Localization and characterization of atrial depolarization waves on the surface electrocardiogram in dogs with rapid supraventricular tachycardia.

BACKGROUND: Supraventricular tachycardias (SVTs), despite having various anatomical substrates and pathophysiological mechanisms, frequently show similar electrocardiographic presentations. OBJECTIVES: To locate and characterize atrial deflections (ADs) on 12-lead electrocardiograms in dogs with sustained rapid SVT and assess the utility of different electrocardiographic variables in differentiating types of tachycardia. ANIMALS: Ninety-two dogs with orthodromic atrioventricular reciprocating tachycardia, 17 with atrial flutter, 33 with focal atrial tachycardia recorded and confirmed by electrophysiological study, and 40 dogs with sinus tachycardia. METHODS: Atrial deflection position on the 12-lead surface electrocardiogram was assessed according to the sequence of intracardiac activation. Its features were evaluated together with the relationship between AD and QRS complex interval (AD-R) and QRS complex and AD interval (R-AD). RESULTS: Orthodromic atrioventricular reciprocating tachycardia was characterized by an AD-AD interval of 213 ± 30 ms, mean electrical axis (MEA) of AD of -90 (-90/-78)°, R-AD interval of 75 (65-80) ms, and R-AD/AD-R of 0.54 (0.45-0.64). Atrial flutter was characterized by an AD-AD interval of 199 ± 57 ms, MEA of 76° (72/81), R-AD of 120 (72-144) ms, and R-AD/AD-R of 0.81 (0.63-1.13). Focal atrial tachycardia was characterized by an AD-AD interval of 270 ± 38 ms, MEA of 49 (-72/76)°, R-AD of 160 (120-200) ms, and R-AD/AD-R of 1.45 (0.92-1.67). Sinus tachycardia was characterized by an AD-AD interval of 292 ± 31 ms, MEA of 66° (52/73), R-AD of 215 (192-222) ms, and R-AD/AD-R of 2.68 (2.25-3.08). CONCLUSIONS AND CLINICAL IMPORTANCE: Analyzing AD on 12-lead electrocardiogram is helpful in differentiating the most common SVTs in dogs.

Electrocardiographic patterns of ventricular pre-excitation in dogs with right-sided accessory pathways.

INTRODUCTION: The aim of the study was to describe the electrocardiographic features of ventricular pre-excitation (VPE) patterns characterized by the presence of delta (δ) wave, short P-δQRS interval, wide δQRS complexes in dogs with right-sided accessory pathways. ANIMALS, MATERIALS AND METHODS: Twenty-six dogs with a confirmed accessory pathways (AP) via electrophysiological mapping were included. All dogs underwent a complete physical examination, 12-lead ECG, thoracic radiography, echocardiographic examination and electrophysiologic mapping. The AP were located in the following regions: right anterior, right posteroseptal, right posterior. The following parameters were determined: P-δQRS interval, δQRS duration, δQRS axis, δQRS morphology, δ-wave polarity, Q-wave, R-wave, R'-wave, S-wave amplitude, and R/S ratio. RESULTS: In lead II, the median δQRS complex duration was 82.4 (IQR 7.2) and the median P-δQRS interval duration was 54.6 (IQR 4.2) msec. The median δQRS complex axis in the frontal plane was: + 68° (IQR 52.5) for right anterior APs, - 24 ° (IQR 24) for right postero-septal APs, - 43.5 ° (IQR 27.25) for right posterior APs (P = 0.007). In lead II, the polarity of the δ wave was positive in 5/5 right anterior APs and negative in 7/11 postero-septal APs and 8/10 in right posterior APs. In precordial leads of all dogs, R/S was ≤ 1 in V1 and > 1 in all leads from V2 to V6. CONCLUSION: Surface electrocardiogram can be used to distinguish right anterior APs from right posterior and right postero-septal ahead of an invasive electrophysiological study.

A study of the inter- and intra-operator variability on selected echocardiographic measurements in dogs.

Standard transthoracic echocardiography is considered the non-invasive gold standard for the diagnosis of most cardiac diseases. Defining reproducibility, repeatability, and reliability of this exam is imperative to reduce errors in clinical evaluations. The present study aimed at: (1) evaluating the reproducibility and repeatability of 15 echocardiographic parameters in dogs by analyzing measurements obtained from several operators with different levels of experience and comparing them to the ones obtained from two board-certified operators (gold standards - GSs); (2) assessing whether different formative paths have an influence on the variability of the echocardiographic measurements. Fifty-one operators have been included in this study, along with two diplomates of the European College of Veterinary Internal Medicine - Cardiology. Ten dogs were enrolled, 5 Golden Retrievers and 5 Cavalier King Charles Spaniels. Echocardiographic examination was performed on each dog by one GS and several operators on the same day. Results show the highest deviation from the GS and a poor inter-operator reproducibility for the M-mode measurements of the interventricular septum and the left ventricular free wall. Differently, M-mode-obtained internal diameters of the left ventricle in systole and diastole, and measurements of the aortic annulus and root show moderate to excellent intra- and inter-operator reliability and a good concordance with the GSs, demonstrating that all the operators correctly assess left ventricular systolic function and dilation, and evaluate the aortic valve. Furthermore, a specialist clinical activity, more than the acquired theoretical knowledge, affects the reliability of the echocardiographic examination by reducing the difference from the GS' measurements.

Retrospective evaluation of hypertrophic cardiomyopathy in 68 dogs.

BACKGROUND: There is a lack of clinical data on hypertrophic cardiomyopathy (HCM) in dogs. HYPOTHESIS/OBJECTIVES: To investigate signalment, clinical signs, diagnostic findings, and survival in dogs with HCM. ANIMALS: Sixty-eight client-owned dogs. METHODS: Retrospective multicenter study. Medical records were searched between 2003 and 2015. The diagnosis of left ventricular (LV) hypertrophy was made by echocardiographic examination. RESULTS: Three hundred and forty-five dogs with LV hypertrophy were identified, of which 277 were excluded. The remaining 68 dogs were 0.3 to 14 years old and predominantly <10 kg (85%), and without a sex predilection. Twenty-four % were Shih Tzu and 24% terrier breeds. Most (80%) had a systolic heart murmur. Owner-determined exercise intolerance (37%) and syncope (18%) were most commonly reported signs. The majority (84%) of dogs had symmetrical LV hypertrophy, whereas asymmetrical septal and LV free wall hypertrophy was observed in 9% and 6% of dogs, respectively. Isolated basal interventricular septal hypertrophy was not observed. Commonly recorded were systolic anterior motion of the mitral valve (60%) and LV diastolic dysfunction (89% of dogs where diastolic function was evaluated). Six dogs died unexpectedly, and 3 developed congestive heart failure. Known survival times were between 1 day and 114 months after diagnosis. CONCLUSIONS AND CLINICAL IMPORTANCE: Hypertrophic cardiomyopathy in dogs should be considered as a differential diagnosis if LV hypertrophy is identified. Small breed dogs are overrepresented, and it is uncommon for dogs with HCM to develop CHF although sudden death can occur.

Immunofluorescent Localization of Plakoglobin Is Altered in Endomyocardial Biopsy Samples from Dogs with Clinically Relevant Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC).

Diagnosing the early stages of canine Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC) is complicated by day-to-day arrhythmia variability, and absence of reliable, transthoracic echocardiographic features. Definitive diagnosis requires histopathologic identification of transmural fibrofatty replacement of the right ventricle. Reduction of immunofluorescent signal for plakoglobin (PG) at the intercalated disc (ID) is reported in ARVC-affected humans and boxers. Our objective was to determine whether reduced immunofluorescent signal for PG in endomyocardial biopsy samples (EMBs) correspond with a histopathologic diagnosis of ARVC. Here, 49 dogs were evaluated: 43 with advanced cardiac disease and 6 non-clinical boxers with mild to moderate ventricular arrhythmia (VA) burden. EMBs were obtained from all dogs; samples were prepared with antibodies recognizing cadherin (PC) and PG and evaluated with confocal microscopy. Investigators were blinded to breed and clinical status. ARVC was histopathologically diagnosed in 8 out of 49 dogs. Of these, three out of eight had clinical signs consistent with ARVC (two boxers, one English bulldog) and reduced PG signal at ID; five out of eight were non-clinical boxers with moderate VA and no reduction in PG. A total of 41 out of 49 dogs were histopathologically diagnosed with non-ARVC cardiac disease; 1 out of 41 showed reduction of PG at ID, while 40 out of 41 had no PG reduction. These results suggest that EMB PG signal is reduced in dogs with advanced ARVC, but not in the occult phase of the disease. Additionally, presence of PG at ID supports a diagnosis of non-ARVC cardiac disease in dogs with clinical signs. These results may offer an additional test that helps differentiate advanced ARVC from other myocardial diseases.

Pathological Findings of Canine Idiopathic Pericarditis and Pericardial Mesotheliomas: Correlation with Clinical and Survival Data.

Idiopathic pericarditis (IP) and pericardial mesothelioma (PM) are causes of pericardial effusion in dogs. Pericardiectomy can be a definitive treatment in the case of idiopathic pericardial effusion or a short-term intervention for mesothelioma. The aim of the present study was to investigate which histopathologic parameters are correlated with clinical outcomes in a cohort of dogs that underwent pericardiectomy. The histopathological findings of 22 IPs and 5 PMs were compared with clinical and survival data and the immunohistochemical characterization of immune cells (CD3, CD79α, Iba1). In IP, the mesothelium was lost in 20 cases, reactive in 9, atypical in 3, and mesothelial papillary hyperplasia (MPH) was observed in 4 cases. Numerous macrophages were found in both IPs and PMs especially at the superficial layer of the pericardium. T lymphocytes were observed in mild to moderate numbers and were more numerous than B lymphocytes in both IPs and PMs. MPH was correlated with the quantity of lymphoplasmacytic infiltrate in the superficial layer, inversely related to the thickness of the pericardium, and associated with a longer overall survival. Pericardial fibrosis was present in 19 out of 22 IPs and in all mesotheliomas and was correlated with increased time from initial presentation and pericardiectomy and lymphoplasmacytic infiltrate in the deep zone. Pericardial thickness was correlated with the amount of lymphoplasmacytic and macrophagic infiltrate in the deep zone. Mesothelioma was associated with an increased number of pericardiocentesis procedures before pericardiectomy and with the presence of macrophages in the superficial pericardial layer, edema, fibrin, and hemorrhage. Disease-free interval and overall survival were significantly shorter in patients with mesothelioma compared with IP.

Evaluation of the diagnostic value of an implantable loop recorder in dogs with unexplained syncope.

OBJECTIVE: To evaluate the diagnostic value of an implantable loop recorder (ILR) in dogs with unexplained syncope. DESIGN: Prospective case series. ANIMALS: 12 dogs with recurrent unexplained syncope. PROCEDURES: An ILR was surgically inserted in a pocket created in the subcutaneous tissues of the left hemithorax of each dog. The ILRs were programmed for manual and automatic activation, and event analysis and programming were performed at 3-month intervals and after each syncopal episode. RESULTS: The ILR was manually activated in 7 of 12 dogs at least once within 45 to 218 days (median, 120 days) after implantation. Four dogs had syncopal episodes associated with sinus tachycardia followed by sinus bradycardia and asystolic pauses. Two dogs had ventricular tachycardia, and 1 dog had sinus node dysfunction with prolonged sinus arrest that coincided with loss of consciousness and falling. Four dogs had no additional syncopal episodes after implantation of the ILR. In the remaining dog, the owner was unable to activate the ILR during the only syncopal episode observed for that dog after ILR implantation. In all 12 dogs, analysis of ECG traces after automatic activation of recording revealed normal cardiac rhythms. CONCLUSIONS AND CLINICAL RELEVANCE: Data gained after manual activation of an ILR provided valuable diagnostic and prognostic information in almost all dogs with unexplained syncopal episodes by confirming or disproving an association between syncope and arrhythmias. However, detection of disturbances in cardiac rhythm after automatic activation did not appear to improve the diagnostic value for an ILR implanted in dogs.

Temporal changes in clinical and radiographic variables in dogs with preclinical myxomatous mitral valve disease: The EPIC study.

BACKGROUND: The Evaluation of pimobendan in dogs with cardiomegaly caused by preclinical myxomatous mitral valve disease (EPIC) study monitored dogs with myxomatous mitral valve disease (MMVD) as they developed congestive heart failure (CHF). OBJECTIVES: To describe the changes in clinical and radiographic variables occurring as dogs with MMVD and cardiomegaly develop CHF, compared to similar dogs that do not develop CHF. ANIMALS: One hundred and thirty-five, and 73 dogs that did or did not develop CHF, respectively. MATERIALS AND METHODS: The following variables were evaluated in 2 groups of dogs (dogs that did or did not develop CHF): Heart rate (HR), clinic respiratory rate (RR), home-measured resting respiratory rate (RRR), rectal temperature (RT), body weight (BW), and vertebral heart sum (VHS). Absolute value and rate of change of each variable were calculated for each day a dog was in study. Daily means were calculated and plotted against time. The onset of CHF or last visit before leaving the study were set as reference time points. RESULTS: The most extreme values and rate of change occurred in variables immediately before onset of CHF. Vertebral heart sum increased earliest. Heart rate, RR, and RRR also increased. Rectal temperature and BW decreased. Increases in RR and RRR were most extreme and occurred immediately before CHF. CONCLUSIONS AND CLINICAL IMPORTANCE: Dogs with MMVD and cardiomegaly experience increases in HR, RR, RRR, and VHS, and decreases in BW and RT as they develop CHF. The variables with highest absolute change and rate of change were RR and RRR. These findings reinforce the value of RR and RRR as indicators of impending or incipient CHF.

Evaluation of the presence of selected viral and bacterial nucleic acids in pericardial samples from dogs with or without idiopathic pericardial effusion.

Many viruses have been identified in pericardial fluid and in tissue samples from humans with pericarditis by means of molecular diagnostics. In canine idiopathic pericardial effusion there is as yet no conclusive evidence to support the involvement of an infectious agent. This study was designed to investigate a possible relationship between idiopathic pericardial effusion in dogs and viruses most commonly encountered in humans affected with viral pericarditis. Coxsackievirus B3 RNA, influenza virus type A RNA, human adenovirus type 2 DNA, human cytomegalovirus DNA, and parvovirus B19 DNA were investigated using PCR on pericardial effusion samples and pericardial tissue specimens collected from 14 dogs with idiopathic pericardial effusion. PCR was also used to test for two bacteria, Borrelia burgdorferi and Chlamydia pneumoniae. The same microorganisms were also looked for in pericardial effusions or pericardial washes from 10 dogs with neoplastic pericardial effusion, and in samples collected from 10 dogs which died of a non-cardiac disease. One pericardial effusion sample from a dog with the idiopathic form of the disease tested positive for influenza virus type A and sequencing of the amplicon confirmed the PCR result. In another dog from the same group a cytomegalovirus was detected by PCR in the effusion, but sequencing showed this to be a false-positive result. The genomes of the microorganisms investigated were not detected in neoplastic effusions or pericardial washes. The results indicate that viral and bacterial DNA/RNA of relevance for human pericarditis is rare in pericardial samples from dogs with idiopathic pericardial effusion. The finding of influenza type A viral RNA in pericardial fluid from one dog with the idiopathic form of the disease warrants further investigation.

Congenital heart disease in boxer dogs: results of 6 years of breed screening.

The aim of this study was to analyse the results of 6years (1999-2004) of mandatory breed screening for congenital heart disease in Boxer dogs using physical examination and echocardiography. Records of 1283 Boxers were reviewed and 165 dogs (12.86%) were found to be affected by heart disease, with aortic and pulmonic stenosis being the most frequent cardiac lesions. Comparison of these results with those of a previous survey showed a lower overall prevalence of both outflow obstructions, particularly of the more severe forms. A male predisposition for both aortic and pulmonic stenosis was evident from the study. Consistent with reports from other countries, soft left basilar heart murmurs were detected in both healthy dogs and dogs affected with congenital heart disease.

Development and assessment of a novel precordial lead system for accurate detection of right atrial and ventricular depolarization in dogs with various thoracic conformations.

OBJECTIVE: To assess recording accuracy of right atrial and ventricular depolarization during 12-lead ECG when precordial lead V1 was positioned at each of 5 locations on the thorax of dogs with various thoracic conformations. ANIMALS: 60 healthy client-owned dogs. PROCEDURES: 20 dogs were allocated to each of 3 groups (brachymorphic, mesomorphic, or dolichomorphic) on the basis of thoracic conformation. Each dog remained unsedated and was positioned in right lateral recumbency for a series of five 12-lead surface ECGs, with V1 located adjacent to the sternum in the fifth intercostal space (ICS; control), at the costochondral junction (CCJ) of the right first ICS (1st-R), at the CCJ of the right third ICS, at the right third ICS where the thorax was the widest, and at the CCJ of the left first ICS. Electrocardiographic variables were compared among the 5 ECG tracings. RESULTS: When V1 was at the control location, the P wave was positive for all dogs; however, consistent recording of right atrial and ventricular depolarization (ie, R wave-to-S wave ratio [R/S] < 1) occurred more frequently for brachymorphic dogs (16/20) than for dolichomorphic (7/20) and mesomorphic (6/20) dogs. When V1 was at the 1st-R location, the P wave was negative for most dogs, and R/S was < 1 for the majority of dogs in the brachymorphic (19/20), mesomorphic (17/20), and dolichomorphic (16/20) groups. The median R/S for V1 at the 1st-R location was significantly lower than that for the other 4 V1 locations. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that placement of V1 at the 1st-R location provided correct evaluation of right atrial and ventricular depolarization in most dogs regardless of thoracic conformation.

Prevalence of selected cardiotropic pathogens in the myocardium of adult dogs with unexplained myocardial and rhythm disorders or with congenital heart disease.

OBJECTIVE: To determine the prevalence of nucleic acid from selected cardiotropic pathogens in endomyocardial biopsy samples from dogs with unexplained myocardial and rhythm disorders (UMRD) and compare prevalence with that for a group of control dogs with congenital heart disease (CHD). ANIMALS: 47 client-owned dogs. PROCEDURES: Right ventricular endomyocardial biopsy was performed in dogs with UMRD (dilated cardiomyopathy [n = 25], atrioventricular block [6], and nonfamilial ventricular [4] and supraventricular arrhythmias [2]) or CHD (10) that required right ventricular catheterization. Biopsy samples were evaluated histologically, and PCR assays were used for detection of nucleic acid from 12 pathogens. RESULTS: 197 biopsy samples were collected from dogs with UMRD (n = 172) or CHD (25). At least 1 pathogen was detected in 21 of 37 (57%; 95% confidence interval [CI], 41% to 71%) dogs with UMRD, and canine coronavirus was detected in 1 of 10 (10%; 95% CI, 2% to 40%) dogs with CHD. Dogs with UMRD were significantly more likely than dogs with CHD to have pathogens detected in biopsy samples (OR, 11.8; 95% CI, 1.3 to 103.0). The most common pathogens in dogs with UMRD were canine distemper virus, canine coronavirus, canine parvovirus 2, and Bartonella spp. No pathogens were detected in available blood samples from dogs with pathogens detected in biopsy samples. CONCLUSIONS AND CLINICAL RELEVANCE: Detection of nucleic acids from selected cardiotropic pathogens in myocardial tissue from dogs with UMRD suggested a possible association between the 2. Further studies are needed to explore whether this association is causative or clinically important. (J Am Vet Med Assoc 2019;255:1150-1160).

Long-term incidence and risk of noncardiovascular and all-cause mortality in apparently healthy cats and cats with preclinical hypertrophic cardiomyopathy.

BACKGROUND: Epidemiologic knowledge regarding noncardiovascular and all-cause mortality in apparently healthy cats (AH) and cats with preclinical hypertrophic cardiomyopathy (pHCM) is limited, hindering development of evidence-based healthcare guidelines. OBJECTIVES: To characterize/compare incidence rates, risk, and survival associated with noncardiovascular and all-cause mortality in AH and pHCM cats. ANIMALS: A total of 1730 client-owned cats (722 AH, 1008 pHCM) from 21 countries. METHODS: Retrospective, multicenter, longitudinal, cohort study. Long-term health data were extracted by medical record review and owner/referring veterinarian interviews. RESULTS: Noncardiovascular death occurred in 534 (30.9%) of 1730 cats observed up to 15.2 years. Proportion of noncardiovascular death did not differ significantly between cats that at study enrollment were AH or had pHCM (P = .48). Cancer, chronic kidney disease, and conditions characterized by chronic weight-loss-vomiting-diarrhea-anorexia were the most frequently recorded noncardiovascular causes of death. Incidence rates/risk of noncardiac death increased with age in AH and pHCM. All-cause death proportions were greater in pHCM than AH (65% versus 40%, respectively; P < .001) because of higher cardiovascular mortality in pHCM cats. Comparing AH with pHCM, median survival (study entry to noncardiovascular death) did not differ (AH, 9.8 years; pHCM, 8.6 years; P = .10), but all-cause survival was significantly shorter in pHCM (P = .0001). CONCLUSIONS AND CLINICAL IMPORTANCE: All-cause mortality was significantly greater in pHCM cats due to disease burden contributed by increased cardiovascular death superimposed upon noncardiovascular death.

Clinical and electrocardiographic presentations of transient trifascicular block in three cats.

This report describes transient trifascicular block in three cats presented with lethargy and inappetence, and elevated cardiac troponin I concentrations. The electrocardiogram (ECG) of cat 1 showed a sinus rhythm with pronounced first-degree atrioventricular (AV) block, right bundle branch block, and left anterior fascicular block. The ECG of cat 2 showed truncular left bundle branch block alternating with left anterior fascicular block coupled with prolonged PR intervals, second-degree heart block, and paroxysmal third-degree AV block. The ECG of cat 3 showed first-degree AV block with concomitant right bundle branch block. The diagnosis of trifascicular block was made when paroxysmal third-degree AV block was documented. All cats recovered with medical management within weeks. Each cat resumed a sinus rhythm. Elevated cardiac troponin I concentrations suggested myocarditis that improved.

International collaborative study to assess cardiovascular risk and evaluate long-term health in cats with preclinical hypertrophic cardiomyopathy and apparently healthy cats: The REVEAL Study.

BACKGROUND: Hypertrophic cardiomyopathy is the most prevalent heart disorder in cats and principal cause of cardiovascular morbidity and mortality. Yet, the impact of preclinical disease is unresolved. HYPOTHESIS/OBJECTIVES: Observational study to characterize cardiovascular morbidity and survival in cats with preclinical nonobstructive (HCM) and obstructive (HOCM) hypertrophic cardiomyopathy and in apparently healthy cats (AH). ANIMALS: One thousand seven hundred and thirty client-owned cats (430 preclinical HCM; 578 preclinical HOCM; 722 AH). METHODS: Retrospective multicenter, longitudinal, cohort study. Cats from 21 countries were followed through medical record review and owner or referring veterinarian interviews. Data were analyzed to compare long-term outcomes, incidence, and risk for congestive heart failure (CHF), arterial thromboembolism (ATE), and cardiovascular death. RESULTS: During the study period, CHF, ATE, or both occurred in 30.5% and cardiovascular death in 27.9% of 1008 HCM/HOCM cats. Risk assessed at 1, 5, and 10 years after study entry was 7.0%/3.5%, 19.9%/9.7%, and 23.9%/11.3% for CHF/ATE, and 6.7%, 22.8%, and 28.3% for cardiovascular death, respectively. There were no statistically significant differences between HOCM compared with HCM for cardiovascular morbidity or mortality, time from diagnosis to development of morbidity, or cardiovascular survival. Cats that developed cardiovascular morbidity had short survival (mean ± standard deviation, 1.3 ± 1.7 years). Overall, prolonged longevity was recorded in a minority of preclinical HCM/HOCM cats with 10% reaching 9-15 years. CONCLUSIONS AND CLINICAL IMPORTANCE: Preclinical HCM/HOCM is a global health problem of cats that carries substantial risk for CHF, ATE, and cardiovascular death. This finding underscores the need to identify therapies and monitoring strategies that decrease morbidity and mortality.

Anatomic distribution and electrophysiologic properties of accessory atrioventricular pathways in dogs.

OBJECTIVE: To evaluate the anatomic distribution and electrophysiologic properties of accessory pathways (APs) in dogs. DESIGN: Case series. ANIMALS: 10 dogs with tachyarrhythmias associated with an AP. PROCEDURES: Each dog underwent electrophysiologic testing to determine the inducibility of documented and undocumented arrhythmias and to identify location, conduction properties, and antegrade and retrograde effective refractory periods of the APs. Radiofrequency catheter ablation was then performed. RESULTS: 15 APs were identified; 7 dogs each had a single AP, and 3 had multiple APs. Fourteen of the 15 APs were right-sided (6 right free wall, 4 posteroseptal, 3 midseptal, and 1 anteroseptal), and 1 was left-sided (left free wall). All APs conducted in an all-or-none fashion. Unidirectional retrograde conduction was observed in 11 APs, and bidirectional conduction was observed in 4. All documented tachyarrhythmias could be induced during electrophysiologic testing; atrial fibrillation was also inducible in 2 dogs. Mean +/- SD cycle duration of orthodromic atrioventricular reciprocating tachycardia was 215.80 +/- 44.87 milliseconds. Mean shortest R-R interval during atrial fibrillation was 247.33 +/- 83.17 milliseconds. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that in dogs, most APs are right-sided, had unidirectional retrograde conduction, and are associated with various arrhythmias, including orthodromic atrioventricular reciprocating tachycardia and atrial fibrillation without evidence of pre-excitation.

Prognostic indicators for dogs with dilated cardiomyopathy.

The purpose of this study was to investigate the prognostic value of various clinical, ECG, echocardiographic, and Doppler echocardiographic variables in dogs with dilated cardiomyopathy. The relationship to survival of 11 variables was evaluated in 63 dogs. Studied variables were age at time of diagnosis, class of heart failure (HF), dyspnea, ascites, atrial fibrillation (AF), ejection fraction (EF), E-point septal separation, end-diastolic volume index, end-systolic volume index (ESV-I), and restrictive or nonrestrictive transmitral flow (TMF) pattern. Median survival time was 671 days (lower 95% confidence limit, 350 days). Survival curves showed that severity of HF, ascites, ESV-I greater than 140 mL/m2, EF less than 25%, and restrictive TMF pattern had a significant negative relation to survival time. Thirty-nine dogs with both sinus rhythm and AF presented adequate TMF recordings; in these dogs, after stratification by TMF pattern, the restrictive TMF pattern was the most important negative prognostic indicator. We conclude that in dogs with dilated cardiomyopathy the restrictive TMF pattern appears to represent a useful prognostic indicator. Class of HF, ascites, ESV-I, and EF are also useful indexes if an adequate TMF pattern is not recorded.