs of different sizes, together with pneumograms. IBI variability was quantified by standard time-domain criteria. From beat-to-beat instantaneous heart rate (hR, beats/min), RSA was the difference between inspiratory peak (hR-peak) and expiratory trough (hR-trough), in percent of mean HR. RSA averaged 40.1 % ±4.5, or more than three times that of humans, with large inter-animal variability. On average, RSA contributed 38 % of the total IBI variability. RSA did not differ between sexes and did not correlate with body weight. It had modest negative correlations with HR (P < 0.05) and BR (P < 0.05), and a very strong negative correlation with hR-trough (P < 0.001). In two separate dogs, during panting, RSA was absent. In the transition from resting to panting, RSA continued like at rest for several breaths, despite the tachypnea, underlying the importance of central mechanisms in the origin of RSA. In conclusion, RSA in dogs is very large and explains less than half of their sinus arrhythmia. Rather than HR, BR or hR-peak, changes in the vago-sympathetic control, represented by hR-trough, are the most likely source of variability of RSA among subjects.

The Mitral INsufficiency Echocardiographic score: A severity classification of myxomatous mitral valve disease in dogs.

BACKGROUND: There is no commonly shared severity score for myxomatous mitral valve disease (MMVD) based on routinely acquired echocardiographic variables. HYPOTHESIS/OBJECTIVES: To propose an easy-to-use echocardiographic classification of severity of MMVD in dogs. ANIMALS: Five hundred and sixty dogs with MMVD. METHODS: This was a retrospective, multicenter, observational study. The proposed Mitral INsufficiency Echocardiographic (MINE) score was based on 4 echocardiographic variables: left atrium-to-aorta ratio, left ventricular end-diastolic diameter normalized for body weight, fractional shortening, and E-wave transmitral peak velocity. Specific echocardiographic cutoffs were defined based on previous prognostic studies on MMVD, and severity scores were assigned as follows: mild (score: 4-5), moderate (score: 6-7), severe (score: 8-12), late stage (score: 13-14). RESULTS: Median survival time was significantly different (P < .05) between the proposed severity classes: mild (2344 days, 95% confidence interval [CI] 1877-2810 days), moderate (1882 days, 95% CI 1341-2434 days), severe (623 days, 95% CI 432-710 days), and late stage (157 days, 95% CI 53-257 days). A MINE score >8 was predictive of cardiac death (area under the curve = 0.85; P < .0001; sensitivity 87%, specificity 73%). In the multivariable analysis, all the echocardiographic variables of the MINE score were independent predictors of death because of heart disease (P < .001). CONCLUSIONS AND CLINICAL IMPORTANCE: The MINE score is a new easy-to-use echocardiographic classification of severity of MMVD, which has been proven to be clinically effective as it is associated with survival. This classification provides prognostic information and could be useful for an objective echocardiographic assessment of MMVD.

Reference intervals for transthoracic echocardiography in the American Staffordshire Terrier.

This study reports the echocardiographic reference intervals in the American Staffordshire Terrier (AST). The echocardiographic variables obtained in 57 healthy adult AST were compared with published data from the general canine population and other breeds. In the AST, the left ventricular volumes were lower than values reported in Boxers and Dobermans (P<0.0001), but higher than in small breeds (P<0.0001). The left ventricular ejection fraction was higher than Boxers and Dobermans (P<0.0001), but lower than small breed dogs (P=0.027). The aortic peak velocity values were similar to Boxers (P=0.55) but higher than the general canine population (P<0.0001). The reference intervals presented in this study are clinically useful for an accurate echocardiographic interpretation and screening in the AST.

A radiographic study of breed-specific vertebral heart score and vertebral left atrial size in Chihuahuas.

Although echocardiography is the gold standard for the diagnosis of cardio-structural disease, thoracic radiography is a rapid, cost-effective, and widely accessible method for evaluating cardiac size in dogs. The vertebral heart score (VHS) and the vertebral left atrial size (VLAS) are established as objective measures of cardiomegaly on thoracic radiographs. However, several studies have shown significant variations in the VHS among different breeds. The Chihuahua is predisposed to both congenital and acquired cardiac diseases. The aim of this prospective, single-center, cross sectional study was thus to evaluate the VHS and the VLAS in healthy adult Chihuahua dogs. A total of 30 Chihuahuas were included. The VHS values in our sample population of Chihuahuas were 10.0 ± 0.6 (95% range, 8.9-11.0). This was significantly greater than the canine reference value of 9.7 ± 0.5 established by Buchanan and Bücheler (P = .002). The VLAS of Chihuahuas in our study was 1.8 ± 0.2 (95% range, 1.3-2.1). This was significantly lower than the values previously reported by Malcolm et al (2.07 ± 0.25; P = .0004). The VHS and the VLAS were not influenced by sex, body weight, short or long hair, and body condition score in normal Chihuahuas. Our results indicated that breed-specific reference values for radiographic VHS and VLAS are needed. In Chihuahuas, the values found in this study can be used as a normal reference in order to help avoid overinterpretation of cardiomegaly in these dogs.

Fatal Pulmonary Hypertension and Right-Sided Congestive Heart Failure in a Kitten Infected with Aelurostrongylus abstrusus.

Aelurostrongylus abstrusus is considered the most important respiratory nematode of domestic cats worldwide. This parasite inhabits the alveoli, alveolar ducts, and bronchioles and causes a subacute to chronic respiratory clinical disease. Clinical signs may occur in domestic cats of any age, though they are more often described in young animals. Physical examination, echocardiography, thoracic radiography, pulmonary and cardiac pathological findings, classical, and molecular parasitological analysis of a six-month-old kitten referred at the Veterinary Teaching Hospital of the University of Pisa (Italy) led to a diagnosis of parasitic bronchopneumonia caused by A. abstrusus, which was complicated by severe pulmonary hypertension (PH) and right-sided congestive heart failure (R-CHF) that caused the death of the animal. Cases of reversible PH associated with A. abstrusus infection have been seldom reported in cats. This is the first report of fatal PH and R-CHF in a kitten with clinical aelurostrongylosis.

Radiographic vertebral left atrial size: A reference interval study in healthy adult dogs.

Thoracic radiography is a useful technique for the evaluation of cardiac dimensions, especially when echocardiography is not possible. The vertebral left atrial size (VLAS) has recently been proposed as a new radiographic method for quantifying left atrial dimensions in dogs. The aims of this retrospective, reference interval, observational study were to describe values for VLAS in a group of healthy adult dogs and to compare intraobserver and interobserver agreement for VLAS versus vertebral heart score (VHS) methods. Thoracic radiographs of 80 healthy adult dogs were evaluated. Normal left atrial size was determined based on an echocardiographic left atrial-to-aorta ratio < 1.6. The VLAS and vertebral heart score values were measured from right lateral radiographs. The correlations between VLAS, the vertebral heart score, and the left atrial-to-aorta ratio were evaluated. The effects of body weight, sex, and age were also tested using regression analyses. The median value of VLAS were 1.9, with a reference interval of 1.4-2.2. A positive correlation was found between VLAS and vertebral heart score values (r = 0.53; P < .0001). No effect of body weight, sex, and age on VLAS was detected. Excellent intraobserver and interobserver agreements were found for both VLAS and vertebral heart score methods (intraclass correlation coefficients ≥ 0.91). Findings from this sample of healthy dogs indicated that VLAS is a repeatable radiographic method for quantifying left atrial size. Further studies are warranted to evaluate this measure in clinically affected dogs.

Left atrial anteroposterior diameter in dogs: reference interval, allometric scaling, and agreement with the left atrial-to-aortic root ratio.

Left atrial enlargement (LAE) is a well-known negative prognostic factor in dogs with myxomatous mitral valve disease (MMVD). Left atrial-to-aortic root ratio (LA/Ao) is the most commonly used method to evaluate left atrial (LA) size in dogs, while the left atrial anteroposterior diameter (LAD) has been proposed as an additional measurement of LA size in different species. The aim of this study was to establish a normal reference range of LAD normalized to body weight (LADn) in dogs using allometric scales, and to evaluate the agreement between LADn and LA/Ao in the detection of LAE in dogs with MMVD. This was a retrospective, multicenter, observational study. We included 330 healthy dogs, 30 dogs with MMVD in ACVIM stage B1, 30 dogs in ACVIM stage B2, and 30 dogs in ACVIM stage C. The reference range for the LAD, depending on body weight, was between 16.91 mm and 49.68 mm. The reference range for the LADn in healthy dogs was between 10.49 and 15.72. LADn was significantly greater in dogs with MMVD compared to healthy dogs, and a significant difference in LADn was noted between different ACVIM stages (P<0.001). The most accurate cut-off value of LADn to differentiate between dogs in groups B2 and C was 20.3 (sensitivity, 83.3%; specificity, 83.3%). There was a misclassification rate of 37% between LADn and LA/Ao in the detection of LAE in group B1. This study provides a normal reference range for LAD in dogs, which can be used as an additional tool to assess LAE in dogs with MMVD.