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.     

Electrocardiographic and echocardiographic features of trypanosomiasis in dogs inoculated with North American Trypanosoma cruzi isolates.

Purebred Beagles were inoculated with Trypanosoma cruzi isolates from a North American opossum or armadillo (Tc-W), and dog (Tc-D). Although Tc-D established infection in dogs, the dogs did not develop cardiac abnormalities. Dogs inoculated with Tc-W developed acute myocarditis associated with increases in P-R interval, atrioventricular block, depression of R wave amplitude and shifts in mean electrical axis. Echocardiograms were normal during this stage. Three Tc-W-inoculated dogs died during the acute stage. Following the acute stage, 5 of 8 Tc-W-inoculated dogs entered an indeterminate stage in which ECG changes were minor and echocardiograms were normal. Progression to the chronic stage in 5 of the 8 Tc-W-inoculated dogs was indicated by development of ventricular-based arrhythmias, mainly ventricular premature contractions, between postinoculation days 60 and 170. In some dogs, ventricular premature contractions were multifocal. Electrocardiographic abnormalities progressively degenerated to various forms of ventricular tachycardia. Worsening ECG coincided with loss of left ventricular function as measured by echocardiography. Mean percent ejection fraction and percentage of fractional shortening decreased to 63% and 52% of control values, respectively. The left ventricular free wall (LVFW) thickness decreased and % septal: % LVFW thickening ratio increased, indicating a relative preservation of septal wall motion and LVFW hypokinesis.     

Incidence of post-anaesthetic arrhythmias in the dog

A total of 50 dogs, judged to be free of cardiovascular disease on the basis of physical and electrocardiographic (ECG) examination, underwent ECG monitoring during recovery from general anaesthesia. Fifteen of these dogs (30 per cent) developed some form of cardiac arrhythmia during the recovery period. The arrhythmias most frequently observed were premature ventricular contractions and atrioventricular conduction defects of varying degrees of severity. The observed arrhythmias had ceased by the end of the observation period and did not require specific therapy. There was no apparent correlation between the duration of anaesthesia, the type of medical or surgical procedure and the development of arrhythmias. However, the dogs developing arrhythmias were older than those that did not. The relatively high frequency of occurrence of cardiac arrhythmias must be considered in the evaluation of ECG data from dogs being monitored during recovery from anaesthesia.     

Holter monitoring in 36 dogs with myxomatous mitral valve disease

Objective Describe the presence of arrhythmias in dogs with myxomatous mitral valve disease (MMVD) and the potential association with class of heart failure and left atrial enlargement. Compare the standard electrocardiogram (ECG) with Holter monitoring for assessing heart rate (HR). Experimental procedure The study group of 36 dogs weighing less than 20 kg was divided into MMVD and no clinical signs (preclinical) or MMVD and clinical signs (clinical). A standard echocardiogram, ECG and 24-h Holter recording were obtained in all dogs. Results Minimum and mean Holter HRs were higher in the clinical group than in the preclinical group. Clinical dogs had more ventricular arrhythmias than preclinical dogs. An enlarged left atrium was associated with the presence of more supraventricular arrhythmias. Conclusions Arrhythmias are a common finding in dogs with MMVD and Holter monitoring is a reliable tool for both HR monitoring and diagnosis.     

Comparison of acute hemodynamic effects of lidocaine and procainamide for postoperative ventricular arrhythmias in dogs

Heart rate and systolic, diastolic, and mean pressures were measured in two groups of dogs during treatment of postoperative ventricular arrhythmias either with intravenous (IV) 2% lidocaine hydrochloride or procainamide hydrochloride. Hemodynamic parameters were not significantly changed after IV administration of either drug. Additionally, changes in hemodynamic parameters for dogs treated with 2% lidocaine were not significantly different from those of dogs treated with procainamide. When dosed appropriately in the clinical setting, one bolus of IV procainamide was safe for the treatment of postoperative ventricular arrhythmias.     

Cardiac arrhythmias associated with multiple trauma in dogs

Premature ventricular contractions and ventricular tachycardia were detected in 10 dogs 1 to 48 hours after trauma. All dogs were treated aggressively if the arrhythmias became severe. One dog died, 8 were discharged with stable cardiac rhythm, and 1 was euthanatized. Necropsy revealed gross and microscopic lesions of acute myocardial necrosis, probably of ischemic origin. Cardiac arrhythmias were associated with thoracic trauma, neurologic injury, severe shock, and/or extensive tissue trauma.     

Ventricular Arrhythmias in Dogs Undergoing Splenectomy: A Prospective Study

Fifty dogs undergoing splenectomy for splenic masses (n = 40), torsion of the splenic pedicle (n = 5), and immune-mediated disease (n = 5) were evaluated preoperatively and postoperatively for ventricular arrhythmias and the relationship between ventricular arrythmia and splenic disease. The ability of 1 -minute electrocardiograms recorded every 6 hours (ECGs/q6hr) to detect ventricular arrythmia was compared with continuous 48-hour Holter monitoring. Based on continuous Holter monitoring, splenectomized dogs had a high incidence (22 of 50) of rapid ventricular tachycardia. The incidence of rapid ventricular tachycardia was significantly higher in dogs with ruptured splenic masses (16 of 23) than without rupture (1 of 17) ( P < .001). When the results of ECG/q6hr were compared with the results of continuous Holter monitoring, ECG/q6hr was normal in 29% (4 of 14) of dogs with rapid ventricular tachycardia at > 3,000 ventricular extrasystoles (VE)/hr; 50% (4 of 8) of dogs with rapid ventricular tachycardia at 1,000 to 3,000 VE/hr and 100% (6 of 6) of dogs with 10 to 300 VE/hr without rapid ventricular tachycardia. Although dogs undergoing splenectomy had a high incidence of ventricular arrythmias, one-minute ECGs/q6h were unreliable for detection of ventricular arrythmias even when high-frequency extrasystoles occurred.     

Effects of xylazine and acetylpromazine upon induced ventricular fibrillation in dogs anesthetized with thiamylal and halothane.

Ventricular arryhythmias including ventricular fibrillation were produced with epinephrine in dogs induced to an anesthetic state with thiamylal and maintained with halothane. In dogs given (premedicated) xylazine 20 minutes prior to anesthesia, ventricular arrhythmias, including ventricular fibrillation, were induced with much smaller doses of epinephrine than in nonpremedicated dogs. Dogs premedicated with acetylpromazine 20 minutes prior to anesthesia with thiamylal and halothane displayed protection from epinephrine-induced arrhythmias. Caution is advised from using xylazine in the presence of halothane if epinephrine is to be administered.     

Cardiomyocyte calcium cycling in a naturally occurring German shepherd dog model of inherited ventricular arrhythmia and sudden cardiac death

ObjectiveTo further characterize arrhythmic mechanisms in German shepherd dogs (GSDs) affected with inherited ventricular arrhythmias by evaluating intracellular calcium cycling and expression of calcium handling genes.AnimalsTwenty five GSDs, 9 backcross dogs, and 6 normal mongrel dogs (controls) were studied. The GSDs and backcross dogs were from a research colony of inherited ventricular arrhythmias. The control research dogs were purchased.MethodsAction potentials (APs) and pseudo-electrocardiograms (ECG) were recorded from left ventricular (LV) wedge preparations of GSDs and normal dogs. Midmyocardial (Mid) LV cells from GSDs and normal mongrels were isolated by enzymatic digestion. Cells were either field stimulated or voltage clamped and calcium transients were measured by confocal microscopy using the indicator Fluo-3AM. Expression of calcium handling genes was measured by quantitative RT-PCR.ResultsMean calcium transient decay (tau) was not different between affected GSDs and control dogs, but striking cell-to-cell variability for tau was observed within affected GSDs and between affected GSDs and controls (P < 0.0001 each); within-dog variability accounted for 75% of total variability. Calcium sparks and afterdepolarizations occurred in GSD but not control cells. ATP2A2/SERCA2a expression was significantly reduced (P = 0.0063) in affected GSDs and inversely correlated (P = 0.0006) with severity of ventricular arrhythmias.ConclusionsGerman shepherd dogs with inherited ventricular arrhythmias have electrophysiologic abnormalities in calcium cycling associated with reduced ATP2A2/SERCA2a expression. These animals provide a unique opportunity to study calcium remodeling at the genetic and molecular level in familial ventricular arrhythmias.     

Acute cardiovascular effects of diltiazem in anesthetized dogs with induced atrial fibrillation

Atrial fibrillation (AF) is one of the most important arrhythmias of dogs. In a previous study, we determined the dosage of intravenously administered diltiazem necessary to reduce ventricular response (VR), cardiac output (CO), and mean systemic arterial pressure (P(Ao)) to values similar to those observed during sinus rhythm (SR) before induction of AF. The present study was conducted to establish an acute, effective dosage of diltiazem given PO. AF was produced by rapid atrial pacing in healthy, anesthetized Beagle Hounds. Dogs were instrumented to record hemodynamic and electrophysiological parameters. Four dogs were given 2.5 mg/kg diltiazem, and another 4 dogs were given 5 mg/kg diltiazem by stomach tube, whereas 4 other dogs received vehicle in equivalent volumes. Plasma concentrations of diltiazem were measured at various intervals after dosing. A dosage of 5 mg/kg diltiazem produced plasma concentrations of 32-100 ng/mL 3 hours after administration, concentrations within the published effective range for dogs with naturally occurring AF. Between 2 and 3 hours after this dosage, the rate pressure product (RPP) and an index of left ventricular efficiency returned to values similar to those observed during SR. Thus, we believe that diltiazem at anorally administered dosages of 5 mg/kg should be considered to produce therapeutic blood concentrations and favorable hemodynamic effects in dogs with naturally occurring AF. These data must be extrapolated with caution to dogs with long-standing AF produced by natural causes.     

Ventricular Tachyarrhythmias in 106 Cats: Associated Structural Cardiac Disorders

Background: Ventricular tachyarrhythmias occur in association with cardiac and extracardiac disorders in many species of animals, but information identifying concurrent disorders in cats with such arrhythmias is scarce. Methods: We investigated coexisting diseases by retrospectively evaluating medical records of cats with ventricular tachyarrhythmias seen during a 51‐month period at 1 institution. For comparative purposes, we evaluated records of dogs with similar arrhythmias during the same time period. All cats and dogs had premature ventricular complexes, accelerated idioventricular rhythm, ventricular tachycardia, or some combination of these arrhythmias, and all had undergone echocardiography during the same visit that led to the diagnosis of ventricular tachyarrhythmia. Results and Conclusions: Most (102/106; 96%) cats had at least 1 echocardiographically apparent abnormality concurrent with ventricular tachyarrhythmias. Ventricular tachyarrhythmias in cats were most commonly associated with myocardial disease (eg, left ventricular concentric hypertrophy [n = 66], restrictive or unclassified cardiomyopathy [n = 17], and dilated cardiomyopathy [n = 6]). When comparing dogs and cats that had ventricular tachyarrhythmias and were diagnosed on the same clinical service of the same institution, an echocardiographically apparent cardiac lesion was seen more often in cats (102/106, 96%) than in dogs (95/138, 69%) (P < .001).     

Occurrence and recurrence of gastric dilatation with or without volvulus after incisional gastropexy

This study investigated recurrence of gastric dilatation without (GD) or with volvulus (GDV) after incisional gastropexy (IG) in dogs that underwent IG for prevention of GDV. Signalment, concurrent surgical procedures, presence of GD or GDV at the time of IG were obtained from medical records of dogs that underwent IG. Owners were contacted to determine whether the dogs experienced GD or GDV after IG, dates of postoperative GD or GDV episodes, survival status, date of death for deceased dogs. Gastric dilatation and GDV recurrence rates were calculated for 40 dogs that had at least 2 y follow-up from the time when IG was performed and for dogs that experienced GD or GDV during the follow-up period. No dogs experienced GDV after IG and 2 dogs (5.0%) experienced GD after IG. The results suggest that GD and GDV rates after IG may be comparable to recurrence rates after other methods of gastropexy.     

Polymorphism,coupling interval and prematurity index in dogs with degenerative mitral valve disease and ventricular arrhythmias

Ventricular arrhythmias (VA) are a recognized concern in dogs with degenerative mitral valve disease (DMVD). The coupling interval (CI) and the prematurity index (PI) have been shown to accurately differentiate between benign and malignant VA in people, where ventricular arrhythmias are known to be associated with an increased risk of development of signs of heart failure or sudden death. In this study, we characterized ventricular arrhythmias in dogs with symptomatic and asymptomatic DMVD. Seventy dogs with naturally-occurring DMVD and ventricular arrhythmias were retrospectively studied. A cross-sectional investigation including dogs with either symptomatic (stages C/D; n?=?41) or asymptomatic (stages B1/B2; n?=?29) DMVD was performed. Electrocardiographic tracings were reviewed to calculate both the CI and PI. In eight dogs these indices were compared with those obtained from both a Holter recording and a standard ECG tracing and no statistical differences were found (CI, p?=?0.97; PI, p?=?0.17). Even though CI and PI were determined in all animals enrolled in the study, VPC characteristics were only compared between symptomatic and asymptomatic dogs when a 24-h Holter recording was available (n?=?49). The PI was different (p?=?0.01) between symptomatic (0.65?±?0.17) and asymptomatic (0.56?±?0.18) dogs, but CI was considered similar (p?=?0.91). Also, the symptomatic dogs had more polymorphic VPC (p?=?0.002) and supraventricular arrhythmias (p?=?0.0002) than the asymptomatic animals. Polymorphism, and repeating patterns of ventricular premature complexes, were characteristics frequently present in overtly symptomatic animals affected by mitral endocardiosis.     

Prospective screening for occult cardiomyopathy in dogs by measurement of plasma atrial natriuretic peptide, B-type natriuretic peptide, and cardiac troponin-I concentrations

OBJECTIVE: To evaluate the use of measuring plasma concentrations of atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP), and cardiac troponin-I (cTnI) to detect dogs with occult dilated cardiomyopathy (DCM). ANIMALS: 118 client-owned dogs. PROCEDURES: Dogs were prospectively examined by use of ECG; echocardiography; and evaluation of concentrations of ANP, BNP, and cTnI. Occult DCM was diagnosed by evaluation of echocardiographic left ventricular dimensions and detection of ventricular arrhythmias on ECG. Sensitivity and specificity of assays for measurement of plasma concentrations of ANP, BNP, and cTnI to detect dogs with occult DCM were determined. RESULTS: Occult DCM was diagnosed in 21 dogs. A concentration of > 6.21 pg/mL for BNP had a sensitivity of 95.2% and specificity of 61.9% for identifying dogs with occult DCM. In contrast, concentrations of ANP and cTnI had relatively low predictive values. CONCLUSIONS AND CLINICAL RELEVANCE: Blood-based screening for occult DCM in dogs can be accomplished by use of a BNP assay. Additional studies should be performed to optimize this method of screening dogs to detect occult DCM.     

Correlation of QT dispersion with indices used to evaluate the severity of familial ventricular arrhythmias in Boxers

OBJECTIVE: To measure QT interval duration and QT dispersion in Boxers and to determine whether QT variables correlate with indices of disease severity in Boxers with familial ventricular arrhythmias, including the number of ventricular premature complexes per day, arrhythmia grade, and fractional shortening. ANIMALS: 25 Boxers were evaluated by ECG and echocardiography. PROCEDURE: The QT interval duration was measured from 12-lead ECG and corrected for heart rate (QTc), using Fridericia's formula. The QT and QTc were calculated for each lead, from which QT and QTc dispersion were determined. Echocardiography and 24-hour ambulatory ECG were performed to evaluate for familial ventricular arrhythmias. Total number of ventricular premature complexes, arrhythmia grade, and fractional shortening were determined and used as indices of disease severity. RESULTS: There was no correlation between any QT variable and total number of ventricular premature complexes, arrhythmia grade, or fractional shortening. No difference between QT dispersion and QTc dispersion was identified, and correction for heart rate did not affect the results. CONCLUSIONS AND CLINICAL RELEVANCE: QT interval duration and dispersion did not correlate with indices of disease severity for familial ventricular arrhythmias. Heart rate correction of the QT interval did not appear to be necessary for QT dispersion calculation in this group of dogs. QT dispersion does not appear to be a useful noninvasive diagnostic tool in the evaluation of familial ventricular arrhythmias of Boxers. Identification of affected individuals at risk for sudden death remains a challenge in the management of this disease.     

Failure of spectro-temporal mapping to detect ventricular late potentials in dogs

OBJECTIVE: To determine whether ventricular late potentials (LP) identified by time-domain analysis (TDA) of the signal-averaged ECG could be identified by three-dimensional frequency-domain analysis (FDA). ANIMALS: 11 dogs (9 of which subsequently died suddenly) with ventricular tachyarrhythmias (10 with ventricular tachycardia) and abnormal TDA of the signal-averaged ECG. PROCEDURE: Signal-averaged ECG that were abnormal when analyzed in the time domain subsequently were processed further in the frequency domain. Correlation ratios were calculated, and spectro-temporal maps were plotted, which were then compared with control data. RESULTS: Three-dimensional FDA did not detect LP. CONCLUSIONS AND CLINICAL RELEVANCE: LP may be detectable by TDA of the signal-averaged ECG and may be a specific marker for VT and sudden death in some dogs. However, FDA by use of the method applied in this study is invalid.     

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.     

Effects of gastric distention-volvulus on coronary blood flow and myocardial oxygen consumption in the dog

Gastric distention-volvulus (GDV; at 50 mm of Hg gastric inflation pressure) was experimentally induced in 8 dogs anesthetized using pentobarbital. Hemodynamic indices including heart rate, mean arterial pressure, cardiac output, and coronary blood flow (4 dogs) were measured during a 20-minute period of GDV and for 10 minutes after decompression. Arterial and coronary venous oxygen tensions were also measured for calculation of myocardial oxygen extraction (7 dogs) and myocardial oxygen consumption (4 dogs). Dogs were monitored for 72 hours postoperatively for the occurrence of arrhythmias, then were euthanatized for gross and histologic examination of the heart. Experimental GDV resulted in significant (P less than 0.05) decreases in cardiac output (89%), mean arterial pressure (45%), and coronary blood flow (50%) compared with control values. Myocardial oxygen extraction increased (30%) and overall myocardial oxygen consumption decreased (50%), compared with control values. Evidence of subendocardial necrosis was seen in 6 dogs, 4 of which had developed ventricular arrhythmias 8 to 24 hours postoperatively.     

Retrospective evaluation of the use of amiodarone in dogs with arrhythmias (from 2003 to 2010)

Objectives : To evaluate the efficacy of amiodarone in dogs with refractory supraventricular and ventricular arrhythmias and to document the side effects in treated dogs. Methods : Records of 28 dogs were retrospectively searched to document indication for amiodarone administration, heart rate, alkaline phosphatase, alanine aminotransferase, thyroxine (T4) and thyroid stimulating hormone values before and after starting treatment and during follow‐up periods. Results : Sixteen dogs with supraventricular and 12 dogs with ventricular arrhythmias were treated with amiodarone. Amiodarone treatment significantly reduced the heart rate (P<0.001) and resulted in improvement in the severity of the arrhythmia and clinical signs in 26 dogs. There were no significant differences in alkaline phosphatase (P=0.596), alanine aminotransferase (P=0.842), T4 (P=0.789) and thyroid stimulating hormone (P=0.064) before and after starting amiodarone. On maintenance therapy, median amiodarone blood levels were within the accepted reference range (0.5 to 2.0 mg/L) at 0.8 mg/L (range 0.2 to 11.6 mg/L), but the majority of the desethylamiodarone levels were below normal at 0.1 mg/L (range 0.1 to 0.9 mg/L), based on human reference intervals (0.5 to 2.0 mg/L). Clinical Significance : Amiodarone may be an effective and safe alternative to treat supraventricular and ventricular arrhythmias in dogs, when common anti‐arrhythmic drugs are not effective or contraindicated.     

Familial Ventricular Arrhythmias in Boxers

The purposes of this study were to evaluate families of Boxers with ventricular arrhythmias to determine whether this disorder is a familial trait and, if so, to determine the mode of inheritance. Eighty-two Boxers were evaluated by physical examination, electrocardiogram, echocardiogram, and 24-hour ambulatory electrocardiogram. Dogs were considered affected if at least 50 premature ventricular complexes (PVCs) were observed during a 24-hour period. All dogs were at least 6 years of age at evaluation. Complete cardiovascular examinations were performed on dogs from 6 extended families. The 2 most complete pedigrees were used to determine the pattern of inheritance. The number of PVCs observed during a 24-hour period in affected dogs ranged from 112 to 4,894 (mean +/- SD, median; 1,309 +/- 2,609, 1,017). The number of PVCs observed during a 24-hour period in the unaffected dogs ranged from 0 to 16 (7 +/- 10, 12). Pedigree evaluation was performed to determine pattern of inheritance. An autosomal dominant pattern was determined to be most likely because a sex predisposition was not observed, affected individuals were observed in every generation, and 2 affected individuals produced unaffected offspring. We conclude that familial ventricular arrhythmias is inherited as an autosomal dominant trait in some Boxers.