Ambulatory electrocardiographic evaluation of clinically normal adult Boxers.

OBJECTIVE: To determine the prevalence of ventricular arrhythmias in clinically normal adult Boxers. DESIGN: Prospective cross-sectional study. ANIMALS: 301 Boxers (181 females and 120 males) > 1 year old with echocardiographically normal systolic function and no history of syncope or congestive heart failure. PROCEDURES: Physical examination, which included echocardiography, was performed on all dogs. A 24-hour ambulatory ECG was performed on each dog, and results were evaluated to assess ventricular arrhythmias. Statistical evaluation was performed to determine correlations between the total number of ventricular premature complexes (VPCs)/24 h, grade of ventricular arrhythmia, and age of the dogs. RESULTS: Age of dogs ranged from 1 to 16 years (median, 4 years). Number of VPCs/24 h in each dog ranged from 0 to 62,622 (median, 6 VPCs/24 h). Grade of arrhythmias ranged from 0 to 3 (median, 1). Age was correlated significantly with number of VPCs/24 h (r = 0.43) and with grade of arrhythmia (r = 0.37). Number of VPCs/24 h was significantly correlated with grade of arrhythmia (r = 0.82). CONCLUSIONS AND CLINICAL RELEVANCE: Clinically normal adult Boxers generally had < 91 VPCs/24 h and an arrhythmia grade < 2. Boxers with > 91 VPCs/24 h were uncommon and may have represented dogs with arrhythmogenic right ventricular cardiomyopathy or other disease processes that could have resulted in the development of ventricular arrhythmias.

A prospective genetic evaluation of familial dilated cardiomyopathy in the Doberman pinscher.

BACKGROUND: The Doberman Pinscher is one of the most common breeds of dogs to develop dilated cardiomyopathy (DCM), a primary heart muscle disorder characterized by myocardial dysfunction, cardiac arrhythmias, and congestive heart failure. In the Doberman Pinscher, the disease is typically adult onset, and a familial etiology has been suggested. HYPOTHESIS: DCM in the Doberman Pinscher, is a familial disease linked to a specific genetic marker. ANIMALS: The study comprised an extended family of Doberman Pinschers with a history of DCM. METHODS: Participating dogs were prospectively evaluated over an 8-year period. Phenotype of participating dogs was determined by annual echocardiography and ambulatory electrocardiography, and the pedigree was evaluated to determine a specific mode of inheritance. Three hundred seventy-two microsatellite markers were selected and genotyped to cover the 38 autosomal chromosomes. Phenotyping, genotyping, and pedigree information was entered into a database, and parametric, 2-point analysis was performed. Markers were considered to be linked to the development of DCM if the logarithm of odds LOD score was >/= 3.0. RESULTS: An autosomal dominant mode of inheritance was defined by the appearance of the disease in multiple generations, equal gender representation (P = .973) and male-to-male transmission. A maximum LOD score of 1.31 was obtained for I marker on chromosome 20, a score not high enough to be associated with DCM. CONCLUSION: DCM in the Doberman Pinscher is a familial disease inherited as an autosomal dominant trait. The causative gene(s) responsible for this condition remain unresolved. Association studies by means of array technology may provide new insights into gene identification.

Septicemia in a young dog following treatment of patent ductus arteriosus via coil occlusion.

CASE DESCRIPTION-A 12-week-old female English Springer Spaniel was evaluated for lethargy, vomiting, and pyrexia 1 week after treatment of patent ductus arteriosus (PDA) via coil occlusion. CLINICAL FINDINGS-Test results were consistent with septicemia, and the assumption was made that the PDA occlusion coils were infected. Radiography revealed partial migration of the coil mass into the pulmonary artery and signs of congestive heart failure. TREATMENT AND OUTCOME-After successful treatment of the septicemia and heart failure, surgical removal of the coils and resection of the PDA were undertaken. Although the coil that embolized to the pulmonary vasculature was left in place, the dog's clinical signs resolved. CLINICAL RELEVANCE-This case highlights the fact that as PDA coil occlusion devices become more widely used in dogs, practitioners must be prepared to treat implant infections aggressively, with both medical and surgical interventions if necessary.

Clinical, echocardiographic, and electrocardiographic abnormalities in Boxers with cardiomyopathy and left ventricular systolic dysfunction: 48 cases (1985-2003).

OBJECTIVE: To identify clinical, echocardiographic, and electrocardiographic abnormalities in Boxers with cardiomyopathy and echocardiographic evidence of left ventricular systolic dysfunction. DESIGN: Retrospective study. ANIMALS: 48 mature Boxers. PROCEDURE: Medical records were reviewed for information on age; sex; physical examination findings; and results of electrocardiography, 24-hour ambulatory electrocardiography, thoracic radiography, and echocardiography. RESULTS: Mean age of the dogs was 6 years (range, 1 to 11 years). Twenty (42%) dogs had a systolic murmur, and 9 (19%) had ascites. Congestive heart failure was diagnosed in 24 (50%) dogs. Seventeen (35%) dogs had a history of syncope. Mean fractional shortening was 14.4% (range, 1% to 23%). Mean left ventricular systolic and diastolic diameters were 4.5 cm (range, 3 to 6.3 cm) and 5.3 cm (range, 3.9 to 7.4 cm), respectively. Twenty-eight (58%) dogs had a sinus rhythm with ventricular premature complexes (VPCs), and 20 had supraventricular arrhythmias (15 with atrial fibrillation and 5 with sinus rhythm and atrial premature complexes). Sixteen of the dogs with supraventricular arrhythmias also had occasional VPCs. Morphology of the VPCs seen on lead II ECGs was consistent with left bundle branch block in 25 dogs, right bundle branch block in 8, and both in 11. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that Boxers with cardiomyopathy and left ventricular dysfunction frequently have arrhythmias of supraventricular or ventricular origin. Whether ventricular dysfunction was preceded by electrical disturbances could not be determined from these data, and the natural history of myocardial disease in Boxers requires further study.

Clinical patent ductus arteriosus in adult genetically epilepsy-prone rats.

Persistent patent ductus arteriosus (PDA) and clinically silent PDAs are relatively common congenital cardiac defects in humans. We report here the occurrence of symptomatic PDA in adults from a colony of genetically epilepsy-prone rats (GEPRs). Affected rats displayed severe ventral edema. Echocardiography revealed PDA in several animals. Necropsy findings included cardiomegaly, hepatic hyperemia and centrilobular necrosis indicative of passive congestion, and vascular changes consistent with pulmonary hypertension. All affected rats were descendants of one of two brother-sister breeding pairs established from a single litter in April 2000. Clinically silent PDAs were also detected in the colony. Histological examination of the ligamentum arteriosus showed normal vascular tissue in asymptomatic GEPR and Sprague-Dawley rats. PDAs are likely to have a genetic component in the GEPR colony and may provide a novel model for the study of pathogenesis and therapy of this condition.

Use of signal-averaged electrocardiography in the evaluation of arrhythmogenic right ventricular cardiomyopathy in boxers.

OBJECTIVE: To assess signal-averaged electrocardiography (SAECG) for evaluation of Boxers with arrhythmogenic right ventricular cardiomyopathy (ARVC) and identify dogs at risk for sudden death (SD) or death related to congestive heart failure (CHF). DESIGN: Prospective study. ANIMALS: 94 Boxers with ARVC and 49 clinically normal non-Boxers (controls). PROCEDURE: Boxers were screened for ARVC, and severity was estimated by use of echocardiography, 24-hour ambulatory ECG, and SAECG. Statistical evaluation was performed to identify significant differences in SAECG variables relative to clinical outcome, frequency of ventricular arrhythmias, and systolic function. Sensitivity, specificity, and positive and negative predictive values were evaluated for each SAECG variable for occurrence of SD or death related to CHF. Late potentials were also evaluated as a predictor of cardiac-related death. RESULTS: Differences were detected in SAECG variables on the basis of clinical outcome, systolic function, and frequency of ventricular arrhythmias. More severely affected dogs had significantly more abnormal SAECG findings. The presence of late potentials, defined as 2 abnormal root mean square values (of 4), was associated with high sensitivity, specificity, and negative predictive value for cardiac-related SD or death secondary to CHF CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that SAECG is a useful noninvasive diagnostic test to evaluate dogs affected with ARVC and identify individuals at risk for cardiac-related death.

Assessment of heart rate variability in Boxers with arrhythmogenic right ventricular cardiomyopathy.

OBJECTIVE: To assess heart rate variability (HRV) in Boxers with arrhythmogenic right ventricular cardiomyopathy (ARVC), assess the ability of HRV analysis to identify differences in Boxers on the basis of severity of their arrhythmia, and evaluate the use of HRV to determine whether persistently high sympathetic tone is present in these dogs. DESIGN: Prospective study. ANIMALS: 24 Boxers with ARVC and 10 clinically normal non-Boxer dogs. PROCEDURE: Boxers were categorized as dogs with congestive heart failure (CHF), dogs with < or = 2 ventricular premature complexes (VPCs)/24 h (designated unaffected), or dogs with > 1,000 VPCs/24 h (designated affected). Ambulatory electrocardiography (24 hours) was performed in each dog. Recordings were analyzed for HRV variables at a commercial laboratory; differences in HRV variables among groups were compared with 1-way ANOVA. RESULTS: Compared with control non-Boxer dogs and Boxers without CHF (affected and unaffected Boxers), HRV was reduced in Boxers with CHF. No differences in HRV variables were detected between affected and unaffected Boxers. Inconsistent differences were identified between the control dogs and Boxers without CHF that had various degrees of arrhythmias. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that persistently high sympathetic tone is not a consistent feature of ARVC. Differences in some HRV variables between Boxers without CHF and control dogs suggest that Boxers may have different autonomic control of heart rate, compared with that of clinically normal non-Boxer dogs. The usefulness of HRV analysis appears limited to Boxers with ARVC that have systolic dysfunction and CHF.

Evaluation of spontaneous variability in the frequency of ventricular arrhythmias in Boxers with arrhythmogenic right ventricular cardiomyopathy.

OBJECTIVE: To evaluate spontaneous variability in the frequency of ventricular arrhythmias and assess the influence of day of ECG recording and day of week on arrhythmia frequency in Boxers affected with arrhythmogenic right ventricular cardiomyopathy (ARVC). DESIGN: Prospective study. ANIMALS: 10 Boxers with ARVC with prior ambulatory ECG recordings that included > or = 500 ventricular premature complexes/24 h. PROCEDURE: Consecutive 24-hour ambulatory ECG recordings were obtained during a 7-day period in each dog. The number of ventricular premature complexes and grade of the arrhythmia were obtained from each recording. For each dog, the number of ventricular premature complexes for each recording was evaluated to identify any differences relative to the day of recording (recording 1 to 7) and day of the week (Monday through Sunday). RESULTS: Spontaneous variability accounted for as much as 80% of the change in frequency of ventricular premature complexes in dogs with frequent arrhythmias; this value was almost 100% in dogs with less frequent arrhythmias. Grade of arrhythmia was less variable but was also inversely related to frequency of arrhythmia. No significant differences in frequency values were identified among days of recording or among days of the week. CONCLUSIONS AND CLINICAL RELEVANCE: Changes of < or = 80% in the frequency of ventricular arrhythmias may be within the limit of spontaneous variability in dogs with ARVC. This degree of variability should be considered in evaluations of ambulatory ECG recordings, particularly in the assessment of the efficacy of antiarrhythmic drugs.

Arrhythmogenic right ventricular cardiomyopathy causing sudden cardiac death in boxer dogs: a new animal model of human disease.

BACKGROUND: Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a primary familial heart muscle disease associated with substantial cardiovascular morbidity and risk of sudden death. Efforts to discern relevant pathophysiological mechanisms have been impaired by lack of a suitable animal model. METHODS AND RESULTS: ARVC was diagnosed in 23 boxer dogs (12 male; 9.1+/-2.3 years old). Clinical events alone or in combination included sudden death (n=9; 39%), ventricular arrhythmias of suspected right ventricular (RV) origin (n=19; 83%), syncope (n=12, 52%), and heart failure (n=3; 13%). Right ventricular enlargement or aneurysms occurred in 10 (43%). Striking histopathological abnormalities were present in each boxer dog but not in controls, including severe RV myocyte loss with replacement by fatty (n=15, 65%) or fibrofatty (n=8, 35%) tissue. Focal fibrofatty lesions were also present in both atria (n=8) and the left ventricle (LV) (n=11). Fatty replacement occupied substantially greater RV wall area in ARVC dogs than controls (40.4+/-18.8% versus 13.8+/-3.4%, respectively) (P<0.001); residual myocardium was correspondingly reduced (56.6+/-19.2% versus 84.8+/-3.8% in controls) (P<0.001). MRI demonstrated bright anterolateral and/or infundibular RV myocardial signals, confirmed as fat by histopathology. Myocarditis appeared in the RV (n=14, 61%) and LV (n=16, 70%) and in each dog with sudden death, but not in controls. Familial transmission was evident in 10 of the 23. CONCLUSIONS: We describe a novel, spontaneous, and genetically transmitted animal model of ARVC associated with sudden death in the boxer dog, closely resembling the human disease. This model may aid in understanding the pathogenic mechanisms of ARVC.

Determination of electrocardiographic parameters in healthy llamas and alpacas.

OBJECTIVE: To determine electrocardiographic parameters in healthy llamas and alpacas. ANIMALS: 23 llamas and 12 alpacas. PROCEDURE: Electrocardiography was performed in nonsedated standing llamas and alpacas by use of multiple simultaneous lead recording (bipolar limb, unipolar augmented limb, and unipolar precordial leads). RESULTS: Common features of ECGs of llamas and alpacas included low voltage of QRS complexes, variable morphology of QRS complexes among camelids, and mean depolarization vectors (mean electrical axes) that were directed dorsocranially and to the right. Durations of the QT interval and ST segment were negatively correlated with heart rate. CONCLUSIONS AND CLINICAL RELEVANCE: ECGs of acceptable quality can be consistently recorded in nonsedated standing llamas and alpacas. Features of ECGs in llamas and alpacas are similar to those of other ruminants. Changes in the morphology of the QRS complexes and mean electrical axis are unlikely to be sensitive indicators of ventricular enlargement in llamas and alpacas.

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.

Comparison of the effects of four antiarrhythmic treatments for familial ventricular arrhythmias in Boxers.

OBJECTIVE: To evaluate the effect of 4 antiarrhythmic treatment protocols on number of ventricular premature complexes (VPC), severity of arrhythmia, heart rate (HR), and number of syncopal episodes in Boxers with ventricular tachyarrhythmias. DESIGN: Randomized controlled clinical trial. ANIMALS: 49 Boxers. PROCEDURE: Dogs with > 500 VPC/24 h via 24-hour ambulatory ECG (AECG) were treated with atenolol (n = 11), procainamide (11), sotalol (16), or mexiletine and atenolol (11) for 21 to 28 days. Results of pre- and posttreatment AECG were compared with regard to number of VPC/24 h; maximum, mean, and minimum HR; severity of arrhythmia; and occurrence of syncope. RESULTS: Significant differences between pre- and posttreatment number of VPC, severity of arrhythmia, HR variables, or occurrence of syncope were not observed in dogs treated with atenolol or procainamide. Significant reductions in number of VPC, severity of arrythmia, and maximum and mean HR were observed in dogs treated with mexiletine-atenolol or sotalol; occurrence of syncope was not significantly different between these 2 treatment groups. CONCLUSIONS AND CLINICAL RELEVANCE: Treatment with sotalol or mexiletine-atenolol was well tolerated and efficacious. Treatment with procainamide or atenolol was not effective.