Noninvasive electrocardiographic parameters to assess interventricular dyssynchrony in dogs with bundle branch blocks.

OBJECTIVES: To define electrocardiographic features of complete left bundle branch block (LBBB) and right bundle branch block (RBBB), and the use of R-peak time (RPT) to identify interventricular dyssynchrony in dogs with BBB. ANIMALS, MATERIALS AND METHODS: Twelve-lead ECG tracings of 20 dogs with RBBB, 20 with LBBB, and 60 healthy dogs were retrospectively analyzed and RPT was measured in precordial leads. Interventricular dyssynchrony index (IDI) was than calculated. RESULTS: In RBBB, mean electrical axis (MEA) was -111° [-120/-100°], V1RPT was significantly longer (61 ms [55-72 ms]) than left precordial leads RPT (V2:25 ms [22-30 ms]; V3:25 ms [22-29 ms]; V4:24 ms [21-29 ms]; V5:25 ms [22-29 ms]; V6:25 ms [22-29 ms]) and when compared to normal dogs (P < 0.001). In LBBB, MEA was 76° [70/81°], RPT in left precordial leads was significantly longer (V2:49 ms [34-58 ms]; V3:49 ms [43-57 ms]; V4:52 ms [45-62 ms]; V5:53 ms [45-63 ms]; V6:55 ms [45-63 ms]) than V1RPT (17 ms [15-20 ms]) and when compared to normal dogs (P < 0.001). V1RPT > 28 ms and V5RPT > 36 ms were found to predict the presence of RBBB and LBBB with a sensitivity of 100% and 96.7%, and a specificity of 96.7% and 99.5%, respectively. The IDI was 23% [16-29%] in normal dogs and significantly greater in dogs with RBBB (33% [30-38%]; P < 0.001) and LBBB (32% [23-41%]; P = 0.006). CONCLUSIONS: This study defines ECG features and RPT in dogs with BBB. Electrical interventricular dyssynchrony can be defined using IDI in dogs with BBB.

Radiofrequency catheter ablation of cranial vena cava flutter in four dogs.

Four dogs were referred to our institution for incessant supraventricular tachycardias causing weakness; congestive heart failure was present in one dog. At admission, all dogs had a surface electrocardiogram showing a narrow QRS complex tachycardia with a ventricular rate ranging from 80 to 300 bpm, variable atrioventricular conduction ratio from 1:1 to 3:1, and positive atrial depolarizations in inferior leads (II, II, III, and aVF), with isoelectric lines between them. Three of four dogs had a dilated cardiomyopathy phenotype; one dog had a heart base tumor involving the cranial vena cava wall. According to the electrocardiographic findings, a presumptive diagnosis of reverse typical or atypical atrial flutter was considered, and endocardial mapping was planned for each dog. During the electrophysiologic study, continuous atrial activation compatible with atypical atrial flutter was observed in all dogs, with concealed entrainment obtained at the level of the isthmus located at the distal portion of the cranial vena cava, close to the entrance into the right atrium. A linear radiofrequency catheter ablation was performed from the right atrial wall to the distal part of the cranial vena cava with a permanent interruption of the isthmic conduction in all dogs at a 6-month follow-up.

Heart rhythm characterization during sudden cardiac death in dogs.

INTRODUCTION/OBJECTIVES: Inherited or acquired arrhythmic disorders and cardiac disease have been associated with sudden cardiac death (SCD) in dogs. The electrical mechanism related to death in most of these cases is unknown. This retrospective study aimed to describe arrhythmic events in dogs that experienced SCD during Holter monitoring. ANIMALS, MATERIALS AND METHODS: Nineteen client-owned dogs that experienced SCD during Holter examination were included. Clinical records from a Holter service database were reviewed, and both the rhythm preceding death and the dominant rhythm causing SCD were analysed. Clinical data, Holter diaries and echocardiographic diagnosis were also evaluated. RESULTS: Structural heart disease was identified in 12/19 dogs (dilated cardiomyopathy in five dogs, arrhythmogenic right ventricular cardiomyopathy in four dogs, myxomatous mitral valve disease in two dogs, and suspected myocarditis in one dog), five of which had concurrent congestive heart failure. Sudden cardiac death was related to ventricular premature complexes or monomorphic ventricular tachycardia degenerating into ventricular fibrillation in 42% of dogs, polymorphic ventricular tachycardia, or torsade de pointes-like inducing ventricular fibrillation in 21%, and asystole or presumptive agonal pulseless electrical activity triggered by malignant bradyarrhythmias in 37%. CONCLUSIONS: The most common rhythm associated with SCD in our population of dogs was ventricular tachycardia leading to ventricular fibrillation, although bradyarrhythmia-related SCD, possibly related to inappropriate vagal reflexes, was also a notable cause.

R-peak time in clinically healthy dogs with different thoracic conformations.

R-peak time (RPT) is an electrocardiographic parameter that represents the time taken for electrical activation to spread from the endocardium to the epicardium. In human medicine, right ventricular RPT is measured from lead V1 to lead V2, and left ventricular RPT from lead V5 to lead V6. The aim of the present study was to define RPT duration in a group of clinically healthy dogs with different thoracic conformations. Sixty clinically healthy dogs underwent a 12-lead electrocardiogram recorded using a previously described precordial system. The dogs were allocated into three morphologic groups. In the brachymorphic group, the median and 25th-75th percentiles for RPT in V1 were 10.5 ms (10-12 ms); V2, 18 ms (16.5-20 ms); V3, 19 ms (18-22 ms); V4, 20 ms (17-23.5 ms); V5, 21 ms (18.5-24 ms); and V6: 22 ms (18.5-25.5 ms). In the mesomorphic group, RPT in V1 was 16 ms (14-18 ms); V2, 22 ms (20-24 ms); V3, 23 ms (21-25 ms); V4, 23 ms (22-25 ms); V5, 25 ms (23-27 ms); and V6, 28 ms (25-30 ms). In the dolichomorphic group, RPT in V1 was 15 ms (13-17 ms); V2, 29 ms (26-32.5 ms); V3, 30 ms (27-33.5 ms); V4, 29.5 ms (26-35 ms); V5, 30 ms (28-34 ms); and V6, 31.5 ms (28-35 ms). RPT in V1 was significantly shorter than RPT in V2 to V6 in all morphotypes (P < 0.05). In all precordial leads, RPT was significantly different between morphotypes (P < 0.05). These results are in agreement with previous findings in humans and with the observation that V1 reads the right ventricle and V2 to V6 read the left ventricle. These preliminary data provide RPT ranges in clinically healthy dogs of different morphotypes.

Bartonella-associated inflammatory cardiomyopathy in a dog.

A 6-year-old, male, mongrel dog was presented for acute onset of dyspnea and cough. At admission, the dog was cachectic and severely depressed. The electrocardiogram showed a sinus rhythm conducted with left bundle truncular branch block and interrupted by frequent multiform ventricular ectopic beats organized in allorhythmias. Thoracic radiographs revealed a marked cardiomegaly with perihilar edema, whereas transthoracic echocardiography revealed a dilated cardiomyopathy with segmental dyskinesis. Furosemide, enalapril, pimobendan, and mexiletine were prescribed, and a Holter was scheduled after resolution of congestive heart failure. Three days later, the dog died suddenly during sleep. Histopathology revealed diffuse myocyte hypertrophy with multifocal hemorrhages, alternating to areas of severe replacement fibrosis and lymphoplasmocytic infiltrates. Immunohystochemistry stains were strongly positive for T-lymphocyte infiltration (CD3) and weakly positive for B-lymphocytes (CD79). Polymerase chain reaction was positive for Bartonella spp. Based on these results, a post-mortem diagnosis of bacterial inflammatory cardiomyopathy was made.

Utility of Tissue Doppler Imaging in the Echocardiographic Evaluation of Left and Right Ventricular Function in Dogs with Myxomatous Mitral Valve Disease with or without Pulmonary Hypertension.

BACKGROUND: In human medicine, right ventricular (RV) functional parameters represent a tool for risk stratification in patients with congestive heart failure caused by left heart disease. Little is known about RV alterations in dogs with left-sided cardiac disorders. OBJECTIVES: To assess RV and left ventricular (LV) function in dogs with myxomatous mitral valve disease (MMVD) with or without pulmonary hypertension (PH). ANIMALS: One-hundred and fourteen dogs: 28 healthy controls and 86 dogs with MMVD at different stages. METHODS: Prospective observational study. Animals were classified as healthy or having MMVD at different stages of severity and according to presence or absence of PH. Twenty-eight morphological, echo-Doppler, and tissue Doppler imaging (TDI) variables were measured and comparison among groups and correlations between LV and RV parameters were studied. RESULTS: No differences were found among groups regarding RV echo-Doppler and TDI variables. Sixteen significant correlations were found between RV TDI and left heart echocardiographic variables. Dogs with PH had significantly higher transmitral E wave peak velocity and higher E/e' ratio of septal (sMV) and lateral (pMV) mitral annulus. These 2 variables were found to predict presence of PH with a sensitivity of 84 and 72%, and a specificity of 71 and 80% at cut-off values of 10 and 9.33 for sMV E/e' and pMV E/e', respectively. CONCLUSIONS AND CLINICAL IMPORTANCE: No association between variables of RV function and different MMVD stage and severity of PH could be detected. Some relationships were found between echocardiographic variables of right and left ventricular function.